Water vapor and hydrogen gas diffusion barrier characteristics of Al2O3–alucone multi-layer structures for flexible OLED display applications

Abstract

Organic light emitting diodes (OLEDs) and amorphous oxide semiconductors (AOSs), which are very important technologies in high performance flexible displays, have issues related to degradation due to diffusion of water and hydrogen, respectively. To solve these issues, gas diffusion barrier properties were evaluated with aluminum oxide deposited by atomic layer deposition (ALD) and alucone deposited by molecular layer deposition (MLD) using trimethylaluminum (TMA) as a metal precursor and H₂O and hydroquinone (HQ) as co-reactants, respectively. The water vapor transmission rate (WVTR) and hydrogen gas permeability (HGP) were measured for the fabricated films via electrical calcium tests and vacuum time-lag, respectively. To enhance the diffusion barrier properties, Al₂O₃/alucone hybrid multi-layer structures were successfully deposited through an in situ ALD/MLD process. The 4.5 dyads of the Al₂O₃/alucone structure showed improved barrier properties compared to the single Al₂O₃ film with a WVTR of 8.24 × 10⁻⁵ g m⁻² day⁻¹ and a HGP of 9.93 × 10⁻⁵ barrer, and factors related to gas diffusion in multi-layer structures were discussed. The stability to external stress was also evaluated based on the WVTR change rate after the bending test, and we confirmed that the stability of the multi-layer structures was improved due to the flexibility of inserted alucone layers. All the developed structures had a high optical transmittance of >80% in the 300–800 nm wavelength region based on UV-vis measurements.