Temporal signatures of resistivity in bending of indium tin oxide-coated flexible transparent conductive films for flexible electronics: Influence of coating thickness and bending radius

The study is focused on the fundamental understanding of behaviors of polymer films coated with indium tin oxide (ITO) of varying thicknesses and thus various conductivities/transparencies in repeated bending by tracking the electrical resistivity real-time using a specially designed multi-purpose flexing system. The results show that temporal increases of resistance provide important clues as to the initiation and progress of failure. In tension, the resistance typically remains flat unless a critical minimum radius of curvature is breached that leads to progressive cracking of ITO coating bringing rapid rise of resistance. This critical minimum radius of curvature increases with the increase of ITO coating thickness making the higher conductivity films more susceptible to damage. In compression mode, similar temporal signature can be found when bent to a curvature below a critical minimum radius. When cracks form in both modes, the resistance signature changes to one of oscillation and the high and low values observed at each cycle progressively increase with more cycles leading ultimately to catastrophic failure.