Low voltage blue-phase liquid crystal display with insulating protrusion sandwiched between dual-layer electrodes

In order to lower the operating voltage of blue-phase liquid crystal display (BPLCD), a BPLCD with insulating protrusion, which is sandwiched between dual-layer electrodes, is proposed. There are four electrodes in this structure; thus, we investigate different driving methods to find a proper driving method. The effect of protrusion’s dielectric constant on operating voltage of the proposed BPLCD is explored under various electrodes’ parameters. As a result, the operating voltage of the proposed BPLCD with protrusion’s dielectric constant of 1,000 is 9.8 V, which is reduced by ~ 4.67× compared with that of conventional in-plane switching (IPS) BPLCD (45.8 V). Moreover, the zigzag electrode structure is adopted to reduce the large off-axis image distortion index. Besides, the azimuth distortion index is defined to describe the gamma shift between the minimum and maximum gamma shift curves at a certain polar angle. The results show that the off-axis image distortion index can be reduced to 0.0834, the azimuth distortion index is 0.0810 and the viewing cone of contrast ratio larger than 1,000:1 is over 50ºas the zigzag proposed BPLCD is used.     

Low gamma shift blue-phase liquid crystal display with electric field induced multi-domain electrode structure

ABSTRACT

To reduce the gamma shift of blue-phase liquid crystal display (BPLCD), the multi-domain electrode structure with four sub-electrodes is proposed. The effects of electrodes’ parameters on electro-optical curve and gamma shift are calculated, and the gamma shift and contrast ratio at full viewing-cone are also investigated. For the proposed protrusion BPLCD, the operating voltage is reduced by ~73%, and the transmittance is increased by ~20% compared with the conventional in-plane switching BPLCD. The results also show that the off-axis image distortion index can be reduced from 0.4318 to 0.0875 at the polar angle of 60°, and it works well under various electrodes’ sizes. Moreover, the indistinguishable gamma shift can be obtained at full viewing-cone for the proposed BPLCD, and the uniform light distribution and high contrast ratio can be obtained as well.     

Low-gamma shift asymmetrical double-side blue-phase liquid crystal display

ABSTRACT

A single-domain blue-phase liquid crystal display (BPLCD), which has asymmetrical double-side electrode structure, is proposed to reduce gamma shift. Firstly, the electro-optical curve and gamma shift of the proposed BPLCD are discussed under the comparison with conventional in-plane switching (IPS) BPLCD. And then, its gamma shift is investigated under various conditions. Compared with the conventional IPS-BPLCD, the operating voltage can be reduced by ~31%, and the transmittance is increased by ~6%. The indistinguishable gamma shift can be obtained under various electrodes’ sizes, when the cell gap is appropriate. The results also indicate that if the electrodes’ height and Kerr constant of BPLC increase, the operating voltage can be further reduced (only 9.6 V in this work), and the gamma shift almost do not change. Moreover, a certain misalignment between the top and bottom glasses are permitted, which is good for reducing the fabrication difficulty. In terms of viewing angle, the proposed BPLCD has an average contrast ratio of ~5000:1, and the gamma shifts at full viewing angles are all indistinguishable.     

Blue-phase liquid crystal display with high dielectric material

A blue-phase liquid crystal display (BPLCD) with low operating voltage and high transmittance is demonstrated by using a high dielectric material, which is used as an insulation layer or protrusion fixed on the pixel and common electrodes in in-plane switching (IPS) mode. The operating voltage is reduced to about 14 V and the transmittance is improved for the BPLCD with high dielectric constant protrusion. Compared with the conventional protrusion electrode structure, the proposed protrusion can make manufacturing process simple and easy because the electrode has no complex shape. The results will be significant in designing optimal BPLCDs.     

Low-voltage blue-phase liquid crystal display with single-penetration electrodes

A blue-phase liquid crystal display (BPLCD) with single–penetration (S-P) electrodes is proposed to reduce the operating voltage. X-shape inclined-electric field is induced by the S-P electrodes with 2 ~ 3 μm height, which can lower the operating voltage by ~45%, and improve the transmittance compared with BPLCD with conventional in-plane electrodes. Moreover, the wide viewing angle and very small image distortion index can be obtained in this structure with a half-wave biaxial film. The proposed structure shows simple etching control and easy one-drop filling process of blue-phase liquid crystal compared with dual-convex-penetration electrodes.     

