Fabrication of arbitrary curvature focused PZT thin film ultrasonic transducer with tunable acoustic impedance based on micropatterned flexible substrate

This paper presents a novel micro-fabrication of acoustic impedance matching layer on a high-frequency focused piezoelectric ultrasonic transducer. The proposed fabrication method allows the acoustic impedance of the matching layer designable, so better acoustic energy transmission and operating bandwidth can be achieved. A micromachining technique is used to make micro-cavities on a flexible metal sheet. The patterned sheet forms a designed curvature with proper shaping and lead titanium zirconium (PZT) slurry is deposited on the processed metal sheet. The detailed PZT film deposition process is described. The structure of PZT micro-bumps on a curved thin PZT layer is therefore obtained. This structure can be released from the metal sheet and the sputtering electrode process is followed. After coating parylene with a designed thickness, the fabricated PZT micro-bumps and surrounded parylene construct a 1-3 composite, and the acoustic impedance of this composite allows to meet design requirement. The transducer fabricated in this proposed technique is demonstrated with a center frequency of 25 MHz and a -6dB bandwidth of 75%.