A new vertical‐alignment LC mode with high‐transmittance and fast‐response‐time features

Abstract— A novel pixel design for vertical‐alignment LCDs with superior transmittance has been developed. The new liquid‐crystal mode, refered to as the hole‐induced vertical‐alignment mode (Hi‐VA), uses a via hole of an organic layer on a TFT substrate to achieve multi‐domain alignment. Compared to the conventional design, the Hi‐VA mode has a transmittance of up to 135% with a contrast ratio of 2000:1. Moreover, the new structure is free from ITO patterning or protrusion on the color‐filter side, which makes the fabrication process simple and low cost.     

Analysis of image sticking on a real MVA Cell

Abstract— Image‐sticking phenomenon is one of the most important issues affecting LCDs, especially LCD TV. It is known that image sticking is caused by residual DC voltage. An analysis of the cause that induces image sticking on a real LCD cell is very difficult to perform and is rarely reported. In this paper, the impurities that cause boundary image sticking on a real MVA cell was analyzed by examining a cross section of a cell, the bulk LC layer, the vicinity of the LC layer, the LC layer/PI alignment film interface using microanalysis methods such as infrared micro‐spectroscopy (μ‐IR) and micro‐sampling mass spectrometry (μ‐MS). It is clarified that there is quite a bit of aromatic acid at the boundary of the image‐sticking area than in the normal area at the LC/PI alignment film interface on the color‐filter side, not the TFT side, and it is assumed that aromatic carboxylic acid, a negative charged material, is condensed at the LC/PI alignment film interface on the color filter side by an electrically driven DC component inducing an electric‐condenser residual DC voltage.     

Photoalignment of LCoS LCDs

Because the pixel area of liquid‐crystal‐on‐silicon (LCoS) microdisplays is about 100 times smaller than that of direct‐view liquid‐crystal displays (LCDs), the limitations of the conventional alignment by brushing are obvious: Scratches and particle contamination caused by brushing become visible due to the strong optical magnification required for LCoS LCDs both in front or rear projection. As an alternative, photoalignment with the linear photo‐polymerization (LPP) technology avoids the generation of defects, thus increasing production yields considerably. For application in LCoS LCDs, alignment layer materials must match the high‐voltage holding ratio (VHR) specifications of TFT‐LCDs. The VHR performance of the newly developed second‐generation LPP materials is shown to be similar to standard TFT polyimides used for conventional brushed alignment. We report investigations of pretilt‐angle generation by photoalignment on reflective CMOS substrates. UV light reflected from the CMOS surface during LPP exposure affects the resulting pretilt angle. Compared to pretilt angles on transmissive substrates, the reflected UV light can induce lower, higher, or identical pretilt angles, depending on LPP material properties. In any case, the pretilt angles are well defined, which results in perfect LCD alignment.     

Advanced liquid‐crystal materials for TFT monitor and TV applications

Notebook applications have been one of the most important driving forces behind the remarkable growth of liquid‐crystal displays (LCDs). LCDs have recently been well accepted in the monitor market and large growth is forecasted because of the replacement of CRTs. The next challenge for LCDs is the TV market. These new application areas are supported by advanced LC technologies such as film‐compensated twisted nematic (TN), in‐plane switching (IPS), and vertically aligned (VA) modes. Each TFT technology requires a corresponding LC material improvement. We will review the recent liquid‐crystal material development for these advanced LC technologies.     

Electro‐optical characteristics of ion‐beam‐aligned FFS‐LCDs on diamond‐like‐carbon thin film

Abstract— A fringe‐field‐switching (FFS) mode cell having LC alignment has been developed by using a non‐rubbing method, a ion‐beam‐alignment method on a‐C:H thin film, to analyze the electro‐optical characteristics of this cell. The suitable inorganic thin film for FFS‐LCDs and the alignment capabilities of nematic liquid crystal (NLC) have been studied. An excellent voltage‐transmittance (V‐T) and response‐time curve for the ion‐beam‐aligned FFS‐LCDs were observed using oblique ion‐beam exposure on DLC thin films.     