Optimisation of blue-phase liquid crystal with protrusion

The optimised structures of blue-phase liquid crystal display (BPLCD) with various protrusions were discussed in this article. The voltage-dependent transmittances for the cell with four protrusion shapes, wall-shaped electrode, trapezoid electrode, double penetration electrode and elliptical electrode, are simulated. The electrode gap and width and protrusion height’s effects on the optimised cell gap and the corresponding operating voltage are calculated. The optimised cell has the lowest operating voltage and relative high transmittance. The results are significant on design BPLCD with low operating voltage.     

Reflective blue phase liquid crystal displays with double-side concave-curved electrodes

Reflective blue phase liquid crystal display (BPLCD) is a promising candidate for field sequential colour displays with reflective liquid-crystal-on-silicon (LCoS). However, the issue of high operation voltage still hinders its widespread applications. We propose a reflective BPLCD with double-side concave-curved electrode and research its operation voltage and electro-optic characteristics in simulation, which is compared to the transmissive mode. The effect of double-side electrodes on horizontal electric field and operation voltage is analysed. The improvement of concave-curved electrodes on reflectance is discussed. A reflective BPLCD has two times the optical path difference compared to the transmissive mode. By using double-side concave-curved electrodes, the reflectance increased by 23% and the operation voltage reduced by 32% compared to the traditional in-plane switching mode. This work enables BPLC to be integrated with reflective LCoS.     

Multi-layer protruded electrodes for reducing the operating voltage and gamma shift of fringe-field switching LCDs

ABSTRACT

To reduce the operating voltage and gamma shift of the nematic liquid crystal display (LCD), a single-domain-protruded fringe-field switching (PFFS) electrode structure is designed. In this work, a kind of nematic liquid crystal (NLC) is introduced firstly. Then, the operating voltage and gamma shift of the proposed PFFS LCD are investigated under various electrodes’ parameters. Besides, its light leakage and contrast ratio are also discussed. The results show that the operating voltage of the PFFS LCD is only 1.40 V, here the electrodes’ width is 2 μm and electrodes’ gap is 4 μm. The gamma shift of the PFFS LCD can be reduced to the indistinguishable level under various electrodes’ sizes, if the height of the insulation layer is proper. For contrast ratio, it is larger than 200:1 at full viewing-angle, and the zone of 500:1 covers 60° polar angle.     

Low-voltage and high-transmittance blue-phase liquid crystal display with concave electrode

A low-voltage and high-transmittance blue-phase liquid crystal display (BPLCD) with concave electrodes is proposed. We use in-plane switching electrodes on the etched substrates to generate the concave electrodes. The proposed device can generate a strong in-plane field with a large horizontal component to increase the transmittance and reduce the operating voltage. As a result, a low voltage ~9 V and reasonably high transmittance ~71.7% can be achieved. Moreover, due to the generated multi-domain structures in the etched areas, this BPLCD can obtain a symmetric and wide viewing angle and the contrast ratio of 1000:1 is obtained over 60° viewing cone.     

A simple transflective liquid crystal display with composite dielectric layer

ABSTRACT

A simple transflective liquid crystal display with a vertically aligned cell using a composite dielectric layer is demonstrated. The top substrate has a top planar common electrode, two transparent dielectric layers with different dielectric constants are coated on the bottom planar pixel electrode to generate linearly varying electric potential from the transmissive region (T region) to the reflective region (R region), while two bumpy reflectors are coated under the bottom substrate. In this device, with the composite dielectric layer, the common and pixel electrodes generate a strong electric potential in the T region and a relatively weak electric potential in the R region. Consequently, the T and R regions accumulate the same electro-optical characteristics. The simulation results show that the display exhibits reasonably low operating voltage, high optical efficiency and well-matched voltage-dependent transmittance (VT) and reflectance (VR) curves. Besides, the driving mode and the fabrication process of the transflective liquid crystal display are fairly simple and it is suitable for mobile applications.     

