Characterization of transparent aluminium oxide and indium tin oxide layers on polymer substrates

The structural, mechanical and gas barrier properties of aluminium oxide an d indium tin oxide coatings deposited by DC reactive sputtering on poly(eth ylene terephthalate) has been investigated. The oxygen and water vapour tra nsmission rates of the films were measured as a function of temperature in order to assess the effectiveness of the oxides as gas barriers. Both types of composites exhibited good resistance to water vapour transmission. Howe ver, the indium tin oxide coating was significantly more effective as a gas barrier than the conventional aluminium oxide. The microstructural integri ty of the oxide coatings was examined using scanning electron microscopy an d atomic force microscopy. It was found that the sputtered layers featured a relatively low density of defects. The aluminium oxide films featured lar ger and many more defects than the indium tin oxide composites. This differ ence, along with a preliminary observation of a difference in the chemical interaction of water vapour with indium tin oxide (ITO) and aluminium oxide (AIO(chi)), is believed to offer an explanation to the observed gas barrie r properties. In addition to displaying good gas barrier characteristics, t he ITO films were found to have better resistance to mechanical damage than either aluminium oxide and silicon oxide films. (C) 2001 Elsevier Science B.V. All rights reserved.