Thin Film Encapsulation Layer Research Articles

Recent Achievements for Flexible Encapsulation Films Based on Atomic/Molecular Layer Deposition.

The purpose of this paper is to review the research progress in the realization of the organic-inorganic hybrid thin-film packaging of flexible organic electroluminescent devices using the PEALD (plasma-enhanced atomic layer deposition) and MLD (molecular layer deposition) techniques. Firstly, the importance and application prospect of organic electroluminescent devices in the field of flexible electronics are introduced. Subsequently, the principles, characteristics and applications of PEALD and MLD technologies in device packaging are described in detail. Then, the methods and process optimization strategies for the preparation of organic-inorganic hybrid thin-film encapsulation layers using PEALD and MLD technologies are reviewed. Further, the research results on the encapsulation effect, stability and reliability of organic-inorganic hybrid thin-film encapsulation layers in flexible organic electroluminescent devices are discussed. Finally, the current research progress is summarized, and the future research directions and development trends are prospected.

High light extraction performance using evanescent waves for top emission OLED applications with thin film encapsulation.

We report high light extraction from the top emission OLED (TEOLED) device structure by improving mainly the waveguide mode loss in the atomic layer deposition processed thin film encapsulation (TFE) layer. A novel structure incorporating the light extraction concept using evanescent waves and the hermetic encapsulation of a TEOLED device is presented here. When the TEOLED device is fabricated using the TFE layer, a substantial amount of generated light is trapped inside the device due to the difference in refractive index (RI) between the capping layer (CPL) and the aluminum oxide (Al2O3) layer. By inserting a low RI layer at the interface between the CPL and Al2O3, the direction of the internal reflected light is changed by the evanescent waves. The high light extraction with the low RI layer is attributed to the presence of evanescent waves and an electric field in the low RI layer. The novel fabricated TFE structure, CPL/ low RI layer/ Al2O3/ polymer/ Al2O3, is reported here. The current efficiency of the fabricated blue TEOLED device using this low RI layer is improved by about 23% and the blue index value is enhanced by about 26%. This new approach for light extraction will be applicable to future encapsulation technology for flexible optoelectronic devices.

A Low-Temperature Curable Conformal Adhesive Layer for Monolithic Lamination of Thin Film Encapsulation

Lamination of a thin film encapsulation (TFE) layer is regarded as one of the most promising methods that enable the reliable operation of organic electronic devices by attaching the TFE layers thereon directly using an adhesive layer. In this study, a low-temperature curable adhesive thin film with low glass transition temperature (T g) is newly designed and synthesized. Low T g allows conformal contact at the interface of the adhesive layer and the substrate subsequently leads to the enhancement of adhesion, and thus the barrier performance of the lamination of barrier film increases. In order to fabricate a low-T g adhesive layer, glycidyl methacrylate (GMA) was copolymerized with a 2-hydroxyethyl acrylate (HEA) monomer in the vapor phase via initiated chemical vapor deposition. With a 5 µm thick p(GMA-co-HEA) adhesive layer, a strong adhesion was readily achieved by curing it at 60 °C for 1 h, with the peel strength of 16.6 N/25 mm, and the water vapor transmission rate of the glass-laminated encapsulation was as low as 3.4 × 10−3 g/m2 · day under accelerating conditions (38 °C, 90% relative humidity). We believe the low-temperature curable thin adhesive layer will serve as a powerful material for the lamination of organic electronic devices in a damage-free way.

Crosslinking and densification by plasma-enhanced molecular layer deposition for hermetic seal of flexible perovskite solar cells

Flexible perovskite solar cells are new energy devices with a promising future due to their numerous advantages, such as high defect tolerance, strong solar absorption and low non-radiative carrier recombination rates. However, their operational stability is still an ongoing challenge during upgrading, and their inferior moisture corrosion resistance is still a major issue for better performances. Thin-film encapsulation could effectively enhance the operational stability of perovskite solar cells but obtaining encapsulation films with excellent barrier performance always come at the expense of poor flexibility. Therefore, the development of novel encapsulation materials with both barrier performance and flexibility is urgent for the compatibility of flexible applications. In this work, "Plasma-Enhanced Molecular Layer Deposition" was used for the first time to prepare a highly cross-linked, densified flexible encapsulation material AlOC at 40 ℃ to break through the traditional technology. The resulting encapsulation material can be applied to flexible perovskite solar cells as a barrier film without any damage. The as-obtained encapsulation film exhibited a water vapor transmittance rate of 1.44 × 10−5 g m−2 day−1 and preserved 95 % of its initial barrier performance after 10,000 bends with a 3 mm bend radius. Such performance was the best among the reported thin-film encapsulation layers of flexible perovskite solar cells.

