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 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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

A polarisation-independent blue-phase liquid crystal microlens using an optically hidden dielectric structure

A polarisation-independent blue-phase liquid crystal microlens using an optically hidden dielectric structure is proposed. In this design, the non-uniform electric field across the lens aperture is obtained by the modulation of the effective dielectric constant of an optical hidden layer. As the applied voltage varies from 0 to 150V_rms, the focal length of the lens can be tuned from ∞ to 16.6 mm. Simulation results show that this device has a parabolic-like profile and exhibits polarisation-independent property.     

A blue-phase liquid crystal lens array based on dual square ring-patterned electrodes

We propose a blue-phase liquid crystal (BPLC) lens array based on dual square ring-patterned electrodes. A high dielectric constant layer is used to smoothen out the horizontal electric field and reduce the operating voltage. By creating a potential difference between the dual square ring-patterned electrodes, gradient electric fields are generated and lens-like phase profile is obtained. Besides, the focal length of the BPLC lens is adjustable with voltage changes and all simulation results indicate that the BPLC lens array is polarisation-insensitive.     

A transflective polymer-stabilised blue-phase liquid display with partitioned wall-shaped electrodes

A transflective polymer-stabilised blue-phase liquid crystal display (BP-LCD) with partitioned wall-shaped electrodes is proposed. The etched polymer layer contributes to balance the optical phase retardation between transmissive (T) and reflective (R) regions. The partitioned wall-shaped electrodes generate uniform and horizontal fields throughout the entire LC layer to induce isotropic-to-anisotropic transition in the blue-phase liquid crystal medium through Kerr effect. Consequently, the accumulated phase retardation along beam path is large, resulting in reasonable low operation voltage and high transmittance both in T and R regions. This approach enables the BP-LCD to be addressed by amorphous silicon thin-film transistors. Moreover, it exhibits wide viewing angle and a well-matched gamma curve.     

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.     

Step-shaped electrode for low-voltage and high-optical-efficiency blue-phase transflective liquid crystal displays

A step-shaped electrode design is proposed for Polymer Stabilised Blue Phase (PSBP) Transflective LCD (TR-LCD). This new electrode design is capable of delivering very high optical efficiency (both T and R) of >95% with operation voltage of ~13 V (or >~90% with ~9 V). The step-shaped electrode helps generate strong horizontal electric fields across the whole cell and suppress the formation of dead zone.     

A hysteresis-free polymer-stabilised blue-phase liquid crystal

We report a polymer-stabilised blue-phase liquid crystal (BPLC) in an in-plane-switching (IPS) cell with negligible hysteresis and good stability. Long ultraviolet (UV) wavelength and top-side (no IPS electrode) exposure create uniform polymer network, which in turn helps to suppress hysteresis. The effect of photoinitiator is also investigated. Although a BPLC precursor without photoinitiator requires a higher UV dosage to stabilise the polymer network, it is favourable for keeping high resistivity and reducing image sticking.     

Three-dimensional corrugated electrode structure for low-voltage high-transmittance blue-phase liquid crystal displays

We propose new electrode designs for the corrugated Polymer-Stabilised Blue-Phase Liquid Crystal Displays (PSBP-LCDs). In these new designs, the electrode structure varies not only in x/z-axis directions but also in the y-axis (transverse) direction. In this way, an additional electric field is created in transverse y-axis direction which is found to help improve the transmission of the dead zones that exist in the previously proposed corrugate PSBP-LCD structure. The transmission can increase by about 5% to 8 % or higher, depending on the period of the corrugated structure. Using these new structures, it is possible to obtain > 90% in transmission with low operation voltage of about 10 V.     

Electrically tunable polarisation-independent blue-phase liquid crystal binary phase grating via phase-separated composite films

A simple method for fabricating polarisation-independent blue-phase liquid crystal phase grating is demonstrated by implementing photopolymerisation-induced phase separation through a binary photomask. The dynamic focusing property of the proposed liquid crystal grating is independent of the polarisation state of incident light. The efficiency of various diffraction orders for the phase grating was measured as a function of the applied voltage. Experimental results show that the maximum diffraction efficiency reaches 36% for the ±1 order, which approaches the theoretical limit ~41%. The measured rise time is 1.4 ms and fall time is 2.2 ms. Such a tunable grating has great potential for photonic applications.