A study on the gas permeability properties of PEALD-grown TiO2 with respect to film thickness

Abstract

In recent years, organic electronic devices have required a thin film encapsulation that protects the device from oxygen and moisture. Thin film encapsulation (TFE) is most effective in preventing oxygen permeation and water vapor into the flexible devices. Thin film encapsulation has been studied on various inorganic materials through various deposition methods such as initial sputtering and plasma enhanced chemical vapor deposition (PECVD). However, it is difficult to obtain high quality inorganic thin film and problems such as particle generation occur in application and mass production. PEALD (Plasma enhanced Atomic Layer Deposition) can be used for low temperature process. Surface control reaction significantly reduces particle problems in the gas phase, and PEALD has the advantage of obtaining a high quality inorganic thin film. Also, it has excellent coverage at particle and high aspect ratio, which is very advantageous for thin film encapsulation. In this study, we investigated the properties and gas permeabilities of TiO2 films on flexible PEN substrates deposited by PEALD for encapsulate the OLEDs. As a result, the effects of deposition parameters on TiO2 film properties in terms of growth rate, refractive index, crystallinity, and gas permeability will be discussed. As a result, the growth rate of TiO2 thin films using O2 plasma was found to be about 0.74 Å / cycle at the deposition temperature of 100 ℃ and the refractive index was about 2.40 at the wavelength of 500nm. TiO2 thin films started to exhibit crystallinity from above 60 nm. And it was expected that the grain boundary would be a path through which the gas could pass, and the permeation preventing property would be reduced. It was confirmed that the same tendency can be obtained by measurement of the hydrogen gas permeability of the smallest atom size among the gases.