Effects of defects in SiO₂ thin films prepared on polyethylene terephthalate by high-temperature E-beam deposition

In this study, we characterized silicon oxide (SiO₂) thin film prepared on polyethylene terephthalate (PET) substrates by electron-beam (e-beam) deposition for transparent barrier application. As the chamber temperature is increased from 30 to 110°C, the roughness increases while water vapor transmission rate (WVTR) decreases. Under these conditions, WVTR of PET can be reduced from a level of 0.57 g/m²/day (bare subtrate) to 0.05 g/m²/day after application of a 200-nm-thick SiO₂ coating at 110°C. A more efficient way to improve permeation of PET was carried out by using a double sided coating of a 5-μm-thick parylene film. It was found that WVTR for PET substrates can be reduced to a level of -0.2 g/m²/day. The double-sided parylene coating on PET could contribute in lowering the stress of oxide film, which greatly improves the WVTR data. These results indicate that the Sip₂/parylene/PET barrier coatings have a high potential for flexible organic light-emitting diode (OLED) applications.