Multi-domain Vertical Alignment Research Articles

54.1: Invited Paper: High‐Transmission and High‐Contrast‐Ratio AIFF MVA LCDs without Rubbing, Protrusion, ITO Slit and Photoalignment Process

High‐transmission, high contrast ratio and low‐power‐consumption amplified intrinsic fringe field (AIFF) multi‐domain vertical alignment (MVA) LCD's are developed for microdisplay for augmented reality, portable smart phones, GPS, tablet, and LC TV display applications. The AIFF MVA design eliminates all protrusions and ITO slits in TFT and CF.substrates, resulting in high transmission and high yield. The no‐pretilt fabrication process is low cost, does not require PI rubbing and special photoalignment process, and uses standard IC, LC, and PI materials. AIFF MVA is the only LCD mode without edge disclinations. It is compatible with the RGBW square pixel designs for low power consumption LCD applications.

Light Leakage of Multidomain Vertical Alignment LCDs Using a Colorimetric Model in the Dark State

Light leakage from liquid crystal displays in the dark state is relatively larger and leads to a degraded contrast ratio and color shift. This work describes a novel colorimetric model based on the Muller matrix that includes depolarization of light propagating through liquid crystal molecules, polarizers, and color filters. In this proposed model, the chromaticity can be estimated in the bump and no-bump regions of an LCD. We indicate that the difference between simulation and measurement of chromaticity is about 0.01. Light leakage in the bump region is three times that in no-bump region in the dark state.

Micropatterned Vertical Alignment Liquid Crystal Mode With Dual Threshold Voltages for Improved Off-Axis Gamma Distortion

We proposed an eight-domain vertical alignment (VA) liquid crystal (LC) mode, operated by dual pixel domains of fishbone-structured electrodes for dual threshold (F-DT) voltages in the VA mode, which can improve off-axis gamma distortions without additional electronic circuits and fabrication procedures compared with the conventional multidomain VA modes. In the proposed F-DT VA mode, different threshold voltage levels can be obtained for the main- and subpixel regions by utilizing different field-induced LC reorientations determined by the pixel electrode structures, whose properties are especially enhanced in low-voltage regimes. When the relative area ratio ( ${R} _{A}={A}_{\text {main}}/{A}_{\text {sub}}$ ) between the main- and subpixel domains was ${R} _{A}=\text {5}$ , these dual threshold properties of the F-DT VA mode improved the off-axis gamma distortion index (GDI) value up to 34.04% at the oblique viewing condition of $\theta = {60}^{\circ }$ , compared to the conventional patterned VA (PVA) modes, while maintaining the maximum transmittance level. The proposed pixel electrode design scheme could be applied to further improve the GDI value simply by controlling ${R}_{A}$ , where the GDI of the F-DT VA mode was improved by 39.17% and 17.05% at ${R} _{A}= {2}$ , compared to the conventional PVA and micropatterned VA modes, respectively.

Construction of Polymer-Stabilized Automatic MultiDomain Vertical Molecular Alignment Layers with Pretilt Angles by Photopolymerizing Dendritic Monomers under Electric Fields.

The synthesized itaconic acid-based dendritic amphiphile (Ita3C12) monomers and the methacryl polyhedral oligomeric silsesquioxane (MAPOSS) cross-linkers were directly introduced for the construction of automatic vertical alignment (auto-VA) layers in the host nematic liquid crystal (NLC) medium. The auto-VA layer can be stabilized by irradiating UV light. For the automatic fabrication of a polymer-stabilized multidomain VA (PS auto-MDVA) layer with a pretilt angle, Ita3C12 and MAPOSS were photopolymerized under the electric field by irradiating UV light on the multidomain electrode cell. Mainly because of the pretilted NLC at zero voltage, the electro-optic properties of the PS auto-MDVA cell were dramatically improved. From the morphological observations combined with surface chemical analyses, it was found that various sizes of protrusions on the solid substrates were automatically constructed by the two-step mechanisms. We demonstrated the PS auto-MDVA cell with the enhancement of electro-optic properties as a single-step process and investigated how the protrusions were automatically developed during the polymer stabilization.

Depolarization effect in liquid crystal displays.

We develop a rigorous model to simulate an LCD's contrast ratio (CR) and viewing angle by considering the depolarization effect in thin-film transistor substrate, LC layer, color filter (CF) array, etc. To mitigate the depolarization effect, we propose a new device structure by adding a thin in-cell polarizer between LC layer and CF array. Based on the analysis using our new model, the maximum CR of a multi-domain vertical alignment (MVA) LCD can reach > 20,000:1, while for the fringe-field switching (FFS) mode it can reach > 3000:1. We also discuss other approaches to further enhance the CR. Our model is a powerful tool to analyze the CR degradation mechanism and to guide the future LCD device and material optimizations.

