The notion of mechanical computation has been revived in the past few years, with the advances of nanofabrication techniques. Although electromechanical devices are inherently slow, they offer zero or very low off-state current, which reduces the overall power consumption compared to the fast complementary-metal-oxide-semiconductor (CMOS) counterparts. This energy efficiency feature is the most crucial requirement for most of the stand-alone battery-operated gadgets, biomedical devices, and the internet of things (IoT) applications, which do not require the fast processing speeds offered by the mainstream CMOS technology. In particular, using Micro-Electro-Mechanical (MEM) resonators in mechanical computing has drawn the attention of the research community and the industry in the last decade as this technology offers low power consumption, reduced circuit complexity compared to conventional CMOS designs, run-time re- programmability and high reliability due to the contactless mode of operation compared to other MEM switches such as micro-relays. In this thesis, we introduce digital circuit design techniques tailored for clamped-clamped beam MEM resonators. The main operation mechanism of these circuit blocks is based on fine-tuning of the resonance frequency of the micro-resonator beam, and the logic function performed by the devices is mainly determined by factors such as input/output terminal arrangement, signal type, resonator operation regime (linear/non-linear), and the operation frequency. These proposed circuits include the major building blocks of any microprocessor such as logic gates, a full adder which is a key block in any arithmetic and logic operation units (ALU), and I/O interface units, including digital to analog (DAC) and analog to digital (ADC) data converters. All proposed designs were first simulated using a finite element software and then the results were experimentally verified. Important aspects such as energy per operation, speed, and circuit complexity are evaluated and compared to CMOS counterparts. In all applications, we show that by proper scaling of the resonator’s dimensions, MHz operation speeds and energy consumption in the range of femto-joules per logic operation are attainable. Finally, we discuss some of the challenges in using MEM resonators in digital circuit design at the device level and circuit level and propose solutions to tackle some of them.

L'impression par transfert, une technique utilisée pour transférer divers matériaux tels que des molécules d'ADN, de la résine photosensible ou des nanofils semi-conducteurs, s'est dernièrement révélée utile pour la réalisation de structures de silicium statiques sous le nom de micro-maçonnerie. L'étude présentée ici explore le potentiel de la technique de micro-maçonnerie pour la fabrication de résonateurs MEMS. Dans ce but, des microplaques de silicium ont été transférées sur des couches d'oxyde avec cavités intégrées à l'aide de timbres de polymère afin de créer des structures de type plaques suspendues. Le comportement dynamique de ces structures passives a été étudié sous pression atmosphérique et sous vide en utilisant une excitation externe par pastille piézo-électrique mais aussi le bruit thermomécanique. Par la suite, des résonateurs MEMS actifs, à actionnement électrostatique et détection capacitive intégrés, ont été fabriqués en utilisant des étapes supplémentaires de fabrication après impression. Ces dispositifs ont été caractérisés sous pression atmosphérique. Les facteurs de qualité intrinsèques des dispositifs fabriqués ont été évalués à 3000, ce qui est suffisant pour les applications de mesure à pression atmosphérique et en milieu liquide. Nous avons démontré que, puisque l'adhérence entre la plaque et l'oxyde est suffisamment forte pour empêcher une diaphonie mécanique entre les différentes cavités d'une même base, plusieurs résonateurs peuvent être facilement réalisés en une seule étape d'impression. Ce travail de thèse montre que la micro-maçonnerie est une technique simple et efficace pour la réalisation de résonateurs MEMS actifs de type plaque à cavité scellée. / Lately, transfer printing, a technique that is used to transfer diverse materials such as DNA molecules, photoresist, or semiconductor nanowires, has been proven useful for the fabrication of various static silicon structures under the name micro-masonry. The present study explores the suitability of the micro-masonry technique to fabricate MEMS resonators. To this aim, silicon microplates were transfer-printed by microtip polymer stamps onto dedicated oxide bases with integrated cavities in order to create suspended plate structures. The dynamic behavior of fabricated passive structures was studied under atmospheric pressure and vacuum using both external piezo-actuation and thermomechanical noise. Then, active MEMS resonators with integrated electrostatic actuation and capacitive sensing were fabricated using additional post-processing steps. These devices were fully characterized under atmospheric pressure. The intrinsic Q factor of fabricated devices is in the range of 3000, which is sufficient for practical sensing applications in atmospheric pressure and liquid. We have demonstrated that since the bonding between the plate and the device is rigid enough to prevent mechanical crosstalk between different cavities in the same base, multiple resonators can be conveniently realized in a single printing step. This thesis work shows that micro-masonry is a powerful technique for the simple fabrication of sealed MEMS plate resonators.

