Reliability of sputtered aluminum thin film on flexible substrate under high cyclic bending fatigue conditions

Aluminum thin films on flexible substrates are very popular as a back electrode in solar photovoltaic technology. However, during their manufacturing and use, the package is subject to cyclic bending, which leads to cracks in the conductive thin film and ultimately failure of the package. This paper investigates the effect of film thickness, bending diameter (BD), and number of cycles (NOC) on crack development and the percentage change in electrical resistance (PCER) of aluminum thin films under cyclic bending conditions. PCER-NOC diagrams are constructed at all considered factor-level combinations. These curves are used in comparisons between high and low levels of BD and film thickness. The Design of Experiment tool is used to investigate the effect and significance of film thickness, BD, NOC, and the interactions between them on the PCER. In this regard, all factors are found to be significant. Furthermore, thickness-NOC and BD-NOC interactions are significant, while thickness-BD interaction is not significant. Moreover, a finite element model is built to investigate the area of the highest stress on the aluminum thin film, in other words, the area with the most fatigue potential.