A study on crack propagation and electrical resistance change of sputtered aluminum thin film on poly ethylene terephthalate substrate under stretching

This work is designed to study crack development and resistance changes in aluminum thin films under stretching. Crack development and relative electrical resistance change (δR/R₀) of aluminum thin film on 127-μm poly ethylene terephthalate substrates were investigated as a function of engineering strain. Four thicknesses were considered for the aluminum thin films: 50, 100, 200, and 500 nm. The engineering stress-engineering strain curves were very similar for all thicknesses. Three strain rates were considered in this study: 0.1 min^{- 1}, 0.5 min^{- 1} and 1.0 min ^{- 1}. Before the yield point, there was no stress difference under different strain rates. However, after the yield point, stress was higher at a higher strain rate. It was found that δR/R₀ was very sensitive to the film thickness. Optical microscope images at high magnification showed that cracks were observed at 2% strain for 100, 200, and 500 nm-thick films and at 8% strain for the 50 nm-thick films. Short lateral cracks (perpendicular to the original cracks) were observed at 20% strain for the 100 and 200 nm thick films and at 30% for the 500 nm thick films.