Review of various measurement methodologies of migration ion influence on LCD image quality and new measurement proposal beyond LCD materials

Nowadays, thin‐film transistor liquid crystal displays (TFT‐LCDs) have realized high reliability of display characteristics by improving liquid crystal (LC) materials and cell fabrication processes. In order to improve display reliability, measurement methodologies are important to see the progress of improvement of materials and processes; thus, our group has proposed voltage holding ratio (VHR), ion impurity, residual direct current (DC) and elastic constants for LC cells, and the optical anisotropy of an alignment layer on indium tin oxide (ITO) glass substrate for LCD industry. In case of an ion impurity, we have succeeded in measuring the ion impurity amount in TFT‐LCD. Furthermore, we have recently proposed ion impurity measurement methodology for beyond LCD applications that are organic light emitting diode (OLED) and organic photovoltaics (OPV). In this review, I introduce each measurement methodology for LCDs and beyond LCDs in detail.     

Fast‐response study of polymer‐stabilized VA‐LCD

Abstract— Polymer stabilization is introduced in VA‐type LCDs, and fast response time can be achieved along with a high contrast ratio.¹ A small amount of reactive monomer is mixed with liquid crystal and forms a polymer layer above the alignment layer by using a UV process. The pre‐tilt angle of the liquid crystal is stabilized, and a faster response time can be realized when the bias pre‐tilt angle from 90° is increased. The properties of reactive monomers and liquid crystal and the conditions of the UV process were studied. Based on the application of the proper monomer and LC, and an optima UV process, a 65‐in. 240‐Hz full‐HD TFT‐LCD, with a faster response time and high contrast ratio, has been developed.     

Pixel‐isolated liquid‐crystal mode by using a patterned anisotropic phase separation for flexible LCDs

Abstract— A pixel‐isolated liquid‐crystal (PILC) mode for enhancing the mechanical stability of flexible‐display applications is proposed. Because liquid‐crystal (LC) molecules in this mode are isolated in each pixel by patterned or phase‐separated microstructures, and the two substrates are tightly attached to each other by a solidified polymer layer, the LC alignment is stable against external pressure, and the cell gap of our structure is uniformly preserved against bending deformation of the plastic substrates. The mechanical stability of the PILC structure having plastic substrates was tested for its electro‐optic properties.     

Moving‐image‐sticking phenomenon induced by an outside force in liquid‐crystal displays

Abstract— Image deformation caused by an outside force is observed to remain for hours at high gray levels for liquid‐crystal displays (LCDs) in the multi‐domain (MD) vertical‐alignment (VA) mode. This so‐called moving‐image‐sticking phenomenon demonstrated a non‐symmetric luminance profile for the left and right viewing direction for MDVA‐mode LCDs which have original symmetric viewing‐angle characteristics. The generation of a stable reverse‐tilt domain by an outside force was assumed to be the cause of this phenomenon, and the stability of a reverse‐tilt domain under an electric fringe field was calculated by changing the electric‐fringe‐field distribution which determines the LC tilt direction. The domain of a given tilt direction is calculated to change to other tilt direction induced by a fringe field at a low gray condition, but to remain unchanged at a high gray condition. This agrees with the observed trends of duration time of the moving‐image‐sticking phenomenon.     

Deformed nanostructure of photo‐induced biaxial cholesteric films and their application in VA‐mode LCDs

Abstract— Novel biaxial retardation films made from photo‐induced deformed cholesteric liquid‐crystal (LC) nanostructures using reactive mesogen mixtures (RMMs) for a viewing‐angle compensation of vertically aligned liquid‐crystal displays (VA‐LCDs) was developed. The deformed cholesteric LC nanostructure has been observed by X‐ray‐diffraction (XRD) measurement. The birefringence of the film was described well by our optical model based on a form birefringence theory. The VA‐LCDs with photo‐induced biaxial cholesteric films have excellent viewing‐angle properties.     

