MICROFABRICATION OF BULK PZT TRANSDUCERS AND DEVELOPMENT OF A MINIATURIZED TRAVELING WAVE MOTOR

Abstract

Diverse applications including consumer electronics, robotic systems, and medical devices require compact, high-torque motors capable of operating at speeds in the range of 10s to a 1000 rpm. Traveling wave ultrasonic motors are a perfect fit for these specifications as they generate higher torques for a given size-scale compared to electrostatic and electromagnetic motors. Furthermore, the electrostatic and electromagnetic motors require an additional gearing mechanism to operate at low speeds, which adds more complexity to the system. The miniaturization of ultrasonic rotary traveling wave motor has had limited success due to lack of high-resolution, high-precision fabrication techniques. This dissertation describes the development of a novel microfabrication technique for the manufacture of bulk lead zirconate titanate (PZT) microsystems involving only two lithography steps that enables the realization of bending-mode piezoelectric microsystems from a single homogeneous layer of bulk piezoceramic, requiring a few hours to fabricate. This novel fabrication process and device design concept is applied to the development of a new class of bulk PZT rotary traveling wave micromotor fabricated using a single sheet of commercially available bulk PZT. For the microfabrication of bulk PZT microsystems, relationships between micro powder blasting process parameters and PZT etching characteristics are presented, including key process parameters such as particle size, nozzle pressure and nozzle-to-substrate distance, with etch rate and etch anisotropy evaluated as a function of these parameters and space resolution. Furthermore, the photolithographic masking of bulk PZT using dry film photoresist, yielding a facile method for achieving precise and high-resolution features in PZT is presented. The work on the development of a new class of homogeneous bulk PZT unimorphs, which eliminates the need of additional elastic layers found in traditional piezoelectric bimorphs, is also reported. The developed fabrication and actuation process are key parameters to developing miniaturized bulk PZT traveling wave motor. The challenges of generating traveling waves are described in detail, followed by the successful demonstration of bi-directional traveling waves and rotor motion. The stator and rotor performance under varying stator/rotor preload forces and actuation conditions have been characterized.