A Nano- to Macroscale Tribological Study of PFTS and TCP Lubricants for Si MEMS Applications

The reliability and lifetime of cyclic contacting Si MEMS is limited by adhesion and their tribological performance. In this study, the tribological effects of adding a lubricant (tricresyl phosphate, TCP) to a bound self-assembled monolayer (perfluorodecyltrichlorosilane, PFTS) at different length scales were examined using a quartz crystal microbalance (QCM), an atomic force microscope (AFM), a reciprocating microtribometer, and a macroscopic reciprocating tribometer. The results showed that the addition of TCP to a PFTS layer increased the number of cycles possessing low friction and wear by at least a factor of four in the macroscopoic tribometer. Differences in friction response over the range of experimental scales were correlated to contact size and pressure. QCM measurements of TCP on PFTS showed a non-zero slip time, which suggests favorable tribological performance in larger length-scale regimes. This non-zero slip time also may indicate TCP mobility.