Bandwidth Extension Technique of Piezoelectric Micromachined Ultrasonic Transducers for Air Coupled Applications

This paper presents a stiffness hardening-based excitation method for a PZT-based Piezoelectric Micromachined Ultrasonic Transducers (PMUTs). And its large bandwidth performance was firstly verified in acoustic calibration. The PMUT chips are fabricated with a central resonant frequency of 173 and 655 kHz for the first and second vibration modes, respectively. According to the mechanical and acoustic calibration, the proposed PMUT cell with optimized electrodes design achieved a fractional bandwidth (FBW) of 21% and 5.4% for the 1st and 2nd vibration mode, respectively, in air-coupled working condition, with an actuation voltage of 2 V AC and a 15 V DC bias. By this means, the air-coupled working bandwidth of the device was increased up to 12 times larger than the traditional linear excitation method. This presents a promising way for the application of air-coupled ultrasonic data transmission.