Omnidirectionally Stretchable Metal Films with Preformed Radial Nanocracks for Soft Electronics

Flexible and stretchable conductive thin films are required for the development of soft electronics; however, few existing films satisfy the requirements for both electrical/mechanical performances and process practicability. This study describes a simple approach to fabricate omnidirectionally and highly stretchable nanocracked metal thin films on thiolated elastomeric substrates by exploiting the eruption of a residual solvent contained in an elastomeric substrate during metal thermal evaporation. Also, the effects of residual solvent content in the substrate on the crack topography of a metal thin film and its resultant stretching characteristics are investigated. The solvent content in the range of 0.2-0.3 wt % facilitates the formation of radial nanocracks with a high density of small cracks, which is most suitable for dissipating omnidirectional tensile stress. When a strain of 100% is applied to the elastomeric substrate, the electrical resistance of the radially nanocracked stretchable Au film increases only slightly compared to that of the uncracked Au film. Furthermore, the film shows high stability under repeated stretching cycles and harsh mechanical conditions, enabling its application to stretchable interconnects for a flexible light-emitting diode array. This method provides an effective approach to obtain high-quality thin metal electrodes for use in flexible and wearable devices.