A MEMS vibrating ring gyroscope with on-chip capacitive stress sensors for drift compensation

MEMS gyroscopes are commonly used for rotation measurement in navigation. Even though the noise performance of these sensors has improved in the last few decades, the long-term drift problem is still prominent for these sensors. Longterm drift error is caused by external factors such as temperature and induced stress on the MEMS chip. With this work, we present an on-chip solution for the compensation of long-term drift. Due to its compact and singular anchor morphology, a vibrating ring gyroscope design was employed. Eight bridge-type capacitive stress sensors were placed periodically at the inner section of the ring surrounding the inner anchor, which adds localized stress measurement capability to the design. Another eight stress sensors were placed at the outer section of the ring surrounding the electrodes of the device. Tensile stress was applied on a testbed, and the output of the stress sensors and the gyroscope were recorded. Then, the gyroscope was subjected to a zero rate output(ZRO) test in mismatch and matched frequency configurations. The compensated output of the device was able to reach 0.008 /h in mismatched mode and 0.003 /h in matched mode without any signs of drift. The stress and the gyroscope output were partitioned into 12 hour blocks to increase the performance of the least squares fitting algorithm. We have observed a decrease in the compensation performance due to possible nonlinear and hysteresis effects generated during the long-term operation. Finally, we were able to show that the change in temperature wasn't sufficient enough to explain the frequency change of the drive and sense modes.