Friction and wear of rotating pivots in MEMS and other small scale devices

Micro-electromechanical systems (MEMS) is a rapidly growing interdisciplinary technology dealing with the design and manufacture of miniaturised machines or moving (or micro) mechanical assemblies (MMAs) with major dimensions at the scale of tens, to perhaps hundreds, of microns. Because they depend on the cube of a representative dimension, component masses and inertia rapidly become small as size decreases whereas surface or tribological effects, which scale with the square of dimension, become increasingly important. In this paper, the effects of design, material properties and applied operating conditions on the evolution of both friction forces and dimensional and volumetric wear rates are explored for normally loaded rotating pivots of various geometries. It is demonstrated that if such MEMS–MMAs are to have acceptable lifetimes then loaded contacting surfaces will need to be of inherently low wear material pairings. The difference in scale between these small devices and conventional wear testing rigs also creates problems in matching conditions between micro- and macro-situations and suggests that wear data might usefully be obtained from suitably designed MEMS devices acting as miniature wear test machines.