Preparation of Superhydrophobic Silica Thin Films for Antistiction of MEMS Devices Using a Novel Sol-Gel Process

Based on the theory of superhydrophobicity for low surface energy coatings, we describe a superhydrophobic antistiction silica coating for MEMS devices. The process uses a novel sol-gel process sequence with a eutectic liquid as a templating agent. The eutectic liquid displays negligible vapor pressure and very low melting point (12degC at ambient conditions) to reduce solvent loss during the high speed spincoating process. After a fluoroalkyl silane treatment, superhydrophobicity is achieved on the as-prepared silica thin film. The solvent can be extracted after the gelation and aging processes. Spin speed effect, eutectic liquid:TEOS ratio in the solution were systematically studied in order to optimize the surface roughness to ensure excellent super-hydrophobicity. Comparison of the silica thin films with silicon pillar surfaces showed that superhydrophobicity for the traditional sol-gel derived silica films demonstrated significant improvement, especially under humid conditions. The AFM force curve obtained with a tipless probe showed that the interaction force is greatly reduced on a rough silica superhydrophobic surface. This result offers great potential to reduce stiction failures in MEMS devices.