Wide Band BAW Filter Based on Single-Crystalline LiNbO₃ Thin Film With Insulating Bragg Reflector

Bulk acoustic wave (BAW) filter with large bandwidth is an urgent need in fifth-generation (5G) communication systems. In the present work, 43° Y-cut lithium niobate (LN) single-crystal film is prepared on multilayer oxide film, and bulk acoustic filter with oxide Bragg reflector (BR) is successfully achieved. The design method of the filter and the fabrication process are presented. Atomic force microscope (AFM) and scanning electron microscope (SEM) are used to characterize the quality of thin films. The results demonstrate the feasibility of transferring single-crystal film onto multilayer oxide, which is efficient for the confinement of acoustic energy. The resonator has effective electromechanical coupling coefficient of 14.6% and figure of merit (FOM) of 32.94. The filter with a compact size of 600
$\mu \text{m}\,\,\times 400\,\,\mu \text{m}$
has a relative bandwidth of 10.3% at a center frequency of 3.128 GHz, which is promising for the application of 5G systems.