Effective Water Vapor Transmission Rate Research Articles

Atmospheric pressure roll‐to‐roll plasma enhanced CVD of high quality silica‐like bilayer encapsulation films

A glow like atmospheric pressure dielectric barrier discharge in a roll‐to‐roll setup was used to synthesize 90 nm silica‐like bilayer encapsulation films composed of a 30 nm dense “barrier layer” and a comparatively less dense 60 nm “buffer layer” onto a polyethylene 2,6 naphthalate substrate by means of plasma enhanced chemical vapor deposition. Tetraethyl orthosilicate was used as the precursor gas, together with a mixture of nitrogen, oxygen, and argon. The microstructure, chemical composition, morphology, and permeation properties of the films were studied as a function of the specific energy delivered per precursor molecule, and oxygen concentration in the gas mixture, during the deposition of the barrier layer. The presence of the buffer layer within the bilayer architecture critically enhanced the encapsulation performance of the bilayer films, and this in conjunction with increasing the specific energy delivered per precursor molecule during the barrier layer deposition to a value of 20 keV, enabled an effective water vapor transmission rate as low as 6.9 × 10−4 g m−2 d−1 (at 40 °C, 90% relative humidity (RH)) to be achieved. Furthermore, the bilayer film structure has given rise to a remarkable 50% reduction in deposition energy consumption per barrier area with respect to single layer silica‐like films of equivalent encapsulation performance and thickness.

Experimental investigation of defect-assisted and intrinsic water vapor permeation through ultrabarrier films.

In the development of ultrabarrier films for packaging electronics, the effective water vapor transmission rate is a combination of permeation through pinhole defects and the intrinsic permeation through the actual barrier film. While it is possible to measure the effective permeation rate through barriers, it is important to develop a better understanding of the contribution from defects to the overall effective barrier performance. Here, we demonstrate a method to investigate independently defect-assisted permeation and intrinsic permeation rates by observing the degradation of a calcium layer encapsulated with a hybrid barrier film, that is, prepared using atomic layer deposition (ALD) and plasma enhanced deposition (PECVD). The results are rationalized using an analytical diffusion model to calculate the permeation rate as a function of spatial position within the barrier. It was observed that a barrier film consisting of a PECVD SiN(x) layer combined with an ALD Al2O3/HfO(x) nanolaminate resulted in a defect-assisted water vapor transmission rate (WVTR) of 4.84 × 10(-5) g/m(2) day and intrinsic WVTR of 1.41 × 10(-4) g/m(2) day at 50 °C/85% RH. Due to the low defect density of the tested barrier film, the defect-assisted WVTR was found to be three times lower than the intrinsic WVTR, and an effective (or total) WVTR value was 1.89 × 10(-4) g/m(2) day. Thus, improvements of the barrier performance should focus on reducing the number of defects while also improving the intrinsic barrier performance of the hybrid layer.

The impact of the nano-pore filling on the performance of organosilicon-based moisture barriers

Promising results in terms of moisture and oxygen permeation barrier properties have been reported for organic/inorganic multilayers, but the impact of the organic interlayer on the overall barrier performance is still under discussion. It is generally accepted that the organic interlayer acts as a smoothening layer, allowing for the decoupling between defects/pinholes present in the polymer substrate and the inorganic layer. It is, however, also hypothesized that the organic interlayer infiltrates into the nano-pores present in the inorganic barrier layer, therefore affecting the barrier properties at microstructural level. In the present work, the moisture permeation barrier performance of SiO2/organosilicon multilayers deposited by means of initiated- and plasma enhanced-chemical vapor deposition is investigated. Calcium test measurements were used to discriminate between the overall water permeation (effective water vapor transmission rate, WVTR) through the layer and the permeation through the matrix porosity (intrinsic WVTR). The improvement in terms of intrinsic barrier performance was found to correlate with the residual nano-porosity content, due to the filling/infiltration of the organosilicon monomer in the SiO2 nano-pores. However, such improvement upon the deposition of the organosilicon interlayer is limited to a factor four. These results, in combination with the analysis of the local defects present in the multilayer structure, lead to the conclusion that the main contribution of the organosilicon interlayer to the overall barrier performance is the decoupling of the above-mentioned local defects/pinholes.

