Comparison of organic and inorganic alignment layers for low‐power liquid‐crystal devices using low‐frequency applied‐voltage waveforms

Abstract— Bistable displays are known to have low‐power consumption, but they usually lack the ability to display full‐color video‐rate images. Operating active‐matrix liquid‐crystal displays (AMLCDs) with an ultra‐wide refresh‐rate range, down to ～1 Hz, can lower the power consumption to that of bistable devices and offer video rates as well. A SiO^x‐layer‐based liquid‐crystal (LC) alignment technique is studied here to overcome the ion problems typically encountered with low‐refresh‐rate devices. The effect of ions on the voltage‐holding ratio (VHR) and residual DC voltage (RDC) with SiO^x‐based LC alignment is compared with those for polyimide‐based LC alignment. It is found that only SiO^x alignment provides high VHR and small RDC, with good stability over time. Therefore, it is shown that SiO^x alignment is an excellent candidate for low‐power AMLCDs operated with an ultra‐wide refresh‐rate range.     

Narrow‐gap field‐sequential TN‐LCD with and without nanoparticle doping

Abstract— The fabrication and demonstration of field‐sequential‐color (FSC) LCDs using modules of narrow‐gap twisted‐nematic (NTN) LCDs with and without doping of newly synthesized PγCyD‐ZrO² nanoparticles is reported. Two types of FSC‐LCDs are demonstrated: one is a direct multiplexed NTN‐LCD and the other is TFT driven. The advantages of FSC‐LCDs include their high legibility even under direct sunlight, and the mechanism for the doping of nanoparticles in LCDs is discussed.     

Novel liquid‐crystal materials for AMLCDs

Abstract— We have developed novel liquid‐crystal (LC) materials with a difluoromethyleneoxy CF₂O) moiety as the linkage group in order to satisfy the various requirements of active‐matrix liquid‐crystal displays (AMLCDs). We measured the physical properties of the CF₂O LC materials. The novel CF₂O LC materials have excellent physical properties, that is, high dielectric anisotropy, low viscosity, a broad nematic range, high reliability, etc. It was revealed that several advantages can be obtained by the introduction of CF₂O moiety into the LC molecules. The mixture containing CF₂O LC materials for various applications indicated a decrease in rotational viscosity of about 15–25% compared with that for conventional LC mixtures. Also, these novel mixtures with CF₂O LCM demonstrated a higher voltage‐holding ratio (VHR). It was confirmed that mixtures containing CF₂O LC materials have suitable characteristics for various applications, for example, low‐driving‐voltage note‐book PCs, quick response monitors, and transflective applications.     

Spatio‐temporal scanning backlight mode for field‐sequential‐color optically‐compensated‐bend liquid‐crystal display

Abstract— A spatially and temporally scanning backlight consisting of ten isolated micro‐structured light guides has been developed to be combined with a fast‐response optically‐compensated‐bend‐mode field‐sequential‐color LCD in which the liquid‐crystal cell does not contain color filters. The sequential fields of three primary colors are generated by illumination of the red‐, green‐, and blue‐light‐emitting diodes, each illuminating for one‐half of the field, resulting in a luminance of 200 cd/m² for the LCD. The effect of light leakage between the blocks in the scanning backlight in field‐sequential‐color applications was measured and will be described.     

Flexible color LCD panel driven by low‐voltage‐operation organic TFT

Abstract— A flexible color LCD panel driven by organic TFTs (OTFTs) was successfully demonstrated. A pentacene OTFT with an anodized Ta₂O₅ gate insulator, which can be operated at low voltage, was developed. In order to improve the electrical performance of the OTFT, the gate insulator was surface treated by processes such as O₂ plasma, UV light irradiation, and hexamethyldisilane treatments. The fabricated OTFT exhibited a mobility of 0.3 cm²/V‐sec and a current on/off ratio of 10⁷ with a low operating drain voltage of ?5 V. A fast‐response‐time flexible ferroelectric LCD, which contains polymer networks and walls, was integrated with the OTFTs by using a lamination and a printing technique. As a result, color images were achieved on the fabricated panel by using a field‐sequential‐color method at a low driving voltage of less than 15 V_pp.     

