Lamb wave resonators and resonator filters in periodical poled Z-cut LiTaO3 plate

Abstract

An electric field distribution in a top electrode plane/periodical poled (PP) plate/bottom electrode plane looks like a cross-field model (by Smith) of an interdigital transducer (IDT) to generate a surface acoustic wave (SAW). Therefore, this structure has the possibility to generate an acoustic wave. This structure generates a SAW when the plate is thick, and a plate wave when the plate is thin. Although SAW resonators and resonator filters require grating reflectors at both sides of the IDT, previously reported devices composed of PP-plate on thick substrate don't include any grating reflectors, because they don't have electrode fingers. Therefore, their frequency responses are very weak. Proposing and applying effective edge reflections on the PP-plate instead of grating reflectors, authors fabricated Lamb wave resonators and resonator filters in PP Z-LiTaO3 plates. As a result, resonators with impedance ratio of 34 dB and resonator filters with a low loss of 2.4 dB and 3 dB bandwidth of 2.2% were obtained.