Demonstration of Thin Film Bulk Acoustic Resonator Based on AlN/AlScN Composite Film with a Feasible [Formula: see text]

Film bulk acoustic resonators (FBARs) with a desired effective electromechanical coupling coefficient ([Formula: see text]) are essential for designing filter devices. Using AlN/AlScN composite film with the adjustable thickness ratio can be a feasible approach to obtain the required [Formula: see text]. In this work, we research the resonant characteristics of FBARs based on AlN/AlScN composite films with different thickness ratios by finite element method and fabricate FBAR devices in a micro-electromechanical systems process. Benefiting from the large piezoelectric constants, with a 1 μm-thick Al(0.8)Sc(0.2)N film, [Formula: see text] can be twice compared with that of FBAR based on pure AlN films. For the composite films with different thickness ratios, [Formula: see text] can be adjusted in a relatively wide range. In this case, a filter with the specific N77 sub-band is demonstrated using AlN/Al(0.8)Sc(0.2)N composite film, which verifies the enormous potential for AlN/AlScN composite film in design filters.