Ultra‐FFS TFT‐LCD with super image quality,fast response time,and strong pressure‐resistant characteristics

Fringe‐field‐switching (FFS) devices using liquid‐crystal (LC) with a negative dielectric anisotropy exhibit high transmittance and wide viewing angle simultaneously. Recently, we have developed an “Ultra‐FFS” thin‐film‐transistor (TFT) LCD using LC with a positive dielectric anisotropy that exhibits high transmittance, is color‐shift free, has a high‐contrast ratio in a wide range, experiences no crosstalk and has a fast response time of 25 msec. In this paper, the device concept is discussed, and, in addition, the pressure‐resistant characteristics of the devices compared with that of the twisted‐nematic (TN) LCD is discussed.     

Single‐cell‐gap transflective liquid‐crystal display using double‐ and single‐mode approaches

Abstract— In this paper, many popular methods to study transflective liquid‐crystal‐displays (LCDs) have been discussed, and several new transflective LCD configurations with a single‐cell gap have been proposed. The traditional double‐cell‐gap method gives the best match of the transmittance/reflectance voltage curve (TVC/RVC) and also the widest viewing angle, but also brings the highest fabrication complexity. The single‐cell‐gap transflective LCD is much easier to fabricate and also shows a good match of TVC/RVC. A new methodology has been shown to find optimal configurations for single‐cell‐gap transflective LCDs. New configurations using multimode in a single pixel include twisted nematic (TN) optically compensated bend (OCB), TN electrically controlled birefringence (ECB), and TN low‐twisted nematic (LTN). TN and hybrid‐aligned nematic (HAN) modes have been investigated for single‐mode transflective LCDs. The results exhibit high contrast ratio, a good match of TVC/RVC, as well as wide viewing angle.     

A field‐sequential‐color display with a local‐primary‐desaturation backlight scheme

Abstract— Field‐sequential‐color technology eliminates the need for color filters in liquid‐crystal displays (LCDs) and results in significant power savings and higher resolution. But the LCD suffers from color breakup, which degrades image quality and limits practical applications. By controlling the backlight temporally and spatially, a so‐called local‐primary‐desaturation (LPD) backlight scheme was developed and implemented in a 180‐Hz optically compensated bend (OCB) mode LCD equipped with a backlight consisting of a matrix of light‐emitting diodes (LEDs). It restores image quality by suppressing color breakup and saves power because it has no color filter and uses local dimming. A perceptual experiment was implemented for verification, and the results showed that a field‐sequential‐color display with a local‐primary‐desaturation backlight reduced the color breakup from very annoying to not annoying and even invisible.     

An overview of product issues in wide‐viewing TFT‐LCDs

Abstract— Several TFT‐LCD devices exhibiting high image quality have been developed and commercialized, overcoming the narrow viewing‐angle characteristics of conventional twisted‐nematic (TN) devices. Nevertheless, no single device dominates large‐sized TFT‐LCDs. In this paper, the product issues of existing LC devices related to manufacturing process and performance are discussed.     

A novel field‐sequential blue‐phase‐mode AMLCD

Abstract— Through the realization of a blue‐phase‐mode (hereinafter, the operational mode of liquid crystal having a blue phase is referred to as a blue‐phase mode), a display using an improved field‐sequential method was confirmed to be capable of display at a frame rate of 180 fps (field frequency of 540 Hz) or higher. Under this condition, an image without annoyance caused by color breakup was obtained. Moreover, a novel field‐sequential AMLCD integrated with a scan driver by combining the liquid‐crystal‐display (LCD) technology using blue phase and oxide‐semiconductor technology has been developed.     

