Title :
Frictional Aging and Sliding Bifurcation in Monolayer-Coated Micromachines
Author :
Corwin, Alex D. ; de Boer, Maarten P.
Author_Institution :
Micro-Syst. & Micro-Fluidics Lab., GE Global Res., Niskayuna, NY
fDate :
4/1/2009 12:00:00 AM
Abstract :
Using a high-performance polycrystalline-silicon micromachined actuator that also functions as a friction tester, we have found frictional forces that cannot be explained by Amontons´ law with a constant coefficient of friction. In our friction test, a constant tangential force is applied while normal load is ramped down at a rate mathdotF n after a hold time t h at a hold load F h. When coated by a monolayer of FOTAS (CF3 C5F10C2H4Si(N(CH3)2)3), we find that there is no unique coefficient of static friction mus , but instead that mus depends on all three of these parameters. The dependence on t h implies static friction aging, but the rate of static friction aging can be suppressed by greater hold force. When sliding motion begins, we have identified a critical normal force to shear force ratio such that any motion initiating above the critical ratio proceeds with time-dependent frictional creep over several hundred nanometers, whereas any motion initiating below the critical ratio proceeds with a large inertial jump. These effects demonstrate that contact aging effects extend from the micrometer to the nanometer scale and are relevant to micromachined interfaces.
Keywords :
ageing; friction; microactuators; micromachining; constant tangential force; friction tester; frictional aging; hold force; monolayer-coated micromachines; polycrystalline-silicon micromachined actuator; shear force; sliding bifurcation; static friction; Actuators; friction; stepper motors;
Journal_Title :
Microelectromechanical Systems, Journal of
DOI :
10.1109/JMEMS.2008.2011717