Rayleigh waves in nonpolar Al0.7Sc0.3N(112-0) films with enhanced electromechanical coupling and quality factor

This work reports on the growth of 1 µm nonpolar a-plane Al(0.7)Sc(0.3)N(1120) thin films on an r-plane sapphire Al(2)O(3)(1102) via magnetron sputter epitaxy. The electro-acoustic properties of the film structures were characterized using surface acoustic wave (SAW) resonators. Measured electrical responses were found to be strongly anisotropic in terms of the wave propagation direction. We identified a sagittal polarized Rayleigh wave mode with large coupling (𝑘^2(eff)= 3.7%), increased phase velocity (𝑣= 4825 m/s), as well as high quality factor (Q > 1000) for SAW propagation along the c-axis [0001] and normalized thicknesses ℎ/𝜆=0.2. Finite element method simulations using electro-acoustic properties of Al(0.7)Sc(0.3)N obtained from the density functional theory reproduce our experimental results.