Fringe-field Switching Research Articles

P‐176: New liquid crystal materials for high‐contrast displays of the fringe‐field switching mode

Since the establishment of liquid crystal display industries, larger sizes, faster response, higher contrast ratio, higher resolution and lower power consumption have become a pursuing target of various panel suppliers. Considering the marvelous viewing angle of the fringe‐field switching (FFS) mode, FFS displays with a higher contrast ratio are able to show more details in the dark pictures, resulting in a much better viewing experience. Herein, to develop the next‐generation liquid crystal (LC) materials for high‐contrast FFS panels, various high‐contrast LC (HCLC) materials were designed. By minimizing Δn and maximizing Kave, HCLCs exhibited lower light leakage in dark states, leading to a higher contrast ratio compared to the reference. Two HCLCs for improving the operation voltage, transmittance, contrast ratio and response time were developed by optimizing the properties of HCLC materials. Furthermore, FFS monitors with a contrast ratio of 2820:1 and a color gamut of 96.4% NTSC were demonstrated.

P‐246: Late‐News Poster: Effective flicker reduction through luminance compensation between pixels in the fringe field switching mode using positive dielectric liquid crystals

We develop the positive dielectric liquid crystals for flicker free that saves the power consumption and improves the image quality. The dielectric constant was optimized for a low flexoelectric effect and flicker is advanced by adding the LC component which reduces the luminance difference between frames. We confirmed that the a‐Si TFT LCD Panel incorporating the developed LC operates without flicker at the driving frequency of 40Hz.

P‐224: Late‐News Poster: Development of 660Hz LCD with Low Resistance Gate LTPS Backplane

16‐inch FHD+ (Full High Definition Plus, 1920*1200) LCD featuring LTPS TFTs with a new low‐resistance alloy gate metal and fast response AFFS (Advanced Fringe Field Switching) liquid crystal technology has been developed, which achieves a ClearMR value of 9000 at 480Hz frame rate and fulfills the requirement for product reliability test. These technologies, including the new gate metal TFTs and employing Fast‐Response time liquid crystal, have also been implemented in a 17.3‐inch FHD (Full High Definition, 1920*1080) gaming laptop LCD. This larger panel operates at an even higher frame rate of 660Hz and higher ClearMR values with GtG (Gray to Gray) liquid crystal response time within 1ms. These advancements mark significant progress in the field of high‐performance gaming displays.

Recent progress in liquid crystal devices and materials of TFT-LCDs

Thin-film-transistor-liquid crystal displays (TFT-LCDs) still dominate most of the display markets due to a big leap in image quality while keeping low cost and superior reliability, and its evolution is continuing to compete with emerging emissive displays. In this paper, recent progress in liquid crystal technologies mainly focusing on fringe-field switching (FFS) and polymer-stabilized vertical alignment (PS-VA) modes and materials for improving electro-optic performances is reviewed.

56‐2: Invited Paper: World's First 1 Hz Driving Fringe‐Field Switching (FFS) LCD for Power Saving

Here, we demonstrate world's first 1 Hz driving fringe‐field switching (FFS) LCD via development of low flexoelectric coefficient LCs with high voltage holding ratio (VHR). The evaluation of the 1 Hz driving 13.4‐inch FFS LCD laptop panel shows no flicker, and the power consumption is reduced by 83% compared to the 60 Hz driving. We believe this result opens a new chapter of FFS LCDs for low‐power consumption.

Reducing the Power Consumption of VR Displays with a Field Sequential Color LCD

To achieve 60 pixels per degree (PPD) and 100° field of view (FoV) while keeping a reasonably high aperture ratio for active-matrix liquid crystal displays (LCDs), field sequential color (FSC) is a promising approach. We evaluate the physical properties of a high birefringence nematic LC mixture and then use these data to simulate the performance of a fringe-field switching (FFS) LCD. Such an FFS LCD exhibits a fast average gray-to-gray response time (~1.5 ms) to enable FSC operation. By removing the spatial color filters, FSC operation triples the resolution density and optical efficiency, which are critical to high-resolution density and low power consumption virtual reality applications. Wide color gamut (96.2% of the DCI-P3 standard) and superior color uniformity are also demonstrated using such an FSC LCD.

