Prospects of emerging polymer‐stabilized blue‐phase liquid‐crystal displays

Abstract— The prospects of emerging polymer‐stabilized blue‐phase liquid‐crystal displays, or more generally, Kerr‐effect‐induced isotropic‐to‐anisotropic transition, are analyzed with special emphases on the temperature effects. As the temperature increases, both the Kerr constant, induced birefringence, and response time decrease but at different rates. The proposed physical models fit well with experimental results. Some remaining technical challenges associated with this promising display technology are discussed.     

Study of polymer‐network structure on polymer‐stabilized blue phase

Abstract— To understand the mechanism of the disclination defect of the liquid‐crystal (LC) phase, this study was conducted to directly analyze the polymer‐network (PN) structure of polymer‐stabilized blue phase (PSBP), which is minutely formed on all LC layers. The PN was examined after first removing the glass decap and then the LC. Important to note is that the removal of the glass decap did not affect or damage the PN structure. The PN was determined to be a stable structure without any change to the thickness of the layer. When removing the LC, both hexane and acetone solutions were used. Moreover, there was no structural deformation to the PN when using the hexane solution. The results of the study show that the actual size of the polymer chain is in fact 50–60 nm, five times larger than previous theories which estimated the size to be only 10 nm. In addition, this study confirmed that the pores between the PN are 100–200 nm. The PN structure was shown to be susceptible to change based on different heating temperatures. In summation, now that defect lines of a LC display (LCD) could be directly measured, further progress and development in the theoretical interpretations of the Kerr effect on PSBP can be realized.     

A reflective polarizer‐free display using dye‐doped polymer‐stabilized blue‐phase liquid crystals

Abstract— A reflective polarizer‐free display using dye‐doped polymer‐stabilized blue‐phase liquid crystal (DDPSBP‐LC) has been demonstrated. The mechanism is a combination of electrically tunable light absorption and Bragg reflection. In this paper, the influence of light absorption in DDPSBP‐LC by changing the dye concentration and absorption paths has been studied. Increased dye concentration can improve the contrast ratio of DDPSBP‐LC; however, the response time is the tradeoff. Increasing the cell gap can improve the contrast ratio of DDPSBP‐LC; however, the response time remains the same. The study of DDPSBP‐LC can help in shutter‐glass applications of 3‐D displays and electronic paper.     

A continuous‐viewing‐angle‐controllable liquid‐crystal display using a blue‐phase liquid crystal

Abstract— A continuous‐viewing‐angle‐controllable liquid‐crystal display (LCD) using a blue‐phase liquid crystal is proposed. To realize both wide‐viewing‐angle (WVA) mode and narrow‐viewing‐angle (NVA) mode with a single liquid‐crystal panel, each pixel is divided into a main pixel and a subpixel. The main pixel is for displaying images in both modes. The subpixel is for displaying images in WVA mode and controlling the viewing angle in NVA mode. The device exhibits a good viewing‐angle‐controlling characteristic and high transmittance.     

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.     

A viewing‐angle‐controllable blue‐phase liquid‐crystal display

Abstract— A viewing‐angle‐controllable liquid‐crystal display (LCD) is proposed. When the device is only driven by an in‐plane electric field, it exhibits a wide‐viewing‐angle (WVA) mode. And it exhibits narrow‐viewing‐angle (NVA) mode when it is driven by a vertical electric field as well as an in‐plane electric field. In this manner, the viewing angle of the device can be controlled from 100° to 30°. The device exhibits a good viewing‐angle‐controlling characteristic and high transmittance.     

High‐performance polymer‐stabilized blue‐phase LCD with low driving voltage

We have developed a polymer‐stabilized blue‐phase LCD in which the diffraction wavelength of blue‐phase liquid crystal is in the ultraviolet region and which is driven at a low voltage of V₁₀₀ = 27 V. Prototypes of 3.4‐in polymer‐stabilized blue‐phase LCDs were made, which include a highly reliable crystalline oxide semiconductor. We succeeded in fabricating not a test cell but a display having a contrast ratio higher than 1000 : 1 for the first time in the world.     

