Piezoelectric thick films and their application in MEMS

Piezoelectric thick films (up to 10 μm thick) and piezoelectric micromachined ultrasonic transducer (pMUT) have been successfully demonstrated at low temperatures of 650 °C using a composite thick film processing route. Submicron-sized PZT powder was dispersed into sol–gel solution to form homogeneous slurry for spin-coating on silicon substrate. Issues associated with recipe of the slurry, deposition process and sintering of films have been summarized with a view to optimizing the properties of the films and pMUTs. Typical microstructure, ferroelectric and piezoelectric properties of the composite films are given. Thermal stability of bottom electrode, a key issue about device fabrication, has also been investigated. The ultrasound-radiating performance of the pMUT element in response to a continuous alternating current driving voltage has been reported. The generated sound pressure level is 116.8 dB at 76.3 kHz at a measuring distance of 12 mm. The pMUT is suitable for application of airborne object recognition.