A single-cell-gap transflective liquid crystal display with a vertically aligned cell

A single-cell-gap transflective liquid crystal display with a vertically aligned cell using square ring electrode is demonstrated. The top substrate has a top planar common electrode, a square ring pixel electrode is coated on the bottom substrate, while a bumpy reflector is coated under the bottom substrate. In this device, the planar common electrode and square ring pixel electrode generate a strong longitudinal electric field in the transmissive region (T region) and a weak fringe field in the reflective region (R region). As result, the T and R regions accumulate the same optical phase retardation. The simulation results show that the display exhibits reasonably low operating voltage, high transmittance and well-matched voltage-dependent transmittance and reflectance curves. Besides, fabrication process of the transflective liquid crystal display is very simple.     

Low voltage and high transmittance transflective blue-phase liquid crystal display with opposite polar electrodes

A single-cell-gap transflective polymer-stabilised blue-phase liquid crystal display with opposite polar pixel electrodes on an etched substrate is proposed. In the proposed structure, the space between common electrodes is adopted as transmissive region, and the space above the common electrode is adopted as reflective region. By optimising the electrode parameters of the transmissive and reflective regions, well-matched voltage-dependent transmittance and reflectance curves can be obtained. In addition, the device has good performances of low operating voltage (~3.2 V), high optical efficiency and a wide viewing angle.     

Blue-phase liquid crystal display with insulating protrusion

In order to lower the saturation voltage and enhance the transmittance of in-plane switching blue-phase liquid crystal display (IPS-BPLCD), IPS-BPLCD with insulating protrusion is proposed. The single-protrusion (only set on the top of pixel electrode) and double-protrusion (set on the top of pixel and common electrodes) structures are investigated in this work. The potential distribution changes when the protrusion is used. There is a thicker transverse electric field in BPLC range, because the stronger electric field at the edges of the electrodes is decentralised into BPLC range. As a result, the saturation voltage is reduced from 36.3 V to 28.9 V when the double-protrusion structure is used, and transmittance is increased by ~20%. The contrast ratio is larger than 1000:1 in 60° viewing cone using a half-wave biaxial film. Both single-protrusion and double-protrusion structures have the uniform gamma curves at large oblique viewing angles. Moreover, the off-axis image distortion index is 0.1590 at 60º polar angle when zigzag electrodes are used.     

Optimal pixel design for low driving, single gamma curve and single cell-gap transflective fringe-field switching liquid crystal display

When a dielectric layer, in-cell retarder (ICR) is formed between the electrode and LC layer to obtain a single-gap transflective fringe-field switching (FFS) display, the driving voltage is highly increased due to the thickness of the dielectric material. In particular, the driving voltage of the transmissive part becomes very high, and goes beyond the driver integrated circuit (IC) range for mobile application because the homogenously aligned liquid crystal director should rotate twice as far as that in the reflective part. The correlation between the driving voltage and electrode structures was investigated. It was found that the problem could be solved by optimisation of the common electrode structure such that the electrode structure changed from a plane to slit shape (in-plane field is mainly used instead of fringe field), realising a high performance FFS transflective display.     

High performance LCD for augmented reality and virtual reality displays

For augmented reality and virtual reality displays, high-resolution density, high luminance, and fast response time are critically needed. High-resolution density helps eliminate the screen-door effect; high luminance and fast response time enable low duty ratio operation, which plays a key role for suppressing image blurs. By using a low viscosity material and new diamond-shaped electrode configuration, we demonstrate a fringe field switching liquid crystal display, abbreviated as d-FFS LCD, with high transmittance, fast grey-to-grey response time, low operation voltage, wide viewing angle, and indistinguishable colour shift and gamma shift. We also investigate the rubbing angle (α) effects on transmittance and response time. When α = 0°, the virtual wall effect is strong, resulting in fast response time but compromised transmittance. When α ≥ 1.2°, the virtual walls disappear, as a result, the transmittance increases dramatically, but the trade-off is in slower response time.     

