Highly sensitive piezoelectric micromachined ultrasonic transducer (pMUT) operated in air

Abstract

Piezoelectric micromachined ultrasonic transducer (pMUT) gains increasing interests from researchers. It overcomes the inherent shortcomings of conventional bulk ultrasonic transducers such as acoustic impedance mismatching. In addition, pMUT does not require the extremely large input voltage as capacitive micromachined ultrasonic transducer (cMUT), which is potential to be integrated into portable electronics. The lead zirconate titanate (PZT) based pMUT has the best performance. Leveraging on our newly developed pulse poling process, the morphotropic phase boundary composition PZT (MPB-PZT) thin film is of high piezoelectric constant (d31=105pm/V) and low dielectric loss (~0.06). Benefited from such high performance PZT thin film and optimized design, the fabricated pMUT (500×300μm) achieves a displacement sensitivity of 807nm/V at its resonant frequency (482kHz) without DC offset. Compared to previously reported PZT pMUTs, even the dimension is much smaller; the sensitivity is still superior to them. The in-air transmitting performance is evaluated as well. A single pMUT element is able to generate 63.7dB sound pressure level (SPL) at 10 mm in air with only 2V input. The low input voltage not only provides low power consumption, but also prevents the unwanted PZT repolarization. The proposed highly sensitive pMUT shows its promise for integration with portable electronics.