High electromechanical coefficient k_t ²=19% thick ScAlN piezoelectric films for ultrasonic transducer in low frequency of 80 MHz

Ultrasonic in the frequency ranges of 20-100 MHz is not well-developed because of less applications or less suitable piezoelectric materials as shown in Table I. In a photoacoustic imaging, PVDF are usually used for ultrasonic transducers in the 10-50 MHz band. However, their electromechanical coupling coefficient k_t ² of 4% is not enough for the practical uses. To excite ultrasonic in the 20-100 MHz, 125 μm-25 μm thick piezoelectric film is required. It is difficult to fabricate such a thick piezoelectric film without a crack caused by the internal stress during the deposition. A film deposition technique can realize the piezoelectric layer on a complicated surface such as curved or concave surface, which is difficult in the case of the single crystal plate. In this study, we demonstrated high efficient 81 MHz ultrasonic generation by using 43 μm extremely thick ScAlN films.