Comparison Between Damping Coefficients of Measured Perforated Micromechanical Test Structures and Compact Models

Measured damping coefficients of six different perforated micromechanical test structures are compared with damping coefficients given by published compact models. The motion of the perforated plates is almost translational, the surface shape is rectangular, and the perforation is uniform validating the assumptions made for compact models. In the structures, the perforation ratio varies from 24% - 59%. The study of the structure shows that the compressibility and inertia do not contribute to the damping at the frequencies used (130kHz - 220kHz). The damping coefficients given by all four compact models underestimate the measured damping coefficient by approximately 20%. The reasons for this underestimation are discussed by studying the various flow components in the models.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838

Experimental analysis of viscous and material damping in microstructures through the interferometric microscopy technique with climatic chamber

This study describes an experimental analysis of energy dissipation due to damping sources in microstructures and micro electro-mechanical systems (MEMS) components using interferometric microscopy techniques. Viscous damping caused by the surrounding air (squeeze film damping) and material damping are measured using variable geometrical parameters of samples and under different environmental conditions. The equipment included a climatic chamber designed (built ad hoc) which was used to modify the surrounding air pressure. Results show the relationship between damping coefficients and sample geometry caused by variation in air flow resistance and the relationship between quality factor and air pressure. The experimental results will provide a useful data source for validating analytic models and calibrating simulations. A thorough discussion about interferometry applied to experimental mechanics of MEMS will also contribute to the reduction of the knowledge gap between specialists in optical methods and microsystem designer

Study On The Accuracy Of Squeeze Film Damping Calculation With Finite Element Analysis

Squeeze film damping due to the air trapped between oscillating membrane structure and a fixed substrate is a critical consideration in the design of MEMS devices because it can adversely affect the dynamic behaviour of the system. Therefore, the development of MEMS depends highly on the modelling and numerical simulation in order to optimize and verify their design before the batch production process. In this thesis, a method to model squeeze film damping with finite element approach to attain sufficiently high accuracy while considerably reducing the degrees of freedom is proposed, and its effectiveness is studied by comparing with other methods. The numerical analysis was performed using commercial ANSYS software. The structures were modelled using three-dimensional (3D) element and two-dimensional (2D) element. Results obtained by finite element models are compared with existing experimental measurements and analytical solutions. It was found that for the computation of damping coefficient, two-dimensional model yields slightly similar accuracy with three-dimensional model with respect to experimental data for low number of holes. In contrast, for highly perforated membranes, the proposed two-dimensional model is shown to be more accurate. The results clearly validate the proposed model to achieve good accuracy for damping coefficient solution while consuming considerably less computer time and memory

CMOS-MEMS resonant pressure sensors: optimization and validation through comparative analysis

The final publication is available at Springer via http://dx.doi.org/10.1007/s00542-016-2878-3An optimized CMOS-MEMS resonant pressure sensor with enhanced sensitivity at atmospheric pressure has been reported in this paper. The presented work reports modeling and characterization of a resonant pressure sensor, based on the variation of the quality factor with pressure. The relevant regimes of air flow have been determined by the Knudsen number, which is the ratio of the mean free path of the gas molecule to the characteristic length of the device. The sensitivity has been monitored for the resonator design from low vacuum to atmospheric levels of air pressure. This has been accomplished by reducing the characteristic length and optimization of other parameters for the device. While the existing analytical model has been adapted to simulate the squeeze film damping effectively and it is validated at higher values of air pressure, it fails to compute the structural damping mechanisms dominant in the molecular flow regime, i.e. at lower levels of air pressure. This discrepancy has been solved by finite element modeling that has incorporated both structural and film damping effects. The sensor has been designed with an optimal geometry of 140 × 140 × 8 µm having 6 × 6 perforations along the row and column of the plate, respectively, for maximum Q, with an effective mass of 0.4 µg. An enhanced quality factor of 60 and reduced damping coefficient of 4.34 µNs/m have been obtained for the reported device at atmospheric pressure. The sensitivity of the manufactured device is approximately -0.09 at atmospheric pressure and increases to -0.3 at 40 kPa i.e. in the lower pressures of slip flow regime. The experimental measurements of the manufactured resonant pressure sensor have been compared with that of the analytical and finite element modeling to validate the optimization procedure. The device has been manufactured using standard 250 nm CMOS technology followed by an in-house BEOL metal-layer release through wet etching.Peer ReviewedPostprint (author's final draft

Thin Film Piezoelectric on Substrate Resonators Electrical Characterization and Oscillator Circuit Design

