Running-in of sidewall friction in bulk-fabricated microtribotester

Sidewall friction is of great significance for many MEMS devices such as micromotors, microgears and microhinges. Because sidewalls in MEMS devices are different from inplane surfaces both chemically and topographically, friction and wear occurring on sidewalls are expected to have its own characteristics. A microtribotester has been developed with the bulk-fabrication technology to measure the sidewall friction and wear, and static friction and dynamic friction measurements have been reported previously. In this paper, experiment results of the microtribotester for a testing period of 55 hours are presented. It is found that the coefficient of dynamic friction reduces gradually with the increase in rubbing cycle, being similar to most macroscale tribopairs. The morphology and chemical components of the wear debris generated in the testing process were analyzed on scanning electron microscope and EDX. From the analysis results, it is concluded that the silicon sidewalls undergoes oxidation during the test.