High-performance water vapor barriers via amorphous alumina-polycrystalline zinc oxide hybrids with a self-wrinkling morphology

This work presents a materially and structurally designed barrier thin film with a self-wrinkling morphology, which consists of composites of amorphous alumina (a-Al2O3) and polycrystalline zinc oxide (ZnO). The pure ZnO, Al2O3 films, and Al2O3-ZnO composited film are deposited on polyethylene terephthalate (PET) by magnetron co-sputtering at room temperature. The water vapor transmission rate (WVTR) for the composited film with about 30 % ratio of Al2O3 to ZnO is down to 0.026 g·m−2·day−1 from 1.184 g·m−2·day−1 of pure ZnO film at 38 °C/90 % RH, indicating that the nanocomposite structure of amorphous Al2O3 and crystalline ZnO can significantly improve the water-resistance performance. Theoretical calculations demonstrate that the amorphous Al2O3 can dramatically suppress the defect fraction within ZnO from 4.65 % to 0.08 %. Furthermore, a self-wrinkling morphology with Al2O3-ZnO composited film deposited on PET/acrylic is designed to have the WVTR value as low as 1.30 × 10−3 g·m−2·day−1. Due to the stress release when forming micro-scale wrinkles, the more smooth and dense Al2O3-ZnO composited film can markedly sharpen up the barrier property. The low WVTR barriers via amorphous and crystalline hybrid composites with self-wrinkling morphology by magnetron sputtering potentially serve as a low-cost and large-scale production path for electronics encapsulation as compared to atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD).