MEMS technology has led to the development of new uncooled infrared imaging detectors. One type of these MEMS detectors consist of arrays of bi-metallic photomechanical pixels that tilt as a function of temperature associated with infrared radiation from the scene. The main advantage of these detectors is the optical readout system that measures the tilt of the beams based on the intensity of the reflected light. This removes the need for electronic readout at each of the sensing elements and reduces the fabrication cost and complexity of sensor design, as well as eliminates the electronic noise at the detector. The optical readout accuracy is sensitive to the uniformity of individual pixels on the array. The hypothesis of the present research is that direct measurements of the height change corresponding to tilt through holographic interferometry will reduce the need for high pixel uniformity. Measurements of displacements for a vacuum packaged detector with nominal responsivity of 2.4nm/K are made with a Linnik interferometer employing the four phase step technique. The interferometer can measure real-time, full-field height variations across the array. In double-exposure mode, the current height map is subtracted from a reference image so that the change in deflection is measured. A software algorithm locates each mirror on the array, extracts the measured deflection at the tip of a mirror, and uses that measurement to form a pixel of a thermogram in real-time. A blackbody target projector with temperature controllable to 0.001K is used to test the thermal resolution of the imaging system. The achieved minimum temperature resolution is better than 0.25K. The double exposure technique removes mirror non-uniformity as a source of noise. A lower than nominal measured responsivity of around 1.5nm/K combined with noise from the measurements made with the interferometric optical readout system limit the potential minimum temperature resolution. Improvements need to be made both in the holographic setup and in the MEMS detector to achieve the target temperature resolution of 0.10K.

En raison de leurs propriétés physiques et leur stabilité chimique, les semi-conducteurs à large bande interdite comme les nitrures d’éléments III doivent permettre de réaliser des dispositifs ayant une meilleure performance dans des environnements sévères. De plus, leur piézoélectricité et la possibilité de les utiliser en technologie monolithique sur silicium rendent cette filière particulièrement intéressante pour intégrer des microsystèmes électro-mécaniques MEMS avec des composants actifs HEMT dans la perspective de réalisation d’une nouvelle génération de capteurs. Le développement des MEMS en matériau nitrures nécessite une bonne connaissance et une bonne maîtrise des propriétés mécaniques des matériaux. La première partie de la thèse consiste donc en la caractérisation des modules d’Young et des contraintes résiduelles dans les couches minces de nitrures épitaxiées par épitaxie par jets moléculaires sur substrat silicium. Pour extraire ces paramètres mécaniques, nous avons mesuré et modélisé des micro-dispositifs de test constitués par des poutres bi-encastrées ou encastrées-libres de longueurs variées et des indicateurs mécaniques. La deuxième partie consiste en l’étude de la transduction électro-mécanique d’actionnement des résonateurs formés par une poutre intégrant une hétérostructure AlGaN/GaN. Les résonateurs sont actionnés par une diode Schottky intégrée sur la poutre. Les actionneurs ont été caractérisés en amplitude et en fréquence de vibration sous différentes conditions de polarisation par vibrométrie laser par effet Doppler. Une modélisation à été effectuée de façon analytique et de façon numérique par éléments finis en utilisant COMSOL multiphysique afin de comprendre le mécanisme d’actionnement et de mettre en évidence le rôle de l’hétérostructure AlGaN/GaN sur le fonctionnement de l’actionneur. / Due to their physical properties and chemical stability, wide band gap semiconductors such as group III nitrides should enable devices with a better performance in harsh environments. In addition, their piezoelectricity and the possibility of monolithic integration on silicon, make this technology particularly attractive for integrating microelectromechanical systems (MEMS) with active devices such as HEMTs for the purpose of developing a new generation of sensors. The development of MEMS using nitride materials requires a good knowledge and understanding of the mechanical properties of materials. The first part of this thesis concerns the determination of the Young modulus and the residual stress in the thin films of nitrides grown by molecular beam epitaxy on silicon substrate. In order to extract these mechanical parameters, we measured and modelled test devices such as clamped-clamped beams, free-clamped beams with different lengths and mechanical indicators. The second part of the thesis consists in studying the piezoelectric actuation of MEMS resonators based on an AlGaN/GaN heterostructure. The resonators are actuated by a Schottky diode integrated onto the beam. The amplitude of the actuated resonator and the resonant frequency were measured under various bias conditions using Doppler laser vibrometry. We performed analytical modelling and finite element modelling using COMSOL Multiphysics® in order to unerstand the actuation mechanism and to evidence the role of the AlGaN/GaN heterostructure on the actuator operation.

