BAW Resonator with an Optimized SiO/TaO Reflector for 5G Applications.

In the present work, a lithium niobate (LN) 43°Y cut LN film is transferred onto a substrate with 11 layers of SiO/TaO and solidly mounted resonators with a reflector are successfully fabricated with the multilayer structure. The design method and fabrication process are demonstrated. The finite element model and the Mason model are used. Scanning electron microscopy and atomic force microscopy are used to characterize film quality. An optimized design of a Bragg reflector to suppress the leakage of acoustic energy by thickness shear mode is proven to be effective. The influence of the reflector on parasitic modes and filter out-of-band suppression is analyzed. The resonator for 3.5 GHz shows an effective electromechanical coupling coefficient of 17.9%, and the figure of merit is 40.4, which is suitable for band pass filter on the N78 band with high rejection.