107 research outputs found

    Silicon microaccelerometer fabrication technologies

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    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

    MEMS Accelerometers

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    Micro-electro-mechanical system (MEMS) devices are widely used for inertia, pressure, and ultrasound sensing applications. Research on integrated MEMS technology has undergone extensive development driven by the requirements of a compact footprint, low cost, and increased functionality. Accelerometers are among the most widely used sensors implemented in MEMS technology. MEMS accelerometers are showing a growing presence in almost all industries ranging from automotive to medical. A traditional MEMS accelerometer employs a proof mass suspended to springs, which displaces in response to an external acceleration. A single proof mass can be used for one- or multi-axis sensing. A variety of transduction mechanisms have been used to detect the displacement. They include capacitive, piezoelectric, thermal, tunneling, and optical mechanisms. Capacitive accelerometers are widely used due to their DC measurement interface, thermal stability, reliability, and low cost. However, they are sensitive to electromagnetic field interferences and have poor performance for high-end applications (e.g., precise attitude control for the satellite). Over the past three decades, steady progress has been made in the area of optical accelerometers for high-performance and high-sensitivity applications but several challenges are still to be tackled by researchers and engineers to fully realize opto-mechanical accelerometers, such as chip-scale integration, scaling, low bandwidth, etc

    MME2010 21st Micromechanics and Micro systems Europe Workshop : Abstracts

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    A thin monocrystalline diaphragm pressure sensor using silicon-on-insulator technology.

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    The sensors market is huge and growing annually, of this a large sector is pressure sensors. With increasing demands on performance there remains a need for ultraminiature, high performance pressure sensors, particularly for medicai applications. To address this a novel capacitive pressure sensor consisting of an array of parallel connected diaphragms has been designed and fabricated from SIMOX substrates. The benefits of this include single crystal silicon diaphragms, small, well controlled dimensions, single sided processing and the opportunity for electronics integration. Theoretical modelling of this structure predicts a high sensitivity and low stress device with opportunities for scaling to suit alternative applications. A novel, process technology was developed to achieve the required structure with the inclusion of procedures to address the specific issues relating to the SIMOX material. The sensor was fully characterised and the results demonstrated high performance compared with similar reported devices. Alternative structures such as cantilevers, bridges and resonators were fabricated as a demonstrative tool to show the feasibility of this technology in a wider field of applications

    Laterally Movable Gate Field Effect Transistor (LMGFET) for microsensor and microactuator applications

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    Laterally Movable Gate Field Effect Transistor (LMGFET) invented at LSU as a microactuator is the subject of study in this research. The gate moving in lateral direction in a LMGFET changes channel width but keeps the channel length and the gap between the metal gate and the gate oxide constant. LMGFET offers linear change in drain current with gate motion and a large displacement range. This research is the first demonstration of LMGFET. In this dissertation, a post-IC LIGA-like process for LMGFET microstructure fabrication has been developed that is compatible with monolithic integration with CMOS circuitry. A two-mask post-IC process has been developed in this research for LMGFET fabrication. This novel process utilizes S1813 photoresist as a sacrificial layer in conjunction with a thicker resist like AZ P4620 or SU-8 as an electroplating mold. New curing temperatures for the sacrificial layer photoresist have been determined for this purpose. LMGFET microstructures have been successfully integrated with CMOS circuitry on the same chip to form integrated microsystem. LMGFET microstructure driven by a comb-drive with serpentine retaining spring shows sensitivities Sel of 2 and 1.43 nA/V respectively at 5 and 25 Hz. These numbers reflect that LMGFET is capable of measuring nm range displacement. Electrical characteristics of a depletion type LMGFET structure are measured and show an average sensitivity Sl of - 4 ”A/”m at drain to source voltage VDS of 10 V with the gate shorted to source. Several applications of microsystems utilizing LMGFET microstructures as a position sensor or an accelerometer, a spectrum analyzer or an electro-mechanical filter and a mechanical/optical switch are described

