Resistance characteristics of ultra-low-force electric contacts were investigated experimentally in order to establish a design method for mechanical relays based on microsystem technology. First, we developed an experimental apparatus to measure contact resistance under extremely small contact forces with accuracies of 5μN in force control. 1μN in force measurement, and 1mΩ in resistance measurement. Next, contact resistances of Au, Ag, and Pd electrodes were measured. The force-resistance characteristics had hysteresis between opening and closing contact loads but stabilized to less than 1Ω for forces less than 1mN even though the contact surfaces were not clean. Au-Au contacts were found to have resistance less than 0.1Ω for a force of 100μN. Finally a prototype microrelay with Au sputtered contacts and a contact force of 100μN was fabricated and stable switching performance was demonstrated.
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