Mitigating early fracture of amorphous metallic thin films on flexible substrates by tuning substrate roughness and buffer layer properties

Abstract Ductility mismatch between brittle amorphous thin films and flexible polymer substrate often leads to limited elongation and early failure of the system. A combined experimental and computational study was carried out to investigate the roles of buffer layer material type, thickness, and substrate roughness on the fracture toughness of the amorphous thin film/polymer system. Experimentally, about 1 μm thick amorphous aluminum-manganese thin films were deposited on polyimide substrates and tested in tension. The reliability of such systems was found to be strongly influenced by the film/substrate interface adhesion. Several strategies to improve the adhesion of the interface were conducted, including roughening the surface of the substrate, and adding a buffer layer with a desired mechanical properties and thickness. Computationally, finite element simulations of the same system were carried out under tension. It was found that by introducing substrate roughness and adding a Cr buffer layer of 75 nm, the interface toughness of the film/substrate can be increased by almost twenty times. The results of the present work may shed light on the interfacial engineering strategies for improving reliability of future flexible electronics.