Thin Film Encapsulation Research Articles

Large‐Area Flexible Thin Film Encapsulation with High Barrier and Super‐Hydrophobic Property

AbstractWith the development of optoelectronic devices toward miniaturization, flexibility, and large‐scale integration, conventional submillimeter rigid encapsulation techniques rarely achieve conformational functionality while blocking water and oxygen. At the same time, the sensitivity of electronic devices with organic/metal/semiconductor components to humidity and oxygen severely impairs their operational stability and lifetime. Here, a nanometer to micrometer scale organic/inorganic hybrid thin film encapsulation (TFE) with the self‐cleaning ability for flexible encapsulation is developed. The water vapor transmittance rate of polyethylene terephthalate substrate coated with the TFE is as low as 1.65 × 10−4 g m−2 day−1, and the barrier improvement factor reaches 104 at 38 °C and 90% relative humidity. This value is equivalent to 9.81 × 10−6 g m−2 day−1 at ambient conditions, sufficient to improve the lifetime of water‐sensitive electronic devices. Meanwhile, this TFE shows a super‐hydrophobic performance, with a water contact angle of 168.4°. In addition, the resulting barrier films exhibit outstanding optical properties, with an average optical transmittance of 86.88% in the visible region. This versatile TFE can promote the development of optoelectronic devices toward miniaturization and large‐scale integration in the future.

85‐4: Plasma‐Polymerized HMDSO for Thin Film Encapsulation of Micro‐OLED

Plasma‐Polymerized Hexamethyldisiloxane (pp‐HMDSO) was developed as buffer layer by plasma enhanced chemical vapor deposition (PECVD) together with SiN barrier layers to form thin film encapsulation (TFE) stack that can reduce the whole TFE thickness to less than 1µm for an ultra‐high resolution Micro‐OLED application. The pp‐HMDSO film featured excellent particle coverage was close to 100% transmittance in the whole visible light region and was nearly stress free.

Improved mechanical properties of Al2O3/acrylic laminates for flexible thin film encapsulation by introducing wavy interfaces

Improved mechanical properties of Al2O3/acrylic laminates for flexible thin film encapsulation by introducing wavy interfaces

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.

8.3: A Method for Measuring Droplet Volume of Electrospray Deposition Based on AdaBoost Regression

OLED (organic light‐emitting diode) displays have become the next generation of mainstream display technology due to their high luminous efficiency and flexibility, and the manufacturing technology of OLEDs has a critical impact on their longevity and display quality. ESD (Electrospray Deposition) is an innovative technique to achieve micron‐scale membrane structures to meet the requirements for effective manufacturing of organic TFE (thin film encapsulation) layers for use in organic light‐emitting diode displays. Measuring array droplet deposition volume produced by Electrostatic Spray Deposition plays a vital role in the consistency control of film thickness.This paper presents a method for measuring the deposition volume of array droplets. The volume of the deposited droplets is estimated by establishing the mapping relationship between a large number of deposition variables (including the print parameters and the features of the deposited droplets) and the volume. This paper uses a data set containing 427 samples to build a machine learning (ML) model. The AdaBoost regressor is selected to ensure accuracy and avoid overfitting. Based on this measurement method, a deposition droplet measurement system (DDMS) is established, and the performance of the proposed method is verified. The results show that volume prediction performance (R2) reached 0.96, the regression volume error is about 0.51%, and the average time for each droplet measured is 0.5ms.is

A Study of Al2O3/MgO Composite Films Deposited by FCVA for Thin-Film Encapsulation.

Al2O3 and MgO composite (Al2O3/MgO) films were rapidly deposited at low temperatures using filtered cathode vacuum arc (FCVA) technology, aiming to achieve good barrier properties for flexible organic light emitting diodes (OLED) thin-film encapsulation (TFE). As the thickness of the MgO layer decreases, the degree of crystallinity decreases gradually. The 3:2 Al2O3:MgO layer alternation type has the best water vapor shielding performance, and the water vapor transmittance (WVTR) is 3.26 × 10-4 g·m-2·day-1 at 85 °C and 85% R.H, which is about 1/3 of that of a single layer of Al2O3 film. Under the action of ion deposition, too many layers will cause internal defects in the film, resulting in decreased shielding ability. The surface roughness of the composite film is very low, which is about 0.3-0.5 nm depending on its structure. In addition, the visible light transmittance of the composite film is lower than that of a single film and increases with the increase in the number of layers.

