Protecting an atomic layer deposited aluminum oxide barrier coating on a flexible polymer substrate

Atomic layer deposited (ALD) inorganic thin film coatings can produce high barrier properties against moisture and gas. However, if an ALD film is exposed to mechanical stress, it may lose these properties. In this study, a 40-nm thick aluminum oxide (Al2O3) ALD barrier layer turned out fragile on a low density polyethylene (LDPE) coated paper substrate during web handling. In such handling, the processing steps, such as bending, roll contacts, and friction, weakened the structure of the barrier. However, when the Al2O3 layer was deposited on polyethylene terephthalate coated paper, no loss of barrier properties was observed after web handling. We show here that an Al2O3 ALD barrier layer can be protected on an LDPE substrate against mechanical stress by adding a shielding polyethylene layer on top of the ALD coating. After this addition, oxygen permeation through the protected surface remained unchanged during web handling. The results of this study demonstrate that the protective layer was necessary to maintain the excellent barrier properties and intactness of the ALD layer on an LDPE substrate.