Thickness dependent barrier performance of permeation barriers made from atomic layer deposited alumina for organic devices

Organic devices like organic light emitting diodes (OLEDs) or organic solar cells degrade fast when exposed to ambient air. Hence, thin-films acting as permeation barriers are needed for their protection. Atomic layer deposition (ALD) is known to be one of the best technologies to reach barriers with a low defect density at gentle process conditions. As well, ALD is reported to be one of the thinnest barrier layers, with a critical thickness – defining a continuous barrier film – as low as 5–10 nm for ALD processed Al₂O₃. In this work, we investigate the barrier performance of Al₂O₃ films processed by ALD at 80 °C with trimethylaluminum and ozone as precursors. The coverage of defects in such films is investigated on a 5 nm thick Al₂O₃ film, i.e. below the critical thickness, on calcium using atomic force microscopy (AFM). We find for this sub-critical thickness regime that all spots giving raise to water ingress on the 20 × 20 μm² scan range are positioned on nearly flat surface sites without the presence of particles or large substrate features. Hence below the critical thickness, ALD leaves open or at least weakly covered spots even on feature-free surface sites. The thickness dependent performance of these barrier films is investigated for thicknesses ranging from 15 to 100 nm, i.e. above the assumed critical film thickness of this system. To measure the barrier performance, electrical calcium corrosion tests are used in order to measure the water vapor transmission rate (WVTR), electrodeposition is used in order to decorate and count defects, and dark spot growth on OLEDs is used in order to confirm the results for real devices. For 15–25 nm barrier thickness, we observe an exponential decrease in defect density with barrier thickness which explains the likewise observed exponential decrease in WVTR and OLED degradation rate. Above 25 nm, a further increase in barrier thickness leads to a further exponential decrease in defect density, but an only sub-exponential decrease in WVTR and OLED degradation rate. In conclusion, the performance of the thin Al₂O₃ permeation barrier is dominated by its defect density. This defect density is reduced exponentially with increasing barrier thickness for alumina thicknesses of up to at least 25 nm.     

Repeatedly foldable AMOLED display

In this study, a 5.9‐inch foldable active‐matrix organic light emitting diode (AMOLED) display was developed. A folding test was performed repeatedly. The display survived the folding test (100,000 folds) with a curvature radius of 2 mm. To protect an organic light emitting diode (OLED) against moisture, inorganic passivation layers are provided on the upper and lower sides of the flexible display. Using our transfer technology, high density passivation layers can be obtained. The measured water vapor transmission rate of the layer is 7 × 10^?6 g/m²?day or less, which improves OLED reliability. With these techniques, we have developed a book‐type display, which is repeatedly foldable like a book, and a tri‐fold display including a display area, which is foldable in three.     

Thin‐film barriers using transparent conducting oxides for organic light‐emitting diodes

Abstract— This study covers thin‐film barriers using inorganic barriers of transparent conducting oxides (TCOs) such as zinc oxide (ZnO) and indium tin oxide (ITO). The TCOs were fabricated using a sputtering method with a process gas of pure argon at room temperature. ITO showed better properties as a barrier than the ZnO and exhibited the electronic performance necessary to perform additional functions. The ITO has superior barrier performance because it has a lower crack density due to its partial amorphous phase. For organic/inorganic multilayer barriers, the organic underlayer decreased the water‐vapor transmission rate (WVTR) more than the organic upper layer, indicating that the planarization effect was important in reducing the WVTRs. The results of this organic/ITO multilayer barrier study are expected to be useful in finding a practical solution to OLED encapsulation.     

Characteristics of SiOxNy films deposited by inductively coupled plasma enhanced chemical vapor deposition using HMDS/NH3/O2/Ar for water vapor diffusion barrier

SiO_xN_y thin films were deposited by inductively coupled plasma enhanced chemical vapor deposition (ICP-PECVD) using hexamethyldisilazane (HMDS, 99.9%)/NH₃/O₂/Ar at a low temperature, and examined for use as a water vapor diffusion barrier. The film characteristics were investigated as a function of the O₂:NH₃ ratio. An increase in the O₂:NH₃ ratio decreased the level of impurities such as -CH_x, N-H in the film through a reaction with oxygen. Thereby, a more transparent and harder film was obtained. In addition, an increase in the O₂:NH₃ ratio decreased the nitrogen content in the film resulting in a more SiO₂-like SiO_xN_y film. Using SiO_xN_y fabricated with an O₂:NH₃ ratio of 1:1, a multilayer thin film consisting of multiple layers of SiO_xN_y/parylene layers was formed on a polyethersulfone (PES, 200 μm) substrate, and its water vapor transmittance rate (WVTR) was investigated. A WVTR < 0.005 g/(m² day) applicable to organic thin film transistors or organic light emitting diodes was obtained using a multilayer composed of SiO_xN_y (260 nm)/parylene (< 1.2 μm) on the PES.     

Atomic layer deposited TiOx/AlOx nanolaminates as moisture barriers for organic devices

Atomic layer deposited nanolaminates of alternating AlO_x and TiO_x thin-films are investigated as moisture barriers for organic electronic devices. Direct encapsulation on organic light emitting diodes (OLEDs) is tested in aging experiments and compared to calcium corrosion tests of equivalent barrier films. This allows for a direct assessment of moisture barrier performance in simple as well as more complex systems. Thickness variations are performed for the nanolaminate single and total layer thickness, with an optimum single layer thickness of 1–2 nm observed. This correlates to the maximum number of dyads once completely closed single layers are produced. For large single layer thickness and low dyad count, strong lateral diffusion from the edges occurs in the OLEDs, which likely correlates to poor mechanical stability. At optimum single layer thickness, barriers remain mechanically and chemically stable up to 100 nm total thickness. OLEDs encapsulated with such nanolaminate barriers show no significant degradation after 2500 h of continuous aging.     

