Transverse Mode Suppression In The Aln Lamb Wave Resonators By "Piston Mode"

Type I Lamb wave modes exhibit a strong affinity toward multimode behavior, especially the high-transduction-efficiency modes: S-0 and S-1 mode. Apodization, the standard technique to suppress the transverse modes for IDT-excited resonators, suffers from drawbacks such as additional loss and reduction of the effective coupling coefficient (k(eff)(2)). Most Lamb wave modes in AlN show a positive slope in the dispersion branch, so that a border region of lower eigenresonance frequency is required for spurious mode suppression. Based on dispersion calculations and finite element method (FEM) simulations, we demonstrate that by changing the transducer layout, the guiding can be improved and a "piston mode" can be obtained for the type I Lamb wave modes.