Continued demands for better control of the operating conditions of structures and processes have led to the need for better means of measuring temperature (T), pressure (P), and relative humidity (RH). One way to satisfy this need is to use MEMS technology to develop a sensor that will contain, in a single package, capabilities to simultaneously measure T, P, and RH of its environment. Because of the advantages of MEMS technology, which include small size, low power, very high precision, and low cost, it was selected for use in this thesis. Although MEMS sensors that individually measure T, P, and RH exist, there are no sensors that combine all three measurements in a single package. In this thesis, a piezoresistive pressure sensor and capacitive humidity sensor were developed to operate in the range, of 0 to 2 atm and 0% to 100%, respectively. Finally, a polysilicon resistor temperature sensor, which can work in the range of -50ºC to 150ºC, was analyzed. Multimeasurement capability will make this sensor particularly applicable for point-wise mapping of environmental conditions for advanced process control. In this thesis, the development of sensors for such an integrated device is outlined. Selected results, based on the use of analytical, computational, and experimental solutions (ACES) methodology, particularly suited for the development of MEMS sensors, are presented for the pressure, relative humidity, and temperature sensors.

Mercury (Hg) has always been a serious risk to the environment and human health. It is a very common contamination in petroleum industry, which may lower product quality, threaten operation safety and worker’s health even at a very low concentration. Consequently the detection of mercury is very necessary. Gold is widely used as sensing material of mercury because it has a specific affinity with mercury and the adsorption of mercury changes characteristics of gold such as resistivity and effective mass density. In this thesis, common methods for sensing mercury vapor concentration were summarized and a surface acoustic wave (SAW) sensor utilizing the adsorption of mercury on gold electrodes was proposed for 1 μg/m3 level low concentration mercury vapor detection. The working principle of SAW sensor was studied and finite element method models were built to optimize the sensor design. The influence of several physical structure parameters such as electrode width and pitch on the sensor sensitivity and response time were studied using the simulation model. According to the simulation results a prototype of SAW sensor was designed and fabricated. The sensor was then analyzed with network analyzer and tested with mercury vapor. Preliminary results were presented and analyzed in this work. Finally potential future work was proposed and discussed.

Le contrôle des écoulements vise à modifier le comportement naturel d’un écoulement fluidique. Dans le domaine des transports, contrôler les phénomènes fluidiques tels que le décollement peut permettre d’économiser du carburant, d’améliorer les performances des véhicules ou encore d’assurer davantage la sécurité des passagers. Dans ce contexte, des capteurs avec de fines résolutions temporelle et spatiale sont requis afin de connaître l’écoulement à contrôler et adapter en temps réel le contrôle. Dans ce travail, l’objectif a été de développer des micro-capteurs de frottement et de pression pour les mesures en écoulements turbulents et le contrôle de décollement. Tout d’abord un micro-capteur calorimétrique a été conçu et réalisé par des techniques de microfabrication pour mesurer simultanément le frottement pariétal et la direction de l’écoulement. Le micro-capteur a ensuite été intégré en paroi d’une soufflerie afin de réaliser son étalonnage statique et dynamique et d’étudier sa sensibilité à la direction de l’écoulement. Troisièmement, le micro-capteur calorimétrique a été utilisé pour caractériser des écoulements décollés. Plusieurs micro-capteurs avec électronique miniaturisée ont été intégrés avec succès dans une maquette de volet et des essais de contrôle actif ont été réalisés. Enfin, la quatrième partie concerne le développement d’un micro-capteur de pression et d’un micro-capteur multi-paramètres réunissant les deux technologies. L’ensemble de ces micro-capteurs ont été caractérisés avec succès et montrent des résultats prometteurs pour caractériser les écoulements turbulents et permettre la mise en place de contrôle d’écoulement en boucle fermée. / Flow control aims at artificially changing the natural behaviour of a flow. In transport industries, controlling fluidic phenomena such as boundary layer separation allows saving fuel and power, improving vehicles performances or insuring passenger’s safety. In this context, sensors with accurate spatial and temporal resolution are required. Such devices enable to estimate the flow to control and allow real-time adaptation of the control. In this work, the objective is to develop wall shear stress and pressure micro-sensors for turbulent flows measurements and flow separation control.Firstly, a calorimetric micro-sensor was designed and realized using micromachining techniques for measuring simultaneously the wall shear stress amplitude and the flow direction. Secondly, the micro-sensor was flush-mounted at the wall of a wind tunnel for static and dynamic calibrations. Thirdly, it was used to characterized separated flows. Several configurations were studied: separation on airfoil profile, separation and reattachment downstream a 2D square rib and the separation on a flap model. Several micro-sensors with embedded electronics were successfully integrated on a flap model and active flow control experiments were performed. Finally, the fourth part of the document concerns the development of a pressure micro-sensor and the development of a multi-parameter micro-sensor combining both technologies.All these micro-sensors have been successfully realized and characterized and demonstrate promising results for measuring turbulent flows and implementing closed loop reactive flow control

