Recent instrument development for aerosol measurement has focussed on small-scale, on-line measurements that can be incorporated into miniaturised sensor nodes as part of ambient or personal air quality monitoring networks. As a result, optical particle counters (OPCs) have risen in popularity given their ability to consistently size and count individual particles. OPCs have limitations, however, in their inability to detect ultrafine particles (considered the most influential to human health) or to measure particle mass directly (the standard metric for air quality). The growing field of microelectromechanical systems (MEMS) offers a potential alternative by implementing microresonators as mass sensors. MEMS resonators have high mass sensitivities and have recently seen implementation as particulate matter (PM) monitors. The field of MEMS PM instruments is still limited with a variety of implemented resonator topologies and sampling mechanisms. In general, however, they offer real-time, high sensitivity measurements at low flow rates. The aim of this thesis was to further examine the viability of implementing MEMS resonators for PM measurement with a focus on practical considerations for real-world applications. To this end, a new microresonator-based impactor was developed - the MEMS Impactor Stage (MIS) - capable of accommodating various nozzle and resonator combinations. Square lateral bulk acoustic resonators were the primary topology, but the results within the thesis are widely applicable. A series of laboratory studies covered the resonator lifetime, reusability, detection limits, and response to environmental changes. The resonator displayed a high sensitivity throughout, capable of detecting ultrafine particles, but is vulnerable to misinterpretation. Beyond mass measurement, studies introduced possible extensions to hygroscopicity and compositional applications. Ambient particle measurements with the MIS, simulating a real-world application to air quality monitoring, showed the capabilities as a PM instrument while highlighting concerns to be addressed for future instrument design. A microresonator-based impactor has potential as an alternative to OPCs, but its cross sensitivity to deposition patterns and environmental effects must be accounted for prior to implementation as PM monitor.

The interest in tiny wireless applications raises the demand for an integrated reference oscillator with the same performance as the macroscopic quartz crystal reference oscillators. The main challenge of the thesis is to prove that it is possible to build a MEMS based oscillator that approaches the accuracy level of existing quartz crystal oscillators. The MEMS resonator samples which Philips provides are measured and an equivalent electrical model is designed for them. This model is used in the simulations of the Pierce oscillator and the transresistance amplifier oscillator that are evaluated in this thesis. Finally the Pierce oscillator is implemented in the A BCD2 process and manufactured at Philips Semiconductors in Nijmegen, The Netherlands. A test board, for measuring the Pierce oscillator together with a MEMS resonator or a quartz crystal resonator, is built. The Pierce oscillator is then measured with a quartz crystal resonator. In order to simulate the higher series resistance of the MEMS resonators a resistor is put in series with the quartz crystal. The Pierce oscillator is working with a series resistance of 1 kΩ. With higher series resistance the Pierce oscillator stops working. In circuit simulations the Pierce oscillator is working with a series resistance of about 5 kΩ in the MEMS resonator model. To be sure whether the Pierce oscillator has enough gain for the MEMS resonators, it needs to be measured with them. Temperature variations in the MEMS resonators need to be handled and the phase noise performance of the oscillator must be improved, in order for the MEMS based reference oscillator to be a successful replacement for the quartz crystal reference oscillator.

Kyoto University (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 / 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

