Pin-joint design effect on the reliability of a polysilicon microengine

Accelerated stress experiments were performed on a class of pin joints to determine reliability. We varied parameters that affected the area of the rubbing surfaces and the gap between those surfaces. Most of the pin joints failed due to seizure. We observed bimodal failure distributions where the lower distribution was associated with an adhesion event with no observable wear debris. The upper distribution of failures was associated with agglomerations of wear debris, which may have seized the pin joint. The effect of surface coatings was also studied. We found that for supercritical carbon dioxide (SCCO₂) dried microengines; the largest effect was due to gap spacing. For microengines with a self-assembled monolayer coating (SAMS), we observed minimal difference in the lifetimes of failed devices.