Properties of azo‐dye alignment layer on plastic substrates

Abstract— The alignment properties of the azo‐dye photo‐alignment material SD‐1/SDA‐2 on plastic substrates are investigated. Important liquid‐crystal cell parameters, such as azimuthal and polar anchoring energy, pretilt angle, voltage holding ratio, and the corresponding electro‐optical properties are presented. Excellent alignment with high anchoring energy can be achieved with a polarized UV dose less than 1.0 J/cm². A reflective six‐digit flexible passive‐matrix‐driven TN‐LCD for smart‐card applications showing excellent electro‐optical properties is demonstrated.     

A study on reducing image‐sticking artifacts in wide‐screen TFT‐LCD monitors

Abstract— In order to improve the image quality of flat‐panel displays, the image retention of a display has to be reduced. But at the same time, display devices also have to produce durable images while they are used for long periods of time in a single session. To achieve high‐quality images with reduced image sticking in TFT‐LCD devices, we have increased their voltage‐holding ratio (VHR). This technology ensures the achievement of durable images over long periods of time and also reduces the image‐sticking problem. There are many ways to achieve increased VHR. In terms of the characteristics of the TFT devices, reducing the leakage‐current effects is the most frequently applied method in the display industry.     

Azo‐dye aligning layers for liquid‐crystal cells

Abstract— The photo‐induced alignment of liquid crystal onto a photochemical stable azo‐dye film was studied for liquid‐crystal display (LCD) applications. The photo‐aligning of azo dye takes place due to the pure reorientation of the molecular absorption oscillators perpendicular to the UV‐light polarization. The order parameters S = ?0.4 (80% of the maximum absolute value S_m = ?0.5) was measured at a wavelength of 372 nm from the polarized absorption spectra. The temperature‐stable pretilt angle of 5.3° was obtained by a two‐step exposure of azo‐dye film using normally incident polarized light followed by oblique non‐polarized light. The azimuthal anchoring energy of the photo‐aligned substrate was A_? > 10^?4 J/m², which is of the same magnitude as the anchoring of the rubbed PI layer. The VHR value of the photo‐aligned LC cell was also found to be very high (98–99%) at room temperature and more than 95% at T=80°C. The thermal stability of the photo‐aligned azo‐dye layers is sufficiently high, while UV stability has to be improved, _e.g., by polymerization. The new LCD aligning technology based on photochemical stable azo‐dye layers is envisaged.     

A single‐cell‐gap transflective blue‐phase liquid crystal display based on fringe in‐plane switching electrodes

A transflective blue‐phase liquid crystal display (TRBP‐LCD) based on fringe in‐plane switching (FIS) electrodes is proposed. The proposed structure generates combined fringe and in‐plane electric fields that cause more liquid crystal (LC) molecules to reorient almost in plane above and between the pixel electrodes. The fringe field is mainly generated in the transmissive (T) region, and the horizontal electric field is mainly generated in the reflective (R) region. By optimizing the width of the pixel electrodes and the gap between two adjacent pixel electrodes, the different electric field intensity in the T and R regions contribute to balance the optical phase retardation between the T and R regions. As a result, the proposed TRBP‐LCD exhibits a low operating voltage and high optical efficiency, while it preserves a relatively simple fabrication process.     

Transflective twisted‐nematic liquid‐crystal display with double twisted‐nematic cell and twisted liquid‐crystal retarder

Abstract— Two configurations, (i) a double‐cell‐gap twisted nematic (DTN) liquid‐crystal display (LCD) and (ii) a single‐cell‐gap twisted‐nematic (TN) liquid‐crystal display (LCD) using a twisted LC retarder, were optimized for transflective liquid‐crystal displays. For the DTN configuration, both the single‐cell‐gap approach and the double‐cell‐gap approach were considered. The optimized configurations exhibit a high contrast ratio, wide viewing angles, and achromatic (black/white) switching in both the transmissive and reflective modes. They are easy to fabricate and also possess a perfect dark state. Both are suitable for high‐quality transflective TFT‐LCDs.     

