Reduction of Defects in SiOx Vapor Permeation Barriers on Polymer Substrates by Introducing a Sputtered Interlayer

Abstract

This paper investigated the water-vapor permeability of silicon oxide (SiOx) barriers grown on poly(ethylene terephthalate) (PET) substrates using plasma-enhanced chemical vapor deposition (PECVD). The water-vapor transmission rate (WVTR) of granular-type SiOx barriers is dependent upon the density of microscopic pinholes in the barriers. A two-step hybrid process, consisting of (i) a sputtering stage for 10-nm-thick Al2O3 interlayer growth and (ii) a subsequent PECVD stage for thicker SiOx film growth, was proposed in this study. Granules and pinholes in SiOx barriers were simultaneously eliminated by introducing an Al2O3 interlayer on the PET surface prior to the SiOx PECVD process. Plasma-induced reconstruction of PET surfaces was prevented by applying a reactive sputtering process to grow the Al2O3 interlayer. High-quality barriers were developed from SiOx growth on the sputtered interlayer. Low WVTR values in the range of 10-3 g m-2 d-1 were recorded in tests using a MOCON instrument. The WVTR was two orders of magnitude smaller than that of conventional SiOx barriers directly grown on PET substrates without the Al2O3 interlayer.