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^{\prime}{}-{35}^{2} are attractive for quasi-shear mode FBAR and shear horizontal (SH)-type SAW devices. In 2007, our group reported k^{\prime}{}-{35}^{2}= 6.8\% for a polycrystalline ZnO film with a 23° tilt to the surface normal. Furthermore, in 2020, our group reported that Mg-substituted ZnO significantly improves thickness-extensional mode k-{t}^{2}. 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 thickness-extensional mode, quasi-shear mode electromechanical coupling coefficient k^{\prime}{}-{35}^{2} and thickness-extensional mode electromechanical coupling coefficient k^{\prime}{}-{t}^{2} 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.