Long chain alkylsilane monolayers used in the release process to protect MEMS devices from adhesion due to water adsorption also provide a very low coefficient of friction. One such monolayer, perfluorodecyltrichlorosilane (PFTS) has been shown to have very good thermal stability, keeping a water contact angle above 100° in air up to 400°C.  The monolayer will however wear under mechanical rubbing, causing the MEMS device to irreversibly adhere rendering it useless. Vapor phase lubricants (VPL) used in conjunction with self-assembled monolayers. may be the key to extending the life of rubbing contacts in MEMS. It is believed that the temperature characteristics of the VPL and its ability to replenish itself will provide a sufficient protective layer for the PFTS and extend the life of MEMS devices well into the range where their use in military and industrial applications can be fully realized. Here we have studied two vapor phase lubricants, tricresyl phosphate (TCP) and t-butyl phenyl phosphate (TBPP) on a PFTS monolayer. Previous work done with a quartz crystal microbalance has suggested that TBPP would be a better lubricant than TCP.  We have evaluated the effectiveness of these lubricant systems using a MEMS sidewall tribometer in a vacuum environment. Relationships between lubricant composition, behavior in an isolated asperity contact in the quartz crystal microbalance studies, and performance in a MEMS friction device will be discussed.
A Study of the Tribological Properties of Bound Plus Mobile Phase Lubricants With QCM and MEMS Sidewall Tribometers
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Hook, A, Neeyakorn, W, Krim, J, & Dugger, MT. "A Study of the Tribological Properties of Bound Plus Mobile Phase Lubricants With QCM and MEMS Sidewall Tribometers." Proceedings of the World Tribology Congress III. World Tribology Congress III, Volume 2. Washington, D.C., USA. September 12–16, 2005. pp. 777-778. ASME. https://doi.org/10.1115/WTC2005-63676
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