Thickness mode high frequency MEMS piezoelectric micro ultrasound transducers

Thickness mode piezoelectric micro-electromechanical system (MEMS) ultrasound transducers, operating in the 50-75 MHz range, have been fabricated using a composite sol gel technique in combination with wet etching. The composite sol gel technique involves producing a PZT powder/sol composite slurry, which when spun down yields films a few micrometers thick. Repeated layering, and infiltration, has been used to produce PZT films between 20 and 40μm thick. Due to the low firing temperature (<720oC) it has also been possible to integrate these PZT films with a micro-machined silicon support wafer. These PZT thick films have been structured using a wet etching technique to create free standing pillars that have been shown to resonate in thickness mode in the frequency range of 50-75 MHz. Examples of these structures and their resonant behaviour are presented.