Extremely High Barrier Performance of OrganicâInorganic

Research Article www.acsami.org

Extremely High Barrier Performance of Organic−Inorganic Nanolaminated Thin Films for Organic Light-Emitting Diodes Kwan Hyuck Yoon,† Harrison S. Kim,† Kyu Seok Han,† Seung Hun Kim,‡ Yong-Eun Koo Lee,† Nabeen K. Shrestha,† Seung Yong Song,‡ and Myung Mo Sung*,† †

Department of Chemistry, Hanyang University, Seoul 04763, Republic of Korea Display Research Center, Samsung Display, Yongin-si, Gyeonggi-do 17113, Republic of Korea

‡

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S Supporting Information *

ABSTRACT: This work presents a novel barrier thin film based on an organic−inorganic nanolaminate, which consists of alternating nanolayers of self-assembled organic layers (SAOLs) and Al2O3. The SAOLs-Al2O3 nanolaminated films were deposited using a combination of molecular layer deposition and atomic layer deposition techniques at 80 °C. Modulation of the relative thickness ratio of the SAOLs and Al2O3 enabled control over the elastic modulus and stress in the films. Furthermore, the SAOLs-Al2O3 thin film achieved a high degree of mechanical flexibility, excellent transmittance (>95%), and an ultralow watervapor transmission rate (2.99 × 10−7 g m−2 day−1), which represents one of the lowest permeability levels ever achieved by thin film encapsulation. On the basis of its outstanding barrier properties with high flexibility and transparency, the nanolaminated film was applied to a commercial OLEDs panel as a gas-diffusion barrier film. The results showed defect propagation could be significantly inhibited by incorporating the SAOLs layers, which enhanced the durability of the panel. KEYWORDS: organic−inorganic nanolaminate, gas-diffusion barriers, atomic layer deposition, molecular layer deposition, organic-light emitting diodes

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glass lid with epoxy resin.6 Although the glass lid has the capacity to protect devices effectively from the penetration of water vapor and oxygen, the epoxy sealant cannot fully protect the OLEDs from gas diffusion.10,12 On the other hand, a thermo-compressive glass frit in combination with laser joining technology has been employed for the formation of highquality hermetic sealing.13,14 However, this can damage the OLEDs due to the generation of high temperatures by the laser sealing process. Moreover, the glass lid itself is not adaptable to flexible applications, suggesting that hermetic sealing technologies are not appropriate for flexible displays. Recently, thin film encapsulation (TFE) has emerged as an attractive method that can create a flexible encapsulating layer over a large area without the use of the sealants. Earlier, various inorganic thin film packaging technologies were investigated, such as inorganic single layers (SiNx, SiO2, Al2O3, AlOxN1−x, TiO2, etc.) and multilayers (SiNx/SiO2, Al2O3/SiO2, Al2O3/TiO2, Al2O3/ZrO2, etc.) prepared by evaporation,15 sputtering,16,17 plasmaenhanced chemical vapor deposition (PECVD),18,19 atomic layer deposition (ALD),20−22 and plasma-enhanced ALD (PEALD).23,24 However, due to the low-temperature fabrication process of these inorganic barrier materials, pinholes are introduced into the films; these act as pathways for gas

INTRODUCTION Organic light-emitting diodes (OLEDs) have emerged as a potent candidate for next-generation displays due to their multiple advantages in terms of color reproduction, wide viewing angles, fast response times, and low-voltage operation.1−3 Moreover, they offer additional advantages related to their flexibility, lightweight, and simplicity of processing even for large-area applications. As a result, OLEDs are suitable for several specific applications such as those that involve lightweight, bendable, and wearable displays.4,5 Currently, several OLEDs-based commercial products, including smart phones, tablet PCs, and TVs, have already been launched in consumer markets, demonstrating that OLEDs are compatible with industrial production. However, the metal electrodes and organic materials currently being used in OLEDs are very sensitive to moisture and air, limiting their lifespan.6−8 This is the key issue that hinders the successful application of OLEDs in the field of next-generation flexible displays. For commercial applications, the lifespan of an OLEDs-based product should exceed at least 10 000 h, a longevity which requires an oxygen transmission rate (OTR) of below 10−5 cm−3 m−2 day−1 and a water-vapor transmission rate (WVTR) of approximately 10−6 g m−2 day−1.8−10 In particular, water causes a more significant degradation of OLEDs than oxygen,7,11 and hence, the WVTR requirement must be achieved for effective encapsulation. Among the various available encapsulation methods, the most common is the hermetic sealing of the OLEDs using a © 2017 American Chemical Society

Received: December 2, 2016 Accepted: January 20, 2017 Published: January 20, 2017 5399

DOI: 10.1021/acsami.6b15404 ACS Appl. Mater. Interfaces 2017, 9, 5399−5408

Research Article

ACS Applied Materials & Interfaces

Figure 1. Schematic diagram of the fabrication procedure of SAOLs-Al2O3 nanolaminated thin films using MLD and ALD.

flash evaporation techniques for the deposition of organic layers in multilayer structures, other techniques (e.g., sol−gel, screen printing, vapor deposition polymerization, and chemical vapor deposition) have also been employed.25−29 However, the resulting multilayer thin films have shown no remarkable improvement in the barrier performance and still exhibit inadequate transparency and flexibility. Consequently, a fabrication method that can produce organic−inorganic multilayer thin films with substantially enhanced barrier properties is currently in high demand. One promising approach to overcoming the above limitations is to use the molecular layer deposition (MLD) technique for organic layers and atomic layer deposition (ALD) for inorganic layers. Both techniques are based on self-limiting surface reactions and can produce very thin, chemically bound conformal films that are uniform over a large area with precisely controlled thicknesses at the angstrom level with high reproducibility. Most importantly, films based on MLD/ALD contain a limited number of pinholes, and the individual deposition processes can be easily combined because they can be carried out in the same reaction chamber. Most hybrid nanolaminated barrier thin films deposited by MLD/ALD technologies have used an organic nanolayer called alucone and various oxide materials (e.g., Al2O3, TiO2/Al2O3, and ZrO2/ Al2O3) as inorganic nanolayers.35,42−48 However, as was also demonstrated by the previous studies,61−67 our preliminary study revealed that these hybrid nanolaminates do not show adequate barrier performance due to the poor air-stability of alucone.43,49 Recently, alkylsiloxane self-assembled monolayers (SAMs) were used to fabricate hybrid nanolaminated barrier

permeation through the barriers.15,18 Although increasing the film thickness can technically enhance the barrier performance,15,17 it inevitably decreases the flexibility and transparency of thin films. Recent studies have suggested that multilayer structures consisting of alternating inorganic and organic layers can create effective gas-diffusion barriers for OLEDs.25−29 In this multilayer structure, the inorganic layer serves as a thin barrier while the organic polymer layer serves as a decoupler of the pinholes in the inorganic layer.9,30−32 The organic layers spatially separate the defects or pinholes in each inorganic layer. Thus, a water molecule must travel a much longer distance before reaching subsequent pinholes in successive inorganic layers. As a result of this lag time effect,31 the gas transmission rate through multilayer films is delayed significantly. Moreover, the organic layer lends flexibility to the films and reduces the film stress relative to films consisting of only an inorganic layer.33−35 The multilayered encapsulation barrier from Vitex Systems consists of alternating layers of Al2O3 and polyacrylate with a several tens of nanometers-thick inorganic layer and several comparatively thicker organic layers on the micrometer scale. These inorganic and organic layered components are deposited using sputtering and flash evaporation techniques, respectively.8,25,36,37 However, both evaporation and sputtering methods deposit uniform films on a large scale only with great difficulty and often suffer from particle-related problems. These particles introduce many defects into the films, which leads to moisture penetration into the OLEDs.38,39 Additionally, outgassing of the physically adsorbed organic molecules within the films degrades the barrier performance.37,40,41 Apart from 5400


