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.     

Single electro-optic curve for RGB colours in blue-phase liquid crystal display

The double-layer penetration electrode structure is proposed to obtain the low-operating voltage blue-phase liquid crystal display (BPLCD) with single electro-optic curve for red-green-blue (RGB) colours in every pixel, which is more suitable for the field-sequential-colour display. The different influences of electrode’s parameters and driving methods on the electro-optical properties of the proposed BPLCD are investigated. The results demonstrate that the operating voltage can be reduced from 53.80 V to 23.00 V for red colour. Besides, the coincident voltage-dependent transmittance curves for RGB colours are obtained by adjusting the applied voltage of sub-electrode. Thus, RGB lights can pass through every pixel with single electro-optic curve, which is good for resolution enhancement and single gamma driving. Besides, the maximum gamma shift of the proposed BPLCD is less than 0.1099 at 60° polar angle for the red colour, and the gamma shift difference between red and blue colours is only 0.0542. If the high dielectric constant material is used as the protrusion, the operating voltage can be further decreased, which is close to that of the BPLCD with wall-shaped electrode structure.     

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.     

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.     

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.     

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.     

Effects of rubbing angle on maximum transmittance of in-plane switching liquid crystal display

Measurements of the maximum transmittance of an in-plane switching liquid crystal display showed that it increases as rubbing angle is increased from 10 to 20°. This dependence was analysed in terms of the local variation of electric field intensity between electrodes, which in turn makes liquid crystal at various positions between the electrodes rotate to different angles. The local variation of electric field becomes prominent, especially in the case that the distance between the electrodes is much larger than the cell gap or electrode width.     

Transflective blue-phase liquid crystal display with dielectric protrusion

A transflective blue-phase liquid crystal display (TRBP-LCD) with dielectric protrusions is proposed. The dielectric protrusions are fixed on the in-plane-switching (IPS) electrodes. The potential drops very slowly in the dielectric protrusions, thus the total field penetrating depth is significantly enlarged and the operating voltage is lowered, which helps suppressing electrostriction effect. The different heights of the dielectric protrusions in the transmissive (T) and reflective (R) regions contribute to balance the optical phase retardation between the T and R regions. The simulation results verify that the proposed TRBP-LCD can achieve low operating voltage and good sunlight readability.     

Transflective blue-phase liquid crystal display with polar opposite electrodes

A submillisecond response, wide view and single-cell-gap transflective (TR) display employing a blue-phase liquid crystal is proposed. The device employs polar opposite in-plane switching (IPS) electrodes. To balance the optical phase retardation between transmissive (T) and reflective (R) regions, the IPS electrodes are formed with unequal gaps in the two regions. This display exhibits reasonably high optical efficiency and well-matched voltage-dependent transmittance and reflectance curves.     

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 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.     

A transflective and viewing angle controllable blue-phase liquid crystal display

A polymer-stabilised blue-phase liquid crystal display (PSBP-LCD) with double-side in-plane switching (DS-IPS) electrode structure is proposed. This structure shows the transflective characteristics because the bottom electrodes are made by aluminium material. For transflective displays, it exhibits a well-matched voltage-dependent transmission and reflection curves through designing the width and gap of the top electrodes. When a bias voltage is applied on the top electrodes, it exhibits as a good viewing angle controllable display.     

Study of polymer-stabilised blue phase liquid crystal on a single substrate

One outstanding feature of the polymer-stabilised blue phase (PSBP) is that it is unnecessary to form an alignment film, which requires a high-temperature baking process. Therefore, PSBPs may enable flexible liquid crystal displays (LCDs) on plastic substrates. In this study, polymer stabilisation of a blue phase (BP) on a single substrate was performed without using a conventional sandwich-type cell, and the electro-optical properties are demonstrated to be similar to those of a sandwich-type PSBP LCD cell. It was experimentally shown that the oxygen which inhibits radical polymerisation is required to be excluded in order to complete the polymer stabilisation in blue phase.     

A transflective blue-phase liquid crystal display with alternate electrodes

A transflective polymer-stabilised blue-phase liquid crystal display (BP-LCD) with alternate electrodes is proposed. The alternate electrodes are composed of right triangle electrodes and slanted electrodes. To balance the optical phase retardation between the transmissive (T) and reflective (R) regions, the legs of the right triangle electrodes in the T region generate uniform horizontal electric field, the hypotenuses of the right triangle electrodes and slanted electrodes in the R region generate uniform oblique electric field. As result, the T and R regions obtain the same optical phase retardation. This display exhibits reasonably high transmittance, low operating voltage, wide viewing angle and well-matched voltage-dependent transmittance and reflectance curves.     

Greyscale generation for optically driving liquid crystal display

It is very difficult to display greyscale for an optically driving liquid crystal display (ODLCD) because the driving unit and display unit are separate, and there are no electronics in the display part of ODLCD. In this paper, two greyscale generation methods are proposed to achieve this goal. Six and nine grey levels are separately achieved through the two methods.     

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.     

Photoracemization broadening of selective reflection and polarization band of glassy chiral-nematic films

Glass-forming liquid crystals consisting of a cyclohexane central core with (S)-1-phenyl-ethylamine and (4-cyanophenyl)naphthalene pendants were synthesized as hosts for racemizable (R)-dinaphtho[2,1-d:1',2'-f][1,3]dioxepin, a chiral dopant. Chiral-nematic films 14, 22, and 35 mum thick were prepared for thermal and photoinduced racemization at temperatures from 95 to 130°C, i.e. in the mesomorphic temperature range, over a period of hours to days. Spatially modulated photoracemization was accomplished with an insignificant contribution from the thermal process at temperatures around 100°C over a period of up to 3 h. With an absorbance per unit thickness of 6.2 mum^-1 at 334 nm, the photochemical process was essentially confined to the irradiated surface, thereby setting up counter-diffusion of the two enantiomers through the film, and hence the pitch gradient as visualized by atomic force microscopy. The significantly widened selective reflection band was interpreted with the Good-Karali theory extended for a gradient-pitch film. Furthermore, the bandwidth was found to increase with decreasing racemization temperature or with increasing film thickness, further validating the presence of a pitch gradient as a result of controlled photoracemization.     

Reduction of gamma distortions in liquid crystal display by anisotropic voltage-dividing layer of reactive mesogens

We demonstrate a new concept of reducing the off-axis gamma distortions in a liquid crystal display by the formation of an anisotropic voltage-dividing layer (AVDL) on the alignment layer. The AVDL was prepared using reactive mesogens (RMs) by simple spin-coating, followed by the photo-polymerisation under the exposure of ultraviolet light (UV) through a photomask and the removal of residual RMs. The UV exposure time for the photo-polymerisation was found to be critical for the uniform alignment of the liquid crystal molecules on the AVDL. Owing to the capacitance difference between the sub-domains produced by the AVDL, the threshold voltage shift was naturally appeared in sub-domain by domain so that the reduction of the gamma distortions in the off-axis was achieved in a simple way.