Friction behavior in microsystems
In active microsystems, low lateral propulsive forces act under high contact pressures, thereby requiring a low friction coefficient µ for successful operation. The maximum acceptable friction coefficient is determined by the available driving forces. This chapter focuses on the reduction of microfriction at the contacting interfaces, the use of micropatterned surfaces, and the realization of microguidance. For an investigation on flat-flat-microcontact, specific test equipment was built and used. Physical Vapor Deposition (PVD) and Plasma Enhanced Chemical Vapor Deposition (PECVD) were used for applying thin films. In contrast to macroscopic examples, microfriction under single asperity contact correlates to the applied normal force. At a low load range from 50-100µN, the friction coefficient decreases with increasing load. Above a critical value the friction coefficient decreases with increasing load due to inelastic effects. Under multi asperity microcontact, the friction coefficient is dependent on the contact pressure. To tailor the resulting friction coefficients, the influence of different micropatterns are studied. For carbon based films the friction coefficient µ can be decreased below 0.1.