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ACS Applied Materials & Interfaces thin films using MLD/ALD-based TiO2.50 SAMs were deposited using MLD with a Ti-linker at 150 °C and served as stable decoupler layers. However, the SAM-TiO2 nanolaminated thin film demonstrated a barrier performance that was not adequate for the protection of OLEDs. Herein, we investigate novel organic−inorganic nanolaminated thin films that combine self-assembled organic layers (SAOLs) with an inorganic Al2O3 layer through MLD and ALD. SAOLs are highly ordered organic nanolayers with high density and stability.51−53 The nanolaminate demonstrates extremely high gas barrier efficiency with desirable flexibility. In addition, the SAOLs-Al2O3 barrier film was applied to a commercial OLEDs panel; this demonstrated excellent encapsulation performance, leading to remarkably high durability of the panel in air.

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RESULTS AND DISCUSSION Fabrication of SAOLs-Al2O3 Nanolaminated Thin Films by Using MLD and ALD. A schematic outline for the fabrication of a representative SAOLs-Al2O3 nanolaminated thin film by successive deposition of alternating layers of SAOLs and Al2O3 using MLD and ALD, respectively (Figure 1). First, alkylsiloxane-based self-assembled organic layers (SAOLs) were grown on a substrate through the repeated sequential adsorption of CC-terminated alkylsilane and aluminum hydroxide via ozone activation.51−53 Subsequently, the inorganic Al2O3 layer was deposited in the same reaction chamber by ALD, followed by the deposition of SAOLs. Note that the thickness of each organic and inorganic layer increases proportionately to the number of MLD and ALD cycles, respectively. Thus, the growth rates of the SAOLs and Al2O3 layers at 80 °C were found to be approximately 11 and 1 Å cycle−1, respectively, enabling us to control the thicknesses of the SAOLs and Al2O3 nanolayers precisely in each sample by adjusting the number of MLD and ALD cycles. To study the film properties, including the mechanical properties and barrier performance, five different samples were fabricated, as detailed in Table 1. In each nanolaminated thin film, 10-, 20-, and 40

Figure 2. Cross-sectional TEM image of SAOLs-Al2O3 nanolaminated structure grown by MLD and ALD at 80 °C.

Mechanical Properties of SAOLs-Al2O3 Nanolaminated Thin Films. The sample films, as described in Table 1, were subjected to nanoindentation analysis in order to measure their hardness (H) and elastic modulus (E), while their stresses were analyzed using residual stress measurements. Figure 3a and Table S1 show the measured values of E and H for the sample films. The E and H values were the highest for the pure Al2O3 film and then gradually decreased as the SAOLs thickness increased. This finding demonstrates that the E and H values of the nanolaminated films can be modulated by

Table 1. Structures of the SAOLs Organic Thin Film, SAOLs-Al2O3 Nanolaminates, and Al2O3 Inorganic Thin Filma film structure

SAOLs [nm]

SAOLs SAOLs-Al2O32:1 ratio 1:1 ratio 1:2 ratio Al2O3

103.1 40.3 20.2 10.4

Al2O3 [nm]

dyad

total [nm]

20.0 20.1 20.1 100.0

5 5 5

103.1 300.2 202.0 152.5 100.0

The thickness of the thin films was measured by spectroscopic ellipsometry. a

nm-thick organic layers were paired with a 20 nm-thick Al2O3 layer, and five dyads were stacked sequentially. Total thickness of inorganic Al2O3 layers in the nanolaminated structure was kept to be 100 nm in each of the films. For comparison, 100 nm-thick pure SAOLs and Al2O3 thin films were also deposited. Figure 2 shows the TEM image for a representative SAOLsAl2O3 film that contains five dyads, each consisting of 10.4 nmthick SAOLs and 20.1 nm-thick Al2O3 layers. Notably, the nanolaminated thin film has an amorphous structure. Thus, water molecules can be prevented from permeating along the grain boundaries in the crystalline films.15,20,54

Figure 3. (a) Elastic modulus and hardness; (b) residual film stress versus the film thickness ratio of SAOLs and Al2O3 in nanolaminated thin films. 5401


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ACS Applied Materials & Interfaces Table 2. Measured and Calculated WVTRs of Al2O3 and SAOLs-Al2O3 Nanolaminated Thin Films barrier film

WVTR in condition 1a [g m−2 day−1]

Al2O3 SAOLs-Al2O3 2:1 ratio 1:1 ratio 1:2 ratio a

5.84(±1.67) 1.62(±1.02) 1.69(±1.03) 1.58(±0.95)

× × × ×

WVTR in condition 2b [g m−2 day−1]

−3

10 10−3 10−3 10−3

1.65(±1.29) 3.33(±2.10) 3.47(±2.08) 3.22(±2.10)

× × × ×

−3

10 10−4 10−4 10−4

calculated WVTR at RT [g m−2 day−1] 5.13(±3.33) 3.20(±0.69) 3.32(±0.73) 2.99(±0.62)

× × × ×

10−6 10−7 10−7 10−7

Acceleration conditions at 85 °C, 85% RH; b70 °C, 90% RH.

electrode encapsulated by the pure Al2O3 thin film exhibited a change in conductance after approximately 36 h of exposure. Additionally, the conductance reached a near-zero value at 1140 h, indicating the complete oxidation of the Ca film. In contrast, the conductance change of the Ca electrode encapsulated with the nanolaminated thin films showed a significant lag time of approximately 300 h before undergoing a linear decrease that was proportionate to the exposure time. In the steady-state permeation regimes, only 24% of the Ca electrode was estimated to be oxidized in 1140 h; the electrode was expected to become fully oxidized after more than 4000 h. It is noteworthy that the lag time in the nanolaminated is estimated to be longer than 50 000 h under ambient condition. The WVTRs for all of the samples were derived by fitting eq 1, and the data values are presented in Table 2; the permeation rates represent the mean values taken from 20 test samples. It should be noted that all of the nanolaminated thin films achieved remarkably lower WVTR. Furthermore, the temperature-dependent permeation rate was calculated using the Arrhenius equation.58

