High Quality Liquid Crystal Displays and Smart Devices - Volume 2: Surface alignment, new technologies and smart device applications
A liquid-crystal display (LCD) is a flat-panel display or other electronically-modulated optical device that uses the light-modulating properties of liquid crystals. Liquid Crystal Displays are already widely used in consumer electronics, but research and development is still ongoing. The shifting focus of research follows a pattern of improved definition, increased display size, wider viewing angles and faster responses, with improvements in each area influencing the next. There is also growing interest in the use of liquid crystal materials in novel applications including sensing devices, spatial modulators and light-shielding windows. This book discusses the latest LCD technologies, with their challenges, opportunities, and problems to be solved, at a level suited to an academic and research-professional audience. There is a particular focus on display quality such as image sticking, contrast ratio and colour hue that has not been dealt with thoroughly elsewhere. Current and future trends in liquid crystal materials and technologies based on their evolving role and new applications are discussed in detail.
Other keywords: surface alignment; display quality; nonmechanical photo-alignment; field sequential ferroelectric LCDs; colour hue; satellite communication antennas; gas sensors; Image flickering; security devices; smart windows; glass-free 3D-LCD-TVs; field-sequential-colour LCDs; liquid crystal displays; contrast ratio; LC-devices; LC lenses; optical design; VR/AR displays; planar alignment materials; actuators; liquid crystal molecules; image sticking; reflection mode LCDs; power consumption
- Book DOI: 10.1049/PBCS068G
- Chapter DOI: 10.1049/PBCS068G
- ISBN: 9781785619236
- e-ISBN: 9781785619243
- Page count: 408
- Format: PDF
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Front Matter
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1 Evolution of alignment material technology
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The alignment layer is one of the important components in LCDs because the film makes an impact for the display quality by controlling the initial alignment of liquid crystals. It also affects the electrical properties of panels which decide the reliability of LCDs. In this chapter, the design of alignment materials responded to mass fabrication process, such as the printing, the rubbing and so on, is described. In addition, the required properties of the alignment materials to generate and keep high display quality in LCDs are reviewed from the viewpoint of the alignment of liquid crystals and electrical properties of the film and LC cells. Finally we introduce alignment materials for new technology using the irradiation of UV, the photo-alignment and PSA technology. Photo-alignment technology is just applying FFS LCDs for smartphones and laptop computers with high density. PSA technology is widely applied to TV applications. The design of alignment materials corresponding to the each panel and fabrication process is also explained.
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2 Photo-alignment technology for vertically aligned LCDs
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Rolic® light-controlled molecular orientation (LCMO) is a state-of-the-art photoalignment technology used in todays mass production for vertically aligned (VA) liquid crystal display (LCD), where high-resolution LC director patterning with well-defined azimuthal and pretilt angles is required. We provide a description of the LCMO mechanism and show the positive impact of the lower pretilt angle on the intrinsic transmittance of VA-LCDs. Novel LCMO-VA materials for ultra-high definition LCDs are also presented.
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3 Azo-dye photoalignment materials
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The new azo-dye photoaligning films are robust and possess very good aligning properties for liquid crystal (LC) cells such as anchoring energies and voltage holding ratios as well as a high thermo and UV stability both in glass and plastic substrates with very high resolution on submicron level. The most important characteristics of azo-dye photoaligning films will be compared with those of rubbed polyimide films usually used for LC alignment. In this chapter, we will also describe the new applications of azo-dye photoalignment: (i) LC display devices, such as ferroelectric LCD for IPS, field sequential color and microdisplay applications; (ii) LC photonics devices, such as LC lenses; (iii) LC E-paper devices, such as electrically and optically rewritable LC E-paper; (iv) nanoscopic optically engineered polymeric thin film polarizers.
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4 Alignment materials and their surface deformation induced by manufacturing processes
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Liquid crystal displays (LCDs) are used for displaying still and moving images in all types of large or small display media, including monitors for laptop computers or desktop personal computers, display panels for TVs, mobile phones, smartphones, on-board navigation, viewfinders for video cameras, preview screens for digital cameras, projection displays and information display monitors in public spaces. In order to utilize liquid crystal (LC) material in LCDs for such applications, an electro-optical response is applied, in which the transmitted light intensity is controlled by the application of a set voltage to the driver devices. For this purpose, the alignment control of LC molecules is essential. In this chapter, alignment materials and their surface deformation anisotropy for alignment control of LC molecules are discussed.
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5 Analysis and inspection of alignment membrane in LCDs
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The role and importance of the alignment layer in liquid crystal displays (LCDs) are presented in theoretical point of view. Principle and validity of the reflection polarimetry for evaluating directly the property of the alignment layers are shown. The technique for evaluating the image sticking, which is considered to be brought from deterioration of the alignment membrane, is briefly presented with some examples.
