Continuous anti-stiction coatings using self-assembled monolayers for gold microstructures

Abstract

We have experimented with using continuous self-assembled monolayer (SAM) coatings on different surfaces, such as gold and silicon nitride, as anti-stiction coatings for radio-frequency microelectromechanical systems (RF MEMS). SAMs are coated on gold and silicon nitride surfaces in order to fabricate stiction-free gold structures after the wet release process. SAM coatings on gold and silicon nitride surfaces change the contact angle of a water droplet from 70.60degrees to 112.6degrees and from 36.7degrees to 115.8degrees, respectively. From atomic force microscopy, we can see that there is little change in the roughness of the gold and silicon nitride before and after the SAM coating. Using the electroplating technique and the wet release process, we have fabricated 4 mum thick gold cantilevers and bridges on a gold surface with a 6.5 mum gap from the substrate. Cantilevers and bridges are fabricated with different lengths in the range of 100-1000 mum with separations of 100 mum. It is observed that cantilevers and bridges with a length of 1000 mum on a gold substrate a-re released and standing free. A 1000 mum long gold cantilever has only 16.5 mum tip end deflection after the wet release process and SAM coating, much smaller compared with the 120 mum tip end deflection with the dry release process. Gold cant