This thesis work builds on the concept of reconfiguring the antenna properties (frequency, polarization, radiation pattern) using Radio Frequency (RF) Micro Electro Mechanical Systems (MEMS). This is a part of the overall research performed at the RF Micro/Nano Electro Mechanical Systems (uNeMS) Laboratory at Utah State University, which includes design, microfabrication, test, and characterization of uNeMS integrated cognitive wireless communication systems (Appendix A). In the first step, a compact and broadband Planar Inverted F Antenna (PIFA) is designed with a goal to accommodate reconfigurability at a later stage. Then, a Frequency Reconfigurable Antenna (FRA) is designed using MEMS switches to switch between the Public Safety (PS) bands, 152-162 MHz and 406-512 MHz, while maintaining the integrity of radiation pattern for each band. Finally, robust mechanical designs of the RF MEMS switches accompanied by different analyses have been performed. These analyses are instrumental in obtaining high yield, reliable, robust microfabrication processes including thin film metal deposition and patterning.

Long the dominant method of wafer planarization in the integrated circuit (IC) industry, chemical-mechanical polishing is starting to play an important role in microelectromechnical systems (MEMS). We present an experiment to characterize a polysilicon CMP process with the specific goal of examining MEMS sized test structures. We utilize previously discussed models and examine whether the same assumptions from IC CMP can be made for MEMS CMP. We find that CMP at the MEMS scale is not just pattern density dependent, but also partly dependent on feature size. Also, we find that new layout designs relevant to MEMS can negatively impact how well existing CMP models simulate polishing, motivating the need for further model development. / Singapore-MIT Alliance (SMA)

Performance and manufacturability are two important issues that must be taken into account during MEMS design. Existing MEMS design models or systems follow a process-driven design paradigm, that is, design starts from the specification of process sequence or the customization of foundry-ready process template. There has been essentially no methodology or model that supports generic, high-level design synthesis for MEMS conceptual design. As a result, there lacks a basis for specifying the initial process sequences. To address this problem, this paper proposes a performance-driven, microfabrication-oriented methodology for MEMS conceptual design. A unified behaviour representation method is proposed which incorporates information of both physical interactions and chemical/biological/other reactions. Based on this method, a behavioural process based design synthesis model is proposed, which exploits multidisciplinary phenomena for design solutions, including both the structural components and their configuration for the MEMS device, as well as the necessary substances for the chemical/biological/other reactions. The model supports both forward and backward synthetic search for suitable phenomena. To ensure manufacturability, a strategy of using microfabrication-oriented phenomena as design knowledge is proposed, where the phenomena are developed from existing MEMS devices that have associated MEMS-specific microfabrication processes or foundry-ready process templates. To test the applicability of the proposed methodology, the paper also studies microfluidic device design and uses a micro-pump design for the case study. / Singapore-MIT Alliance (SMA)

Abstract Micro-electromechanical systems (MEMS) are subject to inevitable and inherent uncertainties in their dimensional and material parameters. Those lead to variability in their performance and reliability. Manufacturing processes leave substantial variability in the shape and geometry of the device due to its small dimensions and high feature complexity, while the material properties of a component are inherently subject to scattering. The effects of these variations have to be considered and a modeling methodology is needed in order to ensure required MEMS performance under uncertainties. Furthermore, in the design of high-Q micro-resonators, dissipation mechanisms may have detrimental effects on the quality factor (Q). One of the major dissipation phenomena to consider is thermoelastic damping, so that performances are directly related to the thermoelastic quality factor, which has to be predicted accurately. The purpose of this research is to develop a numerical method to analyze the effects of geometric and material property random variations on the thermoelastic quality factor of micro-resonators. The extension of the Perturbation Stochastic Finite Element Method (PSFEM) to the analysis of strongly coupled multiphysic phenomena allows the quantification of the influence of uncertainties, making available a new efficient numerical tool to MEMS designers. Résumé Dans le domaine des microsystèmes électromécaniques (MEMS), les micro-résonateurs jouent un rôle important pour le développement de micro-capteurs de plus en plus précis (ex : micro-accéléromètres). Dans cette optique daugmentation de la précision, les pertes dénergie qui limitent les performances des micro-résonateurs doivent être identifiées et quantifiées. Le facteur limitant des micro-résonateurs actuels est leur facteur de qualité thermo-élastique, qui doit donc être prédit de manière précise. De plus, suite à la tendance actuelle de miniaturisation et complexification accrues des MEMS, les sources de dispersions sont très nombreuses, à la fois sur les constantes physiques des matériaux utilisés et sur les paramètres géométriques. La mise au point doutils numériques permettant de prendre en compte les incertitudes de manière efficace est donc primordiale afin daméliorer les prestations densemble du microsystème et dassurer un certain niveau de robustesse et de fiabilité. Le but de cette recherche est de développer une méthode numérique pour analyser les effets des variations aléatoires des propriétés matérielles et géométriques sur le facteur de qualité thermo-élastique de micro-résonateurs. Pour ce faire, lapproche dite perturbative de la méthode des éléments finis stochastiques (PSFEM) est étendue à lanalyse de phénomènes multiphysiques fortement couplés, fournissant ainsi aux acteurs de lindustrie des MEMS un nouvel outil de conception efficace.

