High Electromechanical Coupling Radial Extension Mode Resonators Realized in Al0.7Sc0.3N

Abstract

This work reports aluminum scandium nitride (Al $_{\mathrm {1-x}}$ ScxN/AlScN) (x =0.3/Al0.7Sc0.3N) Lamb wave resonators (LWR) operating in length extensional (LE), width extensional (WE), and radial extensional (RE) modes. COMSOL Multiphysics and experimental measurements show that the RE mode achieves a much higher electromechanical coupling, $k_{t}^{2}$ , when compared to the more traditionally utilized LE and WE modes. The higher ${k} _{t}^{2}$ is due to the constructive addition of the $d_{31}$ and $d_{32}$ piezoelectric coefficients due to the RE mode shape. Experimentally, the RE mode resonator achieved a $k_{t}^{2}$ of 14.1%, which was much larger than the $k_{t}^{2}$ of 9.1% and 4.8% measured for the WE and LE mode devices fabricated on the same wafer. The RE mode achieves a high $Q_{p}$ of 1302 measured in air yielding a figure-of-merit (FOM $= k_{t}^{2}Q_{p}$ ) of 157. Based on the high $k_{t}^{2}$ and FOM, Al0.7Sc0.3N-based RE resonators show potential for applications in piezoelectric microelectromechanical filters and oscillators. [2024-0231]