X-Band Bulk Acoustic Wave Resonators With High Figure of Merit Based on Al₀.₈Sc₀.₂N

Bulk Acoustic Wave (BAW) resonators encounter two significant challenges in the super high frequency (SHF) band. Firstly, the thicknesses of the piezoelectric layer and electrodes within the resonator are markedly reduced. This dimensional constraint results in a diminished electromechanical coupling coefficient (Kt2). Secondly, the quality factor (Q) of the resonator deteriorates at SHF frequencies. The Kt2 can be enhanced through Sc doping. However, the introduction of Sc can degrade the quality of the piezoelectric layer material. In this study, Metal-Organic Chemical Vapor Deposition (MOCVD) is employed to deposit an AlN buffer layer, which is subsequently augmented using Physical Vapor Deposition (PVD) to achieve Al0.8Sc0.2N with exceptionally high crystalline quality. Utilizing a 6-inch single-crystalline AlN Bulk Acoustic Resonator (SABAR) fabrication process, we successfully develop an X-band BAW resonator. The resonator exhibits a Kt2 of 6.84%, a quality factor (Q) of 1245, and a figure of merit (FOM) of 84, demonstrating a significant advancement in the performance metrics of BAW resonators in the X band.