Design of Polyimide based Piezoelectric Micromachined Ultrasonic Transducer for Underwater Imaging Application

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Micromachined ultrasonic transducer has been used in many application for example non-destructive test, medical diagnostic and underwater application. One of the underwater application is underwater acoustic imaging system. Underwater acoustic imaging system needs a transducer with wide bandwidth to perform high resolution image. In previous paper, Capacitance Micromachined Ultrasonic Transducer (CMUT) and Piezoelectric Micromachined Ultrasonic Transducer (PMUT) was studied in acoustic imaging. In this paper, PMUT was designed and studied their receiving sensitivity. The target operating frequency is in between 300 kHz to 700 kHz for underwater acoustic imaging. Simulation using Comsol 5.0 was used to determine the PVDF thickness, pitch element and substrate's material, Polyimide and Silicon for desired frequency and high receiving sensitivity. In this paper, Polyimide was used as substrate rather than previous paper was used Silicon as substrate. The positive and ground electrode with lateral structure was fabricated onto Polyimide substrate. The polyvinylidene difluoride, (PVDF) used as sensing element was placed on top of electrodes to obtain polarization and with lateral structure of electrodes, PMUT will induced the d33 mode polarization. The Pulse-echo method was used in experiments to determine the receiving sensitivity. PMUT was obtained receiving sensitivity at -80.84 dB rev 1V/uPa with resonance frequency, 525 kHz. Low frequency for PMUT was obtained at 450 kHz and high frequency for PMUT was obtained at 650 kHz. Bandwidth for PMUT is 38.1%.