Characteristic analysis of multi-layer piezoelectric substrate for SAW filters by effective surface permittivity method

The aim of this study is to characterize the wave propagation and to figure out the phase velocity and electromechanical coupling coefficient of a multi-layer piezoelectric substrate, which is used in surface acoustic wave (SAW) filters. To successfully estimate the values of the electromechanical coupling coefficients for bulk materials (single layer) and multi-layer structures, the effective surface permittivity (ESP) method was used. In order to analyze the ESP of a single layer, the material properties, such as stiffness tensor, piezoelectric stress tensor, permittivity tensor, and mass density are determined; while calculating the ESP of a multiple layer, the material properties are selected and transferred. The simulation results agree with the experimental results with the margin of error less than 7% for quartz in single layer. In analyzing the double layer materials; that is, ZnO/Diamond and LiNbO₃/Diamond, K² number and phase velocity are obtained. For triple layers, the simulation are performed to demonstrate that ZnO/PZT/Diamond is a better substrate with 12000 m/s phase velocity and K² = 0.82. The results of this work demonstrate that numerical computations based on the chosen formalisms applied on non-piezoelectric film, diamond, are first brought out and benefit the researchers who wish to calculate surface acoustic wave properties in piezoelectric multi-layer structures.