Full-wave analysis of piezoelectric boundary waves propagating along metallic grating sandwiched in between two semi-infinite layers

This paper describes full-wave analysis of piezoelectric boundary acoustic waves (PBAWs) propagating along a metallic grating sandwiched in between two semi-infinite layers. In the analysis, the finite element method (FEM) is used for the grating region while the spectral domain analysis (SDA) is applied for an isotropic overlay region as well as a piezoelectric substrate region. Combination of the FEM and SDA makes the numerical analysis very fast and precise. As an example, the analysis was made on the PBAWs propagating in an SiO₂ overlay/Cu grating/rotated Y-cut LiNbO₃ structure. It is shown that both the shear-horizontal (SH) type and Rayleigh-type PBAWs are supported in the structure, and that their velocities are very close to each other. Thus spurious responses due to the Rayleigh-type PBAW should completely be suppressed for device implementation. Discussions are made in detail on the influence of Cu grating thickness, substrate rotation angle, and metallization ratio on excitation and propagation characteristics of the SH- and Rayleigh-type PBAWs.