Analysis of SAW properties of epitaxial ZnO films grown on R-Al2O3 substrates

ZnO thin films with a high piezoelectric coupling coefficient are widely us ed for high frequency and low loss surface acoustic wave (SAW) devices when the film is deposited on top of a high acoustic velocity substrate, such a s diamond or sapphire. The performance of these devices is critically depen dent on the quality of the ZnO films as well as of the interface between Zn O and the substrate. In this paper, we report the studies on piezoelectric properties of epitaxial (11 (2) over bar0) ZnO thin films grown on R-plane sapphire substrates using metal organic chemical vapor deposition (MOCVD) t echnique. The c-axis of the ZnO film is in-plane. The ZnO/R-AL(2)O(3) inter face is atomically sharp. SAW delay lines, aligned parallel to the c-axis, were used to characterize the surface wave velocity, coupling coefficient, and temperature coefficient of frequency as functions of film thickness to wavelength ratio (h/lambda). The acoustic wave properties of the material s ystem were calculated using Adler's matrix method, and the devices were sim ulated using the quasi-static approximation based on Green's function analy sis.