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 mu m-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 5.8kHz under the bias voltage of 2V in reduced pressure of 0.1torr. For an input angular rate of 50 degrees/sec, an output signal of 20mV has been measured from the tuned microgyroscope for an AC drive voltage of 2V with a DC bias voltage of 3V.