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6 Electrical evaluation of alignment layers and LC panels
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This chapter describes a basic overview of electrical measurements such as voltage holding ratio (VHR), ion impurity, residual DC (RDC) voltage and capacitance- voltage (C-V) for elastic constant measurement of liquid crystals. Furthermore, ion impurity measurement in a thin film transistor liquid crystal display (TFT-LCD) panel is also described to find a root cause of image-sticking phenomena.
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7 Analysis method of image sticking
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In this chapter, we present a method to analyze the image-sticking phenomenon of the liquid crystal display (LCD). Image-sticking phenomenon is one of the severe problems that deteriorate image quality of not only LCD but also other display systems such as OLED and CRT. First, we have categorized the main factors of the image sticking and then simulated the proportion of these factors by using the experimental data. We expect that this method of analysis can be utilized to understand the basic mechanism of the image sticking and to solve the chronic problem of LCDs.
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8 New alignment process and its application
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Until recently, it has been thought that for LCD fabrication it was necessary to coat an LC alignment film, such as a polyimide (PI) film, on the substrate before filling the LC material. Generally, plastic substrates for flexible displays are incompatible with the thermal processes for curing a PI layer after the coating process on the substrate. Recently, LC alignment techniques that do not require a PI layer have been proposed. In this chapter, the slit coater method as a PI-free LC alignment technique is introduced.
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9 Liquid crystal self-alignment technology
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The preparation method for uniaxially homogeneous and vertical alignments of liquid crystal (LC) molecules was proposed without using a conventional alignment layer such as polyimide film. The method produces the self-alignment layer (SAL) by the polymerisation of the monomers in the LC layer above the TNI of the LC material. The fringe-field-switching (FFS) and the vertical alignment (VA) modes LC cells with the SALs (self-FFS or self-VA cells) produced from the monomers exhibited equivalent level of alignment state and electro-optical properties compared with the conventional LC cells having the polyimide-film alignment layers. The self-FFS and the self-VA cells would be useful for next-generation displays such as flexible liquid crystal displays (LCDs) because the method does not need high-temperature process over 200 °C.
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10 Color-reflective LCD based on cholesteric liquid crystals
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Cholesteric liquid crystals (hereafter Ch LCs) are self-assembled systems consisting of elongated chiral organic molecules. They possess a helical structure where the local average direction of the molecules twists spatially around an orthogonal helical axis. Their refractive index varies periodically, and thus exhibits a Bragg reflection band centered at the wavelength λ = [(ne + no)/2]P and with the bandwidth Δλ = (ne - no)P, where ne and no are the extraordinary and ordinary refractive indices of the LC, respectively, and P is the helical pitch. They can be used to make reflective displays which do not need polarizers and have high reflectance. In this chapter, various mechanisms, which can be used to modify the reflection of the displays, are described. The performance of the displays is also discussed.
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11 Enhancement of optical output and low-power consumption in nanoparticle-embedded liquid crystal devices
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We present unique optical effects in nanoparticle (NP)-embedded liquid crystal devices. For conducting this research, we synthesized PgCyD-ZrO2 and we prepared NP system comprised of seven NPs of Aerosil R-812 (EVONIK) through a sonication, where the original Aerosil has the size of 400 nm. LCD device cells embedded with these NPs exhibit the optical enhancement effects such as reduction of laser speckle patterns, increase of output intensity, viewing angle, and color gamut and further reduction of power consumption evaluated through luminance efficiency. This chapter is written by updating the previous publications [1-8] through describing the details of syntheses of NP and giving physical modeling of light scattering based on Rayleigh-Gans scattering theory accompanying an updated figure and also the effect of raising effective temperature called Kobayashi temperature and pretilt increasing effect with simulation.
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12 Ferroelectric micro LC display
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Ferroelectric micro LC display is one of the transmissive liquid crystal on silicon (LCOS) displays, and it has some advantages for small and high resolution with low power consumption. This technology using ferroelectric LCs is useful for wearable device, such as head mounted display.
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13 LC GRIN lens technology
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Liquid crystals (LCs) are attractive to optical devices which are expected to make the optical function or performance variable. Many technologies for various applications have been investigated and LC GRIN (GRadient-INdex) lens is a typical of those technologies. Based on the purpose of variable optical device, it is important to clarify the target of function and performance, and in order to achieve the target, the device structure and materials need to be developed. Also, optical performance evaluation is significant because the optical devise using LC generally presents specific characteristics such as polarisation dependence. In this chapter, display applications of LC GRIN lens technology is focused and future applications, breakthrough issues, or performance limitation are discussed.
