Conduction properties of microscopic gold contact surfaces

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Abstract
Electroplated gold surfaces of the type used for MEMS switches were surveyed by atomic force microscopy (AFM) to define the surface topographical features, and by x-ray photoelectron spectroscopy (XPS) to determine the chemical composition of the contact surface. The gold surfaces were contacted with electrochemically sharpened gold and tungsten probes using an interface force microscope (IFM), capable of simultaneously measuring contact currents from 10 fA to 10 mA and forces ranging from 0.01 to 100 uN. Both attractive and repulsive forces were observed, and attractive forces on the probe tip were found to exist at significant distances (greater than 5 nm) from the gold surface. The radius of the probe tip is on the order of a micron, making it a useful model system for a single-asperity contact on an actual MEMS switch-contact surface. The results of these single-contact measurement events are compared with contact measurements made with MEMS switches of various sizes and actuation schemes to understand the origins of contact resistance and switch failure.

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