Quasi-Shear Mode Electromechanical Coupling Coefficient of c-Axis Tilted MgZnO Thin Films

Thickness-shear mode piezoelectric thin films with high electromechanical coupling coefficient k'(2)(35) are attractive for quasi-shear mode FBAR and shear horizontal (SH)-type SAW devices. In 2007, our group reported k'(2)(35) = 6.8% for a polycrystalline ZnO film with a 23 degrees tilt to the surface normal. Furthermore, in 2020, our group reported that Mg-substituted ZnO significantly improves thickness-extensional mode kJ. In this study, we report the fabrication of c-axis tilted MgZnO films. By using Mason's equivalent circuit model including both quasi-shear mode and thicknessextensional mode, quasi-shear mode electromechanical coupling coefficient k'(2)(35) and thickness-extensional mode electromechanical coupling coefficient kV were estimated to be 5.0% and 0.97%, respectively. The resonator excites not only fundamental mode but also 2nd overtone mode because of an existence of a piezoelectrically inactive layer. Therefore, Mason's model including piezoelectrically inactive layer showed good agreement with the experimental data.