In this work we measure the evolution of the adhesion force between two MEMS sidewalls in repeated contact. We use an optical displacement measurement technique to obtain single contact cycles with nanonewton accuracy. We find that when a contact is broken, the snap-off is not always instantaneous, but may happen gradually. The contact shows viscoelastic deformation, hinting at the presence of a tribo-synthesized rubber-like compound on the surface. The variability of the measured adhesion parameters is an important indicator for a change of the surface mechanics. We found that the adhesion force varies by a factor 2 during 3 million cycles, which presents a major reliability concern for MEMS devices with contacting surfaces.
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