ABSTRACT
Film bulk acoustic resonators (FBARs) with a desired effective electromechanical coupling coefficient (Keff2) 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 Keff2. 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 Al0.8Sc0.2N film, Keff2 can be twice compared with that of FBAR based on pure AlN films. For the composite films with different thickness ratios, Keff2 can be adjusted in a relatively wide range. In this case, a filter with the specific N77 sub-band is demonstrated using AlN/Al0.8Sc0.2N composite film, which verifies the enormous potential for AlN/AlScN composite film in design filters.
