Cover Window Research Articles

84‐5: Late‐News‐Paper: Flexible Cover Window Film with Improved Optical Clarity

SK Innovation and SK ie technology have developed and commercialized cover window films (FCW®) composed of functional coatings on transparent polyimide (PI) film for a foldable displays. We report on the development of PI film with high visual clarity, which can provide glass‐like feel to public users. Advances were achieved by engineering drying kinetics on the process of film fabrication, and the technology is applied to the commercial product of transparent PI film.

84‐3: Invited Paper: Advanced Cover Window and Thin‐film Encapsulation Technologies for Foldable AMOLED Display

Foldable AMOLED enable some component technologies integration and continuously improvement. A roll to roll process integrated cover window with circular polarizer show the high mechanical strength and R3mm folding ability with AMOLED panel. And also, the advanced solution‐coated gas barrier is proposed to OLED thin film encapsulation for new flexible AMOLED form factor applications.

Superhydrophobic, antireflective, flexible hard coatings with mechanically ultra-resilient moth-eye structure for foldable displays

Biomimetic inspiration from the moth-eye structure has led to many studies combining nanoimprint lithography (NIL) to realize low cost and large area anti-reflection (AR) coatings. However, the scope of application is severely limited by poor mechanical performance due to the intrinsic properties of the coating materials and the nanosized patterns. In this work, we demonstrate a moth-eye structured epoxy-siloxane molecular hybrid (ME-ESMH) fabricated using single UV-based NIL (UV-NIL) on a colorless polyimide (CPI), to be utilized as a flexible cover window (FCW) for foldable displays. Low reflection, a superhydrophobicity and good inward foldability were achieved, together with excellent thermal and chemical resistance. Furthermore, in situ uniaxial compression tests revealed that the fabricated structure can be elastically deformed and nearly restored to its original shape even after a large degree of compression. Our findings provide an easy-to-integrate solution for flexible hard coatings with superhydrophobic and AR properties, applicable to foldable optoelectronics.

Facile preparation of wear-resistant and anti-fingerprint hard coating with chemisorption of fluorosilane by simple wet coating

Epoxy-siloxane hybrid hard coating (HC) has been reported to be applicable to foldable display cover window film due to its glass-like hardness and plastic-like flexibility, which are trade-off characteristics. In addition, to provide an anti-fingerprint (AF) function with abrasion resistance to HC, the addition of a durable hydrophobic function on the HC surface is essential. Herein, durable hydrophobic and abrasion resistant F-HC was reported by chemical adsorption of fluorosilane on HC with simple wet coating. TEOS-derived silica primer increased the hydroxyl groups (–OH) on surface of HC, then it improved the sol-gel condensation with fluorosilane. The fluoro-treatment reduced the coefficient of friction to maintain hydrophobicity (<10% of the initial water contact angle) and optical transparency (~90%) after 5000 cycles of a steel-wool test and 2000 cycles of an eraser abrasion test. Performance was dependent on plasma treatment, annealing condition, and pretreatment on the HC surface for the stronger chemisorption of fluorosilane.

Shock absorption of semi-interpenetrating network acrylic pressure-sensitive adhesive for mobile display impact resistance

With the development of mobile display shapes from flat to flexible, the conventional glass cover window must be replaced by a film-type window. However, film-type cover windows have low impact resistance owing to their poor shock absorption. Therefore, to realize their application to flexible displays, it is essential to characterize and improve the shock-absorbing characteristics of the display film. In this study, a semi-interpenetrating network (semi-IPN) acrylic pressure-sensitive adhesive (PSA) consisting of a crosslinked network structure with a linear acrylic polymer chain was developed. The influence of the multi-functional monomer content and UV dose on the properties of the semi-IPN PSA was studied. The peel strength of the semi-IPN PSA was higher than 10 N/25 mm, which is generally considered as the PSA standard for mobile displays. With an increase in crosslink density, the storage modulus increased, but the damping factor decreased. To evaluate shock absorption, a falling ball impact tester was used to estimate the shock absorption ratio (ΔF) of the film. The semi-IPN PSA incorporating 30 phr of the multi-functional monomer exhibited higher ΔF (31.2%) than that of a conventional UV-curable PSA film (24.6%). This shows that even with the relatively low damping factor of the semi-IPN PSA, its structure could improve shock absorption. Moreover, we suggested two mechanisms for shock absorption of the semi-IPN PSA, energy dissipation into the PSA layer and extended contact time.