modifying the relative thickness ratio between the organic and inorganic layers. Thus, the incorporation of organic layers into Al2O3 layers to form nanolaminated hybrid films can reduce the film strain, thereby preventing the structure from cracking under external strain. Residual stress also plays a key role in the mechanical flexing of encapsulation films. It is well-known that an internal tensile stress can lead to cracks in the films.9,55 Consequently, a residual compressive stress should be present in the encapsulation films in order to improve the tensile strength and layer/substrate adhesion.9,55,56 Moreover, improved barrier performance of encapsulation films can be achieved by adopting an optimal degree of compressive stress.55,56 Figure 3b reveals that the SAOLs thin film is under compressive stress, whereas the Al2O3 thin film is under tensile stress. However, it is important to observe that all three SAOLs-Al2O3 nanolaminated films are under compressive stress. Note that the tensile stress in the Al2O3 layer can be compensated for by the compressive stress in SAOLs. Figure 3b also shows that increasing the proportion of SAOLs in the entire film allows the stress in the nanolaminates to become more compressive. These results suggest that modulating the optimal degree of internal stresses is an effective route to improve both the barrier performance and the mechanical reliability. Barrier Properties of SAOLs-Al2O3 Nanolaminated Thin Films. The water-vapor transmission rate (WVTR) was measured using a Ca corrosion test to investigate the barrier properties of the SAOLs-Al2O3 nanolaminated thin films with regards to moisture. This test is based on the fact that when a Ca metal film electrode is oxidized by water, it is converted into Ca(OH)2, which is an electrical insulator.57 Thus, the WVTR through the barrier film can be quantified according to the change in the conductivity of the calcium film. The WVTR (permeation; P) can be obtained from the plot of the conductance change (1/R) versus exposure time (t) when exposed to the acceleration conditions based on the following equation:57

P = P0e−ΔEA / RT

where P0 is a constant characteristic constant for the reaction, EA is an activation energy of the permeation, R is the gas constant, and T is the absolute temperature. The permeation rates (P) were measured at three different temperature/relative humidity conditions, 50 °C/50%, 70 °C/90%, and 85 °C/85% RH. In accordance with the previously reported calculation procedure of WVTRs,59 P were converted into the rates at an absolute humidity of 8.7 g m−3 (24 °C, 40% RH). From the Arrhenius plot shown in Figure S2, we obtained activation energy (EA) values of 73.1 and 50.8 kJ mol−1 for the SAOLsAl2O3 nanolaminated film and Al2O3 film, respectively. The measured EA for the Al2O3 film was closer to a previously reported value.20,21 Based on the activation energy, the estimated permeability of the SAOLs-Al2O3 nanolaminated thin film with a 1:2 ratio showed an ultralow WVTR of 2.99 × 10−7 g m−2 day−1 at room temperature (RT) and 40% RH. This value, which satisfies the WVTR requirement for TFE, is among the lowest WVTR values ever reported (Table S2). These results, including the longer lag time and higher EA, indicate that the pathway for permeation becomes more tortuous when SAOLs are incorporated into Al2O3 layers. In order to confirm the reliability of the WVTR values obtained by the Ca corrosion test based on conductance monitoring, a modified Ca test model was also employed using an array of Ca dots. This test relies on the color change from dark gray to transparent due to the oxidation of Ca metal dots, which enables visual monitoring of the local defects or pinholes as a function of the exposure time. For the test, an array of 144 square-shaped Ca dots (0.50 mm × 0.50 mm) was deposited on glass substrates by thermal evaporation. The Ca dot array was subsequently encapsulated by pure Al2O3 and SAOLsAl2O3 nanolaminated thin films. The encapsulated Ca dot array

(1)

M(H 2O) l d R P = −n δρ M(Ca) b dt

(2)

(1)

Here, n is a stoichiometric coefficient (n = 2 for water) and M(H2O) and M(Ca) correspond to the molar masses of water and Ca, respectively. δ denotes the density of Ca, and ρ is the resistivity of Ca, and l and b are the length and width of the Ca active layer, respectively. Pure Al2O3 and three different SAOLs-Al2O3 nanolaminated thin films, as described in Table 1, were deposited on the Ca test sample using the ALD and MLD/ALD methods, respectively. The Ca corrosion test was conducted under two acceleration conditions: (i) 85 °C and 85% relative humidity (RH) and (ii) 70 °C and 90% RH. The changes in the conductance of the Ca film as a function of the exposure time to the acceleration condition (85 °C and 85% RH) are shown in Figure S1 (Supporting Information). The Ca 5402


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Figure 4. Array of 144 Ca dots encapsulated by 100 nm-thick Al2O3 and SAOLs-Al2O3 nanolaminated films with 2:1, 1:1, and 1:2 ratios. Photographs were taken as a function of the exposure time to an acceleration environment of 85% RH at 85 °C.

understand the effect of incorporating SAOLs into Al2O3 on water permeation, we analyzed the color changes of the Ca dots as a function of the number of dyads in the nanolaminated films, as shown in Figure S4. The total thickness of the Al2O3 layers in each barrier film was fixed at 100 nm. The number of oxidized Ca dots significantly decreased until the nanolaminated films contained more than three dyads of SAOLs and Al2O3 nanolayers. This result suggests that the SAOLs layer decouples pinholes in Al2O3 nanolayer, thereby interrupting the propagation of pinhole defects through the entire barrier film. It should also be noted that water permeation through the pinholes is decelerated by increasing the number of laminated dyads. Bending Properties of SAOLs-Al2O3 Nanolaminated Thin Films. In addition to the required barrier performance, the encapsulation films for flexible devices must also be able to resist the repetitive strain caused by the bending of devices during handling. Due to the presence of organic layers, the SAOLs-Al2O3 nanolaminated thin film should have enhanced flexibility as compared to the pure Al2O3 thin film; therefore, it may be suitable for flexible device applications. In order to demonstrate the flexible properties of the barrier thin films, we investigated the barrier performance after repeatedly bending the films. Evaluation of the barrier properties was carried out based on the Ca conductance and Ca dot array tests. A 100 nmthick pure Al2O3 thin film or a 150 nm-thick SAOLs-Al2O3 (1:2 ratio) nanolaminate was deposited as a barrier film over Ca metal electrodes or Ca dot arrays on polyethylene terephthalate (PET) substrates. First, the Ca conductance tests were performed by exposing the samples to an accelerated environment of 85 °C and 85% RH before and after the bending processes, which were conducted using a bending radius of 15 or 10 mm and repeated for 1000 bending cycles. Figure S5 shows the bending test procedure. The WVTR for the pure Al2O3 film on PET increased significantly from 7.65 × 10−6 g m−2 day−1 to 2.91 × 10−3 g m−2 day−1 when the film was bent with a 10 mm bending radius. In contrast, the SAOLs-Al2O3 nanolaminated film demonstrated only a slightly increased WVTR, rising from