Electronic systems require at least one reference signal to enable system synchronization. Oscillators and resonators are frequency selective devices that generate a desired reference signal for the systems. MEMS frequency selective devices offer alternative solutions for mechanically vibrating devices. MEMS are suitable for vibration applications by their rugged structure. In the present work, resonant behavior of thin film piezoelectric on substrate resonator (TPoS) is studied. Equivalent electrical circuit model parameters are extracted. It is observed that TPoS resonance characteristics are influenced by design aspects. The effects of perforated and continuous electrode designs on resonant behavior and also the change in resonance characteristics with the substrate thickness are reported. The colpitts oscillator circuit is implemented on a PC Board with a 27 MHz TPoS resonator and a 27 MHz quartz resonator. Jitter results are presented for both device.School of Electrical & Computer Engineerin

Summary of Research 2000, Department of Mechanical Engineering

The views expressed in this report are those of the authors and do not reflect the official policy or position of the Department of Defense or U.S. Government.This report contains project summaries of the research projects in the Department of Mechanical Engineering. A list of recent publications is also included, which consists of conference presentations and publications, books, contributions to books, published journal papers, and technical reports. Thesis abstracts of students advised by faculty in the Department are also included

Classical and fluctuation-induced electromagnetic interactions in micronscale systems: designer bonding, antibonding, and Casimir forces

Whether intentionally introduced to exert control over particles and macroscopic objects, such as for trapping or cooling, or whether arising from the quantum and thermal fluctuations of charges in otherwise neutral bodies, leading to unwanted stiction between nearby mechanical parts, electromagnetic interactions play a fundamental role in many naturally occurring processes and technologies. In this review, we survey recent progress in the understanding and experimental observation of optomechanical and quantum-fluctuation forces. Although both of these effects arise from exchange of electromagnetic momentum, their dramatically different origins, involving either real or virtual photons, lead to different physical manifestations and design principles. Specifically, we describe recent predictions and measurements of attractive and repulsive optomechanical forces, based on the bonding and antibonding interactions of evanescent waves, as well as predictions of modified and even repulsive Casimir forces between nanostructured bodies. Finally, we discuss the potential impact and interplay of these forces in emerging experimental regimes of micromechanical devices.Comment: Review to appear on the topical issue "Quantum and Hybrid Mechanical Systems" in Annalen der Physi

