A Silicon MEMS Quatrefoil Suspension Gyroscope

This paper discusses the design and experimental characterization of a vacuum packaged MEMS gyroscope with a novel quatrefoil suspension system fabricated on a (100) single-crystal silicon substrate. The design process focused on the production of a high-quality factor gyroscope with inherent robustness to frequency split between secondary degenerate modes. Thermoelastic damping (TED) and anchor damping were estimated using finite element analysis applied to representative designs. The gyroscopic operation was demonstrated by driving one of the secondary degenerate elliptical modes while sensing the response on the other elliptical mode: both modes achieved a quality factor exceeding 1 million at an operating frequency of 426 kHz. The implementation of mode matching by electrostatic frequency tuning decreased the initial frequency split between the two near-degenerate modes from 4.2 Hz as-fabricated to less than 0.01 Hz. The mechanical sensitivity was improved by a factor of 25.4 for mode-matched operations in comparison to the untuned case. Additionally, the angle random walk (ARW) and bias instability (BI) improved to 0.01 ° /
${\sqrt {hr}}$
and
$0.34~^{\circ }/hr$
, i.e. by a factor of 7.7 and 8.24 respectively. Finally, the force to rebalance method was implemented to increase the measurement bandwidth and the dynamic range of the sensor, demonstrating a linear scale factor for a rotation rate of ±400°/s. The limitations on the measured metrics arise from the current board-level integration, and associated interface and control electronics. [2023-0070]