SOI wafer+Design, Modeling, and Fabrication of a High-Q AlN Annular Gyroscope with Sub-10◦ /h Bias Instability

This study presents a high-performance piezoelectric MEMS yaw gyroscope based on lead-free aluminum nitride (AlN), fabricated on a 〈111〉 single-crystal silicon device layer. The gyroscope features a wide annular resonator operating in the second-order in-plane wineglass mode at 132 kHz, achieving a mechanical quality factor (Q) of 75,000—the highest reported among silicon-based piezoelectric gyroscopes.

Key innovations include:

1. Geometry and Mode Optimization: Analytical modeling links output charge to area-integrated in-plane stress under vibration. The annular width is optimized to enhance both the mechanical Q-factor and piezoelectric transduction efficiency. A 16-sector electrode layout aligns with the stress distribution to prevent charge cancellation.

2. Backside Trench Fabrication: The device is fabricated without front-side release holes, preserving structural continuity and minimizing thermoelastic damping (TED), a primary source of intrinsic loss in MEMS resonators.

3. Multiphysics Simulation: Finite element analysis evaluates the interplay between structural geometry, TED-limited Q, and piezoelectric transduction. Parametric sweeps of annular width indicate that an optimal width of 420 μm balances high Q, strong electromechanical coupling, and manageable resonance frequency.

4. Experimental Validation: The gyroscope is characterized under vacuum (~0.01 Pa), yielding a resonant frequency of ~132 kHz with a 28 Hz frequency split. Open-loop measurements show an angular random walk (ARW) of 0.34°/√h and bias instability of 8.19°/h. These metrics rival state-of-the-art lead-based PZT devices while using an environmentally friendly, RoHS-compliant AlN material.

Overall, the study demonstrates that careful co-design of resonator geometry, electrode placement, and fabrication process enables high-Q, lead-free piezoelectric MEMS gyroscopes with performance comparable to traditional PZT-based gyros, providing a sustainable pathway for high-precision inertial sensing applications.