Micromachined Vibratory Gyroscopes Designed for Precision of Measurements and Environmental Robustness
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Micromachined Vibratory Gyroscopes Designed for Precision of Measurements and Environmental Robustness


This Ph.D. dissertation investigates how precision of measurement and environmental robustness can be addressed simultaneously in designing the Coriolis Vibratory Gyroscopes (CVGs). Toward implementation of such sensors, this thesis focuses on sensor's design and demonstration of functionalities, realizing devices based on Microelectromechanical System (MEMS) manufacturing techniques. This thesis investigated and demonstrated the following two different paradigms:

Realization of precision sensors that are capable of surviving the extreme events of shock and vibrations while the sensors are not in operation. Toward this objective, we developed and implemented a capacitive Trap-and-Hold (TAH) concept as an add-on feature intended to increase survivability of low-frequency MEMS CVGs by immobilizing the proof-mass of the oscillatory system in the event of shock and vibration and then recovering the sensor's high-sensitivity operation after the extreme events. To demonstrate the mechanism, a design of MEMS Dynamically Amplified dual-mass Gyroscope (DAG) was implemented as the test vehicle. This design was chosen for an increased amplitude of sensing response to enhance the signal-to-noise ratio and thus increase the precision of measurements. To accomplish such measurements, we investigated the effects of resonant mode ordering and energy dissipation with respect to the geometrical parameters. We demonstrated that the design is capable of achieving the noise characteristics of 0.007 deg/rt-hr of Angular Random Walk and 0.08 deg/hr of in-run bias instability. Two wafer-level fabrication processes using through-wafer-interconnect (TWI) techniques were investigated in order to realize the TAH add-on mechanism to DAGs. The TWI technique was experimentally validated to improve the DAG’s shock survivability under 5g shocks while preserving its noise characteristics. Realization of precision sensors that are capable of operating through extreme events of shock and vibrations. Toward this objective, we developed Fused Silica MEMS Dual-Shell Gyroscopes (DSGs). A Thru-Glass-Vias (TGVs) planar electrode substrate for electrostatic gyroscope actuation and detection was designed, fabricated, and integrated with DSG in a single microsystem. Effects of fabrication imperfections and assembly errors on structural symmetry and sensor performance were analyzed. An electromechanical tuning model for electrostatic compensation of structural asymmetry in DSGs was developed, taking into account the effect of assembly errors to realize near-mode-matched gyroscope operation with frequency matching on the order of 0.1 Hz for high angular rate measurements, followed by an experimental demonstration of the gyroscope operation with noise characteristics of 0.017 deg/rt-hr of Angular Random Walk and 0.2 deg/hr of in-run bias instability.

Factors that impact the structural symmetry and energy dissipation mechanisms in MEMS resonators were also analyzed and implemented to improve gyroscope performance in the realization of both paradigms. The impact of metallization on quality factor and electrical conductivity in Fused Silica devices was quantified and linked to the in-run noise performance using a developed analytical model. An existing trade-off between metallization and quality factor was investigated. It was concluded that optimization of the metal coating parameters was necessary to achieve optimal gyroscope noise characteristics. Finally, the effects of Electromechanical Amplitude Modulation (EAM) on electrical dissipation, nonlinearity, scale factor instability, and in-run noise performance of CVGs were investigated. Analytical models to predict the impact of EAM effect were developed, followed by experimental validation. Optimization of EAM parameters was demonstrated to achieve improved performance of MEMS CVGs.

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