    A high precision fully integrated accelerometer

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    Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 193-196).by Michael Anthony Ashburn, Jr.M.S

    Design and fabrication of suspended-gate MOSFETs for MEMS resonator, switch and memory applications

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    Wireless communication systems and handset devices are showing a rapid growth in consumer and military applications. Applications using wireless communication standards such as personal connectivity devices (Bluetooth), mobile systems (GSM, UMTS, WCDMA) and wireless sensor network are the opportunities and challenges for the semi-conductor industry. The trend towards size and weight reduction, low power consumption and increased functionalities induces major technological issues. Today, the wireless circuit size is limited by the use of lots of external or "off-chip" components. Among them, quartz crystal, used as the time reference in any wireless systems, is the bottleneck of the miniaturization. Microelectromechanical systems (MEMS) is an emerging technology which has the capability of replacing the quartz. Based on similar technology than the Integrated Circuit (IC), MEMS are referred as electrostatically, thermally or piezoelectrically actuated mechanical structures. In this thesis, a new MEMS device based on the hybridization of a mechanical vibrating structure and a solid-sate MOS transistor has been developed. The Resonant Suspended-Gate MOSFET (RSG-MOSFET) device combines both advantages of a high mechanical quality factor and the transistor intrinsic gain. The physical mechanisms behind the actuation and the behavior of this device were deeply investigated and a quasi-static model was developed and validated, based on measured characteristics. Furthermore, the dynamic model of the RSG-MOSFET was created, taking into account the non-linear mechanical vibrations of the gate and the EKV model, used for MOSFET modeling. Two fabrication processes were successfully developed to demonstrate the proof of concept of such a device and to optimize the performances respectively. Aluminum-silicon (Al-Si1%) and pure silicon-based RSG-MOSFETs were successfully fabricated. DC and AC characterizations on both devices enabled to understand, extract and evaluate the mechanical and MOSFET effects. A specifically developed RF characterization methodology was used to measure the linear and non-linear behaviors of the resonator and to evaluate the influence of each polarization voltages on the signal response. RSG-MOSFET with resonant frequencies ranging from 5MHz to 90MHz and quality factor up to 1200 were measured. Since MEMS resonator quality factor is strongly degraded by air damping, a 0-level thin film vacuum packaging (10-7 mBar) process was developed, compatible with both AlSi-based and silicon-based RSG-MOSFET. The technology has the unique advantage of being done on already released structure and the room temperature process makes it suitable for above-IC integration. In parallel, a front-end compatible process was defined and major build blocks were developed in industrial environment at STMicroelectronics. This technology is based on the Silicon-On-Nothing technology, originally developed for advanced transistor, and therefore making the MEMS resonator process compatible with CMOS co-integration. DC characterizations of SG-MOSFET had shown interesting performances of this device for current switch and memory applications. Mechanical contact of the gate with the MOSFET channel induces a current switching slope greater than 0.8mV/decade, much better than the theoretical MOSFET limit of 60mV/decade. Maximum switch isolations of -37dB at 2 GHz and -27dB at 10GHz were measured on these devices. A novel MEMS-memory has been demonstrated, based on the direct charge injection to the storage media by the mechanical contact of the metal gate. Charge injection and retention mechanisms were investigated based on measured devices. Cycling study of up to 105 cycles were performed without noticing major degradations of the electrical behavior neither mechanical fatigue of the suspended gate. The measured retention time places this memory in between the DRAM and the FLASH memories. A scaling study has shown integration and compatibilities capabilities with existing CMOS

    Development of MEMS Piezoelectric Vibration Energy Harvesters with Wafer-Level Integrated Tungsten Proof-Mass for Ultra Low Power Autonomous Wireless Sensors

