The earliest year is 2003. Thanks go to Ben Wallberg in the University of Maryland Libraries for helping with the data import.
- W. W. Yu, "Inkjet-Printed Paper Surface Enhanced Raman Spectroscopy Devices for Trace Chemical Analysis," Bioengineering, Dissertation, 2013, Advisor(s): I. M. White. link
[Abstract]
The needs of an ever growing human population are fueling demands for better and cheaper sensors for the early detection of harmful chemicals, pathogens and diseases markers from a variety of sources such as food, water, bodily fluids and contaminated surfaces. To address this, recent innovations utilize Microelectromechanical Systems (MEMS) technology to integrate multiple laboratory functions onto millimeter-sized chips to form Micro Total Analysis Systems (µTAS) or Lab-on-chip (LOC) devices. While sophisticated and powerful, the use of these devices for chemical and biological sensing is limited by complicated fabrication processes, high cost and robustness of the sensors. In this work we have developed a simple and inexpensive but exceptionally sensitive portable chemical and biological sensing platform through the innovative use of paper combined with Surface Enhanced Raman spectroscopy (SERS). Paper is functionalized with plasmonic nanostructures to transform it into a SERS substrate, while the natural properties of paper are leveraged for sample collection, cleanup, and analyte concentration in user-friendly formats such as wipes, dipsticks, and filters. The use of simple deposition methods such as inkjet printing for sensor fabrication combined with paper as the construction material means that sensors can be made at a very low cost. Additionally, the ability to be printed on demand eliminates issues with sensor shelf-life, while the absence of mechanical components makes these paper sensors much more robust than conventional sensors. In this work, practical applications of paper SERS sensors for the detection of food contaminants, narcotics, pesticides and other chemicals at trace levels are presented. Paper SERS sensors, by virtue of their low cost, simplicity of fabrication, high sensitivity and ease of use, promises to make chemical and biological sensing more accessible to the common user.
- N. P. Siwak, "Fabrication and Process Development for an Integrated Optical MEMS Microsystem in Indium Phosphide," Electrical Engineering, Dissertation, 2013, Advisor(s): R. Ghodssi. link
[Abstract]
This dissertation presents the design, fabrication, and evaluation of the first monolithically integrated MEMS resonant sensor system realized in the InP-InGaAs material family. The integration of a MEMS sensor along with the facilitating optical interrogation platform provides for increased manufacturing scalability, sensitivity, and reduced measurement noise and device cost. The MEMS device presented in this dissertation consists of an Indium Phosphide (InP) cantilever waveguide resonator whose displacement is measured optically via a vertically integrated laser diode and waveguide photodetector. All three major components of the sensor were integrated in a single 7.1 µm thick molecular beam epitaxy (MBE) epitaxial growth, lattice matched to an InP substrate. Full fabrication of the integrated MEMS device utilizes 7 projection lithography masks, 4 nested inductively coupled plasma (ICP) etches, and over 60 discrete processing steps. This dissertation focuses on the integration design and the development of specific III-V semiconductor fabrication processes in order to completely fabricate and realize these devices, including specialized ICP etching steps and a MEMS undercutting release etch. The fabricated devices were tested and characterized by investigating the separate component subsystems as well as the total combined system performance. Investigation of device failure and performance degradation is performed and related to non-idealities in the device fabrication and design. A discussion of future work to improve the performance of the system is presented. The work in this dissertation describing the successful fabrication process and analysis of such a complex system is a milestone for III-V based optical MEMS research and will serve as the groundwork for future research in the area of optical MEMS microsystems.
- B. Nouri, "Integrated Single-Photon Sensing and Processing Platform in Standard CMOS," Electrical Engineering, Dissertation, 2013, Advisor(s): P. A. Abshire. link
[Abstract]
Practical implementation of large SPAD-based sensor arrays in the standard CMOS process has been fraught with challenges due to the many performance trade-offs existing at both the device and the system level [1]. At the device level the performance challenge stems from the suboptimal optical characteristics associated with the standard CMOS fabrication process. The challenge at the system level is the development of monolithic readout architecture capable of supporting the large volume of dynamic traffic, associated with multiple single-photon pixels, without limiting the dynamic range and throughput of the sensor. Due to trade-offs in both functionality and performance, no general solution currently exists for an integrated single-photon sensor in standard CMOS single photon sensing and multi-photon resolution. The research described herein is directed towards the development of a versatile high performance integrated SPAD sensor in the standard CMOS process. Towards this purpose a SPAD device with elongated junction geometry and a perimeter field gate that features a large detection area and a highly reduced dark noise has been presented and characterized. Additionally, a novel front-end system for optimizing the dynamic range and after-pulsing noise of the pixel has been developed. The pixel is also equipped with an output interface with an adjustable pulse width response. In order to further enhance the effective dynamic range of the pixel a theoretical model for accurate dead time related loss compensation has been developed and verified. This thesis also introduces a new paradigm for electrical generation and encoding of the SPAD array response that supports fully digital operation at the pixel level while enabling dynamic discrete time amplitude encoding of the array response. Thus offering a first ever system solution to simultaneously exploit both the dynamic nature and the digital profile of the SPAD response. The array interface, comprising of multiple digital inputs capacitively coupled onto a shared quasi-floating sense node, in conjunction with the integrated digital decoding and readout electronics represents the first ever solid state single-photon sensor capable of both photon counting and photon number resolution. The viability of the readout architecture is demonstrated through simulations and preliminary proof of concept measurements.
- S. Hossein Yazdi, "An Optofluidic Surface Enhanced Raman Spectroscopy Microsystem for Sensitive Detection of Chemical and Biological molecules," Bioengineering, Dissertation, 2013, Advisor(s): I. M. White. link
[Abstract]
As the human population grows, there is an increasing demand for early detection of a variety of analytes in different fields. This demand mainly includes early and sensitive detection of pathogens, disease biomarkers, pesticides, food contaminants, and explosives. To address this, lab-on-a-chip (LOC) technology has emerged as a tool to improve portability, automation and sensitivity of sensors by taking advantage of integrated laboratory functions on a miniaturized chip. It is agreed that LOC has the potential to make various sensing modules practical for real- world applications. In this work, we have developed a highly sensitive, portable, and automated optofluidic surface enhanced Raman spectroscopy (SERS) microsystem for chemical and biological detection. SERS is a powerful molecular identification technique that combines laser spectroscopy with optical properties of metal nanoparticles. Optofluidic SERS is defined as the synergistic use of microfluidic functions to improve the performance of SERS. By leveraging microfluidic functions, the optofluidic SERS microsystem mixes and concentrates the sample and nanoparticles resulting in an improved performance as compared to conventional open microfluidic SERS systems. The device requires low sample volume and has multiplexed detection capabilities. Moreover, it is suitable for on-site detection of analytes in the field because of its improved automation and portability due to the integrated fiber optics. The final device consists of two regions of packed silica beads inside microchannels for biomolecular interaction as well as sample concentration for SERS measurements. Additionally, an on-chip micromixer and fiber optics are integrated into the device. Optical fibers aligned to the detection zone make the biosensor alignment-free, which greatly improves automation. Practical applications for the detection of real-world analytes (e.g., pesticides, fungicides, food contaminants, and DNA sequences) are demonstrated utilizing our optofluidic SERS microsystem. Detection of biological samples could be extended to proteins and proteolytic enzymes through displacement assays. Consequently, the integration of microfluidic functions, including a microporous reaction zone, a nanoparticle concentration zone, and a micromixer, combined with the use of integrated fiber optics and portable spectrometers, make our microsystem suitable for on-site detection of analytes at trace levels.
- B. M. Hanrahan, "Tribology of Microball Bearing MEMS," Material Science and Engineering, Dissertation, 2013, Advisor(s): R. Ghodssi. link
[Abstract]
This dissertation explores the fundamental tribology of microfabricated rolling bearings for future micro-machines. It is hypothesized that adhesion, rather than elastic hysteresis, dominates the rolling friction and wear for these systems, a feature that is unique to the micro-scale. To test this hypothesis, specific studies in contact area and surface energy have been performed. Silicon microturbines supported on thrust bearings packed with 285 µm and 500 µm diameter stainless steel balls have undergone spin-down friction testing over a load and speed range of 10-100mN and 500-10,000 rpm, respectively. A positive correlation between calculated contact area and measured friction torque was observed, supporting the adhesion-dominated hysteresis hypothesis. Vapor phase lubrication has been integrated within the microturbine testing scheme in a controlled and characterized manner. Vapor-phase molecules allowed for specifically addressing adhesive energy without changing other system properties. A 61% reduction of friction torque was observed with the utilization of 18% relative humidity water vapor lubrication. Additionally, the relationship between friction torque and normal load was shown to follow an adhesion-based trend, highlighting the effect of adhesion and further confirming the adhesion-dominant hypothesis. The wear mechanisms have been studied for a microfabricated ball bearing platform that includes silicon and thin-film coated silicon raceway/steel ball materials systems. Adhesion of ball material, found to be the primary wear mechanism, is universally present in all tested materials systems. Volumetric adhesive wear rates are observed between 4x10^-4 µm^3/mN*rev and 4x10^-5 µm3/mN*rev were determined by surface mapping techniques and suggest a self-limiting process. This work also demonstrates the utilization of an Off-The-Shelf (OTS) MEMS accelerometer to confirm a hypothesized ball bearing instability regime which encouraged the design of new bearing geometries, as well as to perform in situ diagnostics of a high-performance rotary MEMS device. Finally, the development of a 3D fabrication technique with the potential of significantly improving the performance of micro-scale rotary structures is described. The process was used to create uniform, smooth, curved surfaces. Micro-scale ball bearings are then able to be utilized in high-speed regimes where load can be accommodated both axially and radially, allowing for new, high-speed applications. A comprehensive exploration of the fundamental tribology of microball bearing MEMS has been performed, including specific experiments on friction, wear, lubrication, dynamics, and geometrical optimization. Future devices utilizing microball bearings will be engineered and optimized based on the results of this dissertation.
- K. E. Gregorczyk, "Atomic Layer Deposition of Ru and RuO2: New Process Development, Fabrication of Heterostructured Nanoelectrodes, and Applications in Energy Storage," Material Science and Engineering, Dissertation, 2013, Advisor(s): G. W. Rubloff. link
[Abstract]
The ability to fabricate heterostructured nanomaterials with each layer of the structure having some specific function, i.e. energy storage, charge collection, etc., has recently attracted great interest. Of the techniques capable of this type of process, atomic layer deposition (ALD) remains unique due to its monolayer thickness control, extreme conformality, and wide variety of available materials. This work aims at using ALD to fabricate fully integrated heterostructured nanomaterials. To that end, two ALD processes, using a new and novel precursor, bis(2,6,6-trimethyl-cyclohexadienyl)ruthenium, were developed for Ru and RuO2 showing stable growth rates of 0.5 Å/cycle and 0.4 Å/cycle respectively. Both process are discussed and compared to similar processes reported in the literature. The Ru process is shown to have significantly lower nucleation while the RuO2 is the first fully characterized ALD process known. Using the fully developed RuO2 ALD process, thin film batteries were fabricated and tested in standard coin cell configurations. These cells showed high first cycle gravimetric capacities of ~1400 mAh/g, which significantly degraded after ~40 cycles. Rate performance was also studied and showed a decrease in 1st cycle capacity as a function of increased rate. These results represent the first reports of any RuO2 battery studied beyond 3 cycles. To understand the degradation mechanisms witnessed in the thin film studies in-situ TEM experiments were conducted. Single crystal RuO2 nanowires were grown using a vapor transport method. These nanowires were cycled inside a TEM using Li2O as an electrolyte and showed a ~95% volume expansion after lithiation, ~26% of which was irreversible. Furthermore, a chemical irreversibility was also witnessed, where the reaction products Ru and Li2O remain even after full delithiation. With these mechanisms in mind heterostructured nanowires were fabricated in an attempt to improve the cycling performance. Core/shell TiN/RuO2 and MWCNT/RuO2 structures were fabricating using the ALD process developed in this work. While the TiN/RuO2 structures did not show improved cycling performance due to connection issues, the MWCNT/RuO2 structure showed a stable areal capacity of ~600 μAh/cm2 after ~20 cycles and were easily cycled 100 times.
- A. Gerratt, "Silicon and Polymer Components for Microrobots," Mechanical Engineering, Dissertation, 2013, Advisor(s): S. Bergbreiter. link
[Abstract]
This dissertation presents the characterization and implementation of the first microfabrication process to incorporate high aspect ratio compliant polymer structures in-plane with traditional silicon microelectromechanical systems (MEMS). This discussion begins with in situ mechanical characterization of microscale polymer springs using silicon-on-insulator-MEMS (SOI-MEMS). The analysis compares microscale samples that were tested on-chip with macroscale samples tested using a dynamic mechanical analyzer. The results describe the effect of the processing steps on the polymer during fabrication and help to guide the design of mechanisms using polymers. Characterization of the dielectric breakdown of polymer thin films with thicknesses from 2 to 14 um between silicon electrodes was also performed. The results demonstrate that there is a strong dependence of the breakdown field on both the electrode gap and shape. The breakdown fields ranged from 250 V/um to 635 V/um, depending on the electrode geometry and gap, approaching 10x the breakdown fields for air gaps of the same size. These materials were then used to create compliant all-polymer thermal and electrostatic microactuators. All-polymer thermal actuators demonstrated displacements as large at 100 um and forces as high as 55 uN. A 1 mm long electrostatic dielectric elastomer actuator demonstrated a tip displacement as high as 350 um at 1.1 kV with a electrical power consumption of 11 uW. The actuators are fabricated with elastomeric materials, so they are very robust and can undergo large strains in both tension and bending and still operate once released. Finally, the compliant polymer and silicon actuators were combined in an actuated bio-inspired system. Small insects and other animals use a multitude of materials to realize specific functions, including locomotion. By incorporating compliant elastomer structures in-plane with traditional silicon actuators, compact energy storage systems based on elastomer springs for small jumping robots were demonstrated. Results include a 4 mm x 4 mm jumping mechanism that has reached heights of 32 cm, 80x its own height, and an on-chip actuated mechanism that has been used to propel a 1.4 mg projectile over 7 cm.
- J. Felder, "Extreme Vertical Displacement, High Force Silicon Microstage Zipper Actuatoars," Mechanical Engineering, Thesis, 2013, Advisor(s): D. L. DeVoe. link
[Abstract]
Large vertical deflection, high force microactuators are desired in MEMS for a variety of applications. This thesis details a novel large-displacement electrostatic "zipper" microactuator capable of achieving hundreds of microns of out-of-plane deflection and delivering high forces, fabricated entirely from SOI (silicon-on-insulator). This technology is novel in its use of SiO2 as both a high quality dielectric and the stressed layer of the bimorph. Geometries are explored analytically, numerically and experimentally to provide the greatest electromechanical output while constraining the device footprint to 1mm2. Device performance was benchmarked against previously established out-of-plane microactuators. We report the first instance of zipper-inspired electrostatic "microstage" actuators whose flat center stage and vertical actuation mode is ideal for carrying and moving a load. Fabricated microstages are capable of achieving out-of-plane deflections up to 1.2 mm, force outputs up to 1 mN, pull-in voltage as low as 20 V, and switching times of 1 ms.
- S. Chowdhury, "Planning for Automated Optical Micromanipulation of Biological Cells," Mechanical Engineering, Dissertation, 2013, Advisor(s): S. K. Gupta. link
[Abstract]
Optical tweezers (OT) can be viewed as a robot that uses a highly focused laser beam for precise manipulation of biological objects and dielectric beads at micro-scale. Using holographic optical tweezers (HOT) multiple optical traps can be created to allow several operations in parallel. Moreover, due to the non-contact nature of manipulation OT can be potentially integrated with other manipulation techniques (e.g. microfluidics, acoustics, magnetics etc.) to ensure its high throughput. However, biological manipulation using OT suffers from two serious drawbacks: (1) slow manipulation due to manual operation and (2) severe effects on cell viability due to direct exposure of laser. This dissertation explores the problem of autonomous OT based cell manipulation in the light of addressing the two aforementioned limitations. Microfluidic devices are well suited for the study of biological objects because of their high throughput. Integrating microfluidics with OT provides precise position control as well as high throughput. An automated, physics-aware, planning approach is developed for fast transport of cells in OT assisted microfluidic chambers. The heuristic based planner employs a specific cost function for searching over a novel state-action space representation. The effectiveness of the planning algorithm is demonstrated using both simulation and physical experiments in microfluidic-optical tweezers hybrid manipulation setup. An indirect manipulation approach is developed for preventing cells from high intensity laser. Optically trapped inert microspheres are used for manipulating cells indirectly either by gripping or pushing. A novel planning and control approach is devised to automate the indirect manipulation of cells. The planning algorithm takes the motion constraints of the gripper or pushing formation into account to minimize the manipulation time. Two different types of cells (Saccharomyces cerevisiae and Dictyostelium discoideum) are manipulated to demonstrate the effectiveness of the indirect manipulation approach.
- X. Chen, "ALD Processes and Applications to Nanostructured Electrochemical Energy Storage Devices," Material Science and Engineering, Dissertation, 2013, Advisor(s): G. W. Rubloff. link
[Abstract]
Next generation Li-ion batteries (LIB) are expected to display high power densities (i.e. high rate performance, or fast energy storage) while maintaining high energy densities and stable cycling performance. The key to fast energy storage is the efficient management of electron conduction, Li diffusion, and Li-ion migration in the electrode systems, which requires tailored material and structural engineering in nanometer scale. Atomic layer deposition (ALD) is a unique technique for nanostructure fabrications due to its precise thickness control, unprecedented conformality, and wide variety of available materials. This research aims at using ALD to fabricate materials, electrodes, and devices for fast electrochemical energy storage. First, we performed a detailed study of ALD V2O5 as a high capacity cathode material, using vanadium tri-isopropoxide (VTOP) precursor with both O3 and H2O as oxidant. The new O3-based process produces polycrystalline films with generally higher storage capacity than the amorphous films resulting from the traditional H2O-based process. We identified the crucial tradeoff between higher gravimetric capacity with thinner films and higher material mass with thicker films. For the thickness regime 10-120 nm, we chose areal energy and power density as a useful metric for this tradeoff and found that it is optimized at 60 nm for the O3-VTOP ALD V2O5 films. In order to increase material loading on fixed footprint area, we explored various 3-dimentional (3D) substrates. In the first example, we used multiwall carbon nanotube (MWCNT) sponge as scaffold and current collector. The core/shell MWCNT/V2O5 sponge delivers a stable high areal capacity of 816 μAh/cm2 for 2 Li/V2O5 voltage range (4.0-2.1 V) at 1C rate (nC means charge/discharge in 1/n hour), 450 times that of a planar V2O5 thin film cathode. Due to low density of MWCNT and thin V2O5 layer, the sponge cathode also delivers high gravimetric power density in device level that shows 5X higher power density than commercial LIBs. In the other example, Li-storage paper cathodes, functionalized of conductivity from CNT and Li-storage capability from V2O5¬, presented remarkably high rate performance due to the hierarchical porosity in paper for Li+ migration. The specific capacity of V2O5 is as high as 410 mAh/g at 1C rate, and retained 116 mAh/g at high rate of 100C. We found V2O5 capacities decreased by about 30% at high rates of 5C-100C after blocking the mesopores in cellulose fiber, which serves to be the first confirmative evidence of the critical role of mesoporosity in paper fibers for high-rate electrochemical devices. Finally, we made high density well-aligned nanoporous electrodes (2 billion/cm2) using anodic alumina template (AAO). ALD materials were deposited into the nanopores sequentially - Ru or TiN for current collection, and V2O5 for Li-storage. Ru metal by ALD shows high conductivity and conformality, and serves best as the current collector for V2O5. The capacity of V2O5 reaches about 88% of its theoretic value at high rate of 50C. Such electrodes can be cycled for 1000 times with 78% capacity retention.