Using angle-selective optical film to enhance the light extraction of a thin-film encapsulated 3D reflective pixel for OLED displays.

Light extraction improvement is still an important issue for active-matrix organic light-emitting diode displays (AMOLEDs). In our previous work, a three-dimensional (3D) reflective pixel configuration embedding the OLED in the concave 3D reflector and patterned high-index filler had been proposed for significant enhancement of the pixel light extraction. In this work, influences of thin film encapsulation (TFE) on light extraction of such reflective 3D OLED pixels are considered as well by simulation studies. Unfortunately, the optical simulation reveals strong reduction of the light extraction efficiency induced by TFE layers. As such, an additional angle-selective optical film structure between the pixel and the encapsulation layers is introduced to control the angular distribution of the light coupled into the encapsulation layers and to solve TFE-induced optical losses. As a result, TFE-induced losses can be substantially reduced to retain much of light extraction efficiency. The results of this study are believed to provide useful insights and guides for developing even more efficient and power-saving AMOLEDs.

Application of optical property-enhancement film to improve efficiency and suppress angle dependence of top-emitting organic light-emitting diodes

In this paper, we propose the application of an optical property-enhancement film that complements the angular dependence and total reflection of top-emitting organic light-emitting diodes (TEOLEDs). The optical property-enhancement film is composed of a porous pyramid arrangement applied on a thin-film encapsulation layer of TEOLEDs and is applied to distribute the transmitted light evenly. The results confirm that the change in the electroluminescence spectrum for each angle was effectively reduced because the TEOLEDs demonstrated uniform light distribution. In addition, reducing the total internal reflection in the film structure made it possible to improve the external quantum efficiency by approximately 35% and current efficiency by 38%.

59‐3: A Thin, Transparent Encapsulation Film with Excellent Gap‐filling Performance for Ultra‐High‐Resolution OLEDs via Vapor‐phase Deposited Polymeric Layer

A thin polymer film was developed by vapor‐phase deposition method, termed initiated chemical vapor deposition (iCVD) that can replace the inkjet process. The thin polymer film was integrated together with the PECVD SiNx layers to form a high performance thin film encapsulation (TFE) layer for ultra‐high resolution OLEDs, featured by excellent gap‐filling properties, full transparency in whole visible light region, and minimal shadow effect.

Nanoscale Film Thickness Gradients Printed in Open Air by Spatially Varying Chemical Vapor Deposition

Nanoscale films are integral to all modern electronics. To optimize device performance, researchers vary the film thickness by making batches of devices, which is time-consuming and produces experimental artifacts. We present thin films with nanoscale thickness gradients that are rapidly deposited in open air for combinatorial and high-throughput (CHT) studies. Atmospheric pressure spatial atomic layer deposition reactor heads are used to produce spatially varying chemical vapor deposition rates on the order of angstroms per second. We printed ZnO and Al2O3 films with nm-scale thickness gradients in as little as 45 seconds and performed CHT analysis of a MIM diode and perovskite solar cell. By testing 360 Pt/Al2O3/Al diodes with 18 different Al2O3 thicknesses on a single substrate, we identified a thicker insulator layer (6.5 to 7.0 nm) for optimal diode performance than has been reported previously. An Al2O3 thin film encapsulation layer was deposited by atmospheric pressure chemical vapor deposition (AP-CVD) on a perovskite solar cell stack for the first time and a convolutional neural network was developed to analyze the perovskite stability. The rapid nature of AP-CVD enables thicker films to be deposited at a higher temperature than is practical with conventional atomic layer deposition. The CHT analysis showed enhanced stability for 70 nm encapsulation films.

