Ultrasonic micromotors: physics and applications

Initial observations of phenomena in a prototype ultrasonic micromotor structure are presented. Small polysilicon blocks are translated and rotated using traveling ultrasonic flexural waves in thin membranes. The 2-micron-thick blocks ranged in size from 50 μm square to 250 by 500 μm. The acoustic wavelength was 100 μm, and the few-megahertz transducer voltage was typically 5; motion was observed at voltages as low as 1.5 V. The acoustic wave power was about 1 mW. Linear motion quickly moved the blocks off of the 3 mm by 8 mm membrane region; stable rotational motion was also observed. Blocks moved linearly at about 10 mm/s and rotated at about 150 r.p.m., depending on the drive voltage. Motion was observed in air, vacuum, and helium ambients