Micro-g MEMS accelerometer based on time measurement

Programa Doutoral em Engenharia Electrónica e de ComputadoresThe MEMS sensor market has experienced an amazing growth on the last decades, with accelerometers being one of the pioneers pushing the technology into widespread use with its applications on automotive industry. Since then, accelerometers have been gradually replacing conventional sensors due mainly to its lower cost. As the performance of MEMS accelerometers improves, the applications range where they replace conventional accelerometers increases. Nowadays, there is still a large range of applications for which suitable MEMS accelerometers are yet to be developed. This work focuses on the development of a high performance accelerometer taking advantage of the high sensitivity of a non-linear phenomenon that occurs in electrostatically actuated movable capacitive microdevices: electrostatic pull-in. Although the pull-in effect has been known for more than 40 years, it is usually avoided when dealing with movable microstructures as it leads to a region of instability, where the position of movable parts cannot be fully controlled. In the last decade, the pull-in displacement profile of 1-DOF parallel-plates devices has been the subject of research that revealed the presence of a so-called meta-stability. This meta-stability occurs in specific damping and voltage actuation conditions and translates as a non-linear displacement profile, rather than simple time-of-flight. This feature makes the pull-in time duration significantly longer, and it happens to be extremely sensitive to intervenient forces, such as external acceleration. Basically, measuring the pull-in time of specifically designed microstructures (while maintaining the other parameters constant) allows the measurement of the external acceleration that acts on the system. Using a pull-in time measurement rather than direct capacitance/displacement/acceleration transduction presents several advantages. The most important is the fact that time can be measured very accurately with technology readily available. For instance, if one uses a 100MHz clock on the time counting mechanism, which corresponds to a time measurement resolution of 100 ns, given the 0.26 μs/μg sensitivity of the accelerometer developed in this work, an acceleration resolution of 0.38 μg could be achieved. One of the main challenges of the time based accelerometer development is the damper design, as damping is of outmost importance in defining the accelerometer performance parameters, namely sensitivity and noise. A new squeeze-film damper geometry design has been presented and studied. It consists of flow channels implemented on the parallel-plates that relieve the squeeze-film damping pressures generated when the device is moving. This geometry has proved to be very effective in increasing the capacitance/damping ratio in parallel-plates, which was up to now a great challenge of in-plane parallel-plates design. This work reports the development of an open-loop accelerometer with 0.26 μs/μg sensitivity and 2.7 μg /√Hz noise performance. The MEMS structures used for its experimental implementation were fabricated using a commercially available SOI micromachining process. The main drawbacks of this accelerometer were the low system bandwidth and non-linearity. Closed-loop approaches using electrostatic feedback were explored in this work in order to overcome these limitations, and the dynamic range was successfully extended to 109 dB along with improvements on the linearity. From the thorough damping study performed in this work, a new application for the pullin time using the same microstructures was developed. It consists of a gas viscosity sensing application. At the low frequencies operated, damping is directly proportional to the viscosity of the gas medium. The experimental results obtained with gases with viscosities ranging from 8 μP to 18 μP have shown a sensitivity of 2 ms/μP, making the pull-in time viscosity sensor a very promising approach.Nas últimas décadas assistiu-se a um imenso crescimento no mercado de sensors MEMS, tendo os acelerómetros sido uma das maiores forças impulsionadoras desse crescimento devido às suas aplicações na indústria automóvel. Desde então, a gama de aplicações destes sensores expandiu-se multidirecionalmente, novas aplicações emergiram e acelerómetros convencionais em aplicações já existentes foram substituídos por acelerómetros MEMS. Isto deve-se essencialmente ao seu baixo custo e pequenas dimensões. Há no entanto, aplicações para as quais o desempenho dos acelerómetros MEMS ainda não é suficiente. O objectivo deste trabalho é desenvolver um acelerómetro de elevado desempenho tirando partido da elevada sensibilidade do efeito de pull-in a forças externas tais como a aceleração. O efeito de pull-in, descrito pela primeira vez há mais de 40 anos, ocorre em dispositivos capacitivos com partes móveis. Este é um efeito não-linear geralmente evitado/indesejado, uma vez que se traduz numa instabilidade que dificulta o controlo da posição das partes móveis. Na última década foi dedicada alguma investigaçao científica a este fenómeno, tendo sido descoberta a existência de um perfil de deslocamento particular, denominado meta-estabilidade, em determinadas condições de amortecimento e de actuação electrostática. Esta característica do pull-in torna a sua duração extremamente sensível a variações nas forças intervenientes, incluindo aceleração externa. Assim sendo, a medição do tempo de pull-in de micro-estruturas especificamente concebidas para o efeito pode ser utilizada para medir aceleração. Esta abordagem apresenta vantagens significativas em comparação com a transdução direta de capacidade para aceleração (caso da generalidade dos acelerómetros capacitivos). Nomeadamente, a variável tempo pode ser medida com elevada precisão com relativa facilidade e sem necessidade de desenvolvimentos tecnológicos (o que não é o caso da medição de capacidade). Por exemplo, o uso de uma frequência de relógio de 100 MHz no mecanismo de contagem de tempo permite uma resolução de 100 ns na medição de tempo, o que corresponde, considerando a sensibilidade de 0.26 μs/μg do acelerómetro desenvolvido neste trabalho, a uma resolução na medição de acceleração de 0.38μg. Um dos maiores desafios do desenvolvimento de um acelerómetro baseado no tempo de pull-in é o desenho do amortecedor, pois a sensibilidade e o ruído/resolução do sensor final dependem do nível de amortecimento. Uma nova geometria para o amortecedor (estabelecido por um mecanismo de squeeze-film) é apresentada e estudada neste trabalho. Esta consiste em abrir canais nas placas paralelas facilitando assim o fluxo de ar quando as placas se movem. Ficou provado que esta geometria é eficaz na redução da razão capacidade/amortecimento, o que constituía um problema recorrente no desenho de dispositivos de placas paralelas in-plane. Neste trabalho é descrito o desenvolvimento de um acelerómetro em malha aberta com uma sensibilidade de 0.26 μs/μg e 2.7 μg /√Hz de ruído. As estruturas MEMS utilizadas na sua implementação foram fabricadas num processo de microfabrico SOI comercial. As principais desvantagens desta abordagem são pequena gama dinâmica devido à não-linearidade da resposta. Neste trabalho foram exploradas abordagens em malha fechada, usando feedback electrostático, de modo a ultrapassar estas limitações, tendo sido alcançado um aumento da gama dinâmica para 109 dB, com grandes melhoria na linearidade. Uma nova aplicação para o tempo de pull-in foi também desenvolvida: medição de viscosidade de gases. Uma vez que as microstruturas utilizadas são operadas a baixas frequências, o amortecimento é proporcional à viscosidade. O estudo efectuado mostra que o tempo de pull-in é muito sensível ao amortecimento e portanto a variações de viscosidade. Os resultados experimentais obtidos com gases e misturas de gases com viscosidades entre 8 μP e 18 μP mostraram uma sensibilidade de 2 ms/μP, confirmando o potencial da utilização de tempo de pull-in na medição de viscosidade.The author, Rosana Maria Alves Dias, was supported by Portuguese Foundation for Science and Technology (SFRH/BD/46030/2008)

Silicon microaccelerometer fabrication technologies

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (leaves 275-282).by Charles Heng-Yuan Hsu.Ph.D