Water Vapor Transmission Properties of Silicon Nitride Passivation for Organic Light Emitting Diodes

Abstract

Recently, passivation technique for organic light emitting diodes (OLEDs) has become important to improve life time of OLEDs device, as the demand of OLEDs for display and illumination increases. Nowadays, a very common technique is the encapsulation of OLEDs devices with a glass or metal lid. However, for large-area, flexible, or transparent applications, glass-lid encapsulation is not suitable. A promising alternative is thin film barriers of oxide or nitride, such as SiO2, SiN, Al2O3. Thesematerials can be deposited by CVD (Chemical Vapor Deposition), ALD (Atomic Layer Deposition) and Sputter. We demonstrated the water vapor transmission properties of Silicon Nitride according to deposition conditions such as plasma power, gas flow, and deposition pressure using Plasma Enhanced Chemical Vapor Deposition (PECVD). High deposition pressure could result in better WVTR property. It seems that deposition pressure is concerned with packing density of SiN film. To realize the packing density of SiN film, etching rate, curvature, and FTIR were measured. In order to obtain more dense structure, we designed multi-layer structure like SiN / SiO2, Al2O3, Parylene / SiN. When SiO2, Al2O3, Parylene were getting thicker,WVTR of films was decreased. It seemed that SiO2, Al2O3, Parylene act as barriers of water and oxygen. Due to this barrier effect, the passivation employing SiO2, Al2O3,Parylene showed better WVTR property compare with single layer structure.