Decoupled Surface Micromachined Gyroscope With Single-Point Suspension

Abstract

This paper focuses on the performance of a new micromechanical gyroscope for automotive and consumer applications. Its most characteristic properties are a single-point mechanical suspension, seismic masses vibrating in antiphase tuning fork motion, as well as the spatial separation of the drive oscillator and the sense oscillator for minimizing electromechanical crosstalk between drive mode and sense mode. In detail, nonlinearities in the damping behavior of the drive unit were measured and analyzed theoretically. They can be attributed to fringe field effects in the comb drive unit. New design rules were defined to overcome this effect. Furthermore, an ambient pressure level of 1 mbar was found to yield optimum sensitivity of the sensor element for a given excitation amplitude of the drive unit. Further reduction of pressure does not improve the results. The temperature-dependent performance of the gyroscope was measured at an ambient pressure of 3 mbar. The temperature coefficient of frequency was measured to be -45.3 ppm/K for the drive mode (bending) and -35.5 ppm/K for the sense mode (torsional). The temperature coefficient of sensitivity was determined to be -858 ppm/K in the case of operating with constant drive amplitude. This value could be reduced to 17.5 ppm/K over the full observed temperature range by adapting the drive amplitude as a linear function of temperature in an optimal way. The resolution limit of the sensor element was found to be about 0.08°/ s/√{Hz} at application-relevant ambient pressure levels ranging from 1 to 10 mbar.