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.     

Low‐voltage and high‐transmittance blue‐phase liquid‐crystal device with slanted electrodes

Abstract— A low‐voltage (～10 V_rms) and high‐transmittance (～90%) polymer‐stabilized blue‐phase liquid‐crystal (BPLC) device with a slanted‐electrodes structure is proposed. Unlike the vertical‐field‐switching (VFS) mode in which oblique incident light and a vertical field are employed, the proposed device utilizes normal incident light and an oblique field. The slanted electrodes generate a strong and uniform oblique electric field, which contributes in obtaining low voltage and high transmittance. Moreover, no couple films or prism sheets are needed, which helps to enhance the optical efficiency and simplify of the device structure. This device has great potential application for emerging BPLC displays and photonic devices.     

Transflective blue‐phase liquid‐crystal display with corrugated electrode structure

Abstract— A transflective polymer‐stabilized blue‐phase liquid‐crystal display (BP‐LCD) with a corrugated electrode structure is proposed. To balance the optical phase retardation between the transmissive (T) and reflective (R) regions, two device structures are proposed. The first device structure has the same inclination angles but different cell gaps in the T and R regions. And the second device structure has the same cell gap but different inclination angles in the T and R regions. Both of the device structures can obtain well‐matched VT and VR curves. This display exhibits low operating voltage, high optical efficiency, and a wide viewing angle.     

Polarization‐independent blue‐phase liquid‐crystal gratings driven by vertical electric field

Abstract— A blue‐phase liquid‐crystal grating is proposed by applying a vertical electric field with lateral periodic distribution. Simulation on electric‐field distribution was also carried out, the results of which suggest the alternation of isotropic and ordinary refractive indices in the lateral direction. Through the electrode configuration design, both 1 D and 2D gratings were demonstrated with high transmittance of ca. 85%. The diffraction efficiency of the first order reached up to 38.7% and 1 7.8% for the 1D and 2D cases, respectively. The field‐induced fast phase modulation permits a rapid switching of diffraction orders down to the submillisecond scale.     

Blue phase dual‐view liquid crystal display based on directional backlight system

We design a blue phase dual‐view liquid crystal display (BP DVLCD) based on a directional backlight system. Combining the patterned electrodes with the directional backlight system, the cross‐talk ratio is reduced to only 1.17%. Moreover, the resolution and brightness will be tripled by using field‐sequential color display. In the preferred viewing area, the BP DVLCD has a high contrast ratio of ~1700:1.     

Template effect on reconstruction of blue phase liquid crystal

The reconstruction capability of the blue phase (BP) template with low polymer concentration was investigated. A threshold polymer concentration to reconstruct the BP with the chiral three‐dimensional template was confirmed in different kinds of polymer systems. The anchoring energy of the template may reassemble the double twist cylinder structure of BP liquid crystal (BPLC) by refilling either the same‐handed or reverse‐handed chiral materials within a certain range of helical twisting power (HTP). Meanwhile, because of the lowered anchoring energy, the kerr constant of the reconstructed BPLC increased by 104%, from 1.81 nm/V² to 3.70 nm/V², by refilling the reverse‐handed chiral material.     

Viewing angle switchable blue‐phase liquid crystal display with low voltage and high transmittance

We propose a viewing angle switchable blue‐phase liquid crystal display with low voltage and high transmittance. In this device, in‐plane protrusions are used to lower operating voltage and improve the transmittance. Besides, the top electrode can control viewing angle of the proposed display. When no voltage is applied to the top electrode, the display shows wide viewing angle mode. On the contrary, this display shows narrow viewing angle mode. So, this device exhibits low operating voltage, high transmittance, and good viewing angle controllable characteristics.     