Hydrogen-assisted low-temperature plasma-enhanced chemical vapor deposition of thin film encapsulation layers for top-emission organic light-emitting diodes

In this work, we developed a single high-performance SiNx encapsulation layer that can be directly integrated into organic devices by low-temperature plasma-enhanced chemical vapor deposition (PECVD). We investigated a hydrogen-assisted low-temperature PECVD process at a temperature of 80 °C. The thin film density improved with an increased hydrogen gas ratio, and the moisture permeability was less than 5 × 10−5 g/m2·day. To verify the stability of the PECVD process, we applied the SiNx encapsulation layer directly to top-emitting organic light-emitting diodes. The results showed minor changes in the current-density–voltage characteristics after the PECVD process, as well as high reliability after a water dipping test.

Highly durable organic photodetector for complementary metal oxide semiconductor image sensors

Utilizing organic electronics compatible with conventional semiconductor fabrication processes is extremely difficult because of their low chemical resistivity and poor environmental durability. To preserve the intrinsic functionality of organic materials, only a few fabrication processes can be used. Moreover, it is essential to achieve process expandability and silicon-process compatibility to develop high-resolution electronics suitable for mass production. Therefore, we developed wet-process-compatible organic photodetectors by replacing the conventional shadow-mask process with photolithography. This suppresses particle deposition during the serial fabrication processes, providing high operational stability. The fabricated green organic photodiodes exhibit a low dark current (1.0 × 10−11 A/cm2) with high photon–electron conversion efficiency (EQE = 65%). The charge collection and charge separation efficiencies are stable (ηcc = 84.6% and ηcs = 97.7%, respectively). Moreover, the organic semiconductors are compatible with conventional wet- and dry-etching processes owing to thin-film encapsulation layers. Finally, the novel organic image sensor can withstand 500 h under 85 °C/85% relative humidity and 1000 thermal cycles (−55–125 °C). Because of its robustness and strong barrier properties, the novel process architecture reported herein can be extended to any organic electronic devices, including widely commercialized organic light-emitting diodes and organic photovoltaic devices.

Two-step fabrication of thin film encapsulation using laser assisted chemical vapor deposition and laser assisted plasma enhanced chemical vapor deposition for long-lifetime organic light emitting diodes

A thin film encapsulation layer was fabricated through two-sequential chemical vapor deposition processes for organic light emitting diodes (OLEDs). The fabrication process consists of laser assisted chemical vapor deposition (LACVD) for the first silicon nitride layer and laser assisted plasma enhanced chemical vapor deposition (LAPECVD) for the second silicon nitride layer. While SiN x thin films fabricated by LAPECVD exhibits remarkable encapsulation characteristics, OLEDs underneath the encapsulation layer risk being damaged during the plasma generation process. In order to prevent damage from the plasma, LACVD was completed prior to the LAPECVD as a buffer layer so that the laser during LACVD did not damage the devices because there was no direct irradiation to the surface. This two-step thin film encapsulation was performed sequentially in one chamber, which reduced the process steps and increased fabrication time. The encapsulation was demonstrated on green phosphorescent OLEDs with I–V-L measurements and a lifetime test. The two-step encapsulation process alleviated the damage on the devices by 19.5% in external quantum efficiency compared to the single layer fabricated by plasma enhanced chemical vapor deposition. The lifetime was increased 3.59 times compared to the device without encapsulation. The composition of the SiNx thin films was analyzed through Fourier-transform infrared spectroscopy (FTIR). While the atomic bond in the layer fabricated by LACVD was too weak to be used in encapsulation, the layer fabricated by the two-step encapsulation did not reveal a Si–O bonding peak but did show a Si–N peak with strong atomic bonding. • Thin film encapsulation by laser assisted plasma enhanced chemical vapor deposition. • Buffer layer by laser assisted chemical vapor deposition prior to encapsulation. • Increase of stability and protection of plasma damage through in-line pre-deposition. • 3.59 times increased LT80 in green phosphorescent organic light emitting diodes.

