Neste trabalho é proposto um dispositivo MEMS do tipo micro-transdutor acústico capacitivo, CMUT (sigla em inglês - Capacitive Micromachined Ultrasonic Transducer). Em vez de usar piezoeletricidade, o CMUT tem um array de capacitores, onde cada capacitor possui um eletrodo inferior fixo, uma cavidade e o eletrodo superior composto de uma placa flexível. Quando submetida a uma tensão CC adequada, a placa se deflete se aproximando do eletrodo inferior devido à força eletrostática. Assim a placa fica tensionada podendo vibrar quando excitada por uma tensão CA. Neste caso o CMUT opera como emissor de ondas acústicas. A placa também pode ser excitada por uma onda acústica agindo em sua superfície. Neste caso o dispositivo opera como sensor. Uma das contribuições desse trabalho é o processo de fabricação simplificado com o uso do fotorresiste SU-8 como parte da estrutura do dispositivo. Sua facilidade de processamento e suas propriedades físicas lhe conferem estabilidade e rigidez adequadas para tal fim. Foram realizadas modelagens e simulações analíticas e computacionais do comportamento da placa. Os resultados auxiliaram no melhor entendimento do comportamento do dispositivo sob tensão mecânica devido a uma carga ou uma tensão de polarização. Esses resultados também auxiliaram na definição de parâmetros iniciais do processo de fabricação. Durante o processo de fabricação, foram realizados diversos testes a fim de se encontrar o processo mais adequado à infraestrutura disponível. No processo escolhido, a base do dispositivo é fabricada num substrato de vidro com eletrodos inferiores de alumínio depositados por evaporação. Os pilares são fabricados em SU-8, depositado por spin coatting. A placa é colada posteriormente utilizando-se fotorresiste AZ. O AZ é depositado sobre um pedaço de folha de cobre ou alumínio. As duas partes são colocadas em contato e para promover a colagem é aplicada pressão durante a cura. As amostras foram caracterizadas eletricamente utilizando-se um medidor de impedância RCL. Foram levantadas curvas de impedância, capacitância e ângulo de fase em função da frequência (1 kHz a 1 MHz). Além do sinal CA utilizado pelo instrumento durante a medição foi aplicado um nível CC que variou conforme as dimensões dos protótipos. Também foram levantadas curvas de impedância, capacitância e angulo de fase em função de uma carga mecânica aplicada. Para valores de polarização mais elevados, foram montados circuitos específicos. Estes circuitos são capazes de polarizar o CMUT, aplicar um sinal CA para medição e proteger demais componentes e instrumentos dos aparatos de medição. O dispositivo respondeu bem a aplicação de carga mecânica, excitação por sinal CA e excitação com onda mecânica. Os resultados mostraram que o dispositivo apresenta bom potencial para ser aplicado na análise de fluidos. / This work presents a new process to fabricate an acoustic micro transducer to be used as a microsensor or a microactuator. The acoustic transducers are based on the electrostatic effect and consist on arrays of microfabricated capacitors. Such devices are commonly referred as CMUT, Capacitive Micromachined Ultrasonic Transducer. The bottom electrode (evaporated aluminum) of each capacitor is fixed on the surface of glass substrate, while the top electrode is a thin plate structure of copper or aluminum suspended on a cavity surrounded by posts. Since the top electrode is flexible, it bends toward the bottom electrode when a DC bias is applied. In this way, the top electrode can be forced to vibrate using an AC signal to be used as an acoustic wave emitter. Conversely, an ultrasound receiver is achieved as the measured capacitance changes when the DC biased top electrode moves following an external acoustic wave pressure. An innovation of this work is the use of the photoresist SU-8 to fabricate the post structures surrounding the cavities of the capacitive micro transducers. Its relatively simple processing steps and adequate mechanical properties make the SU-8 a convenient choice as an inexpensive structural material. The bottom part of the device is prepared on a glass substrate using an aluminum layer evaporated and etched to form the bottom electrodes. Then, SU-8 is spin coated, baked and etched adequately to form the posts surrounding the cavities. The top part is prepared by simply spinning an AZ-type photoresist on aluminum or copper plate. Finally, both halves are bonded under pressure on a hot plate. Several modeling and simulation analyses were performed in order to estimate the working performance of the micro transducers. The results of simulations helped to define the initial parameters and materials for the fabrication process. Samples submitted to a DC bias were initially characterized using an RCL meter in order to infer impedance, capacitance and phase angle behavior as a function of frequency (from 1 kHz to 1 MHz). Protection circuits were used in order to test CMUTs with high DC bias. These circuits allow to apply high DC bias, and an AC signal while other measuring equipments are protected. The device responded to application of mechanical loading, excitation by an AC signal and excitation by mechanical wave as well. The results showed that the device has good potential to be applied to the analysis of fluids.