was exposed to a controlled environment with a constant temperature and humidity (85 °C and 85% RH). Figure 4 shows photographs of the samples at exposure time of 24, 120, 360, and 720 h under the controlled environment. In accordance with the results of the Ca conductance test, the Al2O3 thin films (top row in Figure 4) showed significantly lower barrier performance than the nanolaminates. Nearly 50% and 70% of the Ca dots were completely oxidized and became transparent after 480 and 720 h of exposure, respectively. On the other hand, all of the SAOLs-Al2O3 nanolaminated thin films displayed outstanding barrier performance; only two out of 144 Ca dots were oxidized after 720 h of exposure, revealing a very high degree of homogeneity in terms of the barrier properties with a failure ratio of less than 2%. These results suggest that the barrier properties of the nanolaminated thin films, in relation to water-vapor permeation, do not depend on the thickness of the SAOLs. For comparison, pure SAOLs films were also deposited on Ca dots; these were all oxidized after just 10 h of exposure. Additionally, the oxidation of the Ca dot array provides information related to the existence of pinholes and their distributions. Although the 100 nm-thick Al2O3 barrier film has a moderate WVTR value (5.13 × 10−6 g m−2 day−1), about 13% of the Ca dots were oxidized completely after only 24 h of exposure, as shown in Figure 4 and Figure S3. Moreover, the number of the oxidized Ca dots increased progressively with exposure time. The rapid oxidation of Ca dots is attributed to the pinholes in the Al2O3 thin film deposited at a low temperature (80 °C),60,61 which form direct pathways for water-vapor permeation throughout the film.8,9,22,31 In contrast to the pure Al2O3 barrier film, the Ca dot array encapsulated by the SAOLs-Al2O3 nanolaminated thin film displayed only a few oxidized dots even after 720 h of exposure. Previous studies revealed that Al2O3 ALD thin films were corroded to show certain changes in surface morphology and film thickness when immersed in hot water at 90 °C.23,62 Any damage for the SAOLs-Al2O3 nanolaminated thin films, however, could not be found in the 90 °C hot water, which means that SAOLs might have acted as capping layers for the water corrosion. To better 5403


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Figure 5. (a) Array of 144 Ca dots encapsulated by 100 nm-thick Al2O3 or 150 nm-thick SAOLs-Al2O3 (1:2 ratio) nanolaminated thin films after bending for 1000 cycles with a 15 or 10 mm bending radius. Photographs were taken before and after exposure to an acceleration environment of 85% RH at 85 °C. Surface images of cracks in the 100 nm-thick Al2O3 film on a PET substrate after bending with a 15 mm radius. Images were taken with an (b) optical microscope and (c) scanning electron microscope.

5.43 × 10−7 g m−2 day−1 to 1.31 × 10−6 g m−2 day−1, after the same bending process. Subsequently, the Ca dot array tests were also conducted as shown in Figure 5a. The Ca dots encapsulated by the pure Al2O3 film were completely oxidized after only 24 h of exposure. This result implies that the external strain induced mechanical failure in the Al2O3 film. Indeed, channeling cracks were formed on the Al2O3 surface after bending, as shown in the optical microscopy and scanning electron microscopy (SEM) images of Figure 5b,c. Hence, water vapor easily penetrated through cracks to reach the Ca dots beneath the film. However, all of the Ca dots encapsulated by the SAOLs-Al2O3 nanolaminated film survived 24 h of exposure. At 720 h of exposure, after bending with a 15 or 10 mm radius, only 10 or 20 of the 144 Ca dots were oxidized, respectively. These results suggest that the nanolaminated thin film has better mechanical flexibility to allow better endurance to external strain, which is in good agreement with results of the elastic modulus and residual stress. These results demonstrate that the nanolaminated film is useful for the preparation of a flexible gas-diffusion barrier. Encapsulation of OLEDs Panels with SAOLs-Al2O3 Nanolaminated Thin Films. To practically evaluate the encapsulation thin films, we applied these nanolaminates to actual OLEDs panels and measured their functionality over time. A barrier test based on the OLEDs panel provides more realistic information about the encapsulation performance of the nanolaminated thin films. In this test, 3.5-in.-diagonal OLEDs panels were employed, as shown in Figure S6. A bare OLEDs panel was encapsulated by a 150 nm-thick SAOLs-

Al2O3 (1:2 ratio) nanolaminated thin film using MLD/ALD and exposed to accelerated condition of 85 °C and 85% RH for 720 h (30 days). For comparison, a 100 nm-thick pure Al2O3 thin film was also tested to determine its suitability as an encapsulation film. The lighting performance of the panels was monitored periodically, and the test results are shown in Figure 6. Initially, a clear white-light emission was observed from the

Figure 6. Photographs of the OLEDs panels before and after 720 h of exposure to an acceleration environment of 85 °C and 85% RH. (a) 100 nm-thick Al2O3 and (b) 150 nm-thick SAOLs-Al2O3 nanolaminated thin films were applied as the encapsulation layer. Insets show optical microscopy images of individual RGB cells in the respective OLEDs panels. RGB cell images were taken in the dark in order to clearly display the red, blue, and green lighting (scale bar: 100 μm). 5404


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ACS Applied Materials & Interfaces OLEDs panels that were encapsulated by either the pure Al2O3 thin film or the nanolaminate film. However, numerous dark spots were observed on the OLEDs panel encapsulated by the pure Al2O3 barrier film, and they grew larger as the exposure time increased (Figure 6a). The formation of dark spots is due to the existence of pinholes in the Al2O3 layer through which water vapor permeated to damage the pixels of the OLEDs panel.61,63 The dark region occupied more than 70% of the area of the 3.5 in. panel after 720 h of exposure. Furthermore, lateral diffusion of water vapor was also observed at the edges of the OLEDs panel. When water permeated through the interface between the barrier layer and OLEDs, dark regions showed up along the edges and then grew laterally in contrast to the radial growth of pinholes in the panel.64,65 This result demonstrates once again that the pure Al2O3 barrier film cannot protect the real OLEDs panel from moisture. In the case of the OLED panel encapsulated by the SAOLs-Al2O3 nanolaminated film, only nine tiny dark spots were observed without any edge degradation after 720 h of exposure to the accelerated condition (Figure 6b). These findings suggest that the MLD/ ALD process is compatible with the materials that comprise the OLEDs panel. Additionally, it is clear that the SAOLs-Al2O3 nanolaminated thin films are deposited conformally without causing any damage to the complex structure of the OLEDs. These results also reveal two roles of the SAOLs layer: providing an increased lag time to delay the formation of dark spots; and putting the encapsulation film under compressive stress to improve adhesion between the film and OLEDs, thereby preventing lateral diffusion at the edges of the panel. In addition to the efficient barrier performance, the SAOLsAl2O3 nanolaminated thin film must have high optical transparency to visible light in order to be used as a barrier film in a real OLEDs panel. Figure S7 reveals that the SAOLsAl2O3 nanolaminate has about 95% optical transparency in the visible and near-IR light region, indicating that the nanolaminate can be used as an encapsulation film in a real OLEDs panel. Furthermore, the red, green, and blue (RGB) color emission from the OLEDs panels encapsulated by the barrier films was investigated after exposing the panels to the accelerated environment. The insets of Figure 6 show representative optical microscopy images of the RGB color emission from individual RGB cells in the OLEDs panels after 720 h of exposure. A distinct RGB color emission was observed for the OLEDs panel encapsulated by the SAOLs-Al2O3 nanolaminated film, while a partially deteriorated emission was observed for the OLEDs panel encapsulated by the pure Al2O3 film. Direct Observation of Pinhole Decoupling by Organic Nanolayers in SAOLs-Al2O3 Nanolaminated Thin Films. For this study, several dark spots were created in the OLEDs panels, and their temporal behaviors after encapsulating the OLEDs with barrier thin films were monitored by observing the light-emission from the panel as a function of time. In order to prepare the initial OLEDs panels with dark spots, two sets of 3.5 in. OLEDs panels were encapsulated by a 20 nm-thick Al2O3 layer and exposed to air at room temperature. After 1 h, several dark spots appeared in the OLEDs panels as shown in Figure 7. The first set of the OLEDs panels with the dark spots was further coated with an 80 nm-thick Al2O3 thin film and then introduced into an environment chamber that was maintained at 85 °C and 85% RH. After 100 h of exposure to the accelerated condition, the initial dark spots grew radially, increasing in size by an average of 20 times. New dark spots of

