Al2O3 multi-density layer structure as a moisture permeation barrier deposited by radio frequency remote plasma atomic layer deposition

Abstract

Al2O3 films deposited by remote plasma atomic layer deposition have been used for thin film encapsulation of organic light emitting diode. In this study, a multi-density layer structure consisting of two Al2O3 layers with different densities are deposited with different deposition conditions of O-2 plasma reactant time. This structure improves moisture permeation barrier characteristics, as confirmed by a water vapor transmission rate (WVTR) test. The lowest WVTR of the multi-density layer structure was 4.7 x 10(-5) gm(-2) day(-1), which is one order of magnitude less than WVTR for the reference single-density Al2O3 layer. This improvement is attributed to the location mismatch of paths for atmospheric gases, such as O-2 and H2O, in the film due to different densities in the layers. This mechanism is analyzed by high resolution transmission electron microscopy, elastic recoil detection, and angle resolved X-ray photoelectron spectroscopy. These results confirmed that the multi-density layer structure exhibits very good characteristics as an encapsulation layer via location mismatch of paths for H2O and O-2 between the two layers.