M.S. Thesis Presentation by Sarne M. Hutcherson
Wednesday, October 6, 2004

(Dr. Wenjing Ye, Chair)

"Theoretical and Numerical Studies of the Air Damping of a Disk-Shaped Resonator in a Sub-micron Gap"

Abstract

Micromachined mechanical resonators are emerging devices that have the potential to be the next generation of ultra-high-frequency filters in addition to many other uses. A critical performance measurement of these devices is the quality factor. A high quality factor often indicates high device sensitivity. Among different energy loss mechanisms, viscous damping contributes significantly to the total energy loss when the device is operated in air or in a low vacuum. While there has been a lot of research done in modeling air damping on resonators, most of the reported work employs continuum theory and thus is only valid for cases when gas rarefaction effects are not significant. This work focuses on the modeling of air damping on resonators when gas rarefaction effects are important. Two cases will be considered, namely a vertically oscillating microbeam operated in a low vacuum and a laterally oscillating disk-shaped resonator operated at ambient pressure but with a submicron air gap between the device and its driving electrodes.

Since continuum theory is no longer valid for these cases, the energy loss is obtained by studying the interactions between each individual gas molecule and the moving structures. Both theoretical and numerical studies were conducted and comparisons with some existing experimental data were performed. The numerical studies will involve molecular dynamics (MD) and Direct Simulation Monte Carlo (DSMC) simulation techniques to model the behavior of the rarefied gas. The energy and momentum transfer from the device to the gas is considered and the The goal of this thesis work is to develop accurate approaches and tools for the determination of viscous damping on resonators that are in low-pressure environments or of micro- or nano-scale feature size.