High Quality Liquid Crystal Displays and Smart Devices - Volume 1: Development, display applications and components
2: Tokyo University of Agriculture and Technology, Tokyo, Japan
3: Ukai Display Device Institute, Ukai, Japan
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: liquid crystalline organic semiconductors; TFT-LCD; smart devices; functional light-guide plate; high quality LCD; backlighting unit optics; quantum dot technology; curved LCD; high dynamic range era; in-plane switching technology; automotive displays; liquid crystal materials; liquid crystal displays; vertically aligned LCD; ultrahigh-resolution LCD; film substrate; flexible devices; oxide semiconductor TFT; active-matrix LCD; flexible LCD optical design; optical microdeflectors; LCD-TV technology; optical microreflectors; fringe-field switching technology; AMOLED display technology; picture performance evolution; oxide semiconductors; thin film transistors
- Book DOI: 10.1049/PBCS068F
- Chapter DOI: 10.1049/PBCS068F
- ISBN: 9781785619250
- e-ISBN: 9781785619267
- Page count: 415
- Format: PDF
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Front Matter
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1 History of LCD: milestone, state-of-the-art and future directions
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In commemoration of the 50th anniversary of liquid crystal display (LCD), we review a chronological development of the history of LCD from the 1950s, when liquid crystal (LC) was a laboratory curiosity, to the growth arriving upon 100 BD industry, and thus, LCD is now an indispensable information terminal in our ordinary life and business. In this chapter, we place an emphasis on how individual research group has resolved problems for getting across barriers for producing historical original products that were the rank of milestone that became seeds for the next development and current LCD. Further, we briefly introduce the current state-of-the-art LCD technologies and foresee the next direction.
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2 In-plane switching technology
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We present an overview of in-plane switching (IPS) technologies in terms of historical background, nascent fundamental findings and developments, breakthroughs in addressing display performance issues, and the evolution of materials and device structures. The focus is on how IPS technology has been developed along with changes in the required display characteristics as the target display products continue to evolve. In addition, innovative manufacturing processes, such as photo-alignment technology, have led to the further evolution of IPS technology. Starting with the fundamental frameworks at an early stage, the evolution and development of IPS technology are described as extensively as possible.
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3 Fringe-field switching technology
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Fringe-field switching (FFS) liquid crystal display (LCD) mode has been the mainstream for thin-film transistor (TFT) LCDs with superior image quality and low power consumption since the advent of tablet PC like iPad and high-resolution retina mobile displays in 2010. Its application has expanded to displays for automobiles, mobile phones, high-resolution notebooks and monitors, televisions, and also most of the displays that require high-quality images. This chapter first describes switching fundamentals and electrode-structural advantages of the FFS mode for high-resolution and high-aperture displays with the introduction of lowtemperature poly-silicon (LTPS). In recent progress, the FFS mode has interesting features such that the flexoelectric effect arises noticeably when the driving frequency becomes approximately lower than 30 Hz as a power-saving mode. The flexoelectric effect basically gives rise to deterioration in image-quality, causing the so-called image-flickering. Thus, second, this chapter discusses the flexoelectric effect associated with structural conditions and physical properties of liquid crystals and possible solutions to minimise the flexoelectric effects in the FFS mode. Afterwards, superior electro-optic performance and low-power consumption driving of the flexoelectric FFS mode will be discussed in detail, such as light efficiency, high transmittance at the low-frequency driving.
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4 Vertically aligned liquid crystal display
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Vertically aligned liquid crystal displays (VA-LCDs) have many advantages over other LC modes. The contrast ratio in the normal direction is very high and gives a wide viewing range through the adoption of multidomain, half-tone and optical compensation technology. As there is no rubbing step, the yield with mass production is higher than other modes with a rubbing process. It also has the advantage of being able to create transflective displays. Therefore, VA LCDs are widely used for television (TV), monitors, notebooks, mobile devices and automotive applications. In this chapter, various VA-LCD modes and their respective advantages are discussed.
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5 Evolving LCD-TV technology
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Liquid crystal display-television (LCD-TV) has made remarkable progress, starting with a pocket size of only 2 in. and now large TVs with 65 in. and 4K2K resolution are about to become the center products of the market. More recently, a larger TV with 70 in. and 8K4K resolution was also released. In addition to the evolution of diagonal size and resolution, image quality performance such as viewing angle, contrast ratio, and color reproducibility has also been greatly improved. The competing IPS with VA mode LCD TV splits the market into two, total shipments exceeding 200 million units. In this chapter, we will explain in detail how the performances of both IPS and VA modes have been improved since entering the TV era. Finally, we will introduce the IPS pixel technology which realizes a high aperture ratio with resolution 8K4K LCD, and the IPS liquid crystal technology which realizes a contrast ratio of more than 1 million to 1 comparable to that of organic light-emitting diode (OLED).
