The Resonating Star Gyroscope: A Novel Multiple-Shell Silicon Gyroscope With Sub-5 deg/hr Allan Deviation Bias Instability

We report on the design, fabrication and characterization of a novel multiple-shell silicon vibratory microgyroscope. The resonating star gyroscope (RSG) is formed as a merged superposition of two square shells, yielding in-plane flexural modes that are utilized to sense rotation along the normal axis. The first prototypes of the single-shell RSG were implemented with 65 mum thick trench-refilled polysilicon structural material using the HARPSS process. These devices exhibited open-loop rate sensitivity of approximately 800 muV/deg/s. Despite high-aspect ratio sensing gaps, the device yielded poor sensitivity caused by low resonant-mode quality factors. To alleviate the
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losses caused by the inevitable formation of voids in trench-refilled structural material, the RSG was implemented in (111) single crystalline silicon. A 2.5-mm multiple-shell RSG was fabricated in 40 mum-thick SOI device layer using a simple two-mask process. Multiple-shells enable a higher operating frequency and larger resonant mass, essential components for reducing the mechanical noise floor of the sensor. Experimental data of a high-Q (111) multiple-shell prototype indicates sub-5 deg/hr Brownian noise floor, with a measured Allan deviation bias drift of 3.5 deg/hr. The gyroscope exhibits an open-loop rate sensitivity of approximately 16.7 mV/deg/s in vacuum.