Suppression mechanism of transverse-mode spurious responses in SAW resonators on a SiO2/Al/LiNbO3 structure

The transverse-mode spurious responses could be suppressed successfully by the selectively SiO₂ removal at the dummy region. This paper discusses the suppression mechanism of the transverse-mode spurious responses by the selectively SiO₂ removal technique. The SAW field distribution was analyzed for the SiO₂/Al/LiNbO₃ structure. The field analysis indicated that the selectively SiO₂ removalenhances the SAW reflection coefficient at the boundary between the interdigital and the dummy electrode regions. When the SiO₂ thickness is large, full SiO₂ removal from the dummy electrode region creates another transverse mode resonance. The laser probe observation revealed that it is due to the hybrid mode caused by the coupling of the SH SAW with the Rayleigh SAW at the lateral boundaries. It was also shown that the response can be suppressed by the partial SiO₂ removal from the dummy electrode region. This might be explained by the weakened mutual coupling between the SH and Rayleigh SAWs at the lateral boundaries. This weakening is caused by the reduction of the SAW velocity difference between the dummy electrode and IDT regions.