This research project was part of the microfluidic program in the CRC for Microtechnology, Australia, during 2000 to 2003. The aim of this research was to investigate the feasibility of applying geometric variations in a microchannel to create effects other than pure molecular diffusion to enhance microfluidic mixing. Geometric variations included the shape of a microchannel, as well as the various obstacle structures inside the microchannel. Generally, before performing chemical or biological analysis, samples and reagents need to be mixed together thoroughly. This is particularly important in miniaturized Total Analysis Systems (�TAS), where mixing is critical for the detection stage. In scaling down dimensions of micro-devices, diffusion becomes an efficient method for achieving homogenous solutions when the characteristic length of the channels becomes sufficiently small. In the case of pressure driven flow, it is necessary to use wider microchannels to ensure fluids can be pumped through the channels and the volume of fluid can provide sufficient signal intensity for detection. However, a relatively wide microchannel makes mixing by virtue of pure molecular diffusion a very slow process in a confined volume of a microfluidic device. Therefore, mixing is a challenge and improved methods need to be found for microfluidic applications. In this research, passive mixing using geometric variations in microchannels was studied due to its advantages over active mixing in terms of simplicity and ease of fabrication. Because of the nature of laminar flow in a microchannel, the geometric variations were designed to improve lateral convection to increase cross-stream diffusion. Previous research using this approach was limited, and a detailed research program using computational fluid dynamic (CFD) solvers, various shapes, sizes and layouts of geometric structures was undertaken for the first time. Experimental measurements, published experimental data and analytical predictions were used to validate the simulations for selected samples. Mixing efficiency was evaluated by using mass fraction distributions. It was found that the overall performance of a micromixer should include the pressure drop in a microdevice, therefore, a mixing index criterion was formulated in this research to combine the effect of mixing efficiency and pressure drop. The mixing index was used to determine optimum parameters for enhanced mixing, as well as establish design guidelines for such devices. Three types of geometric variations were researched. First, partitioning in channels was used to divide fluids into mixing zones with different concentrations. Various designs were investigated, and while these provided many potential solutions to achieving good mixing, they were difficult to fabricate. Secondly, structures were used to create lateral convection, or secondary flows. Most of the work in this category used obstacles to disrupt the flow. It was found that symmetric layouts of obstacles in a channel had little effect on mixing, whereas, asymmetric arrangements created lateral convection to enhance crossstream diffusion and increase mixing. Finally, structures that could create complex 3D advections were investigated. At high Reynolds numbers (Re = 50), 3D ramping or obstacles generated strong lateral convection. Microchannels with 3D slanted grooves were also investigated. Mixers with grooved surfaces generated helicity at low Reynolds numbers (Re � 5) and provided a promising way to reduce the diffusion path in microchannels by stretching and folding of fluid streams. Deeper grooves resulted in better mixing efficiency. The 3D helical advection created by the patterned grooves in a microchannel was studied by using particle tracing algorithms developed in this research to generate streaklines and Poincare maps, which were used to evaluate the mixing performance. The results illustrated that all the types of mixers could provide solutions to microfluidic mixing when dimensional parameters were optimized.

A novel flexure-based biaxial compression/shear apparatus has been designed, built, and utilized to conduct tribological studies of interfaces relevant to MEMS. Aspects of our new apparatus are detailed and its capabilities are demonstrated by an investigation of two interfaces for MEMS applications. Tribological tests may be performed with normal and tangential forces in the µN to N range and relative sliding displacements in the nm to mm range. In this testing range, the new experimental apparatus represents an improvement over existing techniques for tribological studies at the small scale. / Singapore-MIT Alliance (SMA)

With the flourishing development of MEMS, it is possible to combine micro-sensors with micro-actuator and apply to the organ transplant in medical fields or as an embedded sensor on buildings or bridges. Generally batteries is are used as the kinetic energy source, but it involves the issue of recycling. Therefore, development of a self-generator utilizing vibrational source from environment is another better choice. This study succeeds in building up the transform mode of electricity in an electro-magnetic vibration-induced micro-generator. The electricity characteristics of micro-generator are obtained by Mathematical software analysis. MEMs technology can be used to fabricate and assemble the microstructure , planar coils and magnetic films. The analytic results of maximum power and minimum volume by using a mathematics model are achieved. The validity of this model is verified by comparing the theoretical and experiment data from the literature.

