This dissertation performs a simulation investigation into the nonlinear static and dynamic characteristics of electrostatically driven shaped micro-actuators in micro-electro-mechanical systems (MEMS). The model proposed in the current nonlinear pull-in deflection study considers various boundary conditions for the electrostatically actuated structures, e.g. the cantilever beam and the fixed-fixed beam, and takes account of the electrical field fringing effect and the axial residual stress. Initially, the Adomian decomposition method is employed to evaluate the response of a micro-actuator incorporating a rectangular micro-beam and a flat electrode by obtaining the closed-form solution of the corresponding nonlinear equation. Since no iteration is required in solving the nonlinear deformation, this decomposition method is one of the most efficient methods available for evaluating the unstable pull-in behavior of an electrostatically driven micro-actuator. The present study implements both small and large deflection assumptions when simulating the response of the micro-actuator in order to explore the possible effects of the two models on the accuracy of the simulation results. The shaped micro-beam with a curved electrode micro-actuator is further assessed using the differential quadrature method (DQM) to examine the influence of the nonlinear pull-in effect. This dissertation also studies the contact force and the pull-in deflection of shaped micro-tweezers. The DQM is employed to solve the nonlinear interaction between the curved electrostatic field force and the corresponding deflection of the shaped cantilever actuators. The numerical results confirm the ability of the DQM to treat this form of nonlinear actuator problem accurately, efficiently and systematically. To evaluate the dynamic characteristics of the electrostatic micro-actuator, the DQM is applied to solve the natural frequencies of a fixed-fixed shaped beam vibrating around its statically deflected position under electrostatic loading. The proposed model not only takes account of the nonlinear interaction between the curved electrostatic field force and the restoring force of the shaped micro-beam, but also considers mid-plane stretching, axial residual stress, and electrical field fringing effects. It is shown that an excellent agreement exists between the simulation results obtained using the proposed model and those measured experimentally. This study also investigates the micro-beam and electrode shape effect on the natural frequencies of the actuator system. The analytical results indicate that variations in the shape of the micro-beam or of the electrode not only influence the electrostatic field distribution, but also significantly alter the dynamic characteristics of the micro-actuator. Furthermore, the results demonstrate that the shaped micro-beam with a curved electrode micro-actuator increases the working voltage range of the micro-actuator by a factor of approximately six times compared to that of a micro-actuator incorporating a rectangular micro-beam and a flat electrode. A continuing trend nowadays is the integration of micro-electro-mechanical devices with electronic circuitry to fabricate MEMS devices such as micro-switches, optical micro-mirrors, etc. It is known that when an electrical voltage is applied to these devices, the micro-actuators will undergo a residual vibration before reaching their permanent position. Hence, this dissertation investigates the residual vibration phenomenon of cantilever beam type micro-switches with air squeeze-film damping between the micro-beam and substrate. The present simulations of various shaped micro-actuators provide an understanding of the nonlinear static and dynamic behaviors of these devices and as such provide designers with the information required to properly and accurately control the device operating range during the design stage.

This paper is going to emphasize on the air squeeze film damping effect on micro-mechanical resonant beam in MEMS. In general, the low energy density of electrode force will cause high-voltage power supply to drive the electro- micro resonators; reducing the distance between the electrode and resonant beam can be the most efficient way to solve this problem. But bringing different exciting frequency of system and environmental pressure to the air squeeze film effect might cause it changes form similarly to the damping qualities, and this will also change the dynamic characteristics of micro resonator. The dynamic model for double clamped micro-mechanical resonant beam is proposed by using Lagrange¡¦s equation in this study. The corresponding eigenvalue problems of resonant beam are formulated and solved by employing the hypothetical mode method. Under the presumption of viscous damping model, we may obtain a damping factor which includes the parameters of size, temperature and air pressure when energy transfer model is employed to simulate the squeeze film damping effect of two immediate objects. Eventually, the damping ratio and the dynamic characteristics of resonant microbeam are derived by means of exploring the frequency response function of system. Besides, the frequency change of micro-mechanical resonant beam due to an axial force is also considered in the thesis.

In this study, copper metals were used to fabricate five different flow field plates with various open ratios using MEMS technology. Five samples were prepared for experiments with rib width varying as 150, 200, 300, 450, and 600 £gm at a fixed channel width (300 £gm). The open ratio of flow field plates was varied from 60.0% to 37.9%. Experiments with different operating parameters of anode/cathode pressure drop, cell operating temperature, and gas backpressure were conducted. Furthermore, a simple lumped capacitance model was used to predict the temperature evolution of the fuel cell system. Then, the optimum flow field design and cell operating parameters were finally found. Based on the aforementioned experiments an optimal open ratio ofunity was found like 49.2%. Further, an optimal open ratio in terms of the net power gain factor (= power gain/power consumption) of 38.7% can be obtained for the cases under study. Durability and reliability for copper bipolar plate were examined for long range tests (each run with at least 5 hours duration for consecutive two months). This strongly suggests that copper sheets can be considered as one of possible candidates for flow field material.

