Realization of highly-dense Al2O3 gas barrier for top-emitting organic light-emitting diodes by atomic layer deposition

Abstract

In this paper Al₂O₃ films are prepared with a method of atomic layer deposition (ALD) as the thin film encapsulation technology for top-emitting organic light-emitting diodes (TE-OLED). Time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-Ray Reflectometry (XRR) and X-ray photoelectron spectroscopy (XPS) are used to analyze the effect of different chemical precursors and behavioral factors on the performance of the Al₂O₃ thin films. The analyses disclosed that Al₂O₃ films prepared with a trimethylaluminum (TMA) and H₂O (TMA + H₂O) process contained more unreacted –CH₃ groups, and the films with a TMA + O₃ process show a large number of carbon-based impurities. However, the Al₂O₃ films prepared using H₂O and O₃ in turn in a deposition cycle as oxygen sources exhibited higher density and purity, leading to a superior water vapor transmission rate (WVTR) as low as 5.43 × 10⁻⁵ g per m² per day estimated with the calcium (Ca) corrosion method at 40 °C/100%. The TE-OLED with Al₂O₃ (TMA + H₂O + O₃) thin film as an encapsulated layer has longer lifetimes, and produces no black spots under operational times up to 400 hours.