Three-dimensional finite element simulation of Love mode surface acoustic wave in layered structures including ZnO piezoelectric film and diamond substrate

Three-dimensional (3D) finite element method (FEM) was used to simulate the surface acoustic wave (SAW) propagation properties in layered structures including ZnO piezoelectric film and diamond substrate. The excitation conditions of Love mode and Rayleigh mode SAWs are discussed considering the ZnO crystal orientation and the SAW propagation direction which are specified using Euler angles (alpha, beta, gamma). The phase velocity and electromechanical coupling coefficient K-2 of Love mode SAW in the ZnO/diamond structure are provided as functions of the normalized ZnO layer thickness h(ZnO)/lambda and the Euler angles (alpha, beta, gamma). The results show that the maximum K-2 of 4.26% is reached at h(ZnO)/lambda. = 0.3 and (alpha, beta, gamma) = (0, 90, 0) for Love mode SAW; the associated phase velocity is 3436 m/s and the temperature coefficient of frequency (TCF) value is -26.5 ppm/degrees C. The TCF properties are greatly improved by adding a Si02 layer between the ZnO film and the diamond substrate. A zero TCF can be obtained when the normalized SiO2 thickness h(sio2)/lambda. is 0.25 and the h(Zno)/lambda. is 0.2, where the corresponding K-2 is 3.26% and the phase velocity is 3126 m/s.