Insight into the wave transformation mechanisms via numerical simulation of acoustic fields in Piezoelectric/Metal grating/Dielectric structures

The mechanism of SAW transformation with variation of film thickness is investigated in Piezoelectric/Metal grating/Dielectric structures via simulation of acoustic fields. By way of example, YX and 128°YX cuts of lithium niobate are considered as substrates, with Cu grating and isotropic SiO₂ as overlay. The motions, which accompany the wave propagation in the sagittal plane, are visualized, and the added contour plots show variation of shear-horizontal displacements. The transformation of the wave nature with SiO₂ thickness increasing from zero to few periods is observed for each wave propagating in the analyzed material structures. Examples of wave transformation into boundary waves and into normal modes propagating in SiO₂ film are demonstrated. The difference in the behavior of SAW modes in the grating is correlated with velocity versus film thickness dependences.