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    La gĂ©nĂ©ration d’énergie localisĂ©e et Ă  petite Ă©chelle, par transformation de l’énergie vibratoire disponible dans l’environnement, est une solution attrayante pour amĂ©liorer l’autonomie de certains noeuds de capteurs sans-fil pour l’Internet des objets (IoT). GrĂące Ă  des microdispositifs inertiels rĂ©sonants piĂ©zoĂ©lectriques, il est possible de transformer l’énergie mĂ©canique en Ă©lectricitĂ©. Cette thĂšse prĂ©sente une Ă©tude exhaustive de cette technologie et propose un procĂ©dĂ© pour fabriquer des microgĂ©nĂ©rateurs MEMS offrant des performances surpassant l’état de l’art. On prĂ©sente d’abord une revue complĂšte des limites physiques et technologiques pour identifier le meilleur chemin d’amĂ©lioration. En Ă©valuant les approches proposĂ©es dans la littĂ©rature (gĂ©omĂ©trie, architecture, matĂ©riaux, circuits, etc.), nous suggĂ©rons des mĂ©triques pour comparer l’état de l’art. Ces analyses dĂ©montrent que la limite fondamentale est l’énergie absorbĂ©e par le dispositif, car plusieurs des solutions existantes rĂ©pondent dĂ©jĂ  aux autres limites. Pour un gĂ©nĂ©rateur linĂ©aire rĂ©sonant, l’absorption d’énergie dĂ©pend donc des vibrations disponibles, mais aussi de la masse du dispositif et de son facteur de qualitĂ©. Pour orienter la conception de prototypes, nous avons rĂ©alisĂ© une Ă©tude sur le potentiel des capteurs autonomes dans une automobile. Nous avons Ă©valuĂ© une liste des capteurs prĂ©sents sur un vĂ©hicule pour leur compatibilitĂ© avec cette technologie. Nos mesures de vibrations sur un vĂ©hicule en marche aux emplacements retenus rĂ©vĂšlent que l’énergie disponible pour un dispositif linĂ©aire rĂ©sonant MEMS se situe entre 30 Ă  150 Hz. Celui-ci pourrait produire autour de 1 Ă  10 ÎŒW par gramme. Pour limiter la taille d’un gĂ©nĂ©rateur MEMS pouvant produire 10 ÎŒW, il faut une densitĂ© supĂ©rieure Ă  celle du silicium, ce qui motive l’intĂ©gration du tungstĂšne. L’effet du tungstĂšne sur la sensibilitĂ© du dispositif est Ă©vident, mais nous dĂ©montrons Ă©galement que l’usage de ce matĂ©riau permet de rĂ©duire l’impact de l’amortissement fluidique sur le facteur de qualitĂ© mĂ©canique Qm. En fait, lorsque l’amortissement fluidique domine, ce changement peut amĂ©liorer Qm d’un ordre de grandeur, passant de 103 Ă  104 dans l’air ambiant. Par consĂ©quent, le rendement du dispositif est amĂ©liorĂ© sans utiliser un boĂźtier sous vide. Nous proposons ensuite un procĂ©dĂ© de fabrication qui intĂšgre au niveau de la tranche des masses de tungstĂšne de 500 ÎŒm d’épais. Ce procĂ©dĂ© utilise des approches de collage de tranches et de gravure humide du mĂ©tal en deux Ă©tapes. Nous prĂ©sentons chaque bloc de fabrication rĂ©alisĂ© pour dĂ©montrer la faisabilitĂ© du procĂ©dĂ©, lequel a permis de fabriquer plusieurs prototypes. Ces dispositifs ont Ă©tĂ© testĂ©s en laboratoire, certains dĂ©montrant des performances records en terme de densitĂ© de puissance normalisĂ©e. Notre meilleur design se dĂ©marque par une mĂ©trique de 2.5 mW-s-1/(mm3(m/s2)2), soit le meilleur rĂ©sultat rĂ©pertoriĂ© dans l’état de l’art. Avec un volume de 3.5 mm3, il opĂšre Ă  552.7 Hz et produit 2.7 ÎŒW Ă  1.6 V RMS Ă  partir d’une accĂ©lĂ©ration de 1 m/s2. Ces rĂ©sultats dĂ©montrent que l’intĂ©gration du tungstĂšne dans les microgĂ©nĂ©rateurs MEMS est trĂšs avantageuse et permet de s’approcher davantage des requis des applications rĂ©elles.Small scale and localized power generation, using vibration energy harvesting, is considered as an attractive solution to enhance the autonomy of some wireless sensor nodes used in the Internet of Things (IoT). Conversion of the ambient mechanical energy into electricity is most often done through inertial resonant piezoelectric microdevices. This thesis presents an extensive study of this technology and proposes a process to fabricate MEMS microgenerators with record performances compared to the state of the art. We first present a complete review of the physical and