Hygroscopic interlayers for multilayer Al2O3 barrier films

Abstract

We developed hygroscopic interlayers to constitute flexible Al2O3 deposited moisture-barrier films and investigated their moisture-barrier properties and flexibility. The hygroscopic interlayers were made from titanium (IV) methoxide (TiMO) and lithium acetylacetonate (Li(acac)) and deposited by thermal evaporation. The hygroscopic interlayers were confirmed to absorb moisture to form TiOTi bonds in a TiMO layer and LiOH, LiH bonding in a Li (acac) layer. The water vapor transmission rate (WVTR) for a 25 nm thick Al2O3 layer on a polyethylenenaphthalate substrate was 4.6 × 10−4 g/(m2·day) in the absence of a hygroscopic layer, whereas the WVTR for the Al2O3 (12.5 nm)/hygroscopic layer (100 nm)/Al2O3 (12.5 nm) barrier film reached 1.5 × 10−4 g/(m2·day) with a Li(acac) interlayer and 1.7 × 10−4 g/(m2·day) with a TiMO interlayer. When compared to a 25 nm thick Al2O3 single layer with no hygroscopic layers, the WVTR was reduced by 62% with a thick TiMO interlayer and by 63% with a Li(acac) interlayer placed between the Al2O3 layers. The two kind of multilayer barrier films showed improved flexibility when the hygroscopic interlayer was introduced. The WVTR increased by 131% after performing 1000 bending cycles to a bending radius of 1.5 cm, while the 25 nm single Al2O3 layer showed a larger increase of 374%. The hygroscopic interlayers thus improved both the moisture-barrier property and flexibility.