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.

Parallel-plate electrostatic actuators driven by a voltage difference between two electrodes suffer from an operation range limited to 30% of the gap that has significantly restrained their applications in Microelectromechanical systems (MEMS). In this thesis, the travel range of an electrostatic actuator made of a micro-cantilever beam electrode above a fixed electrode is extended quasi-statically to 90% of the capacitor gap by introducing a voltage regulator (controller) circuit designed for low frequency actuation. The developed large-stroke actuator is valuable contribution to applications in optical filters, optical modulators, digital micro-mirrors and micro-probe based memory disk drives. To implement the low-frequency large-stroke actuator, the beam tip velocity is measured by a vibrometer, the corresponding signal is integrated in the regulator circuit to obtain the displacement feedback, which is used to modify the input voltage of the actuator to reach a target location. The voltage regulator reduces the total voltage, and therefore the electrostatic force, once the beam approaches the fixed electrode so that the balance is maintained between the mechanical restoring force and the electrostatic force that enables the actuator to achieve the desired large stroke. A mathematical model is developed for the actuator based on the mode shapes of the cantilever beam using experimentally identified parameters that yields good accuracy in predicting both the open loop and the closed loop responses. The low-frequency actuator also yields superharmonic resonances that are observed here for the first time in electrostatic actuators. The actuator can also be configured either as a bi-stable actuator using a low-frequency controller or as a chaotic resonator using a high-frequency controller. The high-frequency controller yields large and bounded chaotic attractors for a wide range of excitation magnitudes and frequencies making it suitable for sensor applications. Bifurcation diagrams reveal periodic motions, softening behavior, period doubling cascades, one-well and two-well chaos, superharmonic resonances and a reverse period doubling cascade. To verify the observed chaotic oscillations, Lyapunov exponents are calculated and found to be positive. Furthermore, a chaotic resonator with a quadratic controller is designed that not only requires less voltage, but also produces more robust and larger motions. Another metric of chaos, information entropy, is used to verify the chaotic attractors in this case. It is found that the attractors have a common information entropy of 0.732 independent of the excitation amplitude and frequency.

This thesis develops methods to exploit static and dynamic instabilities in electrostatic MEMS to develop new MEMS devices, namely dynamically actuated micro switches and binary micro gas sensors. Models are developed for the devices under consideration where the structures are treated as elastic continua. The electrostatic force is treated as a nonlinear function of displacement derived under the assumption of parallel-plate theorem. The Galerkin method is used to discretize the distributed-parameter models, thus reducing the governing partial differential equations into sets of nonlinear ordinary-differential equations. The shooting method is used to numerically solve those equations to obtain the frequency-response curves of those devices and the Floquet theory is used to investigate their stability. To develop the dynamically actuated micro switches, we investigate the response of microswitches to a combination of DC and AC excitations. We find that dynamically actuated micro switches can realize significant energy savings, up to 60 %, over comparable switches traditionally actuated by pure DC voltage. We devise two dynamic actuation methods: a fixed-frequency method and a shifted-frequency method. While the fixed-frequency method is simpler to implement, the shifted-frequency method can minimize the switching time to the same order as that realized using traditional DC actuation. We also introduce a parameter identification technique to estimate the switch geometrical and material properties, namely thickness, modulus of elasticity, and residual stress. We also develop a new detection technique for micro mass sensors that does not require any readout electronics. We use this method to develop static and dynamic binary mass sensors. The sensors are composed of a cantilever beam connected to a rigid plate at its free end and electrostatically coupled to an electrode underneath it. Two versions of micro mass sensors are presented: static binary mass sensor and dynamic binary mass sensor. Sensitivity analysis shows that the sensitivity of our static mass sensor represents an upper bound for the sensitivity of comparable statically detected inertial mass sensors. It also shows that the dynamic binary mass sensors is three orders of magnitude more sensitive than the static binary mass sensor. We equip our mass sensor with a polymer detector, doped Polyaniline, to realize a formaldehyde vapor sensor and demonstrate its functionality experimentally. We find that while the static binary gas sensor is simpler to realize than the dynamic binary gas sensor, it is more susceptible to external disturbances.

