Among various thin film encapsulation (TFE) methods, thin films prepared by atomic layer deposition (ALD) have been shown to provide superior protection against the permeation of moisture and oxygen. This technique has numerous of advantages such as excellent uniformity, precise thickness control, and strong adhesion. Therefore, with ozone-based ALD, we conducted the influence of the thickness of aluminum oxide (Al₂O₃) on moisture barrier properties. From the results of an electrical calcium test, Al₂O₃ had two distinctly different permeation regimes. Between 10 and 25 nm of Al₂O₃ thickness, the water vapor transmission rate (WVTR) decreased exponentially from 6.3 × 10^-3 to 1.0 × 10^-4 g m^-2 day^-1 (1/60 times). In contrast, as thickness increased from 25 to 100 nm, the WVTR values decreased by only two-thirds, from 1.0 × 10^-4 to 6.6 × 10^-5 g·m^-2·day^-1. To better understand the change from an exponential to a sub-exponential regime, defect density and refractive index of Al₂O₃ were measured. The thickness dependence on defect density and refractive index was analogous with one of moisture barrier performance. These results confirmed the existence of a critical thickness at which the WVTR decreased drastically

Keywords: Aluminum oxide, Ozone, Atomic layer deposition, Water vapor transmission rate