Thin film stack transducer for simultaneous generation of longitudinal and shear waves at same frequency

It is difficult to generate longitudinal and shear bulk waves simultaneously at same frequency. In this study, we propose new film stack transducer structure consisting of two layers of c-axis 23°-tilted ZnO films. The upper layer and lower layer in the stack have same thicknesses, and the c-axis tilt direction in the both layers are symmetric with respect to the film surface normal. This film stack transducers were fabricated on silica glass substrate by using RF magnetron sputtering technique. Crystallographic properties of the transducer were determined by XRD pole figure analysis. Detailed conversion loss characteristics of the transducer were also discussed. Simultaneous generation of both waves at same frequency was then experimentally demonstrated in the VHF range. We also included thin film fabrication technique for obtaining two layers of c-axis-tilted ZnO films with good crystalline orientation.