This thesis presents the theory, design, fabrication, and measurement results of novel reconfigurable impedance tuner, phase shifter, and vector modulators using the RF MEMS technology. The presented circuits are based on triple stub topology, and it is shown both theoretically and experimentally in this thesis that it is possible to control the insertion phase and amplitude of the input signal simultaneously using this topology. The presented circuits are implemented using an in-house, surface micromachining fabrication process developed at METU, namely METU RF MEMS Fabrication Process, which is implemented using six masks on quartz substrates. The RF MEMS impedance tuner is designed to operate in 6-20 GHz frequency band, and it covers the Smith Chart with 1331 impedance points. The measurement results of 729 impedance points of the fabricated impedance tuner show that a wide Smith Chart coverage is obtained in the entire band. The RF MEMS phase shifter is designed to cover 0-360 degrees range 10 degree steps at 15 GHz center frequency. The measurement results of the fabricated phase shifter show that the average phase error is 1.7 degrees, the average insertion loss is -3.1 dB, and the average return loss is -19.3 dB for the measured 21 phase states. The phase shifter can also work up to 30 GHz and 40 GHz with average insertion losses of -5 dB and -8 dB, respectively. The designed RF MEMS vector modulator operates in 22.5-27.5 GHz band, and it has 3 amplitude and 8 phase states. The measurement results of the fabricated vector modulator show that the amplitude error is 0.5 dB, the phase error is 4 degrees, and the return loss is -15 dB on average among the 24 measured states at each of 22.5, 25, and 27.5 GHz frequencies.

This thesis, for the first time in the literature, presents the effect of quadrature error compensation on the performance of a fully decoupled MEMS gyroscope and provides experimental data on the sources of quadrature error. Dedicated quadrature error cancellation electrodes operating with only differential DC potentials are designed. Gyroscopes with intentionally placed imperfections are fabricated with SOG based SOI process which provides higher yield and uniformity compared to SOG process. Tests show that the fully closed loop system with quadrature cancellation operates as expected. Gyroscope performance is improved up to 7.8 times for bias instability, 10 times for angle random walk (ARW) and 800 times for output offset with quadrature cancellation. The actual improvement is higher since some sensors cannot be operated without quadrature cancellation and they are not included in improvement calculations. The best obtained performance is bias instability of 0.39

Zugl.: Freiburg (Breisgau), Univ., Diss., 2009

Parallel-plate electrostatic actuators driven by a voltage difference between two electrodes suffer from an operation range limited to 30% of the gap that has significantly restrained their applications in Microelectromechanical systems (MEMS). In this thesis, the travel range of an electrostatic actuator made of a micro-cantilever beam electrode above a fixed electrode is extended quasi-statically to 90% of the capacitor gap by introducing a voltage regulator (controller) circuit designed for low frequency actuation. The developed large-stroke actuator is valuable contribution to applications in optical filters, optical modulators, digital micro-mirrors and micro-probe based memory disk drives. To implement the low-frequency large-stroke actuator, the beam tip velocity is measured by a vibrometer, the corresponding signal is integrated in the regulator circuit to obtain the displacement feedback, which is used to modify the input voltage of the actuator to reach a target location. The voltage regulator reduces the total voltage, and therefore the electrostatic force, once the beam approaches the fixed electrode so that the balance is maintained between the mechanical restoring force and the electrostatic force that enables the actuator to achieve the desired large stroke. A mathematical model is developed for the actuator based on the mode shapes of the cantilever beam using experimentally identified parameters that yields good accuracy in predicting both the open loop and the closed loop responses. The low-frequency actuator also yields superharmonic resonances that are observed here for the first time in electrostatic actuators. The actuator can also be configured either as a bi-stable actuator using a low-frequency controller or as a chaotic resonator using a high-frequency controller. The high-frequency controller yields large and bounded chaotic attractors for a wide range of excitation magnitudes and frequencies making it suitable for sensor applications. Bifurcation diagrams reveal periodic motions, softening behavior, period doubling cascades, one-well and two-well chaos, superharmonic resonances and a reverse period doubling cascade. To verify the observed chaotic oscillations, Lyapunov exponents are calculated and found to be positive. Furthermore, a chaotic resonator with a quadratic controller is designed that not only requires less voltage, but also produces more robust and larger motions. Another metric of chaos, information entropy, is used to verify the chaotic attractors in this case. It is found that the attractors have a common information entropy of 0.732 independent of the excitation amplitude and frequency.