Research of Liquid-Crystal Materials for a High-Performance FFS-TFT Display

A novel liquid-crystal compound of more than 99.95% purity with high performance (such as a high clearing point, large dielectric anisotropy, high optical anisotropy, low viscosity, and large elastic constants) was designed and synthesized according to the fringe-field switching thin-film-transistor-liquid-crystal display requirements (FFS-TFT). Then, a mixed liquid-crystal material suitable for an FFS-TFT display was developed by mixing this compound with other reported compounds, developing a product whose quality was that of the highest level of similar foreign products and which fully met the customer's use requirements (BOE), and thus able to completely replace similar imported materials.

Asymmetrically anchored liquid crystal cell for display and photonics applications

ABSTRACTAsymmetrically anchored liquid crystal (LC) cells have different anchoring energies between the top and bottom substrates. A substrate with patterned electrodes has comparatively weak anchoring energy. Therefore, asymmetrically anchored LC cells exhibit more twisted deformation in the on-state than conventional in-plane switching or fringe-field switching cells. In this study, we introduced asymmetrically anchored LC cells for display and photonic applications. We first introduced asymmetrically anchored LC cells to achieve high transmittance for LC displays. The LC molecules can rotate between the two substrates more easily because one of the two substrates has weaker anchoring energy. This resulted in a significant increase in transmittance. Three-terminal electrodes can be used to provide a vertical trigger pulse to an LC cell, thereby overcoming the delayed turn-off switching of an asymmetrically anchored cell without reducing transmittance. Next, we introduced an adjustable polarisation rotator with an asymmetrically anchored LC cell. To offer optical waveguiding, the arrangement of LC molecules can be controlled into a twisted configuration. During the cover of the wavelength range of 400–800 μm, we confirmed that the proposed LC cell can rotate the polarisation axis of linearly polarised light by up to 90°.

P‐5.6: Analysis of ITO Residue in 4mask process applied in Extra large‐size FFS LCDs

Indium tin oxide (ITO) residue is a serious problem in 4mask process applied in Fringe Field Switching (FFS) mode LCDs. In this paper, we analyzed the composition and structure of the residues and the reasons for their formation. ITO grains grow with increasing temperature during copper sputtering. As a result, it is hardly etched in the subsequent wet etching process, resulting in residues.

Fountain fringe field switching (FFFS) for wide viewing angle LCDs

To reduce or completely remove the viewing angle dependence of liquid crystal (LC) displays and devices, we have recently introduced a new electrode structure for LC displays. This electrode structure has openings (holes) in the pixel electrode (PixE) for generating fringe electric field with azimuthal degenerated distribution of the field lines around each hole, resembling a fountain. Such a field is promoting azimuthally degenerated switching of the LC molecules and thus generation of images with 360° viewing angle constant contrast when a pair of crossed circular polarisers are used. A theoretical model of the fountain fringe field, generated around a single circular hole and plurality of such holes in the PixE, is presented.

Amorphous IGZO Thin-Film Transistor Gate Driver in Array for Ultra-Narrow Border Displays

A gate driver in array (GIA) design based on the amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) is developed for narrow border displays. In the design, each TFT in the gate driver circuits is divided into a certain number of smaller size devices, which can be placed in different subpixels. Therefore, the pixel aperture ratio loss is minimized, and uniform placement of the gate driver circuits over the pixel array area is able to be achieved. The proposed step-like repeating block structure further reduces the occupied area of the signal interconnects. A 12.4-inch fringe field switching (FFS) liquid crystal display (LCD) panel of ultra-narrow border (0.5 mm) is demonstrated with reliable operation based on this GIA design, proving its potential for practical applications.

Flicker‐Free Fringe‐Field Switching Liquid Crystal Display Operable at Extremely Low Frequencies for Power Saving

The cover illustrates the fringe-field switching liquid crystal (LC) mode that is operable at extremely low-frequency regimes for power-saving in portable displays without image flickering issues. The ionic charges within LCs are effectively trapped by the fullerene-doped LC alignment layer. Further details can be found in the article number 2100174 by Hak-Rin Kim and co-workers.