This thesis describes the hardware design of a positioning system which locates a vehicle relative to a digital map of an underground mine. The mines of interest are potash mines of Saskatchewan, and they are at a depth of approximately 1000 meters and they cover an area larger than 10 kilometers by 10 kilometers. An important application of an in-mine positioning system is tracking a ground penetrating radar system. Ground penetrating radar is used to determine the current condition of the mine ceiling and to evaluate its risk of delamination. A ground penetrating radar system is driven along a mine tunnel and measurements are logged. It is necessary to record position information along with the radar signal and this can be done with the aid of a positioning system. The design and evaluation of the hardware system that supports a positioning system, which can locate a vehicle inside a mine tunnel with reasonable accuracy and cost is described in this thesis. The hardware system includes a dead reckoning system (DRS), which is built using MEMS (Micro Electro Mechanical System) accelerometer and gyroscope sensors and ultrasonic distance sensors, along with a data acquisition system.

In this thesis, an adapted form of dynamic Electrostatic Force Microscopy is presented as an alternative technique for non-contact dynamic characterization of beam resonators. The actuation of the test resonant beam was accomplished by applying a modulated signal to a probe cantilever that was positioned closely above the resonant beam. The frequency response of the coupled electrostatic interaction between the conductive beams was studied close to the resonance of the test beams. Modulation of the input signal allowed the test resonator to be actuated without requiring on-chip circuitry, and the probing frequency range kept independent of the resonant frequency of the probe cantilever. The resonant response of three test cantilever beams were experimentally characterized using two softer probe cantilevers. A model was constructed to describe the coupled electrostatic interaction and simulations were performed to compare predictions from the model to experimental data. The amplitude response shape, resonant frequency and quality factor from the model fit well with experimental results, showing that the resonant response of a resonator can be characterized using this technique. However, the phase and voltage variation responses were not well characterized, indicating further work to develop the force expressions in the model is needed. / October 2006

Els dispositius MEMS han demostrat la seva utilitat en un gran ventall d'aplicacions de sensat i actuació. L'extensió al domini de RF d'aquests elements mecànics són ara una de les peces clau per sistemes altament reconfigurables referències de freqüència i processadors de senyals. Aquesta tesi es centra en algunes de les aplicacions dels dispositius MEMS en el domini de RF: referències de freqüència per oscil·ladors, filtres i mescladors. Els resonadors que es presenten en aquesta tesi s'han fabricat completament en tecnologies CMOS comercials per aprofitar la integració de MEMS i circuiteria complementària i el baix cost de fabricació d'aquestes tecnologies. Diferents tipus de ressonadors MEMS s'han dissenyat i fabricat a fi d'avaluar les seves prestacions en diferents propietats. La validesa de la tècnica emprada per fabricar els MEMS en tecnologies CMOS futures s'ha demostrat fabricant i testant amb èxit resonadors MEMS en dos tecnologies diferents: de diferents fàbriques i nodes tecnològics (0.35um i 0.18um). La freqüència de ressonància d'aquests dispositius mecànics es troben a les bandes de HF i VHF. Tots aquests dispositius basats en bigues flexurals, presenten un major factor de qualitat Q que els tancs LC integrats i són a més a més sintonizables en freqüència, amb una mida inferior a la dels citats tancs LC. Els ressonadors MEMS-CMOS descrita a la tesi presenten un valor de Qxf en el rang entre 1GHz i els 10GHz mesurats a l'aire. Aquests valors es milloren mesurant al buit arribant als 100GHz, majors a qualsevol altre ressonador basat en tecnologia CMOS. Les aplicacions de mesclat i filtrat de senyals també s'estudien. Dins d'aquestes aplicacions, la meta és definir una banda passant plana combinant diferents ressonadors. El prototipus d'un filtre paral·lel basat en ponts i un amplificador diferencial CMOS monolític presenta una banda passant plana de 200kHz a una freqüència central de 21.66MHz quan es mesura a l'aire. També es demostra el filtrat emprant un únic ressonador del tipus tuning fork. Com a mesclador, és destacable la possibilitat de convertir a alta i baixa senyals de 1GHz amb un ressonador de 22MHz Com a oscil·ladors monolítics, es mostra un oscil·lador operatiu per tensions DC baixes (<5V), gràcies a la reducció del gap del ressonador. L'oscil·lador basat en un tuning fork aconsegueix valors de soroll de fase de -87dBc/Hz@10kHz i -98.7dBc/Hz@100kHz, millor que altres oscil·ladors CMOS monolític reportats. / MEMS devices demonstrated a wide range of sensing and actuation applications. These mechanical elements present nowadays extension to the RF world as key elements for highly reconfigurable systems, frequency references and signal processors. This thesis focuses on some of the applications of MEMS devices in the RF domain: frequency references for oscillators, filters and mixers. The resonators presented in this thesis are completely fabricated in commercial CMOS technologies to take profit of monolithic MEMS and complementary circuitry integration and low cost fabrication inherent of these technologies. Several kinds of MEMS resonators (clamped-clamped beams, free-free beams and double ended tuning forks) were designed and fabricated to evaluate their performance according to different properties. Two different CMOS technologies, from two different foundries and also different technological node (0.35um and 0.18um) were successfully used to validate the monolithic fabrication approach on future CMOS technologies. The resonance frequencies of these resonators are located on the HF and VHF range. All these devices, based on flexural beams, show superior Q than integrated LC tanks and are also tunable. Moreover, their size is significatively lower than the one of the aforementioned LC tanks. The CMOS-MEMS resonators reported in this thesis show a Qxf value in the range between 1GHz and 10GHz in air and these values are further improved in vacuum up to 100GHz, higher than any other reported resonator based on CMOS technology. Filtering and mixing applications were also studied. The goal in these applications was to define a flat band-pass combining different resonators. A prototype of parallel filter was measured using two CC-beams and a monolithic CMOS differential amplifier. The filter shows a flat bandpass up to 200kHz in air at a center frequency of 21.66MHz. Filtering with a single resonator was also demostrated with a DETF. A mixer based on a 22MHz CC-beam resonator was able to up and downconvert a signal from/to 1GHz. Monolithic oscillators with MEMS elements as frequency references have shown oscillation with a reduced applied DC voltage (<5V) thanks to the reduction of the gap. The DETF based oscillator shows good phase noise performance of -87dBc/Hz@10kHz and -98.7dBc/Hz@100kHz better than previously reported monolithic oscillators whereas operating at a lower DC voltage.