<p>Couplers are one of the most frequently used passive devices in microwave circuitry. The main function of a coupler is to divide (or combine) a radio frequency signal into (from) two separate signals by a specific ratio and phase difference. With the need for smaller electronic devices, a reduction in the area of a distributed coupler would prove to be valuable. The purpose of this research is to develop, simulate, fabricate and test high aspect ratio microstructure couplers that are smaller in area than existing distributed couplers, and have comparable or better performance. One method used to reduce the area of a distributed coupler is to replace single or multiple transmission lines with lumped element equivalent circuits. One category of lumped elements that has not been extensively implemented is high aspect ratio lumped elements. High aspect ratio lumped elements fabricated with deep X-ray lithography are able to take advantage of using the vertical dimension, and reduce their planar area. In this thesis high aspect ratio lumped elements are used in the design of 3-dB microstructure couplers that show significant area reduction compared to equivalent distributed couplers.</p> <p>The designs of the microstructure couplers were based on the lumped element equivalent circuits of a 3-dB branch-line and a 3-dB rat-race distributed coupler. Simulations were performed to determine the lumped element values that would provide the largest 3-dB bandwidth while still maintaining close to ideal coupling and through values, return loss bandwidth, isolation bandwidth, and phase. These lumped element values were then implemented in the microstructure coupler designs as high aspect ratio microstructure lumped elements. 3-D electromagnetic simulations were performed which verified that the structures behaved electrically as couplers. The microstructure couplers were designed to be 220 &#x00B5;m tall nickel structures with capacitance gap widths of 6 µm.</p> <p>Fabrication of the microstructure couplers using deep X-ray lithography was performed by the microfabrication group at IMT/KIT in Karlsruhe, Germany. Before testing, detailed visual inspection and the etching of the structures was performed at the Canadian Light Source.</p> <p>A total of five microstructure couplers were tested. Four of the tested couplers were based on the 3-dB branch-line coupler, and the fifth coupler was based on the 3-dB rat-race coupler. The microstructure branch-line design that had the best overall results was fabricated on quartz glass substrate and had an operation frequency of 5.3 GHz. The 3-dB bandwidth of the coupler was measured to be better than 75.5% and extrapolated to be 95.0%. At the centre frequency the through and coupled values were -4.32 dB and -4.44 dB. The phase difference between the couplers output ports was designed to be 90.0° and was measured to be 95.8°. The ±5° phase bandwidth was measured to be 12.7% and the isolation bandwidth was 28.8%. The measured results from the other couplers were comparable to simulation results.</p> <p>The main advantage of the microstructure coupler designs over existing distributed couplers is that the microstructure couplers show a significant area reduction. The branch-line microstructure designs were at least 85% smaller in area than their distributed equivalent on quartz glass. The rat-race microstructure design showed an area reduction of 90% when compared to its distributed equivalent on quartz glass.</p>

