Comparative analysis of distributed mass micromachined gyroscopes fabricated in SCS-SOI and EFAB

This paper studies a design approach that yields robust vibratory MEMS gyroscopes. The design is based on multiple drive-mode resonators with incrementally spaced frequencies, distributed symmetrically around the center of a supporting frame. These resonators are structurally constrained in the tangential direction with respect to the supporting frame. In the presence of an angular rotation rate about the z-axis, a harmonic Coriolis force is induced on each proof mass. These force vectors lie in the tangential direction, generating a resultant torque on the supporting frame. The net Coriolis torque excites the supporting frame into torsional oscillation about the z-axis, which is capacitively detected to generate angular rate measurement. Two batches of prototypes have been fabricated using in-house single crystal silicon on insulator (SCS-SOI) bulk-micromachining and EFABTM process commercially available from Microfabrica. Wideband drive operation was demonstrated in SOI devices. EFAB process yielded 850 Hz devices with quality factor 250 in air (bandwidth 3 Hz) and 850 in vacuum. Increase of temperature from 25° to 125°C shifts the resonant frequency down by roughly bandwidth, while quality factor drops by 8%. Parasitics model associated with EFAB consists of only a lumped capacitor and is simpler than two-parametric parasitics circuit in SOI devices. Nonlinear parametric excitation of motion at resonant frequency by super-harmonic AC voltage was experimentally characterized. This actuation method provides high amplitude of motion and separates motion from parasitics in frequency domain. The actuation method can potentially further improve the bandwidth and gain characteristics of distributed mass gyroscope.