Fabrication Process and Performance Analysis of AlN based Piezoelectric Micromachined Ultrasonic Transducer with a Suspended Structure

This paper presents a novel process flow of AlN based ultrasonic transducer with fully suspended structure and TSV 3D integration. In order to obtain the greater displacement sensitivity and output sound pressure, the suspended structure is proposed, which is achieved by etching sacrificial aluminum trenches and utilizing double-sided DRIE of the silicon substrate. It is capable of greatly reducing tensile stress caused by deflection on the edge of the membrane, thereby improving the performance of PMUT, such as acoustic and electromechanical performance. With the help of FEM and COMSOL, simulation has been conducted and the results show that the suspension structure possesses lower resonant frequency and a larger membrane deflection sensitivity, which means higher penetration and acoustic energy. A PMUT with the suspension structure is fabricated. Its impedance diagram is obtained by using impedance analyzer. The resonance frequency of the transducer is 66.35 kHz, and the sound pressure value measured by a hydrophone is 0.453 Pa.