Wideband multimode transducer consisting of c-axis tilted ZnO/c-axis normal ZnO multilayer

Wideband ultrasonic transducers are required for acoustic imaging and nondestructive evaluation. In this study, we have fabricated transducer consisting of c-axis tilted ZnO/c-axis normal ZnO multilayer on the Au(111)/Ti/silica glass substrate. We have investigated the crystalline orientations and frequency characteristics of the multilayer transducer. An X-ray diffraction analysis and a scanning electron microscopy analysis of the transducer revealed that the c-axis normal ZnO layer was grown on the Au(111) layer during the initial stage of ZnO layer deposition. As ZnO grain growth proceeded, c-axis normal growth change to the c-axis tilted ZnO layer growth. This multilayer transducer excited secondovertone modes of longitudinal and shear waves as well as the fundamental mode in the UHF range. Therefore, the frequency bandwidth of the multilayer transducer was broader than that of a single layer transducer consisting of a c-axis tilted ZnO layer.