Impact of Coupling Between Multiple SAW Modes on Piston Mode Operation of SAW Resonators

This paper investigates piston mode operation (PMO) when two kinds of surface acoustic waves (SAWs) exist and are coupled to each other. The extended thin plate model is used for the analysis. First, a PMO condition is derived in a closed form. It is verified that PMO is possible without adding phase shifters by the use of two SAW coupling. It is also shown that this operation offers suppression of the transverse modes for a wider frequency range than the conventional PMO. Then, parameters defined in the model are extracted for various SiO
₂
-overlay/Al-grating/128° YX-LiNbO
₃
substrate structures, and the structure satisfying the PMO condition is designed. Finally, the structure is also analyzed using the 3-D finite element method. The result agrees well with that calculated by the extended thin plate model.