Energy harvesting is a technology for generating electrical power from ambient or wasted energy. It has been investigated extensively as a means of powering small electronic devices. The recent proliferation of devices with ultra-low power consumption - devices such as RF transmitters, sensors, and integrated chipsets - has created new opportunities for energy harvesters. There is a variety of ambient energies such as vibration, thermal, solar, stray current, etc. Depending on energy sources, different kinds of energy conversion mechanism should be employed. For energy harvesters to become practical, their energy conversion efficiency must improve. This efficiency depends upon advances in two areas: the system or structural design of the energy harvester, and the properties of the materials employed in energy conversion. This dissertation explores developments in both areas. In the first area, the role of nano-, micro-, and bulk structure of the energy conversion materials were investigated. In the second area, piezoelectric energy harvesters and a magneto-thermoelectric generator are treated from the perspective of system design. In the area of materials development, PbTiO3 (PTO) nanostructures consisting of nanofibers and three-dimensional (3-D) nanostructure arrays were hydrothermally synthesized. The growth mechanism of the PTO nanofibers and 3-D nanostructures were investigated experimentally and theoretically. The PTO nanostructures were composed of oriented PTO crystals with high tetragonality; these arrays could be promising candidates for nanogenerators. Different designs for energy harvesters were explored as a means of improving energy conversion efficiency. Piezoelectric energy harvesters were designed and constructed for applications with a low frequency vibrational energy and for applications with a broadband energy spectrum. A spiral MEMS piezoelectric energy harvester design was fabricated using a silicon MEMS process and demonstrated to extract high power density at ultra-low resonance frequencies and low acceleration conditions. For a broadband energy harvester, a magnetically-coupled array of oscillators was designed and built that broadened the harvester's effective resonance frequency with considerably improved output power. A new design concept for thermal energy harvesting that employs a magneto-thermoelectric generator (MTG) design was proposed. The MTG exploits a thermally-induced second order phase transition in a soft magnetic material near the Curie temperature. The MTG harvested electric power from oscillations of the soft magnet between hot and cold sources. For the MTG design, suitable soft magnetic materials were selected and developed using La0.85Sr0.15MnO3-Ni0.6Cu0.2Zn0.2Fe2O4 magnetic composites. The MTG was fabricated from a PVDF cantilever and a gadolinium (Gd) soft magnetic material. The feasibility of the design for harvesting energy from the waste heat was demonstrated by attaching an MTG array to a computer CPU. / PHD

Biomolecular interactions are fundamentally important for a wide variety of biological processes. Understanding the temperature dependence of biomolecular interactions is hence critical for applications in fundamental sciences and drug discovery. Micro-Electro-Mechanical Systems (MEMS) technology holds great potential in facilitating temperature-dependent characterization of biomolecular interactions by providing on-chip microfluidic handling with drastically reduced sample consumption, and well controlled micro- or nanoscale environments in which biomolecules are effectively and efficiently manipulated and analyzed. This dissertation is focused on a high-through and miniaturized differential scanning calorimeter for thermodynamic study of bio-molecules using MEMS techniques. The dissertation firstly introduces the overall design and operation principles. This miniaturized DSC was fabricated based on a polyimide (PI) thin film. Highly temperature sensitive vanadium oxide was used as the thermistor material. A PDMS (Polydimethylsiloxane) microfluidic chamber was separately fabricated and then bonded firmly with the PI substrate by a stamp-and-stick method. Meanwhile, the micro heater design was optimized to reach better uniformity. A heating stage was constructed for fast and reliable scanning. In this study, we used syringes to deliver the 0.63 μL liquid sample into both the sample and reference chambers. All the testing processes were functionalized using the LabVIEW programs. The sensing material was also characterized. To seek a higher temperature coefficient of resistance (TCR) and less resistive behavior, explorations about various PVD (physical vapor deposition) parameters and annealing conditions were conducted for optimization. In this research, we found vanadium oxide deposited under certain conditions leads to the highest TCR value (a maximum of 2.51%/oC). To better understand the material’s property, we also did the XRD (X-ray Diffraction), SEM (Scanning electron microscope). The micro calorimeter was calibrated using a step thermal response. The time constant was around 3s, the thermal conductance was 0.6mW/K, and the sensitivity was 6.1V/W. The static power resolution of the device at equilibrium is 100 nW, corresponding to 250 nJ/K. These performances confirmed the design and material to be appropriate for both good thermal isolation and power sensitivity. We demonstrated the miniaturized DSC’s performance on several different kinds of protein samples: lysozyme, and mAb (monoclonal antibody) and a DVD IgG (double variable domain immunoglobulin G). The results were found to be reasonable by comparing it with the commercial DSC’s tests. Finally, this instrument may be ideal for incorporation into high throughput screening workflows for the relative comparison of thermal properties between large numbers of proteins when only small quantities are available. The micro-DSC has the potential to characterize the thermal stability of the protein sample with significantly higher throughput and less sample consumption, which could potentially reduce the time and cost for the drug formulation in the pharmaceutical industry. / Ph. D. / Virtually all biological phenomena depend on molecular interactions, which is either intra-molecular as protein folding/unfolding or intermolecular as in ligand binding. A basic biology problem is to understand the folding and denaturation processes of a protein: the kinetics, thermodynamics and how a protein unfolds and folds back into its native state. Both folding/unfolding and denaturation processes are associated with enthalpy changes. The thermodynamics of binding compounds helps a great deal to understand the nature and potency of such molecules and is essential in drug discovery. As a label-free and immobilization-free method, calorimetry can evaluate the Gibbs free energy, enthalpy, entropy, specific heat, and stoichiometry, and thus provides a fundamental understanding of the molecular interactions. Calorimetric systems including isothermal titration calorimeters (ITC) and differential scanning calorimeters (DSC) are the gold standard for characterizing molecular interactions. In this research, a micro DSC is developed for direct thermodynamic study of bio-molecules. Compared with the current commercial DSC, it is on a much smaller scale. It consumes much less sample and time in each DSC measurement. It can enable comprehensive high-content thermodynamics study in the early stage of drug discovery and formulation. It also enables direct, precise, and rapid evaluation of the folding and unfolding of the large biomolecules like proteins, DNAs, and enzymes without labeling or immobilization. It can also be used as a powerful tool to study the membrane proteins, which is often impractical or impossible before.

