Multi-Coefficient Eigenmode Operation – Breaking Through 10°/hr Open-Loop Bias Instability in Wideband Aluminum Nitride Piezoelectric BAW Gyroscopes

Abstract

This paper introduces a modification to the eigenmode operation of resonant gyroscopes. The so-called multi-coefficient eigenmode operation can improve cross-mode isolation due to spatially non-orthogonal imperfection, which is one of the causes of residual quadrature error in conventional eigenmode operation. A 1400µm annulus aluminum nitride (AlN) on Silicon bulk acoustic wave (BAW) resonator with gyroscopic in-plane bending modes at 2.98MHz achieves near 60dB cross-mode isolation when operated as a gyroscope using multi-coefficient eigenmode architecture. The as-born frequency mismatches in multiple devices are compensated by physical laser trimming as an alternative to the displacement feedback tunning mechanism. The demonstrated AlN piezoelectric BAW gyroscope shows a large open-loop bandwidth of 150Hz and a high scale factor of 9.5nA/°/s on a test board in a vacuum chamber. The measured angle random walk is 0.145°/√hr, and the bias instability is 8.6°/hr, showing significant improvement compared to the previous eigenmode AlN BAW gyroscope. The result from this paper proves that with multi-coefficient eigenmode operation, the piezoelectric AlN BAW gyroscopes can have a comparable noise performance as their capacitive counterpart while having the unique advantage of large open-loop bandwidth and not requiring large DC polarization voltages.