This thesis describes the hardware design of a positioning system which locates a vehicle relative to a digital map of an underground mine. The mines of interest are potash mines of Saskatchewan, and they are at a depth of approximately 1000 meters and they cover an area larger than 10 kilometers by 10 kilometers. An important application of an in-mine positioning system is tracking a ground penetrating radar system. Ground penetrating radar is used to determine the current condition of the mine ceiling and to evaluate its risk of delamination. A ground penetrating radar system is driven along a mine tunnel and measurements are logged. It is necessary to record position information along with the radar signal and this can be done with the aid of a positioning system. The design and evaluation of the hardware system that supports a positioning system, which can locate a vehicle inside a mine tunnel with reasonable accuracy and cost is described in this thesis. The hardware system includes a dead reckoning system (DRS), which is built using MEMS (Micro Electro Mechanical System) accelerometer and gyroscope sensors and ultrasonic distance sensors, along with a data acquisition system.

In this thesis, new metrology hardware is designed, fabricated, and tested to provide improvements over current MEMS metrology. The metrology system is a micromachined scanning interferometer having a sub-nm resolution in a compact design. The proposed microinterferometer forms a phase sensitive diffraction grating with interferometric sensitivity, while adding the capability of better lateral resolution by focusing the laser to a smaller spot size. A detailed diffraction model of the microinterferometer was developed to simulate the device performance and to suggest the location of photo detectors for integrated optoelectronics. A particular device is fabricated on a fused silica substrate using aluminum to form the deformable diffraction grating fingers and AZ P4620 photo resist (PR) for the microlens. The details of the fabrication processes are presented. The structure also enables optoelectronics to be integrated so that the interferometer with photo detectors can fit in an area that is 1mm x 1mm. The scanning results using a fixed grating micromachined scanning interferometer demonstrated that it could measure vibration profile as well as static vertical(less than a half wave length) and lateral dimension of MEMS. The SI, which is integrated with photo diodes, demonstrated its operation by scanning a cMUT. The PID control has been tested and resulted in improvement in scanned images. The integrated micromachined scanning interferometer demonstrated that the deformable grating could be used to tune the measurement keep the interferometer in quadrature for highest sensitivity.