Investigation of factors affecting bias stability and scale factor drifts in Coriolis vibratory MEMS gyroscopes

This Ph.D. dissertation studies factors affecting bias stability and scale factor drifts in micromachined Coriolis vibratory gyroscopes with electrostatic/capacitive transduction. The work provides improved understanding of the factors affecting accuracy of measurements, leading to novel design approaches in both mechanical and signal processing domains.;This thesis developed a capacitive detection scheme with inherent self-calibration. The method, called Side-Band Ratio (SBR) detection, is robust to variations of such critical parameters as the nominal capacitance, frequency and amplitude of the probing voltage, and electronics gain. The SBR technique allows to drastically improve gyroscope scale factor accuracy and repeatability while simultaneously increasing signal-to-noise ratio and bias stability by 20 to 30 dB.;This thesis proposed a temperature robust gyroscope with improved gain-bandwidth characteristics. The introduced concept was analyzed theoretically and characterized experimentally. Devices with 2.5 kHz operational frequency were designed, fabricated, and tested in air, demonstrating sense-mode 3 dB bandwidth of 250 Hz, achieved for the first time without sacrifice of the resonant gain. The new gyroscope's uncompensated temperature coefficients of bias and scale factor were 313 (°/h)/°C and 351 ppm/°C, respectively. The gyroscope provides low temperature sensitivity on par with quartz tuning fork gyroscopes and bandwidth increased beyond the capabilities of conventional gyroscopes. At the same time, rate sensitivity, quadrature, resolution, and angle random walk of the new gyroscope are as good as for the state-of-the-art conventional gyroscopes.;This thesis also investigated the effects of design and die attachment on the gyroscope quality factor. The presented family of ultra-high quality factor gyroscopes with reduced sensitivity to packaging stresses utilizes two and four coupled masses actuated in anti-phase by means of a mechanical synchronization system. Prototypes characterized in vacuum demonstrated drive-mode quality factor of 67,000 and ultra-high sense-mode quality factor of 125,000. The ultra-high mechanical scale factor of 0.4 nm/(711) translates into drastically improving sensor noise performance and bias stability.