Moisture barrier properties of low-temperature atomic layer deposited Al₂O₃ using various oxidants

In this study, the growth characteristics and film properties of the atomic layer deposition (ALD) of Al₂O₃ are systemically identified using various oxidants (i.e., H₂O, H₂O₂, CH₃COOH, and O₃). Among these reactants, ALD Al₂O₃ grown by using H₂O₂ exhibits excellent density and refractive index, which may be attributed to the large number of hydroxyl groups on the surface after reactant exposure, forming a dense film. When CH₃COOH is used for the ALD Al₂O₃ oxidant, poor quality films with relatively small density and refractive index and high carbon impurities were deposited possibly due to the formation of carbon species, such as carbonates or formates. In the case of ALD Al₂O₃ that uses O₃, the film property is barely changed with the growth temperature increase because the reaction between trimethylaluminum and O₃ is incomplete in low-temperature region (<150 °C), and impurities that are difficult to eliminate remain. Among these Al₂O₃ films prepared by using different oxidants, H₂O₂-grown Al₂O₃ at 120 °C exhibits the lowest water vapor transmission rates, ca. 2.7 × 10⁻⁴ g/m²⋅day, owing to the high density of the film with negligible amount of impurities. Therefore, ALD Al₂O₃ using H₂O₂ is expected to be a promising encapsulation layer for future flexible OLED devices with excellent characteristics.