Delta function model analysis of SSBW spurious response in SAW devices

The authors propose a delta function model analysis of surface skimming bulk wave (SSBW) response by defining two physical parameters, K_B² and X_c, characterizing SSBW excitation and propagation. K_B² corresponds to the electromechanical coupling factor of surface acoustic waves (SAWs) and gives the SSBW excitation strength on the substrate surface. X_c is the critical propagation length representing how SSBW amplitudes decay with propagation. The analysis was applied to the characterization of a SAW TV-IF (intermediate frequency) filter fabricated on an X-112°Y-LiTaO₃ substrate. The results obtained by the analysis were in good agreement with experiments, and clearly showed how the SSBW response affects the filter performance. The values of K_B² and X_c were determined for an SiO₂-film/36°YX-LiTaO₃ substrate which may be used for SAW devices, and its SSBW spurious response level was estimated. It was theoretically predicted and experimentally confirmed that the SSBW excitation stength and SSBW spurious response are considerably reduced by properly choosing the thickness of the SiO₂ -film