A HARPSS polysilicon vibrating ring gyroscope

This paper presents the design, fabrication, and testing of an 80-mum-thick, 1.1 mm in diameter high aspect-ratio (20:1) polysilicon ring gyroscope (PRG). The vibrating ring gyroscope was fabricated through the high aspect-ratio combined poly and single-crystal silicon MEMS technology (HARPSS), This all-silicon single-wafer technology is capable of producing electrically isolated vertical electrodes as tall as the main body structure 50 to 100's (mum tall) with various size air-gaps ranging from submicron to tens of microns. A detailed analysis has been performed to determine the overall sensitivity of the vibrating ring gyroscope and identify its scaling limits. An open-loop sensitivity of 200 muV/deg/s in a dynamic range of +/- 250 deg/s was measured under low vacuum level for a prototype device tested in hybrid format. The resolution for a PRG with a quality factor (Q) of 1200, drive amplitude of 0.15 mum, and sense node parasitic capacitances of 2 pF was measured to be less than 1 deg/s in 1 Hz bandwidth, limited by the noise from the circuitry. Elimination of the parasitic capacitances and improvement in the quality factor of the ring structure are expected to reduce the resolution to 0.01 deg/s/(Hz)(0.5).