MEMS Lubrication by Tribochemical Reaction

A means of providing replenishable lubrication to rubbing silicon surfaces is demonstrated. Alcohol at a small fraction of saturation vapor pressure is introduced in a nitrogen environment. Pin-on-flat sliding experiments in this environment reveal a friction coefficient near 0.2, and absence of wear above a critical alcohol concentration. This lubrication approach was also demonstrated in microfabricated silicon machines, where the devices operated at least a factor of 10⁴ longer without failure when alcohol vapor was present in the nitrogen gas environment, compared to devices in dry N₂ with a chemisorbed monolayer alone. When water vapor was added to the environment, vapor lubrication by alcohol was inhibited at concentration ratios of water:alcohol = 2.5:1.