Field‐induced photo‐reactive alignment technology for the vertical‐alignment liquid‐crystal mode

Abstract— An advanced vertical‐alignment liquid‐crystal (VA‐LC) technology based on field‐induced photo‐reactive alignment (FPA) as an advanced alignment mode for VA is proposed. FPA realizes uniform alignment and a faster rising response time, especially at high voltage. This technology can generate a pre‐tilt angle only by using photo‐reactive alignment material so that the tact time is shorter and the long‐term reliability is higher than that of conventional photo‐reactive processes, which require additional photo‐reactive monomers. The advanced hybrid FPA was developed by adopting both the tilted alignment with a pre‐tilt angle and conventional vertical alignment. By using an advanced hybrid structure, the response time and contrast ratio can be further improved.     

Defect‐free deformed‐helix ferroelectric liquid‐crystal mode in a vertically aligned configuration (Invited Paper)

Abstract— A novel deformed‐helix ferroelectric liquid‐crystal (DHFLC) mode in a vertically aligned (VA) configuration is described. In this configuration, several unique features of display performance such as uniform alignment, fast response, and analog gray‐scale capability are obtained. Particularly, this VA‐DHFLC mode allows for the defect‐free uniform alignment of both the FLC molecules and the smectic layers over a large area without employing additional processes such as rubbing or electric‐field treatment that are generally required for planar FLC modes. Based on the VA‐DHFLC mode, a transflective display having a single‐gap geometry with in‐plane electrodes on two substrates in the transmissive regions and on one substrate in the reflective regions is described.     

Local dimming light‐guiding plate type backlight system using alignment‐controlled polymer‐dispersed liquid crystals

A new technology which enables a local brightness control according to the displayed images has been expected in the thin and lightweight backlight systems to improve a contrast ratio and power consumption of the liquid crystal displays (LCDs). In this paper, we have proposed a novel local‐dimming backlight system using alignment‐controlled polymer‐dispersed liquid crystals as a light‐guiding plate and investigated the forming conditions of polymer‐dispersed liquid crystals to achieve both a high‐luminance ratio and a fast response speed. As a result, we found that a luminance ratio and response speed of the backlight system can be improved by using bifunctional LC monomer materials and forming fine and rigid polymer network in the LCs, and achieved high luminance ratio of 16:1 and fast response time less than 0.5 ms. In addition, we fabricated the twisted nematic‐mode LCD using the local dimming light‐guiding plate‐type backlight based on this design, and successfully realized eight times higher contrast ratio than that of the traditional twisted nematic‐mode LCD.     

Homeotropic alignment of liquid crystals on ITO surface using LBL assembly

In this work, the very thin layer‐by‐layer (LBL) film that was constructed by dip coating method on indium tin oxide surface can be used in liquid crystal (LC) displays devices. The obtained results indicate that the ultrathin LBL film shows the homeotropic alignment layer, and a uniform vertical alignment of LC molecules was gained very easily. The progress of vertical‐aligned LC cells with a LBL layer was evaluated. The obtained threshold voltage and response time of the LC cell were 2.472 V and 12.5 ms, respectively. So, the competitive performance of the LC cell could allow new sign at a low‐cost budget with rubbing process in LC display technology.     

Color plastic bistable nematic display fabricated by imprint and ink‐jet technology

Abstract— Plastic displays require new manufacturing processes and techniques to achieve acceptable cost and performance. A novel additive, low‐temperature atmospheric‐pressure self‐aligned means of fabricating integrated plastic substrates for full‐color LCDs and a bistable LC mode based on microstructure alignment are presented. By using imprinting rather than photolithographic patterning, a scalable, low‐cost manufacturing route is possible. A 2‐in.‐diagonal 128 × 128‐pixel display was made to demonstrate the principles involved, which has retained an image for in excess of 2 years.     

