Photoacoustic Imaging Based on Broadened Bandwidth Aluminum Nitride Piezoelectric Micromachined Ultrasound Transducers

This letter reports broadened bandwidth aluminum nitride (AlN) piezoelectric micromachined ultrasound transducers (BB-PMUT) for photoacoustic imaging (PAI). PMUT based on microelectromechanical systems (MEMS) technology has gained significant attention for PA endoscopic imaging inside colorectal and even blood vessels due to its miniature size, high sensitivity, and versatility. Broadened bandwidth, resulting from variable membrane cavity size during the fabrication process, provides benefits to imaging spatial resolution improvement. Moreover, AlN thin film is a nontoxic material, which makes it harmless for biomedical applications with potential of complementary metal-oxide semiconductor (CMOS) MEMS integration. In this letter, a BB-PMUT is designed and fabricated. The vibration modes, impedance, and bandwidth are analyzed. The BB-PMUT provides a wider fractional bandwidth (65%) for signal detection, which significantly increases the resolution compared with traditional single frequency PMUT design. We have conducted experimental validation on an agar sample to present the sensor's performance in improving axial resolution.