With the continued evolution of MEMS-based gas chromatography, the drive to develop new standalone systems with lower power consumptions and higher portability has increased. However, with improvements come tradeoffs, and trying to reduce the pressure drop requirements of previously reported semi-packed columns causes a significant sacrifice in separation efficiency. This thesis covers the techniques for evaluating the separation column in a gas chromatography system as well as the important parameters that have the most effect on a column’s efficiency. Ionic liquids are introduced as a stable and versatile stationary phase for micro separation columns. It then describes a MEMS-based separation column design utilizing density modulation of embedded micro-pillars which attempts to optimize the balance between separation efficiency and pressure drop. / Master of Science / Gas chromatography is a technique used by scientists to separate and identify chemical compounds present in a given test mixture. It is a versatile technique that can be used for qualitative and quantitative analysis of complex mixtures in a variety of applications. However, typical gas chromatography systems are confined to a lab because they are large and consume a lot of power. In order to overcome these problems, different research groups have focused their attention towards the development of portable MEMS-based gas chromatography systems. By miniaturizing the various components of a gas chromatography system, these two main issues can be alleviated. This thesis covers the strategies used to develop and evaluate the separation column of a gas chromatography system and introduce a new MEMS-based column design that will further reduce the power consumption.

To support the large growth in wireless devices, such as personal data assistants (PDAs), wireless local area network (WLAN) enabled laptop computers, and intelligent transportation systems (ITS), the FCC allocated three high-frequency bands for unlicensed operation. Of particular interest is the 5-6 GHz Unlicensed National Information Infrastructure (UNII) band intended to support high-speed WLAN applications. The UNII band is further split into three smaller 100 MHz sub-bands: 5.15 - 5.25 GHz; 5.25-5.35 GHz; and 5.725-5.825 GHz. VCOs that can be switched between each of the three UNII sub-bands offer flexibility and optimum phase-locked loop (PLL) design versus non-switchable VCOs. This work presents switched-tank voltage controlled oscillators (VCOs) designed in Motorolaà ­s 0.18 à µm HIP6WRF BiCMOS process that could be used in multiband receivers covering the three UNII sub-bands. The first VCO was optimized for low power consumption. The VCO draws a total of 6.75 mA from a 1.8 V supply including buffer amplifiers. The VCO is designed with a switched-capacitor LC tank circuit that can switch to two center frequencies, 5.25 GHz and 5.775 GHz, with 200 MHz of varactor-supplied tuning range. The simulated output voltage swing is 2.0 V peak-to-peak and is kept constant between sub-bands by an active PMOS load integrated into the biasing circuitry. The second VCO was optimized for a high output voltage swing by replacing the current biasing circuit with a degenerating inductor. This design targeted three center frequencies, 5.2 GHz, 5.3 GHz, and 5.775 GHz, with 100 MHz of tuning range. This design has an output peak-to-peak voltage swing of 5.2 V but consumes an average of 16.5 mA from a 1.8 V supply. The two fabricated circuits exhibit tuning ranges similar to the simulated results; however, the center frequencies of each decrease due to interconnect parasitics there were unaccounted for in the designs. The measured center frequencies are 4.4 GHz and 5.37 GHz for the first design, and 4.4 GHz and 4.7 GHz for the second design (with one state inoperative due to a faulty switch). The phase noise of the fabricated VCO designs was limited primarily by the low quality factor (Q-factor) of the on-chip LC tank circuits. Oscillators referenced with high-Q off-chip components such as quartz crystal references and surface acoustic wave (SAW) resonators in a PLL can exhibit much improved performance; however, these off-chip components add packaging/assembly cost and higher bill of materials, impedance matching issues, and parasitics that can significantly affect performance for RF applications. Thus, there is tremendous incentive for integrating high-Q components on-chip with the eventual goal of consolidating all of the RF/analog/digital components onto a single wireless-enabled