Friction forces on the microscale: implications for micromotors

Friction has long since been outlined as one of the key areas where efficiency is lost in microdevices. In some cases it is the factor which dictates whether or not they function at all. The tribological characteristics of microsystems are generally more sensitive to a variety of physical, chemical and environmental effects than macroscopic cases. This study investigates frictional properties for microengineered rotors made out of nickel by the LIGA and LIGA related processes. The material properties and general morphology of these rotors would be similar to the rotors in micromotor and microengineered turbine systems. Preliminary results indicate a strong dependency of the friction coefficient on the normal load with the smallest structures and loads exhibiting the highest friction. This relation was found for both silver, alumina and nickel test substrates. The increase in the magnitude of the friction coefficient for the smallest structures has obvious implications for the efficient design of microdevices. A method for reducing the load dependency based on surface polishing of the rotors is discussed