Improved pulse-echo imaging performance for flexure-mode pMUT arrays

Piezoelectric micromachined ultrasound transducers (pMUTs) are potential candidates for catheter-based ultrasound phased arrays. pMUTs consist of lead zirconate titanate (PZT) thin film membranes formed on silicon substrates and are operated in flexure mode by driving the PZT film above its coercive field to induce flextensional motion. The fundamental operation of pMUT devices has been demonstrated; however, pulse-echo imaging has been limited to date. The objective of this work was to optimize transducer design for improved pulse-echo imaging performance. Flexure mode operation was optimized by (1) increasing transmit voltage above the PZT coercive field to induce ferroelectric domain switching, and (2) using partial cycle transmit pulses to increase the polarization in the PZT thin film and increase receive signal. As a result, pulse-echo images of tissue were obtained. 1-D arrays operating at 5 MHz were capable of resolving targets in a commercial tissue phantom as well as human anatomy. Real-time 3-D imaging was also demonstrated using 2-D arrays at 5 and 12.5 MHz. These results suggest that pMUTs have sufficient performance for application in ultrasound imaging with frequency range suitable for catheter-based phased-array transducers.