Adhesive and corrosive wear at microscales are quantitatively distinguished in lifetime tests of resonant bulk-fabricated silicon microelectromechanical systems (MEMS). By analyzing the oscillation decay characteristics in different vapor environments, we find that wear is dominated by asperity adhesion during the initial stages of rubbing in dry N 2 or O 2 /N 2 mixtures; in these situations the transient wear rate is inversely proportional to the wear depth. But in water or ethanol vapors, chemical reactions between the corrosive adsorbed layer and the silicon substrate limit the wear rate to a constant. These observations are consistent with atomic explanations. The differences between adhesive and corrosive wear explain the advantages offered by lubricating with alcohol vapors rather than using dry environments for tribo-MEMS devices. Compared to ethanol, the relatively poor anti-wear effect of water vapor is explained by aggressive and rapid tribo-reactions.
This paper designs a composite microtribology experiment system (CMES) to observe the sidewall friction of silicon micro-component pairs. The CMES is composed of a microtribological chip, an out-chip driving system, a video acquiring system, a laser triangulation displacement measure system (LTDMS), and a data processing system. Each microtribological chip has four cantilever friction pairs arranged anti-symmetrically. The size of the cantilever is 200um×50um×5um. The out-chip driving system loads the normal press force on the microtribological chip and produces reciprocating vibration meanwhile to achieve the friction. The video acquisition system is made up of a zoom microscope, a CCD, and a monitor. The LTDMS includes a diode laser, two optical focusing system, and a PSD (Position Sensitive Detectors). Both the video acquiring system and the LTDMS measures the friction characteristics from static to dynamic. The preliminary experiments shows: 1) The CMES has sufficient robustness and reliability. 2) The phenomenon of stick-slip is observed at static state by the LTDMS; 3) and the friction coefficient decreases with the increasing of the reciprocating frequency.
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