Water vapor barrier properties of transparent SnO2-SiOx composite films on polymer substrate

Composite thin films consisting of silicon oxide and tin oxide have been deposited on polycarbonate substrates as gas barrier films, using a thermal evaporation process in an oxygen gas environment. Water vapor permeation through the composite films is significantly affected by the chemical interaction of water vapor with the composite oxide films and the microstructure of the composite oxide films. The chemical interaction of water vapor with oxide films has been investigated by the considering the refractive index obtained from ellipsometry and the OH group peak from X-ray photoelectron spectroscopy, and the microstructure of the composite oxide films has been characterized using atomic force microscopy. As the tin oxide is added to the silicon oxide, the refractive index and OH group peak intensity of the composite films increase, and the water vapor transmission rate through the composite oxide films shows a lower value than that through the single-element oxide films, such as tin oxide and silicon oxide alone. The results are discussed in terms of the chemical interaction with water vapor and the microstructure of the oxide films. Finally, the water permeation mechanism related to the diffusivity and solubility of water vapor was qualitatively analyzed on the basis of the results of Fourier transform infrared spectroscopy.