Performance of aluminum-doped zinc oxide thin films under bending fatigue conditions

Aluminum-doped zinc oxide (AZO) film is a promising candidate for low cost transparent conductive oxide (TCO) applications. It is a viable alternative to indium tin oxide (ITO), the dominant material used in TCO. Although AZO has good electrical and optical properties, its mechanical properties must be thoroughly considered in the design and manufacturing of flexible devices. During the manufacture and use, thin films' are subjected to bending fatigue (cyclic bending) which leads to degradation and ultimately failure of the films. This work was designed to investigate the effects of the bending frequency, bending diameter, ways of bending, and number of bending cycles on the percentage change in electrical resistance (PCER) and transmittance of 575 nm thick AZO films, which were deposited on 127 μm Kapton substrate using RF-magnetron sputtering technique. Both the film and the substrate were subjected to cyclic bending test under controlled study parameters. The design of experiments technique (DOE) was used to investigate the significant factors on the PCER as well as to provide an average estimate of the effect of each factor and two-factor interaction through the main effects plot and the two-factor interaction plot, respectively. Moreover, the transmittance spectra were studied at different number of bending cycles. The primary result shows that the PCER is very sensitive to all study parameters. However, it increases rapidly in the first 400 bending cycles and then increases linearly until 1000 bending cycles. The result also points out that the PCER is large while the small bending diameter and low bending frequency are applied. Also the two ways bending experiment leads to the larger PCER compared with the one way bending test. The fresh films average transmittance (from 660 to 950 nm wavelength) is 59.6%, which decreased to about 3.4% after 1000 cycles of bending.