WEAR AT MICROSCOPIC SCALES AND LIGHT LOADS FOR MEMS APPLICATIONS

The fabrication of micro electro mechanical systems (MEMS) such as micromotors is mainly based on silicon and its compounds and their tribological behaviour plays a key role in the performance of such systems. In this paper the wear of MEMS-compatible materials has been investigated for a range of contact areas and contact forces typical of micro electro mechanical systems. Special test specimens incorporating a range of micromachined micro structures on their top surfaces were fabricated in order to simulate those conditions. The micro structures were coated with diamond-like carbon (DLC), silicon nitride, silicon dioxide, and doped polysilicon. A specimen-on-disc arrangement was used for the wear experiments and dead weight loading was applied. The results show that the wear rate of DLC and single-crystal silicon sliding on DLC decreases with increasing sliding distance whereas silicon dioxide and silicon nitride showed linear wear behaviour. The effect of contact morphology and contact pressure was investigated for doped polysilicon sliding on DLC. The results can be attributed to the differing mechanical and chemical properties of the materials leading to wear mechanisms ranging from asperity fracture to asperity deformation.