Improvement of Durability in Silicon Nitride Barrier Films for Flexible OLED Displays under High Temperature and High Hu
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1030-G01-09
Improvement of Durability in Silicon Nitride Barrier Films for Flexible OLED Displays under High Temperature and High Humidity Conditions Kunio Akedo, Atsushi Miura, Koji Noda, and Hisayoshi Fujikawa TOYOTA Central R&D Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi, 480-1192, Japan ABSTRACT We have developed a new silicon nitride (SiNx) multilayer barrier film by a plasmaenhanced chemical vapor deposition (CVD) for a flexible organic light emitting diode (OLED), which consists of SiNx films in two different deposition conditions, that is, a transparent SiNx layer (tr-SiNx) deposited with NH3 gas and an ultra-thin SiNx layer (cap-SiNx) deposited without NH3 gas, which caps over the former layer. This barrier film is expected to exhibit high durability under high temperature and high humidity conditions even at high deposition rate over 100 nm / minute, because the transparent SiNx layer, that is easily oxidized under such conditions, is protected by the cap-SiNx layer and the interface between them, and also show good transparency, because the opaque cap-SiNx layer is enough thin to be almost transparent to visible light. Thus, the multi-layer SiNx barrier film indicates the specific features as a high barrier performance, high transparency, and high productivity, and makes it possible to apply flexible OLED displays to automobile use. INTRODUCTION Light-emitting diodes based on organic materials [1] are highly attractive candidates for flat-panel displays and the backlights of liquid crystal displays. Nowadays, thanks to developments in materials, device structures, and process techniques, organic light emitting diodes (OLEDs) with a high luminous efficiency [2,3] and a long lifetime [4] have been demonstrated, and red, green, and blue light emitting devices are already available. Moreover, OLED displays with transparent plastic substrates and barrier thin films are expected to find applications in next-generation wide-area flat-panel displays that are thin, lightweight, and flexible. Barrier thin films are fabricated on both sides of OLED devices in order to prevent moisture ingress directly from the air and moisture penetration through the substrates which don’t have enough impermeability to moisture for the OLEDs. Recently, many barrier films have been reported, such as Barix multilayer barrier films by a vacuum evaporation method [5], silicon oxy-nitride films by a sputtering method [6], aluminum oxide films by an atomic layer deposition method [7], and so on. Inorganic thin films created by a chemical vapor deposition (CVD) method also have been regarded as being well suited to this application because they offer a high barrier performance, good coverage, and high productivity. Indeed, silicon nitride (SiNx) films have already been shown to be well suited to OLED barrier films for encapsulation [8]. In addition to their excellent features, they also show low flexibility because they are so fragile that easily crack when bending. However it has been improved by adopting new barrier films by a CVD meth
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