Fast liquid crystal light shutter with polymer stabilisation

We present a fast-switching liquid crystal device comprising fringe field switching (FFS) electrode structure deposited onto one of the device substrates. Initially, the liquid crystal in the device has a homeotropic alignment. The generated periodic electric field by the FFS electrode results in a periodic splay/bend elastic deformation, thus giving rise to flexoelectric polarization along the substrate normal. At low applied voltages, this periodic elastic deformation, is substantially localized in a very thin portion of the liquid crystal layer adjacent to the substrate surface bearing the electrode and it is stabilized by a polymer network. Thus, the flexoelectric polarization becomes permanently present in the device and has non-zero value at field-off state. The polymer network with splay/bend configuration occupies very small part of the liquid crystal layer (∼0.5 μm), which is thinner than the light wavelength and therefore is optically invisible. Simultaneously with the formation of the polymer network, possessing splay/bend configuration, a polymer network with polymeric bundles oriented preferably along the substrates’ normal is formed. As we will show, the presence of the polymer network, consisting of surface and bulk parts, reduces substantially the switching times of the liquid crystal device more than one order bringing them to μs range.

Flicker‐Free Fringe‐Field Switching Liquid Crystal Display Operable at Extremely Low Frequencies for Power Saving

A fringe‐field switching (FFS) liquid crystal (LC) mode used with a negative dielectric LC (n‐LC) that is operable at an extremely low‐frequency signal voltage regime, without image flickering, is proposed. By doping charge‐trapping fullerenes (doping concentration: 0.2 wt%) into a low‐resistivity polyimide LC alignment layer of the FFS n‐LC mode, the mobile ionic‐charge density within the n‐LC layer can be drastically decreased. Thus, excellent voltage‐holding ratios of 98.24% and 87.91% are achievable in the proposed FFS n‐LC mode at low operation frequencies of 0.5 Hz and 0.2 Hz, respectively, corresponding to the improvement rates of 155.69% and 1127.05% at each operation frequency, compared with the FFS n‐LC mode without the fullerene doping case. The evaluation results by the modulation flicker level reveal that the operation frequency of the proposed device scheme can be decreased significantly (≈0.2 Hz) without inducing the perceptible image‐flickering problems.

A Novel Technique for Determination of Residual Direct-Current Voltage of Liquid Crystal Cells with Vertical and In-Plane Electric Fields

Generation of residual direct-current (DC) voltage (VrDC) induces serious image sticking of liquid crystal displays (LCDs). In this study, a novel technique to determine the VrDC of LC cells is proposed. We found that the VrDC could be determined from a current-voltage (I-V) curve obtained by the application of triangular voltage. In the case of a vertically aligned twisted nematic (VTN) mode LC cell, where a vertical electric field is applied, the I-V curve shows maximum and minimum current peaks owing to rotation of an LC director, and the VrDC is able to be determined from an average value of the two peaks. On the other hand, in the case of a fringe field switching (FFS) mode LC cell, where an in-plane (lateral) electric field is applied from comb electrodes, the current peaks derived from the rotation of the LC director do not appear. Therefore, we could not adopt the same way with that of the VTN mode LC cell. However, we found that there were two minimum current peaks derived from minimum capacitances of the FFS mode LC cell, and could determine the VrDC by using these two current peaks. The proposed technique would be useful for the evaluation of the VrDC of the LCDs, where the electric field is applied both vertically and laterally.

Photocontrollable Resistivity Change in Nanoparticle-Doped Liquid Crystal Alignment Layer: Voltage Holding and Discharging Properties of Fringe-Field Switching Liquid Crystal Modes