Emerging Quantum-Dots-Enhanced LCDs

Quantum dots (QDs)-based backlight greatly enhances the color performance for liquid crystal displays (LCDs). In this review paper, we start with a brief introduction of QD backlight, and then present a systematic photometric approach to reveal the remarkable advantages of QD backlight over white LED, such as much wider color gamut, higher optical efficiency, enhanced ambient contrast ratio, and smaller color shift. Some popular LC modes are investigated, including twisted nematic, fringing field switching (FFS) for touch panels, multi-domain vertical alignment (MVA) for TVs, and blue phase liquid crystal (BPLC) for next-generation displays. Especially, QD-enhanced BPLC combines the major advantages of FFS and submillisecond response time. It has potential to become a unified display solution.

Optical design and roll‐to‐roll fabrication process of microstructure film for wide viewing LCDs

AbstractWe have developed a new microstructure film for wide viewing liquid crystal displays (LCDs). By attaching it to the surface of a conventional LCD, the viewing angle characteristics of LCD has drastically improved without causing a blur of the frontal image and a decrease in the contrast ratio under bright ambient light conditions. This film can be applied to various LC modes including twisted nematic and multidomain vertical alignment by changing its internal micrometer‐size 3D structure. Further, this film can be mass‐produced efficiently by self alignment roll‐to‐roll process.

In-plane switching of vertically aligned negative liquid crystals for high transmittance and wide viewing angle

We propose a method for in-plane switching of vertically aligned negative liquid crystals (LCs) for high transmittance and wide viewing angle. By applying an in-plane electric field using a double-layered electrode structure, LC molecules can be rotated by the vertical as well as the in-plane components of the applied field over the entire region so that high transmittance can be achieved. The threshold voltage difference can be obtained simply by varying the electrode structure, which can reduce the off-axis gamma shift in a multidomain vertical alignment LC cell.

P.100: Multi‐domain Vertical Alignment of Liquid Crystals Through Control of the Anchoring Energy

AbstractWe propose a method for multi‐domain vertical alignment of liquid crystals without additional transistors. By irradiating UV light to the polyimide through a patterned photomask, we can obtain different threshold voltage in a VA cell. There is no light leakage in the initial dark state so that the contrast ratio is not reduced in the proposed structure. We expect that the proposed method can be used to realize an eight‐domain structure for reduction of the off‐axis gamma shift

Simulation‐based look‐ahead release planning for color filter fabs

AbstractThis study presents a look‐ahead release planning approach on the basis of AutoMod simulation model for a sixth‐generation thin film transistor liquid crystal display color filter (CF) fab in north Taiwan. The studied CF fab has two identical lines with the processes of black matrix (BM), color layer [red, green, and blue (RGB)], indium tin oxide, and photo spacer (PS). These two lines share two supporting processes, multi‐domain vertical alignment (MVA) and laboratory (LAB). MVA has the capability and flexibility to provide the functions of RGB and PS, whereas LAB can provide the functions of BM and RGB. The production release planning becomes complex because of the equipment flexibility in supporting each other. An AutoMod simulation model is therefore developed and validated using real data from the fab. The AutoMod simulation model is well representative of the real system with less than 10% difference in throughput in all production stations. Using simulation to look ahead, a production controller can predict potential equipment idleness and make adjustment to better utilize equipment capacity. On the basis of simulation with design of experiments, the proposed simulation‐based look‐ahead release plan is demonstrated to be effective in improving system throughput.

Analysis of display defects in the multi-domain vertical alignment mode liquid crystal display

Two types of display defects were found at special positions near the pixel indium tin oxide (ITO) edge in the multi-domain vertical alignment (MVA) mode liquid crystal display (LCD). Through simulated and experimental results, the formation mechanisms of these two types of display defects, the detailed configurations of liquid crystal (LC) orientations at the display defect regions and the principle to suppress the defect dark line were analyzed and discussed. It was further found that the occurrence of the dark line was related to the positioning accuracy of substrate assembly. The reason of the dark line occurrence related with the positioning accuracy and the manufacturing margin were provided here.

3D Modeling of Single-Domain and Multi-Domain Vertical Alignment LCDs for Direct-View and Microdisplay Geometries

We successfully developed a 3D liquid crystal display (LCD) modeling program and applied the program to modeling the single-domain vertical alignment (VA) and intrinsic fringe field controlled multi-domain vertical alignment (IFF MVA) LCDs. Our study showed that proper and stable IFF MVA operation was obtained in the microdisplay geometry but not in the direct-view geometry, whereas regular VA operation was obtained in the direct-view geometry but not in the microdisplay geometry.

From First to Fourteen Optics of Liquid Crystals Meeting, Geometrical Optics Approximation to 2 × 2, and Optical Bistability to Multi-Domain Vertical Alignment LCDs

As a liquid crystal researcher, I was delighted to attend the first Optics of Liquid Crystals meeting, chaired by Professor Santamato and held in Napoli, Italy 25 years ago in 1986. Over the ensuing years, I was fortunate to present papers at following OLC meetings, and had the opportunity to serve in organization and advisory committees. To celebrate the OLC's 25th year anniversary, I have provide commentary on the early OLC meetings followed by a review on the optical field induced Freedericksz transition and the intrinsic optical bistability, geometrical optics approximation, generalized geometrical optics approximation and the 2 × 2 matrix, and also the progress in the wide-viewing angle LCDs and multi-domain vertical alignment LCDs.

