A Mode-Matched Silicon-Yaw Tuning-Fork Gyroscope With Subdegree-Per-Hour Allan Deviation Bias Instability

In this paper, we report on the design, fabrication, and characterization of an in-plane mode-matched tuning-fork gyroscope (M-2-TFG). The M-2-TFG uses two high-quality-factor (Q) resonant flexural modes of a single crystalline silicon microstructure to detect angular rate about the normal axis. Operating the device under mode-matched condition, i.e., zero-hertz frequency split between drive and sense modes, enables a Q-factor mechanical amplification in the rate sensitivity and also improves the overall noise floor and bias stability of the device. The M-2-TFG is fabricated on a silicon-on-insulator substrate using a combination of device and handle-layer silicon etching that precludes the need for any release openings on the proof-mass, thereby maximizing the mass per unit area. Experimental data indicate subdegree-per-hour Brownian noise floor with a measured Allan deviation bias instability of 0.15 degrees/hr for a 60-mu m-thick 1.5 mm x 1.7 mm footprint M-2-TFG prototype. The gyroscope exhibits an open-loop rate sensitivity of approximately 83 mV/degrees/s in vacuum.