Capacitive micromachined ultrasonic transducers (CMUTs) have been developed as an alternative to piezoelectric transducers for ultrasonic imaging in non-destructive testing applications. These CMUTs offer substantial advantages over their piezoelectric counterparts, which include a highly miniaturized system, easy integration with electronic control circuitry, a wider bandwidth, and a higher sensitivity. In this thesis, the design, fabrication and characterization of several single and array CMUT devices are reported. Many sizes of CMUTs, aiming to operate at different resonant frequencies, were fabricated using a PolyMUMPs sacrificial technique. An analytical and finite element model was used to further understanding of the physical behaviour of the transducer. The basic functionality of the CMUT devices was investigated through capacitance and electrical impedance measurements. These devices showed greater change in the capacitance and impedance data while operating close to their collapse voltages. This higher change in both capacitance and impedance is a result of a larger membrane displacement. The acoustic output power is directly related to the magnitude of the membrane’s displacement. The transducers performance thus can be enhanced by operating close to their collapse voltage and obtained higher sensitivity. The optical characterization, performed on the single devices and on the 1-D arrays, provided a better understanding of the membrane vibration modes and displacement profiles at different resonant frequency modes. Acoustic measurements were performed to demonstrate the transmission capability of the CMUTs. The generated acoustic signals were detected using a commercial detector. These acoustic experiments demonstrated that these CMUTs can potentially be used as ultrasonic transducers alternative to piezoelectric transducers.

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.

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.

MEMS Accelerometers are broadly used in the area of vibration sensor. Their applications range from seismic disturbances, to automotive industry such as airbag systems, active suspension, and smart braking. Traditionally, the acceleration is detected electrically by measuring either capacitive variations or piezoelectric signals. Those approaches suffer from a number of drawbacks, such as low sensitivity due to low signal-to-noise ratio (SNR), small dynamic range, high temperature sensitivity, etc. In this thesis, a MEMS-based optical accelerometer is designed and analyzed. The device can be fabricated on a silicon-on-insulator (SOI) wafer, on which a double-leg single-mode optical rib waveguide is used to propagate 1.55μm laser beam. The device integrates the waveguide with a mechanical oscillator, and is able to detect in-plane vibrations of the oscillator by taking advantages of optical interference. According to the analysis, the maximum working range of the oscillator can be as large as 50μm and the acceleration sensitivity can be below 1μg/Hz¹/². Device fabrication and characterization are also carried out and described in the thesis. All necessary fabrication steps and details as well as characterization setups are given. Due to several fabrication challenges in UBC (e.g. malfunctioned equipment), a complete device has not been fabricated. More fabrication and characterizations are to be continued as future work.

Zugl.: Chemnitz, Techn. Universiẗat, Diss., 2009.

Univ., Diss., 2002--Kassel

MEMS Accelerometers are broadly used in the area of vibration sensor. Their applications range from seismic disturbances, to automotive industry such as airbag systems, active suspension, and smart braking. Traditionally, the acceleration is detected electrically by measuring either capacitive variations or piezoelectric signals. Those approaches suffer from a number of drawbacks, such as low sensitivity due to low signal-to-noise ratio (SNR), small dynamic range, high temperature sensitivity, etc. In this thesis, a MEMS-based optical accelerometer is designed and analyzed. The device can be fabricated on a silicon-on-insulator (SOI) wafer, on which a double-leg single-mode optical rib waveguide is used to propagate 1.55μm laser beam. The device integrates the waveguide with a mechanical oscillator, and is able to detect in-plane vibrations of the oscillator by taking advantages of optical interference. According to the analysis, the maximum working range of the oscillator can be as large as 50μm and the acceleration sensitivity can be below 1μg/Hz¹/². Device fabrication and characterization are also carried out and described in the thesis. All necessary fabrication steps and details as well as characterization setups are given. Due to several fabrication challenges in UBC (e.g. malfunctioned equipment), a complete device has not been fabricated. More fabrication and characterizations are to be continued as future work. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

