Interfacial Slippage and Fricion Studies on Material of Interest to Microelectromechanical Systems (MEMS)

Abstract

I have studied the water vapor adsorption onto quartz crystal microbalance crystals in different type of gas surrounding. The noble gas alone has no charge and therefore can not have a Coulomb interaction with the water molecules, only van der Waals interactions. However, the study reveals how dissolved gas increases the hydrophobicity of water, which has the impact on the slip time and sliding friction of water film. This effect strongly influences the slippage of water film.

I also performed a quartz crystal microbalance (QCM) study of the nanotribological properties of organo-phosphate (tricresylphosphate and t-butyl phenylphosphate) layers adsorbed from the vapor phase onto silicon (amorphous silicon and MEMS-like polysilicon), and octadecyltrichlorosilane (OTS) treated silicon and gold surfaces. The latter systems have been studied in order to explore whether organophosphates and OTS in combination might prove synergistic from a tribological point of view. There is a strong possibility that this combination will also exhibit synergistic tribological behaviors when tested on actual MEMS devices. Therefore, it is important to perform QCM measurement on silicon that is as close to that of MEMS devices. In order to perform this study, we have developed a deposition method involving a Si-Ge layer that enables the growth of polycrystalline silicon on top of Cu QCM electrodes. The structural and morphological properties of these samples have been characterized with Raman spectroscopy and atomic force microscopy (AFM), confirming that they are similar in nature to the silicon in actual MEMS devices.