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 of tissue phantoms. The PMUT contained 65 array elements; each element having 60 diaphragms of 60 µm diameter and 75 µm 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 MHz and 8 MHz. Hydrophone measurements showed 16.2 kPa average peak ultrasound pressure output at 7.5 mm from one element excited with 5 Vpp 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 photoacoustic imaging. 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 photoacoustic imaging using PMUTs.