Vertical Alignment Liquid Crystal Display Research Articles

Optical efficiency modulation of vertical alignment liquid crystal displays with transparent shielding and storage electrode

A high-transmittance vertical alignment liquid crystal display (VA-LCD) using a transparent shielding and storage electrode (TSS) design is proposed. The aperture ratio of the proposed four domain TSS pixel with size of 52 × 156 μm improves approximately by 40% over the conventional pixel due to the shielding and storage metal electrode can be replaced by TSS electrode. Experimental results shown that the transmittance of TSS designed panel with 3.2 μm cell gap is 35% higher than that with conventional pixel design, whereas it is only enhanced by 21% when the cell gap is 2.6 μm. The liquid crystal dynamics simulation results revealed that both the effective birefringence and the azimuthally controlled director profile of the liquid crystal layer decreases with TSS pixel design, and these adverse impacts are magnified as the cell gap decreases. This is due to that the introduction of TSS common electrode not only weakens the vertical electric field but also affects the horizontal electric field of liquid crystal layer, which leads to a greater loss of optical efficiency under lower cell gap, resulting in the worse transmittance promotion. The proposed method is expected to be advantageously employed in enhancing transmittance of VA-LCDs for power saving.

High-transmittance vertical-alignment liquid crystal display with subpixel electrode shielding electric field design

A proposed pixel structure named ‘Sub-pixel Electrode Shielding (SES)’ is developed to improve the transmittance of eight-domain vertical alignment liquid crystal display (LCD). In the SES pixel, the sub pixel electrode is designed to partially overlap with data line and encircle the main pixel to shield the effects of data signal on the common signal. Therefore, the array common electrode and data signal shielding lines of conventional pixel can be removed to enhance the aperture ratio. Results show that the 65 inch ultra-high-definition (UHD) LCD panel with this proposed SES pixel design achieves a transmittance of 5.9%, which is 7.3% higher than the panel with conventional pixel design, and shows the same viewing angle characteristic as the conventional one.

Eliminate the backflow effect by polymer monomer RM257 in VA-LCD

ABSTRACT The mutual influence between the tilt angle change and the flow effect in the liquid crystal display (LCD) is called the backflow effect. The backflow effect is manifested in the form of optical bounce (OB) in the applying voltage vertical alignment liquid crystal display (VA-LCD). The OB phenomenon greatly increases the response time and limits the application of the VA-LCD in LC devices that require fast response speed. In this article, a small amount of bi-functional linear polymer monomer RM257 added in VA-LCD can eliminate the OB phenomenon after polymerisation, and fast response speed is achieved. A small amount of RM257 increases the saturation voltage, and slightly reduces the transmittance of the bright state. The polarising optical microscope (POM) and scanning electron microscope (SEM) is used to analyse the physical mechanism of the lower transmittance and eliminating the backflow effect. The VA-LCD with polymer monomer has the simple manufacturing process and fast response speed, and has an important significance for the broad application of VA-LCD.

Liquid Crystal Mixtures Including High Reliability Fluorinated Diluter and Reactive Monomer for Polymer Sustained Vertical Alignment and Polyimide-less Liquid Crystal Displays

Liquid Crystal Mixtures Including High Reliability Fluorinated Diluter and Reactive Monomer for Polymer Sustained Vertical Alignment and Polyimide-less Liquid Crystal Displays

P‐145: A New Optical Concept for High Duty Cycle Vertical Alignment Liquid Crystal Displays

Optical film compensated passive matrix vertically aligned liquid crystal displays (PMVA‐LCDs) become more and more popular in many applications such as, industral control, automotive, e‐metering, medical, sports, smart home etc. because of its high contrast ratio and wide viewing angle. However, the current solution of PMVA‐LCD has a shortcoming on its steepness of the transmission‐voltage curve (T‐V curve), which limits its driving duty cycle . Here we demonstrate a new development of a PMVA‐LCD to achieve high duty cycle, up to 1/128, by electro‐optical simulations and experiments.

P‐153: High Performance Photo‐aligned Surface of Vertical Alignment Liquid Crystal Displays for Mass Production

Photoalignment technology has been proven useful in the patterned alignment display industry. For large area display, most of the available in‐plane switching (IPS) mode TVs or panels use photoalignment technology. Not only it allows free pattern alignment direction to the liquid crystal compared to the conventional rubbed polyimide, but also it provides high yield and stability. However, the cost of the photoalignment technology could be very high. The materials often require polarized deep UV irradiation with a finite dosage to generate pretilt angles. Due to the improper control of rubbing on the alignment layer, the low yield rate problem still exists in the passive LCD world, especially for vertical photoalignment LCDs. It would be ineffective to improve the yield rate problem with this technology. Furthermore, the required materials are not common in the market. In view of the situation, a Vertical Alignment (VA) surface by non‐polarized LED light irradiation with a large wavelength is proposed and demonstrated in this paper. The cost of the LED exposure equipment is relatively more affordable. In a series of factory pilot runs on the proposed alignment characteristics, it shows comparable result to conventional polyimides in terms of performance. It achieves a stable and uniform pretilt angle, with high anchoring energy and fast response time. To conclude, the proposed robust alignment layer could benefit the industry with a better performance at low cost.

