Influence of Coupling Between Rayleigh and SH SAWs on Rotated $Y$ -Cut LiNbO₃ to Their Propagations

This paper investigates the influence of coupling between Rayleigh and shear-horizontal (SH) surface acoustic waves (SAWs) on rotated Y-cut LiNbO ₃ to their electromechanical coupling. For the purpose, a coupling-of-mode (COM) model including the coupling between two SAWs is developed, and the coupling influences to their excitation in addition to electromechanical coupling factors are discussed. Then, its validity is confirmed by comparison of its results with the finite-element method analysis. Comparing with the conventional COM shows this extended COM model could fit the complex value area much better in the dispersion curve analysis. After that, variation of COM parameters with the device design is discussed. Then, all COM parameters are fit by polynomial equations and the procedures to find the optimal rotation angle are obtained in terms of the SH mode suppression. It indicates that the optimal angle changes rapidly at certain Cu thickness, which is due to decoupling between two SAW modes. At last, structure based on the low-cut LiNbO ₃ is discussed and the validity of this COM model is further confirmed.