Orientadores: Peter Jurgen Tatsch, Stanislav Moshkalyov / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-06T08:35:07Z (GMT). No. of bitstreams: 1 FioravanteJunior_NemerPaschoal_M.pdf: 3096593 bytes, checksum: 671d75f088339782b5b4b1dd5fc4463c (MD5) Previous issue date: 2004 / Resumo: O principal objetivo deste trabalho é o aperfeiçoamento dos processos de fotolitografia utilizados no Centro de Componentes Semicondutores (CCS) da Universidade Estadual de Campinas ¿ UNICAMP. Visa determinar os parâmetros de maior relevância do processo de fotolitografia utilizado no CCS para fabricação de estruturas micrométricas e a partir da sua caracterização identificar os seus valores ótimos. Os parâmetros tais como o contraste, a aderência, a resolução e a dimensão mínima dos padrões fotogravados foram estudados a fim de se determinar as possibilidades de melhoria e as limitações dos processos. No decorrer deste trabalho foi utilizado basicamente o fotorresiste AZ 5214E com o qual foi possível o desenvolvimento de processos repetitivos que permitiram a fabricação de estruturas periódicas com largura de até 2µm e estruturas isoladas com largura de até 0,8µm / Abstract: The aim of this work is to improve the photolithographic processes of the CCS/Unicamp. This work attempts findout and optimize the most significant process parameters for the fabrication of micrometric structures. Contrast, adhesion, resolution, and minimum dimension for the shapes were studied in order to improve the process and also determine their limitations. A procedure for the processing of AZ 5214E photoresist was established so that periodic structures with dimension as low as 2 µm and isolated structures down to 0,8 µm can be produced reproductively / Mestrado / Microeletronica / Mestre em Engenharia Elétrica

Due to the increasing demand for high power and reliable miniaturized energy storage devices, the development of micro-supercapacitors or electrochemical micro-capacitors have attracted much attention in recent years. This dissertation investigates several strategies to develop on-chip micro-supercapacitors with high power and energy density. Micro-supercapacitors based on interdigitated carbon micro-electrode arrays are fabricated through carbon microelectromechanical systems (C-MEMS) technique which is based on carbonization of patterned photoresist. To improve the capacitive behavior, electrochemical activation is performed on carbon micro-electrode arrays. The developed micro-supercapacitors show specific capacitances as high as 75 mFcm-2 at a scan rate of 5 mVs-1 after electrochemical activation for 30 minutes. The capacitance loss is less than 13% after 1000 cyclic voltammetry (CV) cycles. These results indicate that electrochemically activated C-MEMS micro-electrode arrays are promising candidates for on-chip electrochemical micro-capacitor applications. The energy density of micro-supercapacitors was further improved by conformal coating of polypyrrole (PPy) on C-MEMS structures. In these types of micro-devices the three dimensional (3D) carbon microstructures serve as current collectors for high energy density PPy electrodes. The electrochemical characterizations of these micro-supercapacitors show that they can deliver a specific capacitance of about 162.07 mFcm-2 and a specific power of 1.62mWcm-2 at a 20 mVs-1 scan rate. Addressing the need for high power micro-supercapacitors, the application of graphene as electrode materials for micro-supercapacitor was also investigated. The present study suggests a novel method to fabricate graphene-based micro-supercapacitors with thin film or in-plane interdigital electrodes. The fabricated micro-supercapacitors show exceptional frequency response and power handling performance and could effectively charge and discharge at rates as high as 50 Vs-1. CV measurements show that the specific capacitance of the micro-supercapacitor based on reduced graphene oxide and carbon nanotube composites is 6.1 mFcm-2 at scan rate of 0.01Vs-1. At a very high scan rate of 50 Vs-1, a specific capacitance of 2.8 mFcm-2 (stack capacitance of 3.1 Fcm-3) is recorded. This unprecedented performance can potentially broaden the future applications of micro-supercapacitors.