chip, commonly called RF system-on-a-chip (SoC). Microelectromechanical (MEM) resonators have received significant attention based on their ability to provide high on-chip Q-factors at RF frequencies using fabrication techniques that are compatible with modern IC processes. MEM resonators transduce electrical signals into extremely low-loss mechanical vibration and vice versa. Consequently, this thesis also describes the modeling, simulation, and fabrication of contour-mode disk-shaped MEM resonators. This resonator geometry is capable of providing high-Q oscillation at frequencies exceeding 1 GHz at sizes easily within the limits of modern photolithography techniques. Finite element analysis is used to predict the frequency response of disk resonators under various operating conditions and to determine variables that are most critical to the resonator design. A silicon-on-insulator (SOI) fabrication process for constructing the disk is also discussed. Finally, the possible future integration of MEM resonators with multiband VCOs in a common IC process is proposed. / Master of Science

This work is focused on the design, fabrication and characterization of high performance MEMS-based micro gas chromatography columns having wide range of applications in the pharmaceutical industry, environmental monitoring, petroleum distillation, clinical chemistry, and food processing. The first part of this work describes different approaches to achieve high-performance microfabricated silicon-glass separation columns for micro gas chromatographic (µgC) systems. The capillary width effect on the separation performance has been studied by characterization of 250 µm-, 125 µm-, 50 µm-, and 25 µm-wide single-capillary columns (SCCs) fabricated on a 10à 8 mm2 die. The plate number of 12500/m has been achieved by 25 µm-wide columns coated by a thin layer of polydimethylsiloxane stationary phase using static coating technique. To address the low sample capacity of these narrow columns, this work presents the first generation of MEMS-based "multicapillary" columns (MCCs) consisting of a bundle of narrow-width rectangular capillaries working in parallel. The second contribution of this work is the first MEMS-based stationary phase coating technique called monolayer protected gold (MPG) for ultra-narrow single capillary (SCC) and multicapillary (MCC) microfabricated gas chromatography (μGC) columns yielding the highest separation performance reported to date. This new μGC stationary phase has been achieved by electrodepositing a uniform functionalized gold layer with an adjustable thickness (250nm-2µm) in 25μm-wide single columns as well as in four-capillary MCCs. The separation performance, stability, reproducibility and bleeding of the stationary phase have been evaluated over time by separating n-alkanes as non-polar and alcohols as polar gas mixtures. / Master of Science

This thesis reports the fabrication of three dimensionally independent on-chip microchannels using a CMOS-compatible single mask deep reactive ion etching (DRIE) process for cooling 3D ICs. Three dimensionally independent microchannels are fabricated by utilizing the RIE lag effect. This allows complex microchannel configurations to be fabricated using a single mask and single silicon etch step. Furthermore, the microchannels are sealed in one step by low temperature oxide deposition. The micro-fin channels heat transfer characteristics are similar to previously published channel designs by being capable of removing 185 W/cm2 before the junction temperatures active elements exceed 85°C. To examine the heat transfer characteristics of this proposed on-chip cooler, different channel geometries were simulated using computational fluid dynamics. The channel designs were simulated using 20°C water at different flow rates to achieve a laminar flow regime with Reynolds numbers ranging from 200 to 500. The steady state simulations were performed using a heat flux of 100 W/cm2. Simulation results were verified using fabricated test chips. A micro-fin geometry showed to have the highest heat transfer capability and lowest simulated substrate temperatures. While operating with a Reynolds number of 400, a Nusselt number per input energy (Nu/Q) of 0.24 W-1 was achieved. The micro-fin geometry is also capable of cooling a substrate with a heat flux of 100W/cm2 to 45ºC with a Reynolds number of 525. These channels also have a lower thermal resistance compared to external heat sinks because there is no heat spreader or thermal interface material layer. / Master of Science