Folding-stability criteria of thin-film encapsulation layers for foldable organic light-emitting diodes

We have investigated thin-film encapsulation layers that can be stable without the occurrence of cracks even when the layer is repeatedly folded with a small radius down to 1 mm. The folding stability criteria were also identified for the cases where the encapsulation layer deviates by a certain distance from the stress neutral plane inside a foldable device. An organic-inorganic multilayer structure having the inorganic layer thickness of 5 nm has always been shown to be stable against repeated folding with a radius of 1 mm even though the multilayer is located far from the stress neutral plane. In addition, the folding stability of the organic-inorganic multilayer encapsulation layer was evaluated when contaminant particles were present on the surface of foldable devices. To this end, the step coverage over the contaminant particles and the folding-stability criteria of the encapsulation structure were investigated. It was confirmed that the organic-inorganic multilayer structure was stable to repeated folding in a radius of 1 mm when the coating angle covering the particles was loosened to 140° or more through planarization and thin-film encapsulation.

P‐166: Tuning the Refractive Index of Silicon‐Oxynitride Films for Light‐Extraction Enhancement of OLED Devices

Adding light extraction film is an effective way to enhance the light extraction of OLEDs. By matching the index difference between OLED and resin, the thin film encapsulation (TFE) layers covering the entire surface of the top‐emission OLED device and located between OLED and resin could be functioned as the light extraction film. In this study, an approach to obtain high refractive index SiON films was investigated. We successfully achieved three gradient index changes in SiON films.The Fourie Transform Infrared (FTIR) spectra were tested to analyze the content of Si‐N and Si‐O bond in the SION films. The moisture permeability of the SiON films were also tested.

Hermetic seal for perovskite solar cells: An improved plasma enhanced atomic layer deposition encapsulation

Unstable nature against moisture is one of the major issues of metallic halide perovskite solar cell application. Thin-film encapsulation is known as a powerful approach to notably enhance the operational stability of perovskite solar cells in humid environment. However, encapsulation layers with ideal gas barrier performance always require harsh fabrication conditions with high temperature and harmful precursors. For this reason, here we provide a mild encapsulation strategy to maintain the original performance of solar cell devices by utilization of ethylene glycol-induced immediate layer to minimize the damage of plasma-enhanced atomic layer deposition to perovskite solar cells. The organic-inorganic alternating encapsulation structure has exhibited a water vapor transmittance rate of 1.3 × 10−5 g m−2·day−1, which is the lowest value among the reported thin film encapsulation layers of perovskite solar cells. Our perovskite solar cells have survived at 80% relative humidity and 30 °C for over 2000 h while preserving 96% of its initial performance.

3.4: Applications of TFE mask‐less technology for foldable AMOLED displays

Thin‐film encapsulation (TFE) for foldable AMOLED display is necessary to have good reliability and excellent bendability. TFE mask induces particles easily and crack occurs in thick TFE layer during panel bending. We developed TFE with Al2O3 layer for high water‐proof and very thin thickness, satisfying the requirement of reliability and bendability. The Al2O3 layer in TFE structure was deposited by low temperature atomic layer deposition (ALD) method, and we realized TFE mask‐less process through adapting dry‐etch parameters for Al2O3 etch, finding that BCl3 has very excellent dry‐etch selectivity between inorganic layer (SiOx/SiNx/SiOxNy) and Al2O3. Besides, we also attempted to make the organic layer of TFE acted as etch mask, and it proved to be feasible, indicating that all the TFE masks could be taken out effectively. Moreover, we proved good optic and reliability characteristics of AMOLED display with mask‐less TFE structure.

Quantitative analysis of nano-defects in thin film encapsulation layer by Cu electrodeposition

Thin-film encapsulation (TFE) is of great importance as a barrier film to protect organic devices and displays. A serious problem with the application of TFE is degradation of organic devices with penetration of oxygen and water vapor through pinholes having sub-micron size. Though many studies were tried to identify the pinholes, quantitative analysis of pinhole area has not been found yet. In this study, total pinhole area in TFE layer was quantitatively analyzed with the help of the Cu bumps electrodeposited on the pinholes. Empirical growth rate of the Cu bumps revealed that bump radius (r) and plating time (t) had a relationship of r3 ∝ t. While size of the pinholes was deduced from starting point of Cu bump growth, number of the pinholes was extracted from size distribution of the Cu bumps. Unique feature of Cu bump morphology is also explained with a compositional analysis, demonstrating dissolution of Ni underlayer and its involvement in the formation of the Cu bumps.

