Effect of a hard coating layer on the damp heat stability of Ga-doped ZnO thin films on polyethylene terephthalate substrates

We investigated the damp heat stability of Ga-doped ZnO (GZO) thin films grown on polyethylene terephthalate (PET) substrates. In order to find the effect of the hard coating layer, GZO thin films were grown on PET substrates with and without a hard coating layer by rf-magnetron sputtering at room temperature. After the deposition, a damp heat stability test was performed at 60 .deg. C with a relative humidity of 90% for up to 150 hr. At the initial stage of the damp heat stability test, a rapid decay of the electrical property of GZO thin film was observed in both samples. In this experiment, the main mechanism of the degradation was a reduction of the mobility rather than the carrier concentration. The mobility of GZO on hard coated PET was saturated after the initial stage while there was further deterioration in the GZO thin film on bare PET. The origin was investigated with transmission electron microscopy and the result showed that the interfacial structure between the GZO thin film and the substrate play an important role in the damp heat stability.