Theoretical and experimental study of high electromechanical coupling SAW resonators based on a-plane ( 11 2 ¯ 0 ) Al0.56Sc0.44N films

In this work, a high-quality Al_0.56Sc_0.44N piezoelectric thin film-based surface acoustic wave (SAW) resonator was developed. The Al_0.56Sc_0.44N was deposited on a r-plane Al₂O₃ substrate by reactive magnetron sputtering. X-ray diffraction (XRD) spectroscopy showed that the grown Al_0.56Sc_0.44N films are single-phased and a-plane oriented. The FWHM 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 were 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 Al_0.56Sc_0.44N thin films were fabricated, showing an exceptionally high of 4.6%. This result demonstrates a significant potential of AlScN films with the a-plane orientation in RF application.