High-Performance Film Bulk Acoustic Resonator and Filter Based on an Al_0.8Sc_0.2N Film Prepared by a Low-Temperature Staged Deposition Method

The poor crystal quality of AlScN films is a serious obstacle to the development of broadband film bulk acoustic resonator (FBAR) filters. To address this issue, a low-temperature staged deposition method was proposed, in which a single-crystalline AlN buffer layer was deposited on a silicon substrate using pulsed laser deposition (PLD) and subsequently sputtered to produce a high-quality Al0.8Sc0.2N film by physical vapor deposition (PVD). The results showed that the single-crystalline AlN buffer layer created by PLD had a low dislocation density, which was attributable to the low-temperature growth and unique benefits of PLD. Growth of the Al0.8Sc0.2N film on the single-crystalline AlN buffer layer resulted in significant improvements in crystal quality, surface roughness, and stress. The produced FBAR has a high figure of merit (FOM) of 187, a 61.2% improvement over the PVD method, owing to the higher quality of the Al0.8Sc0.2N film. At a center frequency of approximately 3.41 GHz, the designed filter had a 3-dB bandwidth of 314 MHz with a minimum insertion loss of −0.984 dB and a maximum insertion loss of −1.646 dB in the passband. This work presents a novel approach for advancing the development of high-performance FBARs and high-frequency broadband FBAR filters.