A MEMS piezoresistive pressure sensor provides a low-cost and accurate means of detecting and quantifying small-scale disturbances in underwater environments. A highly sensitive MEMS pressure sensor has been developed that can be packaged in two different ways – one in a cylindrical housing, and the other in a flexible, yet robust, strip configuration – enabling more freedom for the user to choose an option that fits their needs. The sensing element of each consists of four piezoresistive elements in a Wheatstone Bridge configuration arranged on a deformable buried-oxide layer, which is then bonded to a Silicon base layer with a hollow cavity carved using reactive-ion etching. Previous work has shown the survivability of these sensors in an underwater environment and also measurements of low frequency pressure changes due to flow and varying turbulence intensities. The present work is focused on evaluating these pressure sensors and testing the limits of the sensing element in the low, medium, and high frequency regime (<100Hz to >1kHz) to gain further insight into the performance. Five experimental tests were developed and conducted to guide this research objective. The sensor responses under different flow conditions were measured and analyzed with selected filtering and resampling techniques to eliminate background noises. First, the sensors were calibrated to ensure their linearity and to determine their pressure sensitivities. Then, using bench-top testing rigs and a water tunnel, the sensor performance was evaluated in submerged environments when subjected to multiple small-scale flow disturbances across the tested frequency regime. It was found that the present sensors are capable of providing more accurate measurements across a tested frequency regime of 0 to 20,000Hz when compared to other off-the-shelf products. Testing in submerged environment showed that the sensors are capable of detecting small-scale pressure fluctuations as a result of eddies which are evident in a Von Karman vortex street and a turbulent flow. Despite the presence of EMI noise within a water tunnel, the sensors demonstrated a decay of pressure fluctuations that is consistent with previous research in the field. Overall, the present work increases understanding of the sensors' performances across a broad range of frequencies and provides insight into potential uses and future work. / Master of Science / Pressure sensors are an important, if not the most important, measurement device available today. Pressure sensors play an integral role in the everyday lives for everyone around the world; from applications in medicine, aerospace, autonomy and computation, these sensors provide real-time feedback and help gain a deeper understanding of a system. However, with the technological advances in the Modern Age, there has been a growing need for smaller, cheaper, and faster sensors. As a result, engineers continued to improve sensor performance in the past century with new technologies. A micro-electromechanical system (MEMS) pressure sensor offers a low-cost and energy efficient method to quantify pressure fluctuations within a system. This work focuses on evaluating the performance of three MEMS pressure sensors for use in a submerged environment to detect small-scale pressure fluctuations across a broad range of frequencies. Five different tests were conducted to investigate this research objective. The first three were performed in a controlled underwater environment from which direct conclusions could be made. The last two were performed in an uncontrolled underwater environment from which comparisons to literature and known phenomena were used to draw conclusions. A key result showed that the sensor measurements aligned with prior research in the field. Multiple data reduction techniques were also used during post-processing to ensure accurate data was being collected. The studies showed that the developed MEMS pressure sensors provided the same capabilities as other commercially available pressure measurement devices, all the while displaying a higher sensitivity and broader frequency range. Furthermore, the survivability and robustness of the sensor was proven when subjected to large- and small-scale flow disturbances in a water tunnel.

No description available.

Le sujet de cette thèse porte sur la réalisation d'un bloc de transposition de fréquence de 1 à 20GHz à base de composants MEMS. Cette thèse s'est traduite par la conception et la réalisation d'un nouveau type de capacité MEMS RF variable, qui se base sur des structures rotatives de type gyroscope pour l'actionnement, et sur une variation de surface pour la variation de capacité. Comparée à différentes architectures publiées à ce jour, cette structure a l'avantage d'avoir la partie actionnement (la partie MEMS) et la partie RF (la capacité) isolées électriquement, ce qui permet d'éviter le phénomène d'auto actionnement avec la puissance du signal RF traversant. Un autre avantage de la structure développée est la possibilité d'avoir simultanément 8 capacités variables sur une puce unique, avec un seul système d'actionnement. La fabrication de ces puces nécessite l'utilisation d'un wafer SOI pour la partie MEMS et d'un wafer en verre pour la partie RF, ce qui offre la possibilité d'une mise en boitier du MEMS directement pendant le procédé de fabrication. Ces travaux ont également porté sur l'étude du phénomène de pullin dans le cadre des peignes interdigités incurvés (curved combdrive), laissant apparaître les paramètres physiques critiques lors du dimensionnement. Cette étude paramétrique a été utilisée pour améliorer la structure d'actionnement en utilisant des peignes interdigités à largeur de doigt et à gap variable, pour repousser ce phénomène de pullin en dehors de la plage utile d'actionnement. Cette nouvelle capacité variable a ensuite été intégrée dans un système simple d'oscillateur accordable sur alumine pour valider ses performances RF et pourra être associée à un mélangeur pour réaliser le bloc complet de transposition de fréquence / This thesis deals with the realisation of a frequency transposition block from 1 to 20 GHz based on MEMS components. It results in the design and fabrication of a new kind of tuneable RF MEMS capacitor based on a rotational gyroscope structure for the actuation part and on a surface variation for the capacitance change. Compared to other architectures published, this structure presents the advantage to have an actuation part (the MEMS part) and a RF part (the capacitor) that are electrically separated in order to avoid the phenomenon of self-actuation with RF signal crossing power. Another advantage of this structure is the possibility to simultaneously tune 8 different capacitors on a single chip, with only one actuation system. The fabrication of the chips requires the use of a SOI wafer for the MEMS part and a glass wafer for the RF part, which offers on chip packaging opportunity. This work also focused on the study of the pull-in effect in the case of curved comb-drives, highlighting the most critical physical parameters for the design. This parametric study has been used to improve the actuation structure and more particularly the topology of the curved comb-drives by variation of the finger width and gap. These modifications were done in order to push the pull-in effect out of the actuation operating range. This new tuneable capacitor has been integrated into a simple VCO circuit on alumina to validate the RF performances and could be associated to a RF mixer in order to realize the full frequency transposition block