Suppression of Transverse-mode Spurious Responses in Thin Film Lamb Wave Resonators by Bandgap Engineering

Thin film S0 mode Lamb wave resonators with reduced spurious transverse-mode responses are designed, fabricated and evaluated. The proposed solution consists of a higher velocity busbar topology which improves the waveguiding under the active part of the resonator. To suppress the spurious responses a narrow matching layer is introduced between the busbar and the active part of the resonator. 3D finite element analysis was initially used to verify the approach. Both eigen-frequency and frequency response analyses were used to reveal the physics of the waveguiding and the energy confinement effects in the proposed topology. Finally, measurements of S0 Lamb wave resonators have confirmed the efficient suppression of the spurious transverse modes. The proposed technique can successfully be employed also in S0 Lamb wave resonators with suspended edges (referred by some authors also as contour-mode resonators), while eliminating the need of tethers thus improving the heat dissipation.