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Broadband piezoelectric micromachined ultrasonic transducers based on dual resonance modes

Piezoelectric micromachined ultrasonic transducers (PMUTs) have the potential for broad bandwidth, thus enabling high resolution imaging. However, previous PMUTs had fractional bandwidths of only ~50% or smaller because of the thick multilayer PMUT structure. Here, we demonstrate broadband PZT PMUTs that achieve a 97% fractional bandwidth by utilizing a thinner structure excited at two adjacent mechanical vibration modes. PMUTs were fabricated and characterized in the mechanical, electrical and acoustic domains, and a 30 μm × 200 μm ribbon PMUT demonstrates a large displacement sensitivity of 500 nm/V in air and pressure response of 0.3 kPa/V in fluid, equivalent to 13.6 kPa/V average pressure on the PMUT surface, measured 1.4 mm away from the PMUT.