P‐159: The Transmittance Improved of Polymer Stabilized Vertical Alignment Liquid Crystal Displays by Chiral Doping

High transmittance is desired for high‐resolution liquid crystal display (LCD). In this work, the transmittance of Polymer Stabilized Vertical Alignment (PSVA) LCD mode has been greatly improved by chiral doping, and the mechanism of such chiral PSVA mode is illustrated for the first time. Compared with normal PSVA mode, the present chiral PSVA mode exhibited transmittance higher than 10%, accompanishing with comparably high contrast ratio and wide viewing angle. This novel chiral PSVA technology can be used in various LCD applications.

47.5: A new optical concept for high duty vertical alignment liquid crystal displays

Passive matrix driven vertical alignment liquid crystal displays (PMVA‐LCD) become more and more popular in many applications like industry, automotive, e‐metering, medical, sports, smart home etc. regarding its high contrast and wide view angle. However, the current solution of vertical alignment liquid crystal display has a shortcoming on the steepness of the transmissive‐voltage curve (T‐V curve) of the displays, which limits the driving duty of displays. We developped a new optical concept to achieve high duty, up to 1/128, PMVA‐LCD displays by optical‐electro simulations and experiments.

34‐1: A Novel Reactive Monomer for Self Vertical Alignment Liquid Crystal Displays

Conventionally, the alignment layer like polyimide is necessary for Liquid Crystal (LC) initial alignment. In this study, we have developed a novel reactive monomer (RM) for self vertical alignment (SVA). Doping this SVA RM into LC, we become able to manufacture VA mode Liquid Crystal Display panel without alignment layer. This technology would bring many merits to LCD performance.Also, this technology is very good compatibility with the Polymer Sustained Alignment (PSA) technology, that is widely used for LCD TV application etc. We report our achievement, comparing PSA.

Mobile ion induced electric field effect in polymer-stabilized vertical alignment liquid crystal display

Mechanisms of radical polymerization on the surface of the alignment layer in polymer stabilized vertical alignment (PS-VA) liquid crystal display (LCD)are suggested. When DC voltage is applied between top and bottom electrode, it is observed that the liquid crystal molecules distort alignment directions, which deteriorate luminance uniformity during UV irradiation process. It is revealed that the liquid crystal movement is attributed to mobile ions, (K+, OH−), smearing out from the interface at the lower layer of the pixel electrode. The mobile ions are generated from the developer remains after color filter formation process. To minimize the influence of the mobile ions, the thickness of the insulating SiNx layer under the pixel electrode and the color filter is increased, which contribute to luminance reduction rate from 20% to less than 1%.

Fabrication of New Liquid Crystal Device Using Layer-by-Layer Thin Film Process

Indium tin oxide (ITO) transparent electrodes are troubled with high cost and poor mechanical stability. In this study, layer-by-layer (LBL)-processed thin films with single-walled carbon nanotubes (SWNTs) exhibited high transparency and electrical conductivity as a candidate for ITO replacement. The repetitive deposition of polycations and stabilized SWNTs with a negative surfactant exhibits sufficiently linear film growth and high optoelectronic performance to be used as transparent electrodes for vertically aligned (VA) liquid crystal display (LCD) cells. The LC molecules were uniformly aligned on the all of the prepared LBL electrodes. VA LCD cells with SWNT LBL electrodes exhibited voltage-transmittance (V-T) characteristics similar to those with the conventional ITO electrodes. Although the response speeds were slower than the LCD cell with the ITO electrode, as the SWNT layers increased, the display performance was closer to the LCD cells with conventional ITO electrode. This work demonstrated the good optoelectronic performance and alignment compatibility with LC molecules of the SWNT LBL assemblies, which are potential alternatives to ITO films as transparent electrodes for LCDs.

P‐153: High Contrast Ratio LCD with an In‐cell Polarizer

We develop a rigorous model to simulate an LCD's contrast ratio (CR) and viewing angle by considering the depolarization effect. To improve CR, an in‐cell polarizer is added between LC layer and color filter array. The obtained maximum CR of a multi‐domain vertical alignment LCD is boosted to > 20,000:1.

Submillisecond-response liquid crystal for high-resolution virtual reality displays.

We report a vertically-aligned liquid crystal display (LCD) device with submillisecond response time, high transmittance, and low operation voltage. The top substrate has a common electrode, while the bottom substrate consists of hole-patterned fringing-field-switching (FFS) pixel electrodes. A negative dielectric anisotropy LC is employed. In the voltage-on state, the LC directors are reoriented by the fringing fields surrounding the hole area and by the longitudinal and fringe fields outside the hole area. After design optimization, we are able to achieve 85% peak transmittance under crossed circular polarizers. During the relaxation process, the standing walls exert a strong restoring force, leading to submillisecond gray-to-gray response time. Moreover, this device enables high resolution density because only one thin-film transistor per pixel is needed and the bottom FFS electrode has built-in capacitor. This device is particularly attractive for the emerging virtual reality displays.

