Localized Lubrication of Micromachines: A Novel Method of Lubrication on Micromechanical Devices

Abstract

The effective lubrication of Micro-Electro-Mechanical Systems (MEMS) has been a major hurdle for the micro-machine industry, limiting commercially available designs and mechanisms in such machines to mostly non-contacting ones. Silicon (Si) is a common material for fabrication of MEMS devices, which has very poor tribological properties (high wear rates and coefficient of friction). MEMS lubrication techniques usually involve highly expensive and/or complex processes such as vapour deposition and hermetic packaging to extend the wear life. This study presents a novel method of applying lubricant onto a specifically designated location on MEMS, extending its wear life by several orders of magnitudes. In a feasibility study, a fixed amount of PFPE, which is well documented to be a good lubricant in the hard disc industry, providing a very thin monolayer film as protection, was delivered using the proposed method, between two contacting Si pieces which were then subjected to reciprocation sliding at an applied normal load of 0.5 N (approximately 125 kPa of apparent pressure) and a sliding velocity of 5 mm s⁻¹. The tribological properties (coefficient of friction and wear behaviour) were studied to ascertain the effectiveness of this lubrication method, compared both across polished and unpolished Si surfaces, as well as among varying methods of lubrication; namely dip-coating, vapour-deposition and the novel method of localized lubrication. Unpolished surfaces were also used to replicate the practical rough surfaces on MEMS devices, especially sidewalls. The results have revealed that the current localized lubrication method is very effective in reducing the coefficient of friction and increasing wear life in the reciprocating sliding motion between the two surfaces and was then applied to actual devices custom designed and fabricated for tribological testing of sidewalls, which has shown to reduce both the static and dynamic friction against the sliding sidewalls, as well as the adhesion forces on contact between the sidewalls.