Fabrication, development and characterization of micro/nano actuation based sensors and applications for gas composition analysis

Micro/nano actuation based sensors for gas sensing have generated a great deal of interest due to their ability to detect minute gas concentrations. Currently, gas detection typically relies on changes in cantilever mass or surface stress when a gas interacts with the sensor. Because the detection involves a chemical reaction, the types of gases that can be detected are limited and the detection process is not repeatable and irreversible. Therefore, it is the purpose of this study to develop microresonators, using a new fabrication method, and to investigate the application of these devices as non-reaction based gas sensors.;Lateral silicon microresonators were successfully fabricated by implementing a new fabrication technique that included using electron-beam lithography to pattern an SOI wafer for iron thin-film deposition. The 5 nm iron film was then used as a masking layer for the deep reactive ion etching (DRIE) process. The microresonators were actuated using an electrostatic force and the resonance frequency was detected using a piezoresistive method. Both analytical and computational modeling; as well as experimental testing, were performed to characterize the microresonators. The dependence of the resonance frequency response on the AC bias, DC bias and damping conditions of the gas environment were studied. For the first time, the resonant frequency shifts of the resonator due to viscous damping were experimentally found to be directly related to the molar mass of the gas in a gas environment with a known pressure; thereby, providing a non-reaction based method for determining the composition of the gas environment. Specifically, the microresonators developed in this study successfully determined the CO2 concentration for different CO 2/air gas compositions. The advantages of this gas analysis method are that it is simple, repeatable, reversible and not limited to reactive gases.