Zero Group Velocity Lamb Mode Resonators on 36°-yx LiNbO3 thin Plates

Abstract

The propagation of Lamb modes along thin 36°-yx LiNbO3 plates, 100 µm thick, was theoretically and experimentally investigated. Numerical calculations and three-dimensional finite element modelling (3D-FEM) simulations were performed to find the plate thickness-to-wavelength ratios corresponding to Lamb modes with zero group velocity (ZGV). Three ZGV points were found corresponding to the first and third order symmetric modes S1 and S3, and to the second order antisymmetric Lamb mode A2. Resonators based on the ZGV-S1 mode were fabricated. To compensate for deviations from the zero-group velocity condition due to inaccuracies in the fabrication process of the resonator and/or in the simulations, the effects of short gratings on the confinement of the wave energy were explored. Two simple resonator configurations were implemented onto the LiNbO3 plate surface which consist in one interdigitated Cr/Au electrode (IDT), with and without few grounded guarding strips on each side of the IDT. The Q of the ZGV resonator with just nine-strip-gratings on both sides of the IDT resulted lager (Q = 2200) than that without reflectors (Q = 1800).