Flexible Al2O3/plasma polymer multilayer moisture barrier films deposited by a spatial atomic layer deposition process

Abstract

Al2O3/plasma polymer multilayers were developed and characterized for the moisture barrier films of flexible organic devices. The inorganic Al2O3 thin films were deposited by a spatial atomic layer deposition process and the organic layers were deposited by plasma polymerization in the same chamber using CHF3, benzene, and cyclohexane precursors. The deposition rate, light transmittance, and surface roughness of the plasma polymer films obtained from the three precursors were investigated. The three plasma polymer layers were introduced between Al2O3 layers and their effect on the water permeability and flexibility of each Al2O3/plasma polymer multilayer structure was evaluated. The multilayer structure with hydrocarbon from cyclohexane shows better flexibility than that with fluorocarbon by CHF3 and hydrocarbon by benzene. Polymer interlayers with plasma thicker than 20 nm are necessary for reasonable flexibility. The authors increased the number of layers up to 21 to improve the water permeability and flexibility. The water vapor transmission rate (WVTR) of a 100 nm-thick Al2O3/plasma polymer was reduced to 8.5 × 10−5 g/m2 day with the 21-layer structure. This WVTR value is 58% lower than that of the 100 nm-thick single-layer Al2O3. The WVTR of a 100 nm-thick single-layer Al2O3 increased by 900% when it was bent 1000 times with a bending radius of 1 cm due to film cracks, while, under the same conditions, the 21-layer structure showed only a 32% increase in the WVTR. These results indicate that the nanometer-scale-thick plasma polymer can be an effective solution for multilayer moisture barrier films.