The influence of Circuit Parameters on Molten Bridge Surface Degradation in a Au/MWCNT MEMS Switch Contact

The influence of circuit parameters on an Ohmic (metal-metal contact) MEMS (microelectromechanical system) switch contact pair are investigated under hot-switching (carrying current) circuit conditions below the arcing-threshold. A novel MEMS relay testing platform is used to investigate microscale contact surface change between individual switching events. The contact materials are a composite contact material of vertically-aligned carbon-nanotubes with a metallic (Au) layer, paired with an Au-coated ball contact. The evolution of the contact surface is evaluated along with the energy associated with the molten-metal bridge (MMB) phenomena. Circuit voltage is varied between 4 and 8 V DC and current between 20 and 50 mA to determine their influence on surface degradation. Two modes of voltage transient are observed. The first has been linked to the formation of a MMB and the second to a delamination event (DE) where the contacts separate with no MMB apparent. Results are presented on the relative likelihood of the DE or the MMB events occurring. After 100k cycles at switching conditions of 4V, 20 mA the contact surface demonstrates negligible wear. Increasing the current (4 V, 50 mA) or the voltage (8 V, 20 mA) both increase the average energy associated with opening and the contact wear. The increase in MMB energy and wear with supply voltage is unexpected and is discussed.