An array of electret-biased frequency-selective resonant microelectromechanical system (MEMS) acoustic sensors was proposed to perform analysis of stress pulses created during an impact between two materials. This analysis allowed classification of the stiffness of the materials involved in the impact without applying post-impact signal processing. Arrays of resonant MEMS sensors provided filtering of the incident stress pulse and subsequent binning of time-domain waveforms into frequency-based spectra. Results indicated that different impact conditions and materials yielded different spectral characteristics. These characteristics, as well as the resulting sensor array responses, are discussed and applied to impact classification. Each individual sensor element in the array was biased by an in situ charged electret film. A microplasma discharge apparatus embedded within the microsensor allowed charging of the electret film after all device fabrication was complete. This enabled electret film integration using high-temperature surface micromachining processes that would typically lead to discharge of traditionally formed electret materials. This also eliminated the traditional wafer-bonding and post-fabrication assembly processes required in conventional electret integration approaches. The microplasma discharge process and resulting electret performance are discussed within the context of the MEMS acoustic sensor array.

Compliant microelectrodes have been designed in a microcable geometry that can be used individually or in an array and either as a shank-style electrode or as a string-like electrode that can be threaded around features such as the peripheral nerve. The fabrication process, using spin-cast micromolding (SCuM), is simple and adaptable to different patterns. The microcables were fabricated using polydimethyl siloxane (PDMS) for the insulating substrate and thin-film gold for the conductive element. The thin, metal film and the low tensile modulus of the PDMS substrate created an electrode with a composite tensile modulus lower than other compliant electrodes described in the literature. The gold film increased the composite modulus approximately three-fold compared to the unaltered PDMS. The durability of the electrodes and tolerance for stretch was also tested. The microcables were found to be conductive up to 6% strain and to regain conductivity after release from multiple applications of 200% strain. The tolerance for high-strain shows that the electrodes can be deployed for use and stretched or pulled into place as needed without damaging the conductivity. The microcable electrode recording sites were electrically characterized using frequency-based impedance modeling and were tested for electrophysiological recording using a peripheral nerve preparation. A suitable insertion mechanism was designed to use the microcables as shank-style cortical electrodes. The microcables were coated on one side with fibrin, which, when dry, stiffens the microcables for insertion into cortical tissue. A 28-day implant study testing the inflammatory response to fibrin coated PDMS microcable electrodes showed a positive, but relatively low inflammatory response, as measured by glial fibrillary astrocytic protein (GFAP; indicating activated astrocytes) immediately at the tissue edge of the implant site. The response of the control, silicon shank-style electrodes, was varied, but also trended toward low levels of GFAP expression. The GFAP staining was possibly due to the clearance of the fibrin from the implant site in addition to the presence of the PDMS-based electrode. Implant studies extending beyond 28 days are necessary to determine whether and to what degree the inflammation persists at the implant site of PDMS-based electrodes.

Traumatic brain injury (TBI) affects 1.4 million people a year in the United States alone and despite the fact that 96% of people survive a TBI, the health and socioeconomic consequences can be grave, partially due to the fact that very few clinical treatments are available to reduce the damage and subsequent dysfunction following TBI. To better understand the various mechanical, electrical, and chemical events during neural injury, and to elucidate specific cellular events and mechanisms that result in cell dysfunction and death, new high-throughput models are needed to recreate the environmental conditions during injury. This thesis project focuses on the creation of a novel and clinically relevant single-cell injury model of traumatic brain injury (TBI). The implementation of the model requires the development of a novel injury device that allows specialized micro-interfacing functionality with neural micro environments, which includes the induction of prescribed strains and strain rates onto neural tissue, such as groups of cells, individual cells, and cell processes. The device consists of a high-resolution micro-electro-mechanical-system (MEMS) microtweezer microactuator tool that is introducible into both biological and aqueous environments and can be proximally positioned to specific targets in neural tissue and neural culture systems. This microtweezer, which is constructed using traditional photolithography and micromachining processes, is controllable by a custom developed software-automated controller that incorporates a high precision linear actuator and utilizes a luer-based microtool docking interface. The injury studies will include examination of intracellular calcium concentration over the injury time course to evaluate neuronal plasma membrane permeability, which is a significant contributor to secondary injury cascades following initial mechanical insult. Mechanical strain and strain rate input tolerance criteria will also be used to determined thresholds for cellular dysfunction and death.

This dissertation presents the application of MEMS-based approaches for the construction of engineered tissue substitutes. MEMS technology can offer the physical scale, resolution, and organization necessary for mimicking native tissue architecture. Micromachined nozzles and templates were explored for the fabrication of acellular, biomimetic collagenous fibrous scaffolds, microvascular tissue structures, and the combination of these structures with cell-based therapeutics. The influence of the microstructure of the tissue constructs on their macro-scale characteristics was investigated.

