A mode-matching 130-kHz ring-coupled gyroscope with 225 ppm initial driving/sensing mode frequency splitting

A degenerate mode 130-kHz ring-coupled gyroscope with auxiliary transducer array is designed to enhance the sensitivity as well as the mode-matching feature. The proof-of-concept device with 3 μm transducer´s gap is fabricated using a conventional (100) silicon-on-insulator (SOI) wafer process with only two lithography steps. The auxiliary parallel-plate transducer array is located at the maximum displacement of the vibrating ring to enhance the electromechanical coupling while reducing the sensing noise. The in-plane trefoil mode (n=3) is adopted to alleviate the initial frequency splitting in (100) crystalline silicon device layer. The average frequency split for the drive/sense modes over multiple tested devices is only 225 ppm with the mean resonance frequency of 130 kHz. The measured Q-factor is 50 in atmospheric pressure and up to 10,000 in vacuum. Owing to the larger transduction area benefitting from the transducer array design, a low dc-bias voltage (V_P) of 3 V in vacuum (21 V in air) is sufficient to sustain the driving loop oscillation. As integrated with the sensing circuits to operate the proposed gyroscope, a scale factor of 2.2 mV/°/s and resolution of 0.26 °/s, respectively, are characterized in atmospheric pressure.