Figure 7. Growth of dark spots in the OLEDs panels encapsulated by (a) an 80 nm-thick pure Al2O3 thin film and (b) four dyads of the SAOLs-Al2O3 (10 nm/20 nm for each dyad) nanolaminated thin film. In both (a) and (b), illustrations for water permeation to create dark spots (top) and photographs of the resultant OLED panel (bottom) are shown. The illustrations and photos on the left correspond to the initial OLEDs panels containing several dark spots, which were created by exposing each panel coated with a 20 nm-thick Al2O3 film to air at room temperature for 1 h. The right illustrations and photos show the progress of the initial dark spots in the OLEDs panels after exposure to an accelerated environment of 85 °C and 85% RH for 100 h.

various sizes were also observed, as shown in Figure 7a. As discussed above, the progressive radial growth of the dark spots as a function of the exposure time demonstrates that these defects have the characteristics of pinholes.61,63,65 The Al2O3 thin films deposited at 80 °C usually have many pinholes or defects of different sizes. For the OLEDs panel with only the 20 nm-thick Al2O3 layer, the large pinholes may have induced visible dark spots in the panel while the small defects were still invisible. Despite the additional deposition of the 80 nm-thick Al2O3 layer, the initial dark spots grew larger and new dark spots also appeared after 100 h of exposure. These results clearly reveal that the additional 80 nm-thick Al2O3 film cannot prevent the growth and propagation of existing defects.66 The second set of the OLEDs panels with several dark spots (Figure 7b) was further coated with four dyads of SAOLs-Al2O3 nanolaminated thin film. The additional nanolaminated thin film exerted an entirely different effect on the panel as compared to the case of the additional 80 nm-thick pure Al2O3 layer, despite the fact that the total thickness of Al2O3 was the 5405


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studies were prepared by mechanical grinding and polishing (∼10 μm thick) followed by Ar ion milling using a Gatan Precision Ion Polishing System (Model 691). The elastic modulus and hardness of the thin films were measured by a nanoindenter (G200, Agilent) using a continuous stiffness measurement (CSM). An XP Berkovich diamond tip with a radius of 20 nm and a length of 30 μm was used as an indenter. For the nanoindenter test, the total thickness of all of the films was 500 nm, with different thickness ratios between Al2O3 and SAOLs, as descibed in Table 1. A depth of 50 nm (a tenth of the total thickness) was used as the maximum penetration depth in order to reduce the substrate effect. The residual stress was determined by the wafer curvature method and Stoney’s equation.67 To obtain the intrinsic stress of the films, Young’s modulus was measured by nanoindentation. The curvature was measured before and after film growth on a 4-in. wafer with a stress measurement system (FSM 500TC, Frontier Semiconductor) at 24 °C. To measure the change of curvature precisely, Al2O3 or SAOLs-Al2O3 nanolaminated thin films on the backside of the wafer were removed using an HF solution. Ca Test Method. To prepare the Ca conductance test, Ag electrodes were evaporated on glass substrates through a shadow mask with a 500 μm channel. Subsequently, 200 nm-thick Ca metal films were thermally evaporated between two Ag electrodes. In order to ensure contact with the electrodes, the width of the Ca layer was 500 μm and its length was 800 μm. The conductance properties of the Ca test samples were measured with a semiconductor parameter analyzer (HP 4155C, Agilent Technologies). For evaluation of WVTRs on PET substrate, the same procedure was performed. The conductance properties of the Ca test samples on PET were measured before and after the bending process that were conducted using a bending radius of 15 or 10 mm and repeated for 1000 bending cycles. The array consisted of 144 square-shaped Ca dots with dimensions of 0.50 mm × 0.50 mm and a thickness of 100 nm. After Ca evaporation, the test samples were transferred in Ar gas to the MLD/ALD chamber to avoid oxidation.

same. The number of dark spots did not increase, and the size of the initial dark spots grew only slightly, even after 100 h of exposure to the accelerated condition. These results can be explained by a mechanism that is similar to the one reported previously for laminate-type TFE.9,30−32 This mechanism is illustrated schematically in Figure 7b. SAOLs spatially decouple the pinholes in successive Al2O3 nanolayers, and hence, the pinholes in the Al2O3 layer cannot propagate vertically to the top outer layer in the barrier film unlike the barrier film made solely of Al2O3. Thus, water molecules must travel a longer distance before reaching an available pinhole site in the next Al2O3 layer. As a result, the diffusion of water molecules through the entire barrier film is decelerated significantly.

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CONCLUSIONS In conclusion, we developed SAOLs-Al2O3 nanolaminates as a novel TFE for OLEDs by using a combination of MLD and ALD processes at 80 °C. The nanolaminated thin film demonstrated an optical transmittance of more than 95% in the visible region and a WVTR of 2.99 × 10−7 g m−2 day−1 at RT, which is one of the lowest water permeability rates that have ever been demonstrated by a thin OLEDs gas-diffusion barrier. The outstanding barrier performance of the SAOLsAl2O3 nanolaminated is due to the fact that the SAOLs decouple pinhole defect sites in successive Al2O3 nanolayers, thereby decelerating water permeation across the laminated structure. In addition, the nanolaminated films exhibited highly effective and homogeneous barrier properties with a failure ratio of less than 2% over a large area. When the nanolaminated film deposited on a PET substrate was bent 1000 times with a 10 mm bending radius, it exhibited a WVTR of 1.31 × 10−6 g m−2 day−1 with strong durability. The SAOLs-Al2O3 nanolaminated thin film also proved itself to be an efficient gasdiffusion barrier when applied to a commercial OLEDs panel. Owing to its ultralow water permeation rate, homogeneity of performance, transparency, and flexibility, the SAOLs-Al2O3 nanolaminated film is a promising candidate for the practical TFE of OLEDs.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b15404. Nanoindentation, residual stress measurement, WVTRs of various barrier thin films, Ca test, and UV−visible spectroscopy results of the samples (PDF)

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EXPERIMENTAL SECTION

Sample Fabrication. Al2O3 thin films were deposited onto various substrates (Si, glass, PET) at 80 °C using trimethylaluminum (Aldrich; 97%) and H2O as ALD precursors. Ar served as a carrier and purging gas with a flow rate of 100 sccm. Trimethylaluminum (TMA) and water were evaporated at 20 °C. Each ALD cycle consisted of 1 s exposure to TMA, 5 s Ar purge, 1 s exposure to water, and 5 s Ar purge. Alkene-terminated self-assembled organic layers (SAOLs) were deposited by exposing the substrates to 7-octenyltrichlorosilane (7OTS) (Aldrich; 96%) with H2O vapor at 80 °C in the same reaction chamber. 7-OTS and water were evaporated at 80 and 20 °C, respectively. Exposure times in this process were 5 s for the 7-OTS with water vapor and 10 s for the Ar purge. The reactor pressure during the ALD and MLD processes was about 400 mTorr. The terminal CC groups of the SAOLs were converted to carboxylic acid groups (COOH) via ozone treatment in the ALD chamber. Ozone was generated by an ozone generator and the 7-OTS coated samples were dosed for 20 s at 80 °C. Highly active aluminum hydroxyl groups were formed on the COOH-terminated SAOLs via TMA adsorption. This was followed by the exchange reaction of water molecules in order to provide highly active adsorption sites for the anchoring of the subsequent organic layer. The SAOLs-Al2O3 nanolaminated thin films were grown using the cyclic MLD/ALD process. Sample Characterization. The thin films were analyzed by an ellipsometer (SE MG-1000, Nano-View) and a JEOL-2100F transmission electron microscope. Specimens for cross-sectional TEM

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Myung Mo Sung: 0000-0002-2291-5274 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Nano-Material Technology Development Program (2012M3A7B4034985) and by the Creative Materials Discovery Program (2015M3D1A1068061) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning. This work was also supported by a grant from the National Research Foundation of Korea (NRF), funded by the Korea government (MSIP) (No. 2014R1A2A1A10050257).