High-performance barrier using a dual-layer inorganic/organic hybrid thin-film encapsulation for organic light-emitting diodes

We report an inorganic/organic hybrid barrier that combines the alternating deposition of a layer of ZrO2 using low temperature atomic layer deposition and a 16-μm-thick layer of UV-curable NOA63 epoxy using spin-coating. The effective water vapor transmission rates of single ZrO2 film was improved by adding solution epoxy from 3.03×10−3g/m2day to 1.27×10−4g/m2day in the hybrid NOA63/ZrO2/NOA63/ZrO2 films at 20°C and a relative humidity of 60%. In consequence, the organic light-emitting diodes encapsulated with inorganic/organic hybrid barriers were undamaged by environmental oxygen and moisture and their luminance decay time improved by a considerable extent.

Enhancement of the barrier performance in organic/inorganic multilayer thin-film structures by annealing of the parylene layer

A multilayered barrier structure was fabricated by chemical vapor deposition of parylene and subsequent plasma-enhanced chemical vapor deposition of SiOx or SiNx. The barrier performance against water vapor ingress was significantly improved by annealing the parylene layer before the deposition of either SiOx or SiNx. The mechanism of this enhancement was investigated using atomic force microscopy, Raman spectroscopy, and X-ray diffraction. The surface roughness of the parylene before the deposition of either SiOx or SiNx was found to correlate closely with the barrier performance of the multilayered structures. In addition, removing absorbed water vapor in the film by annealing results in a lower water vapor transmission rate in the transient region and a longer lag time. Annealing the parylene leads to a large decrease in the effective water vapor transmission rate, which reaches 7.2±3.0×10−6g/m2/day.

Passivation Properties of UV-Curable Polymer for Organic Light Emitting Diodes

We found using UV-curable polymer (NOA63 from Norland Optics) film as a passivation layer, which was very simple and convenient to perform, could provide a temporary barrier for the organic light emitting devices (OLEDs). The NOA63 protective layer significantly restricted the moisture that penetrated into the OLEDs, but did not affect its luminescent characteristics. The decay time of device reaching 70% initial luminance was 1860 min, 6.8 folds longer than that of device without encapsulation. The effective water vapor transmission rate achieved 0.031 g/m2/day at 20°C and 50% relative humidity condition.

Development of highly flexible and ultra-low permeation rate thin-film barrier structure for organic electronics

A flexible thin-film encapsulation architecture for organic electronics was built and consisted of a silicon oxide/alumina and parylene layer deposited over Ca sensors on a barrier-coated polyethylene terephthalate substrate. The film's effective water vapor transmission rate was 2.4±1.5×10−5g/m2/day at 20°C and 50% relative humidity. Flexural tests revealed that for films deposited on the polyethylene terephthalate substrate, the barrier layer failed due to cracking at a curvature radius of 6.4mm, corresponding to a strain of 0.8%. Adding an epoxy top coat of suitable thickness shifted the neutral axis toward the encapsulation layer, reducing the induced strain. Barrier performance was maintained under the 6.4mm radius of curvature in this encapsulation structure. Thus, shifting the neutral axis via device structural design is an effective method of extending the flexibility of thin-film encapsulation structure without compromising the performance loss as a barrier layer.

유기반도체용 고성능 박막 봉지재의 제조 및 평가

유기전자재료의 발전으로 박막화, 유연화, 경량화가 가능하면서, 저가의 생산비용으로 제조 될 수 있는 유기반도체의 개발 및 상용화에 대한 연구가 활발히 이루어지고 있다. 하지만, 유기반도체를 구성하는 유기재료 및 전극재료가 미량의 수분과 반응으로 성능이 저하되는 문제로 상용화의 큰 걸림돌이 되고 있다. 따라서 유기재료 및 전극을 동작환경의 수분으로부터 보호할 수 있는 고성능 투습방지막 개발에 대한 연구가 많이 진행되고 있다. 본 연구에서는 SiO<SUB>x</SUB>/parylene 및 SiN<SUB>x</SUB>/parylene 구조를 이용한 다중 구조의 고성능 박막 봉지막을 개발하고, 개발된 박막을 Ca-corrosion test 를 이용하여 수분투과율을 측정하였다. 또한 박막 봉지재를 유기태양전지에 적용하여 유기태양전지의 수명과 투습특성과의 관계를 확인하였다.