- J. Betz, "New Sensing Modalities for Bacterial and Environmental Phenomena," Bioengineering, Dissertation, 2013, Advisor(s): G. W. Rubloff. link
[Abstract]
Intercellular communication is a ubiquitous phenomenon across all domains of life, ranging from archaea to bacteria to eukarya. In bacteria, this is often achieved using small molecules that allow bacteria to sense and respond to environmental cues about the presence, identity, and number of neighboring bacteria. This confers survival and competitive advantages to bacteria by providing a coordinated, population-scale response to a given stimulus in the environment. This dissertation describes the development of a microfluidic system for immobilizing and culturing of cells that also enables control over the genetic composition of the bacteria and their subsequent response to environmental stimuli via a new nonviral nucleic acid delivery mechanism. This nonviral nucleic acid delivery occurs outside the parameter space of traditional nonviral nucleic acid delivery methods such as electroporation and chemical transformation. The bacteria are immobilized in an optically clear alginate hydrogel which simulates the physical and chemical environment normally experienced by bacteria in a biofilm. Complementing the microfluidic cell culture work, surface enhanced Raman spectroscopy (SERS), a label-free vibrational spectroscopic technique that lends itself well to use in aqueous systems, was used to detect bacterial signaling molecules. SERS was performed with three different examples of bacterial communication molecules: the universal quorum sensing molecule autoinducer-2 (AI-2), the species-specific Pseudomonas Quinolone Signal (PQS), and the stationary phase indicator molecule indole. SERS substrates were formed by galvanic displacement, a substrate fabrication method that can be adapted to many SERS applications. Taken together, these new sensing modalities represent a step toward developing systems that allow researchers to investigate, understand, and ultimately control a cell's response to its environment.
- C. Shao, "Microfluidic Planar Phospholipids Membrane System Advancing Dynamics Studies of Ion Channels and Membrane Physics," Mechanical Engineering, Dissertation, 2012, Advisor(s): D. L. DeVoe. link
[Abstract]
The interrogation of lipid membrane and biological ion channels supported within bilayer phospholipid membranes has greatly expanded our understanding of the roles membrane and ion channels play in a host of biological functions. Several key drawbacks of traditional electrophysiology systems used in these studies have long limited our effort to study the ion channels. Firstly, the large volume buffer in this system typically only allows single or multiple additions of reagents, while complete removal either is impossible or requires tedious effort to ensure the stability of membrane. Thus, it has been highly desirable to be able to rapidly and dynamically modulate the (bio)chemical conditions at the membrane site. Second, it is difficult to change temperature effectively with large thermal mass in macro device. Third, traditional PPM device host vertical membranes, therefore incompatible with confocal microscopy techniques. The miniaturization of bilayer phospholipid membrane has shown potential solution to the drawbacks stated above. A simple microfluidic design is developed to enable effective and robust dynamic perfusion of reagents directly to an on-chip planar phospholipid membrane (PPM). It allows ion channel conductance to be readily monitored under different dynamic reagent conditions, with perfusion rates up to 20 µL/min feasible without compromising the membrane integrity. It is estimated that the lower limit of time constant of kinetics that can be resolved by our system is 1 minute. Using this platform, the time-dependent responses of membrane-bound ceramide ion channels to treatments with La3+ and a Bcl-xL mutant were studied and the results were interpreted with a novel elastic biconcave distortion model. Another engineering challenge this dissertation takes on is the integration of fluorescence studies to micro-PPM system. The resulting novel microfluidic system enables high resolution, high magnification and real-time confocal microscope imaging with precise top and bottom (bio)chemical boundary conditions defined by perfusion, by integrating in situ PPM formation method, perfusion capability and microscopy compatibility. To demonstrate such electro-optical chip, lipid micro domains were imaged and quantitatively studied for their movements and responses to different physical parameters. As an extension to this platform, a double PPM system has been developed with the aim to study interactions between two membranes. Potential application in biophysics and biochemistry using those two platforms were discussed. Another important advantage of microfluidics is its lower thermal mass and compatibility with various microfabrication methods which enables potential integration of local temperature controller and sensor. A prototype thermal PPM chip is also discussed together with some preliminary results and their implication on ceramide channel assembly and disassembly mechanism.
- K. Saadin, "On Chip Isolation and Enrichment of Tumor Initiating Cells," Chemical Physics, Dissertation, 2012, Advisor(s): I. M. White. link
[Abstract]
We report for the first time a microdevice that enables the selective enrichment and culture of breast cancer stem cells using the principles of mammosphere culture. For nearly a decade, researchers have identified breast cancer stem cells within heterogeneous populations of cells by utilizing low-attachment serum-free culture conditions, which lead to the formation of spheroidal colonies (mammospheres) that are enriched for cancer stem cells. While this assay has proven to be useful for identifying cancer stem cells from a bulk population, ultimately its utility is limited by difficulties in combining the mammosphere technique with other useful cellular and molecular analyses. However, integrating the mammosphere technique into a microsystem can enable it to be combined directly with a number of functions, including cell sorting and analysis, as well as popular molecular assays. In this work, we demonstrate mammosphere culture within a polydimethylsiloxane (PDMS) microsystem. We first prove that hydrophobic PDMS surfaces are as effective as commercial low-attachment plates at selectively promoting the formation of mammospheres. We then demonstrate the culture of mammospheres as large as 0.25 mm within a PDMS microsystem. Finally, we verify that reagents can be delivered to the cell culture wells exclusively by diffusion-based transport, which is necessary because the cells are unattached. This microsystem component can be integrated with other microfluidic functions, such as cell separation, sorting, and recovery, as well as molecular assays, to enable new discoveries in the biology of cancer stem cells that are not possible today.
- M. P. Mosteller, "An Optical Density Detection Platform with Integrated Microfluidics for In Situ Growth, Monitoring, and Treatment of Bacterial Biofilms," Systems Engineering, Thesis, 2012, Advisor(s): R. Ghodssi. link
[Abstract]
Systems engineering strategies utilizing platform-based design methodologies are implemented to achieve the integration of biological and physical system components in a biomedical system. An application of this platform explored, in which an integrated microsystem is developed capable of the on-chip growth, monitoring, and treatment of bacterial biofilms for drug development and fundamental study applications. In this work, the developed systems engineering paradigm is utilized to develop a device system implementing linear array charge-coupled devices to enable real time, non-invasive, label-free monitoring of bacterial biofilms. A novel biofilm treatment method is demonstrated within the developed microsystem showing drastic increases in treatment efficacy by decreasing both bacterial biomass and cell viability within treated biofilms. Demonstration of this treatment at the microscale enables future applications of this method for the in vivo treatment of biofilm-associated infections.
- Y. W. Kim, "An Atomic Layer Deposition Passivated Surface Acoustic Wave Sensor for Bacterial BioFilm Growth Monitoring," Electrical Engineering, Thesis, 2012, Advisor(s): R. Ghodssi. link
[Abstract]
This thesis reports for the first time the design, fabrication, and testing of a reusable Surface Acoustic Wave (SAW) sensor for biofilm growth monitoring. Bacterial biofilms cause severe infections, and are often difficult to remove without an invasive surgery. Thus, their detection at an early stage is critical for effective treatments. A highly sensitive SAW sensor for biofilm growth monitoring was fabricated by depositing a high quality zinc oxide (ZnO) piezoelectric thin film by pulsed laser deposition (PLD). The sensor was successfully passivated by aluminum oxide (Al2O3) using Atomic Layer Deposition (ALD) to prevent ZnO damage from long term media contact. The sensor was reusable over multiple biofilm formation experiments using the ALD Al2O3 passivation and an oxygen plasma biofilm cleaning method. The SAW sensor was studied with Escherichia coli biofilm growth in Lysogeny Broth (LB) and in 10% Fetal Bovine Serum (FBS) as a simulated an in vivo environment. A multiple MHz level resonant frequency shift measured at the output of the SAW sensor in both LB and 10% FBS corresponded to the natural biofilm growth progression. These repeatable E. coli biofilm growth monitoring results validate the novel application of a SAW sensor for future implantable biofilm sensing applications.
- K. Jiang, "Microfluidic Production of Polymeric Functional Microparticles," Chemistry, Dissertation, 2012, Advisor(s): S. R. Raghavan and D. L. DeVoe. link
[Abstract]
This dissertation focuses on applying droplet-based microfluidics to fabricate new classes of polymeric microparticles with customized properties for various applications. The integration of microfluidic techniques with microparticle engineering allows for unprecedented control over particle size, shape, and functional properties. Specifically, three types of microparticles are discussed here: (1) magnetic and fluorescent chitosan hydrogel microparticles and their in-situ assembly into higher-order microstructures; (2) polydimethylsiloxane (PDMS) microbeads with phosphorescent properties for oxygen sensing; (3) macroporous microparticles as biological immunosensors. First, we describe a microfluidic approach to generate monodisperse chitosan hydrogel microparticles that can be further connected in-situ into higher-order microstructures. Microparticles of the biopolymer chitosan are created continuously by contacting an aqueous solution of chitosan at a microfluidic T-junction with a stream of hexadecane containing a nonionic detergent, followed by downstream crosslinking of the generated droplets by a ternary flow of glutaraldehyde. Functional properties of the microparticles can be easily varied by introducing payloads such as magnetic nanoparticles and/or fluorescent dyes into the chitosan solution. We then use these prepared microparticles as "building blocks" and assemble them into high ordered microstructures, i.e. microchains with controlled geometry and flexibility. Next, we describe a new approach to produce monodisperse microbeads of PDMS using microfluidics. Using a flow-focusing configuration, a PDMS precursor solution is dispersed into microdroplets within an aqueous continuous phase. These droplets are collected and thermally cured off-chip into soft, solid microbeads. In addition, our technique allows for direct integration of payloads, such as an oxygen-sensitive porphyrin dye, into the PDMS microbeads. We then show that the resulting dye-bearing beads can function as non-invasive and real-time oxygen micro-sensors. Finally, we report a co-flow microfluidic method to prepare uniform polymer microparticles with macroporous texture, and investigate their application as discrete immunological biosensors for the detection of biological species. The matrix of such microparticles is based on macroporous polymethacrylate polymers configured with tailored pores ranging from hundreds of nanometers to a few microns. Subsequently, we immobilize bioactive antibodies on the particle surface, and demonstrate the immunological performance of these functionalized porous microbeads over a range of antigen concentrations.
- L. Haspert, "Nano-engineering and Simulating Electrostatic Capacitors for Electrical Energy Storage," Material Science and Engineering, Dissertation, 2012, Advisor(s): G. W. Rubloff. link
[Abstract]
Electrical energy storage solutions with significantly higher gravimetric and volumetric energy densities and rapid response rates are needed to balance the highly dynamic, time-variant supply and demand for power. Nanoengineering can provide useful structures for electrical energy storage because it offers the potential to increase efficiency, reduce size/weight, and improve performance. While several nanostructured devices have shown improvements in energy and/or power densities, this dissertation focuses on the nanoengineering of electrostatic capacitors (ESC) and application of these high-power electrostatic capacitors in electrical energy storage systems. A porous nano-template with significant area enhancement per planar unit area coated with ultra-thin metal-insulator-metal (MIM) layers has shown significant improvements in areal capacitance. However, sharp asperities inherent to the initial nano-template localized electric fields and caused premature (low field) breakdown, limiting the possible energy density (E = ½ CV2/m). A nanoengineering strategy was identified for rounding the template asperities, and this showed a significant increase in the electrical breakdown strength of the device, providing rapid charging and discharging and an energy density of 1.5 W-h/kg - which compares favorably with the best state-of-the-art devices that provide 0.7 W-h/kg. The combination of the high-power ESC with a complementary high-energy-density electrochemical capacitor (ECC) was modeled to evaluate methods resulting in the combined power-energy storage capabilities. While significant improvements in the ESC's energy density were reported, the nanodevices display nonlinear leakage resistance, which directly relates to charge retention. The ECC has distinctly different nonlinearities, but can retain a greater density of charge for significantly longer, albeit with slower inherent charging and discharging rates than the ESC. The experimentally derived dynamic model simulating the nonlinear performance of the ESC and ECC devices indicated this hybrid-circuit reduces the time required to charge the ECC to near-maximum capacity by a factor of up to ~ 12.
- K. Gerasopoulos, "Integration and Characterization of Tobacco Mosaic Virus Based Nanostructured Materials in Three-Dimensional Microbattery Architectures," Material Science and Engineering, Dissertation, 2012, Advisor(s): R. Ghodssi. link
[Abstract]
The realization of next-generation portable electronics, medical implants and miniaturized, autonomous microsystems is directly linked with the development of compact and efficient power sources and energy storage devices with high energy and power density. As the components of these devices are continuously scaled down in size, there is a growing demand for decreasing the size of their power supply as well, while maintaining performance comparable to larger assemblies. This dissertation presents a novel approach for the development of microbattery electrodes that is based on integrating both micro and nano structured components for the formation of hierarchical electrodes. These electrodes combine both high energy density (enabled by the high surface area and mass loading) with high power density (due to the small thickness of the active battery materials). The key building block technologies in this work are the bottom-up self-assembly and metallization of a biological template and the top-down microfabrication processes enabled by Microelectromechanical Systems (MEMS) technology. The biotemplate used is the Tobacco mosaic virus (TMV), a rod-like particle that can be genetically modified to express functional groups with enhanced metal binding properties. In this project, this feature is combined with standard microfabrication techniques for the synthesis of nanostructured energy-related materials as well as their hierarchical patterning in device architectures. Specifically, synthesis of anode (TiO2) and cathode (V2O5) materials for Li-ion batteries in a core/shell configuration is presented, where the TMV biomineralization is combined with atomic layer deposition of the active material. These nanostructured electrodes demonstrate high energy storage capacities, high rate capabilities and superior performance to electrodes with planar geometries. In addition, a toolbox of biofabrication processes for the defined patterning of virus-templated structures has been developed. Finally, the nanocomposite electrodes are integrated with three-dimensional micropillars to form hierarchical electrodes that maintain the high rate performance capabilities of nanomaterials while exhibiting an increase in energy density compared to nanostructures alone. This is in accordance with the increase in surface area added by the microstructures. Investigation of capacity scaling for varying active material thickness reveals underlying limitations in nanostructured electrodes and highlights the importance of this method in controlling both energy and power density with structural hierarchy. These results present a paradigm-shifting technology for the fabrication of next-generation microbatteries for MEMS and microsystems applications.
- M. P. Dandin, "CMOS Single-Photon Avalanche Diodes and Micromachined Optical Filters for Integrated Fluorescence Sensing," Bioengineering, Dissertation, 2012, Advisor(s): P. A. Abshire and E. Smela. link
[Abstract]
This dissertation presents a body of work that addresses the two most pressing challenges in the field of integrated fluorescence sensing, namely, the design of integrated optical sensors and the fabrication of high-rejection micro-scale optical filters. Two novel enabling technologies were introduced. They are: the perimeter-gated single-photon avalanche diode (PGSPAD), for on-chip photon counting, and the benzotriazole (BTA)-doped thin-film polymer filter, for on-chip ultraviolet light rejection. Experimental results revealed that the PGSPAD front-end, fabricated in a 0.5 μm standard mixed-signal CMOS process, had the capability of counting photons in the MHz regime. In addition, it was found that a perimeter gate, a structural feature used to suppress edge breakdown in the diode, also maximized the signal-to-noise-ratio in the high-count rate regime whereas it maximized sensitivity at low count rates. On the other hand, BTA-doped filters were demonstrated utilizing three commonly used polymers as hosts. The filters were patternable, utilizing the same procedures traditionally used to pattern the undoped polymer hosts, a key advantage for integration into microsystems. Filter performance was analyzed using a set of metrics developed for optoelectronic characterization of integrated fluorescence sensors; high rejection levels (nearing -40 dB) of UV light were observed in films of only 5 μm in thickness. Ultimately, BTA-doped filters were integrated into a portable sensor, and their use was demonstrated in two types of bioassays.
- I. Chakraborty, "Near-Grazing and Noise-Influenced Dynamics of Elastic Cantilevers with Nonlinear Tip Interaction Forces," Mechanical Engineering, Dissertation, 2012, Advisor(s): B. Balachandran. link
[Abstract]
Within this dissertation work, numerical, analytical, and experimental studies are conducted with macro-scale and micro-scale elastic structures in the presence of nonlinear force interactions. The specific physical systems explored within this work are an atomic force microscope (AFM) micro-cantilever and a macro-scale cantilever experiencing similar tip interaction forces as the AFM cantilever operated in tapping mode. The tip sample forces in an AFM operation are highly nonlinear, with long-range attractive forces and short-range repulsive forces. In the macro-scale case, magnetic attractive forces and repulsive forces, which arise due to impacts with a compliant surface are used to generate similar nonlinear tip interaction forces. For elastic structures subjected to off-resonance base excitations, bifurcations close to grazing events are studied in detail, and the observed nonlinear phenomena are found to be common across the considered length scales. The dynamics of the considered systems are studied with a reduced-order computational model based on Galerkin projection with a single mode approximation. Along with studies on the bifurcation behavior, the effects of added Gaussian white noise on the system dynamics are also examined. Non-smooth system dynamics is studied by constructing local maps near the discontinuity. Period-doubling events are examined by using Poincaré maps and discontinuity mapping analysis. An important component of this dissertation research is the investigations into the effects of noise on the dynamics of these structures. Experimental and numerical efforts are used to examine the stochastic dynamics of the cantilever structures when a random component is added to the harmonic input. The noise effects are studied when the excitation frequency is close to a system resonance as well as when it is off-resonance. An analytical-numerical method with moment evolution equations is used to study the effects of noise. The effects of noise on contact and adhesion phenomena are explored. Through this dissertation work, the importance of considering noise-influenced dynamics in micro-scale applications such as AFM operations is illustrated. In addition, this work helps shed light on universality of nonlinear phenomenon across different length scales.