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REFERENCES

(1) Tang, C. W.; VanSlyke, S. A. Organic Electroluminescent Diodes. Appl. Phys. Lett. 1987, 51, 913−915.

5406


Research Article

ACS Applied Materials & Interfaces (2) Dawson, R. M. A.; Shen, Z.; Furst, D. A.; Connor, S.; Hsu, J.; Kane, M. G.; Stewart, R. G.; Ipri, A.; King, C. N.; Green, P. J.; Flegal, R. T.; Pearson, S.; Barrow, W. A.; Dickey, E.; Ping, K.; Tang, C. W.; Van Slyke, S. A.; Chen, F.; Shi, J.; Sturm, J. C.; Lu, M. H. 4.2: Design of an lmproved Pixel for a Polysilicon Active-Matrix Organic LED Display. Dig. Tech. Pap. - Soc. Inf. Disp. Int. Symp. 1998, 29, 11−14. (3) Baldo, M.; Lamansky, S.; Burrows, P.; Thompson, M.; Forrest, S. Very High-Efficiency Green Organic Light-Emitting Devices Based on Electrophosphorescence. Appl. Phys. Lett. 1999, 75, 4−6. (4) Gu, G.; Burrows, P.; Venkatesh, S.; Forrest, S. R.; Thompson, M. E. Vacuum-Deposited, Nonpolymeric Flexible Organic Light-Emitting Devices. Opt. Lett. 1997, 22, 172−174. (5) Görrn, P.; Sander, M.; Meyer, J.; Kröger, M.; Becker, E.; Johannes, H. H.; Kowalsky, W.; Riedl, T. Towards See-Through Displays: Fully Transparent Thin-Film Transistors Driving Transparent Organic Light-Emitting Diodes. Adv. Mater. 2006, 18, 738− 741. (6) Burrows, P. E.; Bulovic, V.; Forrest, S. R.; Sapochak, L. S.; McCarty, D. M.; Thompson, M. E. Reliability and Degradation of Organic Light Emitting Devices. Appl. Phys. Lett. 1994, 65, 2922− 2924. (7) Papadimitrakopoulos, F.; Zhang, X.-M.; Higginson, K. A. Chemical and Morphological Stability of Aluminum Tris(8-Hydroxyquinoline) (Alq): Effects in Light-Emitting Devices. IEEE J. Sel. Top. Quantum Electron. 1998, 4, 49−57. (8) Burrows, P. E.; Graff, G. L.; Gross, M. E.; Martin, P. M.; Hall, M.; Mast, E.; Bonham, C. C.; Bennett, W. D.; Michalski, L. A.; Weaver, M. S.; Brown, J. J.; Fogarty, D.; Sapochak, L. S. Gas Permeation and Lifetime Tests On Polymer-Based Barrier Coatings. Proc. SPIE 2000, 4105, 75−83. (9) Lewis, J. S.; Weaver, M. S. Thin-Film Permeation-Barrier Technology for Flexible Organic Light-Emitting Devices. IEEE J. Sel. Top. Quantum Electron. 2004, 10, 45−57. (10) Park, J.-S.; Chae, H.; Chung, H. K.; Lee, S. I. Thin Film Encapsulation for Flexible AM-OLED: a Review. Semicond. Sci. Technol. 2011, 26, 034001. (11) Schaer, M.; Nüesch, F.; Berner, D.; Leo, W.; Zuppiroli, L. Water Vapor and Oxygen Degradation Mechanisms in Organic Light Emitting Diodes. Adv. Funct. Mater. 2001, 11, 116−121. (12) Carcia, P. F.; McLean, R. S.; Groner, M. D.; Dameron, A. A.; George, S. M. Gas Diffusion Ultrabarriers on Polymer Substrates Using Al2O3 Atomic Layer Deposition and SiN Plasma-Enhanced Chemical Vapor Deposition. J. Appl. Phys. 2009, 106, 023533. (13) Knechtel, R. Glass Frit Bonding: an Universal Technology for Wafer Level Encapsulation and Packaging. Microsyst. Technol. 2005, 12, 63−68. (14) Cruz, R.; da Cruz Ranita, J. A.; Macaira, J.; Ribeiro, F.; da Silva, A. M. B.; Oliveira, J. M.; Fernandes, M. H. F. V.; Ribeiro, H. A.; Mendes, J. G.; Mendes, A. Glass−Glass Laser-Assisted Glass Frit Bonding. IEEE Trans. Compon., Packag., Manuf. Technol. 2012, 2, 1949−1956. (15) Chatham, H. Oxygen Diffusion Barrier Properties of Transparent Oxide Coatings on Polymeric Substrates. Surf. Coat. Technol. 1996, 78, 1−9. (16) Henry, B. M.; Dinelli, F.; Zhao, K.-Y.; Grovenor, C. R. M.; Kolosov, O. V.; Briggs, G. A. D.; Roberts, A. P.; Kumar, R. S.; Howson, R. P. A Microstructural Study of Transparent Metal Oxide Gas Barrier Films. Thin Solid Films 1999, 355, 500−505. (17) Erlat, A. G.; Henry, B. M.; Ingram, J. J.; Mountain, D. B.; McGuigan, A.; Howson, R. P.; Grovenor, C. R. M.; Briggs, G. A. D.; Tsukahara, Y. Characterisation of Aluminium Oxynitride Gas Barrier Films. Thin Solid Films 2001, 388, 78−86. (18) da Silva Sobrinho, A. S.; Czeremuszkin, G.; Latreche, M.; Wertheimer, M. R. Defect-Permeation Correlation for Ultrathin Transparent Barrier Coatings on Polymers. J. Vac. Sci. Technol., A 2000, 18, 149−157. (19) Sugimoto, A.; Ochi, H.; Fujimura, S.; Yoshida, A.; Miyadera, T.; Tsuchida, M. Flexible OLED Displays Using Plastic Substrates. IEEE J. Sel. Top. Quantum Electron. 2004, 10, 107−114.

