| AVS 54th International Symposium | |
| Tribology | Friday Sessions |
| Session TR4+SE-FrM |
| Session: | Friction and Wear of Engineered Surfaces Macro- to Nanoscale Approaches |
| Presenter: | B. Hanrahan, University of Maryland |
| Authors: | B. Hanrahan, University of Maryland M. McCarthy, University of Maryland C. Zorman, Case Western Reserve University A.V. Sumant, Argonne National Laboratory R. Ghodssi, University of Maryland |
| Correspondent: | Click to Email |
PowerMEMS devices supported on microball bearings have been successfully demonstrated at low operating speeds. Continued research on the tribological properties of these support structures is necessary for the realization of robust high-speed devices. Critical dimensions need to be maintained within tight tolerances when operating high speed micromachines. The wear between stationary and moving elements must, therefore, be minimized to reduce the change in critical dimensions over the lifetime of the device. Accordingly, the mechanism of wear between silicon and hardened steel microballs is the focus of this work. Silicon test structures, 23 mm in length, were fabricated with 300 µm wide deep-etched rectangular trenches acting as housings for the microballs. The 285 µm steel balls were sandwiched between two test structures under an applied normal loading. Oscillatory motion is generated between the two structures using an externally controlled stepper motor at 400 rpm and a traveling distance of 4mm. At periodic time intervals, the test device is disassembled and inspected using an optical profilometer to determine changes in the surface topography. To the best of our knowledge, this is the first investigation of wear in MEMS-fabricated ball bearings. Initial results show both deposition and removal of material within the microfabricated trenches. At 50,000 cycles, equivalent to 200 meters of travel, an increase in average surface roughness from 7.5 nm to 30.2 nm is observed. These results suggest the adhesion and subsequent shearing of contacting materials, increasing the overall roughness. The properties of the mating materials play a critical role in determining the wear mechanism. To expand the scope of the study, solid thin film lubrication has been explored. Silicon carbide and ultra-nanocrystalline diamond are ideal candidates for wear resistant films because of their high hardness, low interfacial energy, and compatibility with MEMS fabrication processes. In our analysis we will present a detailed investigation of the wear mechanisms of steel balls on silicon with and without solid lubrication.