- S. D. Baron, "A Platform Towards In Situ Stress/Strain Measurement in Lithium Ion Battery Electrodes," Electrical Engineering, Thesis, 2012, Advisor(s): R. Ghodssi. link
[Abstract]
This thesis demonstrates the design, fabrication and testing of a platform for in situ stress/strain measurement in lithium ion battery electrodes. The platform - consisting of a microelectromechanical system (MEMS) chip containing an electrochemical cavity and an optical sensing element, a custom electrochemical package and an experimental setup - was successfully developed. Silicon was used as an active electrode material, and a thin-film electrochemical stack was conceived and tested. Finally, multiple experiments showed correlation between the active material volume change inside the battery and a signal change in the optical sensing element. The experimental results, combined with the MEMS implementation of the sensing element provide a promising way to evaluate electrochemical reaction-induced stress monitoring in a simple and compact fashion, while experiments are carried out in situ.
- B. Balakrisnan, "Microfabrication and Modeling of Dielectric Elastomer Actuators," Mechanical Engineering, Dissertation, 2012, Advisor(s): E. Smela. link
[Abstract]
Dielectric elastomer actuators (DEAs) are a class of polymeric actuators that have gained prominence over the last decade. A DEA is comprised of a polymer sandwiched between two compliant electrodes. When voltage is applied between the two electrodes, electrostatic attraction between the electrodes compresses the elastomer in that direction and stretches it in the other two directions. DEAs produce dimensional changes (strains) up to 300% upon application of an electric field. DEAs have tremendous potential for applications requiring large displacements and have been demonstrated for many macro-scale (centimeter and larger) applications such as robots, loudspeakers, and motors. There are potentially many useful applications for micro-scale DEAs (less than millimeter-sized devices with micron-sized actuators) in the fields of micro-robotics, micro-optics, and micro-fluidics. However, miniaturization of DEAs is challenging because many of the materials and DEA fabrication methods used on the macro-scale cannot be adapted for micro-scale fabrication of DEAs. This thesis explores the feasibility of developing fabrication strategies for micro-scale DEAs by adapting micro-electromechanical systems (MEMS) technology. In addition, fabrication protocols for micro-scale DEAs have been developed. The other aspect of this thesis is the design of bending DEAs. Benders are useful because for a given actuation strain, greater deflection can be observed by controlling the stiffnesses and thicknesses of different layers. A general guideline for designing bending DEA configurations such as unimorph, bimorph, and multilayer stacks was developed using a multilayer analytical model. The design optimization is based on the effect of thickness and stiffness of different layers on curvature, blocked force, and work. Complaint electrodes and their design are important for DEAs to enable the elastomer to stretch unrestricted. Thus, design criteria for the fabrication of crenellated electrodes and crenellated elastomers with electrodes were investigated. This guideline enabled design of structures with appropriate axial or bending stiffnesses based on the amplitude, angle, length, and thickness. Simple analytical equations for axial and bending stiffness for crenellated electrodes with different shapes were derived. In addition, numerical simulations of crenellated elastomer with stiff electrode were performed
- Z. Zhang, "Morphologic Instability of Graphene and its Potential Applications," Mechanical Engineering, Dissertation, 2011, Advisor(s): T. Li. link
[Abstract]
Graphene is a monolayer of graphite. The surge of interest in graphene, as epitomized by the Nobel Prize in Physics in 2010, is largely attributed to its exceptional properties. Ultra thin, mechanically tough, electrically conductive, and transparent graphene films promise to enable a wealth of possible applications ranging from thin-film solar cells, flexible displays, to biochemical sensing arrays. However, significant gaps remain to realize these potential applications, largely due to the difficulty of precisely controlling graphene properties. Graphene is intrinsically non-flat and tends to be randomly corrugated. The random graphene morphology can lead to unstable performance of graphene devices as the corrugating physics of graphene is closely tied to its electronic properties. Future success of graphene-based applications hinges upon precise control of the graphene morphology, a significant challenge largely unexplored so far. This dissertation aims to explore viable pathways to tailoring graphene morphology and leverage possible morphologic instability of graphene for novel nano-device applications. Inspired by recent experiments, we propose and benchmark a strategy to precisely control the graphene morphology via extrinsic regulation (e.g., substrate surface features, patterned nanowires and nanoparticles). A general energetic framework is delineated to quantitatively determine the extrinsically regulated graphene morphology through energy minimization. Such a framework is benchmarked by determining the graphene morphology regulated by various types and dimensions of nanoscale extrinsic scafffolds, including two dimensional herringbone and checkerboard corrugations on substrate surfaces and one dimensional substrate surface grooves and patterned nanowires. The results reveal a snap-through instability of the graphene morphology, that is, depending on interfacial bonding energy and substrate surface roughness, the graphene morphology exhibits a sharp transition between two distinct states: (1) closely conforming to the substrate surface and (2) remaining nearly flat on the substrate surface. This snap-through instability of graphene holds potential to enable graphene-based functional nano-devices (e.g., ultrasensitive nano-switches). Another type of morphologic instability of graphene is the spontaneous scrolling of graphene into a carbon nanoscroll (CNS). The spiral multilayer nanostructure of CNSs is topologically open and thus distinct from that of carbon nanotubes (CNTs). The unique topological structure of CNSs can enable an array of novel applications, e.g., hydrogen storage, water channels and ultrafast nano-oscillators. However, the realization of CNS-based applications is hindered by the lack of reliable approach to fabricating high quality CNSs. We propose a simple physical approach to fabricating CNSs via CNT-initiated scrolling of graphene on a substrate. The successful formation of a CNS depends on the CNT diameter, the carbon-carbon interaction strength and the graphene-substrate interaction strength. We further demonstrate that the resulting CNS/CNT nanostructure can be used as an ultrafast axial nano-oscillator that operates at 10s GHz. Such CNS-based nano-oscillators can be excited and driven by an external AC electric field, further illustrating their potential to enable nano-scale energy transduction, harnessing and storage.
- D. Sander, "CMOS Image Sensor for Lab-on-a-Chip Microsystem Design," Electrical Engineering, Dissertation, 2011, Advisor(s): P. Abshire. link
[Abstract]
The work described herein serves as a foundation for the development of CMOS imaging in lab-on-a-chip microsystems. Lab-on-a-chip (LOC) systems attempt to emulate the functionality of a cell biology lab by incorporating multiple sensing modalidites into a single microscale system. LOC are applicable to drug development, implantable sensors, cell-based bio-chemical detectors and radiation detectors. The common theme across these systems is achieving performance under severe resource constraints including noise, bandwidth, power and size. The contributions of this work are in the areas of two core lab-on-a-chip imaging functions: object detection and optical measurements.
- P. H. Dykstra, "A Microfluidic Programmable Array for Label-free Detection of Biomolecules," Electrical Engineering, Dissertation, 2011, Advisor(s): R. Ghodssi. link
[Abstract]
One of the most promising ways to improve clinical diagnostic tools is to use microfluidic Lab-on-a-chip devices. Such devices can provide a dense array of fluidic components and sensors at the micro-scale which drastically reduce the necessary sample volumes and testing time. This dissertation develops a unique electrochemical sensor array in a microfluidic device for high-throughput, label-free detection of both DNA hybridization and protein adsorption experiments. The device consists of a patterned 3 x 3 grid of electrodes which can be individually addressed and microfluidic channels molded using the elastomer PDMS. The channels are bonded over the patterned electrodes on a silicon or glass substrate. The electrodes are designed to provide a row-column addressing format to reduce the number of contact pads required and to drastically reduce the complexity involved in scaling the device to include larger arrays. The device includes straight channels of 100 micron height which can be manually rotated to provide either horizontal or vertical fluid flow over the patterned sensors. To enhance the design of the arrayed device, a series of microvalves were integrated with the platform. This integrated system requires rounded microfluidic channels of 32 micron height and a second layer of channels which act as pneumatic valves to pinch off selected areas of the microfluidic channel. With the valves, the fluid flow direction can be controlled autonomously without moving the bonded PDMS layer. Changes to the mechanism of detection and diffusion properties of the system were examined after the integration of the microvalve network. Protein adhesion studies of three different proteins to three functionalized surfaces were performed. The electrochemical characterization data could be used to help identify adhesion properties for surface coatings used in biomedical devices or for passivating sensor surfaces. DNA hybridization experiments were performed and confirmed both arrayed and sensitive detection. Hybridization experiments performed in the valved device demonstrated an altered diffusion regime which directly affected the detection mechanism. On average, successful hybridization yielded a signal increase 8x higher than two separate control experiments. The detection limit of the sensor was calculated to be 8 nM.
- M. J. Carrier, "Improvements in Microboiling Device Design," Material Science and Engineering, Thesis, 2011, Advisor(s): G. W. Rubloff. link
[Abstract]
Small ribbon heaters (10 - 20 um wide) have been used for many years to study the formation of microbubbles in liquids when short voltage pulses are applied. This thesis describes improvements in the device design with an emphasis on smaller and more sensitive heaters. I used a novel method of creating 250 nanometer wide heaters to keep both the fabrication time and costs as low as possible by using a focused ion beam to create the heaters from a set of larger devices. Ribbon heaters are usually fabricated on a thin SiO2 layer on a silicon wafer which acts as a large heat sink whose effect becomes more pronounced the smaller the heater width. Suspending the heaters on a thin membrane dramatically increased their sensitivity in microboiling experiments. The suspended devices required the development of a very low stress platinum deposition process.
- M. I. Beyaz, "An Integrated Electromagnetic Micro-Turbo-Generator Supported on Encapsulated MicroBall Bearings," Electrical Engineering, Dissertation, 2011, Advisor(s): R. Ghodssi. link
[Abstract]
This dissertation presents the development of an integrated electromagnetic micro-turbo-generator supported on encapsulated microball bearings for electromechanical power conversion in MEMS (Microelectromechanical Systems) scale. The device is composed of a silicon turbine rotor with magnetic materials that is supported by microballs over a stator with planar, multi-turn, three-phase copper coils. The micro-turbo-generator design exhibits a novel integration of three key technologies and components, namely encapsulated microball bearings, incorporated thick magnetic materials, and wafer-thick stator coils. Encapsulated microball bearings provide a robust supporting mechanism that enables a simple operation and actuation scheme with high mechanical stability. The integration of thick magnetic materials allows for a high magnetic flux density within the stator. The wafer-thick coil design optimizes the flux linkage and decreases the internal impedance of the stator for a higher output power. Geometrical design and device parameters are optimized based on theoretical analysis and finite element simulations. A microfabrication process flow was designed using 15 optical masks and 110 process steps to fabricate the micro-turbo-generators, which demonstrates the complexity in device manufacturing. Two 10-pole devices with 2 and 3 turns per pole were fabricated. Single phase resistances of 46 and 220 Ohms were measured for the two stators, respectively. The device was actuated using pressurized nitrogen flowing through a silicon plumbing layer. A test setup was built to simultaneously measure the gas flow rate, pressure, rotor speed, and output voltage and power. Friction torques in the range of 5.5-33 µNm were measured over a speed range of 0-16 krpm (kilo rotations per minute) within the microball bearings using spin-down testing methodology. A maximum per-phase sinusoidal open circuit voltage of 0.1 V was measured at 23 krpm, and a maximum per-phase AC power of 10 µW was delivered on a matched load at 10 krpm, which are in full-agreement with the estimations based on theoretical analysis and simulations. The micro-turbo-generator presented in this work is capable of converting gas flow into electricity, and can potentially be coupled to a same-scale combustion engine to convert high-density hydrocarbon energy into electrical power to realize a high-density power source for portable electronic systems.
- P. Banerjee, "Exploiting Process Synergy between Anodic Aluminum Oxide Nanotemplates and Atomic Layer Deposition: from Thin Films to 3D Nano-Electronic Devices," Material Science and Engineering, Dissertation, 2011, Advisor(s): G. W. Rubloff. link
[Abstract]
Self-assembled, 3D nanoporous templates present an opportunity to develop devices which are lithography-free, massively scalable and hence, highly manufacturable. Self-limited deposition processes on the other hand, allow functional thin films to be deposited inside such templates with precision and unprecedented conformality. Taken together, the combination of both processes provides a powerful `toolbox' to enable many modern nano devices. In this work, I will present data in three parts. First, I will demonstrate the capabilities of Atomic Layer Deposition (ALD), a self-limited thin film deposition technique in preparing nanoalloyed Al-doped ZnO (AZO) thin films. These films are visibly transparent and electrically conducting. Structure-property relationships are established that highlight the power of ALD to tailor film compositions at the nanoscale. Next, I will use ALD ZnO films in conjunction with aged, ALD V2O5 films to form pn junctions which show rectification with an Ion/Ioff as high as 598. While, the ZnO is a well known n-type semiconductor, the discovery of p-type conductivity in aged V2O5 is surprising and is found to be due to the protonic (H+) conductivity of intercalated H2O in V2O5. Thus, we demonstrate a mixed electronic-ionic pn junction for the first time. Finally, I combine the material set of the pn junction with self-assembled, anodic aluminum oxide (AAO) 3D nanoporous templates to create 3D nanotubular pn junctions. The pn junctions are built inside pores which are only 90 nm wide and up to 2 um deep and show rectification with Ion/Ioff of 16.7. Process development and integrations strategies will be discussed that allow for large scale manufacturing of such devices a real possibility.
- A. K. Balijepalli, "Modeling and Experimental Techniques to Demonstrate Nanomanipulation With Optical Tweezers," Mechanical Engineering, Dissertation, 2011, Advisor(s): S. K. Gupta and T. W. LeBrun. link
[Abstract]
The development of truly three-dimensional nanodevices is currently impeded by the absence of effective prototyping tools at the nanoscale. Optical trapping is well established for flexible three-dimensional manipulation of components at the microscale. However, it has so far not been demonstrated to confine nanoparticles, for long enough time to be useful in nanoassembly applications. Therefore, as part of this work we demonstrate new techniques that successfully extend optical trapping to nanoscale manipulation. In order to extend optical trapping to the nanoscale, we must overcome certain challenges. For the same incident beam power, the optical binding forces acting on a nanoparticle within an optical trap are very weak, in comparison with forces acting on microscale particles. Consequently, due to Brownian motion, the nanoparticle often exits the trap in a very short period of time. We improve the performance of optical traps at the nanoscale by using closed-loop control. Furthermore, we show through laboratory experiments that we are able to localize nanoparticles to the trap using control systems, for sufficient time to be useful in nanoassembly applications, conditions under which a static trap set to the same power as the controller is unable to confine a same-sized particle. Before controlled optical trapping can be demonstrated in the laboratory, key tools must first be developed. We implement Langevin dynamics simulations to model the interaction of nanoparticles with an optical trap. Physically accurate simulations provide a robust platform to test new methods to characterize and improve the performance of optical tweezers at the nanoscale, but depend on accurate trapping force models. Therefore, we have also developed two new laboratory-based force measurement techniques that overcome the drawbacks of conventional force measurements, which do not accurately account for the weak interaction of nanoparticles in an optical trap. Finally, we use numerical simulations to develop new control algorithms that demonstrate significantly enhanced trapping of nanoparticles and implement these techniques in the laboratory. The algorithms and characterization tools developed as part of this work will allow the development of optical trapping instruments that can confine nanoparticles for longer periods of time than is currently possible, for a given beam power. Furthermore, the low average power achieved by the controller makes this technique especially suitable to manipulate biological specimens, but is also generally beneficial to nanoscale prototyping applications. Therefore, capabilities developed as part of this work, and the technology that results from it may enable the prototyping of three-dimensional nanodevices, critically required in many applications.
- E. D. Robertson Cleveland, "Atomic Layer Deposition Conformality and Process Optimization: Transitioning from 2-Dimensional Planar Systems to 3-Dimensional Nanostructures," Material Science and Engineering, Dissertation, 2010, Advisor(s): G. W. Rubloff. link
[Abstract]
Conformal coatings are becoming increasingly important as technology heads towards the nanoscale. The exceptional thickness control (atomic scale) and conformality (uniformity over nanoscale 3D features) of atomic layer deposition (ALD) has made it the process of choice for numerous applications found in microelectronics and nanotechnology with a wide variety of ALD processes and resulting materials. While its benefits derive from self-limited saturating surface reactions of alternating gas precursors, process optimization for ALD conformality is often difficult as process parameters, such as dosage, purge, temperature and pressure are often interdependent with one another, especially within the confines of an ultra-high aspect ratio nanopore. Therefore, processes must be optimized to achieve self-limiting saturated surfaces and avoid parasitic CVD-like reactions in order to maintain thickness control and achieve uniformity and conformality at the atomic level while preserving the desired materials' properties (electrical, optical, compositional, etc.).
This work investigates novel approaches to optimize ALD conformality when transitioning from a 2D planar system to a 3D ultra-high aspect ratio nanopore in the context of a cross-flow wafer-scale reactor used to highlight deviations from ideal ALD behavior. Porous anodic alumina (PAA) is used as a versatile platform to analyze TiO2 ALD profiles via ex-situ SEM, EDS and TEM. Results of TiO2 ALD illustrate enhanced growth rates that can occur when the precursors titanium tetraisopropoxide and ozone were used at minimal saturation doses for ALD and for considerably higher doses. The results also demonstrate that ALD process recipes that achieve excellent across-wafer uniformity across full 100 mm wafers do not produce conformal films in ultra-high aspect ratio nanopores. The results further demonstrate that conformality is determined by precursor dose, surface residence time, and purge time, creating large depletion gradients down the length of the nanopore. Also, deposition of ALD films over sharp surface features are very uniform, and verified by profile evolution modeling. This behavior, in contrast to that in high aspect ratio structures, suggests strongly that detailed dynamics, local flow conditions (e.g. viscous vs molecular), surface residence time, and ALD surface reaction kinetics play a complex role in determining ALD profiles for high aspect ratio features.
- J. E. Rajkowski, "Rapid Polymer Prototyping for Low Cost and Robust Microrobots," Mechanical Engineering, Thesis, 2010, Advisor(s): S. E. Bergbreiter. link
[Abstract]
The Rapid Microrobot Prototyping (RaMP) Process uses Loctite(R) photo-patternable polymer products and photolithography to rapidly fabricate robust, inexpensive, and compliant robots. The process is developed and examined on two size scales. On the size scale of several centimeters, two functional robots and a small gripper have been designed and demonstrated with shape memory alloy (SMA) used for actuation. The gripper is 1.2 g and costs $3.21 while the inchworm robot is 7.4 g and costs $7.76 in small numbers. The second robot costs $14.93 in small numbers. On the sub-centimeter scale, designs and considerations for a walking microrobot fabricated with the process and its control are fully described. The design and kinematics of a thermally actuated, one degree of freedom leg for the microrobot are developed and simulated. Several of these units could be combined to rapidly build a 30 mg functional and simple walking microrobot with the ability to lift several grams.