(20) Meyer, J.; Görrn, P.; Bertram, F.; Hamwi, S.; Winkler, T.; Johannes, H.-H.; Weimann, T.; Hinze, P.; Riedl, T.; Kowalsky, W. Al2O3/ZrO2 Nanolaminates as Ultrahigh Gas-Diffusion BarriersA Strategy for Reliable Encapsulation of Organic Electronics. Adv. Mater. 2009, 21, 1845−1849. (21) Carcia, P. F.; McLean, R. S.; Reilly, M. H.; Groner, M. D.; George, S. M. Ca Test of Al2O3 Gas Diffusion Barriers Grown by Atomic Layer Deposition on Polymers. Appl. Phys. Lett. 2006, 89, 031915. (22) Dameron, A. A.; Davidson, S. D.; Burton, B. B.; Carcia, P. F.; McLean, R. S.; George, S. M. Gas Diffusion Barriers on Polymers Using Multilayers Fabricated by Al2O3 and Rapid SiO2 Atomic Layer Deposition. J. Phys. Chem. C 2008, 112, 4573−4580. (23) Kim, L. H.; Kim, K.; Park, S.; Jeong, Y. J.; Kim, H.; Chung, D. S.; Kim, S. H.; Park, C. E. Al2O3/TiO2 Nanolaminate Thin Film Encapsulation for Organic Thin Film Transistors via Plasma-Enhanced Atomic Layer Deposition. ACS Appl. Mater. Interfaces 2014, 6, 6731− 6738. (24) Yun, S. J.; Ko, Y.-W.; Lim, J. W. Passivation of Organic LightEmitting Diodes with Aluminum Oxide Thin Films Grown by PlasmaEnhanced Atomic Layer Deposition. Appl. Phys. Lett. 2004, 85, 4896− 4898. (25) Weaver, M. S.; Michalski, L. A.; Rajan, K.; Rothman, M. A.; Silvernail, J. A.; Brown, J. J.; Burrows, P. E.; Graff, G. L.; Gross, M. E.; Martin, P. M.; Hall, M.; Mast, E.; Bonham, C.; Bennett, W.; Zumhoff, M. Organic Light-Emitting Devices with Extended Operating Lifetimes on Plastic Substrates. Appl. Phys. Lett. 2002, 81, 2929−2931. (26) Kim, K. M.; Jang, B. J.; Cho, W. S.; Ju, S. H. The Property of Encapsulation Using Thin Film Multi Layer for Application to Organic Light Emitting Device. Curr. Appl. Phys. 2005, 5, 64−66. (27) Kim, N.; Potscavage, W. J.; Domercq, B.; Kippelen, B.; Graham, S. A Hybrid Encapsulation Method for Organic Electronics. Appl. Phys. Lett. 2009, 94, 163308. (28) Lee, Y. G.; Choi, Y.-H.; Kee, I. S.; Shim, H. S.; Jin, Y.; Lee, S.; Koh, K. H.; Lee, S. Thin-Film Encapsulation of Top-Emission Organic Light-Emitting Devices with Polyurea/Al2O3 Hybrid Multi-Layers. Org. Electron. 2009, 10, 1352−1355. (29) Jung, K.; Bae, J.-Y.; Park, S. J.; Yoo, S.; Bae, B.-S. High Performance Organic-Inorganic Hybrid Barrier Coating for Encapsulation of OLEDs. J. Mater. Chem. 2011, 21, 1977−1983. (30) Affinito, J. D.; Gross, M. E.; Coronado, C. A.; Graff, G. L.; Greenwell, I. N.; Martin, P. M. A New Method for Fabricating Transparent Barrier Layers. Thin Solid Films 1996, 290, 63−67. (31) Graff, G. L.; Williford, R. E.; Burrows, P. E. Mechanisms of Vapor Permeation Through Multilayer Barrier Films: Lag Time versus Equilibrium Permeation. J. Appl. Phys. 2004, 96, 1840−1849. (32) Greener, J.; Ng, K. C.; Vaeth, K. M.; Smith, T. M. Moisture Permeability Through Multilayered Barrier Films as Applied to Flexible OLED Display. J. Appl. Polym. Sci. 2007, 106, 3534−3542. (33) Cordero, N.; Yoon, J.; Suo, Z. Channel Cracks in a Hermetic Coating Consisting of Organic and Inorganic Layers. Appl. Phys. Lett. 2007, 90, 111910. (34) Miller, D. C.; Foster, R. R.; Zhang, Y.; Jen, S.-H.; Bertrand, J. A.; Lu, Z.; Seghete, D.; O’Patchen, J. L.; Yang, R.; Lee, Y.-C.; George, S. M.; Dunn, M. L. The Mechanical Robustness of Atomic-Layer- and Molecular-Layer-Deposited Coatings on Polymer Substrates. J. Appl. Phys. 2009, 105, 093527. (35) Jen, S.-H.; Lee, B. H.; George, S. M.; McLean, R. S.; Carcia, P. F. Critical Tensile Strain and Water Vapor Transmission Rate for Nanolaminate Films Grown Using Al2O3 Atomic Layer Deposition and Alucone Molecular Layer Deposition. Appl. Phys. Lett. 2012, 101, 234103. (36) Nisato, G.; Kuilder, M.; Bouten, P.; Moro, L.; Philips, O.; Rutherford, N. P-88: Thin Film Encapsulation for OLEDs: Evaluation of Multi-layer Barriers Using the Ca Test. Dig. Tech. Pap. - Soc. Inf. Disp. Int. Symp. 2003, 34, 550−553. (37) Chwang, A. B.; Rothman, M. A.; Mao, S. Y.; Hewitt, R. H.; Weaver, M. S.; Silvernail, J. A.; Rajan, K.; Hack, M.; Brown, J. J.; Chu, X.; Moro, L.; Krajewski, T.; Rutherford, N. Thin Film Encapsulated 5407