Implantable electrodes are the central tool for many techniques and treatments in biomedical research and medicine. There is a trend in these tools towards arrays of tissue-penetrating microelectrodes with low geometric surface areas for purposes of both increasing the specificity of recording/stimulation and reducing tissue damage due to insertion trauma and reactive immune responses. However, smaller electrode sizes present new constraints – both difficulty in fabrication as well as significant limitations on effective charge storage/injection capacities as well as higher impedances, making smaller electrodes less capable of easily passing charge safely and efficiently. Fabricating structures on the scale of tens of microns and below poses significant challenges compared to well established machining at larger sizes. Established sets of techniques such as classic MEMS processes are limited to relatively specific shapes, with significant limitations in their ability to produce curved surfaces and surfaces which are not composed of highly distinct stepped layers. We developed a method for improvement of impedance and charge storage capacity of flat electrodes without affecting geometric surface area (footprint) using Resonant Direct Laser Writing (rDLW) 3D printing to fabricate high surface area 3D structures, which were then rendered conductive. The ability to perform DLW printing at a range of laser powers on opaque reflective surfaces is demonstrated, previously a known limitation of direct laser writing. This is demonstrated through a variety of example prints. This capability opens the door to many new possibilities in micron resolution polymer printing which were previously inaccessible, with potentially far reaching ramifications for microfabrication.

The electrothermomechanical characteristics of an electrically-heated polycrystallinesilicon microactuator are explored. Using finite-difference techniques, an electrothermal model based on the balance of heat dissipation and heat losses is developed. For accurate simulation, the relevant temperature dependent properties from the microactuator material are included in the model. The electrothermal model accurately predicts the steady-state power required to hold position, and the energy consumed during the thermal transient. Thermomechanical models use the predictions of temperature from the electrothermal solution to calculate displacement and force from pseudo-rigid-body approximations and commercial finite-element code. The models are verified by comparing experimental data to simulation results of a single leg-pair on a particular configuration of the device. The particular microactuator studied is called a Thermomechanical In-plane Microactuator, or TIM, and was fabricated with surface micromachining technology. A TIM requires a single releasable structural layer, is extremely flexible in design, and can operate with simple drive and control circuitry. The TIM produces linear motion of a center shuttle when slender legs on either side move the shuttle as a result of constrained thermal expansion. In a single example, when the current through a leg with dimensions 250×3×3.5 µm^3 and suspended 2 µm off the substrate is sufficient to maintain an average temperature of 615 C in air and vacuum environments, model simulated temperatures along the leg have a peak of 860 C in air and 1100 C in vacuum. The final measured and predicted displacement is 14 µm. In air, the power predicted by the model needed to maintain this average temperature profile is 95 mW while consuming 16.4 µJ in 0.22 ms to reach 90 percent of the final average temperature. In a vacuum, only 6.4 mW are required to maintain the same average temperature with 97.6 µJ consumed in 18.5 ms. Simulation results suggest that short-duration high-current pulses can improve the transient response and energy consumed in a vacuum when steady-state temperatures are not required. For a TIM leg with the dimensions above, the maximum measured force is approximately 47 µN per leg-pair when enough current is provided to move the TIM 8 µm as a result of ohmic heating and thermal expansion.

<p dir="ltr">Gyroscopes have become an integral part of many application spaces ranging from consumer electronics to navigation. As navigation and movement tracking becomes necessary through inertial measurement units (that comprises gyroscopes and accelerometers) in myriad of scenarios especially when global navigation and satellite system (GNSS) is not available, stability of gyroscopes plays a detrimental role in the accuracy of navigation. Recent developments in micro-electromechanical systems (MEMS) based gyroscopes enabled them to penetrate into navigation grade application spaces. MEMS based miniaturization approach also revived the interest in nuclear magnetic resonance gyroscopes (NMRGs). In parallel, emerging atomic gyroscope technologies are getting attention such as using quantum defects in single crystal diamond. </p><p><br></p><p dir="ltr">Considering innovative ways MEMS can improve gyroscopes, we investigate solid state gyroscope technologies in piezoelectric MEMS and nuclear spin based platforms for next generation rotation sensing that is shock and vibration insensitive. For the first part of this study, we explore a piezoelectric resonator that can excite wine-glass mode (WGM) and tangential mode. WGM is used for rotation sensing applications in various excitation mechanisms in literature. However, we demonstrate the capability of exciting WGM without the need for segmented electrodes in piezoelectric domain that allows self-alignment of the excitation electrodes using a unique property of Lead Magnesium Niobate-Lead Titanate (PMN-PT). In the second part of the study, we explore Nitrogen-Vacancy (NV) centers in diamond to be used as gyroscopes exploiting the rotation sensitivity of nuclear spins. NV center-based gyroscopes provide solid-state solution with comparable or superior performance without any moving parts. We propose mechanical coupling to NV centers in diamond using piezoelectrically excited bulk acoustic waves (BAW) to extend the coherence time of nuclear spins by dynamical decoupling. We explore piezoelectric coupling design space of AlN thin film BAW resonators (FBARs) to enable efficient mechanical drive to improve Rabi oscillations in diamond to overcome one of the most important bottlenecks of realizing a gyroscope, which is the mitigation and control of nuclear spin and electron spin interaction in diamond NV center system.</p>

