title: Prestress Driven Improvement in Fracture Behavior of in Situ Sputtered Zinc Oxide Thin Films on Stretched Polymer Substrates.
abstract: Flexible electronic devices need to survive bending or stretching operation without mechanical failure. If inorganic thin films are involved in the device structure, the evolution of cracks is a major challenge to overcome. Here, we report a novel way to substantially improve the fracture behavior of films that are based on intentional utilization of residual stress on the films by in situ sputtering on a stretched polymer substrate. The in situ sputtering combined with a stabilization stage yielded ZnO:Al thin films with a nearly 2-fold improvement in crack initiation strain, which indicates greater resistance to bending. The critical strain of the optimal ZnO:Al films was ∼1.83%, which is a significant improvement compared to the current tolerance value of ∼1%. This was accompanied by a ∼300% improvement in fracture energy. We attributed the improved fracture behavior to the presence of residual compressive stresses, which creates a barrier for crack formation by acting opposite to the applied bending strain.
authors.affiliation: Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea.
authors.forename: Hong Rak
authors.initials: HR
authors.lastname: Choi
authors.affiliation: Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea.
authors.forename: Senthil Kumar
authors.initials: SK
authors.lastname: Eswaran
authors.affiliation: Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea.
authors.forename: Yong Soo
authors.initials: YS
authors.lastname: Cho
keywords: flexible electronics; fracture behavior; transparent conducting oxide; zinc oxide