Thin Film Zinc Oxide Microsensors and Microactuators

In this work, a variety of piezoelectric sensors and actuators utilizing zinc oxide (ZnO) thin films for electromechanical transduction are presented which rely on surface-micromachining technologies. Specifically, piezoelectric cantilever actuators, open loop accelerometers, and fixed-beam resonant structures are demonstrated using two novel fabrication processes.
Surface-micromachined cantilever actuators with thicknesses on the order of 2 to 3 um which are capable of producing forces comparable to those of thermal actuators are demonstrated. A multilayer model of the actuators is presented which can more accurately describe the actuator performance, and measured deflections of fabricated actuators are found to compare well with the modeled predictions. The multilayer model is also employed to predict optimal film thicknesses for the actuator by applying a numerical optimization technique.
A simple cantilever microaccelerometer is also developed, with a measured sensitivity of Sq = 0.21 fC/g and 25 g full scale range. The limited dynamic range of the sensor indicates the need for integrated sense electronics. While sensitivity is limited by the relatively small proof mass of the sensor, a second generation accelerometer is presented which is designed to provide increased sensitivity.
Piezoelectric resonant sensors based on clamped-clamped beam structures are also investigated. In these transducers, piezoelectric activity of a ZnO film induces a resonant oscillation in a beam, and the resulting motion is detected using a second ZnO film. The limiting factors for open-loop performance of the resonators are investigated, and two techniques for improving the effective resonator qualify factor are discussed.
The fabrication of the actuators, accelerometers, and resonant devices presented in this work employ two novel processing techniques which rely on surface-micromachining technologies. In the first fabrication technique, an oxide film is used as a sacrificial layer to release the piezoelectric structure, which consists of a ZnO film atop a polysilicon substrate. In the second technique, a sacrificial silicon layer is removed by xenon difluoride to release the piezoelectric structure. The fabrication details are presented, and the merits and disadvantages of each technique are discussed.
Albert P. Pisano
Tim Sands
Publication date: 
July 31, 1997
Publication type: 
Ph.D. Dissertation
DeVoe, D. L. (1997). Thin Film Zinc Oxide Microsensors and Microactuators. United States: University of California, Berkeley.

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