technological limits of this technology to asses the best path of improvement. Reported approaches (geometries, architectures, materials, circuits) are evaluated and figures of merit are proposed to compare the state of the art. These analyses show that the fundamental limit is the absorbed energy, as most proposals to date partially address the other limits. The absorbed energy depends on the level of vibrations available, but also on the mass of the device and its quality factor for a linear resonant generator. To guide design of prototypes, we conducted a study on the potential of autonomous sensors in vehicles. A survey of sensors present on a car was realized to estimate their compatibility with energy harvesting technologies. Vibration measurements done on a running vehicle at relevant locations showed that the energy available for MEMS devices is mostly located in a frequency range of 30 to 150 Hz and could generate power in the range of 1-10 ÎŒW per gram from a linear resonator. To limit the size of a MEMS generator capable of producing 10 ÎŒW, a higher mass density compared to silicon is needed, which motivates the development of a process that incorporates tungsten. Although the effect of tungsten on the device sensitivity is well known, we also demonstrate that it reduces the impact of the fluidic damping on the mechanical quality factor Qm. If fluidic damping is dominant, switching to tungsten can improve Qm by an order of magnitude, going from 103 to 104 in ambient air. As a result, the device efficiency is improved despite the lack of a vacuum package. We then propose a fabrication process flow to integrate 500 ÎŒm thick tungsten masses at the wafer level. This process combines wafer bonding with a 2-step wet metal etching approach. We present each of the fabrication nodes realized to demonstrate the feasibility of the process, which led to the fabrication of several prototypes. These devices are tested in the lab, with some designs demonstrating record breaking performances in term of normalized power density. Our best design is noteworthy for its figure of merit that is around 2.5 mW-s-1/(mm3(m/s2)2), which is the best reported in the state of the art. With a volume of 3.5 mm3, it operates at 552.7 Hz and produces 2.7 ÎŒW at 1.6 V RMS from an acceleration of 1 m/s2. These results therefore show that tungsten integration in MEMS microgenerators is very advantageous, allowing to reduce the gap with needs of current applications

    Engineering Dynamics and Life Sciences

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    From Preface: This is the fourteenth time when the conference “Dynamical Systems: Theory and Applications” gathers a numerous group of outstanding scientists and engineers, who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without a great effort of the staff of the Department of Automation, Biomechanics and Mechatronics. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our invitation has been accepted by recording in the history of our conference number of people, including good colleagues and friends as well as a large group of researchers and scientists, who decided to participate in the conference for the first time. With proud and satisfaction we welcomed over 180 persons from 31 countries all over the world. They decided to share the results of their research and many years experiences in a discipline of dynamical systems by submitting many very interesting papers. This year, the DSTA Conference Proceedings were split into three volumes entitled “Dynamical Systems” with respective subtitles: Vibration, Control and Stability of Dynamical Systems; Mathematical and Numerical Aspects of Dynamical System Analysis and Engineering Dynamics and Life Sciences. Additionally, there will be also published two volumes of Springer Proceedings in Mathematics and Statistics entitled “Dynamical Systems in Theoretical Perspective” and “Dynamical Systems in Applications”
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