Viewing angle controllable fringe and in-plane switching vertical alignment LCD

A viewing angle controllable fringe and in-plane switching vertical alignment liquid crystal display (LCD) structure has been proposed. To realise the change from wide viewing angle (WVA) to narrow viewing angle (NVA) in a single LCD panel, the bias voltage is applied on the common electrode, and NVA can decreases with the increasing bias voltage. In WVA mode, the viewing angle cone (contrast ratio larger than 1000:1) is almost 70° and the contrast ratio is larger than 100:1 in arbitrary azimuthal directions. In NVA mode, the viewing angle cone (10:1) can continuously and uniformly change from 40° to 20°.     

Continuous viewing angle controllable patterned vertical alignment liquid crystal display

A continuous viewing angle switchable patterned vertical alignment liquid crystal display (PVA-LCD) with circle polarisers is proposed. In wide viewing angle (WVA) mode, the viewing cone with contrast ratio larger than 1000:1 is extended to 50° and the contrast ratio larger than 100:1 is extended to 80°. Meanwhile, the viewing cone with contrast ratio more than 10:1 is limited to 40° in all direction for narrow viewing angle (NVA) mode. The viewing angle of the display can be controlled by applying a bias voltage on the common electrode. With the increasing bias voltage, the viewing angle cone with contrast ratio more than 10:1 can be changed from 40° to 20°. The proposed PVA-LCD has high transmittance (~93%) under the circle polarisers because the dead zone in the normal PVA-LCD with linear polarisers is eliminated.     

Photochemical tuning capability of cholesteric liquid crystal cells containing chiral dopants end capped with menthyl groups

In order to investigate the photochemical tuning capability of chiral monomers and polymers containing end‐capped menthyl groups, a new series of chiral dopants was synthesized and added to commercially available nematic liquid crystals to induce cholesteric liquid crystal (LC) phases. The addition of chiral dopants with azo structure led to phototunability of the reflection colour of the LC cells. Photochromic variation of the LC cells due to photoisomerization of the azo compound was investigated. After photopolymerization of the monomers inside the cholesteric LC cells, the centre wavelength of the reflected band of the incident light was found to be fixed and the reflected bandwidth was broadened, resulting in a red shift. A schematic representation of both the photoisomerization of the azo dopants and its effect on variation of twisting pitches is proposed. Real image recording was performed using 365 nm UV through a mask with text. The top and side views of the morphological network structures of a fabricated cholesteric LC cell were investigated using scanning electron microscopy. The results of this investigation demonstrated that RGB reflected colours of LC cells can easily be achieved through the addition of the menthyl‐containing synthesized chiral compounds to nematic LCs. The addition of synthesized AzoM helped further in recording the patterns onto cholesteric LC films using 365 nm UV exposure.     

Low-voltage blue-phase liquid crystal display with diamond-shape electrodes

We propose a new electrode configuration, called diamond-shape in-plane switching, to lower the operation voltage of polymer-stabilised blue-phase liquid crystal (BPLC) displays (BPLCDs). The electrode structure is modified from conventional protruded IPS, where the strip protrusion is changed to diamond shape. By optimising the electrode gap and diamond length, we are able to obtain peak transmittance over 75% at 15 V. It enables single thin-film transistor (TFT) driving, and more importantly, this is based on an industrially proven BPLC material. That means good long-term stability, adequate TFT charging time for high-resolution displays and sub-millisecond response time and acceptable voltage-holding ratio for field sequential displays can be achieved simultaneously. Our device design helps accelerate the emergence of the long-awaited BPLCDs.     

Dyeing wool and cotton fibres with acidic extract of Hibiscus rosa sinensis flower

Abstract

The focus of this work is to extract a natural dye for colouring camel wool as a substitute for synthetic dyes used in the Sadu House of Kuwait. Their target is to keep the tradition of tent and rug production natural in all its manifestations. Therefore, our task was to find an abundant source that provides a colour preferably red to purple. Hibiscus rosa sinensis (HRS) is an abundantly available plant in Kuwait that was explored for extraction of the red dye to colour camel wool permanently. The powdered petals of red flowers of HRS was extracted with 5% acetic acid which yielded a deep red colour that showed a great potential for woollen fibre dyeing. The use of mordants like alum and some metal salts manifested a wide range of fixed colours which intensified at 85 °C. The colours produced had excellent fastness and was accepted by the Sadu House.