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6 Picture performance evolution for the high dynamic range era
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In the past several years, television (TV) picture quality has improved with the introduction of 4K and wide color gamut. In addition, recently HDR (high dynamic range) has nurtured the picture performance evolution. Thus, a picture on the TV becomes much more captivating than ever. But, HDR seems difficult to understand correctly, since it contains a new concept, several different technologies, and standards from the status quo. In this chapter, the meaning, benefit, and ecosystem of HDR will be explained. How HDR effects and what HDR requires of the system of TV/display will be explained for furthering one's understanding and utilization of HDR.
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7 TFT-LCD and AMOLED display technology comparisons
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This chapter discusses comparison of thin-film transistor-liquid-crystal display (TFT-LCD) with active-matrix organic light-emitting diode (AMOLED) regarding their display performance and manufacturing. AMOLED has been expected to realize much excellent display quality, lower power consumption, and lower manufacturing cost than TFT-LCD. Such expectation has been partly realized in the category of small-sized organic light-emitting diode (OLED). However, manufacturing cost remains as an issue, the feasibility of production on glass whose size is comparable to the size of substrate of large format TFT-LCD has yet to be established. Furthermore, we discuss how to build a firm position for TFT-LCD.
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8 Automotive displays
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Due to the improvement of auto-driving technology, how people spend time in their cars will change drastically in the near future. In the case of automotive displays, there are some factors and features that are very different from general displays. For example, the ambient conditions can be severe, e.g. ultra-low temperatures or very bright sunlight. The windows can act as display screens or information displays. Cars will become a kind of living room. Considering these features, some special displays have been developed. In this chapter, these special technologies are introduced.
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9 Requirements for automotive displays
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In this chapter, we would like to give a brief outline of the areas in which automotive displays will be used today and in the future. We would also like to give an insight into the environmental requirements placed on such displays and which aspects must be taken into account during development in order to achieve good optical performance and also to guarantee the required robustness over the lifetime of the display.
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10 The world's largest curved LCD
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With the rapid development of liquid crystal display (LCD) industry in recent years, the size of displays grows amazing large and many giant displays appear in the market. In this chapter, the world's largest curved LCD is introduced, and several technology challenges during the development process are discussed. These technology challenges under curved structure include mechanism of shift between color filter (CF) and thin film transistor (TFT) glass, the risk of glass cracking, corner light leakage and enhanced strength structure for the thinner structure.
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11 Optical design of flexible liquid crystal displays
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Flexible liquid crystal displays (LCDs) have advantages of thin, light weight and afford high-level resolution and reliability, and low power consumption. It dramatically expands portability, installation, and design of displays and creates new viewing methods via novel interfaces and many new applications such as curved automotive displays, large digital signages, and rollable televisions. In this chapter, we introduce the manufacturing technologies required to create flexible LCDs focusing on the optical design of, and bonding spacers and thin flexible substrates for, flexible LCDs.
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12 Flexible LCD
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Liquid crystal displays (LCDs) have pushed the limits of resolution, brightness, colour gamut and numerous other attributes over the years; however, flexibility has found only niche applications to date. In this chapter, we explore what is required to create a flexible LCD and what challenges engineers face in their construction. Breakthroughs in materials have ushered in a possibility for mainstream LCD manufacture to be carried out on plastic, and the increased durability as well options for unconventional form factors will create new product opportunities as a result.
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13 Film substrate for flexible devices
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A polyethylene naphthalate (PEN) film is excellent in mechanical properties, heat resistance, transparency, and chemical properties. It is very suitable as a substrate material for flexible devices. In this chapter, the characteristics of the PEN film is explained while contrasting with the properties of the other types of films.
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14 Thin film transistors for active-matrix LCDs
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Thin film transistors (TFTs) are one of the key devices for active-matrix (AM) liquid-crystal displays (LCDs) with high resolution and excellent image quality. Polycrystalline-Si (poly-Si) TFTs are widely utilised for smartphone displays, and amorphous-Si (a-Si) TFTs are mainly used for large-area LCD TVs. Recently, amorphous metal-oxide semiconductor (AOS) TFTs are promising for not only organic light-emitting diode displays (OLEDs) but also LCDs with super high resolution and high speed scan. Organic semiconductor TFTs may be employed for flexible and inexpensive displays in future. In this chapter, channel materials, device structures, fabrication processes, electrical characteristics, driving methods, etc., are explained in detail.
