Electrostatic Frequency Tuning of a Quatrefoil Suspension Gyroscope

MEMS gyroscopes based on axisymmetric structures rely on the Coriolis coupling between near-degenerate vibration modes as the basis for the measurement of rotation rate. Significant gains in mechanical sensitivity are achieved when the natural frequencies of the two modes are perfectly matched. This paper outlines a systematic approach to mode-matching for a vacuum packaged MEMS gyroscope with a novel quatrefoil suspension system fabricated on a (100) single-crystal silicon (SCS) substrate. This approach identifies mode orientation, implements mode-to-electrode alignment, and electrostatically varies the effective stiffness of one mode to achieve a mode-matched condition. Axisymmetric ring and disc gyroscopes fabricated on a (100) SCS substrate exhibit degeneracy of the higher-order elliptical modes. However, fabrication imperfections and anchoring arrangements can result in a non-zero frequency split between these modes which can be reduced by electrostatic frequency tuning. Frequency tuning is demonstrated in a prototype MEMS gyroscope where the frequency split between the vibration modes is reduced from 5 Hz to less than 0.01 Hz.