ScAlN Thick Film Concave Lens Transducer in the 20-90 MHz

Because they can be easy to deposit on the non-planar structures by sputtering technology, ScAlN films are attractive for fabricating focus type transducers. They possess high electromechanical coupling coefficient $k_{\text{t}}^2$ of 25%, which is comparable with the $k_{\text{t}}^2$ of thin bulk plate PZT. In this study, we present three types of ScAlN thick film transducers deposited on a concave lens. The $k_{\text{t}}^2$ values of two types of transducers were estimated to be 24% and 8.1%, respectively. We conducted experiments with longitudinal waves propagating in water medium and confirmed the excitation and reception of longitudinal waves in the bandwidth of 20-90 MHz and 10-80 MHz. Furthermore, we found that the lens-type free-standing structure transducer excites and receives longitudinal waves in a narrow bandwidth of 84 MHz.