Influence of AlN/ScAlN piezoelectric multilayer on the electromechanical coupling of FBAR

Based on the truth, the electromechanical coupling in the top and bottom Mo electrodes caped AlN can be enhanced by replacing the Sc doped AlN (ScAlN). We tune the electromechanical coupling (k2t) of the film bulk acoustic resonator (FBAR) by varying the thickness ratio in AlN and ScAlN piezoelectric multilayer. We found that the electromechanical coupling of the piezoelectric-multilayer FBAR is area size dependent. In order to investigate the multilayer electromechanical coupling in various thickness ratios, we propose a theory to simulate both materials piezoelectric constants e varying with the area size. In various thickness ratios, the effective piezoelectric constant of the AlN layer increases with the area of FBAR, but the ScAlN layer exhibits an optimal piezoelectric constant in increasing area. Eventually, we realized that increasing the significant piezoelectric constant is inevitable for reducing the size of FBARs.