High Figure of Merit 4.5 GHz Solidly Mounted Resonator Fabricated Using High-Quality Al₀.₈Sc₀.₂N Films

How to simultaneously achieve a high effective electromechanical coupling coefficient and a high Q value for solidly mounted resonator (SMR) has become a key technical problem in filter applications. In this study, a new process flow for SMR devices using a wafer bonding technology is proposed. Based on this method, high-quality Al0.8 Sc0.2 N piezoelectric film grown on the metal-organic chemical vapor deposition (MOCVD) AlN buffer layer was successfully applied to fabricate SMR. A 4.5 GHz SMR resonator was demonstrated with an effective electromechanical coupling coefficient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$({k}_{\textit {eff}}^{{2}})$ </tex-math></inline-formula> of 12.27%, a Qp of 1009, and the figure of merit (FOM) up to 123. The better performance originated from the high-quality piezoelectric films enable SMR to be more widely used in various radio-frequency fields.