密封胶水蒸气渗透性对中空玻璃节能效果的影响分析及测试方法概述

中空玻璃因其独特的结构而具有优异的节能效果,现已成为主要的外围护结构和外装饰材料。本文通过分析水蒸气渗透原理以及渗透的途径,发现密封胶水蒸气透过率参数与中空玻璃的失效关系密切,因此结合JC/T 914—2003要求介绍了丁基热熔密封胶水蒸气透过率的测试方法,以期为相关企业中空玻璃密封胶的质量控制提供一定的指导。     

Growth behavior and improved water–vapor-permeation-barrier properties of 10-nm-thick single Al2O3 layer grown via cyclic chemical vapor deposition on organic light-emitting diodes

We have investigated the growth behavior and water vapor permeation barrier properties of cyclic chemical vapor deposition (C-CVD)-grown 10-nm-thick single layer of Al₂O₃. Al₂O₃ layers grown by C-CVD showed a high density of 3.298 g/cm³ and were amorphous without grain boundaries. A deposition rate of 0.46 nm/cycle was obtained. The C-CVD system was self-limiting, as in the case of atomic layer deposition, which enables precise control of the thickness of the Al₂O₃ layer. A water vapor transmission rate of 1.51 × 10⁻⁵ (g/m²)/day was obtained from a Ca degradation test performed at 85 °C and 85% relative humidity. Moreover, the performance of organic light-emitting diodes, passivated by a C-CVD-grown 10-nm-thick Al₂O₃ single layer, was not affected after 24,000 h of turn-on time; this is strong evidence that C-CVD-grown Al₂O₃ layers effectively prevent water vapor from diffusing into the active organic layer.     

Improved barrier and mechanical properties of Al2O3/acrylic laminates using rugged fluorocarbon layers for flexible encapsulation

Thin film encapsulation (TFE) with high barrier performance and mechanical reliability is essential and challenging for flexible organic light-emitting diodes (OLEDs). In this work, SF₆ plasma treatments were introduced for surface modifications of acrylic in Al₂O₃/acrylic laminates fabricated by atomic layer deposition (ALD) and ink-jet printing (IJP). It was found that micro-/nano-structures and surface fluoridation appeared on the surface of acrylic, and could be modulated by the discharge power and irradiation of plasma treatment. The water vapor transmission rates (WVTR) of Al₂O₃/acrylic multi-layers decreased evidently because of reducing surface polarity and strong cross-link of acrylic after plasma treatments. Furthermore, the rugged surface and relieved residual stress resulted from etching and heating of acrylic could enhance the mechanical property remarkably. The plasma treated Al₂O₃/acrylic multi-layers with only 3 dyads exhibited a low WVTR value of 1.02 × 10⁻⁶ g/m²/day and more stable mechanical property under 200 iterations blending test by comparative measurements, proving that the introduction of SF₆ plasma surface modifications could improve simultaneously the barrier performance and mechanical reliability prominently of the inorganic/organic multi-layers with no need of extra neutral axis design.     

Investigation of brittle failure in transparent conductive oxide and permeation barrier oxide multilayers on flexible polymers

An oxide multilayer structure—consisting of an indium zinc oxide (IZO) conductive layer, a silicon oxide (SiO_x, x = 1.8) water vapor permeation barrier, and an aluminum oxide (Al₂O₃) interlayer—coated on polyethylene terephthalate (PET) is proposed as a transparent flexible substrate for display and photovoltaic applications. Vital properties of the multilayer, such as the low water vapor impermeability of the SiO_x barrier and the high conductance of the IZO film, degraded considerably because of the crack formation in bend geometries, attributed to the large difference between elastic properties of the oxide films and polymers. In order to suppress the crack formation, a 10-nm-thick Al₂O₃ interlayer was sputtered on Ar ion-beam treated PET surfaces prior to a SiO_x plasma-enhanced chemical vapor deposition (PECVD) process. Changes in the conductance and water vapor impermeability were investigated at different bending radii and bending cycles. It was found that the increases in resistance and water vapor transmission rate (WVTR) were significantly suppressed by the ion-beam PET pretreatment and by the sputtered Al₂O₃ interlayer. The resistance and WVTR of IZO/SiO_x/Al₂O₃/PET systems could be kept low and invariable even in severely bent states by choosing the SiO_x thickness properly. The IZO (135 nm)/SiO_x (90 nm)/Al₂O₃ (10 nm)/PET system maintained a resistance of 3.2 × 10^− 4 Ω cm and a WVTR of < 5 × 10^− 3 g m² d^− 1 after 1000 bending cycles at a bending radius of 35 mm.     

Whey Protein Emulsion Film Performance as Affected by Lipid Type and Amount

Beeswax, candelilla wax, carnauba wax, and a high-melting fraction of anhydrous milkfat were homogenized with whey protein to produce edible emulsion films. Lipid type and amount were important in controlling the emulsion film water vapor permeability (WVP). The WVPs of the beeswax and milkfat emulsion films were significantly lower than that of films from lower moisture transmitters, carnauba and candelilla wax. Lipid WVP and degree of viscoelasticity determined the barrier properties of the films. A significant reduction in WVP of whey protein films could be achieved using large volume fractions of lipid depending on lipid type.