Imaging with a Row-Column (RC) Addressed PMUT Array

In this paper, a row-column (RC) addressable rigid piezoelectric micromachined ultrasonic transducer (PMUT) array on SOI substrate is presented. The array consists of 50 x 20 elements spaced at a pitch of 300 μm. The PMUT membranes cavities are fabricated by backside deep reactive ion etching (DRIE). Lead Zirconate Titanate (PZT) thin film is deposited by a sol-gel process with about 1 μm thickness to act as the active piezoelectric layer. With 5 V DC bias, a single PMUT element showed a 6.7 MHz in-air frequency with a 15 nm/V sensitivity, as measured with Laser Doppler Vibrometer (LDV). A hydrophone measurement suggested a pressure response of 200 Pa/V at 2.5 cm underwater while exciting a single PMUT channel. The imaging capability of the RC PMUT array is demonstrated by using it as a 50-channel linear phased array which captured a B-mode ultrasound image of a custom-made metal wire phantom with the plane-wave compounding (PWC).