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14 Essence and practical use of field-sequential colour LCD
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Herein, we present and discuss essential virtue of field-sequential colour liquid-crystal display (FSC-LCD) and how we technically resolved fundamental problems in the FSC-LCD such as the occurrence of flickering, hue rotation at low temperature and colour breakup. And in addition, we present demonstration of the implementations of actual examples of indicators in airports and railway stations, a transparent LCD and an LCD exhibiting good legibility under the direct sunshine.
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15 Color breakup reduction in field-sequential color LCDs
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16 Field-sequential full colour displays using polymer-stabilised ferroelectric LCD
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The effect of polymer stabilisation of liquid crystal alignment is an attractive method for modifying the electro-optical properties of liquid crystals. The polymer stabilisation in ferroelectric liquid crystals allows a bistable switching of a biaxial alignment, which is surface-stabilised ferroelectric liquid crystal display (SS-FLCDs), to alter into uniaxial alignment of V-shaped switching to enable AC driving. We demonstrated an excellent performance to be suitable for a field sequential full-colour LCD exhibiting a fast switching with response time of less than 500 μs.
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17 Optical security devices using UV-curable nematic liquid crystals
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This chapter begins by reviewing current counterfeit-proofing concepts and the security applications of liquid crystal (LC) materials that have been proposed to date. Next, security devices that use intrinsic random features for applications in a variety of fields are reviewed and the core concept of use of random features is discussed. The random optical textures that occur in LC phases, which have generally been considered to be defects for the purposes of most engineering applications, can then be regarded as favourable characteristics for security devices; the use of the unique patterns of these optical textures as identification information, which was previously proposed by the author, is then explained. Because security measures that use these intrinsic random features appear to be an unfamiliar concept for most LC researchers, a more detailed explanation is provided that traces the concept of security measures that use the random features in LC materials, and real data from actual fabricated devices is then provided.
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18 Application of liquid crystals to MEMS
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In this chapter, the applications of liquid crystals (LCs) to microactuators which are suitable for MEMS usage are introduced. The major source of the actuator drive is the LC flows induced by the applied electric fields, and thus this chapter begins with the reviews of the experimental and theoretical aspects of the backflow effect of LCs between parallel plates. Then, the experimental and simulation results on the actuator drive under the pulsed electric fields are presented and the effects of the electric field on the driving performance of the LC actuator are considered. These results suggest that the LC materials have the potential of application to MEMS devices.
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19 Detection of volatile organic chemicals by using liquid crystals
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The detection of volatile organic compounds (VOCs) is drawing much attention in numerous aspects. It is not only highly utilised in the field of detection of toxic and flammable gases but also in the field of disease diagnosis and healthcare. To date, much research has been done by using liquid crystals (LCs). In this chapter, in addition to introducing various prior arts, we investigated the structural dependence of LC materials which have been hardly studied so far. In particular we focused on the use of chiral nematic LCs which show selective reflection and clarified the relationship between these molecular structures and the shift in their reflection spectrum as a result from contact with VOCs. We also propose a mechanism to explain the red- or blue-shift in the peak wavelength of the selective reflection spectrum. Furthermore, enhancement of the sensitivity and the selectivity of this VOC detection method are discussed.
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20 Smart windows
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Smart windows are a promising technology for use in energy-saving buildings and vehicles. Liquid crystals (LCs) and their composites, for which transmission, reflection and absorption vary in response to external stimuli, have great potential for applications in smart windows. Here, LC materials and their applications are described extensively from fundamental to state-of-the-art technologies. In this chapter, we mainly focus on thermoresponsive polymer network liquid crystals (PNLCs) and introduce other potential composites, classified by environmental stimulus (electric fields, heat, and light) and optical modulation (absorption, reflection, and scattering). Furthermore, the potentiality and possible issues that may arise for use of LC composites for smart windows are discussed.
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21 Antenna technology for satellite communications
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Liquid crystals (LCs) have a large anisotropy of refractive index in the visible light region and the microwave region. With the increasing use of mobile communication systems, electrically controllable phase shifters that use LCs for the dielectric layer have gained considerable attention. In this chapter, we first introduce the fundamental characteristics of LCs in the microwave region. In this study, we describe a complex dielectric constant in the microwave region. Next, we describe the microwave phase shifter loaded with LCs. Furthermore, we explain the new antenna technology for satellite communications, which uses LCs as a dielectric material of the variable capacitor for microwave metamaterials.
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Back Matter
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Supplementary material
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Supplementary Material for 'High Quality Liquid Crystal Displays and Smart Devices Volume 2: Surface alignment, new technologies and smart device applications'
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