Analysis of electro‐optical properties of polymer‐stabilized OCB and the application to TFT‐LCDs

Abstract— A 9‐in. full‐color polymer‐stabilized OCB TFT‐LCD with stable bend alignment in the absence of an electric field was developed. The condition of the polymer stabilization, the characteristics of UV‐curable monomers, and their influence on the configurations of the polymer network in the cell were studied. Possible models of the configuration were proposed and their relationship to the electro‐optical properties was analyzed using a novel simulation method considering the distribution of anchoring effects from both alignment surfaces and the polymer network. It was suggested that a good performance such as high contrast ratio and fast response could be expected in the polymer network originating from newly developed monomers composed of multifunctional LC acrylates due to a relatively weak‐anchoring effect and presumably its localization near the alignment surfaces. By using the newly developed monomers under the optimized polymer‐stabilizing process, a high contrast ratio of 250:1 and fast response nearly equal to that of a conventional OCB cell were achieved.     

Molecular design for stabilizing a blue phase III and electro‐optical switching in the blue phase

Abstract— The molecular design of a liquid crystal to stabilize a blue phase III (BPIII) is reviewed, and the electro‐optical switching with a response time on the order of 10^?2 sec for BPIII exhibited by a novel chiral liquid crystal is reported. Binaphthyl derivatives and T‐shaped compounds are presented, and the structure‐property correlations of the chiral compounds are discussed. Two origins of the twisting power of the compounds, i.e., their inherent molecular chirality and the chirality‐induced twist conformation, play an important role in the appearance of the BPIII. Furthermore, BPIII was also induced in some binary mixtures of a host nematic liquid‐crystal possessing molecular biaxiality and a conventional chiral compound. The electro‐optical switching in the BPIII is attributed to an electric‐field‐induced phase transition between the BPIII and nematic (N) phases. BPIII is on the microscopically twisted nematic order, but is macroscopically isotropic. Therefore, the present technology can offer a pronounced black state in the BPIII without surface treatment and a homogeneous bright state in the induced N phase.     

Nanoparticle‐embedded polymer‐dispersed liquid crystal for paper‐like displays

Abstract— A polymer‐dispersed liquid‐crystal (PDLC) matrix template embedded with nano/microparticles can be backfilled/infiltrated with a dye‐doped liquid crystal for a paper‐like reflective display. In this way, a desirable degree of diffusion can be realized to reduce the viewing‐angle dependency of a gain reflector and metallic glare without changing other electro‐optical properties.     

Fast switching and high‐contrast polymer‐stabilized IPS liquid crystal display

We demonstrated that polymer stabilization can significantly improve the response time of in‐plane‐switching liquid crystal display. We carried out a systematic study of the effect of polymer networks on the performance of in‐plane‐switching liquid crystal display. The polymer network has a strong aligning effect on the liquid crystal and has the advantage of reducing the switching time of the display but may have the disadvantage of ruining the contrast ratio because of its scattering effect. Through optimization, we successfully improve the switching time (less than 6 ms) and reduce the scattering and thus retain high contrast ratio (higher than 1000:1).     

A novel polarizer‐free dye‐doped polymer‐dispersed liquid crystal for reflective TFT displays

Abstract— A novel preparation method for dichroic dye‐doped polymer‐dispersed liquid crystals has been developed. This was achieved by creating a porous polymer matrix first by washing out the liquid crystal from a polymer‐dispersed liquid crystal (PDLC), which is then refilled with dye‐doped liquid crystal. Optimizing the liquid crystal used in the refilling results in decreased turn‐on voltage and faster response time. Poster‐standard reflectivity and newspaper‐standard contrast was demonstrated with a 3.8‐in. QVGA reflective TFT display with a drive voltage of 10 V.     

Effect of the grain size on hysteresis of liquid‐crystalline Blue Phase I

Abstract— Three different blue‐phase I liquid‐crystal samples with different grain‐size distribution were studied. Polycrystalline platelet grains reflects light in the visible region and have been observed under a polarizing optical microscope. Green and blue grain areas have been measured and then the statistical histogram by the Gaussian distribution function was fitted and the mean grain size was calculated. The effect of hysteresis on grain size has been compared for the three samples. Hysteresis depends explicitly on the grain‐size distribution. Large grain size has revealed less hysteresis, while small grain size depicted pronounced hysteresis.