In liquid crystal (LC) displays, deriving an optimum resistance level of an LC alignment polyimide (PI) layer is important because of the trade-off between the voltage holding and surface-discharging properties. In particular, to apply a power-saving low-frequency operation scheme to fringe-field switching (FFS) LC modes with negative dielectric LC (n-LC), delicate material engineering is required to avoid surface-charge-dependent image flickering and sticking problems, which severely degrade with lowering operation frequency. Therefore, this paper proposes a photocontrolled variable-resistivity PI layer in order to systematically investigate the voltage holding and discharging properties of the FFS n-LC modes, according to the PI resistivity (ρ) levels. By doping fullerene into the high-ρ PI as the photoexcited charge-generating nanoparticles, the ρ levels of the PI were continuously controllable with a wide tunable range (0.95 × 1015 Ω∙cm to 5.36 × 1013 Ω∙cm) through Ar laser irradiation under the same LC and LC alignment conditions. The frequency-dependent voltage holding and discharge behaviors were analyzed with photocontrolled ρ variation. Thus, the proposed experimental scheme is a feasible approach in PI engineering for a power-saving low-frequency FFS n-LC mode without the image flickering and image sticking issues.

High-efficiency, tunable, fringe-field switching-mode beam steering based on a liquid crystal Pancharatnam phase

We have fabricated, characterized, and analyzed a recently proposed non-mechanical beam steering device based on the Pancharatnam-Berry phase in a liquid crystal. The architecture of our proposed device employs a linear array of phase control elements (PCEs) to locally control the orientation of the liquid crystal director into a cycloidal pattern to deflect transmitted light. The PCEs are comprised of a fringe-field switching electrode structure that can provide a variable in-plane electric field. Detailed optimization of the director configuration is in a good agreement with experimental results showing that the half-wave retardation condition has been uniformly achieved across the aperture. Moreover, efficiency simulations using a finite-difference time-domain algorithm verify a high beam steering efficiency for the proposed device.

Unidirectionally Oriented Multi-Layered Carbon Nanotubes Film for Polarizer

Nanowire-grid polarizer (WGP) that is generally used for a linearly polarized UV light that required for photo-alignment requires to have a very short pitch of about 100 nm to make, which is highly cost process due to nanopattern of metals. Therefore, we propose multi-layered CNT (Carbon nanotube) sheet that can replace the conventional WGPs. In this regard, unidirectionally oriented CNT bundles are proposed which shows a strong optical activity and anisotropic behavior with visible and ultraviolet wavelengths. In addition, a film prepared by oriented CNT bundles shows a high transparency at shorter wavelengths of 380 nm and even less. Furthermore, oriented CNT film exhibits 75-80% of DOP in the region of 350nm ~ 800 nm, especially ~91% in ultraviolet region, and provides wide absorption spectrum due to the π -plasmon of graphite. Moreover, the DOP and optical activity of aligned SWCNT can be further enhanced by improving the degree of alignment of CNT by stretching the polyvinyl alcohol substrate. We prepare a multi-layer CNT polarizer by depositing CNT layers one over another on a Silicon substrate by chemical vapor deposition technique. And then a bundle of CNTs are unidirectionally stretched to make the CNT sheet by using a mechanical rotation tool. The long axis of CNT rods in each sheet is orient parallel to the stretching direction. Then the stacked CNT sheet is transferred to a glass substrate as indicated in Fig 1. (a).The final multi-layered CNT polarizer consists of 3, 5, 8 and 12 CNT sheets stacked together with matching orientations. The relative transmittance of CNT polarizer within visible region is decreasing with increasing number of CNT layers. The incident light with its electric vector parallel (perpendicular) to the stretched CNT axis is effectively absorbed (transmitted) by the multi-layered CNT polarizers. Wavelength-dependent transmittance is showing a good correlation with optical microscopic results, as shown in Fig 1. (b). The transmittance of CNT polarizer at 365 nm is measured to be >10%, 6.5%, 1.0% and 0.5% for 3, 5, 8 and 12 CNT layers, respectively, whereas the iodine polarizer is exhibiting almost zero transmittance. Moreover, the proposed CNT polarizer is capable to extend the absorption of incident light up to deep UV region providing a wider operating wavelength range from 300 nm to400 nm and all multi-layered CNT polarizers exhibit high stability against long time UV exposure. To measure the multi-layer CNT polarizer’s performance, we have employed fringe field switching (FFS) cell with 3.4 μm with film spacers (passivation layer = 0.5 µm / gap between pixel electrodes = 4.5 µm / pixel electrode width = 3.5 µm). As shown in Fig. 1(c), obtained multi-layer CNT polarizer exhibits higher DOP of 91% by matching orientation of stacked CNTs in each layer. Inserted left image in the graph is the FFS cells exposed with 3 CNT layers. It exhibits slight nonuniformity in brightness of low grey scales called mura at 3 V, whereas the cells exposed with 12 CNT layers (right insert image of Fig. 1 (c)) do not show such mura. The proposed CNT polarizer film is expected to be applied as photomask with low-cost. we believe it has strong potentiality to utilize in future photonic and electro-optic devices with broad band gap from UV to infrared. Figure 1

