Highly-impermeable Al2O3/HfO2 moisture barrier films grown by low-temperature plasma-enhanced atomic layer deposition

Polymer substrates are essential components of flexible electronic applications such as OTFTs, OPVs, and OLEDs. However, high water vapor permeability of polymer films can significantly reduce the lifetime of flexible electronic devices. In this study, we examined the water vapor permeation barrier properties of Al2O3/HfO2 mixed oxide films on polymer substrates. Al2O3/HfO2 films deposited by plasma-enhanced atomic layer deposition were transparent, chemically stable in water and densely amorphous. At 60 °C and 90% relative humidity (RH) accelerated condition, 50-nm-thick Al2O3/HfO2 had water vapor transmission rate (WVTR) = 1.44 × 10−4 g m−2 d−1, whereas single layers of Al2O3 had WVTR = 3.26 × 10−4 g m−2 d−1 and of HfO2 had WVTR = 6.75 × 10−2 g m−2 d−1. At 25 °C and 40% RH, 50-nm-thick Al2O3/HfO2 film had WVTR = 2.63 × 10−6 g m−2 d−1, which is comparable to WVTR of conventional glass encapsulation.