Highly robust and transparent flexible cover window films based on UV‐curable polysilsesquioxane nano sol

AbstractFlexible cover window films based on the ultraviolet‐curable polysilsesquioxane are prepared to have enhanced mechanical, optical properties, and bending performance. To figure out the factors determining those properties, post–treatment conditions are varied into the light source, temperature, and relative humidity. Then, the effect of such variables is examined in respect of surface hardness, yellow index (YI), and bending cycle reliability of flexible hard coating. Also, the effect of photoinitiator type in terms of their chemical structure is also investigated. Notably, the relative humidity and thermal treatment are more effective to enhance the mechanical properties rather than light exposure. Indeed, compared to that of reference condition, the cover windows treated with 99% relative humidity and thermal aging at 85°C exhibit improved surface hardness by 24.4 and 19.5%, respectively. However, only the relative humidity is rather effective to enhance the optical properties such as the YI by lowering to the most 2.6. The YI is also improved by varying the chemical structure of the photoinitiator. By virtue of post–treatment and a different photoinitiator, we could achieve flexible cover window films with bending reliability at bending radius of 3 mm for 100,000 cycles, showing good mechanical and optical properties simultaneously.

Optimized design of silicone pad for bended window lamination in organic light-emitting diodes

Recently, various types of displays have been developed for use in smartphones. In particular, the shape of the glass used as the cover window of a smartphone has developed from a flat shape to a vandal shape with multiple curvatures. The lamination process for bonding an OLED backplane to such a bended cover window requires a relatively high level of skill. To develop such a technique, we designed a silicone pad with sufficient adhesive strength to suit the various curvatures. In this paper, we have confirmed the results.

53‐4: Rigid/Soft/Rigid type cover window for foldable display

We present rigid/soft/rigid (RSR) type cover window for the foldable display. We investigated the synthesis of flexible nanosol through sol‐gel reaction and fabricated RSR cover window sample with a home‐made slot die coater. Furthermore, coating thickness uniformity, surface hardness, folding reliability were explored.

53‐3: Invited Paper: Out‐Foldable Smartphone Will Be Real?: Challenges for Developing Glass‐like Cover Plastic Films

An out‐foldable smartphone is more favorable for consumers’ convenience but technologically more difficult than an in‐foldable one. Particularly, for the out‐foldable one, a large elongation of cover window film induced by tensile stress outside display module is required. However, it is difficult to realize the large elongation in the hard coating on the cover film. This invited paper deals with the issues of hard coating and proposes newly developed solution with high scratch‐resistance for out‐foldable smartphone.

Development of optical film for eliminating the ghost image on the cover window for the convex display system

In this study, we have studied a method to evaluate the image quality of a convex display and developed a film that can eliminate the ghost image which is pointed out as the biggest problem of image quality deterioration. The brightness uniformity of the screen varies greatly depending on the measurement position due to the shape of the curved surface display, and the unwanted ghost image is generated by the cover window attached to the curved display. The ghost image can be eliminated considerably by attaching a film having a groove structure, and it is possible to develop an efficient shape on film by controlling the size of the groove structure. As a result, the brightness of the ghost image could be reduced from 39.1 cd/m2 to 4.8 cd/m2, and four splitted images with sharp edges could be displayed as a small blur at the edge, so it possible to improve readability and sharpness of convex display.

