Fracture analysis of channel cracks in flexible multilayer structure films under bending conditions

Recently, the development of various types of flexible electronic devices has received great research attention. However, brittle films, such as transparent conducting oxide electrodes and permeation barrier films, are still needed to maintain the high performance and reliability of flexible devices. In this study, we established a fracture mechanics model of brittle films on a polymer substrate under bending conditions. Using numerical simulation, we investigated the effects of a buffer layer between the brittle film and substrate on the fracture performance when the channel crack was formed in the brittle film. The mechanics model indicated that the Young's modulus and thickness of the buffer layer were the important parameters determining the crack resistance of the film. The buffer layer with higher stiffness than the substrate enhanced the crack resistance of the brittle film as the thickness of the buffer layer increased. In contrast, the buffer layer with lower stiffness than the substrate reduced the crack resistance of the brittle film. In this case, the increase in the thickness of the buffer layer further decreased the fracture performance of the brittle film. The present study is expected to provide practical design guidance to enhance the bending durability of the brittle films and multilayer barrier films on polymer substrates.