The influence of coating structure on micromachine stiction

Stiction and friction in micromachines ir: commonly inhibited through the u se of silane coupling agents such as 1H-, 1H-, 2H-, 2H-perfluorodecyltrichl orosilane (FDTS). FDTS coatings have allowed micromachine parts processed i n water to be released without debilitating capillary adhesion occurring. T hese coatings are frequently considered as densely-packed monolayers, well- bonded to the substrate. In this paper, it is demonstrated that FDTS coatin gs can exhibit complex nanoscale structures, which control whether micromac hine parts release or not. Surface images obtained via atomic force microsc opy reveal that FDTS coating solutions can generate micellar aggregates tha t deposit on substrate surfaces. Interferometric imaging of model beam stru ctures shows that stiction is high when the droplets are present and low wh en only monolayers are deposited. As the aggregate thickness (tens of nanom eters) is insufficient to bridge the 2 mum gap under the beams, the aggrega tes appear to promote beam-substrate adhesion by changing the wetting chara cteristics of coated surfaces. Contact angle measurements and condensation figure experiments have been performed on surfaces and under coated beams t o quantify the changes in interfacial properties that accompany different c oating structures. These results may explain the irreproducibility that is often observed with these films.