In wavelength division multiplexed (WDM) optical communication networks, signals are amplified periodically by optical amplifiers. Since the gain profiles of optical amplifiers are not flat, equalizers are usually used to maintain signal powers at different wavelengths in equal to avoid crosstalk and data loss. However, fixed attenuation can only compensate fixed input power and amplification. In active network, input power and amplifier gain change with time. Active level compensation at each wavelength is needed. An adaptive attenuator is a device with a chromatically variable transmissivity used to equalize channel powers in wavelength-division multiplexing (WDM) fiber-optic communication lines. In this thesis, a method of Fourier analysis of multi-beam interference is developed. It is shown that the total electric field and relative phase delay of each beam form a Fourier transform pair. Thus methods and properties of Fourier analysis are applicable in multi-beam interference analysis and design. Fourier transform based design is presented. Novel devices that apply such design principles are introduced. Principles and structures of novel adaptive attenuators based on various technologies such as segment deformable mirror, liquid crystal, phase modulation array are given. Simulation results for segment deformable mirror based adaptive attenuator are presented. / Master of Science

No / Passive and active devices are essential devices in mobile and base stations’ transceiver. Consequently, these devices dominated the large part of the PCB of the today’s transceiver. However, the tomorrow’s mobile terminals without circuit tunability would be extremely large in size to accommodate present and future radio access technologies (RATs). The stand-alone transceiver for one single RAT is comprised of single passive and active devices and adding two or more RATs for the same transceiver would require adding two or more devices, since all of these RATs standards work on different frequency bands. Apparently, without tunability approach, this will increase the complexity of the system design and will cover a large part of the circuit space leading to power consumptions, loss which results to the poor efficiency of the transceiver. In this work, a miniaturized RF MEMS tunable bandpass is developed to operate in the frequency range from 1.8 to 2.6 GHz.

Cancer is a major health issue that has been associated with over 80 million deaths worldwide in the last decade. Recently, significant improvements have been made in terms of treatment and diagnosis. However, despite these advancements there is still a demand for low-cost, high-accuracy, and easy-to-use technologies capable of classifying cells. Analysis of cell behavior in microfluidic deformability assays provides a label-free method of observing cell response to physical and chemical stimuli. This body of work shows advancements made toward reaching our goal of a robust and cost-effective biosensing device that allows for the identification of normal and cancer cells. These devices can also monitor cell responses to physical and chemical stimuli in the form of mechanical deformation and chemotherapeutic drugs, respectively. Our initial design was a microfluidic device that consisted of three channels with varying deformation and relaxation regions. Cell velocities from the deformations regions allowed us to distinguish between normal and cancer cells at the single-cell level. The next design used a singular deformation channel that was embedded with an array of electrodes in order to measure entry time, transit time and velocities as a single cell passes through the channel. These factors were found to reveal information about the biomechanical properties of single cells. Embedded electrodes were implemented in order to reduce post processing times of the data analysis and provide more insight into the bioelectrical information of cells. Finally, we report a microfluidic device with parallel deformation channels and a single electrode pair to improve throughput and automate data collection of deformability assays. This thesis demonstrates how microfluidic deformability assays, with and without embedded electrodes, show promising capabilities to classify different cells based on their biophysical traits which can be utilized as a valuable tool for testing responses to physical and chemical stimuli. / MS / Cancer is a worldwide health issue with approximately 1.7 million new cases each year in the United State alone. Although a great amount of research has been conducted in this field, the numerous uncertainties and heterogeneity among tumors, which is amplified by the large diversity between patients, has limit progress in both diagnostics and therapy. Traditionally, cancer studies have primarily focused on biological and chemical techniques. However, more recently, researchers have begun to leverage engineering techniques to acquire a new perspective on cancer to better understand the underlying biophysical attributes. Thus far, various engineering methodologies have produced meaningful results, but these techniques are costly and tend to be laborious. As a result, there is a need for low-cost, high-accuracy, and easy-to-use technologies to aid with cancer research, diagnostics, and treatment. An emerging field to alleviate these concerns is microfluidics, which is a science involving the flow of fluids in micro-scale channels. The field of microfluidics shows a great deal of promise for the development of clinically ready devices for analyzing cancer cells at both the population and single cell levels. Investigating the behavior of cancer cells at a single cell level can provide valuable information to help better understand the responsiveness of tumors to physical or chemical stimuli, such as chemotherapeutic drugs. This thesis reports multiple robust and cost-effective biomedical micro-devices that are used to analyze normal and cancerous cells. These devices consist of a microfluidic channel with sensors and are created using micro-fabrication techniques. The unique designs have enabled the evaluation of cells based on their mechanical and electrical properties. Specifically, the mechanical properties can be measured by forcing a cell into a microfluidic channel that is smaller than the diameter of the cell and recording its response to this physical stimulus. Electrical properties are measured simultaneously as the cells are probed for their mechanical properties. In general, the mechanical and electrical properties of cells can be altered when they undergo internal change (i.e. diseased cells) or experience external stimuli. Thus, these properties can be utilized as indicators of cancer progression and can be used to distinguish tumorigenic from non-tumorigenic cells. Data collection from these devices is automated, allowing for the rapid acquisition of mechanical and electrical properties of cells with minimal post-processing. Results from these devices have been promising in their ability to indicate significant differences among various normal and cancer populations based on their mechanical and electrical attributes.