High‐transmittance in‐plane‐switching liquid‐crystal displays using a positive‐dielectric‐anisotropy liquid crystal

Abstract— The in‐plane‐switching (IPS) mode exhibits an inherently wide viewing angle and has been widely used for liquid‐crystal‐display (LCD) TVs. However, its transmittance is limited to ～76% compared to that of a twisted‐nematic (TN) cell if a positive‐dielectric‐anisotropy LC is employed. A special electrode configuration that fuses the switching mechanism of the conventional IPS and the fringe‐field switching (FFS) to boost the transmittance to ～90% using a positive LC has been developed. The new mode exhibits an equally wide viewing angle as the IPS and FFS modes.     

Comb‐on‐plane switching electrodes for liquid‐crystal displays

Abstract— Although the common twisted‐nematic liquid‐crystal displays (TN‐LCD) has excellent contrast and low color dispersion, it suffers from small viewing angle when driven into the homeotropic state. Among the many techniques proposed, in‐plane switching (IPS) has been quite effective in improving viewing angle. However, there may be difficulty in adopting conventional IPS to higher‐definition displays because it suffers from limited storage capacitance and reduced transmittance. A new comb‐on‐plane switching (COPS) electrode design is proposed. Compared to conventional IPS, COPS allows for lower switching voltage and offers advantages including naturally scalable storage capacitance, wide viewing angle with TN‐like high transmittance, and low color dispersion.     

A 5‐in. flexible ferroelectric liquid‐crystal display driven by organic thin‐film transistors

Abstract— An organic thin‐film‐transistor (OTFT) driven color flexible ferroelectric‐liquid‐crystal (FLC) display with 160 × 120 pixels and a resolution of 50 ppi has been developed. The flexible FLC was fabricated on a pentacene‐OTFT array using printing and lamination techniques. To drive the display at a fast driving speed, an OTFT was developed with a short channel length having a large current output. The fabricated OTFT array with a channel length of 5 μm exhibits a carrier mobility of 0.3 cm²/V‐sec and an ON/OFF ratio of over 10⁷ at a low drain voltage of ?6 V. A field‐sequential‐color system with a flexible backlight unit was also developed and used to drive the display. Color moving images were successively shown on the 5‐in. display using an active‐matrix driving technique of the OTFT.     

Electro‐optic properties of an intrinsic half‐V‐mode FLCD and its application to field‐sequential full‐color LCDs using a poly‐Si TFT matrix array

Abstract— An intrinsic half‐V‐mode ferroelectric liquid‐crystal display (FLCD) exhibiting a high contrast ratio (300:1), owing to defect‐free gray‐scale capability, with a high response speed (τ ? 400 μsec) and good switchability with TFTs, has been developed. Furthermore, this FLCD features high‐temperature reliability owing to the use of a special hybrid alignment technique. We successfully fabricated an active‐matrix poly‐Si TFT field‐sequential full‐color (FS FC) LCD with XGA specifications and a 0.9‐in. diagonal using a half‐V‐mode FLCD and an RGB light‐emitting‐diode (LED) array microdisplay. It is shown that the fabricated active‐matrix FS FCLCD exhibits good moving‐image performance with high full‐color display capability.     

Review of viewing‐angle compensation of TN‐mode LCDs using WV film

Abstract— Wide‐view (WV) films for TN‐mode LCDs, which optimize the optical parameters of the polymerized discotic material (PDM) layer and cellulose triacetate (CTA) have been developed. The development concept of the WV film and realization of its concept in the past and for the future will be reviewed. In particular, the discotic molecular alignment control enabled the improvement of the contrast ratio at oblique viewing angles of TN‐mode LCDs. In addition, color shifts at oblique angles are important for large‐screen TN‐mode LCD monitors and LCD‐TV sets. To improve the color‐shift problem, new technologies have been developed.