Mechanical simulation of foldable AMOLED panel with a module structure

Abstract The stress analysis of the flexible AMOLED panel is a fundamental study for designing optimal structures with good foldability. Current research assumes linear elastic models. In the present work, A visco-hyperelastic constitutive model was employed to describe the nonlinear behavior of the optically clear adhesive (OCA). The finite element method for simulating the folded panel was constructed to analyze the effect of panel structure on the stress and strain distributions. Compared with the bending state of the single device, the flexible panel module is shown to have multiple neutral planes. The maximum longitudinal stress of the AMOLED device is located at the folding symmetry, while the maximum strain in the OCA layer is located at the transition area between the bending and unbending areas. Finally, the simulated results show that increasing the thickness of the first OCA layer which located between the cover window and the polarizer is more efficient for preventing peeling effect or delamination occurred to the panel.

Transparent Urethane-Siloxane Hybrid Materials for Flexible Cover Windows with Ceramic-Like Strength, yet Polymer-Like Modulus.

Any transition toward an era of flexible electronics will have to overcome the mechanical limitations of materials. Specifically, the attainment of both strength and flexibility, which are generally mutually exclusive, is required including glass-like wear resistance, plastic-like compliance, and a high level of strain. Here, we fabricate a urethane-methacrylate-siloxane hybrid (UMSH) material. It is found that UMSH, with molecule-level hybridization of urethane linkage and methacrylate-siloxane conetworks, demonstrates ceramic-like high strength (574 MPa), yet polymer-like low modulus (8.42 GPa), and even high strain (6.3%) at fracture with excellent optical transparency. This combination of high strength, flexibility, and optical transparency indicates that this is a suitable material for glass substitution and can be used as a transparent flexible cover window for foldable display.

P‐212: Late‐News Poster: Flexible Cover Window for Foldable Display

We present foldable cover lens of multiple structures based on the anti‐scratch optical film. We studied mechanical properties of surface hardness of flexible cover window by a nanoindentation method. Furthermore, folding reliability was also investigated by repeating normal flat state and bended state of cover window sample.

An FPGA accelerator for PatchMatch multi-view stereo using OpenCL

PatchMatch multi-view stereo (MVS) is one method generating depth maps from multi-view images and is expected to be used for various applications such as robot vision, 3D measurement, and 3D reconstruction. The major drawback of PatchMatch MVS is its large computational amount, and its acceleration is strongly desired. However, this acceleration is prevented by two problems. First, though PatchMatch MVS estimates depth maps by propagating estimation results among neighbor pixels, it is not suitable for GPU-based acceleration. Second, since the shape of a matching window used for stereo matching is changed dynamically, reading its pixels is inefficient in memory access. This paper proposes an FPGA accelerator exploiting on-chip FIFOs efficiently to solve the propagation problem. Moreover, reading pixels of a matching window is improved by a cover window which has the fixed shape and covers the matching window. The FPGA accelerator is designed using a design tool based on Open Computing Language (OpenCL). Although parameters of PatchMatch MVS depend on object images, these parameters can be changed easily by the OpenCL-based design. The experimental results demonstrate that the FPGA implementation achieves 3.4 and 2.2 times faster processing speeds than the CPU and GPU ones, respectively, and the power-delay product of the FPGA implementation is 3.2 and 5.7% of the CPU and GPU ones, respectively.

Biomimetic Chitin–Silk Hybrids: An Optically Transparent Structural Platform for Wearable Devices and Advanced Electronics

AbstractThe cuticles of insects and marine crustaceans are fascinating models for man‐made advanced functional composites. The excellent mechanical properties of these biological structures rest on the exquisite self‐assembly of natural ingredients, such as biominerals, polysaccharides, and proteins. Among them, the two commonly found building blocks in the model biocomposites are chitin nanofibers and silk‐like proteins with β‐sheet structure. Despite being wholly organic, the chitinous protein complex plays a key role for the biocomposites by contributing to the overall mechanical robustness and structural integrity. Moreover, the chitinous protein complex alone without biominerals is optically transparent (e.g., dragonfly wings), thereby making it a brilliant model material system for engineering applications where optical transparency is essentially required. Here, inspired by the chitinous protein complex of arthropods cuticles, an optically transparent biomimetic composite that hybridizes chitin nanofibers and silk fibroin (β‐sheet) is introduced, and its potential as a biocompatible structural platform for emerging wearable devices (e.g., smart contact lenses) and advanced displays (e.g., transparent plastic cover window) is demonstrated.

