Gas barrier layer deposited by Atomic Layer Deposition on polymeric substrate
Date Issued
2006
Date
2006
Author(s)
Kuo, Yueh-Hua
DOI
en-US
Abstract
In this study, we have successfully deposited an Al2O3 inorganic layer by atomic layer deposition (ALD) on polyimide (PI) substrates to achieve the requirement of OLEDs, 10−3 c.c./m2．day of OTR.
Previous literatures have shown that transmission of gases through intrinsically impermeable films proceeds through microscopic defects in the films. The particles cause incomplete coverage of the PI surface by a barrier, which lead to ineffective water vapor and oxygen barriers. We demonstrated that the step coverage of the Al2O3-ALD barriers were far superior to those deposited by other methods. We observed that a 113 Å Al2O3-ALD barrier is adequate to fully cover particles that were up to 6.01 μm in height, which are larger than the size of particles typically found on the surface of a PI substrate. The size of particles found on the surface of a PI substrate were small than 5μm in height. Therefore, the effects of particle-induced defects on permeation can be eliminated with an Al2O3-ALD that is thicker than 113-Å.
Despite having adequate thickness to fully cover particles, our ALD barriers failed to show expected barrier performance, because the PI substrate lacked chemisorption sites that are critical for the barrier to achieving complete surface coverage. We developed a wet treatment method that effectively created chemisorption sites on the PI substrate, which significantly improved the barrier performance of the resulted barriers.
Having determined the minimum required thickness, and achieved desired surface properties, we optimized the deposition conditions of the ALD barriers, which are: deposition temperature at 300℃, TMA/ pulse 0.1s/ exposure 5s/ pumping 5s/Water/ pulse 0.1s/ exposure 30s/ pumping 5s, and critical thickness 77Å.
Besides studying ALD barriers, we developed a simple, yet sensitive, permeation measurement method based on helium permeation to evaluate the barrier properties. We measured the helium permeability of the ALD barriers at different temperatures to determine the activation energy of permeation.
Employing the optimal thickness, surface treatment, and deposition conditions, we produced ALD barriers that reduced the PI substrate’s helium transmission rate (HeTR) from 1040 to 13 c.c./m2．day. These barriers caused the substrate’s activation energy of permeation to increase from 19.88 KJ/mole to 54.76 KJ/mole, indicating that gas permeation through the ALD barrier was not due to flow mostly through macroscopic defects, which is the permeation mechanism for all other known barriers.
OTR value of the optimized ALD barrier, whose HeTR is 13 c.c./m2．day, could not be measured, as it exceeded the lower limit of the methods available to us. Based on known transport mechanisms of gases through a porous membrane, we estimated the ALD barrier’s OTR to be below 1.1 × 10-3 c.c./m2．day, which satisfies the requirement of OLEDs.
Subjects
薄膜封裝
原子層沉積
氣體阻障層
thin film encapsulation
atomic layer deposition (ALD)
gas barrier layer
Type
thesis
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