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Title: Precise Frequency and Mode Control in High Frequency Silicon and Silicon Carbide Resonant Gyroscopes
Committee:
Dr. Ayazi, Advisor
Dr. Ansari, Chair
Dr. Hesketh
Abstract: The object of the proposed research is to study precise frequency and mode control in high frequency MEMS resonators.The frequency and mode control in high Q gyroscopic resonators that utilize high frequency bulk acoustic wave (BAW) modes are challenging due to the large stiffness and strong modal coupling. In the prior art, frequency and quadrature tunning in piezoelectric resonant BAW gyroscope were achieved via dynamic feedback and eigenmode operation. As an alternative, the preliminary research of this proposal has looked into laser trimming of AlN-on-Si BAW gyroscopes to develop and proposed an improvement to the existing eigenmode operation. The improved method will virtually fit each electrode to the corresponding as-born mode shape of the piezoelectric resonator. A novel AlN-on-Si pitch/roll resonant gyroscope design based on the new method is proposed and will be further studied. Monocrystalline 4H silicon carbide (SiC) is a particularly interesting and suitable structural material for Coriolis resonator gyroscopes owing to its ultra-low phononic dissipation and in-plane isotropic lattice. However, SiC is a hard-to-etch material and SiC-on-insulator (SiCOI) substrates are not commercially available. The preliminary research has shown a capacitive SiC BAW gyro with a DRIE-defined gap size of ~2.8um with very small as-born frequency split. To achieve a sub-micron capacitive gap for efficient electrostatic tuning and alignment of the modes, a high-aspect ratio process on SiCOI is proposed, which overcomes TCE mismatch by defining a stress release region on the SiCOI wafer. The remaining work will further improve the proposed process and characterize the HARPSS SiC BAW gyroscope. This work will enable multi-axis piezoelectric resonant gyros and pave the way towards SiC capacitive BAW gyroscope.