- R. Probst, "Optimal Control of Objects on the Micro- and Nano-Scale by Electrokinetic and Electromagnetic Manipulation: for Bio-Sample Preparation, Quantum Information Devices, and Magnetic Drug Delivery," Aerospace Engineering, Dissertation, 2010, Advisor(s): B. Shapiro. link
[Abstract]
In this thesis I show achievements for precision feedback control of objects inside micro-fluidic systems and for magnetically guided ferrofluids. Essentially, this is about doing flow control, but flow control on the microscale, and further even to nanoscale accuracy, to precisely and robustly manipulate micro and nano-objects (i.e. cells and quantum dots). Target applications include methods to miniaturize the operations of a biological laboratory (lab-on-a-chip), i.e. presenting pathogens to on-chip sensing cells or extracting cells from messy bio-samples such as saliva, urine, or blood; as well as non-biological applications such as deterministically placing quantum dots on photonic crystals to make multi-dot quantum information systems. The particles are steered by creating an electrokinetic fluid flow that carries all the particles from where they are to where they should be at each time step. The control loop comprises sensing, computation, and actuation to steer particles along trajectories. Particle locations are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. I address following aspects of this technology. First I explain control and vision algorithms for steering single and multiple particles, and show extensions of these algorithms for steering in three dimensional (3D) spaces. Then I show algorithms for calculating power minimum paths for steering multiple particles in actuation constrained environments. With this microfluidic system I steer biological cells and nano particles (quantum dots) to nano meter precision. In the last part of the thesis I develop and experimentally demonstrate two dimensional (2D) manipulation of a single droplet of ferrofluid by feedback control of 4 external electromagnets, with a view towards enabling feedback control of magnetic drug delivery to reach deeper tumors in the long term. To this end, I developed and experimentally demonstrated an optimal control algorithm to effectively manipulate a single ferrofluid droplet by magnetic feedback control. This algorithm was explicitly designed to address the nonlinear and cross-coupled nature of dynamic magnetic actuation and to best exploit available electromagnetic forces for the applications of magnetic drug delivery.
- A. Luykx, "Fabrication Of All Thin Film Magneto-Electric Coupled Memory Devices," Material Science and Engineering, Thesis, 2010, Advisor(s): I. Takeuchi. link
[Abstract]
We studied a novel approach to MRAM using magneto-electric (ME) coupled devices: heterostructures consisting of at least two materials, one piezoelectric, and the other magnetostrictive, that are connected by mechanical coupling. Strain in one layer is transferred to another layer due to mechanical transduction, causing a change of properties in the layer onto which the strain is applied. In converse magneto-electric coupling an applied voltage to the piezoelectric layer causes a strain change (converse piezoelectric effect) that is mechanically coupled to the magnetostrictive layer, changing its magnetic anisotropy (Villari effect). Our converse ME heterostructure consists of mechanically coupled PZT and FeGa thin films. The PZT layers acquire different strain states when an applied electric field. Mechanical transduction couples this strain to the FeGa, which then changes its magnetic anisotropy. This thesis discusses the fabrication of a converse ME memory element that is non-volatile, low power consuming, and all-thin-film.
- M. T. Khbeis, "Development of a Simplified, Mass-Producible, Hybridized, Ambient, Low Frequency, Low-Intensity Vibration Energy Scavenger (HALF-LIVES)," Electrical Engineering, Dissertation, 2010, Advisor(s): R. Ghodssi. link
[Abstract]
Scavenging energy from environmental sources is an active area of research to enable remote sensing and microsystems applications. Furthermore, as energy demands soar, there is a significant need to explore new sources and curb waste. Vibration energy scavenging is one environmental source for remote applications and a candidate for recouping energy wasted by mechanical sources that can be harnessed to monitor and optimize operation of critical infrastructure (e.g. smart grid). Current vibration scavengers are limited by volume and ancillary requirements for operation such as control circuitry overhead and battery sources. This dissertation, for the first time, reports a mass producible hybrid energy scavenger system that employs both piezoelectric and electrostatic transduction on a common MEMS device. The piezoelectric component provides an inherent feedback signal and pre-charge source that enables electrostatic scavenging operation while the electrostatic device provides the proof mass that enables low frequency operation. The piezoelectric beam forms the spring of the resonant mass-spring transducer for converting vibration excitation into an AC electrical output. A serially poled, composite shim, piezoelectric bimorph produces the highest output rectified voltage of over 3.3 V and power output of 145 uW using ¼ g vibration acceleration at 120 Hz. Considering solely the volume of the piezoelectric beam and tungsten proof mass, the volume is 0.054 cm3, resulting in a power density of 2.68 mW/cm3. Incorporation of a simple parallel plate structure that provides the proof mass for low frequency resonant operation in addition to cogeneration via electrostatic energy scavenging provides a 19.82 to 35.29 percent increase in voltage beyond the piezoelectric generated DC rails. This corresponds to approximately 2.1nW additional power from the electrostatic scavenger component and demonstrates the first instance of hybrid energy scavenging using both piezoelectric and synchronous electrostatic transduction. Furthermore, it provides a complete system architecture and development platform for additional enhancements that will enable in excess of 100 uW additional power from the electrostatic scavenger.
- L. J. Currano, "Latching Microelectromechanical Shock Sensor Systems: Design, Modeling, and Experiments," Mechanical Engineering, Dissertation, 2010, Advisor(s): B. Balachandran and M. Yu. link
[Abstract]
Latching shock sensors are acceleration threshold sensors that trigger when the acceleration level exceeds the designed acceleration threshold. The latching mechanism provides a mechanical memory, which keeps the sensor in a triggered, or latched, state until the sensor is reset. The attractive feature of this type of sensor is that it does not require power during monitoring; power is only needed to query and reset the sensor. Several devices have been presented in the literature, but with limited experimental data and models that provide little to no insight into the dynamics of the latching event. The aim of this work is to further the understanding of the physics and design of micromechanical latching shock sensors by conducting a combination of careful experiments and development of original reduced-ordermodels. These efforts enable one to obtain a detailed picture of the latching dynamics for the first time.
Latching shock sensors have been designed, fabricated, and experimentally evaluated in this work. The model predictions have been compared to the experimental results to verify the validity, including a quantitative comparison of the position of the shock sensor during a latching event captured via high-speed videography. This is the first time a latching event has been imaged in this class of sensors, and the first time, the model predictions of position versus time histories have been validated through experiments. The models have also been used to conduct detailed numerical studies of the shock sensor, amongst other things to predict a latch "bounce" phenomenon during an acceleration event. To understand more thoroughly how the various design parameters affect the latching threshold of the sensor, various parametric and optimization studies have also been conducted with the reduced-order models to guide designs of future latching acceleration threshold sensors.
- E. D. Cobas, "High Frequency Electrical Transport Properties of Carbon Nanotubes," Material Science and Engineering, Dissertation, 2010, Advisor(s): M. S. Fuhrer and I. Takeuchi. link
[Abstract]
Carbon nanotubes (CNTs) have extraordinary electronic properties owing to the unique band structure of graphene and their one-dimensional nature. Their small size and correspondingly small capacitances make them candidates for novel high-frequency devices with cut-off frequencies approaching one terahertz, but their high individual impedance hampers measurements of their high-frequency transport properties. In this dissertation, I describe the fabrication of carbon nanotube Schottky diodes on high-frequency compatible substrates and the measurement of their rectification at frequencies up to 40GHz as a method of examining the high-frequency transport of individual CNTs despite their high impedance. The frequency dependence of the rectified signal is then used to extract the Schottky junction capacitance as a function of applied bias and ambient doping and to look for resonances which might be a signature of a room-temperature Luttinger Liquid.
- S. Chaudhary, "Precise steering of particles in electroosmotically actuated microfluidic devices," Aerospace Engineering, Dissertation, 2010, Advisor(s): B. Shapiro. link
[Abstract]
In this thesis, we show how to combine microfluidics and feedback control to independently steer multiple particles with micrometer accuracy in two dimensions. The particles are steered by creating a fluid flow that carries all the particles from where they are to where they should be at each time step. Our control loop comprises sensing, computation, and actuation to steer particles along user-input trajectories. Particle positions are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. Our method achieves inexpensive steering of particles by using conventional electroosmotic actuation in microfluidic channels. This type of particle steering has significant advantages over other particle steering methods, such as laser tweezers. (Laser tweezers cannot steer reflective particles, or particles where the index of refraction is lower than (or for more sophisticated optical vortex holographic tweezers does not differ substantially from) that of the surrounding medium.). In this thesis, we address three specific aspects of this technology. First, we develop the control algorithms for steering multiple particles independently and validate our control techniques using simulations with realistic sources of initial position errors and system uncertainties. Second, we develop optimal path planning methods to efficiently steer particles between given initial and final positions. Third, we design high performance microfluidic devices that are capable of simultaneously steering five particles in experiment.
- M. B. Tucker, "Some mechanics challenges and solutions in flexible electronics," Mechanical Engineering, Thesis, 2009, Advisor(s): T. Li. link
[Abstract]
Flexible electronics is an emerging field with potential applications such as large area flexible displays, thin film solar panels, and smart prosthesis, to name a few. Promising future aside, there are challenges associated with flexible electronics including high deformability requirements, needs for new manufacturing techniques and high performance permeation barriers. This thesis aims to explore possible solutions to address these challenges. First, a thin stiff film patterned with circular holes is proposed as a deformable platform to be used in flexible electronics in either component and circuit level. Second, we explore possible pathways to improve the quality of transfer printing, a nanofabrication technique that can potentially enable roll-to-roll printing of flexible devices. Third, we investigate the failure mechanism of multilayer permeation barriers for flexible electronics and offer an improved design to achieve better mechanical reliability.
- I. Perez, "Nanoporous AAO: a Platform for Regular Heterogeneous Nanostructures and Energy Storage Devices," Material Science and Engineering, Dissertation, 2009, Advisor(s): G. W. Rubloff. link
[Abstract]
Nanoporous anodic aluminum oxide (AAO) has vast implications as a tool for nanoscience research and as a nanostructure in which nanoscale devices can be fabricated because of its regular and ordered nanopores. Self-assembly plays a critical role in pore ordering, causing nanopores to grow parallel with one another in high density. The mild electrochemical conditions in which porous AAO grows along with its relatively cheap starting materials makes this nanomaterial a cost effective alternative to advanced photolithography techniques for forming high surface area nanostructures over large areas. In this research, atomic layer deposition (ALD) was used to deposit conformal films within in nanoporous AAO with hopes to 1) develop methodologies to characterize ALD depositions within its high aspect ratio nanopores and 2) to better understand how to use nanoporous AAO templates as a scaffold for energy devices, specifically Metal-Insulator-Metal (MIM) capacitors. Using the nanotube template synthesis method, ALD films were deposited onto nanoporous AAO, later removing the films deposited within the templates nanopores for characterization in TEM. This nanotube metrology characterization involves first obtaining images of full length ALD-AAO nanotubes, and then measuring wall thickness as a function of depth within the nanopore. MIM nanocapacitors were also constructed in vertical AAO nanopores by deposition of multilayer ALD films. MIM stacks were patterned into micro-scale capacitors for electrical characterization.
- L. C. Lecordier, "Wafer-Scale Process and Materials Optimization in Cross-Flow Atomic Layer Deposition," Material Science and Engineering, Dissertation, 2009, Advisor(s): G. W. Rubloff. link
[Abstract]
The exceptional thickness control (atomic scale) and conformality (uniformity over nanoscale 3D features) of atomic layer deposition (ALD) has made it the process of choice for numerous applications from microelectronics to nanotechnology, and for a wide variety of ALD processes and resulting materials. While its benefits derive from self-terminated chemisorbed reactions of alternatively supplied gas precursors, identifying a suitable process window in which ALD's benefits are realized can be a challenge, even in favorable cases. In this work, a strategy exploiting in-situ gas phase sensing in conjunction with ex-situ measurements of the film properties at the wafer scale is employed to explore and optimize the prototypical Al2O3 ALD process. Downstream mass-spectrometry is first used to rapidly identify across the [H2O x Al(CH3)3] process space the exposure conditions leading to surface saturation. The impact of precursor doses outside as well as inside the parameter space outlined by mass-spectrometry is then investigated by characterizing film properties across 100 mm wafer using spectroscopic ellipsometry, CV and IV electrical characterization, XPS and SIMS. Under ideal dose conditions, excellent thickness uniformity was achieved (1 sigma/mean 1%) in conjunction with a deposition rate and electrical properties in good agreement with best literature data. As expected, under-dosing of precursor results in depletion of film growth in the flow direction across the wafer surface. Since adsorbed species are reactive with respect to subsequent dose of the complementary precursor, such depletion magnifies non-uniformities as seen in the cross-flow reactor, thereby decorating deviations from a suitable ALD process recipe. Degradation of the permittivity and leakage current density across the wafer was observed though the film composition remained unchanged. Upon higher water dose in the over-exposure regime, deposition rates increased by up to 40% while the uniformity degraded. In contrast, overdosing of TMA and ozone (used for comparison to water) did not affect the process performances. These results point to complex saturation dynamics of water dependent on partial pressure and potential multilayer adsorption caused by hydrogen-bonding.
- D. E. Larios Berlin, "Enzyme Inhibition in Microfluidics for Re-Engineering Bacterial Synthesis Pathways," Bioengineering, Thesis, 2009, Advisor(s): G. W. Rubloff. link
[Abstract]
Enzyme-functionalized biological microfluidic (EF-BioMEMS) systems are an emerging class of lab-on-chip devices that manipulate enzymatic pathways by localizing reaction sites in a microfluidic network. An EF-BioMEM system was fabricated to demonstrate biochemical enzyme inhibition. Further, design optimizations to the EF-BioMEM system have been proposed which improve system sensitivity and performance. The pfs enzyme is part of the quorum-sensing pathway that ultimately produces the bacterial signaling molecule AI-2. An EF-BioMEM system was fabricated to investigate the pfs conversion activity in the presence of a transition state analogue inhibitor. A reduction in enzyme conversion was measured in microfluidics for increasing inhibitor concentration that was comparable to the response expected on a larger scale. This EF-BioMEMS testbed is capable of investigating other compounds that inhibit quorum sensing. Design improvements were demonstrates that improve overall system responsiveness by minimizing unintended reactions from non-specifically bound enzyme. EF-BioMEMS signal-to-background performance increased from 0.72 to 2.43.
- S. T. Koev, "Design, Fabrication, and Testing of a Microsystem for Monitoring Bacterial Quorum Sensing," Electrical Engineering, Dissertation, 2009, Advisor(s): R. Ghodssi. link
[Abstract]
Most pathogenic bacteria communicate with each other using signaling molecules. Their coordinated behavior, known as quorum sensing (QS), enables them to infect host organisms collectively and form drug-resistant biofilms. The study of bacterial signaling pathways may lead to discovery of new antimicrobials. Lab-on-a-chip technology can significantly accelerate the screening of candidate drugs that inhibit QS. This dissertation develops for the first time miniaturized sensors embedded in microfluidic channels to monitor the activity of an enzymatic pathway that produces signaling molecules. These devices can be used as building blocks of future high-throughput systems for drug discovery. The sensors presented here are gold-coated microcantilevers, and they detect the aminoacid homocysteine, a byproduct of the bacterial signaling pathway. It binds to the gold surface, causing stress and cantilever displacement that is measured optically. Samples are synthesized using bacterial enzymes and tested with the sensors. The minimal detected concentration of homocysteine is 1 uM. It is demonstrated that deactivation of the enzymes causes a change in the sensor response; this effect can be used for finding drugs that inhibit the enzyme. The traditional method for measuring cantilever displacement requires an elaborate optical setup, and it can only test one device at a time. Two new methods are developed here to overcome these limitations. The first one uses a transparent cantilever which is also an optical waveguide. Light is coupled from the cantilever to a fixed output waveguide and measured with a photodetector. The cantilever displacement is determined from the change in output power. The change is approximately 0.7% per nanometer displacement. The minimal detectable displacement and surface stress are 6 nm and 1.3 mN/m respectively. The second measurement method uses a transparent cantilever that is close to a reflective substrate. When the device is imaged with an optical microscope, an interference pattern forms. The cantilever displacement is calculated from the lateral shift of the interference fringes. This shift is determined from images of the device using custom software. The response of multiple cantilevers is captured by translating the microscope stage. The minimal detectable displacement and surface stress are 1 nm and 340 uN/m respectively.
- X. Z. Fan, "Enhancement of an Indium Phosphide Resonator Sensor Microsystem through the Development of an Adaptive Feedback Circuit and Electrospray Deposition," Electrical Engineering, Thesis, 2009, Advisor(s): R. Ghodssi. link
[Abstract]
Cantilever resonator sensor enhancement through the development of an adaptive feedback circuit and the use of electrospray deposition is presented. The feedback system adapts to a wide range of resonators by implementing a hill climbing algorithm, locking onto the cantilever's resonance condition. Eight different cantilever-based sensors (length=40-75 μm), resonating at 201.0 kHz to 592.1 kHz, with a minimum standard deviation of 11.8Hz, corresponding to a mass resolution limit of 123 fg for the device, have been dynamically detected using a single circuit. Electrospray deposition of thin-films on multiple substrate materials and released microstructures has been performed. An average deposition rate of 9.5±5 nm/min was achieved with an average surface roughness of 4.5 nm on a 197 nm thick film. This technology will enable a post-processing method for depositing absorbing layers for sensing applications. With the development of these two technologies, the practical functionality of a chip-scale sensor microsystem will be more readily realized.
- S. L. Buckhout-White, "Characterization of Electrodeposited Chitosan: an Interfacial Layer for Bio-assembly and Sensing," Material Science and Engineering, Dissertation, 2009, Advisor(s): G. W. Rubloff. link
[Abstract]
Microfluidics and Lab-on-a-Chip devices have revolutionized the field of analytical biology. To fully optimize the potential of the microfluidic environment it is critical to be able to isolate reactions in specific locations within a channel. One solution is found using chitosan, an amine-rich biopolymer with pH responsive solubility. Induction of hydrolysis at patterned electrodes within the fluidic channel provides a means to spatially control the pH, thus enabling biochemical functionalization that is both spatially and temporally programmable. While chitosan electrodeposition has proven to be reliable at producing films, its growth characteristics are not well understood. In situ optical characterization methods of laser reflectivity, fluorescence microscopy and Raman spectroscopy have been employed to understand the growth rate inter diffusion and lateral resolution of the deposition process. These techniques have also been implemented in determining where a molecule bound to an amine site of the polymer is located within the film. Currently, electrodeposited chitosan films are primarily used for tethering of biomolecules in the recreation of metabolic pathways. Beyond just a biomolecular anchor, chitosan provides a way to incorporate inorganic nanoparticles. These composite structures enable site-specific sensors for the identification of small molecules, an important aspect to many Lab-on-a-Chip applications. New methods for creating spatially localized sites for surface enhanced Raman spectroscopy (SERS) has been developed. These methods have been optimized for particle density and SERS enhancement using TEM and Raman spectroscopy. Through optimization, a viable substrate with retained chitosan amine activity capable of integration into microfluidics has been developed.
