Ultrasonic Micromotors Based on PZT Thin Films

The integration of piezoelectric Pb(Zr,Ti)O3 thin films on silicon substrates for ultrasonic motor applications is reviewed. With suitable buffer and bottom electrode layers the problems due to high processing temperatures in oxygen ambient can be handled. Reproducibility can be increased by stabilized electrode systems and seeding layers for PZT nucleation. Elastic fin micromotors of millimeter size have been fabricated. They achieve the necessary torques, low speeds, and battery voltage operation for applications in wristwatches. However, their efficiency needs to be improved. Better figure of merits of the material still can be achieved. Better designs with larger coupling factors are desirable.