Polarization modeling and predictions for DKIST part 2: application of the Berreman calculus to spectral polarization fringes of beamsplitters and crystal retarders

We outline polarization fringe predictions derived from an application of the Berreman calculus for the Daniel K. Inouye Solar Telescope (DKIST) retarder optics. The DKIST retarder baseline design used six crystals, single-layer antireflection coatings, thick cover windows, and oil between all optical interfaces. This tool estimates polarization fringes and optic Mueller matrices as functions of all optical design choices. The amplitude and period of polarized fringes under design changes, manufacturing errors, tolerances, and several physical factors can now be estimated. This tool compares well with observations of fringes for data collected with the spectropolarimeter for infrared and optical regions at the Dunn Solar Telescope using bicrystalline achromatic retarders as well as laboratory tests. With this tool, we show impacts of design decisions on polarization fringes as impacted by antireflection coatings, oil refractive indices, cover window presence, and part thicknesses. This tool helped DKIST decide to remove retarder cover windows and also recommends reconsideration of coating strategies for DKIST. We anticipate this tool to be essential in designing future retarders for mitigation of polarization and intensity fringe errors in other high spectral resolution astronomical systems.

P‐198: Optically Clear Adhesives Enabling Foldable and Flexible OLED Displays

Flexible, foldable organic light emitting diode (OLED) displays have been conceptually demonstrated but not yet commercialized in a consumer electronics device. We will share progress and understanding of how 3MTM Optically Clear Adhesives (OCAs) can be used to laminate cover windows and touch sensors to enable active, dynamic folding of flexible OLED displays.

Simulating House Cooling Methods to Decrease Energy Consumption by Creating Awareness and Attitude Change

Efficient cooling methods are necessary when living in a tropical climate where high temperatures and high humidity are normal. Air-conditioning units, which are expensive to run and maintain are standard in a majority of houses in Australia's tropic zone due to the design of both historic and modern housing not being fully suited to a tropical region. Significantly, the cost of energy consumption continues to increase. There are simple and inexpensive modifications a homeowner can do to naturally cool the house and preserve energy, such as, painting roofs white, planting screening vegetation and installing shades externally to cover windows, etc. However, many of these alternative techniques are not common knowledge and are not presented to the public in ways that can inform and potentially change behaviour. This paper presents a housing simulation prototype that applies gamification methods to build awareness on ways to reduce cooling power consumption. An interactive guided persuasion methodology is used to educate homeowners about these alternative techniques so they may choose natural cooling methods instead of relying on electrical cooling appliances. The results of the user testing show the simulation design did encourage awareness and motivation to make tangible adaptations to homes.

Erratum: Re: “Management of heat in laser tissue welding using NIR cover window material” Lasers in Surgery and Medicine, 2011;43(10):991–997

Erratum: Re: “Management of heat in laser tissue welding using NIR cover window material” Lasers in Surgery and Medicine, 2011;43(10):991–997

Studies of reflectivity degradation of retroreflectors in LHD and mitigation of impurity deposition using shaped diagnostic ducts and protective windows

Maintaining the reflectivity of first mirrors is indispensable in future fusion devices. While a retroreflector (corner cube mirror) is useful for laser diagnostics, impurities tend to accumulate and form a thick deposition layer in the central region, which causes degradation of reflectivity, due to the hollow shape of the retroreflector. Two mirror structures are tested to retain the reflectivity in the Large Helical Device (LHD). One is a bending mirror structure with a protective cylinder with fins and it could maintain the reflectivity over a three-month experimental campaign. The other is a cover window just in front of the reflector. Candidates of the window materials were exposed to the LHD plasmas and the degradation of the transmissivity of ZnSe and silicon, which are used for infrared and far infrared laser light, respectively, were small.