Low-temperature remote plasma enhanced atomic layer deposition of ZrO2/zircone nanolaminate film for efficient encapsulation of flexible organic light-emitting diodes

Zheng Chen,Yunfei Liu,Xiao Wang,Yu Duan,Hongyu Zhao,Haoran Wang,Yi Zhao,Ping Chen

doi:10.1038/srep40061

Abstract

Encapsulation is essential to protect the air-sensitive components of organic light-emitting diodes (OLEDs) such as active layers and cathode electrodes. In this study, hybrid zirconium inorganic/organic nanolaminates were fabricated using remote plasma enhanced atomic layer deposition (PEALD) and molecular layer deposition at a low temperature. The nanolaminate serves as a thin-film encapsulation layer for OLEDs. The reaction mechanism of PEALD process was investigated using an in-situ quartz crystal microbalance (QCM) and in-situ quadrupole mass spectrometer (QMS). The bonds present in the films were determined by Fourier transform infrared spectroscopy. The primary reaction byproducts in PEALD, such as CO, CO2, NO, H2O, as well as the related fragments during the O2 plasma process were characterized using the QMS, indicating a combustion-like reaction process. The self-limiting nature and growth mechanisms of the ZrO2 during the complex surface chemical reaction of the ligand and O2 plasma were monitored using the QCM. The remote PEALD ZrO2/zircone nanolaminate structure prolonged the transmission path of water vapor and smooth surface morphology. Consequently, the water barrier properties were significantly improved (reaching 3.078 × 10−5 g/m2/day). This study also shows that flexible OLEDs can be successfully encapsulated to achieve a significantly longer lifetime.

Highlights

In previous study, we demonstrated that protective amorphous ZrO2 thin films can be produced at a low growth temperature by thermal ALD using O3 as the oxidant
The remote plasma enhanced ALD (PEALD) method has the advantage of a lower deposition temperature because the plasma enhances the reactivity of the precursors and a remote plasma reactor minimizes the effect of plasma-induced damage to the organic electronic device[28]
In the film growth process, the possible sequential reaction mechanisms of tetrakis(dimethylamino)zirconium (TDMAZ) and the O2 plasma were explored for the first time using an in-situ quartz crystal microbalance (QCM), an in-situ quadrupole mass spectrometer (QMS), and a Fourier transform infrared spssectrometer (FTIR)

Summary

Introduction

We demonstrated that protective amorphous ZrO2 thin films can be produced at a low growth temperature by thermal ALD using O3 as the oxidant. The emerging molecular layer deposition (MLD) method can be used for organic materials to fabricate high-quality thin films This technique provides new types of highly uniform and conformal hybrid inorganic/ organic thin films. The ZrO2 ALD and zircone MLD alloy TFEs were fabricated using the remote plasma enhanced ALD (PEALD) method at a low deposition temperature (80 °C). We found an interesting phenomenon: The film roughness shifted after modifying the relative number of ZrO2 ALD and zircone MLD cycles in the pulse sequence In this approach, an extremely low WVTR of 3.078 × 10−5 g/m2 day was achieved using a 60 nm-ZrO2/zircone hybrid thin film (4 nm-ZrO2/1 nm-zircone) on a polyethylene glycol terephthalate (PET) substrate. The optimized hybrid film TFE of the structure exhibits a superior continuous operation lifetime of approximately 3.1-fold and 9.5-fold than that of the device TFE with pure ZrO2 and zircone-based TFE, respectively, under the controlled environment of 20 °C and a relative humidity of 60%

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Results

Conclusion