Surface Acoustic Waves Propagation in Epitaxial ZnO/α-Al2O3 Thin Film

In this work, we report the studies on piezoelectric properties of epitaxial ZnO thin films grown on R-Al2O3 and C-Al2O3 substrates using plasma-assisted molecular beam epitaxy (MBE). The resulting relationships are found with phi-scans and X-ray diffraction. The epitaxial relationship for ZnO films on R-Al2O3 and C-Al2O3 substrates are found to be (11 (2) over bar0)[0001](ZnO)//(01 (1) over bar2)[01 (1) over bar2](R-Al2O3) and (0001)[10 (1) over bar0](ZnO)//(0001)[2 (11) over bar0]Al2O3, respectively Appropriate dispersion curves relative to Rayleigh waves, for both configurations ZnO/R-Al2O3 and ZnO/C-Al2O3 have been recorded in the frequency range up to 200 MHz utilizing laser ultrasonic equipment. Surface acoustic wave (SAW) propagation in piezoelectric media is basically achieved by the use of the ordinary differential equations method ODE, the generalized stiffness matrix method GSMM and Green's function. These methods are reformulated with respect to the existing decoupling between the sagittal-plane displacement and the transverse displacement with respect to the electric potential. SAW properties, including dispersion curves and electromechanical coupling factor, are characterized. The cut-off velocity of the higher Rayleigh mode for both configurations is different from the corresponding transverse bulk wave. The adopted elastic constants during numerical simulations are obtained from the literature. The positive sign of the elastic coefficient C-14 of sapphire has been adjusted on the basis of ultrasonic measurements. The obtained results set guidelines for the design of high-frequency and low-loss SAW devices.