Les systèmes MEMS et NEMS permettent, par résonance mécanique, des mesures de masse avec une sensibilité et une résolution propices à la caractérisation d'objets de taille micro- et nanométrique. Ces dispositifs, adaptés à une intégration dans des systèmes d'analyse miniatures plus complexes, sont d'intérêt pour la recherche biomédicale et la détection de particules. Toutefois la caractérisation en milieu liquide reste à ce jour délicate, principalement à cause de phénomènes dissipatifs associés à la mise en mouvement du fluide environnant le dispositif vibrant.Afin de lever ce verrou, l’équipe au sein de laquelle s’est déroulée cette thèse a développé des MEMS fluidiques sous forme de plaques minces mises en vibration dans leur plan de manière à limiter l'excitation du fluide environnant. Chaque plaque comporte un canal microfluidique permettant la circulation d'un liquide dont la masse moyenne est précisément déterminée par la fréquence de résonance du système. A terme, l'ambition de ces systèmes est de parvenir à révéler, par un décalage en fréquence, le passage au sein de la plaque vibrante d’une particule unique transportée par le liquide.Deux objectifs ont été atteints dans le cadre de cette thèse. D'une part, le comportement de ces structures en présence de divers liquides a été finement caractérisé ce qui a permis d’évaluer leurs performances réelles en fonction des conditions d'excitation. La résolution mesurée pour ces capteurs est de l’ordre de quelques g.L-1, pour une sensibilité d’environ 100 Hz.(g.L-1)-1.D'autre part, une nouvelle génération de capteurs aux caractéristiques innovantes a été conçue en vue d’abaisser le seuil de détection en diminuant la masse des résonateurs et en améliorant le bruit en fréquence.Ce manuscrit sera articulé autour de quatre chapitres. Le premier propose un état de l’art des techniques existantes pour la caractérisation de particules en fluide, et détaille ensuite les solutions MEMS et NEMS développées à cette fin dans la littérature. Le second chapitre livre les résultats issus de la caractérisation d’une première génération de MEMS fluidiques. Le troisième décrit les observations et mesures réalises, et propose des perspectives d’amélioration de ces composants ainsi que de leur protocole de caractérisation. Enfin, on présente dans le dernier chapitre une nouvelle génération de NEMS conçue et fabriquée au cours de cette thèse ; pour finir sont discutés les choix réalisés et les perspectives d’évolution attendues pour ces composants. / MEMS and NEMS allow sensitive and precise mass detection consistent with micro- and bio- objects analysis. These systems are promising for biomedical research and particle metrology, and can be easily integrated in miniaturized multifunctional systems. Thererfore, characterization in liquid media remains tricky due to viscous dissipation consequent to the movement induced in the fluidic environment.In order to overcome this technological lock, our laboratory previously designed and fabricated specific MEMS devices for fluidic analysis; these thin plate resonators with and embedded microchannel are actuated in liquid media, with four capacitive electrodes providing both actuation and detection. The circulating fluid mass can be precisely measured by monitoring the device’s resonant frequency. The long-term objective is to be able to detect and weigh one single particle transported by the fluid.Two main objectives were fulfilled during these three years. First, the MEMS behaviour in presence of various liquids was evaluated, providing a fine-grained analysis of their performances as mass sensors. The measured resolution of our sensors is about a few g.L-1 with a sensitivity of 100 Hz.(g.m-3)-1.Meanwhile, a new generation of NEMS sensors with innovative features was designed; the objective is to decrease the effective mass and reduce the frequency noise, both for a better mass resolution.This thesis includes four chapters. The first one consists in a review of the existing techniques for particles characterization in fluid as well as MEMS and NEMS solutions for particles metrology described in the litterature. The second part of the manuscript presents the results of the experimental characterizations carried out on the first generation of sensors. The third chapter gathers the conclusions of these measurements and gives an outlook on possible improvements on both the design and the characterization of the sensors. At last, the fourth part describes the new generation of devices and discusses their characteristics in terms of expected resolution and applications.

