5C-4 Optimization of an Integrated Structure Including a Screen-Printed Piezoelectric Thick Film for High Frequency Transducers

Based on previous work, screen-printing technology was used to elaborate an improved integrated piezoelectric structure relatively to a reference sample [Marechal, et. al., 2000], An active PZT layer doped with PGO to lower sintering temperature at 800degC was printed on a porous unpoled PZT substrate which was chosen to withstand such a temperature. Moreover, the acoustical impedance of this substrate is close to that of the deposited piezoelectric thick film, making it an adequate backing for a wideband device. Thus, a short pulse-echo response is obtained, but the resonance frequency is lowered. Additional layers such as a back electrode and a dense barrier layer were interposed between the substrate and the piezoelectric film. These passive and active layers have a significant influence on the performance of the high frequency transducer. Therefore, their thickness and acoustic properties must be controlled precisely for an optimization of the structure. The center frequency and active source radius of the transducer were increased in comparison to the reference sample, resulting in an improved radiation pattern. In vivo human skin images were performed with an imaging system for two of the prototype broadband high frequency transducer