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In RF-MEMS switches many reliability issues are related to the metal contacts in the switching area. The characteristics
of this contact influence not only contact resistance and insertion loss, but also the most relevant switch failure
mechanisms that are wear of ohmic contact, adhesion and stiction.
Gold is widely used for this purpose because of its good conductivity and chemical inertness, but is a soft metal, and the
development of hard contact materials with low resistivity is of great interest for RF-MEMS switch reliability. It is
possible to increase the contact hardness preserving the convenient gold properties alternating gold layers with thin
layers of different metals. The material becomes harder not only by simple alloying but also by the presence of interfaces
which act as barriers for mechanical dislocation migration. A detailed study of mechanical, electrical and morphological
properties of gold-chromium, gold-platinum and gold-palladium multilayers is presented and discussed. It is found that
the annealing treatments are important for tuning hardness values, and a careful choice of the alloying metal is essential
when the material is inserted in a real switch fabrication cycle, because hardness improvements can vanish during
oxygen plasma treatments usually involved in RF-switches fabrication. Platinum is the only metal tested that is
unaffected by oxidation, and also modifies the chromium adhesion layer diffusion on the contact surface.
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