Blue-phase Liquid Crystal Display Research Articles

Reduced off-axis gamma shift of liquid crystal display by intercepting transmittance method

Generally, the brightness and color of one image on a large-area flat panel display are different when people watch a display image under different viewing angles. The gamma shift is used to evaluate the difference of electro-optical performances under different viewing angles, namely the gray-scale display distortion. In order to reduce the gamma shift under the oblique viewing angle, the intercepting transmittance method is proposed and illustrated based on the single-domain in-plane switching blue-phase liquid crystal display (IPS-BPLCD). The results show that the off-axis image distortion index (the quantitative evaluation index of gamma shift) can be reduced by ~72% if the transmittance ratio reduces from 100% to 80% for the IPS-BPLCD with a straight electrode structure. Moreover, the zigzag electrode structure is used as the reference to illustrate the merits of the proposed method. As a result, the operating voltage of the IPS-BPLCD can be reduced by >20%, and the off-axis image distortion index is reduced by ~47% compared with the zigzag electrode structure. Besides this, the effects of the proposed method on contrast ratio, operating voltage and color difference of IPS-BPLCD are investigated as well. In fact, the proposed method is also useful for other LCD modes and electro-optical devices to achieve wide and uniform viewing angles.

Reflective blue phase liquid crystal display with triangular dielectric layer

ABSTRACT We propose a reflective blue-phase liquid-crystal display (LCD) with triangular dielectric layers and a diffuse reflector electrode. The triangular dielectric layers with a high dielectric coefficient on the top and bottom indium tin oxide glass substrates are equivalent to the conductive plates, forming a corrugated electrode structure. This type of reflective blue-phase LCD based on planar electrode and diffuse mirror electrode can offer relatively high reflectance (~74.5%) and low operation voltage (9.2 Vrms) compared to most other devices due to its fairly strong and uniform horizontal electric field component along the whole blue-phase liquid crystal bulk. This design has the advantages of fast response time, easy manufacturing process, a high resolution and full-colour capability. It is a promising future high-quality reflective full-colour microdisplay.

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.

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

ABSTRACTTo 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.

Transflective blue-phase liquid crystal display with dielectric protrusion

ABSTRACTA 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.

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

ABSTRACTThe 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.

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

ABSTRACTWe 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.

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

ABSTRACTIn 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.

P‐17: Novel Pixel Circuit with Inverter Structure Based on a‐IGZO TFT for Blue‐Phase Liquid Crystal Displays

This work presents a new pixel circuit with amorphous indium‐gallium‐zinc‐oxide thin‐film transistors (a‐IGZO TFTs) for blue‐phase liquid crystal displays (BPLCDs). The proposed circuit adopts two pairs of inverter structures to ameliorate the frequency effect of the BPLCs for generating the accurate gray level voltages. Furthermore, to achieve the maximum transmittance of BPLCs, the wide range of the operation voltage is performed. Simulation results show that the proposed pixel circuit produces an operation voltage range of −29.329 V to 29.748 V when the practical source driver integrated circuits (ICs) only supplies an output voltage swing of 0 V to 15 V, successfully inverting the polarity of the BPLCs without the common signal.

Blue-phase liquid crystal display with insulating protrusion

ABSTRACTIn 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.

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

ABSTRACTA 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.

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

ABSTRACTA 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.

Weak Anchoring Interface Inducing Acrylate Copolymer Designs for High‐Performance Polymer‐Stabilized Blue Phase Liquid Crystal Displays

AbstractPolymer‐stabilized blue phase liquid crystal (PS‐BPLC) is emerging as a strong competitor for next‐generation liquid crystal displays and optoelectronic devices. However, the realization of technologies built on PS‐BPLC requires lowering of driving voltage without sacrificing other desirable properties of blue phase liquid crystals. Here, we present a new method for voltage reduction in PS‐BPLC based on the stabilization of BPLC with weak anchoring interface inducing acrylate monomers. This method provides significant voltage reduction while maintaining the electro‐optical performance of BPLCs at the same time. We believe that this approach has a great potential in developing high‐performance photonic devices and displays based on liquid crystals.

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

ABSTRACTReflective 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.

P‐31: New Pixel Circuit Using Constant Charging Current to Achieve High Driving Voltage for Blue‐Phase LCDs

This work proposes a novel pixel circuit based on amorphous indium‐gallium‐zinc‐oxide thin‐film transistors (a‐IGZO TFTs) for blue‐phase liquid crystal displays (BPLCDs) with the in‐plane switching (IPS) mode. The proposed pixel circuit provides a charging current as a constant current source to produce a wide operating voltage range for maximum transmittance of the BPLCs. Based on the simulation results, the proposed pixel circuit supplies a maximum output voltage of 30.14 V with an input voltage swing of 0 V to 9 V generated by the practical source driver integrated circuits (ICs), effectively compensating for the insufficient driving voltage of IPS BPLCDs.

P‐166: Single‐TFT‐driving Blue‐phase LCD with Diamond‐shape Electrodes

We propose a new electrode configuration, called diamond‐shape in‐plane switching (DIPS), to lower the operation voltage of polymer‐stabilized blue‐phase liquid crystal displays (BPLCDs). Using an industrially‐proven BPLC mixture, we can obtain 75% peak transmittance at 15 V, while keeping fast response time. Our DIPS structure enables single‐TFT per pixel to drive BPLCDs.

34‐2: Invited Paper: Novel Four‐Transistor Pixel Circuit Using Source‐Follower Structure for Field‐Sequential‐Color Blue‐Phase Liquid Crystal Displays

We propose a novel pixel circuit using source‐follower structure to be independent of frequency effect of blue‐phase liquid crystal displays (BPLCDs). Simulation results indicated that required gray‐level‐voltages across the BPLC could be achieved accurately when a proper threshold voltage of the driving TFT was chosen. We also successfully fabricated a 12.7‐inch prototype BPLCD using the proposed pixel circuit driven with a field‐sequential‐color method of 240 Hz.

A transflective blue-phase liquid crystal display with alternate electrodes

ABSTRACTA 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.

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

ABSTRACTWe 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.

One-dimensional model for simulating blue-phase liquid crystal display

ABSTRACTWe proposed a one-dimensional model for simulating some performances of blue-phase liquid crystal (BPLC) and polymer-stabilised blue-phase liquid crystal (PSBPLCD). The one-dimensional model treats liquid crystal arrangement of BPLC as cholesteric liquid crystal with high and uniform tilt angle to simulate the Bragg reflection of BPLC. The simulated results agree quite well with the experimental results. The elastic and dynamical equations are formed to calculate the effective elastic parameters and the response times of PSBPLCD. The effective elastic parameter is a constant for low electric field and decreases with the increasing of electric field. The varied effective elastic parameter means the varied restoring force of liquid crystal under the electric field. The dynamical equations are proposed to calculate response times, and the response mechanism of BPLCD is discussed by researching the difference between the decay times from equation and experiment. The sub-millisecond response time results from the weak anchoring of polymer network or the increasing of rotational viscosity of PSBPLC with high-concentration monomer, and the reason of 10 µs response time is the strong anchoring and small amount of chiral dopant and monomer.