<p>This report is a first practical study of micro valves for hydraulics, manufactured by Microstaq Inc. who uses, for hydraulics, new materials and new actuating technologies. The purpose is to evaluate if, in the future, there is any possibility of complementing or exchanging the classical use of electro magnetic solenoids in electro hydraulic applications with this new technology. The valves studied are of MEMS-type (Micro Electro Mechanical Systems), which are etched out of silicon and has an electro thermic actuation. During the study it showed that this new valve technology had some teething troubles. The valves had proplems managing high pressure drops, both regarding strength of materials and performance. If you let the manufacturers further develop this technology there are great potentials for using this in future hydraulic systems.</p>

Improvements for Chip-Chip Interconnects and MEMS Packaging Through Materials and Processing Research Erdal Uzunlar 129 Pages Directed by Dr. Paul A. Kohl The work presented in this dissertation focuses on improvements for ever-evolving modern microelectronic technology. Specifically, three topics were investigated in this work: electroless copper deposition on printed wiring boards (PWBs), polymer-based air-gap microelectromechanical systems (MEMS) packaging technology, and thermal stability enhancement in sacrificial polymers, such as poly(propylene carbonate) (PPC). In the electroless copper deposition study, Ag-based catalysts were identified as a low-cost and equally active alternative to expensive Pd-based catalysts. Hot H2SO4 treatment of PWBs was found as a non-roughening surface treatment method to minimize electrical losses. In MEMS packaging study, a sacrificial polymer-based air-gap packaging technique was improved in terms of identification and simplification of air-gap formation process options, optimization of thermal treatment steps, assessing air-gap formation performance, and analyzing the chemical composition of residue. It was found that non-photosensitive PPC leaves less residue, and creates more reliable air-gaps. The mechanical strength of air-gaps was found to come from residual stress in benzocyclobutene (BCB) caps. In thermal stability of PPC study, the mechanism of thermal stability increase on copper (Cu) surfaces was found as the complex formation between Cu(I) and iodonium of the photoacid generator (PAG), leading to hindrance of acid formation by PAG and restriction of acid-catalyzed decomposition of PPC.

Directional microphones, which suppress noise coming from unwanted directions while preserving sound signals arriving from a desired direction, are essential to hearing aid technology. The device presented in this paper abandons the principles of standard pressure sensor microphones, dual port microphones, and multi-chip array systems and instead employs a new method of operation. The proposed device uses a lightweight silicon micromachined structure that becomes “entrained” in the oscillatory motion of air vibrations, and thus maintains the vector component of the air velocity. The mechanical structures are made as compliant as possible so that the motion of the diaphragm directly replicates the motion of the sound wave as it travels through air. The microphone discussed in this paper achieves the bi-directionality seen in a ribbon microphone but is built using standard semiconductor fabrication techniques and utilizes piezoelectric readout of a circular diaphragm suspended on compliant silicon springs. Finite element analysis and lumped element modeling have been performed to aid in structural design and device verification. The proposed microphone was successfully fabricated in a cleanroom facility at The University of Texas at Austin. Testing procedures verified that the resonant frequency of the microphone, as expected, was much lower than in traditional microphones. This report discusses the theory, modeling, fabrication and testing of the microphone. / text

The focus of this dissertation is on the design and micro-fabrication of an all silicon gas chromatography column with a novel two dimensional resistive heater and on its integration with an ultra-low power Thermal Conductivity Detector (TCD) for fast separation and detection of Volatile Organic Compounds (VOC). The major limitations of the current MEMS-GC column are: direct bonding of silicon to silicon, and peak band broadening due to slow temperature programming. As part of this thesis, a new gold eutectic-fusion bonding technique is developed to improve the sealing of the column. Separation of BETX, alkane mixture and VOCs were demonstrated with the MEMS GC column. The time and power required to ramp and sustain the column’s temperature are very high for the current GC columns. To reduce the time required to separate the compounds, a new temperature gradient programming heating method was developed to generate temperature gradients along the length of the column. This novel heating method refocuses eluding bands and counteracts some of the chromatographic band spreading due to diffusion resulting in an improved separation performance. A low power TCD was packaged and tested in a GC by comparison against FID for the detection of a mixture of VOCs. It demonstrated low power operation of a few milliwatts and a very fast response. The MEMS-GC was also demonstrated for rapid detection of the VOC gases released by pathogenic species of Armillaria fungus.

In this thesis, we present theoretical and experimental investigation into the nonlinear statics and dynamics of clamped-clamped in-plane MEMS arches when excited by an electrostatic force. Theoretically, we first solve the equation of motion using a multi- mode Galarkin Reduced Order Model (ROM). We investigate the static response of the arch experimentally where we show several jumps due to the snap-through instability. Experimentally, a case study of in-plane silicon micromachined arch is studied and its mechanical behavior is measured using optical techniques. We develop an algorithm to extract various parameters that are needed to model the arch, such as the induced axial force, the modulus of elasticity, and the initially induced initial rise. After that, we excite the arch by a DC electrostatic force superimposed to an AC harmonic load. A softening spring behavior is observed when the excitation is close to the first resonance frequency due to the quadratic nonlinearity coming from the arch geometry and the electrostatic force. Also, a hardening spring behavior is observed when the excitation is close to the third (second symmetric) resonance frequency due to the cubic nonlinearity coming from mid-plane stretching. Then, we excite the arch by an electric load of two AC frequency components, where we report a combination resonance of the summed type. Agreement is reported among the theoretical and experimental work.

This report is a first practical study of micro valves for hydraulics, manufactured by Microstaq Inc. who uses, for hydraulics, new materials and new actuating technologies. The purpose is to evaluate if, in the future, there is any possibility of complementing or exchanging the classical use of electro magnetic solenoids in electro hydraulic applications with this new technology. The valves studied are of MEMS-type (Micro Electro Mechanical Systems), which are etched out of silicon and has an electro thermic actuation. During the study it showed that this new valve technology had some teething troubles. The valves had proplems managing high pressure drops, both regarding strength of materials and performance. If you let the manufacturers further develop this technology there are great potentials for using this in future hydraulic systems.

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.