Atomic force microscope based analysis of bound and bound+mobile phase monolayer behavior under mechanical and electrical stress

Abstract

One of the major problems with microelectromechanical systems (MEMS) is the stiction caused by capillary, van der Waals, electrostatic, and chemical forces. Self-assembled monolayers are extensively used to resolve this problem and they have been effective to a certain extent. It has been noted that the molecular weight, entanglement of molecules with asperities, time dependent interactions between asperities and monolayers, and surface migration play major roles in the failure of these coatings. In addition, tribological stressing and diffusion at increased temperature can also cause monolayers to fail. In this study, atomic force microscopy (AFM) and related techniques are used to analyze the behavior of bound monolayer films of 1-decanol and bound 1-decanol combined with a mobile phase (a pentaerythritol ester). Molecular reorientation and surface detachment under electrostatic force increase with increasing electric field between the AFM tip and the film. The AFM tip is used as a single asperity contact to study the atomic scale film failure dynamics of MEMS materials. The micronanotribology of both bound and bound/mobile systems show significant differences in tribochemistry and replenishing characteristics. Bound and mobile phase films exhibit desirable tribological characteristics that extend the reliable life of MEMS devices, which is demonstrated in real device tests.