Ultra-thin thermally grown silicon dioxide nanomembrane for waterproof perovskite solar cells

Recently, perovskite solar cells (PSCs) have been attracting attention as the most promising alternative to conventional photovoltaics, mainly due to their high power conversion efficiency (PCE) of 25.7%. However, prior to commercialization, problems with their long-term stability caused by moisture should be solved. Accordingly, encapsulation is a crucial strategy for enhancing the long-term stability of PSCs, meaning a well-established strategy that includes an excellent barrier that protects them from the external environment while minimizing any damage during encapsulation is required. In this study, a room temperature thin-film encapsulation (RT-TFE) strategy is applied by transferring a defect-free thermally grown silicon dioxide nanomembrane (t-SiO2 NM), which is a well-known superior water molecule barrier, onto the PSCs. The average PCE of the devices decreased by only 0.012% with a standard deviation of 0.4249 during the entire encapsulation process, which was achieved by minimizing any thermal degradation of the photovoltaic components, including the perovskite and hole transport layers. This t-SiO2 NM successfully protected the PSC from external water molecules in an underwater condition for 31 days at room temperature, which is the longest reported survival time of encapsulated PSCs. As a result, the RT-TFE PSC maintained more than 98% of the initial efficiency.

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.

Enhancing the Stability of Perovskite Solar Cells with a Multilayer Thin-Film Barrier

The long-term stability of perovskite solar cells (PSCs) remains a big challenge for the commercialization of this emerging photovoltaic technique. The protection of PSCs with a robust barrier/encapsulation could largely extend their life span. Here, we develop a multilayer thin-film barrier with the architecture of parylene/MgF2/Al2O3 as thin-film encapsulation for PSCs. The water vapor transmission rate of the multiple thin-film barriers can reach a very low value of 1 × 10–4 g m–2 d–1, comparable to that of the thin-film encapsulation in electronic packaging, making the multilayer thin-film barrier robust to block the ingress of H2O/O2 and outward leakage of perovskite decomposition byproducts. As a result, the light and thermal stability of perovskite films and the operational stability of PSCs are effectively improved with multiple thin-film barriers; especially, the encapsulated devices show negligible degradation after operation under the maximum power point tracking under 1sun illumination for 1000 h. In addition, the devices can retain 96% of their initial PCEs on average after aging for 100 h in an 85 °C-85%RH damp heat test.

A Solvent-Free, Thermally Curable Low-Temperature Organic Planarization Layer for Thin Film Encapsulation.

Thin film encapsulation (TFE) is an essential component to ensure reliable operation of environmentally susceptible organic light-emitting diode-based display. In order to integrate defect-free TFE on display with complex surface structures, additional planarization layer is imperative to planarize the surface topography. The thickness of conventional planarization layer is as high as tens of µm, but the thickness must be reduced substantially to minimize the light leakage in smaller devices such as micro light-emitting diodes. In this study, a thin-less than 2 µm-planarization is achieved via solvent-free process, initiated chemical vapor deposition (iCVD). By adapting copolymer from two soft, but curable monomers, glycidyl acrylate (GA) and 2-(dimethylamino)ethyl methacrylate, excellent planarization performance is achieved on various nano-grating patterns. With only 1.5 µm-thick iCVD planarization layer, a 600 nm-deep trench polyurethane acrylate pattern is flattened completely. The TFE fabricated on planarized pattern exhibits excellent barrier property as fabricated on flat glass substrate, which strongly suggests that iCVD planarization layer can serve as a promising planarization layer to fabricate TFE on various types of complicated device surfaces.

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.

10.4: A 2.3‐inch Automotive AMOLED Display with Small Bending Radius

10.4: A 2.3‐inch Automotive AMOLED Display with Small Bending Radius

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%.

Evaluation of encapsulation strategies for solution-processed flexible organic light-emitting diodes

Owing to the sensitivity of organic materials to ambient conditions, encapsulation of organic light-emitting diodes (OLEDs) is critical. In this work, Al2O3 film, deposited by atomic layer deposition (ALD) technique, on flexible polyethylene terephthalate (PET) substrate is used as a barrier film. Al2O3 is also deposited directly on OLED as thin-film encapsulation. Electrical Ca tests are used to measure water vapor transfer rate (WVTR) values, and an optimum WVTR value of 9 *10−4 g/m2/day using 43 nm Al2O3 film has been obtained. The related results on five different encapsulation structures for solution-processed OLEDs: (i) glass to glass encapsulation (G2G) as a reference, (ii) glass to barrier film encapsulation (G2B), (iii) glass to direct thin-film encapsulation (G2D), (iv) barrier to barrier film encapsulation (B2B), and (v) barrier to direct thin-film encapsulation (B2D), are evaluated. The operating half-lifetime values of OLEDs with G2B- and G2D-encapsulation are 54% and 82% of the half-lifetime with G2G encapsulation, respectively. The lifetime of flexible OLED devices with B2D encapsulation is also 34% more than that with B2B encapsulation. Based on the bending stress analysis, the estimated critical bending radius for B2B and B2D encapsulation of flexible OLEDs are 16.83 and 7.07 mm, respectively.