- A. G. Banerjee, "Real-Time Path Planning for Automating Optical Tweezers-Based Particle Transport Operations," Mechanical Engineering, Dissertation, 2009, Advisor(s): S. K. Gupta. link
[Abstract]
Optical tweezers (OT) have been developed to successfully trap, orient, and transport micro and nano scale components of many different sizes and shapes in a fluid medium. They can be viewed as robots made out of light. Components can be simply released from optical traps by switching off laser beams. By utilizing the principle of time sharing or holograms, multiple optical traps can perform several operations in parallel. These characteristics make optical tweezers a very promising technology for creating directed micro and nano scale assemblies. In the infra-red regime, they are useful in a large number of biological applications as well. This dissertation explores the problem of real-time path planning for autonomous OT based transport operations. Such operations pose interesting challenges as the environment is uncertain and dynamic due to the random Brownian motion of the particles and noise in the imaging based measurements. Silica microspheres having diameters between (1-20) µm are selected as model components.
Offline simulations are performed to gather trapping probability data that serves as a measure of trap strength and reliability as a function of relative position of the particle under consideration with respect to the trap focus, and trap velocity. Simplified models are generated using Gaussian Radial Basis Functions to represent the data in a compact form. These metamodels can be queried at run-time to obtain estimated probability values accurately and efficiently. Simple trapping probability models are then utilized in a stochastic dynamic programming framework to compute optimum trap locations and velocities that minimizes the total, expected transport time by incorporating collision avoidance and recovery steps. A discrete version of an approximate partially observable Markov decision process algorithm, called the QMDP_NLTDV algorithm, is developed. Real-time performance is ensured by pruning the search space and enhancing convergence rates by introducing a non-linear value function. The algorithm is validated both using a simulator as well as a physical holographic tweezer set-up. Successful runs show that the automated planner is flexible, works well in reasonably crowded scenes, and is capable of transporting a specific particle to a given goal location by avoiding collisions either by circumventing or by trapping other freely diffusing particles. This technique for transporting individual particles is utilized within a decoupled and prioritized approach to move multiple particles simultaneously. An iterative version of a bipartite graph matching algorithm is also used to assign goal locations to target objects optimally. As in the case of single particle transport, simulation and some physical experiments are performed to validate the multi-particle planning approach.
- S. Yang, "Multidimensional Microfluidic Bioseparation Systems With Spatial Multiplexing," Mechanical Engineering, Dissertation, 2008-12-19, Advisor(s): D. L. DeVoe. link
[Abstract]
Despite the refinement of liquid chromatography and peptide mass fingerprinting techniques for protein analysis, two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) separations of intact proteins remain a core technology for proteomic studies due to their high peak capacities and resolving power. In 2-D PAGE, denatured intact proteins are separated on the basis of their charge state by isoelectric focusing (IEF), followed by a size-based separation using sodium dodecyl sulfate (SDS)-PAGE. While 2-D PAGE is most commonly practiced with backend analysis of proteins by mass spectrometry, 2-D PAGE expression maps alone can provide valuable insight for differential studies, including the analysis of post-translational modifications, by yielding information about the approximate isoelectric point (pI) and molecular weight (MW) of differentially expressed species within complex samples. However, conventional slab-gel 2-D PAGE remains a labor intensive and low throughput process, which significantly constrains its utility. In this dissertation, a novel microfluidic 2-D PAGE platform is developed which employs a combination of multifunctional photopolymerized polyacrylamide (PAAm) gels and a discontinuous sodium dodecyl sulfate (SDS)-PAGE buffer system. The PAAm gel is used as a highly-resolving separation medium for gel electrophoresis, while discrete PAAm gel plugs integrated into specific regions of the chip enable acid, base, and ampholyte solutions to be fully isolated prior to chip operation. The gel plugs allow different separation buffers to be stored within the chip, enabling the use of a discontinuous buffer system chosen to provide sample stacking during the second-dimension separation. The gel plugs are also employed as on-chip SDS containers, allowing defined volumes of SDS to be repeatably injected and complexed with the IEF-focused proteins, without the need for external intervention. The IEF channel itself possesses an angled geometry to minimize sample tailing, and the chip design employs backbiasing channels which eliminate sample leakage and enable uniform sample transfer between the separation dimensions. Validation of the full 2-D system is presented using fluorescently-labeled E. coli cell lysate as a model system.
- A. Jahn, "Controlled Liposome Formation and Solute Encapsulation with Continuous-Flow Microfluidic Hydrodynamic Focusing," Bioengineering, Dissertation, 2008-12-11, Advisor(s): D. L. DeVoe. link
[Abstract]
Liposomes enable the compartmentalization of compounds making them interesting as drug delivery systems. A drug delivery system (DDS) is a transport vehicle for a drug for in vivo drug administration. Drugs can be encapsulated, bound, or otherwise tethered to the carrier which can vary in size from tens of nanometers to a few micrometers. Liposomal DDSs have shown their capability to deliver drugs in a new fashion, allowing exclusive sales of encapsulated drugs to be extended beyond the initial compound's patent expiration date. However, existing methods to form liposomes and encapsulate drugs are based on bulk mixing techniques with limited process control and the produced liposomes frequently require post-processing steps. In this dissertation, a new method is demonstrated to control liposome formation and compound encapsulation that pushes beyond existing benchmarks in liposome size homogeneity and adjustable encapsulation. The technology utilizes microfluidics for future pharmacy-on-a-chip applications. The microfluidic system allows for precise control of mixing via molecular diffusion with reproducible and controlled physicochemical conditions compared to traditional bulk-phase preparation techniques (i.e. test tubes and beakers). The laminar flow and facile fluidic control in microchannels enables reproducible self-assembly of lipids into liposomes in a sheathed flow-field. Confining a water-soluble compound to be encapsulated to the immediate vicinity where liposome formation is expected to occur reduces sample consumption without affecting liposome loading. The ability to alter the concentration and control the amount of encapsulated compounds within liposomes in a continuous-flow mode is another interesting feature towards tailored liposomal drug delivery. The liposome formation strategy demonstrated in this dissertation offers potential for point-of-care drug encapsulation, eliminating shelf-life limitations inherent to current liposome preparation techniques.
- M. E. Vechery, "Plate and Micro-Scale Structures: Analysis and Experiments," Mechanical Engineering, Dissertation, 2008-12-08, Advisor(s): B. Balachandran. link
[Abstract]
Within this work, plate and micro-scale structures are studied. Methodologies are developed to analyze the laminate stiffness, residual forces, moments and stresses, and deformations in these thin composite laminate structures to facilitate better designs, enable device characterization, and enhance device performance. Specific devices studied in this work are cantilevered and clamped-clamped PZT resonators of various lengths, widths, and laminate thicknesses. In order to better understand the behavior of these devices, analytical and experimental methods have been developed. The analytical methods are based on linear and nonlinear beam and plate models, with reduced-order models developed to study dynamic behavior. Parameter identification techniques have been applied to characterize residual stress induced deformation of micro-scale structures. Extensive data has been collected through careful experiments to aid the development of identification techniques and to determine device deflections and individual device residual stress values. An analytical model has been developed to describe the behavior of thin composite laminate plate-like structures. Since an exact solution for plate mode shapes does not exist for all boundary conditions, appropriate combinations of orthogonal functions are assumed for the mode shapes of a plate with all edges simply supported or all edges clamped. These functions make the development of reduced-order models possible for these boundary conditions. In addition, these plate-like structures are asymmetric isotropic laminates. A procedure was applied to calculate the stiffness, forces and moments for a laminate comprised of multiple isotropic layers regardless of symmetry. Parametric identification techniques were developed to identify system parameters and to characterize residual stress induced deformation in plate and micro-scale structures. These techniques are based on linear and nonlinear beam models and reduced-order methodologies, and they enable the first characterization of residual stress in PZT micro scale devices post-fabrication and release processing. The obtained results indicate that post-release residual stress measurements in devices can be considerably different from the corresponding measurements made before release.
- P. H. Dykstra, "An Optical MEMS Sensor for On-chip Catechol Detection," Electrical Engineering, Thesis, 2008-12-08, Advisor(s): R. Ghodssi. link
[Abstract]
This thesis reports the successful design, fabrication and testing of an optical MEMS sensor for the detection of the toxic phenol, catechol. Catechol's presence in food and drinking water posses a health concern due to its harmful effects on cell respiration. By-products of catechol oxidation have demonstrated increased absorbance changes in a chitosan film in the UV and near UV range. Our reported sensor utilizes patterned SU-8 waveguides and a microfluidic channel to deliver catechol samples to an electrodeposited chitosan film for absorbance measurements at 472 nm. Concentrations as low as 1 mM catechol are detected while control experiments including ascorbic acid display no measurable response. By using optical detection methods, our device does not suffer from many of the problems which plague conventional electrochemical based sensors.
- R. Fernandes, "Biological Nanofactories: Altering Cellular Response via Localized Synthesis and Delivery," Bioengineering, Dissertation, 2008-11-19, Advisor(s): W. E. Bentley. link
[Abstract]
Conventional research in targeted delivery of molecules-of-interest involves either packaging of the molecules-of-interest within a delivery mechanism or pre-synthesis of an inactive prodrug that is converted to the molecule-of-interest in the vicinity of the targeted area. Biological nanofactories provide an alternative approach to targeted delivery by locally synthesizing and delivering the molecules-of-interest at surface of the targeted cells. The machinery for synthesis and delivery is derived from the targeted cells themselves. Biological nanofactories are nano-dimensioned and are comprised of multiple functional modules. At the most basic level, a biological nanofactory consists of a cell targeting module and a synthesis module. When deployed, a biological nanofactory binds to the targeted cell surface and locally synthesizes and delivers molecules-of-interest thus altering the response of the targeted cells. In this dissertation, biological nanofactories for the localized synthesis and delivery of the 'universal' quorum sensing signaling molecule autoinducer-2 are demonstrated. Quorum sensing is process by which bacterial co-ordinate their activities at a population level through the production, release, sensing and uptake of signaling autoinducers and plays a role in diverse bacterial phenomena such as bacterial pathogenicity, biofilm formation and bioluminescence. Two types of biological nanofactories; magnetic nanofactories and antibody nanofactories are presented in this dissertation as demonstrations of the biological nanofactory approach to targeted delivery. Magnetic nanofactories consist of the AI-2 biosynthesis enzymes attached to functionalized chitosan-mag nanoparticles. Assembly of these nanofactories involves synthesis of the chitosan-mag nanoparticles and subsequent assembly of the AI-2 pathway enzymes onto the particles. Antibody nanofactories consist of the AI-2 biosynthesis enzymes self assembled onto the targeting antibody. Assembly of these nanofactories involves creation of a fusion protein that attaches to the targeting antibody. When added to cultures of quorum sensing bacteria, the nanofactories bind to the surface of the targeted cells via the targeting module and locally synthesize and deliver AI-2 there via the synthesis module. The cells sense and uptake the AI-2 and alter their natural response. Prospects of using biological nanofactories to alter the native response of targeted cells to a 'desired' state, especially with respect to down-regulating undesirable co-ordinated bacterial response, are envisioned.
- X. Luo, "Programmable Biomolecule Assembly and Activity in Prepackaged BioMEMS," Bioengineering, Dissertation, 2008-10-21, Advisor(s): G. W. Rubloff. link
[Abstract]
Antibiotic resistance is an increasing public health concern and few new drugs for bacterial pathogenesis have been obtained without addressing this resistance. Quorum sensing (QS) is a newly-discovered system mediated by extracellular chemical signals known as "autoinducers", which can coordinate population-scale changes in gene regulation when the number of cells reaches a "quorum" level. The capability to intercept and rewire the biosynthesis pathway of autoinduer-2 (AI-2), a universal chemical signaling molecule, opens the door to discover novel antimicrobial drugs that are able to bypass the antibiotic resistance. In this research, chitosan-mediated in situ biomolecule assembly has been demonstrated as a facile approach to direct the assembly of biological components into a prefabricated, systematically controlled bio-microelectromechanical system (bioMEMS). Our bioMEMS device enables post-fabricated, signal-guided assembly of labile biomolecules such as proteins and DNA onto localized inorganic surfaces inside microfluidic channels with spatial and temporal programmability. Particularly, the programmable assembly and enzymatic activity of the metabolic pathway enzyme Pfs, one of the two AI-2 synthases, have been demonstrated as an important step to reconstruct and interrogate the AI-2 synthesis pathway in the bioMEMS environment. Additionally, the bioMEMS has been optimized for studies of metabolic pathway enzymes by implementing a novel packaging technique and an experimental strategy to improve the signal-to-background ratio of the site-specific enzymatic reactions in the bioMEMS device. I envision that the demonstrated technologies represent a key step in progress toward a bioMEMS technology suitable to support metabolic engineering research and development.
- A. Pillarisetti, "Mechanical Manipulation and Characterization of Biological Cells," Mechanical Engineering, Dissertation, 2008-10-07, Advisor(s): J. P. Desai. link
[Abstract]
Mechanical manipulation and characterization of an individual biological cell is currently one of the most exciting research areas in the field of medical robotics. Single cell manipulation is an important process in intracytoplasmic sperm injection (ICSI), pro-nuclei DNA injection, gene therapy, and other biomedical areas. However, conventional cell manipulation requires long training and the success rate depends on the experience of the operator. The goal of this research is to address the drawbacks of conventional cell manipulation by using force and vision feedback for cell manipulation tasks. We hypothesize that force feedback plays an important role in cell manipulation and possibly helps in cell characterization. This dissertation will summarize our research on: 1) the development of force and vision feedback interface for cell manipulation, 2) human subject studies to evaluate the addition of force feedback for cell injection tasks, 3) the development of haptics-enabled atomic force microscope system for cell indentation tasks, 4) appropriate analytical model for characterizing the mechanical property of mouse embryonic stem cells (mESC) and 5) several indentation studies on mESC to determine the mechanical property of undifferentiated and early differentiating (6 days under differentiation conditions) mESC. Our experimental results on zebrafish egg cells show that a system with force feedback capability when combined with vision feedback can lead to potentially higher success rates in cell injection tasks. Using this information, we performed experiments on mESC using the AFM to understand their characteristics in the undifferentiated pluripotent state as well as early differentiating state. These experiments were done on both live as well as fixed cells to understand the correlation between the two during cell indentation studies. Our results show that the mechanical property of undifferentiated mESC differs from early differentiating (6th day) mESC in both live and fixed cells. Thus, we hypothesize that mechanical characterization studies will potentially pave the way for developing a high throughput system with force feedback capability, to understand and predict the differentiation path a particular pluripotent cell will follow. This finding could also be used to develop improved methods of targeted cellular differentiation of stem cells for therapeutic and regenerative medicine.
- A. Goswami, "Quantitative Hermeticity Assessment of Packages with Micro to Nano-liter Cavities," Mechanical Engineering, Dissertation, 2008-10-07, Advisor(s): B. Han. link
[Abstract]
Hermeticity is a measure of the "leak-proof ness" of packages with internal cavities and is critical for ensuring proper operation of the devices/circuits enclosed in them. The most widely used hermeticity detection technique in the industry is the helium fine leak test. The exiting conduction based governing equation is examined to investigate the volume dependant limits of the test when applied to metal sealed MEMS packages. The results clearly indicate that the test has limited applicability for small internal volumes (1 nanoliter - 1 microliter). The limited applicability of the guidelines specified in Method 1014.11 of the MIL-STD-883F document for hermeticity characterization is also characterized. To cope with these limitations, a regression analysis based procedure is developed and implemented to extract the true leak rate from the apparent leak data. While the apparent leak rate obtained directly from the He mass spectrometer changes with the test parameters, the true leak rate remains constant and this can be used as a metric to evaluate a package seal. The hermeticity of polymer sealed MEMS packages is also studied. Unlike metal sealed packages, gas transport in polymer sealed packages occurs via diffusion. A gas diffusion based model is proposed to study the hermetic behavior of these packages. An effective numerical scheme is developed to implement this model and simulate the change in cavity pressure as gas flows into or out of the cavity through the polymeric seal. An optical interferometry based leak test is developed to experimentally measure this change in cavity pressure. The experimental data is used to verify the validity of the proposed numerical scheme and the assumption of adiabatic boundary conditions made in the numerical model. An inverse method is presented to determine the two diffusion properties, diffusivity and solubility, of the polymeric seal by using the experimental data iteratively with the numerical data. The proposed method offers unique advantages over the routinely practiced/existing gas diffusion property measurement techniques.
- S. Bangalore Prakash, "Integrated CMOS Capacitance Sensor And Microactuator Control Circuits For On-Chip Cell Monitoring," Electrical Engineering, Dissertation, 2008-10-07, Advisor(s): P. Abshire. link
[Abstract]
"Cell Clinics" CMOS/MEMS hybrid microsystems for on-chip investigation of biological cells, are currently being engineered for a broad spectrum of applications including olfactory sensing, pathogen detection, cytotoxicity screening and biocompatibility characterization. In support of this effort, this research makes two primary contributions towards designing the cell-based lab-on-a-chip systems. Firstly it develops CMOS capacitance sensors for characterizing cell-related properties including cell-surface attachment, cell health and growth. Assessing these properties is crucial to all kinds of cell applications. The CMOS sensors measure substrate coupling capacitances of anchorage-dependent cells cultured on-chip in a standard in vitro environment. The biophysical phenomenon underlying the capacitive behavior of cells is the counterionic polarization around the insulating cell bodies when exposed to weak, low frequency electric fields. The measured capacitance depends on a variety of factors related to the cell, its growth environment and the supporting substrate. These include membrane integrity, morphology, adhesion strength and substrate proximity. The demonstrated integrated cell sensing technique is non-invasive, easy-to-use and offers the unique advantage of automated real time cell monitoring without the need for disruptive external forces or biochemical labeling. On top of the silicon-based cell sensing platform, the cell clinics microsystem comprises MEMS structures forming an array of lidded microvials for confining single cells or small cell groups within controllable microenvironments in close proximity to the sensor sites. The opening and closing of the microvial lids are controlled by actuator hinges employing an electroactive polymer material that can electrochemically actuate. In macro-scale setups such electrochemical actuation reactions are controlled by an electronic instrument called potentiostat. In order to enable system miniaturization and enhance portability of cell clinics, this research makes its second contribution by implementing and demonstrating a CMOS potentiostat module for in situ control of the MEMS actuators.