<p>With the advances in MEMS technology, the studies of the properties of magnetic crystals have reached the microscopic level. Critical information such as the magnetization and susceptibility of a magnetic sample can be obtained using a microtorque magnetometer, such as ones incorporating piezoresistive or capacitive detection that have been fabricated and tested by earlier research groups. This type of magnetic information is useful in the study of superconductivity, for example. The microtorque magnetometer designed and fabricated in this thesis has the potential of being used in this field of study.</p> <p>This thesis describes the design, fabrication and testing of a capacitive microtorque magnetometer. By using ANSYS, a computer modelling program, an ideal model of the rotating microtorque magnetometer was devised. Fabrication involved testing a variety of procedures before establishing the successful and efficient method of building the microtorque magnetometer. A fifth order resonant mode was successfully detected during the testing stage. A method of studying the desired resonant mode has been devised and explained in the later chapters of this thesis.</p> / Master of Applied Science (MASc)

Cancer metastasis is the leading cause of death related to cancer diseases. Once the cancer cells depart the primary tumor site and enter the blood circulation, they spread through the body and will likely initiate a new tumor site. Therefore, understanding the cell migration and stopping the spread in the initial stage is the utmost of importance. In this dissertation, we have proposed a 3-D microenvironment that (partially) mimics the structures, complexity and circulation of human organs for cell migration studies. We have developed the tools to fabricate 3-D complex geometries in PDMS from our previously developed single-mask, single-etch technology in silicon. In this work, 3-D patterns are transferred from silicon structures to glass following anodic bonding and high temperature glass re-flow processes. Silicon is etched back thoroughly via wet etching and the glass is used as master device to create 3-D PDMS structures for use in dielectrophoresis cell sorting applications. Furthermore, this work has been modified to fabricate 3-D master devices in PDMS to create 3-D structures in collagen hydrogels to mimic native tissue structures. We have studied the interaction of endothelial cells with model geometries of blood vessels in collagen hydrogel at different concentrations to mimic the biomechanical properties of tissues varying from normal to tumor under the growth factor stimulation. Finally, we have designed and fabricated a silicon-based transmigration well with a 30um-thick membrane and 8um pores. This platform includes a deep microfluidic channel on the back-side sealed with a glass wafer. The migratory behavior of highly metastatic breast cancer cells, MDA-MB-231, is tested under different drug treatment conditions. This versatile platform will enable the application of more complex fluidic circulation profile, enhanced integration with other technologies, and running multiple assays simultaneously. / Ph. D.

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

Recent advances in micro-fabrication technology have ushered a new era in miniaturization of chemical, environmental and energy systems. This foreseeable trend towards miniaturization in chemical, environmental and mechanical systems is expected to revolutionize the ways the human life is being perceived today. The high volume and mass reproducibility is seen as the striking aspect of micro-fabrication based miniature systems, offering economies far exceeding than the economies of scale obtained in large plants. The focus of this thesis work is directed at the thermodynamic feasibility and preliminary prototype design for a meso-scale refrigerator. Miniaturization to sub-centimeter domain will enable configuring these refrigerator units as sheet architectures integrated in layers, facilitating efficient local control of temperature. In the design abstraction, the entire refrigeration unit, comprising motor-compressor, evaporator, condenser, valves and fluidic control, is to be fabricated from several layers of bonded silicon wafers. The material treated in this thesis provides a perspective on the actuation mechanism of the integrated rotor-compressor through an axial-drive high-throughput variable capacitance electrostatic disk motor and underlying stator assembly. The design optimization of the motor actuation dynamics to extract optimal set of design parameters is provided to yield reasonably good output power of the compressor.