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

This study presents a high-performance, lead-free aluminum nitride (AlN) piezoelectric MEMS yaw gyroscope fabricated on a <111> single-crystal silicon layer. The device employs a wide annular resonator operating in the in-plane second-order wineglass mode at 132 kHz, enabling near-degenerate drive and sense modes with ultra-low frequency splitting. The authors co-optimize the annular geometry, piezoelectric electrode placement, and fabrication process to maximize strain-integrated piezoelectric coupling while preserving structural integrity.

A hole-free backside trench release process is used to eliminate front-side etch holes, suppressing thermoelastic damping (TED) and enhancing the mechanical quality factor. Multiphysics simulations guided the parametric optimization of the annular width, balancing resonant frequency, TED-limited Q, and transduction efficiency. The final optimized design adopts a 420 µm annular width, achieving a simulated QTED of 96,000.

Experimental testing under vacuum (~0.01 Pa) demonstrates a Q-factor of 75,000, angular random walk (ARW) of 0.34°/√h, and bias instability (BI) of 8.19°/h in open-loop operation with a native frequency split of 28–30 Hz. These performance metrics are comparable to state-of-the-art PZT-based gyroscopes, despite the lower intrinsic piezoelectric coefficient of AlN. The device uses a fully stress-aligned 16-sector electrode configuration, providing efficient excitation and high-fidelity sensing. Importantly, the lead-free AlN layer ensures RoHS compliance, offering an environmentally sustainable alternative.

In summary, the work demonstrates that careful structural and process co-design enables AlN-based MEMS gyroscopes to achieve high Q, low noise, and competitive bias stability, providing a path toward high-performance, environmentally friendly inertial sensors