Development of an air-coupled piezoelectric micromachined ultrasonic transducer using sol-gel PZT thin film for fast-prototyping

This study demonstrated the first air-coupled pMUT using sol-gel PZT thin film that could deliver ultrasonic waves to mid-air. First, the deposition conditions for making PZT thin film with high remanent polarization were determined. Then, air-coupled pMUTs with resonance frequencies close to 40 kHz were designed using the circular plate model. According to the design, pMUTs with radii measuring 600 μm to 775 μm were fabricated to evaluate the acoustic output pressure. Among these, the pMUT with the 725 μm radius achieved a maximum sound pressure output of 4.42 Pa at 3 cm above when driven with 10 Vpp, and the resonance frequency was 40.48 kHz. Finally, the output pressure of a phased array consisting of sol-gel PZT-based pMUTs with a 725 μm radius was calculated using the k-Wave toolbox. The output pressure of the 11 × 11 pMUT array reached 365.62 Pa when focused at 3 cm above it. This result revealed that the output pressure of the proposed pMUT array could fulfill the requirement for most mid-air ultrasound applications.