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

Varactors form an important part of many communication circuits. They are utilized in oscillators, tunable matching networks, tunable filters and phase-shifters. This thesis deals with the design, analysis, characterization and applications of a novel MEMS varactor. Lower actuation voltage and higher dynamic range are the two important issues widely addressed in the study of MEMS varactors. The pull-in instability, due to which only 33% of the gap between plates could be covered smoothly, greatly reduces useful dynamic range of MEMS varactors. We propose a torsional MEMS varactor that exploits “displacement amplification” whereby pull-in is overcome and wide dynamic range is achieved. The torsion beam in the device undergoes torsion as well as bending. Behavior of the device has been analyzed through torque and force balance. Based on the torque balance and the force balance expressions, theoretical limits of torsion angle and bending for stable operation have been derived. Torsional MEMS varactors and its variants are fabricated through a commercial fabrication process (polyMUMPS) and extensive characterization has been carried out. Capacitance-voltage characteristics show a maximum dynamic range of 1:16 with parasitic capacitance subtracted out from the capacitance values. A bidirectional torsional varactor, in which the top AC plate moves not only towards bottom plate but also away from bottom plate, is also tested. The bottom AC plate is isolated from low resistivity substrate with a thin nitride layer. This gives rise to large parasitic capacitances at higher frequencies. So to avoid this, a varactor with both AC plates suspended in air is designed and fabricated. A dynamic range of 1:8 including parasitic capacitances has been achieved. Self-actuation is studied on fabricated structures and a torsional varactor that overcomes self-actuation has been proposed. Hysteresis behavior of the torsional varactor is analyzed for different AC signals across the varactor plates. Effects of residual stress on C-V characteristics are studied and advantages and disadvantages of residual stress on device performance are discussed. The torsional varactors have been cycled between Cmax and Cmin for 36 hours continuously without any failure. High-frequency characteristics of torsional varactors are analyzed through measurements on one-port and two port configurations. Measurements are done on polyMUMPS devices to study the capacitance variation with voltage, quality factor (Q) and capacitance variation with frequency. Effects of substrate are de-embedded from the device and characteristics of device are studied. An analog phase shifter based on torsional varactor proposed and analyzed through HFSS simulations. Very high tuning range can be achieved with a LC-VCO based on torsional varactors. A LC VCO with the torsional varactor as a capacitor in LC tank is designed. The torsional varactor and IC are fabricated separately and are integrated through wire bonding. Bond-wires are used as inductors.

Silicon alternatives to quartz crystal based oscillators to electronic system clocking are explored. A study of clocking requirements reveals widely different specifications for different applications. Traditional CMOS oscillator-based solutions are optimized for low-cost fully integrated micro-controller clock applications. The frequency variability of these clock generators is studied and techniques to compensate for this variability are proposed. The efficacy of these techniques in reducing variability is proven theoretically and experimentally. MEMS-resonator based oscillators, due to their exceptional quality factors, are identified as suitable integrated replacements to quartz based oscillators for higher accuracy applications such as data converter clocks. The frequency variation in these oscillators is identified and techniques to minimize the same are proposed and demonstrated. The sources of short-term variation (phase noise) in these oscillators are discussed and an inclusive theory of phase noise is developed. Techniques to improve phase noise are proposed. Findings from this research indicate that MEMS resonator based oscillators, may in future, outperform quartz based solutions in certain applications such as voltage controlled oscillators. The implications of these findings and potential directions for future research are identified.

<p>With the advent of increasingly complex radio systems at higher frequencies and the slowing of traditional CMOS process scaling with power concerns, there has been an increased focus on integration, architectural, and material innovations as a continued path forward in MEMS and logic. This work presents the first comprehensive experimental study of resonant body transistors in a commercial 14nm FinFET process, demonstrating differential radio frequency transduction as a function of transistor biasing through electrostatic, piezoresistive, and threshold voltage modulation. The impact of device design changes on unreleased resonator performance are further explored, highlighting the importance of phononic confinement in achieving an f*Q product of 8.2*10¹¹ at 11.73 GHz. Also shown are initial efforts towards the understanding of coupled oscillator architectures and a perovskite nickelate material system. Finally, development of resonators based on two-dimensional materials, whose scale is particularly attractive for high-frequency nano-mechanical resonators and acoustic devices, is discussed. Experiments towards dry transfer of tellurene flakes using geometries printed via two photon polymerization are presented along with optimization of a fabrication process for gated RF devices, presenting new opportunities for high-frequency electro-mechanical interactions in this topological material. </p>