Design and Characterization of High-Density Ultrasonic Transducer Array

This paper is conducted to design, fabricate, and characterize a novel high-density large-scale ultrasonic transducer, which is based on a <inline-formula> <tex-math notation="LaTeX">$64\times 4$ </tex-math></inline-formula> array of 0.753 MHz piezoelectric micromachined ultrasonic transducer (pMUT) with <inline-formula> <tex-math notation="LaTeX">$100~\mu \text{m}$ </tex-math></inline-formula> size and <inline-formula> <tex-math notation="LaTeX">$120~\mu \text{m}$ </tex-math></inline-formula> pitch. The fill factor of the array is 69.4%, which is higher than the other arrays in reports. Sol-gel method with layer-by-layer annealing is used to fabricate isolated piezoelectric lead zirconate titanate elements into a piezoelectric layer. The membrane of the pMUT is released by backside deep silicon etching. The impedance-frequency spectrum of a <inline-formula> <tex-math notation="LaTeX">$4\times 5$ </tex-math></inline-formula> subarray of the transducers is characterized by HP 4294A impedance phase analyzer. As a result, the mean value resonant frequency is 0.753 MHz, in reasonable agreement with COMSOL Multiphysics simulation results. And the array shows good uniformity in resonant frequency. The equivalent circuit of the transducer is extracted from the spectrum and the admittance circle deduced from the circuit is in accordance with experimental data. The results show that the present array has a good application prospect on ultrasonic imaging.