Theoretical and Experimental Study of High‐Electromechanical‐Coupling Surface Acoustic Wave Resonators Based on A‐Plane (112¯0)$\left(\right. 11 \overset{\cdot}{2} 0 \left.\right)$ Al_0.56Sc_0.44N Films

Abstract

Herein, a high‐quality Al0.56Sc0.44N piezoelectric thin‐film‐based surface acoustic wave (SAW) resonator is developed. The Al0.56Sc0.44N is deposited on r‐plane Al2O3 substrate by reactive magnetron sputtering. X‐ray diffraction (XRD) spectroscopy shows that the grown Al0.56Sc0.44N films are single‐phased and a‐plane oriented. The full width at half maximum of the XRD rocking curve is only 0.4°, which is smaller than most of the reported values. The effects of normalized thickness of the piezoelectric layer, electrode materials, and thickness on acoustic properties of the SAW resonators are investigated through the 3D finite‐element method equipped with the hierarchical cascading technique. A monotonically decreasing resonant frequency can be obtained with the mass loading of both the electrode metals. For the devices with a Pt electrode, it is observed that the electromechanical coupling coefficient () exhibits a nonlinear characteristic of first increasing and then decreasing with the increase of electrode thickness. SAW resonators with a nonpolar a‐plane Al0.56Sc0.44N thin films are fabricated, showing an exceptionally high of 4.6%. This result demonstrates a significant potential of AlScN films with the a‐plane orientation in radio frequency application.