Analysis of piezo-resistive read-out signals for a silicon tuning fork gyroscope

Abstract

The paper concerns a silicon micromachined tuning fork gyroscope, which is driven via two piezo-electric thin film actuators. The device responds to an external angular rate by a torsional motion around its sensitive axis due to the Coriolis effect. The shear strain in the upper torsional stem, which is proportional to the angular rate, is detected via a piezo-resistive read-out structure. Due to a change in resistivity at the strain sensitive elements, an electronic signal is generated. The change in voltage, however, does not solely derive from the torsional strain induced by the response of the device to the angular rate. In addition, there are unwanted contributions from the drive motion, e.g., from mechanical imbalance and from asymmetries of the piezoelectric excitation induced by fabrication tolerances. These effects disturb the sensor signal with varying contributions in amplitude and phase. They are identified and compared to results of FEM simulations. Suggestions for an optimized read-out structure are presented.