Thick ScAlN film for high efficient ultrasonic transducer in low frequency of 81 MHz

Large piezoelectricity in 43% Sc doped ScAlN thin film has been recently reported. The thickness extensional mode resonant frequency, where ultrasonic generation efficiency become large, is inversely proportional to the thickness of films. Bulk ScAlN thick plates are attractive for the low frequency and high power ultrasonic applications such as actuators and medical ultrasonics because ScAlN possess lower mechanical and dielectric losses compared with well-used PZT. The thick ScAlN films, however, has not been reported. The electromechanical coupling coefficient kt2 was determined to be 19% using the thickness extensional mode at 81 MHz. This frequency is extremely low compared to well-reported ScAlN thin films in the GHz ranges.