A Study of Mode-Matching and Alignment In Piezoelectric Disk Resonator Gyros Via Femtosecond Laser Ablation

A mode-matching and alignment algorithm for bulk acoustic wave (BAW) resonator gyroscopes via femtosecond laser ablation is presented in this paper and verified on a piezoelectrically-actuated AlN-on-Si disk resonator. Mode-matching is essential to operate piezoelectric BAW resonators as gyros with high sensitivity in air but challenging due to the lack of electrostatic spring-softening effect. In this work, a laser trimming algorithm is implemented to mechanically mode-match and align the two resonant modes of a disk resonator guided by novel numerical maps. After selective laser ablation trimming, the as-born frequency split of 191Hz between 1.4MHz modes of a disk due to fabrication imperfections is reduced to 12Hz, corresponding to 3.8% of its -3dB resonant bandwidth while maintaining a Q-factor of 4600 in air, and 30dB improvement in mode isolation. The laser-trimmed frequencies remain closely matched across the temperature range of -30°C to 90°C, verifying the temperature robustness of laser trimming results. The mode-matched disk resonator is operated as a gyroscope in air and exhibits a large scale factor of 4.12nA/°/s.