Defect-sealing of Al2O3/ZrO2 multilayer for barrier coating by plasma-enhanced atomic layer deposition process

• Inorganic barrier coatings were prepared on PEN by plasma-enhanced atomic layer deposition.
• Reduction of defects reached a plateau in single-component layers.
• Alternating Al2O3 and ZrO2 layers reduced further the number of defects.
• Increase of Al2O3/ZrO2 stacks remarkably reduced the WVTR value to below 5 × 10− 5 g/m2 day.

Barrier layers were coated by plasma enhanced atomic layer deposition. They had inevitable defects for several reasons and these defects deteriorated the diffusion barrier properties. The size of the pinhole defect decreased with the increase of the layer thickness resulting in enhanced barrier properties, until the thickness reached 20 nm for a single-component aluminum oxide (Al2O3) or zirconium oxide (ZrO2) layer. No more enhancement of barrier properties was observed with a further increase of layer thickness, since the defects tended to grow in single-component layers. Alternation of Al2O3 and ZrO2 layers prevented defect growth by covering the defects with another component, and enhanced the barrier properties when compared with single-component layers. Increase of the number of Al2O3/ZrO2 stacks with the same total layer thickness remarkably reduced the water vapor transmission rates value to below 5 × 10− 5 g/m2 day at 38 °C and 100% relative humidity. The Al2O3/ZrO2 multilayer formed on a polyethylene naphthalate substrate at optimized conditions showed light transmittance greater than 86% at a wavelength of 550 nm, for application as flexible display substrate.