Research Article

ACS Applied Materials & Interfaces Flexible Organic Electroluminescent Displays. Appl. Phys. Lett. 2003, 83, 413−415. (38) Selwyn, G. S.; Weiss, C. A.; Sequeda, F.; Huang, C. Particle Contamination Formation in Magnetron Sputtering Processes. J. Vac. Sci. Technol., A 1997, 15, 2023−2028. (39) Ghosh, A. P.; Gerenser, L. J.; Jarman, C. M.; Fornalik, J. E. ThinFilm Encapsulation of Organic Light-Emitting Devices. Appl. Phys. Lett. 2005, 86, 223503. (40) Kwon, J.-S.; Jung, H.; Yeo, I. S.; Song, T.-H. Outgassing Characteristics of a Polycarbonate Core Material for Vacuum Insulation Panels. Vacuum 2011, 85, 839−846. (41) Li, F.-J.; Roh, B.-G.; Lim, H.-T.; Kim, J.-S.; Park, J.-Y.; Yu, H.W.; Park, S.-C.; Tak, Y.-H.; Ahn, B.-C. Mechanism of Droplet Generation in Silver Thin Films for Organic Light-Emitting Diode Displays. Thin Solid Films 2009, 517, 2941−2944. (42) Xiao, W.; Hui, D. Y.; Zheng, C.; Yu, D.; Qiang, Y. Y.; Ping, C.; Xiang, C. L.; Yi, Z. A Flexible Transparent Gas Barrier Film Employing the Method of Mixing ALD/MLD-Grown Al2O3 and Alucone Layers. Nanoscale Res. Lett. 2015, 10, 1−7. (43) Vähä-Nissi, M.; Sundberg, P.; Kauppi, E.; Hirvikorpi, T.; Sievänen, J.; Sood, A.; Karppinen, M.; Harlin, A. Barrier Properties of Al2O3 and Alucone Coatings and Nanolaminates on Flexible Biopolymer Films. Thin Solid Films 2012, 520, 6780−6785. (44) Feng-Bo, S.; Yu, D.; Yong-Qiang, Y.; Ping, C.; Ya-Hui, D.; Xiao, W.; Dan, Y.; Kai-wen, X. Fabrication of Tunable [Al2O3:Alucone] Thin-Film Encapsulations for Top-Emitting Organic Light-Emitting Diodes with High Performance Optical and Barrier Properties. Org. Electron. 2014, 15, 2546−2552. (45) Park, M.; Oh, S.; Kim, H.; Jung, D.; Choi, D.; Park, J.-S. Gas Diffusion Barrier Characteristics of Al2O3/Alucone Films Formed Using Trimethylaluminum, Water and Ethylene Glycol for Organic Light Emitting Diode Encapsulation. Thin Solid Films 2013, 546, 153− 156. (46) Hossbach, C.; Nehm, F.; Singh, A.; Klumbies, H.; Fischer, D.; Richter, C.; Schroeder, U.; Albert, M.; Müller-Meskamp, L.; Leo, K.; Mikolajick, T.; Bartha, J. W. Integration of Molecular-Layer-Deposited Aluminum Alkoxide Interlayers Into Inorganic Nanolaminate Barriers for Encapsulation of Organic Electronics with Improved Stress Resistance. J. Vac. Sci. Technol., A 2015, 33, 01A119. (47) Xiao, W.; Yu, D.; Bo, S. F.; Qiang, Y. Y.; Dan, Y.; Ping, C.; Hui, D. Y.; Yi, Z. The Improvement of Thin Film Barrier Performances of Organic-Inorganic Hybrid Nanolaminates Employing a Low-Temperature MLD/ALD Method. RSC Adv. 2014, 4, 43850−43856. (48) Zhang, H.; Ding, H.; Wei, M.; Li, C.; Wei, B.; Zhang, J. Thin Film Encapsulation for Organic Light-Emitting Diodes Using Inorganic/Organic Hybrid Layers by Atomic Layer Deposition. Nanoscale Res. Lett. 2015, 10, 1−5. (49) Dameron, A. A.; Seghete, D.; Burton, B. B.; Davidson, S. D.; Cavanagh, A. S.; Bertrand, J. A.; George, S. M. Molecular Layer Deposition of Alucone Polymer Films Using Trimethylaluminum and Ethylene Glycol. Chem. Mater. 2008, 20, 3315−3326. (50) Seo, S.; Jung, E.; Lim, C.; Chae, H.; Cho, S. M. Water Permeation Through Organic-Inorganic Multilayer Thin Films. Thin Solid Films 2012, 520, 6690−6694. (51) Lee, B. H.; Ryu, M. K.; Choi, S.-Y.; Lee, K.-H.; Im, S.; Sung, M. M. Rapid Vapor-Phase Fabrication of Organic-Inorganic Hybrid Superlattices with Monolayer Precision. J. Am. Chem. Soc. 2007, 129, 16034−16041. (52) Lee, B. H.; Lee, K. H.; Im, S.; Sung, M. M. Monolayer-Precision Fabrication of Mixed-Organic-Inorganic Nanohybrid Superlattices for Flexible Electronic Devices. Org. Electron. 2008, 9, 1146−1153. (53) Lee, B. H.; Lee, K. H.; Im, S.; Sung, M. M. Vapor-Phase Molecular Layer Deposition of Self-Assembled Multilayers for Organic Thin-Film Transistor. J. Nanosci. Nanotechnol. 2009, 9, 6962−6967. (54) Fisher, J. C. Calculation of Diffusion Penetration Curves for Surface and Grain Boundary Diffusion. J. Appl. Phys. 1951, 22, 74−77. (55) Leterrier, Y. Durability of Nanosized Oxygen-Barrier Coatings on Polymers. Prog. Mater. Sci. 2003, 48, 1−55.

(56) Chen, T. N.; Wuu, D. S.; Wu, C. C.; Chiang, C. C.; Chen, Y. P.; Horng, R. H. High-Performance Transparent Barrier Films of SiOx/ SiNx Stacks on Flexible Polymer Substrates. J. Electrochem. Soc. 2006, 153, F244−F248. (57) Paetzold, R.; Winnacker, A.; Henseler, D.; Cesari, V.; Heuser, K. Permeation Rate Measurements by Electrical Analysis of Calcium Corrosion. Rev. Sci. Instrum. 2003, 74, 5147−5150. (58) Tropsha, Y. G.; Harvey, N. G. Activated Rate Theory Treatment of Oxygen and Water Transport through Silicon Oxide/Poly(ethylene terephthalate) Composite Barrier Structures. J. Phys. Chem. B 1997, 101, 2259−2266. (59) Paetzold, R.; Henseler, D.; Heuser, K.; Cesari, V.; Sarfert, W.; Wittmann, G.; Winnacker, A. High-Sensitivity Permeation Measurements on Flexible OLED Substrates. Proc. SPIE 2003, 5214, 73−82. (60) Groner, M. D.; Fabreguette, F. H.; Elam, J. W.; George, S. M. Low-Temperature Al2O3 Atomic Layer Deposition. Chem. Mater. 2004, 16, 639−645. (61) Maindron, T.; Jullien, T.; André, A. Defect Analysis in Low Temperature Atomic Layer Deposited Al2O3 and Physical Vapor Deposited SiO Barrier Films and Combination of Both to Achieve High Quality Moisture Barriers. J. Vac. Sci. Technol., A 2016, 34, 031513. (62) Abdulagatov, A. I.; Yan, Y.; Cooper, J. R.; Zhang, Y.; Gibbs, Z. M.; Cavanagh, A. S.; Yang, R. G.; Lee, Y. C.; George, S. M. Al2O3 and TiO2 Atomic Layer Deposition on Copper for Water Corrosion Resistance. ACS Appl. Mater. Interfaces 2011, 3, 4593−4601. (63) Bertrand, J. A.; George, S. M. Evaluating Al2O3 Gas Diffusion Barriers Grown Directly on Ca Films Using Atomic Layer Deposition Techniques. J. Vac. Sci. Technol., A 2013, 31, 01A122. (64) Park, S.-H. K.; Oh, J.; Hwang, C.-S.; Lee, J.-I.; Yang, Y. S.; Chu, H. Y. Ultrathin Film Encapsulation of an OLED by ALD. Electrochem. Solid-State Lett. 2005, 8, H21−H23. (65) Yun, W. M.; Jang, J.; Nam, S.; Kim, L. H.; Seo, S. J.; Park, C. E. Thermally Evaporated SiO Thin Films As a Versatile Interlayer for Plasma-Based OLED Passivation. ACS Appl. Mater. Interfaces 2012, 4, 3247−3253. (66) Lee, J. G.; Kim, H. G.; Kim, S. S. Defect-Sealing of Al2O3/ZrO2 Multilayer for Barrier Coating by Plasma-Enhanced Atomic Layer Deposition Process. Thin Solid Films 2015, 577, 143−148. (67) Stoney, G. G. The Tension of Metallic Films Deposited by Electrolysis. Proc. R. Soc. London, Ser. A 1909, 82, 172−175.

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