Fast Switching and Low Operating Vertical Alignment Liquid Crystal Display With 3-D Polymer Network for Flexible Display

Vertical alignment liquid crystal (LC) cell driven by in-plane field with 3-D polymer network exhibited no pooling mura under an external mechanical pressure; however, the operating voltage of the device was increased, because the polymer network hinders field-induced reorientation of LC. In this paper, we adopted a modified cell structure in which a counter electrode on top substrate of the conventional mode is existed, to improve upon this drawback. The proposed device in which the polymer network is formed in bulk of vertically aligned LC layer shows a very fast response time of 2 ms (rise + decay), 57% reduction in operating voltage, and also keeps image quality although the cell is curved.

Transmittance Improvement with Reversed Fishbone-Shape Electrode in Vertical Alignment Liquid Crystal Display

A polymer-stabilized vertical alignment (PS-VA) mode with fishbone-shaped pixel electrode structure is mainly used in large-sized liquid crystal displays (LCDs) owing to its advantages such as wide viewing angle, good transmittance and fast response time. One drawback of this mode is a main bone electrode, which crosses in the center of a pixel. It causes the transmittance to decrease badly because LCs cannot be reoriented in this region, and thus, it is particularly unfavorable in an ultra-high-definition LCD. Here, we propose an innovative structure with the main bone electrode relocated to the edge area in a pixel, and investigate how this reverse directed fishbone-shaped pixel electrode structure affects electro-optic characteristics. The proposed structure shows enhanced electro-optic performance, such as the higher transmittance and the faster response time than the conventional VA mode with fishbone-shaped pixel electrode structure.

New three-gamma-curves-integrated VA LCD design for excellent image quality and enhanced transmittance

ABSTRACTCompared with the in-plane switching (IPS) mode of the liquid crystal display (LCD), the vertical-alignment (VA) LCD mode provides an excellent contrast ratio and a fast response time, but it still has a relative weakness: image quality deterioration as a function of the viewing direction. In the VA mode, the pixel division method, in which two different gamma curves from the divided pixels are integrated, is generally used to improve the off-axis image quality. Reported herein is the new VA mode for enhancing the off-axis image without decreasing the transmittance. The pixels divided into 12 domains instead of 8 using double electrode layers produce three different gamma curves from the high, middle, and low pixels, which are combined and enhance the image quality. In this pixel structure, the middle pixels are formed by two electrode layers and produce the third gamma curve. The new design of the VA mode shows the best off-axis image quality in the VA mode, which is the most comparable with that in the IPS mode, even with the organic light-emitting diode, and will provide a solution for the heavy competition in the ultrahigh-definition (UHD) and large-LCD-TV-panel market in the very near future.

Polymer stabilized vertical alignment liquid crystal display: effect of monomer structures and their stabilizing characteristics

A polymer-stabilized vertical alignment (PS-VA) mode using a new type of photoreactive monomer for polymer stabilization of the liquid crystal (LC) director was developed. Conventional reactive mesogens having a higher molecular weight than those of the host LC tend to aggregate and form large-sized polymer grains when exposed to ultraviolet (UV) light, subsequently deteriorating the quality of the dark state. To address these problems, bis(4-hydroxyphenyl) diacrylates were synthesized with four different linking groups as stabilizing monomers (SMs) which have molecular weights similar to that of the host LC. Their stabilizing characteristics with respect to the molecular size and polarity of SMs were evaluated by examining the electro-optic characteristics of LC cells after UV irradiation. The results showed that the SM containing a small linking group in size between biphenyls with high polarity was favored to achieve excellent polymer stabilization. The SM containing an ether linkage showed excellent electro-optic characteristics with no large-sized polymer grains even in the absence of a photo-initiator. Consequently, we anticipate that SMs, polar and smaller in size, can improve the electro-optic characteristics in PS-VA mode.

Viewing angle compensation of vertical alignment liquid crystal display using a triphenylene-based discotic reactive mesogen

We synthesised a triphenylene-based discotic reactive mesogen 2,3,6,7,10,11-hexakis(but-3-enyloxy)triphenylene (HABET) and investigated its performance as the compensation film for a vertical alignment-liquid crystal display (VA-LCD). The HABET molecule has a negative birefringence with an extraordinary refractive index (ne) that is smaller than the ordinary refractive index (no). The optic axis of the HABET is parallel to the ne direction and was vertically aligned to function as a negative C-plate. We measured the refractive indices and birefringence of the HABET layer in the visible wavelength range. Using the experimental data, we simulated the viewing angle property of the VA-LCD with the HABET negative C-plate and a positive A-plate. The viewing angle property of the VA-LCD with the HABET compensation film was wider than those without the compensation film and those using triacetylcellulose films.

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.