Super-elastic Gold Conductors on Elastomeric Substrates

3-D displays, sensor skins, mechatronic structures, and e-textiles will rely on deformable and stretchable electronic circuits. It is likely that such circuits will be made of rigid semiconductor islands interconnected with one-time deformable or even elastic metallization. However, free-standing metal films fracture at tensile strains in the order of one percent, well short of the approximately ten-percent extension needed for deformable circuits. We have discovered that flat metal lines made on an elastomeric substrate can be stretched reversibly by ten percent without losing electrical conduction. While this phenomenon of "super-elastic" conductive films is as of yet unexplained, it appears to originate in the diversion of mechanical strain around cracks in the film and through the elastomer substrate. We fabricated 1mm thick poly-dimethylsiloxane (PDMS) membranes with up to 50-nm thick, 1-mm wide gold lines deposited by electron beam evaporation. Then we evaluated the structure of the gold films by optical and scanning electron microscopy, and measured the electro-mechanical characteristics in a strain tester, with contact electrodes applied to the film. We find that 50 nm thick lines retain their electrical conduction up to 30 percent strain. Also, when the tensile strain is cycled between 0 and 10 percent, the electrical resistance in the stressed and relaxed states are reproducible. We will describe substrate and conductor preparation, and their structural and electro-mechanical properties.