Stretchability of thin metal films on elastomer substrates

Many flexible electronic surfaces comprise inorganic films on organic substrates. Mechanical failure of such integrated structures of stiff and compliant materials poses a significant challenge. This letter studies the stretchability of metal films on elastomer substrates. Our experiment shows that, when stretched, elastomer-supported metal films rupture at strains larger than those reported for freestanding films. We use a finite element code to simulate the rupture process of metal films. A freestanding metal film ruptures by forming a single neck. By contrast, a metal film on an elastomer substrate may develop an array of necks before rupture. While the pre-rupture necks do not change the electrical conductance appreciably, they elongate the metal film, leading to a large overall rupture strain.