Vapor lubricant transport in MEMS devices

Vapor phase lubrication is considered one of the most likely means of lubricating MEMS devices with replenishable solid films. Since gas phase diffusion is the primary means of vapor lubricant transport into the long, narrow channels of MEMS devices, it is necessary to determine that this is sufficient to replenish lubricant films worn at high rates. The diffusion of vapor phase lubricant into a long, narrow channel has been modeled in order to solve for the lubricant partial pressure distribution along such a channel in a MEMS device. This has been used to estimate the maximum channel length for which vapor phase transport can replenish adsorbed lubricant films. Using reasonable parameters for description of the channel, the vapor lubricant properties, and the diffusion constant, it can be shown that gas phase diffusion is sufficient to support the replenishment of vapor lubricant films being worn at rates as high as 1 monolayer(s) in channels with aspect ratios of 100 or higher.