Journal of the Society for Information Display

Jiun-Haw Lee Editor in Chief The Journal of the Society for Information Display's (JSID's) September and October 2020 issues each feature six papers that report on new research in key areas. Topics include OLED, LCD, thin-film transistors (TFTs), electrophoretic displays, human factors, display measurements, and optics. Furthermore, as a friendly reminder, the 26 “Distinguished Papers, Best of Display Week 2020” published in JSID's April, May, and June 2020 issues will remain open access until the end of the year. A single-cell-gap transflective blue-phase liquid crystal display based on fringe in-plane switching electrodes|Xiang-Yu Zhou et al.|doi:10.1002/jsid.872 In this work, the authors propose a new LCD mode for a transflective blue-phase (TRBP) device, which they refer to as fringe in-plane switching (FIS). This mode combines the advantages of in-plane switching (IPS) and fringe-field switching (FFS). Compared to FFS, FIS has a similar driving voltage but with much higher transmittance. However, FIS has a much lower driving voltage than the IPS mode. By providing fringe and in-plane electric fields simultaneously, the authors obtained a deep-penetrating electric field that greatly improved LCD's transmittance while also lowering the driving voltage. Note that two TFTs were required in a single pixel of FISTRBP-LCD for providing the driving voltage with opposite polarities. Investigation on Ag-containing compound generated in manufacturin go flow-temperature polycrystalline Si active matrix organic light-emitting diode |Yu Jin et al.| doi:10.1002/jsid.895 In this highly practical paper, the authors analyze low-temperature polycrystalline silicon (LTPS) active matrix (AM) OLED's failure caused by silver (Ag) contamination, and explore possible solutions. In observing Ag-contamination in LTPS's real products, they noticed that it resulted in short circuits in certain places. The Ag-compounds originate from the electrochemical formation and are related to migration assisted by an electric field. The authors proposed several methods to alleviate this effect, including a planarization dam that can be used to increase the migration path and weaken the electric field. The paper may stimulate interesting ideas for improving production yield without increasing the complexity during display manufacture. Information About the Journal JSID is published monthly by Wiley. Subscription fees apply, but SID members and student members have free online access via sid.org/Publications.aspx. Many universities also have an institutional subscription. JSID is indexed in the Web of Science. Submit your original manuscript online via mc.manuscriptcentral.com/sid. Author guidelines can be found on the Journal's homepage: tinyurl.com/jsidhome. Editorial board: tinyurl.com/jsideb. Please direct any questions about JSID to its editor in chief at editor@sid.org. EarlyView: accepted papers about to be published can be accessed online via tinyurl.com/jsidev. Invitation to Submit Review Papers The Journal is soliciting review papers on any display-related topic. If you have a great idea for a review paper, please contact the editor at editor@sid.org. Page charges for invited review papers will be waived.

P‐154: New Carbon Nanotubes UV Polarizer for Photoalignment of Liquid Crystals

We propose a unidirectionally aligned multi‐layered carbon nanotubes (CNT) as a UV polarizer for LC photoalignment, which can replace wire‐grid‐polarizer (WGP) with high cost. A 12 multi‐layered CNT polarizer exhibits the degree of polarization up to 91%. The fringe‐field switching (FFS) LC device made by photoalignment with use of the proposed CNT polarizer exhibit uniform LC alignment in whole area and excellent electro‐optics. The work proposes not only cost‐effective novel polarizer replacing WGP for photoalignment of LC but also for photonic component of broadband polarizer from UV to IR.