Adhesion characteristics of MEMS in microfluidic environments

Although much insight has been gained into the problem of stiction for MEMS operating in air, no systematic investigation of the phenomenon in microfluidic environments has been performed. With the increased interest in bio-MEMS and microfluidic applications, characterization of microstructure adhesion in fluids becomes important. The adhesion characteristics of oxide-terminated and self-assembled monolayer (SAM)-coated polycrystalline Si (polysilicon) cantilever beams in various solvents have been investigated. It is found that surfaces behave quite differently in microfluidic environments, when compared to their behavior in air. Oxide-terminated surfaces are found to exhibit much reduced adhesion in water, in comparison to air. In contrast, hydrophobic SAM-coated surfaces experience strong adhesion in water, a behavior opposite to what is observed in air. It is also observed that oxide-terminated surfaces exhibit greater adhesion in hydrocarbons, compared to SAM-coated surfaces, while surfaces show no adhesion in isopropyl alcohol regardless of surface termination.