- K. D. Gerasopoulos, "Nanostructured Nickel-Zinc Microbatteries Using the Tobacco Mosaic Virus," Electrical Engineering, Thesis, 2008-08-18, Advisor(s): R. Ghodssi. link
[Abstract]
The development of nanostructured nickel electrodes using the Tobacco mosaic virus (TMV) for microbattery applications is presented in this Thesis. The TMV is a high aspect ratio cylindrical plant virus that can be used as a template to increase reactive surface area in MEMS-fabricated batteries. Genetically modifying the virus to display multiple binding sites allows for nickel metallization and self-assembly onto various substrates. In this work, the TMV biofabrication technique has been integrated into standard MEMS fabrication processes and novel nickel-zinc microbatteries have been developed using this technology. The nanostructured batteries exhibited appropriate charge-discharge response for up to thirty cycles of operation and demonstrated a six-fold increase in capacity compared to devices with planar electrode geometries. These results, combined with the simplicity and compatibility of the TMV assembly with various MEMS processes, make this approach promising for the development of compact, high-performance small-scale energy conversion devices.
- J. A. McGee, "Monolithic In-Plane Tunable Optical Filter," Electrical Engineering, Thesis, 2008-08-11, Advisor(s): R. Ghodssi. link
[Abstract]
This thesis presents the development of a Micro-Electro-Mechanical System (MEMS) monolithic in-plane tunable optical filter in both Indium Phosphide and Silicon. By placing one mirror of a waveguide-based Fabry-Perot interferometer on an electrostatically-actuated beam, a tunable filter is constructed. This is the first demonstration of a waveguide-coupled MEMS tunable optical filter in any material system. Filters with a tuning range of 40 nm from a wavelength 1550 nm with a linewidth of 35 nm are demonstrated. Future work will concentrate on improving the filter's optical characteristics, limited by etch-induced facet roughness, and integration with active photonic devices.
- M. I. Beyaz, "Closed-Loop Control of a Micropositioner Using Integrated Photodiode Sensors," Electrical Engineering, Thesis, 2008-08-11, Advisor(s): R. Ghodssi. link
[Abstract]
A closed-loop control system with photodiode position sensors has been implemented in a microball bearing supported linear electrostatic micromotor to improve accuracy and reliability. The fabrication sequence of the previously developed micromotor was modified to integrate a photodiode-based position sensing mechanism. Proportional control law is used in the control system and device step response is analyzed for several step sizes at various maximum applied voltages by varying the constant of proportionality. Two critical functions for micropositioning applications have been demonstrated; the device can establish a necessary frame of reference for coordinate-based positioning and autonomously respond to arbitrary disturbances. The closed-loop position control system presented in this work illustrates the feasibility and functionality of smart microsystems using integrated feedback sensors.
- L. Mosher, "Double-Exposure Gray-Scale Photolithography," Electrical Engineering, Thesis, 2008-08-08, Advisor(s): R. Ghodssi. link
[Abstract]
Three-dimensional photoresist structures may be realized by controlling the transmitted UV light intensity in a process termed gray-scale photolithography. Light modulation is accomplished by diffraction through sub-resolution pixels on a photomask. The number of photoresist levels is determined by the number of different pixel sizes on the mask, which is restricted by mask fabrication. This drawback prevents the use of gray-scale photolithography for applications that need a high vertical resolution. The double-exposure gray-scale photolithography technique was developed to improve the vertical resolution without increasing the number of pixel sizes. This is achieved by using two gray-scale exposures prior to development. The resulting overlay produces an exposure dose that is a combination of both exposures. Calibration is utilized to relate the pixel sizes and exposure times to the photoresist height. This calibration enables automated mask design for arbitrary 3D structures and investigation of other effects, such as misalignment between the exposures.
- C. M. Waits, "Microturbopump Utilizing Microball Bearings," Electrical Engineering, Dissertation, 2008-08-05, Advisor(s): R. Ghodssi. link
[Abstract]
This dissertation presents the development of a microfabricated turbopump capable of delivering fuel with the flow rates and pressures required for portable power generation. The device is composed of a spiral-groove viscous pump that is driven by a radial in-flow air turbine and supported using a novel encapsulated microball bearing. First, the encapsulated microball bearing and methods to investigate the wear and friction behaviors were developed. Two primary raceway designs, point-contact and planar-contact designs, were developed with the key design factor being wearing of the raceway. A modification to the planar-contact design was made for the final turbopump that reduced both wear and debris generation. Second, two air turbine platforms were developed using the encapsulated microball bearings to characterize both the bearing and the turbine drive mechanism. A tangential air turbine platform was first developed and characterized using the point-contact bearing mechanism. Rotational speeds > 37,000 rpm were demonstrated and long-term operation (> 24 hours) using this platform, but with large driving pressures (tens of psi) and large raceway wear (tens of microns). Furthermore, the circumferential asymmetry of the turbine design led to difficulty in measuring pressure distribution and sealing for pump applications. Results from the tangential air turbine platform led to an axisymmetric radial in-flow air turbine platform using a planar-contact bearing design. Rotational speeds greater than 85,000 rpm with turbine pressure differentials in the range of 1 psi were demonstrated using this platform. The wear of the raceway was observed to be on the order of single microns (a 10x improvement). The radial in-flow air turbine platform allowed an empirical model to be developed relating the friction torque to the rotational speed and load for the planar-contact bearing. This enabled calculation of the power balance for pumping and a method to characterize future bearing designs and materials. Lastly, a microfabricated turbopump was demonstrated based on a spiral-groove viscous pump and the radial in-flow turbine platform using the planar-contact bearing. Pumping operation was demonstrated with a differential pressure up to +0.3 psi and flow rates ranging from 35 mL/hour to 70 mL/hour, within the range relevant to portable power generation.
- P. Xu, "Bio-inspired VLSI Systems: from Synapse to Behavior," Electrical Engineering, Dissertation, 2008-08-04, Advisor(s): P. Abshire. link
[Abstract]
We investigate VLSI systems using biological computational principles. The elegance of biological systems throughout the structure levels provides possible solutions to many engineering challenges. Specifically, we investigate neural systems at the synaptic level and at the sensorimotor integration level, which inspire our similar implementations in silicon. For both VLSI systems, we use floating gate MOSFETs in standard CMOS processes as nonvolatile storage elements, which enable adaptation and programmability. We propose a compact silicon stochastic synapse and methods to incorporate activity-dependent dynamics, which emulate a biological stochastic synapse. We implement and demonstrate the first silicon stochastic synapse with short-term depression by modulating the influence of noise on the circuit. The circuit exhibits true randomness and similar behavior of rate normalization and information redundancy reduction as its biological counterparts. The circuit behavior also agrees well with the theory and simulation of a circuit model based on a subtractive single release model. To understand the stochastic behavior of the silicon stochastic synapse and the stochastic operation of conventional circuits due to semiconductor technology scaling, we develop the stochastic modeling of circuits and transient analysis from the numerical solution of the stochastic model. The analytical solution of steady state distribution could be obtained from first principles. Small signal stochastic models show the interaction between noise and circuit dynamics, elucidating the effect of device parameters and biases on the stochastic behavior. We investigate optic flow wide field integration based navigation inspired from the fly in simulation, theory, and VLSI design. We generalize the framework to limited view angles. We design and test an integrated motion image sensor with on-chip optic flow estimation, adaptation, and programmable spatial filtering to directly interface with actuators for autonomous navigation. This is the first reported image sensor that uses the spatial motion pattern to extract motion parameters enabled by the mismatch compensation and programmable filters. The sensor is integrated with a ground vehicle and navigation through simple tunnel environments is demonstrated. It provides light weight and low power integrated approach to autonomous navigation of micro air vehicles.
- S. Kosaraju, "Cosserat Analysis of Microscale Structures," Mechanical Engineering, Thesis, 2008-05-23, Advisor(s): B. Balachandran. link
[Abstract]
In this thesis, the application of Cosserat mechanics to micro-scale structures is explored. Different structures considered include micro-scale gyroscopes, micro-cantilevers, and clamped-clamped micro-structures. Two-dimensional formulations with nonlinearities up to third order are derived and presented. Different parameterization schemes are used and the equivalence between the obtained results is discussed. Comparisons with prior results available in the literature are made in terms of inertia properties, stiffness properties, and natural frequencies. The present work points to the importance of considering Cosserat mechanics for examining the motions of micro-scale structures that undergo large as well as coupled deformations.
- C.-W. Tsao, "Interfacing Microfluidic Bioanalysis with High Sensitivity Mass Spectrometry," Mechanical Engineering, Dissertation, 2008-05-20, Advisor(s): D. L. DeVoe. link
[Abstract]
Mass spectrometry (MS) provides quantified information to identify unknown atom and molecules which has become a widely used analytical technique in bioanalysis field. Polymer-based microfluidics device provides benefits of low fabrication cost, fast analysis time and less sample consumption for biological sample process and separation prior to MS analysis. In this dissertation, a table-size, computer-controlled robotic spotting system was developed to couple polymer microfluidics with mass spectrometry as an automatic and high throughput interfacing method. To accomplish this goal, three major subjects, polymer microfabrication, high sensitivity MS target substrate and polymer microfluidics / mass spectrometry interfacing were further evaluated and developed. First, polymer microfabrication techniques such as hot embossing and polymer bonding were discussed. Among those, a novel bonding technique of using UV/Ozone surface treatments for achieving low temperature bonds between poly(methyl methacrylte) (PMMA) and cyclic olefin copolymer (COC) microfluidic substrates is demonstrated. Second, a novel high sensitivity silicon-based matrix-free LDI-MS target substrate, nanofilament silicon (nSi) surfaces, was demonstrated in this dissertation. With electrowetting on nSi surfaces, it is demonstrated as a novel approach for preparing nSi based LDI-MS targets for the analysis of complex peptide samples. Finally, off-line integration of multiplexed polymer microfluidic interfacing with mass spectrometry by direct and automated spotting of peptide sample from multiplexed polymer microfluidic chip is demonstrated as a simple and robust method with uniform spotting volume and MS signal. This automatic contact spotting system is further demonstrated coupling with on-chip peptide reverse phase liquid chromatography (RPLC) separation with nSi surface as a novel microfluidics/ off-line mass spectrometry analysis.
- G. Mijares, "Bioelectronic Sensor for Cellular Assays Using Polyelectrolyte Multilayer-Modified Electrodes," Bioengineering, Thesis, 2008-04-25, Advisor(s): D. L. DeVoe. link
[Abstract]
Cell-based impedance biosensors provide non-invasive, quantitative, and instantaneous detection of cellular responses to applied stimuli. Extracellular matrix proteins, which degrade over time, are commonly used as cell adhesion promoters on planar electrodes, but decrease the lifetime of biosensors. In this work, the feasibility of using non-biological polyelectrolyte multilayers (PEMs) to facilitate cell attachment on titanium-tungsten alloy/gold electrodes for cell assays is investigated. The PEMs-modified electrode system is modeled as an equivalent electrical circuit and the addition of cells to the system is defined by their electrical properties. Electrode performance is characterized by cyclic voltammetry and impedance spectroscopy. The electrodes are found to have the ability to specifically probe non-faradaic processes and show a 15% increase in impedance due to cell proliferation. This thesis work demonstrates the use of PEMs-modified electrodes for the continuous monitoring of cell proliferation and for the future application of probing cell confluency in microfluidic cytotoxicity assays.
- M. P. Dandin, "Towards Integrated Fluorescence Sensing," Electrical Engineering, Thesis, 2008-01-11, Advisor(s): P. A. Abshire. link
[Abstract]
This thesis is an account of ongoing efforts in the Integrated Biomorphic Information Systems Laboratory and the Laboratory for MicroTechnologies towards the implementation of integrated microfabricated biosensing platforms with on-chip fluorescence detection capability. The first chapter is a published, exhaustive, and critical review of state-of-the-art microfluorometers, and it offers a set of performance metrics for evaluating sensors of different architectures. The second chapter consists of material from two journal papers, currently in preparation, in which the development of a polymeric optical filter material for UV fluorescence spectroscopy is presented and its integration with a CMOS active pixel sensor (APS) discussed. The third chapter, which is also an archival publication, presents initial efforts towards achieving high-sensitivity CMOS photodetectors for photon counting-based fluorescence assays in integrated platforms.
- P. P. Mathai, "Applications of Reduced Order Modeling Techniques to Problems in Heat Conduction, Isoelectric Focusing, and Differential Algebraic Equations," Aerospace Engineering, Dissertation, 2008, Advisor(s): B. Shapiro. link
[Abstract]
This thesis focuses on applying and augmenting `Reduced Order Modeling' (ROM) techniques to large scale problems. ROM refers to the set of mathematical techniques that are used to reduce the computational expense of conventional modeling techniques, like finite element and finite difference methods, while minimizing the loss of accuracy that typically accompanies such a reduction. The first problem that we address pertains to the prediction of the level of heat dissipation in electronic and MEMS devices. With the ever decreasing feature sizes in electronic devices, and the accompanied rise in Joule heating, the electronics industry has, since the 1990s, identified a clear need for computationally cheap heat transfer modeling techniques that can be incorporated along with the electronic design process. We demonstrate how one can create reduced order models for simulating heat conduction in individual components that constitute an idealized electronic device. The reduced order models are created using Krylov Subspace Techniques (KST). We introduce a novel `plug and play' approach, based on the small gain theorem in control theory, to interconnect these component reduced order models (according to the device architecture) to reliably and cheaply replicate whole device behavior. The final aim is to have this technique available commercially as a computationally cheap and reliable option that enables a designer to optimize for heat dissipation among competing VLSI architectures. Another place where model reduction is crucial to better design is Isoelectric Focusing (IEF) - the second problem in this thesis - which is a popular technique that is used to separate minute amounts of proteins from the other constituents that are present in a typical biological tissue sample. Fundamental questions about how to design IEF experiments still remain because of the high dimensional and highly nonlinear nature of the differential equations that describe the IEF process as well as the uncertainty in the parameters of the differential equations. There is a clear need to design better experiments for IEF without the current overhead of expensive chemicals and labor. We show how with a simpler modeling of the underlying chemistry, we can still achieve the accuracy that has been achieved in existing literature for modeling small ranges of pH (hydrogen ion concentration) in IEF, but with far less computational time. We investigate a further reduction of time by modeling the IEF problem using the Proper Orthogonal Decomposition (POD) technique and show why POD may not be sufficient due to the underlying constraints. The final problem that we address in this thesis addresses a certain class of dynamics with high stiffness - in particular, differential algebraic equations. With the help of simple examples, we show how the traditional POD procedure will fail to model certain high stiffness problems due to a particular behavior of the vector field which we will denote as twist. We further show how a novel augmentation to the traditional POD algorithm can model-reduce problems with twist in a computationally cheap manner without any additional data requirements.
- H. Bi, "Development of Nano-Pattern Recognition and Correlation Technique for Deformation Measurement of Nano-Scale Structures," Mechanical Engineering, Dissertation, 2008, Advisor(s): B. Han. link
[Abstract]
An imperative need exists for deformation data from interconnects of silicon devices. The need for nano-scale measurements becomes more urgent as the interconnect technology approaches the 50 nm node and beyond. The reliability of devices is determined largely by thermal and mechanical deformations of interconnect layers during manufacturing and operation. These are inferred by computational analysis, but informed physical analysis is vital to measure the variables and to guide and verify the computations. Deformation measurements are needed urgently in the nanometer range. What is needed is in-plane displacement measurements that are accurate within a fraction of nanometers, together with sub-micron spatial resolution. In recent years, several techniques have been proposed to document nano-scale deformations. They include electron-beam moiré (EBM), nano-scale moiré interferometry, SEM/TEM/AFM digital image correlation (DIC), and speckle interferometry with electron microscopy (SIEM). None of the existing techniques provide both the accuracy/sensitivity (sub-nanometer) and spatial resolution (sub-micron), which are required for the analysis of nanostructures. The objective of this thesis is to develop a new deformation measurement technique to cope with the limitations of each existing technique: A hybrid method is proposed to achieve the goal. The proposed method called Nano-Pattern Recognition and Correlation Technique (N-PRCT) uses regularly oriented nano-scale structures that are fabricated on the surface of the specimen. After obtaining the SEM pictures of patterns on the region of interest before and after loading (deformation), the conventional low-pass filter combined with a de-blur filter (Wiener Filter) are applied to eliminate the noise during SEM imaging effectively. A unique practice of E-beam lithography is proposed and implemented to fabricate regularly oriented patterns required for the N-PRCT technique using PMMA as an E-beam resist. The proposed scheme utilizes the standard SEM for imaging to fabricate the patterns without the need of specially designed E-Beam lithography system, which makes the implementation of N-PRCT practical. Yet, the proposed procedure can produce gauge lengths (approximately 150 nm) than those produced by a commercial E-beam lithography system The proposed method is used to determine the thermally-induced deformations of a passivation layer in a flip-chip package. The regular patterns (115 nm in diameter) are produced on the polished cross-section, and the package is subjected to a thermal loading inside SEM using a specially designed thermal conduction stage. Thermal deformations with the displacement measurement accuracy of less than 0.1 nm are obtained in a field of view of 7 um. The results show a shear strain concentration at the interface between the passivation layer and the adjacent metal pad.
- N. P. Siwak, "Indium Phosphide MEMS Cantilever Waveguides with Integrated Readout for Chemical Sensing," Electrical Engineering, Thesis, 2007-11-26, Advisor(s): R. Ghodssi. link
[Abstract]
This thesis presents the development towards an integrated, monolithic, micro-electro-mechanical system (MEMS) cantilever waveguide resonator chemical sensor using the III-V semiconductor indium phosphide (InP). Waveguide cantilevers with resonant frequencies as high as 5.78 MHz, a quality factor of 340, and a sensitivity of 4.4x10^16 Hz/g are shown for the first time in this system. The first demonstration of vapor detection using the sensor platform is performed utilizing an organic semiconductor Pentacene absorbing layer. Vapors are measured from mass shifts of 6.56x10^-14 and 7.28x10^-14 g exhibiting a mass detection threshold of 5.09x10^-15 g. The design, fabrication, and testing of an integrated waveguide PIN photodetector with an In0.53Ga0.47As absorbing layer is reported. Dark currents as low as 8.7 nA are measured for these devices. The first demonstration of a resonating cantilever waveguide measurement is also performed using the monolithically integrated waveguide photodiodes with uncertainty of less than ± 35 Hz. Finally, a future outlook is presented for this monolithic InP sensor system.
