This thesis reports how prototypes of micromachined vacuum sensors were designed, fabricated and characterized. The sensing mechanism of this vacuum sensor is based on the effect of squeeze film damping which is completely different from the existing vacuum sensors. Compared to other sensing mechanisms, the proposed mechanism could provide a better resolution at very low pressures due to the strong correlation between the squeeze-film damping and ambient pressure....[ Read more ]

This thesis reports how prototypes of micromachined vacuum sensors were designed, fabricated and characterized. The sensing mechanism of this vacuum sensor is based on the effect of squeeze film damping which is completely different from the existing vacuum sensors. Compared to other sensing mechanisms, the proposed mechanism could provide a better resolution at very low pressures due to the strong correlation between the squeeze-film damping and ambient pressure.

When a resonator oscillates next to a fixed wall, the film of gas between the resonator and the fixed wall is squeezed in and out of the gap due to the interactions between the gas and the wall. As a result, a damping force, denoted as the squeeze-film damping, is applied to the resonator which dissipates its energy. The dissipated energy is obtained from the measured quality factor of a resonator. To correlate the measured quality factor with ambient pressure at low pressure level, a Monte Carlo simulation program was developed based on gas kinetic theory. This program tracks the motion of each individual molecule and calculates the energy and momentum exchange between the gas molecule and the wall during each collision. The program developed provides good agreement with some experimental results in the literature.

Several prototypes were designed and preliminary modeling using analytical modeling and FEM simulation were carried out. These prototypes were then successfully fabricated using microfabrication technology. They were driven electrically using a biased driving scheme through an interface module. Oscillations of the resonator were observed under a microscope. A sensing circuit was also built to test the prototypes. The prototypes were placed inside a vacuum chamber and measurements at different pressure levels were conducted. By feeding the driving signal with different frequencies, the frequency responses of the prototype were found.