Real-time resistance characterization of ITO film electrode on flexible substrate under periodic impact

Indium tin oxide (ITO) film electrode has been widely used in flexible optoelectronic devices. However, it is prone to crack due to impact, which directly leads to device failure. To prolong its service life, it is critical to investigate the cracking process of ITO under periodic impact. An important method to characterize the ITO film quality is the electrical resistance method. A home-made testing machine was applied to investigate the effect of periodic impact stress, on the electrical resistance increment, ΔR, of the ITO sample in real-time. It is demonstrated that ΔR and its bottom envelope line, Rb, are functions of impact length, b, and impact cycle, N. Generally, when b is fixed and N increases, ΔR increases with fluctuations, and Rb increases monotonously. When N is fixed and b increases, ΔR and Rb increases. Physical models were set up to describe and analyze the physical mechanism for the increment of ΔR and Rb due to impact. When b is fixed and N increases, the effect of N on Rb is divided into Stages #1 and #2. In Stage #1, mainly, it is the initiation and propagation of non-characteristic cracks (NCCs) that affects Rb. In Stage #2, the expansion of characteristic cracks (CCs) influences Rb greatly. Our measurement and analysis methods can be applied to the quality tests of other flexible functional materials, and provide useful guidelines for the development of flexible electronics.