Flexible PZT-based Row-Column Addressed 2D PMUT Array

This paper reports a 30×12 row-column (RC) addressed flexible piezoelectric micromachined ultrasound transducer (PMUT) array with a top-down fabrication process. The fabrication uses a temporary carrier wafer from which the array device is released by deep reactive ion etching (DRIE). About 0.8 μm thick sol-gel processed Lead Zirconate Titanate (PZT) thin film acts as the active piezoelectric. The flexible PMUT membrane includes the PZT film and a 14 μm polyimide as a passive layer. A sidewall made of polyimide measuring 21 μm in thickness with a cavity of 100 μm in diameter, is realized by reactive ion etching (RIE). Laser Doppler Vibrometer (LDV) characterization of the PMUT indicates 2.7 megahertz (MHz) and 2.1 MHz as the resonance frequency in-air and underwater, respectively. Excitation of a single PMUT element coupled with 5 V direct current (DC) bias results in 1.2 nm/V sensitivity in-air whereas when the same is excited along with 10 V DC bias, a pressure response of 40 Pa/V at 1 cm is measured underwater using a hydrophone. The presented results under bending to an 8 mm bending radius show the potential for wearable applications in shallow-depth regions subject to further optimization.