Stretchable Gold Conductors

New, stretchable gold conductors have been developed by Princeton University researchers. The conductors may be the answer to problems that arise when engineers build oddly shaped devices (such as retina-inspired photosensor arrays, for example), or when making connections to sensors attached to the skin or other flexible surfaces. The researchers (Stephanie Lacour, 609-258-3582) built their new conductors by depositing layers of gold about 100 nanometers thick on a substrate of poly-dimethyl siloxane (PDMS), a type of plastic material commonly used in microelectronics-related research and manufacture. (An underlying 5-nanometer layer of chromium helped to ensure that the gold would adhere to the PDMS.) Once they had deposited the gold, the researchers found that compressive stresses in the metal caused the film to buckle, forming parallel wrinkles in strips of the material. The wrinkles smooth out, as expected, when the film is stretched by a few tenths of a percent, but surprisingly the material remained conducting as the film was stretched up to twenty-three percent beyond its relaxed length. Simple strips of gold film, on the other hand, break when stretched as little as one percent. As it was stretched, cracks developed in the gold layer, but current continued to flow along the strip. The researchers suspect that a thin conductive metal layer, perhaps only a single molecule thick, may bridge the cracks and account for the conductivity of the stretched film, although confirmation of this hypothesis is still forthcoming. (Lacour et al., Applied Physics Letters, 14 April 2003)