Fabrication and Characterization of Transparent Conductive ZnO:Al Thin Films Deposited on Polyethylene Terephthalate Substrates

Abstract

"This article deals with the optimization of the process parameters, with regard to multiple performance characteristics, involved in the preparation of transparent conducting Al2O3-doped (2 wt.%) zinc oxide (AZO) thin films deposited onto flexible polyethylene terephthalate (PET) substrates, using radio frequency (RF) magnetron sputtering. Experiments based on the Grey-Taguchi method were conducted to examine the influence of deposition parameters (RF power, sputtering pressure, substrate-to-target distance, and coating time) on the deposition rate, electrical resistivity and structural, morphological and optical transmittance. Experimental results indicate that using the optimal parameter set selected by Grey theory prediction, it is possible to achieve an improvement of 3.8% in deposition rate, of 45.6% in resistivity, and to maintain the transmittance over 80%, compared to that achieved by using the Taguchi method. For the Grey theory prediction, films were deposited using substrate-to-target distance of 80, 85, and 90 mm, while maintaining constant values for the other conditions. A clear decrease in resistivity was observed, as substrate-to-target distance decreased, with the lowest resistivity being obtained at 80 mm, although a better optical transmittance was achieved at a distance of 85 mm. It is evident that the resistivity decreases as the Al buffer thickness increases, with the lowest resistivity 7.0 x 10-4 O-cm, being found for a 15 nm thickness of Al buffer. The transmittance decreases, as the Al buffer thickness increases; transmittance values of 84.5%, 81.8%, and 79.4% correspond to an Al buffer thickness of 5, 10, and 15 nm, respectively. From the results of pull-off testing, the adhesive strength of the AZO film on a PET substrate increases, as the buffer thickness is increased."