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15 Ultrahigh-resolution LCDs with oxide semiconductor TFTs
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Along with the development of liquid crystal displays, semiconductor technology for driving these screens has advanced dramatically. This chapter explains the latest technology, the oxide semiconductor thin-film transistor (TFT), and its display application. The oxide semiconductor TFT features low leakage current and high electron mobility, which are not found in conventional amorphous silicon (a-Si) and low-temperature polycrystalline silicon (LTPS) semiconductors. These characteristics are effective for liquid crystal displays with high definition, a narrow frame and low power consumption, and the oxide semiconductor TFT is widely used in small high-definition displays such as smartphones up to large nextgeneration 8K TVs (7,680 × 4,320 pixel).
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16 Oxide semiconductors for display applications
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Amorphous hydrogenated Si (a-Si:H) had been exclusively used until ~2012 as the backplane TFTs to drive flat panel displays. However, oxide semiconductor-TFTs are becoming a strong alternative due to their high mobility, low off-current, and easy fabrication by conventional sputtering. In particular, transparent amorphous oxide semiconductors (TAOS) with In-Ga-Zn-O (IGZO) compositions are practically applied as the backplane for high-resolution and energy-saving liquid crystal displays (LCDs) and large-sized organic light emitting diode (OLED) TVs. Oxide semiconductors have rather different characteristics compared with conventional semiconductors based on diamond structure. This chapter describes the fundamentals of oxide semiconductors and their TFTs in comparison with a-Si: H from views of chemical bonding and electronic state. In addition, concepts for p-type materials and p/n control are explained along with concrete materials.
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17 Liquid crystalline organic semiconductors
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Organic thin film transistor (OTFT) is expected as a switching device for flexible displays because organic semiconductor thin films can be fabricated by solution process at highest process temperatures lower than 150 °C, which allows us to use flexible and inexpensive plastic substrates. In this chapter, in the light of requirements for practical thin film transistor materials, how the requirements can be satisfied with a new type of organic semiconductor, i.e., liquid crystalline organic semiconductors, is described. At the same time, the state of the art of OTFT materials is described with a representative liquid crystalline organic semiconductor of 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene, Ph-BTBT-10 exhibiting highly ordered smectic liquid crystalline phase.
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18 Liquid crystal materials
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Many liquid crystal materials used in the market for the TN (twisted nematic) liquid crystal displays (LCDs), the STN (super TN) LCDs and the TFT (thin film transistor) addressed LCDs having TN, IPS (in-plane switching), MVA (multidomain vertical alignment) or PSVA (polymer sustained vertical alignment) mode are reviewed. The cases of the development and the industrialization of liquid crystals, in which the author was involved, are also reviewed. Moreover, the relationships between the properties and the chemical structures for the liquid crystal materials are discussed.
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19 Quantum dot technology and its applications
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Quantum dots (QDs) are nanometer-scale semiconductor crystals that work as a phosphor with a very sharp emission spectrum caused by a QD's quantum confinement effect. QD's sharp emission properties are expected to bring a wide color gamut and high energy efficiency to liquid-crystal displays (LCDs), and QDs have already been introduced in some LCDs. However, researchers and engineers working on display technology have insufficient knowledge of QDs. This chapter gives an overview of QDs and describes the principles of their emission and chemical synthesis method. In addition to this general information on QDs, applications for their use in displays, from the backlights of LCDs to an electroluminescent (EL) QD-light-emitting diode (QD-LED), are also described.
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20 Backlighting unit optics: optical micro-reflectors and micro-deflectors for functional light-guide plate
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Transmissive liquid-crystal (LC) display (LCD) devices are being extensively used for man-machine interfaces. A transmissive or transflective LCD requires a backlighting unit (BLU) which is an indispensable device for an LCD. In early time of the LCD-emerging period (1980-95), lack of light ray control and optical design concept were the main issues of BLUs. In order to build up an optical concept for BLU design, for first time, the author devised and developed functional BLU using micro-reflector (MR) and micro-deflector (MD) for light control media, i.e., lightguide plate (LGP) and optical cavity, based on the total internal reflection (TIR) and nearly frustrated TIR (FTIR). The BLU issues were substantially solved and the luminance on the BLU increased and angular luminance cone was controlled that resulted in saving power consumption of the LCDs. In the meantime, the author developed novel fabrication process to accelerate the mass productions of the LGPs by 8-10 times by using metallic sheet pattern of MRs and MDs.
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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 1: Development, display applications and components
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There is a supplementary Errata sheet available for this title.
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