Propagation and Resonance Properties of Love-Type Surface Acoustic Wave on $Y$–$X$ LiTaO3 with TeO2 Thin Film

The propagation characteristics of a Love-type surface acoustic wave (SAW) on Y-cut X-propagating LiTaO3 with an amorphous tellurium dioxide (TeO2) thin film with a low phase velocity were investigated theoretically and experimentally, and an interdigital transducer (IDT) resonator using this structure was fabricated and evaluated. The K2 of the Love-type SAW on TeO2/Y–X LiTaO3 was calculated to be 6.6% at a transition thickness of 0.07λ. The insertion loss of a simple delay line was reduced by loading with TeO2 film because the bulk wave radiation in excitation and/or propagation of the LSAW was markedly suppressed. Beyond the experimental transition thickness of 0.12λ, the suppression of the bulk wave radiation was saturated. According to the propagation characteristics for IDT resonators fabricated using this structure, the admittance ratio increased and the minimum phase decreased until the TeO2 film thickness reached the experimental transition thickness. When the TeO2 film thickness was 0.12λ, such resonance properties as admittance ratio, minimum phase, and resonance quality factor of the Love-type SAW on TeO2/Al/Y–X LiTaO3 were almost equal to those for Au/Y–X LiTaO3 and were better than those for LSAW on Al/39° Y–X LiTaO3, except for the band-width ratio. Moreover, the TCD was initially decreased by loading with TeO2 film but then increased as film thickness increased.