Influence of the polymeric substrate on the water permeation of alumina barrier films deposited by atomic layer deposition

Atomic layer deposited (ALD) barrier films have been deposited onto a wide variety of flexible polymeric substrates to determine their effectiveness as moisture barriers for organic electronics. Little research has however been conducted on the contribution of the substrate to the barrier properties. In this study, alumina (Al2O3) barrier films have been deposited onto different polymeric substrates by ALD to investigate the effect of the substrate type and thickness on the water vapour transmission rate (WVTR). 24 nm Al2O3 films were deposited via plasma enhanced ALD onto 75 and 125 μm thick polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) substrates. Half of the substrates were also O2 plasma pre-treated prior to Al2O3 film deposition to determine its effect on the WVTR. The WVTR of the substrates prior to barrier film deposition was measured using tritiated water (HTO) permeation. Prior to barrier film deposition, it was shown that the WVTR decreased as the substrate thickness increased while PEN had a lower WVTR than PET. After Al2O3 barrier film deposition, the WVTR followed the previously observed trend with lower WVTR for thicker substrates and for PEN over PET. The substrates O2 plasma pre-treated prior to barrier film deposition also showed lower WVTRs, which were attributed to surface cleaning and improved film adhesion. The lowest WVTR measured was 3.1 × 10− 3 g·m− 2/day for a 24 nm Al2O3 film deposited onto O2 plasma pre-treated 125 μm PEN. These results demonstrate that the properties of the polymer substrate influence the WVTR even after barrier film deposition and can therefore be used to improve the barrier properties.