Deformation behaviour of copper thin films deposited by ionized sputtering on flexible polymer substrates

Ductility of metallic thin films is intrinsically limited with grain size and film thickness playing a critical role. Here, it is shown how the energy of depositing metal atoms influences the strain to failure of 200 nm Cu films deposited onto polyethylene terephthalate foils. Films were synthesized by traditional physical vapour deposition dominated by neutral atoms and ionized sputtering where a part of the metal atoms is ionized. Microstructural analysis revealed that increased kinetic energy of film forming species promotes a dense, textured structure with low microstrain. Tensile fragmentation tests showed a significant improvement in crack onset strain from 4.8% to 7.9%, demonstrating the beneficial effect of flux ionization on adhesion and cohesion of the film. The results also suggest that high deposition rates may result in fine-grained morphologies. These results establish a link between processing parameters, microstructure, and failure mechanisms, providing guidelines for optimizing ductility in metallic coatings.