Lateral Field Excitation of Thickness Longitudinal Mode and Shear Mode With ZnO Based on Solidly Mounted Resonator

Coplanar electrodes are used with the c-axis-oriented piezoelectric film to form the pure longitudinal mode and the pure shear mode solidly mounted resonators (SMRs). Aluminum and molybdenum are used as electrode materials to achieve different excitation pure shear mode and pure longitudinal mode. There is no need to make a bottom electrode or etch the piezoelectric layer, which simplifies the manufacturing and makes the structure stable. Furthermore, the cycle time of the process is significantly reduced. However, the control of the thickness of the Bragg reflectors, roughness control, and electrode photolithography are all challenging aspects of SMR manufacturing. In this study, ZnO piezoelectric film, which has a good electromechanical coupling factor and low transmission loss, was used as the c-axis-oriented piezoelectric film. An RF magnetron sputtering system was used to sputter a seed layer to encourage the growth of the zinc-oxide piezoelectric film and improve the c-axis orientation. The pure longitudinal mode and pure shear mode resonance signals were excited using the room temperature positive axis method. The quality factor and electromechanical coupling coefficient of the pure shear mode were 398% and 4.43%, respectively. The quality factor and electromechanical coupling coefficient of the pure longitudinal mode were 171% and 3.83%, respectively. Stability and feature recognition were accomplished in the pure longitudinal mode and the pure shear mode via a simplified and accelerated manufacturing process using electrodes with the same specifications.