Flexible alumina films prepared using high-bias pulse power for OLED thin film encapsulation

To overcome the moisture sensitivity of flexible organic light-emitting diode devices (OLEDs), physical vapor deposition (PVD) technology can be used to prepare films with excellent density for thin film encapsulation (TFE). The internal stress in the film should be modulated to enhance the flexibility, which can prevent structural degradation. To address these issues, a filtered cathode vacuum arc (FCVA) equipped with a superlow duty ratio high-bias pulsed was used to prepare Al2O3 films with low internal stress (−57.6 MPa), excellent visible light transmittance, high packaging density, and good bending resistance. After 1000 bending cycles, the water vapor transmission rate (WVTR) for a film is increased to 5.57 × 10−3 g/m2/day at 85 °C and 85% relative humidity (R.H.). In addition, the molecular dynamics (MD) is employed to investigate the mechanism of film internal stress release, as well as the shallow implantation of ions brought about by high-bias pulse.

Recent Advances in Encapsulation of Flexible Bioelectronic Implants: Materials, Technologies, and Characterization Methods.

Bioelectronic implantable systems (BIS) targeting biomedical and clinical research should combine long-term performance and biointegration in vivo. Here, recent advances in novel encapsulations to protect flexible versions of such systems from the surrounding biological environment are reviewed, focusing on material strategies and synthesis techniques. Considerable effort is put on thin-film encapsulation (TFE), and specifically organic-inorganic multilayer architectures as a flexible and conformal alternative to conventional rigid cans. TFE is in direct contact with the biological medium and thus must exhibit not only biocompatibility, inertness, and hermeticity but also mechanical robustness, conformability, and compatibility with the manufacturing of microfabricated devices. Quantitative characterization methods of the barrier and mechanical performance of the TFE are reviewed with a particular emphasis on water-vapor transmission rate through electrical, optical, or electrochemical principles. The integrability and functionalization of TFE into functional bioelectronic interfaces are also discussed. TFE represents a must-have component for the next-generation bioelectronic implants with diagnostic or therapeutic functions in human healthcare and precision medicine.

A highly bendable thin film encapsulation by the modulation of thermally induced interfacial residual stress

Thin film encapsulation (TFE) is an essential component for reliable operation of organic electronic devices. However, the brittleness of inorganic layer in TFE must be resolved to secure the long-term stability of flexible/bendable devices. In this study, the robustness of the TFE in mechanical deformation is improved by harnessing such an interfacial residual stress. During fabrication of TFE by the alternating deposition of the organic layer via initiated chemical vapor deposition (iCVD) and inorganic Al2O3 via atomic layer deposition (ALD), the lower process temperature of iCVD (30 ℃) than that of ALD (90 ℃) generates a residual stress at the organic/inorganic interface, which was optimized by controlling the organic layer thickness, coefficient of thermal expansion (CTE), and elastic modulus. In order to optimize the residual stress, a new type of copolymer layer was suggested in TFE, synthesized from cyclohexyl acrylate (CHA) and 1,3,5-trimethyl-1,3,5-trivinylcyclosiloxane (V3D3) monomers. The water vapor transmission rate (WVTR) of the fabricated TFE was 3.1 × 10-5 g/m2·day, which was fully retained by optimized residual stress after 1000 times of bending cycles with the bending radius of 2.3 R, corresponding to the tensile strain exceeding 1.09%.

33‐2: Invited Paper: Flexible OLED Displays with Ink‐Jet Printing Technology

TCL CSOT has been investing in ink‐jet printing AMOLED technology for many years, and now CSOT has mastered the complete manufacturing process for IJP display technology, including rigid and flexible technology to manufacture middle and large size OLED displays. Flexible technologies such as panel design, substrate, TFT backplane, EL device, thin film encapsulation, module, and compensation have been developed. Attractive flexible prototypes including 14~31‐inch OLED have been demonstrated in the past three years. TCL CSOT expects to provide innovative flexible OLED displays in the near future.

P‐40: Techniques of Touch Sensing and Display Driving for Avoiding Display Artifacts for Flexible OLED Applications

Currently, use of flexible OLED (Organic Light Emitting Diode) displays is increasing, especially in mobile phone applications due to the high flexibility in industrial design they provide for curved edge and foldable smartphones and tablets. For flexible OLED, TFE (Thin Film Encapsulation) technology is widely used to prevent water and oxygen permeation, and as the name suggests, it is extremely thin. Accordingly, when on‐cell touch panels transition from rigid OLED with ~200 um glass encapsulation to flexible OLED with ~8 um TFE, the distance between display electrodes and the touch sensor becomes considerably closer. The dramatically increased capacitive coupling between the display and touch systems produces a correspondingly increased risk of errors in voltages driven to the display pixels due to touch sensing modulation coupling into the display system, resulting in deteriorated display image quality. In this paper, we introduce touch sensing and display driving techniques for avoiding display artifacts for flexible OLED applications.