Compliant Material for MEMS Contacts and Interconnects
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This dissertation focuses on deformation in metallic materials which are possible choices for flexible electrical contacts. A contact for a micro mechanical switch has been fabricated using electroplated gallium (Ga) on silicon (Si) to create an electrical switch. The resistance increased with cycling but recovered to the original value after a thermal reflow. The hardness of thermally reflowed Ga droplets was 2 MPa when the droplets were unconstrained, and up to 95 MPa for constrained droplets, suggesting that all switching in this study caused permanent deformation at room temperature, and that defects formed during plastic deformation are likely candidates for the increased resistance during cycling. Larger contacts could be run for over 100 cycles with no significant increase in resistance. Electroplated Ga microdroplets have potential for carrying high current density (up to 200 A/cm2). Oxidation behavior was characterized for the thermal reflow process on the Ga droplets, suggesting a passivating 30 nm oxide forms at 100 ºC, and electrical contact resistance nanoindentation suggests the oxide breaks during mechanical contact. A MEMS switch has been fabricated and created using electroplated gallium (Ga) and metal-polymer (gold-Kapton) freestanding membrane for a top and bottom electrode to characterize MEMS contacts and interconnects. Plasma and annealing treatment and an adhesion layer (titanium) was used to improve the low adhesion between the metal and polymer. The resistance of the bottom electrode with plasma treatment and the adhesion layer was lower than the other conditions. Additionally the switching contact of the plasma treated electrode with Ga droplets made higher a current density of the switch at the maximum current value (4.6 × 10-3 A/cm2) and the contact behavior was more stable than the others. The surface defects and deformation of Ga droplets after six switch cycles were restored after thermal reflow, so the same current value was measured compared to the first cycle. However, the resistance increased in steps due to necking between the droplets and bottom electrode.