A Hermetically-Sealed 2.9MHz $\mathrm{N}=3$ Disk BAW Gyroscope with Sub-Degree-Per-Hour Bias Instability

This paper reports on a wafer-level-packaged (WLP) capacitive bulk-acoustic-wave (BAW) gyroscope using a near-solid disk resonator with a bias instability (BI) of 0.85°/h and angle random walk (ARW) of 0.06°/√h, demonstrating the highest performance reported to-date for a megahertz-frequency resonator gyroscope. The design is acoustically decoupled from the substrate with and high translational stiffness for high robustness against linear vibrations and substrate stress variations. High frequency of the gyroscope reduces air damping, allowing for a thermoelastic damping (TED) limited high Q of 165,000 in 1-10Torr package created by getter-free wafer bonding. Stable mode-matched operation is achieved using DC voltages below 15V with optimized electrode designs, offering an open-loop bandwidth of ~10Hz and low uncompensated bias of ~1.4°/s. A regular 925μm-thick and a thinned-down 450μm-thick die created by substrate grinding are characterized across temperature, showing the same behaviors where frequencies and Qs of the n=3 modes remain closely matched, verifying the temperature robustness and stress immunity of the design.