Different carbon based thin films and their microtribological behaviour in MEMS applications

Amorphous carbon based coatings are well known and typically used for high wear resistance and low friction in mechanical contacts and cover a broad variety of application on different metal, ceramic and to some extent also organic substrates. Especially for micro mechanical and micro electro mechanical systems (MEMS) dry lubricants are very essential for applications due to the absence of additional sticking and adhesion phenomena usually induced by liquid lubricants. However, besides the development of thin tribological coatings further improvement of the frictional behaviour can be realized by optimizing the contact situation. Novel results on microstructured surfaces coated with a-C:H and a-C films will be discussed. Furthermore an oscillating friction tester for the investigation of flat to flat contact, closing the gap between the common pin-on-disc tester and the single asperity investigations by means of AFM method will be presented. The perspectives and limitations of the micro areal tester as well as the behaviour of areal micro contacts and microstructured surfaces will be discussed. For further reduction of the friction coefficient microstructures and load-optimized contact areas were investigated. Therefore the resulting contact area, correlated with the resulting local pressure, was varied over three orders of magnitude by variation of both width and spacing of the micro pattern in the range of 5-100 mu m. For optimized combination of sliding carbon film and micro patterned surfaces the friction coefficient was reduced by more than 30% compared to full area contact. (c) 2005 Elsevier B.V. All rights reserved.