A Photoacoustic Imaging Device Using Piezoelectric Micromachined Ultrasound Transducers (PMUTs)

A linear piezoelectric micromachined ultrasound transducer (PMUT) array was fabricated and integrated into a device for photoacoustic imaging (PAI) of tissue phantoms. The PMUT contained 65 array elements, with each element having 60 diaphragms of
$60~\mu \text{m}$
diameter and
$75~\mu \text{m}$
pitch. A lead zirconate titanate (PZT) thin film was used as the piezoelectric layer. The in-air vibration response of the PMUT array elements showed a first mode resonance between 6 and 8 MHz. Hydrophone measurements showed 16.2 kPa average peak ultrasound pressure output at 7.5 mm from one element excited with 5 V
_pp
input. A receive sensitivity of ~0.48 mV/kPa was observed for a PMUT array element with 0 dB gain. The PMUT array was bonded to a custom-printed circuit board to enable compact integration with an optical fiber bundle for PAI. A broad photoacoustic bandwidth of ~89% was observed for the photoacoustic response captured from absorbing pencil lead targets. Linear scanning of a single element of a PMUT array was performed on different tissue phantoms embedded with light-absorbing targets to successfully demonstrate B-mode PAI using PMUTs.