Capillary Induced Stiction and Adhesion of MEMS Materials

Adhesion and stiction are serious problems in microelectromechanical systems (MEMS) fabrication and application. The wettability, surface energies, and nano-scale adhesive forces of commonly used MEMS materials have been examined by contact angle meter and atomic force microscopy. Silicon and silicon compounds have higher surface energy than that of PMMA and SU-8 due to larger polar component of surface energy. The nano-scale adhesive forces of PMMA and SU-8 are 3–4 times smaller than that of as-received silicon with native oxide. It has been shown that the materials with higher surface energy have higher adhesive forces. One efficient way to avoid stiction in silicon microstructures is to deposit a thin fluorocarbon film coating.