Fluoride-containing solutions are widely used to etch silicon dioxide-based films. A critical issue in integrated circuit (IC) and microelectromechanical systems (MEMS) fabrication is achievement of adequate selectivity during the etching of different film materials when they are present in different areas on a device or in a stack. The use of organic fluoride-based salts in aqueous/organic solvent solutions can yield etch selectivities <1.9 for thermally-grown silicon dioxide relative to borophosphosilicate glass films, and thus may also obviate the need to add surfactants to the etch solutions to realize uniform etching. Etch studies with aqueous-organic fluoride salt-based solutions also offer insight into the etch mechanism of these materials. Specifically, the importance of water content in the solutions and of ion solvation in controlling the etch chemistry is described. With respect to fluoride-containing solutions, etching of SiO₂ films using aqueous HF-based chemistries is widely used in IC and MEMS industries. To precisely control film loss during cleaning or etching processes, good control over the contact time between the liquid (wet) chemistry and the substrate is necessary. An integrated wet etch and dry reactor system has been designed and fabricated by studying various geometrical configurations using computational fluid dynamics (CFD) simulations incorporating reaction kinetics from laboratory data and previously published information. The effect of various process parameters such as HF concentration, flow rate, and flow velocity on the etch rates and uniformity of thermally-grown silicon dioxide and borophosphosilicate glass films was studied. Simulations agree with experiments within experimental error. This reactor can also be used to wet etch/clean and dry other films in addition to SiO₂-based films using aggressive chemistries as well as aqueous HF under widely different process conditions. A spectroscopic reflectometry technique has been implemented in-situ in this custom fabricated reactor to monitor the thickness and etch rate in wet etching environments. The advantages of this technique over spectroscopic ellipsometry in specific situations are discussed. A first principles model has been developed to analyze the reflectometry data. The model has been validated on a large number of previously published studies. The match between experimental and simulated thickness is good, with the difference ~ 5 nm. In-situ thickness and etch rate have been estimated using Recursive Least Squares (RLS), Extended Kalman Filter (EKF) and modified Moving Horizon Estimator (mMHE) analyses applied to spectroscopic reflectometry using multiple wavelengths with ZnO employed as a model film. The initial guess for EKF and mMHE has been obtained from a CFD model. It has been shown that both EKF and mMHE are less oscillatory than RLS/LS in the prediction of thickness and ER and more robust when a smaller number of wavelengths are used, in addition, the computational time for EKF is less than that of mMHE/RLS. For no restrictions on computational requirements, LS should be the method of choice whereas in the case of faster etching systems, with the availability of a better process model, EKF should be starting point. The choice of algorithm is thus based on sampling rate for data collection, process model uncertainty and the number of wavelengths required.

The purpose of this work is the development of MEMS-based resonant sensors for liquid-phase biochemical sensing applications. Specifically, the sensors developed here are aimed at embedded or point-of-sampling applications: (1) when there is not enough time to send a sample to a lab for analysis, (2) in resource-poor settings, (3) when collecting analyte and shipping it to a lab would damage the sample, or (4) for in-situ monitoring. To this end, a bulk micromachined resonant cantilever sensor and a surface micromachined sensor based on the spring-softening effect are investigated as transducer elements. The developed cantilever resonators are operated in an in-plane vibration mode to reduce fluid damping and mass loading by the surrounding fluid. The surface of the resonator is either coated with a chemically sensitive polymer film for chemical sensing or with a layer of protein or antibody for biosensor testing. Chemical tests for sensing volatile organic compounds using polymer-coated in-plane resonators in the liquid-phase give estimated limits of detection below 100 ppb. In addition, biosensor tests for the detection of anti-IgG yield estimated limits of detection around 100 ng/ml. In an attempt to further improve sensor reliability and to further lower the limits of detection, a second sensing concept has been investigated. The presented sensing scheme is capacitive with a resonator acting as an analog-to-digital converter. The resonator and the sensing capacitors are coupled via the spring softening effect. Through this mechanism a change in capacitance causes a shift in resonant frequency. Extensive device modeling has been performed and a process has been developed allowing for fabrication and on-chip packaging of these sensor structures. Initial mechanical characterization data show that the resonators do in fact vibrate.

