Vapor Phase Lubrication of MicroElectro Mechanical Systems (MEMS): An atomistic approach to solve friction and stiction in MEMS
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Date
2003-09-05
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Abstract
The motivation for this thesis is the desire to overcome the problem associated with reliability and yield of these staggeringly small devices called MicroElectro Mechanical Systems (MEMS). The field of microelctromechanical systems involves the interaction of the physical environment with electrical signals through the use of microbatch-fabricated devices. MEMS is an emerging technology which finds applications in diverse fields such as automotive, medicine, aeronautics, communication and defense. The device dimensions range well into the micrometer regime and are soon approaching the length scales studied by nanotribologists Though the MEMS technology has made a substantial impact over the past decade at the device or component level, it has yet to realize a wide range commercial success. Stiction, adhesion, friction and wear seem to be the main deterrents to their lifetime, and hence full commercialization of these devices. These problems can be attributed to the high surface-to-volume ratio, substantial solid surface nanocontacts, close proximity of microstructures and a myriad other device complications.
Several researchers have come up with solutions to avoid release-related stiction, but in-use stiction and friction still persist, proving detrimental to the life span of these microstructures. Though a variety of engineering solutions have been employed to solve them, lubrication of these microelectromechanical systems still remains to be a difficult issue because, the semiconductor like fabrication and small size makes lubrication a challenge in crevices and surfaces beyond the line of sight. In this study, an attempt is made to investigate the in-use stiction and frictional effects by screening vapor phase lubricants on materials of relevance to MEMS using modern nanotribological techniques. The surface effects of silicon after screening vapor phase lubricants are studied using Quartz Crystal Microbalance (QCM) technique in ultra high vacuum. The most promising candidates are then screened on specially designed microstructures called Sidewall tribometers or Friction testers, to study the frictional and wear characteristics. The primary advantage of thermally activated vapor phase lubrication approach is conformality and in-situ replenishment of the lubricant as the lubricating film is worn away.
We have studied the adsorption of the vapor phase lubricant t-butyl phenyl phosphate (TBPP) on Si and Si-OTS (octadecyltrichlorosilane) surfaces. Results show that this particular vapor phase lubricant and the SAM coating of OTS show a synergistic relationship. TBPP not only lubricates OTS but acts as a protective coat at high temperatures.
We have managed to build a system for the uptake of vapor phase lubricants on the MEMS friction testers under vacuum conditions. This new and improved friction test setup will help in understanding the frictional characteristics of these microstructures, and possibly aid in developing a reliable solution to overcome the myriad problems associated with friction and stiction of MicroElectro Mechanical Systems. The following thesis report describes the status of the project and a summary of results.
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Keywords
MEMS, Vapor, Lubrication, Stiction, Friction
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Degree
MS
Discipline
Electrical Engineering
