AlScN Multilayer SAW Resonators Achieving K2eff > 4% in Sezawa Mode With Au Bonding Layer

This work proposed AlScN-based surface acoustic wave (SAW) piezoelectric resonators using AlScN/Mo/Au/SiO2/Si multilayer structure. The SAW mode characteristics were analyzed by finite element modeling (FEM) simulation, and the key role of the Au layer in the Sezawa mode excitation frequency and coupling coefficient was verified. By using bonding and laser lift-off process, AlScN-based multilayer SAW resonators were fabricated. Due to the excellent crystallinity of Al0.74Sc0.26N film (X-ray diffraction (XRD) full width at half maximum (FWHM) <1°) and the good matching of multilayer structure, an effective electromechanical coupling coefficient ( $K^{{2}}_{\text {eff}}$ ) of more than 4% was achieved on Si substrate, revealing the potential of such a multilayer film structure to sensing and conversion.