A multi-domain vertical alignment liquid crystal display to improve the V–T property

The voltage–transmittance (V–T) property is important for the liquid crystal displays (LCDs). In this work, we propose a sub-pixel structure with two common electrodes of a multi-domain vertical alignment (MVA) mode. The sub-pixel is divided into two sub-areas and different common electrode voltages are applied to it. The optimal voltage difference of the common electrodes between sub-area 1 and sub-area 2 is proposed. The simulated results on the plotted displays and the voltage–transmittance property of the LCD, which has 1:1 sub-area ratio, have been carried out. The results show that the structure can form MVA liquid crystal display mode, such as 8-domain VA mode. It can improve the V–T property at large oblique viewing angle and make the transmittance difference between the normal direction and the oblique direction viewing angle less than that of conventional 4-domain MVA mode.     

Mechanism of image sticking after long‐term AC field driving of IPS mode

Abstract— An AC electric field to drive the IPS mode of a liquid‐crystal display (LCD) causes a reduction in the contrast after a long period of display operation. This phenomenon is refered to as the AC image‐sticking problem caused by long‐term driving. Thus far, there is no useful method of quantitatively evaluating AC image sticking. LCD panel products that use the IPS mode have been evaluated for a decade. In this paper, a new evaluation parameter (Δθ), which was recently proposed by Suzuki et al., is introduced. It was calculated from the slight difference in the deviation angle of LC molecules from the rubbing direction. Results from several conditions of test samples are presented in this paper as a phenomena that reflect the interaction between the surface of the PI alignment and the LC molecules. The results and discussions describe reasons for azimuthal gliding after long display operation for weak AC voltage driving. It is explained by suitably adopting the Kelvin‐Voigt model which is used to discuss the rheology of viscoelastic material. It is concluded that the surface rheology of PI alignment is one of the most important factors for the contrast reduction of the AC image‐sticking problem.     

EO characteristics for a photoaligned VA‐1/4 π cell on a photopolymer layer

The generation of a liquid‐crystal (LC) tilt angle on a copolymer with chalconyl and cholesteryl moiety characteristics was performed, and the electro‐optical (EO) performance of the photoaligned vertical‐alignment (VA) 1/4 π cell by polarized UV exposure on a homeotropic photopolymer surfaces was studied. The LC tilt angles decreased as UV exposure time increased on the copolymer surfaces. A tilt angle of 87° in NLC was observed with an UV exposure of 3 min on the photoalignment‐2 surface. The LC tilt angle is attributed to increased chalcone moiety with increasing UV exposure time. Excellent voltage‐transmittance (V‐T) curves of the photoaligned VA 1/4 π cell by polarized UV exposure on the photopolymer surface for 3 min containing a cholesteryl moiety of 8% were obtained. The V‐T and response‐time characteristics can be improved by the presence of a cholesteryl moiety in the photopolymer.     

Electrically commanded surfaces: A new liquid‐crystal‐display concept

Abstract— Fast in‐plane switching of the optic axis was realized in liquid‐crystal displays (LCDs) based on the concept of Electrically Commanded Surfaces (ECS). According to this concept, the liquid‐crystal layer in such a display is aligned by means of thin ferroelectric liquid‐crystal‐polymer (FLCP) film deposited onto the inner side of the display substrates. An electric field, applied normal to the substrates, switches the molecules of the ferroelectric film, representing the commanded surface that, via elastic forces, further transfers to the liquid‐crystal layer. The concept of electrically commanded surfaces opens the door to a new generation of advanced LCDs exhibiting extraordinary performance such as fast in‐plane switching.     

Improving content visibility for high‐ambient‐illumination viewable display and energy‐saving display

Abstract— Nowadays, low‐contrast viewing of LC displays (LCDs) occurs very often, which includes the viewing of mobile LCDs at high ambient illumination and the viewing of LCDs at low‐power mode. These cases result in low‐content visibility and low contrast, leading to an unpleasant viewing experience. In this paper, a technique to improve the perceived contrast and visibility of images at low‐contrast viewing conditions is proposed. The proposed approach enhances image brightness with content and ambient adaptive image brightening and highlights visual parts and boundaries with non‐photorealistic rendering. The proposed technique enables longer battery life for mobile LC devices and makes mobile LC devices viewable at high ambient illumination. It also enables TVs with extreme low‐power consumption and smart‐grid responsive TVs.