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/sub B//sup 2/ and X/sub c/, characterizing SSBW excitation and propagation. K/sub B//sup 2/ corresponds to the electromechanical coupling factor of surface acoustic waves (SAWs) and gives the SSBW excitation strength on the substrate surface. X/sub 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/spl deg/Y-LiTaO/sub 3/ 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/sub B//sup 2/ and X/sub c/ were determined for an SiO/sub 2/-film/36/spl deg/YX-LiTaO/sub 3/ 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 SiO/sub 2/-film.<>