This thesis develops methods to exploit static and dynamic instabilities in electrostatic MEMS to develop new MEMS devices, namely dynamically actuated micro switches and binary micro gas sensors. Models are developed for the devices under consideration where the structures are treated as elastic continua. The electrostatic force is treated as a nonlinear function of displacement derived under the assumption of parallel-plate theorem. The Galerkin method is used to discretize the distributed-parameter models, thus reducing the governing partial differential equations into sets of nonlinear ordinary-differential equations. The shooting method is used to numerically solve those equations to obtain the frequency-response curves of those devices and the Floquet theory is used to investigate their stability. To develop the dynamically actuated micro switches, we investigate the response of microswitches to a combination of DC and AC excitations. We find that dynamically actuated micro switches can realize significant energy savings, up to 60 %, over comparable switches traditionally actuated by pure DC voltage. We devise two dynamic actuation methods: a fixed-frequency method and a shifted-frequency method. While the fixed-frequency method is simpler to implement, the shifted-frequency method can minimize the switching time to the same order as that realized using traditional DC actuation. We also introduce a parameter identification technique to estimate the switch geometrical and material properties, namely thickness, modulus of elasticity, and residual stress. We also develop a new detection technique for micro mass sensors that does not require any readout electronics. We use this method to develop static and dynamic binary mass sensors. The sensors are composed of a cantilever beam connected to a rigid plate at its free end and electrostatically coupled to an electrode underneath it. Two versions of micro mass sensors are presented: static binary mass sensor and dynamic binary mass sensor. Sensitivity analysis shows that the sensitivity of our static mass sensor represents an upper bound for the sensitivity of comparable statically detected inertial mass sensors. It also shows that the dynamic binary mass sensors is three orders of magnitude more sensitive than the static binary mass sensor. We equip our mass sensor with a polymer detector, doped Polyaniline, to realize a formaldehyde vapor sensor and demonstrate its functionality experimentally. We find that while the static binary gas sensor is simpler to realize than the dynamic binary gas sensor, it is more susceptible to external disturbances.

Diffraktive Mikrospiegelarrays sind eine seit Jahren etablierte innovative Lösung zur ortsaufgelösten Beleuchtungsmodulation im UV-Spektralbereich. Sie werden hauptsächlich als Schlüsselbauelement in mikrolithografischen Industrieanlagen eingesetzt. Gegenwärtige Untersuchungen befassen sich mit der Erweiterung der Technologie hin zu multispektralen Anwendungen, beispielsweise in der Mikroskopie zur strukturierten Objektausleuchtung. Aufgrund des diffraktiven Arbeitsprinzips mit Phasenmodulationen im Nanometerbereich sowie der Vielzahl von Einzelspiegeln mit individuellem Auslenkverhalten stellt die präzise Ansteuerung der Bauelemente eine wesentliche Herausforderung dar. In diesem Kontext steht die Entwicklung und Validierung eines Verfahrens im Fokus dieser Arbeit, das die Gesamtheit von mehreren Tausend oder auch Millionen Mikrospiegeln abhängig von gewünschtem Beleuchtungsmuster und -wellenlänge auf korrekte Kippwinkel einstellen kann. Der gewählte Ansatz liegt in einem Mess- und Korrekturverfahren aller Einzelspiegelverkippungen. Die als Kalibrierung bezeichnete Methode nutzt ein Weißlichtinterferometer zur profilometrischen Charakterisierung der elektro-mechanischen Übertragungsfunktionen der Aktuatoren, wodurch erstmalig auf diesem Themengebiet der multispektrale Bauelementeinsatz gewährleistet werden kann. Zentrales Ergebnis der Kalibrierroutine ist eine Reduzierung der Streuung der Spiegelverkippungen um einen Faktor größer fünf. Direkte Folge sind erheblich verbesserte optische Projektionsmuster, aufgenommen an einem parallel entwickelten optischen Lasermessplatz mit spektral verschiedenen Quellen. Nachgewiesen wurden im Vergleich zum unkalibrierten Ausgangszustand Kontrastverdoppelungen, Homogenitätssteigerungen und die Sicherstellung der Abbildung von mindestens 64 Graustufen. Die Ergebnisse dokumentieren einerseits die Leistungsfähigkeit von diffraktiven Mikrospiegelarrays in multispektralen Umgebungen mit sehr guten Abbildungseigenschaften. Gleichzeitig konnte die wesentliche Grundlage für einen deutlich erweiterten Einsatz optischer Mikrosysteme im stark wachsenden Anwendungsbereich der diffraktiven Optik bzw. der Ultrapräzisionsoptik geschaffen werden.

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.