Design and analysis of polysilicon and single crystal silicon gyroscopes have been carried out. Variations in suspension design have been explored. Designs that utilize in-plane and out-of-plane sensing are studied. Damping plays an important role in determining the sense response. Reduction in damping directly affects sensor performance. The various damping mechanisms that are prevalent in gyroscopes are studied. Perforations on the proof mass are observed to significantly reduce the damping in the device when operated in air. The effects of perforation geometry and density have been analyzed. The analysis results show that there is a two orders of magnitude reduction in damping of thick gyroscope structures with optimized perforation design. Equivalent circuit lumped parameter models have been developed to analyze gyroscope performance. The simulation results of these models have been compared with results obtained from SABER, a MEMS specific system level design tool from Coventorware. The lumped parameter models are observed to produce faster simulation results with an accuracy comparable to that of Coventorware Three gyroscopes specific to the PolyMUMPS fabrication process have been designed and their performance analyzed. Two of the designs sense motion out-of-plane and the other senses motion in-plane. Results of the simulation show that for a given damping, the gyro design with in-plane modes gives a resolution of 4º/s. The out-of-plane gyroscopes have two variations in suspension. The hammock suspension resolves a rate of 25º/s in a 200 Hz bandwidth while the design with folded beam suspension resolves a rate of 2º/s in a 12 Hz bandwidth. A single crystal silicon in-plane gyroscope has been designed with vertical electrodes to sense Coriolis motion. This design gives an order of magnitude higher Capacitance change for a given rotation in comparison to conventional comb-finger design. The effects of process induced residual stress on the characteristic frequencies of the polysilicon gyroscopes are also studied. The in-plane gyroscope is found to be robust to stress variations. Analysis results indicate that the tuning fork gyroscope with the hammock suspension is the most susceptible to compressive residual stress, with a significant drop in sensitivity at high stress values.

La réalisation des circuits analogiques à hautes performances souffre de difficultés principalement dues à la réduction de la tension d'alimentation et à la réduction de la consommation, qui sont conduites par la prolifération des systèmes portables aliméntés par des batteries, mais pâtit aussi du manque d'outils de CAO permettant d'automatiser la phase de layout qui est assez laborieuse et prend beaucoup de temps. Cette thèse se situe dans ce contexte. Elle traite de deux domaines assez distincts mais complémentaires, à savoir la conception de circuits intégrés analogiques à faible tension d'alimentation, et la génération automatique (ou assistée) du layout de ces circuits à l'aide d'algorithmes et de logiciels appropriés. L'aboutissement de cette thèse est, premièrement, la création d'une nouvelle méthode de conception de circuits intégré analogiques, plus précisement la génération d'une technique de conception de nouvelle structure, plus adaptée aux basses tensions d'alimentation et aux faiblesconsommations, deuxièmement, notre contribution à l'automatisation de la phase du layout des circuits intégrés analogiques, à savoir l'étude détaillée des contraintes analogiques à prendre en compte dans tout outil d'automatisation du layout (Générateur, Placeur, Routeur, Compacteur), ainsi que notre participation au développement de CHIRVAN (outil d'automatisation des masques des circuits intégrés analogiques et mixtes, développés au CNET Grenoble) en aidant à sa mise au point, en l'utilisant, en proposant des améliorations, et surtout en consacrant tous nos efforts à développer un algorithme de placement des cellules analogiques qui prend en compte toutes ces contraintes analogiques

D’ici quelques années, des capteurs de toutes sortes vont envahir notre environnement. Nous en rencontrons déjà beaucoup autour de la voiture, de l’ordinateur ou de la téléphonie. Cette multiplication à grande échelle des capteurs n’est toutefois possible que si, d’une part, ils communiquent sans fil et, d’autre part, ils sont entièrement autonomes du point de vue énergétique. Concernant les systèmes de communication, beaucoup de progrès et de normes sont apparus ces dernières années. La technologie semble être au point, même si des améliorations en terme de consommation sont encore possibles. Quant à l’autonomie énergétique, elle pose actuellement un véritable problème à cause de la durée limitée des piles ou batteries, sans compter leurs problèmes de pollution. L’idée est donc de récupérer l’énergie (mécanique, thermique, chimique ou rayonnante) qui entoure les capteurs pour les alimenter afin de les rendre autonomes durant leurs durées de vie. Suite à une importante étude bibliographique, nous nous sommes orientés vers la récupération de l’énergie de vibrations mécaniques. Une campagne de mesure nous a alors permis d’évaluer l’énergie disponible dans un certain nombre d’environnements et de dimensionner un système qui permette de convertir sur une large bande de fréquences cette énergie mécanique en énergie électrique. Nous avons alors initialisé deux réalisations ; une première macroscopique en tungstène validant le concept et une deuxième en technologie silicium permettant de miniaturiser le récupérateur d’énergie afin de le rendre compatible avec les dimensions des capteurs à alimenter. Les premiers essais avec la structure en tungstène ont montré la possibilité de récupérer environ 480 µW pour une excitation à 50 Hz et d’amplitude 80 µm.

"Based on research results of Sandra Schweizer and Gerhard Lammel during their PhD thesis' at the Swiss Federal Institute of Technology Lausanne in the group of Prof. Philippe Renaud"--Pref. / Includes bibliographical references and index.