A Review of Flexible OLEDs Toward Highly Durable Unusual Displays

Organic light-emitting diodes (OLEDs) are remarkably promising display devices that can function in mechanically flexible configurations on a plastic substrate due to various compelling properties, including organic constituents, ultrathin and simple structure, and low-temperature fabrication. In spite of successful demonstrations of flexible OLEDs, some technical issues of containing relatively thick transparent electrodes made of ceramic materials and an unstable flexible encapsulation system have impeded reaching high levels of reliability and durability toward full commercialization. This review covers recent developments in structure designs for highly durable flexible OLEDs, ranging from alternative transparent electrodes to thin-film encapsulation layers, in which solution concepts for the existing critical issues of flexible OLEDs are addressed. Emerging unusual substrates and their application strategies are additionally introduced to find intimations of future display technologies and hence to disclose nonclassic flexible OLEDs.

Low-temperature remote plasma enhanced atomic layer deposition of ZrO2/zircone nanolaminate film for efficient encapsulation of flexible organic light-emitting diodes

Encapsulation is essential to protect the air-sensitive components of organic light-emitting diodes (OLEDs) such as active layers and cathode electrodes. In this study, hybrid zirconium inorganic/organic nanolaminates were fabricated using remote plasma enhanced atomic layer deposition (PEALD) and molecular layer deposition at a low temperature. The nanolaminate serves as a thin-film encapsulation layer for OLEDs. The reaction mechanism of PEALD process was investigated using an in-situ quartz crystal microbalance (QCM) and in-situ quadrupole mass spectrometer (QMS). The bonds present in the films were determined by Fourier transform infrared spectroscopy. The primary reaction byproducts in PEALD, such as CO, CO2, NO, H2O, as well as the related fragments during the O2 plasma process were characterized using the QMS, indicating a combustion-like reaction process. The self-limiting nature and growth mechanisms of the ZrO2 during the complex surface chemical reaction of the ligand and O2 plasma were monitored using the QCM. The remote PEALD ZrO2/zircone nanolaminate structure prolonged the transmission path of water vapor and smooth surface morphology. Consequently, the water barrier properties were significantly improved (reaching 3.078 × 10−5 g/m2/day). This study also shows that flexible OLEDs can be successfully encapsulated to achieve a significantly longer lifetime.

Investigation of the Defect Size and Density in Thin SiON Filmfor Organic Device Encapsulation

Abstract In this study, thin SiON was grown by plasma enhanced chemical vapor deposited (PECVD) method as a thin-film encapsulation (TFE) layer. For defect visualization, electroplating results in a Cu bump grown at each defect site in the SiON film where electrolytic solution establishes contact with the Ni substrate. It was inferred that the Cu bump density could be representative of the intrinsic defect densities for the SiON film. The defect density values were obtained by monitoring the Cu bumps grown at defect sites in the SiON films and then evaluating the number of densities of the Cu bumps for the corresponding defect densities.At the same time, by analyzing the cross section of the Cu bumps grown on SiON film, a linear relation between the Cu bump diameter and the defect size increase was obtained. We expect that this electroplating method allows for rapid visualization of defect distribution and quality evaluation of TFE layers.

P-96: Heat Transferable Thin Film Encapsulation Inserted Ag Thin Film to Improve Reliability of Flexible Displays

In this study, thin film encapsulation (TFE) with an Ag thin film is proposed to improve the long-term reliability of flexible displays in terms of the barrier property, flexibility, and heat dissipation. By applying thin film encapsulation to bottom-emission organic light-emitting diodes (BEOLEDs) fabricated on glass, the lifetimes of OLED devices were improved, showing differences among TFE layers. The maximum temperatures measured from the backside of the glass substrate were 66.73, 64.15, 59.21 and 39.63 °C after the OLED was operated at a luminance of 10000 cd/m2, and an operational lifetime test results were remarkably consistent with the measurement results of infrared images. Efficient heat dissipation through thermally conductive TFE layers improved the OLED reliability in terms of lifetime.