Surface-bulk hybrid mode in 36°-rotated YX cut of lithium tantalate with periodic metal grating

Abstract

We report on a surface-bulk hybrid acoustic mode, which exists within a limited frequency interval in some piezoelectric substrates within a periodic metal grating. These hybrid modes result from the coupling between a bulk wave and a counter-propagating surface (or leaky) wave. An example of such a hybrid mode, which propagates in 36°-YX cut of lithium tantalate, is described. The hybrid mode gives rise to an additional branch of dispersion relation. The Bragg reflection stop band occurs due to phase match between surface and bulk waves. The lower edge of this stop band manifests itself by a resonance of harmonic admittance, being a reason of undesired resonances in resonator filters.

Analysis of bulk wave effect on harmonic admittance of periodic grating

“…Recently, it was found that in some substrates SSBW builds a surface-bulk hybrid mode (SBH) with SAW or leaky wave [1][2]. It results in parasitic resonances and general deterioration of SAW filter performance.…”