- A. Modafe, "Benzocyclobutene-based Electric Micromachines Supported on Microball Bearings: Design, Fabrication, and Characterization," Electrical Engineering, Dissertation, 2007-11-21, Advisor(s): R. Ghodssi. link
[Abstract]
This dissertation summarizes the research activities that led to the development of the first microball-bearing-supported linear electrostatic micromotor with benzocyclobutene (BCB) low-k polymer insulating layers. The primary application of this device is long-range, high-speed linear micropositioning. The future generations of this device include rotary electrostatic micromotors and microgenerators. The development of the first generation of microball-bearing-supported micromachines, including device theory, design, and modeling, material characterization, process development, device fabrication, and device test and characterization is presented. The first generation of these devices is based on a 6-phase, bottom-drive, linear, variable-capacitance micromotor (B-LVCM). The design of the electrical and mechanical components of the micromotor, lumped-circuit modeling of the device and electromechanical characteristics, including variable capacitance, force, power, and speed are presented. Electrical characterization of BCB polymers, characterization of BCB chemical mechanical planarization (CMP), development of embedded BCB in silicon (EBiS) process, and integration of device components using microfabrication techniques are also presented. The micromotor consists of a silicon stator, a silicon slider, and four stainless-steel microballs. The aligning force profile of the micromotor was extracted from simulated and measured capacitances of all phases. An average total aligning force of 0.27 mN with a maximum of 0.41 mN, assuming a 100 V peak-to-peak square-wave voltage, was measured. The operation of the micromotor was verified by applying square-wave voltages and characterizing the slider motion. An average slider speed of 7.32 mm/s when excited by a 40 Hz, 120 V square-wave voltage was reached without losing the synchronization. This research has a pivotal impact in the field of power microelectromechanical systems (MEMS). It establishes the foundation for the development of more reliable, efficient electrostatic micromachines with variety of applications such as micropropulsion, high-speed micropumping, microfluid delivery, and microsystem power generation.
- N. A. Vickey, "Development of an Advanced Adhesion Test for Polymer Interfaces," Mechanical Engineering, Thesis, 2007-11-19, Advisor(s): B. Han. link
[Abstract]
The bond strength of polymer interfaces within packaged microelectronic devices significantly influences their reliability. In the interest of predictive modeling and to facilitate materials selection during the design process, it is highly desirable to be able to distinguish between the adhesive performances of multiple polymer interfaces. However, typical adhesion testing is normally plagued by large deviations in its test results which make drawing statistical conclusions from adhesion strength data difficult. To remedy this, an investigation into the primary sources of variance associated with the pull test was performed. Four primary factors were identified, load alignment, loading rate, bond thickness, and the edge condition. The control of each of these four parameters was targeted during the development of an improved adhesion test technique. The results are an adhesion measurement method which has successfully reduced the scatter in test results from a standard deviation of 50% to approximately 10%.
- Y. Zhou, "Microfluidics Interfacing to Mass Spectrometry," Mechanical Engineering, Dissertation, 2007-08-14, Advisor(s): D. L. Devoe. link
[Abstract]
Polymer-based microfluidic systems have received considerable attention for high throughput chemical analysis. Recently, the ongoing development of microfluidics interfacing to high-accuracy mass spectrometry to identify large molecules had an important impact on biochemistry. A primary goal of this dissertation is the development of a microfluidic apparatus for performing microscale gel electrophoresis, coupled with integrated electrospray tips for either direct interfacing to mass spectrometry through ESI-MS, or coupling to MALDI-MS through the deposition of separated analyte onto a MALDI target for offline analysis. In this dissertation, microfabrication techniques for polymer-based microchip are developed. A novel electrospray interface is demonstrated with good performance. The optimization of multi-channel electrospray tips for multiplexed analysis from a single microfluidic chip was demonstrated. Gas-phased electrophoretic protein/peptide concentration on a pre-structured MALDI target was further demonstrated via theoretical and experimental analysis. The results for developing μGE-ES using linear polymer gel validate the underlined principles and specify challenges involved in coupling μGE to MS. Finally, cross-linked polyacrylamide gel was explored and characterized using in-situ photo- polymerization method in microchannels.
- M. G. Urdaneta, "Design of a Dielectrophoretic Cell Loading Device," Mechanical Engineering, Dissertation, 2007-08-09, Advisor(s): E. Smela. link
[Abstract]
In recent years there has been an increasing interest in studying individual cells, and structures that physically entrap one or few cells have been developed for this purpose, but the approaches to load cells into these structures leave a lot to be desired. This dissertation discusses the design of a device that loads cells suspended in a solution into microvials using a combination of dielectrophoresis and fluid flow, which offers significant advantages over previous loading approaches. The basic concept is to use fluid flow and dielectrophoretic forces to position a given cell above a given vial, within an array of similar vials, and then bringing the cell into the vial. The loading of several cells flowing in a channel into a vial in a matter of seconds is demonstrated. The design of the loading device spurred the development of novel topics in the area of dielectrophoresis. The structures into which cells are loaded produce "parasitic cages". The effect of multiple electric fields and at multiple frequencies had to be explored to eliminate the parasitic cages, and new theory was developed to describe the phenomenon in a straight forward and convenient way. The design process of dielectrophoretic structures known as flow through sorters was simplified significantly using a method that relies on non dimensional analysis and a figure of merit. These topics investigated have broader applications than just loading cells into vials. The dissertation demonstrates technologies and design and fabrication methods key to the cell loading design. The dissertation ends by describing the design of a device that can be implemented to load cells into vials on integrated circuit chips and outlining this device's expected characteristics and performance based on the theory and methods presented through the dissertation.
- S. Walker, "Modeling, Simulating, and Controlling the Fluid Dynamics of Electro-Wetting On Dielectric," Aerospace Engineering, Dissertation, 2007-08-06, Advisor(s): B. Shapiro and R. H. Nochetto. link
[Abstract]
This work describes the modeling and simulation of a parallel-plate Electrowetting On Dielectric (EWOD) device that moves fluid droplets through surface tension effects. The fluid dynamics are modeled by Hele-Shaw type equations with a focus on including the relevant boundary phenomena. Specifically, we include contact angle saturation, hysteresis, and contact line pinning into our model. We show that these extra boundary effects are needed to make reasonable predictions of the correct shape and time scale of droplet motion. We compare our simulation to experimental data for five different cases of droplet motion that include splitting and joining of droplets. Without these boundary effects, the simulation predicts droplet motion that is much faster than in experiment (up to 10-20 times faster). We present two different numerical implementations of our model. The first uses a level set method, and the second uses a variational method. The level set method provides a straightforward way of simulating droplet motion with topological changes. However, the variational method was pursued for its robust handling of curvature and mass conservation, in addition to being able to easily include a phenomenological model of contact line pinning using a variational inequality. We are also able to show that the variational form of the time-discrete model satisfies a well-posedness result. Our numerical implementations are fast and are being used to design algorithms for the precise control of micro-droplet motion, mixing, and splitting. We demonstrate micro-fluidic control by developing an algorithm to steer individual particles inside the EWOD system by control of actuators already present in the system. Particles are steered by creating time-varying flow fields that carry the particles along their desired trajectories. Results are demonstrated using the model given above. We show that the current EWOD system at the University of California in Los Angeles (UCLA) contains enough control authority to steer a single particle along arbitrary trajectories and to steer two particles, at once, along simple paths. We also show that particle steering is limited by contact angle saturation and by the small number of actuators available in the EWOD system.
- A. J. Dick, "Advantageous Utilization of Nonlinear Phenomena in Micro-Structures and Macro-Structures: Applications to Micro-Resonators and Atomic Force Microscopy," Mechanical Engineering, Dissertation, 2007-08-01, Advisor(s): B. Balachandran and C. D. Mote. link
[Abstract]
Within this work, the nonlinear oscillations of various beam-like structures are studied. Methods are developed to analyze systems of this type to better understand their behavior in order to utilize the nonlinear phenomena associated with them and to provide insights for device development. The specific applications explored within this study are piezoelectric micro-scale resonators, micro-resonator arrays, the cantilever probes of atomic force microscopes, and a macro-scale test apparatus for the AFM probe. In order to analytically, numerically, and experimentally study these systems, various methods are employed. Analytical models are developed, utilizing bending stiffness and axial stretching terms to explain nonlinear behavior. Reduced-order-modeling techniques are applied to develop single-mode and multi-mode approximations and study the dynamic behavior of these structures. Nonlinear analysis methods are used to study these systems and to determine approximate solutions. Discrete models are developed and utilized to conduct numerical simulations. Data collected through experimental observations are utilized to determine system parameters and verify simulation results. Through this work, a multi-variable, parametric identification scheme is developed for characterizing nonlinear oscillators from frequency-response data with jumps in the amplitude values. Parameter values are identified for piezoelectric micro-scale resonators and good agreement is seen with the corresponding model predictions. By using multiple data sets, parameter trends are studied for changes in the input signal. In another nonlinear analysis, a relationship is identified between a nonlinear localization phenomena called Intrinsic Localized Modes (ILMs) and nonlinear vibration modes. A method is developed to derive equations for determining the spatial characteristics of the localizations and the profiles are used to conduct further studies. For a cantilever beam impactor system, a period doubling phenomenon is identified for off-resonance excitation conditions. Changes in this system's response are studied and a method is proposed to utilize this phenomenon to determine conditions for grazing. This work shows how important nonlinearities are in beam structures when oscillations exceed the linear range. More importantly, these studies show how an understanding of the nonlinearities can be used to the advantage of the system.
- A. Lewandowski, "Assembly of Quorum Sensing Pathway Enzymes onto Patterned Microfabricated Devices," Chemical Engineering, Dissertation, 2007-07-31, Advisor(s): W. Bentley. link
[Abstract]
I report patterned protein assembly onto microfabricated devices using our unique assembly approach. This approach is based on electrodeposition of the aminopolysaccharide chitosan onto a selected electrode pattern of the device, and covalent conjugation of a target protein to chitosan upon biochemical activation of a genetically fused C-terminal pentatyrosine "pro-tag." With this approach, assembly is "spatially selective", occurring only at selected electrode patterns, and the entire process occurs under mild experimental conditions. Additionally, assembly is reversible and the devices reusable, as the deposited chitosan can be removed by simple incubation in dilute acid. Finally, the protein is covalently and robustly linked to chitosan through the pro-tag versus the native tyrosines, and thus our approach confers "orientational control". I have examined patterned assembly of metabolic pathway enzymes onto both flat microfabricated chips and into 3-dimensional microfluidic devices. The assembled enzymes retain reproducible catalytic activities and protein recognition capabilities for antibody binding. Additionally, catalytic activity is retained over multiple days, demonstrating enzyme stability over extended time. Finally, substrate catalytic conversion can be controlled and manipulated through the assembly patterned area, or in the case of microfluidic devices, through the substrate flow rate over the assembled enzyme. I specifically examined the patterned assembly of Pfs and LuxS enzymes, members of the bacterial autoinducer-2 (AI-2) biosynthesis pathway. AI-2 is a small signaling molecule that mediates interspecies bacterial communication termed type II "quorum sensing", which is involved in regulating the pathogenesis of a bacterial population. Significantly, this is the first time that Pfs and LuxS have been assembled onto devices. More significantly, Pfs and LuxS have both been assembled onto the same chip; that is, the quorum sensing pathway has been assembled onto a single device. This device could be used to screen inhibitors of AI-2 biosynthesis and discover novel "anti-pathogenic" drugs. In summary, I have demonstrated patterned enzyme assembly onto microfabricated devices. The assembled enzymes retain reproducible catalytic activities and are capable of recognizing and binding antibodies. Importantly, patterned device-assembly of multiple enzymes representing a metabolic pathway is possible. I envision many potential biosensing, bioMEMS, drug screening, and metabolic engineering applications.
- N. Ghalichechian, "Design, Fabrication, and Characterization of a Rotary Variable-Capacitance Micromotor Supported on Microball Bearings," Electrical Engineering, Dissertation, 2007-07-31, Advisor(s): R. Ghodssi. link
[Abstract]
The design, fabrication, and characterization of a rotary micromotor supported on microball bearings are reported in this dissertation. This is the first demonstration of a rotary micromachine with a robust mechanical support provided by microball-bearing technology. One key challenge in the realization of a reliable micromachine, which is successfully addressed in this work, is the development of a bearing that would result in high stability, low friction, and high resistance to wear. A six-phase, rotary, bottom-drive, variable-capacitance micromotor is designed and simulated using the finite element method. The geometry of the micromotor is optimized based on the simulation results. The development of the rotary machine is based on studies of fabrication and testing of linear micromotors. The stator and rotor are fabricated separately on silicon substrates and assembled with the stainless steel microballs. Three layers of low-k benzocyclobutene (BCB) polymer, two layers of gold, and a silicon microball housing are fabricated on the stator. The BCB dielectric film, compared to conventional silicon dioxide insulating films, reduces the parasitic capacitance between electrodes and the stator substrate. The microball housing and salient structures (poles) are etched in the rotor and are coated with a silicon carbide film to reduce friction. A characterization methodology is developed to measure and extract the angular displacement, velocity, acceleration, torque, mechanical power, coefficient of friction, and frictional force through non-contact techniques. A top angular velocity of 517 rpm corresponding to the linear tip velocity of 324 mm/s is measured. This is 44 times higher than the velocity achieved for linear micromotors supported on microball bearings. Measurement of the transient response of the rotor indicated that the torque is 5.620.5 micro N-m which is comparable to finite element simulation results predicting 6.75 micro N-m. Such a robust rotary micromotor can be used in developing micropumps which are highly demanded microsystems for fuel delivery, drug delivery, cooling, and vacuum applications. Micromotors can also be employed in micro scale surgery, assembly, propulsion, and actuation.
- X. Wang, "Understanding Actuation Mechanisms of Conjugated Polymer Actuators: Ion Transport," Mechanical Engineering, Dissertation, 2007-07-30, Advisor(s): E. Smela. link
[Abstract]
This dissertation explored ion transport in conjugated polymers. Study in this dissertation focused on following subjects: 1. Driving mechanisms (migration and diffusion) for ion transport. 2. Correlation among ions, charge, and volume change. 3. Effects of experimental situations (voltage, swelling of polymers, film thickness, ion barrier thickness, electrolyte, and temperature) on ion transport. 4. Developing a physics-based model and conducting numerical simulations for ion transport in conjugated polymers. The research results of this dissertation were summarized mainly in 3 articles and presented in Chapter 3, Chapter 4, and Chapter 5 respectively. Chapter 3 reported preliminary experimental and modeling results of cation ingress in PPy(DBS). Cation ingress in the polymer was displayed through phase front propagations that were formed by electrochromism. Migration was found to dominate ion ingress evidenced by a linear relationship between phase front velocity and reduction potentials. Chapter 4 is a full-scale experimental study of ion transport in PPy(DBS). Besides phase front propagation velocity and broadening, current data and actuation strains of PPy(DBS) were also collected. Comparisons among these data gave more insights of cation transport in PPy(DBS). Diffusion of ions in PPy(DBS) was found to be non-Fickian diffusion, which has not been included in models in the literature. Cation egress was found to be independent with applied potentials, suggesting a diffusion controlled process, while cation ingress was found to be dominated by migration. This difference between cation ingress and cation egress has not been realized before this dissertation. The effect of polymer swelling on cation ingress was characterized for the first time, which suggested an exponential relationship between ion mobility and ion concentration. Chapter 5 reported more advanced theoretical modeling and simulation results. Nernst-Planck-Poisson's equations were used to model hole transport, ion transport, and potential profiles in conjugated polymers. The model was able to explore ion transport with various experimental situations including changing of voltage, ion diffusivity, hole mobility, Einstein relation, electrolyte concentration, and film geometry. The model successfully predicted both ion ingress and ion egress features for PPy(DBS). Predictions of anion transport conjugated polymers such as PPy(ClO4) were also reported.
- S. Koev, "Microcantilever Biosensors with Chitosan for the Detection of Nucleic Acids and Dopamine," Electrical Engineering, Thesis, 2007-05-07, Advisor(s): R. Ghodssi. link
[Abstract]
Microcantilever biosensors allow label-free detection of analytes within small sample volumes. They are, however, often limited in sensitivity or specificity due to the lack of proper bio-interface layers. This thesis presents the use of the biopolymer chitosan as a bio-interface material for microcantilevers with unique advantages. Sensors coated with chitosan were designed, fabricated, and functionalized to demonstrate two distinct applications: detection of DNA hybridization and detection of the neurotransmitter dopamine. The first demonstration resulted in signals from DNA hybridization that exceed by two orders of magnitude values previously published for sensors coated with SAM (self assembled monolayer) interface. The second application is the first reported demonstration of using microcantilevers for detection of the neurotransmitter dopamine, and it is enabled by chitosan's response to dopamine electrochemical oxidation. It was shown that this method can selectively detect dopamine from ascorbic acid, a chemical that interferes with dopamine detection in biological samples.
- J. Hromada, Louis Paul, "Bilayer Lipid Membrane (BLM) Integration into Microfluidic Platforms with Application toward BLM-Based Biosensors," Mechanical Engineering, Dissertation, 2007-04-27, Advisor(s): D. L. DeVoe. link
[Abstract]
Bilayer lipid membranes (BLMs) have been widely used as an experimental tool to investigate fundamental cellular membrane physics and ion channel formation and transduction. Traditional BLM experimentation is usually performed in a macro-sized electrophysiology rig, which suffers from several well-known issues. First, BLMs have short lifetimes (typically on the order of tens of minutes to a few hours) and the laborious, irreproducible membrane formation process must be repeatedly applied for long-term testing. Second, stray capacitance inherent to traditional test rigs limits the temporal response leading, for example, to poor resolution in determining fast ion channel translocation events. Lastly, BLM testing is done within a single site format thus limiting throughput and increasing data collection time. To mitigate the above drawbacks, BLM technology and microfluidic platforms can be integrated to advance the state-of-the-art of BLM-based biosensor technology. Realization of BLM-based microfluidic biosensors can offer significant improvement towards sensor response characteristics (e.g. lower noise floor, increased time response). In addition, microfluidic biosensing chips can be fabricated with multiple BLM test sites that allow for parallel testing thus increasing data collection efficiency. Other benefits that microfluidics offer are: small reagent sensing volumes, disposable packaging, mass manufacturability, device portability for field studies, and lower device cost. Novel polymer microfluidic platforms capable of both in-situ and ex-situ BLM formation are described in this work. The platforms have been demonstrated for the controlled delivery of trans-membrane proteins to the BLM sites, and monitoring of translocation events through these ion channels using integrated thin film Ag/AgCl electrodes. The detailed design, fabrication, and characterization of various micro-fabricated BLM platforms is presented in this dissertation.
- K. Sahasrabudhe, "Nanochannel Fabrication Using Thermo-Mechanical Deformation of Thermoplastics," Mechanical Engineering, Thesis, 2006-12-08, Advisor(s): D. DeVoe. link
[Abstract]
Nanofluidics has been a major field of research for application in areas like single molecule detection. Most of the research efforts have been concentrated in developing novel nanochannel fabrication techniques. Most of these fabrication techniques developed are either expensive or time consuming. A novel, low-cost fabrication technique to generate sub-micrometer wide channels in thermoplastic chips with potential application in single molecule detection is demonstrated. This nanochannel fabrication technique is based on thermo-mechanical deformation of a section of microchannel in thermoplastic chip to nanometer dimensions. A custom, mechanical rig was designed, fabricated and optimized to produce a pre-defined thermo-mechanical deformation in thermo-plastic microchannel chips. Rectangular microchannels with different shapes and sizes were deformed using this rig to optimize the initial microchannel dimensions. Low aspect ratio (height:width) channels with smaller initial dimensions exhibit more potential to reach sub-micrometer widths. However, the nanochannel fabrication consistency was adversely affected by manufacturing and assembly tolerances.
