Development of high-frequency (∼ 100MHz) PZT thick-film ultrasound transducers and arrays

Fabrication of high-frequency (30 MHz--50 MHz) ultrasonic linear arrays is still a challenge. The task is even more difficult to build arrays at a frequency higher than 100 MHz, which has the potential to provide more detail skin texture for early diagnosis of melanoma or to image small objects such as stem cells. Integrating of PZT films into MEMS micro-machined is a potential solution to such high-frequency applications. This thesis presents the development of high-frequency (∼100 MHz) PZT thick-film transducers and arrays.;PZT thick films thicker than 10 mum were fabricated with a composite spin-coating method. The functional properties of the films were improved by optimization of composite solution ball-milling time, PZT sol-gel to powder mass ratio and sol-gel infiltration process. Films suitable for high frequency ultrasonic transducer applications were produced and characterized. The films were found to have a remanent polarization of 37 muC/cm2, a dielectric constant of 1250 (at 1 kHz), and electromechanical coupling coefficient (kt) of 0.34.;High-frequency (∼100 MHz) single-element transducers and linear arrays were afterwards fabricated with the PZT films. The single-element transducer was constructed by transferring the film from silicon substrate to E-solder backing material. The finished transducer was found to have a center frequency of 120 MHz and a bandwidth of 60% with a layer of parylene. Ultrasonic images of the porcine eyeball and normal human skin were also successfully acquired with the transducer. 32-element kerfless high-frequency linear array was fabricated with a 12-mum PZT film by photolithography. The array had a center frequency of 120 MHz, a bandwidth of 60% with parylene matching and an insertion loss of 41 dB. Performance of the array was compared to a PZT-5H ceramic sheet kerfless array fabricated with an identical array pattern.;The development of 32-elment kerfed arrays was also presented. DRIE dry-etching technique was investigated to produce an array with sharp element edges (profile angle > 85°) and narrow kerf (∼12 mum). The kerfed array shows similar performance with kerfless one, except the crosstalk is ∼5 dB lower.