Designing interlayers to improve the mechanical reliability of transparent conductive oxide coatings on flexible substrates

In this study, we investigate the effect of interlayers on the mechanical properties of transparent conductive oxide (TCO) on flexible polymer substrates. Indium tin oxide (ITO), which is the most widely used TCO film, and Ti, which is the most widely used adhesive interlayer, are selected as the coating and the interlayer, respectively. These films are deposited on the polymer substrates using dc-magnetron sputtering to achieve varying thicknesses. The changes in the following critical factors for film cracking and delamination are analyzed: the internal stress (σ ⁱ) induced in the coatings during deposition using a white light interferometer, the crystallinity using a transmission electron microscope, and the surface roughness of ITO caused by the interlayer using an atomic force microscope. The resistances to the cracking and delamination of ITO are evaluated using a fragmentation test. Our tests and analyses reveal the important role of the interlayers, which significantly reduce the compressive σ ⁱ that is induced in the ITO and increase the resistance to the buckling delamination of the ITO. However, the relaxation of σ ⁱ is not beneficial to cracking because there is less compensation for the external tension as σ ⁱ further decreases. Based on these results, the microstructural control is revealed as a more influential factor than σ ⁱ for improving crack resistance.