- K. K. Deng, "Piezoelectric MEMS Disk Resonator and Filter Based on Epitaxial Al0.3Ga0.7As Films," Mechanical Engineering, Dissertation, 2006-11-28, Advisor(s): D. DeVoe. link
[Abstract]
In this work, a new class of disk, contour-mode, piezoelectric, micromechanical resonators based on single-crystal Al0.3Ga0.7As films has been developed. The shape of the disk resonator is based on the velocity propagation profile of the elastic wave in the plane of the piezoelectric film, with lateral dimensions scaled to the half wave length of the desired resonance frequency. The resonators are designed with supports to emulate free-free boundary conditions. Finite element analysis (FEA) model for this resonator is created in Ansys software, the simulation results validate the design concept. The performance parameters extracted from the FEA models show that this novel disk resonator outperforms the beam type counterpart. A unique 7-mask MEMS fabrication process based on the epitaxial, heterostructure Al0.3Ga0.7As films has been developed and successfully implemented to produce the prototypes of the new disk resonators. Fully experimental characterizations on the prototypes were conducted and the measured results from the prototypes are: a Q factor of 7031 at 30.2 MHz with 1.11 kOhm intrinsic motional resistance; a Q factor of 6515 at 40.8 MHz with 1.26 kOhm intrinsic motional resistance; a Q factor of 3300 at 62.3 MHz with 2.43 kOhm intrinsic motional resistance. The measured power handling level is about 1.6 mW, which is the highest power handling capability to date. These measured performance aspects are better than that of the previously developed beam type resonators. Based on this new disk resonator, two novel, two-port resonators (i.e., filters) designs have been introduced. The FEA models of both designs were created and the simulation results verify these design concepts. Equivalent circuit models for these filters were established with the parameters obtained from the FEA models. Furthermore, the optimal electrode configuration to provide minimum insertion loss is obtained through the analytical transadmittance function of the equivalent circuit. The prototypes of the filters were successfully fabricated. Measured results on these prototypes are summarized here: for the circular patter design, the best insertion loss is -45.7 dB at 37.8 MHz with quality factor 4372; for the half plane electrode design, the best insertion loss is -42.8 dB at 38.1 MHz with quality factor 3632.
- R. A. Delille, "Development and Characterization of High-Strain Eectrodes," Mechanical Engineering, Thesis, 2006-08-31, Advisor(s): E. Smela. link
[Abstract]
This thesis, composed of three journal articles, presents a compliant electrode material, based on a novel fabrication procedure. The compliant electrodes consisted of a photopatternable, urethane matrix embedded with platinum nanoparticles. The first in the series of journal articles, "Benchtop Polymer MEMS," characterized the unloaded urethane matrix's compatibility with microfabrication and patterning processes. The second, "Compliant Electrodes Based on Platinum Salt Reduction in a Urethane Matrix," presented a unique manufacturing process for compliant electrodes, which exhibited a secant modulus under 10 MPa, an electrical conductivity of 1 S/cm, and maintained electrical conductivity under mechanical strains of 30%. The third, "High-Strain, High-Conductivity Photopatternable Electrodes," explored a modification to this fabrication method that yielded a dramatic improvement in performance: an electrical conductivity of 50 S/cm, mechanical strains of 150% without loss of conductivity, robustness after thousands of strain cycles, and low hysteresis.
- B. C. Morgan, "Electrostatic MEMS Actuators using Gray-scale Technology," Electrical Engineering, Dissertation, 2006-08-30, Advisor(s): R. Ghodssi. link
[Abstract]
The majority of fabrication techniques used in micro-electro-mechanical systems (MEMS) are planar technologies, which severely limits the structures available during device design. In contrast, the emerging gray-scale technology is an attractive option for batch fabricating 3-D structures in silicon using a single lithography and etching step. While gray-scale technology is extremely versatile, limited research has been done regarding the integration of this technology with other MEMS processes and devices. This work begins with the development of a fundamental empirical model for predicting and designing complex 3-D photoresist structures using a pixilated gray-scale technique. A characterization of the subsequent transfer of such 3-D structures into silicon using deep reactive ion etching (DRIE) is also provided. Two advanced gray-scale techniques are then introduced: First, a double exposure technique was developed to exponentially increase the number of available gray-levels; improving the vertical resolution in photoresist. Second, a design method dubbed compensated aspect ratio dependent etching (CARDE) was created to anticipate feature dependent etch rates observed during gray-scale pattern transfer using deep reactive ion etching (DRIE). The developed gray-scale techniques were used to integrate variable-height components into the actuation mechanism of electrostatic MEMS devices for the first time. In static comb-drives, devices with 3-D comb-fingers were able to demonstrate >34% improvement in displacement resolution by tailoring their force-engagement characteristics. Lower driving voltages were achieved by reducing suspension heights to decrease spring constants (from 7.7N/m to 2.3N/m) without effecting comb-drive force. Variable-height comb-fingers also enabled the development of compact, voltage-controlled electrostatic springs for tuning MEMS resonators. Devices in the low-kHz range demonstrated resonant frequency tuning >17.1% and electrostatic spring constants up to 1.19 N/m (@70V). This experience of integrating 3-D structures within electrostatic actuators culminated in the development of a novel 2-axis optical fiber alignment system using 3-D actuators. Coupled in-plane motion of electrostatic actuators with integrated 3-D wedges was used to deflect an optical fiber both horizontally and vertically. Devices demonstrated switching speeds < 1ms, actuation ranges > 35 um (in both directions), and alignment resolution < 1.25 um. Auto-alignment to fixed indium-phosphide waveguides with < 1.6 um resolution in < 10 seconds was achieved by optimizing search algorithms.
- J. J. Park, "Development of BioMEMS Device and Package for a Spatially Programmable Biomolecule Assembly," Material Science and Engineering, Dissertation, 2006-08-04, Advisor(s): G. Rubloff. link
[Abstract]
We report facile in situ biomolecule assembly at readily addressable sites in microfluidic channels after complete fabrication and packaging of the microfluidic device. Aminopolysaccharide chitosan's pH responsive and chemically reactive properties allow electric signal-guided biomolecule assembly onto conductive inorganic surfaces from the aqueous environment, preserving the activity of the biomolecules. Photoimageable SU8 is used on a Pyrex bottom substrate to create microfluidic channels and a PDMS layer is sealed to the SU8 microchannel by compression of their respective substrates between additional top and bottom Plexiglas plates at the package level. Transparent and non-permanently packaged device allows consistently leak-free sealing, simple in situ and ex situ examination of the assembly procedures, fluidic input:outputs for transport of aqueous solutions, and electrical ports to guide the assembly onto the patterned gold electrode sites within the channel. Facile post-fabrication in-situ biomolecule assembly of internal electrodes is demonstrated using electrodeposition of a chitosan film on a patterned gold electrode. Both in situ fluorescence and ex situ profilometer results confirm chitosan-mediated in situ biomolecule assembly, demonstrating a simple approach to direct the assembly of biological components into a completely fabricated device. We believe that this strategy holds significant potential as a simple and generic biomolecule assembly approach for future applications in complex biomolecular or biosensing analyses as well as in sophisticated microfluidic networks as anticipated for future lab-on-a chip.
- L. S. Li, "Design, Fabrication, and Testing of Micronozzles for Gas Sensing Applications," Electrical Engineering, Dissertation, 2006-04-03, Advisor(s): R. Ghodssi. link
[Abstract]
Real-time identification and quantitative analysis of volatile and semi-volatile chemical vapors are critical for environmental monitoring. Currently available portable instruments lack the sensitivity for routine air quality monitoring, so preconcentrators are employed as front-ends for miniaturized chemical sensors. However, commonly used techniques for sensitivity enhancement have a time constant associated with adsorption:desorption or permeation of gas molecules being concentrated. Little work has been reported on fast-response concentrating techniques for gas sensing applications.
This research is devoted to the development of a fast-response microfluidic gas concentrating device with appropriate flow dynamic shapes and pressure gradients based on the separation nozzle method. It is capable of concentrating heavy gas molecules diluted in light ones when they are flowing at high speeds, thus maintaining the measurement system response time. This is promising for developing real-time preconcentrators to improve the sensitivity of miniature chemical sensors.
In the initial phase of this work, linear test structures were used to characterize viscous effects in microfluidic devices. Unit processes were developed to fabricate encapsulated micronozzles with through-hole inlets and outlets. The mass flow efficiency of the test structures was measured to be in the range of 0.36-0.81, increasing with rising Reynolds number as a result of the decreasing influence of boundary layers.
Single-stage gas concentration devices were designed and fabricated on the basis of the test structures. A gas separation experimental setup and a mass spectrometric analysis apparatus were developed to evaluate the performance of the devices. Analytical and finite element analyses were conducted to better understand and verify the experimental results. As a proof-of-concept, gas separation experiments with two different inert gas mixtures were carried out in conjunction with mass spectrometric analysis. More than two-fold enrichment of SF6 molecules with a response time on the order of 0.01 ms was demonstrated through the device. The effects of design parameters and operating conditions on the separation factor were determined experimentally and compared to the numerical simulation results. This study forms the basis for developing a cascade of the single-stage elements envisioned as a preconcentrator for miniature chemical sensors to realize real-time environmental monitoring.
- L. Li, "Piezoelectric Microbeam Resonators Based on Epitaxial Al0.3Ga0.7As Films," Mechanical Engineering, Dissertation, 2005-11-22, Advisor(s): D. DeVoe. link
[Abstract]
In this work, piezoelectric resonators based on single crystal Al0.3Ga0.7As films are implemented. The combination of Si doped Al0.3Ga0.7As as electrode layers and moderate piezoelectric properties of updoped Al0.3Ga0.7As film leads to lattice matched single crystal resonators with high attainable quality factors and capability of integration with high speed circuits. To validate the fabrication process, simple cantilever beam structures are developed and characterized by laser Doppler vibrometry. In order to achieve higher center frequencies, a clamped-clamped (c-c) beam design is explored. Important resonator parameters including resonance frequency, quality factor, and power handling ability are investigated. Measured quality factors of c-c beams were found to be limited by anchor losses to the substrate. A free-free (f-f) beam design is proposed in order to alleviate the energy dissipation due to anchor losses. Fabricated f-f beam devices show increased quality factors compared to the c-c beam design. Another improvement is the adoption of bimorph configuration instead of unimorph configuration. Compared to unimorph cantilever beam design, bimorph cantilevers showed 80% to 120% of increase in displacement with the same driving voltage without significant change in quality factors. The quality factors of flexural mode resonators in atmospheric pressure are low due to the effect of air damping. For this reason, proper working of flexural mode resonators requires a vacuum package which imposes unwanted complexity in packaging. To solve this problem, length-extensional mode resonators (bar resonators) are proposed to take advantage of low air shear damping. Bar resonators with lengths ranging from 1000 micro-m to 100 mico-m have been fabricated and tested. Measured resonant frequencies range from 2.5 MHz to 72 MHz with good matching to theoretical predictions. The quality factors of bar resonators at their first resonant frequency are measured in air and in high vacuum, showing values between 4,300 - 8,900 and 8,000 - 17,000, respectively, with corresponding measured motional resistances of 7.3 kohm - 10.5 kohm and 4.0 kohm - 7.8 kohm, respectively. The developed bar resonators showed excellent power handling ability up to -10 dBm which is much higher than equivalent electrostatic resonators.
- S. Fanning, "Characterization of Polypyrrole/Gold Bilayers for Micro-Valve Design," Mechanical Engineering, Thesis, 2005-08-29, Advisor(s): E. Smela. link
[Abstract]
Polypyrrole/gold bilayers are being developed as micro-actuators for several applications. The goal of this thesis was to use these bilayers in a micro-valve to control female urinary incontinence. Several substrate materials and designs were investigated, with noteworthy findings, including the development of a bulk micromachining method for titanium based on wet etching. Despite past research on polypyrrole/gold bilayers, the relationships between design parameters and performance were unknown. Work completed in this thesis resulted in data showing how the layer thicknesses and hinge length influence actuator bending and force. Bilayer performance was also examined as a function of temperature and in urine. Bilayer curvature increased at body temperature in a standard electrolyte, but in urine PPy failed at those temperatures.
- Y. Liu, "Fabrication and Characterization of Polypyrrole/Gold Bilayer Microactuators for Bio-Mems Applications," Mechanical Engineering, Dissertation, 2005-08-25, Advisor(s): E. Smela. link
[Abstract]
The proof of concept for conjugated polymer bilayer microactuators had been demonstrated prior to this dissertation with numerous devices, and their advantages in biomedical applications had been recognized. The next step for this technology was implementation in real systems, which required knowledge of the main performance metrics and limitations. In this dissertation, work focused on measuring these metrics for the first time to facilitate the development of cell-clinics, which are microsystems for cell study and for cell-based sensing. The conjugated polymer used throughout the dissertation was polypyrrole doped with dodecylbenzenesulfonate, PPy(DBS), and the second layer in the bilayer was gold. Device fabrication challenges were first identified and addressed, focusing particularly on methods to produce PPy/Au bilayers that did not suffer from delamination. By electroplating Au onto the electrodes or by wet etching them to increase mechanical interlocking, this problem, which had plagued the field for the last decade, was solved. Another important contributor to lifetime, which is a key actuator metric, is loss of electro-activity with extended cycling. This metric was quantified through measurements of the total exchanged charge of PPy(DBS) with cycles of electromechanical redox. This result impacts how these actuators can be used. Two other key metrics on which this work focused were bending angle, analogous to stroke in a linear actuator, and force. It was necessary to determine bending angle as a function of film thickness experimentally because the traditional bilayer beam models could not account for microfabricated bilayer radius of curvature data. Through experimental testing over a wide range of PPy and Au thicknesses, the relationship between PPy:Au thickness ratio and curvature was mapped out. The experimental results demonstrated the existence of strain gradients within the conjugated polymer films, with the material at the surface having greater actuation strain than that at the gold interface. Finally, accurate force measurements had not been done prior to this dissertation research because of the significant challenges involved in developing a method for measuring force in microactuators. This dissertation described the development of such a methodology and provides data for the blocked force as a function of polypyrrole thickness.
- M. W. Pruessner, "Indium Phosphide Based Optical Waveguide MEMS for Communications and Sensing," Electrical Engineering, Dissertation, 2005-07-29, Advisor(s): R. Ghodssi. link
[Abstract]
Indium phosphide (InP) is extensively used for integrated waveguide and photonic devices due to its suitability as a substrate for direct bandgap materials (e.g. In1-XGaXAsYP1-Y) operating at the lambda=1550 nm communications wavelength. However, little work has been reported on InP optical waveguide micro-electro-mechanical systems (MEMS). In this work, InP cantilever and doubly-clamped beams were micromachined on an In0.53Ga0.47As "sacrificial layer" on (100) InP substrates. Young's modulus was measured using nanoindentation and microbeam-bending. Intrinsic stress and material uniformity (stress gradient) were obtained by measuring the profile of doubly-clamped and cantilever beams using confocal microscopy. The study resulted in a Young's modulus of 80.4-106.5 GPa (crystal orientation-dependent). Although InP was grown lattice-matched to the substrate, arsenic from the underlying In0.53Ga0.47As sacrificial layer resulted in intrinsic compressive stress. Adding trace amounts of gallium to the InP layer during epitaxial growth induced tensile stress to offset the effect of arsenic. The materials characterization was extended to develop optical waveguide switches and sensors. In the first device, two parallel waveguides were actuated to vary the spacing between them. By modulating the gap using electrostatic pull-in actuation, the optical coupling strength was controlled via the evanescent field. Low voltage switching (< 10 V), high speed (4 us), low crosstalk (-47 dB), and low-loss (< 10 %) were achieved. Variable coupling over a 17.4 dB dynamic range was also demonstrated. The second device utilized a single movable input waveguide, which was actuated via electrostatic comb-drives to end-couple with one of several output waveguides. Low voltage switching (< 7 V), 140 us switching speed (2 ms settling time), low crosstalk (-26 dB), and low-loss (< 3.2 dB) were demonstrated. Sensing techniques based on mass-loading were developed using end-coupled cantilever waveguides. Here, the mechanical resonance frequency was measured by actuating the cantilever and measuring the end-coupled optical power at the output waveguide. A proof-of-concept experiment utilized a focused-ion-beam to mill the cantilever tip and resulted in a measurable resonance shift with mass-sensitivity delta_m/del a_f=5.1 fg/Hz. The cantilever waveguide devices and measurement techniques enable accurate resonance detection in mass-based cantilever sensors and also enable single-chip sensors with on-chip optical detection to be realized.
- V. Benetis, "Experimental and Computational Investigation of Planar Ion Drag Micropump Geometrical Design Parameters," Mechanical Engineering, Dissertation, 2005-06-07, Advisor(s): M. Ohadi and E. Smela. link
[Abstract]
To deal with increasing heat fluxes in electronic devices and sensors, innovative new thermal management systems are needed. Proper cooling is essential to increasing reliability, operating speeds, and signal-to-noise ratio. This can be achieved only with precise spatial and temporal temperature control. In addition, miniaturization of electric circuits in sensors and detectors limits the size of the associated cooling systems, thereby posing an added challenge. An innovative answer to the problem is to employ an electrohydrodynamic (EHD) pumping mechanism to remove heat from precise locations in a strictly controlled fashion. This can potentially be achieved by micro-cooling loops with micro-EHD pumps. Such pumps are easily manufactured using conventional microfabrication batch technologies. The present work investigates ion drag pumping for applications in reliable and cost effective EHD micropumps for spot cooling. The study examines the development, fabrication, and operation of micropumps under static and dynamic conditions. An optimization study is performed using the experimental data from the micropump prototype tests, and a numerical model is built using finite element methods. Many factors were involved in the optimization of the micropump design. A thorough analysis was performed of the major performance-controlling variables: electrode and inter-electrode pair spacing, electrode thickness and shape, and flow channel height. Electrode spacing was varied from 10 µm to 200 µm and channel heights from 50 µm to 500 µm. Also, degradation of the electrodes under the influence of an intense electric field was addressed. This design factor, though important in the reliability of EHD micropumps, has received little attention in the scientific and industrial applications literature. Experimental tests were conducted with prototype micropumps using the electronic liquid HFE7100 (3M). Flow rates of up to 15 mL/min under 15 mW power consumption and static pumping heads up to 750 Pa were achieved. Such performance values are acceptable for some electronic cooling applications, where small but precise temperature gradients are required.