Behavior of sputtered indium-tin-oxide thin film on poly-ethylene terephthalate substrate under stretching

In this work, two different sheet resistances, 100 and 60 Ω per square of DC-Magnetron sputtered indium tin oxide (ITO) thin film on poly ethylene terephthalate (PET) substrate were stretched up to 15% of the original length under three different strain rates, 0.01, 0.1, and 1.0 min^-1. The cracks development during stretching was monitored using optical microscope. Two types of cracks were observed: in the first type, cracks initiated perpendicularly to the tensile load and propagated towards the edge of the sample, which was observed at 4% strain for both sheet resistances and different strain rates. In the second type, cracks initiated from the first type cracks and propagated perpendicularly to it towards the next original crack. The cracks intensity for both types of cracks was investigated. The intensity of both cracks type increases with the strain and sheet resistance. The electrical resistance was measured every 1% strain during stretching. The relative electrical resistance change (Δ R/R₀) was plotted against strain at different strain rates. It could be concluded that, the relative electrical resistance change under high strain rate is higher at the beginning of the stretching process, but after a certain strain, the relative electrical resistance change under the lower strain rate accelerated till the film becomes non-conductive while the relative electrical resistance change under high strain rate is in acceleration process until reaching non-conductive condition. Analysis of Variance (ANOVA) results showed that the strain and the sheet resistance are significant factors on the relative electrical resistance change at 95% confidence level. The strain rate was not significant factor in the range considered. No two factor interactions are significant as well.