Change in piezoelectric boundary acoustic wave characteristics with overlay and metal grating materials

摘要

This paper describes how the characteristics of shear-horizontal type piezoelectric boundary acoustic waves (PBAWs) change with combination of different overlay and metal grating materials. It is shown that PBAWs are supported in various structures provided that highly piezoelectric material(s) are employed as structural member(s). For verification, numerical simulation of different material combinations is done. The results are in good agreement with the qualitative prediction. That is, large electromechanical coupling factor K2 is obtainable when materials having small mass densities shear modulus c44 and shear velocity VBS; and materials having extremely large shear modulus c44 are chosen, respectively, for overlay and metallic grating. When YX-LiNbO3 is assumed as a substrate, for example, the best choice seems to be SiO2 and Au for overlay and metallic grating, respectively. Although metals with extremely large ¿ and c44 such as W and Ta offer large K2, they may not be acceptable for practical PBAW applications because of their large electric resistivity.