P1J-1 Optimized Piezoelectric Sol-Gel Composite Films for High Frequency Ultrasonic Transducers

High frequency piezoelectric films were prepared using the composite sol-gel technique, by mixing PZT sol and laboratory-made powders, free-cracked thick films were deposited by dip-coating on silicon, alumina and porous PZT substrates. Only 3 composite layers and few final infiltrations were used to prepare 40 mum thick films. Reproducible electromechanical properties, i.e. thickness coupling coefficients around 40%, were obtained after a poling at 15V mum in an oil bath at 170degC. A pulse echo response was measured with a 35 mum thick film deposited on a porous PZT substrate. The corresponding characteristics are an axial resolution of 45 mum (with a bandwidth at 80*%) at -6dB and a center frequency of 20 MHz. These results showed that the composite sol-gel process is a good candidate to produce piezoelectric films with a thickness of few tens of microns with a minimization of fabrication steps.