Demonstration of MHz piezoelectric micromachined ultrasonic transducers array and its potential application for biomedical treatment

Abstract

In this paper, we successfully developed the 24 × 31 piezoelectric micromachined ultrasound transducers (PMUTs) array with 8 inch CMOS compatible processes. Scandium aluminum nitride (ScxAl1−xN) thin film (x = 20%) was used as the piezoelectric material. The PMUTs array was fabricated on 8-inch cavity silicon-on-insulator (CSOI) wafers with the device silicon layer thickness of only 3um and a cavity pitch of 59 μm. The wafer-level electrical test was conducted using inline auto-prober and the yield rate > 90% was achieved across the 8-inch wafer. The following acoustic test on our PMUTs array (1.5 mm × 2.0 mm) indicated the transmit sensitivity of 18.4 kPa/V @ 10 mm @ 11.6 MHz in oil with −3 dB bandwidth of 2.3 MHz. In order to validate the potential of using PMUTs array for biomedical treatments, subsequent ultrasonic heating experiments were carried out on a silicone block. A temperature rise of 4 ℃ was achievable in about 50 seconds. These results demonstrate that the potential of using PMUTs array as a disposable biomedical device in many therapeutic applications, for example, a treatment for dry eye disease.