Demonstration of Thin Film Bulk Acoustic Resonator Based on AlN/AlScN Composite Film with a Feasible Keff2

Film bulk acoustic resonators (FBARs) with a desired effective electromechanical coupling coefficient (K-eff(2)) 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 K-eff(2). 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 mu m-thick Al0.8Sc0.2N film, K-eff(2) can be twice compared with that of FBAR based on pure AlN films. For the composite films with different thickness ratios, K(eff)(2 )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.

Automated summary

This study investigates the resonant characteristics of FBARs based on AlN/AlScN composite films with different thickness ratios and finds that using Al0.8Sc0.2N composite film can result in a higher effective electromechanical coupling coefficient. The effective electromechanical coupling coefficient can be adjusted within a certain range by changing the thickness ratio of the composite film. Additionally, a filter with a specific sub-band has been successfully designed using AlN/Al0.8Sc0.2N composite film.