Fabrication and characterization of annular-array, high-frequency, ultrasonic transducers based on PZT thick film

Abstract

In this work, low temperature deposition of ceramics, in combination with micromachining techniques have been used to fabricate a kerfed, annular–array, high–frequency, micro ultrasonic transducer (with seven elements). This transducer was based on PZT thick film and operated in thickness mode. The 27μm thick PZT film was fabricated using a low temperature (720°C) composite sol–gel ceramic (sol+ceramic powder) deposition technique. Chemical wet etching was used to pattern the PZT thick film to produce the annular array ultrasonic transducer with a kerf of 90μm between rings. A 67MHz parallel resonant frequency in air was obtained. Pulse-echo responses were measured in water, showing that this device was able to operate in water medium. The resonance frequency and pulse-echo response have shown the frequency response presented additional resonance mode, which were due to the lateral modes induced by the small width-to-height ratios, especially for peripheral rings. A hybrid finite-difference (FD) and pseudospectral time-domain (PSTD) method (FD–PSTD) was used to simulate the acoustic field characteristics of two types of annular devices. One has no physical separation of the rings while the other has 90μm kerf between each ring. The results show that the kerfed annular-array device has higher sensitivity than the kerfless one.