Hard Film Coatings for High-Speed Rotary MEMS Supported on Microball Bearings

Abstract: Titanium Nitride (TiN) and Silicon Carbide (SiC) coatings deposited on the surface of silicon raceways are evaluated in a microturbine. Nanoindentation is employed to study the properties of the hard-thinfilm/silicon raceway system and the tribological platform is evaluated through turbine operation curves. TiN films are shown to stay intact over the speeds and forces in the range relevant to future power and energy applications applications, (500-10,000rpm and 10-50mN, respectively), while SiC films wear almost instantaneously. Evaluation of the dynamic friction torque versus normal load relationship between the TiN and bare Si systems suggest the gradual generation of wear debris, comprised of either the raceway or microballs, is negating the benefits of enhanced mechanical properties in TiN

Dynamic friction and wear in a planar-contact encapsulated microball bearing using an integrated microturbine

The demonstration and characterization of a novel planar-contact encapsulated microball bearing using a radial in-flow microturbine are presented. Stable operation of the air-driven silicon microturbine is shown for over 1 000 000 revolutions at speeds, pressure drops, and flow rates of up to 10 000 r/min, 0.45 lbf/in2, and 3.5 slm, respectively. Incorporation of a gas thrust plenum using a novel packaging scheme has enabled comprehensive spin-down friction characterization of the encapsulated microball bearing. An empirical power-law model for dynamic friction has been developed for speeds of 250-5000 r/min and loads of 10-50 mN, corresponding to torques of 0.0625-2.5 muNldrm and friction torque constants of 2.25-5.25 x 10[superscript -4] muNldrm/ r/min. The onset and effect of wear and wear debris have been studied, showing negligible wear in the load bearing surfaces for the operating conditions considered.U.S. Army Research Laboratory (Grant CA#W911NF-05-2-0026