Fabrication and characterization of row-column addressed pMUT array with monocrystalline PZT thin film toward creating ultrasonic imager

In this study, we fabricated a row-column addressed 2-dimensional piezoelectric micromachined ultrasonic transducer (pMUT) array based on the monocrystalline Pb(Zr, Ti)O₃ (Mono PZT)-based thin film, and demonstrated its application as the ultrasound imager. At first, we optimized the island-shaped design as an individual element, and then developed the fabrication process based on the control of the edge shape of an insulative polymer pattern. As a result, the hexagonally arranged arrays with 372 elements at the maximum were fabricated successfully, of which the diameter and pitch were 70 µm and 120 µm, respectively. The resonance frequency, displacement sensitivity, and quality factor in air measured approximately 5.4 MHz, 175 nm/V and 175, respectively. This array exhibited low crosstalk. The actuation of the unaddressed element was less than 10 % of that of the addressed one. In addition, the deviations on the resonance frequencies and displacement sensitivities were as small as only 2 % and 15 %, respectively. Then, the basic acoustic performance in a medium FC-70 was evaluated by using the minimum unit array composed of 5 columns. Also, the transmitting beamforming of a focused ultrasonic burst wave was done by applying driving voltages with a time delay. Finally, an ultrasonic imaging for a metallic object was demonstrated by mechanically scanning the object.