Influencing factors on microtribology of DLC films for MEMS and microactuators

Due to the low coefficient of friction and the high hardness of diamond-like carbon films they are very interesting for application of microtribological coatings for MEMS and microactuators. In contrast to well established films with a few micron thickness of the microtribological properties of very thin films with a thickness below 300 nm will be influenced additionally by the substrate material and the roughness of the sample surface. Therefore, we investigated the behaviour of micrfriction and wear for substrate materials with varying Young's modulus. Also, the influence of the topography and the contact situation of the counterparts were studied. Using single asperity contact the coefficient of friction decreases with decreasing contact radius and lower Young's modulus of the substrate material (165, 70, 5, 6 GPa) by more than 20%. For areal contact an increase of Young's modulus leads to a decrease of friction. The microtribological properties of the thin films were investigated by AFM-methods, pin-on-disc tests, and a tape ballcratering test.