A correlation study between barrier film performance and shelf lifetime of encapsulated organic solar cells

In this study, the overall barrier performance of multilayer thin-films and the shelf lifetime of encapsulated organic solar cells were correlated through the total amount of water vapor that permeated into the solar cell. Effective water vapor transmission rates were measured in both the transient and steady-state transport regimes for multilayer barrier films consisting of SiNx and parylene. The efficiency of pentacene/C60-based solar cells encapsulated with one or two pairs of SiNx/parylene dropped to 50% after permeation of about 1.63g/m2 of water vapor regardless of effective transmission rate of the barrier. From these calculations, cells encapsulated with three dyads were predicted to maintain performance for at least 13,500h while experiments up to 7500h showed less than 10% degradation in performance.

Durable polyisobutylene edge sealants for organic electronics and electrochemical devices

The performance of a desiccant-filled polyisobutylene edge sealant for organic electronics is reported. The sealant was applied through a low temperature lamination process using glass substrates and various seal widths. The performance was tested using the Ca corrosion method at 50°C and 80% relative humidity (RH). Data show an effective water vapor transmission rate (WVTR), on the order of 10−3g/m2/day in the transient regime with a breakthrough time greater than 1400h for seals 1.5mm wide and 0.3mm thick. By changing the sealant architecture, the breakthrough time was increased with similar effective WVTRs. Finally, the sealant was applied to organic electrochromic devices, which displayed a retention of performance after 1000h of storage at 50°C and 80% RH.

A hybrid encapsulation method for organic electronics

We report a thin-film encapsulation method for organic electronics that combines the deposition of a layer of SiOx or SiNx (100 nm) by plasma enhanced chemical vapor deposition followed by a layer of Al2O3 (10–50 nm) by atomic layer deposition and a 1-μm-thick layer of parylene by chemical vapor deposition. The effective water vapor transmission rates of the encapsulation was (2±1)×10−5 g/m2 day at 20 °C and 50% relative humidity (RH). The encapsulation was integrated with pentacene/C60 solar cells, which showed no decrease in conversion efficiency after 5800 h of exposure to air demonstrating the effectiveness of the encapsulation methodology.

Gas Diffusion Barriers on Polymers Using Multilayers Fabricated by Al2O3 and Rapid SiO2 Atomic Layer Deposition

Single Al2O3 atomic layer deposition (ALD) films on polymers have demonstrated excellent gas diffusion barrier properties. Further improvements can be achieved using multilayers of Al2O3 ALD layers with other inorganic layers. In this study, multilayers of Al2O3 ALD and rapid SiO2 ALD were grown on Kapton and heat-stabilized polyethylene naphthalate substrates. Transmission rates for tritium through the films were measured using the radioactive HTO tracer method. Comparison with previous Ca tests and tritium exchange experiments with alcohols indicated that the tritium in HTO may diffuse as either molecular HTO or atomic tritium. Assuming that the tritium diffuses only as HTO, single Al2O3 ALD films reduced the effective water vapor transmission rate (WVTR) to ∼1 × 10-3 g/m2/day. When the Al2O3 ALD film was directly exposed to the saturated H2O/HTO vapor pressure, the barrier properties deteriorated markedly after 4−5 days. Al2O3 ALD barriers that were not subjected to direct H2O/HTO exposure indefinitely...

Application of Atomic Layer Deposition for Gas Permeation Barrier Thin Films

We determined by a Ca-test with optical modeling that a 25 nm thick Al2O3 film, grown by atomic layer deposition on polyester, reduced the effective water vapor transmission rate to < 10-5 g-H2O/m2-day. This is a reduction of more than 105x compared to the bare polyester. The corresponding diffusion coefficient for water vapor through this film was calculated to be D=2.5x10-17 cm2/s, and the threshold thickness for barrier properties was ~ 5 nm of Al2O3. We further concluded that these values were likely at the lower limit of this Ca-test method, because of edge diffusion of gas through the epoxy seal in the test structure.

P‐88: Thin Film Encapsulation for OLEDs: Evaluation of Multi‐layer Barriers using the Ca Test

AbstractWe report on a method to evaluate thin film barriers for direct encapsulation of OLEDs. Based on the corrosion of reactive metal films and modeling thereof, this method is used to quantify the water permeation rate of high‐performance diffusion barriers. This method was first used to measure the barrier properties of flexible plastic substrates for display applications [1]. In the present work the system has been automated for improved repeatability and optical calibration has been performed to assess the sensitivity. Effective water vapor transmission rates down to 10−6 g/m2/day can be detected. Permeation data on a multi‐layer thin film encapsulant was obtained at three temperatures. To demonstrate compatibility in the application, the same thin film encapsulant was used to package actual passive matrix devices. This is the first report of a quantitative measure of an OLED compatible thin film encapsulant.