A surface-micromachined tunable microgyroscope

We present a surface-micromachined microgyroscope, whose resonant frequency is electrostatically-tunable after fabrication. The microgyroscope has two oscillation modes: a sensing mode and a actuating mode. In a theoretical study, the microgyroscope has been designed so that the resonant frequency in the sensing mode is higher than that in the actuating mode. A 4-mask surface-micromachining process for the tunable microgyroscope has been described, including the deep RIE of a 6 μm-thick LPCVD polycrystalline silicon structure layer. In a experimental study, the resonant frequency in the sensing mode has been matched to that in actuating mode by applying an inter-plate bias voltage. Frequency matching for the fabricated microgyroscope has been achieved at 5.8 kHz under the bias voltage of 2 V in a reduced pressure of 0.1 torr. For an input angular rate of 50°/sec, an output signal of 20 mV has been measured from the tuned microgyroscope for an AC drive voltage of 2 V with a DC bias voltage of 3 V