Flexible Thin-Film PZT Ultrasonic Transducers on Polyimide Substrates

We report flexible thin-film lead zirconate titanate (PZT)-based ultrasonic transducers on polyimide substrates. The transducers are bar resonators designed to operate in the width extension mode. The active elements are 1 mu m thick PZT films that were crystallized on Si substrates at 700 degrees C and transferred to 5 mu m thick solution-cast polyimide via dissolution of an underlying release layer. Underwater pitch-catch testing between two neighboring 100 mu m x 1000 mu m elements showed a 0.2 mV signal at a 1.5 cm distance for a driving voltage of 5 V peak at 9.5 MHz. With the same excitation, a 33 kPa sound pressure output at a 6 mm distance and a 32% bandwidth at -6 dB were measured by hydrophone.