L’étude du contact électrique quasi statique à plusieurs échelles permet de comprendre celui des micro-relais MEMS. Au cours de ce travail, une modélisation fine du contact est développée pour valider des lois de comportement établies à partir des mesures obtenues grâce à la mise au point de deux dispositifs expérimentaux originaux : la balance de précision, qui permet de réaliser un contact à l’échelle macroscopique entre barreaux croisés recouverts des films minces des matériaux à tester, et un nanoindenteur instrumenté pour la mesure électrique reproduisant un micro-contact identique à celui des micro-relais. Ils permettent tous deux de mener une étude comparative de différents échantillons en fonction de la force (de la dizaine de µN à quelques N), du courant (du µA à l’A), de l’état de surface (rugosité) ou encore du temps ; le contact étant caractérisé par sa résistance électrique. Ce travail concerne principalement le contact réalisé entre films minces en Au, matériau de contact de référence pour les applications micro-relais MEMS. L’étude des contacts de grande dimension a néanmoins été élargie à Ru, Rh, Pt et à l’alliage Au-Ni.Les résultats obtenus à l’aide de la balance de précision ont démontré la nécessité de prendre en compte l’influence de la configuration en film mince des matériaux de contact, tant du point de vue mécanique (rugosité) qu’électrique (répartition des lignes de courant). Leur comparaison à une modélisation statistique du contact rugueux donne des résultats satisfaisants. Cette approche a par ailleurs nécessité le développement d’un algorithme d’analyse d’image des relevés topographiques réalisés au microscope à force atomique, permettant ainsi de quantifier précisément les positions, taille et rayon de courbure de chaque aspérité de la surface.Les mesures effectuées à l’aide du nanoindenteur ont mis en évidence l’effet de la durée de fermeture des microcontacts sur la valeur de la résistance électrique. Le fluage des aspérités serait en partie responsable de la décroissance temporelle observée, aboutissant à des valeurs de résistance limite comparables à celles calculées à l’aide d'une modélisation numérique du contact entre des aspérités discrétisées et une sphère lisse. / The multi scale study of quasi static electrical contact is aimed at understanding those in MEMS microswitches. In this work, an accurate modeling of contact is developed to validate constitutive relations based on measurements obtained through the development of two original experimental set ups: a precision balance, which enables to perform a macroscopic contact between crossed roads coated with thin films of the materials to be tested, and a nanoindenter instrumented for electrical measurements reproducing microswitches contacts. They both allow a comparative study of different samples depending on the force (from μN to N), current (µA to A), surface condition (roughness) or time, while the contact is characterized through its electrical resistance. The measurements are obtained in the first place for gold, the reference contact material for MEMS microswitches applications. The study of large contacts was nevertheless extended to Ru, Rh, Pt and Au-Ni alloy.The results obtained using the precision balance showed the need to take into account the influence of the thin film configuration of contact materials, both in terms of mechanical (roughness) and electrical (distribution of current lines). Their comparison to a statistical model of rough contact gives satisfactory results. This approach also required the development of an image analysis algorithm of topographic maps obtained through atomic force microscopy. It allows quantifying precisely the position, height and radius of curvature of each surface asperity.Measurements made using the nanoindenter showed the effect of the time of closure of the micro contact on electrical resistance values. The creep of asperities may be partly responsible for the observed time decay, leading to limit resistance values comparable to those calculated using a numerical modeling of the contact between discretized asperities and a smooth sphere.