In-Situ Contact Surface Characterization in a MEMS Ohmic Switch under Low Current Switching

To develop robust microelectromechanical systems (MEMS) switching technology for low voltage direct current (DC) applications (1-12 V) there is a requirement for the investigation of wear caused by hot switching (contact operated while carrying a current load). Previous investigation of contact wear in the ohmic MEMS switch has been limited to either the completion of the contact switching cycles, where the device is destructively opened, or by low switching rates, making lifetime testing impractical. A novel MEMS testing platform is described that is capable of both resolving microscale changes on the contact surface between switching events and sustained high frequency switch cycling, enabling practical lifetime testing. The platform is used to investigate early surface changes in a thin-film Au contact pair on a cycle-by-cycle basis. The contact is closed at forces representative of a practical MEMS contact (<1 mN). The apparatus reveals the microscopic surface change between individual switching events. Hot switched contact wear is dominated by the molten metal bridge (MMB) phenomenon, linked to a characteristic voltage transient at contact opening and the gradual process of contact material transfer; however, during hot switching delamination phenomena are also observed, and associated with a step change in contact voltage and a greater level of surface damage.