UBC Theses and Dissertations
Nonlinear amplification techniques for inertial MEMS sensors Sharma, Mrigank
Inertial sensors, specifically MEMS gyroscopes, suffer in performance with down scaling. Non linear amplification techniques, such as parametric resonance, can be employed in many resonant structures to alleviate this degradation in performance, improve sensitivity and Signal to Noise Ratio (SNR). In this thesis the application of parametric resonance amplification and damping to both modes of a vibratory gyroscope is carried out using specialized combs. Gap-varying combs, which are usually used for the sensing mode are known for producing electrostatic spring modulations. They are used in this thesis to achieve parametric modulation in sense mode, for increasing spectral selectivity and to reduce the equivalent input noise angular rate (from 0.0046 deg/s/√Hz to 0.0026 deg/s/√Hz , for a parametric gain of 5). Additionally, novel shaped combs were used for performing parametric modulation of the driven mode of a resonant gyroscope as well. Analytical modes for both types of parametric amplification are derived and experimentally verified. In order to study the effect of parametric modulation for large signal operation, the dynamic pull-in process is analyzed and modeled in inertial MEMS sensors. The dynamic analytical model is derived and experimentally verified for parametric amplification. The dependence of dynamic pull-in voltage amplitudes on the values of externally-induced accelerations (e.g. Coriolis accelerations in the case of vibratory gyroscopes) is experimentally. The measurements indicate that the dynamic pull-in voltages reduce from 100 V to 56 V for a designed and fabricated MEMS gyroscope (device A) and from 21.77 V to 17.3 V for a MEMS accelerometer (device B), for an equivalent input acceleration signal of 0.319 ms-2, when the structures are actuated at their resonance frequency. In order to further analyze the fundamental limitations of sensing at microscale, a separate noise analysis of MEMS resonant sensors is performed. The frequency-dependent damping theory is used to suggest new optimization methods for the design of MEMS vibratory gyroscopes.
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