A study on gas barrier of polymer substrates
Date Issued
2008
Date
2008
Author(s)
Lee, Yun-Jun
Abstract
Aluminum oxide (Al2O3) thin films are applied to flexible polymer substrates as gas-permeation barriers by atomic layer deposition (ALD), and the barrier performance is evaluated by measuring the helium transmission rate (HeTR) of the barrier-coated PI substrates. The HeTR of the ALD films is reduced from 901.12 to 10.42 cc/m2 day by introducing precursor exposure steps in the initial stage of the ALD process; with the oxygen transmission rate (OTR) reduced to below the sensitivity, 0.1 cc/m2 day, of the available measurement apparatus. This improvement is attributed to enhanced nucleation of the ALD films as a result of the thorough surface-to-precursor interactions during the exposure steps. The barrier performance of the ALD films improves with the film thickness in the thickness range examined in this study, 7-30 nm. Despite having good barrier performance, the ALD Al2O3 films are highly unstable in air due to their strong tendency to hydrolyze in the presence of the ambient moisture, showing 10-fold increase in HeTR upon 50 hr of storage in air. This problem is resolved by laminating the Al2O3 films with ALD HfO2 films, which is performed in one ALD process. The laminated films maintain constant HeTR over 420 hr of storage in air. This improvement is attributed to the hydrophobicity of HfO2, which prevents moisture concentration from building up in the Al2O3 layers, thereby minimizing hydrolysis of the Al2O3 layers.
Subjects
Al2O3
HfO2
ALD
inorganic thin film
gas permeability
Type
thesis
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