The objective of this thesis was to develop a fast-response multifunctional MEMS (Micro Electro Mechanical Systems) sensor for the simultaneous measurement of in-cylinder pressure and temperature in an internal combustion (IC) engine. In a representative IC engine, the pressure and temperature can reach up to about 1.6 MPa and 580 °C, respectively, at the time of injection during the compression stroke. At the peak of the combustion process, the pressure and temperature near the cylinder wall can go beyond 6 MPa and 1000 °C, respectively. Failure of current membrane-based MEMS pressure sensors operating at high temperatures is mainly caused by cross-sensitivity to temperature, which affects the pressure readout. In addition, the slow thermal response of temperature sensors used for such a dynamic application makes real-time sensing within a combustion engine very challenging. While numerous approaches have been taken to address these issues, no MEMS sensor has yet been reported that can carry out real-time measurements of in-cylinder pressure and temperature. The operation of the sensor proposed in this Thesis is based on a new non-planar and flexible multifunctional membrane, which responds to both pressure and temperature variations at the same time. The new design draws from standard membrane-based pressure and thermostatic-based temperature MEMS sensing principles to output two capacitance values. A numerical processing scheme uses these values to create a characteristic sensing plot which then serves to decouple the effects of pressure and temperature variations. This sensing scheme eliminates the effect of cross-sensitivity at high temperatures, while providing a short thermal response time. Thermal, mechanical and electrical aspects of the sensor performance were modeled. First, a semi-analytical thermo-mechanical model, based on classic beam theory, was tailored to the shape of the multifunctional membrane to determine the sensor’s response to pressure and temperature loading. ANSYS® software was used to verify this semi-analytical model against finite element simulations. Then the model was then used to calculate the capacitive outputs of the multifunctional MEMS sensor subjected to in-cylinder pressure and temperature loading during a complete cycle of operation of a typical IC engine as well as to optimize the sensor specifications. Several prototypes of the new sensing mechanism fabricated using the PolyMUMPs® foundry process were tested to verify its thermal behavior up to 125 °C. The experiments were performed using a ceramic heater mounted on a probe station with the device connected to a precision LCR-meter for capacitive readouts. Experimental results show good agreement of the temperature response of the sensor with the ANSYS® finite element simulations. Further simulations of the pressure and temperature response of different configurations of the multifunctional MEMS sensor were carried out. The simulations were performed on an array of 4200 multifunctional devices, each featuring a 0.5 µm thick silicon carbide membrane with an area of 25×25 µm2, connected in parallel shows that the optimized sensor system can provide an average sensitivity to pressure of up to 1.55 fF/KPa (over a pressure range of 0.1-6 MPa) and an average sensitivity to temperature of about 4.62 fF/°C (over a temperature range of 160-1000 °C) with a chip area of approximately 4.5 mm2. Assuming that the accompanying electronics can meaningfully measure a minimum capacitance change of 1 fF, this optimized sensor configuration has the potential to sense a minimum pressure change of less than 1 KPa and a minimum temperature change of less than 0.35 °C over the entire working range of the representative IC engine indicated above. In summary, the new developed multifunctional MEMS sensor is capable of measuring temperature and pressure simultaneously. The unique design of the membrane of the sensor minimizes the effect of cross-sensitivity to temperature of current MEMS pressure sensors and promises a short thermal response time. When materials such as silicon carbide are used for its fabrication, the new sensor may be used for real-time measurement of in-cylinder pressure and temperature in IC engines. Furthermore, a systematic optimization process is utilized to arrive at an optimum sensor design based on both geometry and properties of the sensor fabrication materials. This optimization process can also be used to accommodate other sensor configurations depending on the pressure and temperature ranges being targeted.

Application of neural prostheses in today's medicine successfully helps patients to increase their activities of daily life and participate in social activities again. These implantable microsystems provide an interface to the nervous system, giving cellular resolution to physiological processes unattainable today with non-invasive methods. The latest developments in genetic engineering, nanotechnologies and materials science have paved the way for these complex systems to interface the human nervous system. The ideal system for neural signal recording would be a fully implantable device which is capable of amplifying the neural signals and transmitting them to the outside world while sustaining a long-term and accurate performance, therefore different sciences from neurosciences, biology, electrical engineering and computer science have to interact and discuss the synergies to develop a practical system which can be used in daily medicine practice. This work investigates the main building blocks necessary to improve the quality of acquired signal from the micro-electronics and MEMS perspectives. While all of these components will be ultimately embedded in a fully implantable recording probe, each of them addresses and deals with a specific obstacle in the neural signal recording path. Specifically we present a low-voltage low-noise low-power CMOS amplifier particularly designed for neural recording applications. This is done by surveying a number of designs and evaluating each design against the requirements for a neural recording system such as power dissipation and noise, and then choosing the most suitable topology for design and implementation of a fully implantable system. In addition a surface modification method is investigated to improve the sacrificial properties and biocompatibility of probe in order to extend the implant life and enhance the signal quality.