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京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18990号 / 工博第4032号 / 新制||工||1621(附属図書館) / 31941 / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 引原 隆士, 教授 北野 正雄, 准教授 山田 啓文 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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<p>Motivated by the future prospects of the Windchime project, we show that even a small prototype array of 7 commercial accelerometers can be used to calculate dark matter limits for the well-known B − L coupled dark photon. As a member of the ultralight sector, the dark photon would be observed in high occupancy as a persistent plane wave characterized by de Broglie wavelength and coupling to the standard model via a hypothesized baryon minus lepton quantum number, g_B−L. Such an interaction can be probed by measuring the differential force or acceleration between two bodies of differing B −L charge-to-mass ratios. This is accomplished for a 7 sensor array of MEMS accelerometers by rigidly coupling all the sensors to a material of known B − L charge. Using a log-likelihood ratio test and Fourier transformed data from the prototype array, we are able to set a limit on g_B−L ∼ 10^−11 within a mass range of 10^{−13}−10^{−12}eV . Setting these noncompetitive limits with real data serves as a proof-of-principle demonstration of the limit-setting procedure used in Windchime future projections for B − L coupled ultralight dark matter. Additionally, this basic setup could be used for future studies on the properties of a detector array. </p>

The application of piezoelectric sensors such as the ultrasonic transducer has significantly enhanced the fields of nondestructive evaluation (NDE). Their application of piezoelectric materials allows for the sensing of low energy, high frequency acoustic emission (AE) events such as fatigue cracking in metals and delamination in composites. Utilizing the physical characteristics of these AE waves, the location of these structural defects can then be source located by means of time-of-flight trilateration. The real time sensing of such events has led to the field of structural health monitoring (SHM) and has revolutionized NDE. Furthermore, with the application of modern micro-electromechanical system-based (MEMS) technology, the fields of NDE and SHM can be improved greatly, and sensing instrumentation simplified. A novel piezoresistive-based MEMS strain sensor is presented as this improvement to NDE and SHM. The ultrathin silicon membrane-based (USM) strain sensor's ability to capture an AE signal is demonstrated by a Hsu-Nielsen source and shows comparable frequency content to a commercial piezoceramic ultrasonic transducer. To the knowledge of the authors, this makes the USM strain sensor the first known piezoresistive strain sensor capable of recording low energy AE. The novel improvements to NDE and SHM arise from the sensor's low minimum detectable strain and wide frequency bandwidth, enabling a dual-use application of both AE and static strain sensing. The USM sensor's ability to document quasi-static bending is demonstrated and once again compared with an ultrasonic transducer, which provides no significant response. This dual-use application is proposed to effectively combine the uses of both strain and ultrasonic transducer sensor types within one sensor, lending itself novel and useful to NDE and SHM. The potential benefits include enhanced sensitivity, reduced sensor size and cost, and reduced instrumentation complexity. / Master of Science / Visual inspection for cracks and defects has long been staples of assessing structural health throughout human history. These surface imperfections are an obvious hindrance to structural integrity and routine observation and inspection is needed to ensure a structure's safety. With the progression of technology and the discovery of piezoelectric materials, more advanced methods have been devised to detect and source locate not only surface level but sub-surface cracking. This has been accomplished through the use of piezoelectric ultrasonic transducers to monitor the propagation of acoustic emission (AE) vibrations, which are the result of energy redistribution by events such as cracking. The remote monitoring of AE events has led to the growth of the nondestructive evaluation (NDE) field, where these cracks and defects can be located by the detection of their AE source. These transducers, however, are met with limitations in their applications. Operating off the piezoelectric effect allows for a superb response to low energy, high frequency excitation characteristic of AE, but results in no response to quasi-static strain measurements, such as that of a slowly applied bending load on a plate. In the work herein, modern micro-electromechanical system (MEMS) based technology is utilized to devise a sensor capable of both AE and static strain measurements. The dual sensing of both of these measurements can allow for the source location of cracking events along with the monitoring of structure strain, effectively combining the use of two sensors into one. This dual-application use can have a great impact on the evaluation of critical structures like bridges and aircraft and simplify and reduce costs inherent to nondestructive evaluation.

Voice commanded systems (VCS) have been proved to be vulnerable to signal in- jections mimicking voice commands and explored security flaws in market avail- able products for the time of each respective study. Signal injection caused with the help of amplitude modulated ultrasonic waves (being known as DolphinAt- tacks - DA) were proved to work on several such devices in 2017. In 2019, another study were also successful in achieving signal injections using modulated laser also known as LightCommands (LC). This thesis has investigated the occurring circumstances which enables such injections. Simulations and laboratory trials have shown a thermoacoustic origin enabling LC to be injected and the response differs with respect to microphones physical size. DA utilizes the non-linearity of microphones and more linear microphones have indeed been shown to withstand DAs better and physical parameters have been shown to indicate how DA may be optimized for successful injections. The results have been used to provide ideas on how a VCS system can be designed to be more resilient. / Röststyrda System har visat sig vara sårbara mot signalinjektioner som härmar röstkommandon och utnyttjar kryphål hos produkter som fanns på marknaden i samtid när studierna som först tog upp kryphålen publicerades. Signalinjek- toner inducerade med hjälp av amplitudmodulerat ultraljud (känt som Dolphi- nAttacks - DA) bevisades fungera på flertalet enheter år 2017. 2019 visade en annan studie framgång med signalinjektion genom modulerad laser, även känt som LightCommands (LC). Detta examensarbete har utrett de bakomliggande faktorer som möjliggör sådana injektioner. Simuleringar och laboratorieexperi- ment har visat att termoakustiska effekter möjliggör LC med resultat som beror på mikrofoners fysiska storlek. DA nyttjar ickelinjäritet hos mikrofoner och linjä- rare mikrofoner har visat sig stå emot DA bättre och det har visat sig att DA kan optimeras för bättre lyckade injektioner. Resultaten har används för att bidra till idéer och resonemang från föregående studier på hur lösningar mot LC och DA skulle kunna implementeras och göra mikrofoner och dess tillhörande system tåligare mot sådana angrepp.