Vapor-phase self-assembled monolayers for improved MEMS reliability

This paper presents the application of vapor-phase DDMS (dichlorodimethylsilane) self-assembled monolayer (SAM) coating which significantly reduced stiction behavior in optical MEMS components exposed to humidity. Previously SAMs have been deposited in liquid form, making them unsuitable for application in high aspect ratio MEMS/NEMS structures; now vapor-phase SAM deposition is a novel option for improving MEMS in-use reliability. DDMS and ODS (noctadecyltrimethoxysilane) SAM coatings were tested on surfaces with different pre-treatments and the quality of coatings was assessed through static water contact angle measurements and humidity exposure tests for both test membrane structures (100% stiction on uncoated structures vs. 17% stiction of DDMS SAM coated structures) and optical MEMS FPI components (0% stiction of DDMS SAM coated components). The obtained contact angle of the DDMS SAM coating was ~ 104°. Both long term stability and thermal stability of the DDMS SAM coatings were found to be good.