Piezoelectric Micromachined Ultrasonic Transducer With Superior Acoustic Outputs for Pulse-Echo Imaging Application

This article proposes a novel structured aluminum nitrate (AlN) thin film based piezoelectric micromachined ultrasonic transducer (PMUT) with superior ultrasonic performances that can directly be applied for pulse-echo imaging. The bottom electrode of the PMUT is thickened and serves both as the electrical layer and supporting layer. Large numbers of elements are parallelly connected to form square arrays. This method can not only improve the acoustic output but also reduce the total impedance. The ultrasonic transmitting, receiving behaviors of our developed 6.37 MHz (in air) PMUT array containing vibration elements of horizontal x vertical = 20 × 20 are investigated. It can generate superior acoustic output with a normalized value of 1.71 kPa·V
^-1
·mm
^-2
at 3.6 mm away in deionized water media. Thanks to the lager acoustic output and reduced electrical impedance, ultrasonic pulse-echo imaging with our developed PMUT array is realized only with the assistance of a switch to separate the ultrasound transmission and reception process. We have mechanically scanned a mark in steel plate and generate a B-mode image with great accuracy using the recorded pulse-echo signals. These demonstrate the superior acoustic behavior of our developed PMUT array and open an avenue to the development of portable ultrasonic imaging devices.