PERMEATION BARRIER PROPERTIES OF Al2O3/ZrO2 MULTILAYER DEPOSITED BY REMOTE PLASMA ATOMIC LAYER DEPOSITION

Abstract

Recently, the encapsulation techniques have been researched intensively for various applications such as food packaging, photovoltaic and organic devices. Especially organic devices such as organic light emitting diodes (OLEDs) require highly advanced encapsulation layer because of the early degradation of organic materials by water and oxygen in ambient. One of the most common techniques nowadays is to use glass with UV-cured epoxy resin dispensed at the side edges of devices as glue with getter inside. It is, however, inapplicable for flexible devices due to the high brittleness of glass under the mechanical stress. Therefore, Alternative encapsulation layers require < 10-5 g/m2day of permeation rate to guarantee the life time of >10,000 hrs to realize flexible devices. We report the permeation barrier properties of Al2O3/ZrO2 multi-layers deposited by remote plasma atomic layer deposition. Electrical Ca degradation test was carried out to derive water vapor transmission rate (WVTR) of single Al2O3, ZrO2 and Al2O3/ZrO2 multi-layers at 50°C, 50% relative humidity (RH). Al2O3/ZrO2 multi-layer exhibit better barrier properties compared to single Al2O3 and ZrO2 layer, furthermore, when more number of individual layers are deposited in the same total thickness, the WVTR value reduced further indicating better permeation barrier property. WVTR of single Al2O3 and ZrO2 layers are 9.5x10-3g/m2day and 1.6x10-2g/m2day respectively but when they are deposited alternatively with 1 cycle of each layer, WVTR decrease to 9.9x10-4g/m2day. X-ray diffraction results indicate that single ZrO2 has monoclinic structure which could play a role as permeation path but single Al2O3 and Al2O3/ZrO2 multi-layers show amorphous structure. Cross sectional Al2O3/ZrO2 multi-layer structures and the formation of ZrAlxOy phase are observed by transmission electron microscopy. XPS results indicate that single Al2O3 and ZrO2 contain 33.7% and 37.8% of Al-OH and Zr-OH bonding. However, ZrAlxOy phase contain 30.5% of Al-OH and Zr-OH bonding. The results of transmittance measurement indicate that overall, single Al2O3, ZrO2 and Al2O3/ZrO2 multi-layers show relatively high transmittance over 80% in visible region while single ZrO2 showed lower transmittance than others because of light scattering caused by grain boundary in crystalline film and surface roughness.