High-transmittance Multi-domain Vertical Alignment Liquid Crystal Device with Protrusion Structure

We propose a high-transmittance multi-domain vertical alignment liquid crystal device with a protrusion structure. Disclination lines, which inevitably appear at the boundaries of domains in a multi-domain structure, can be reduced by adding a protrusion structure on the top substrate. The transmittance was improved by 11% using the proposed structure with no change of either the dark state or the operating voltage.

Multi-domain vertical alignment liquid crystal displays with ink-jet printed protrusions

For the fabrication of protrusions in multi-domain vertical alignment liquid crystal displays (MVA-LCDs), a series of complicated and expensive photolithographic processes has to be gone through for the wide viewing angles. In this research, we proposed and demonstrated a new manufacturing approach of the protrusion utilising ink-jet printing technology. Parallel lines were ink-jet printed on the substrates and solidified by a subsequent baking process, and then used as the protrusions of MVA-LCDs. The geometric dimensions of the protrusion patterns were optimised by the comparison of experimental observations and computer simulation results. The MVA-LCD cell was fabricated by arranging the protrusion lines forming right angles between the top and the bottom lines, which resulted in cross-line protrusions. Due to the square-shaped geometric arrangement of the protrusions, the vertically aligned LCs formed the symmetric four-domains in the MVA-LCD cell. With the help of a surface polymer-stabilisation technique, the response time of the LC molecules under the electric field was significantly improved. Therefore, we can conclude that, without sacrificing the viewing angle and response time of MVA-LCD, the printing technique for the formation of the protrusions can give us a new fabrication opportunity with low cost in contrast to the conventional photolithography process.

Pixel electrode structure for high transmittance in a multi-domain vertical alignment liquid crystal display device

We propose a pixel electrode structure for the multi-domain vertical alignment liquid crystal mode with high optical efficiency. We form a micro-slit electrode structure on the top substrate to reduce the width of disclination lines at domain boundaries. We insert additional electrodes on the bottom substrate to improve the transmittance at the edges of each pixel. We confirm that using both structures, the transmittance can be increased from 22.9% to 27.3% with no change in the operating voltage.

Analysis of the generation of multi-domain in vertical alignment (VA) mode caused by the fringe field on the side of the lower substrate

The generation of multi-domain vertical alignment (VA) is important in order to reduce the dependence of electro-optical characteristics on viewing angle characteristics. Fringe fields of different intensities are generated by the control electrode and slit pattern of the pixel electrode on the side of the lower substrate. These fringe fields are used to generate the multi-domain inside the liquid crystal cell. As the voltage of the control electrode is fixed and AC voltage is applied to the pixel electrode, domains of different configurations are induced depending on the (+) or (-) sign of the first frame. Once domains are generated, these remain unchanged for much longer than the duration time of one frame, even at the pixel voltage of the opposite sign.

Capacity improvement for color‐filter fabs through computer modeling and iterative simulation

Abstract— This study proposes the iterative Simulation‐Based Release (ISR) policy for color‐filter (CF) fabs based on iterative simulation. In the studied CF fabs, multi‐domain vertical‐alignment (MVA) equipment has the capability and flexibility to provide additional production capacity of black‐matrix (BM) and red, green, and blue (RGB) layers. Fab throughput can be increased by setting up MVA equipment to process BM and RGB layers when its available production capacity is larger than the scheduled manufacturing target. An AutoMod simulation model was developed and validated based on a real CF fab in Taiwan. A heuristic lot release plan was developed and used as the input of simulation. A better release plan can be developed by taking advantage of the MVA's line idle periods over the planning horizon generated from simulation and releasing new lots to the MVA line to increase its throughput. Release plans can be modified iteratively when the simulation results of the previous release plans show sufficient idle periods for the MVA line operation. The case study demonstrated that the proposed ISR is effective in idle‐time reduction (more than 60%) and throughput improvement (more than 2% in following months).

P‐72: Cost Effective Multi‐domain Vertical Alignment Liquid Crystal Display using Ink‐jet Printed Protrusions

AbstractA multi‐domain vertical alignment device using a new method for forming protrusions is proposed. In the device, the photo‐sensitive ink was printed with line shape forming protrusions on the substrates. Then the cell was assembled with crossed‐line shaped protrusions on top and bottom substrates. Owing to symmetrically positioned protrusions, the vertically aligned LCs form multi‐domain in on state and with the help of surface polymer‐stabilization technique, the response time is greatly improved. Consequently, the proposed device using protrusion by any printing method shows excellent performance such as wide‐viewing‐angle and fast response time without conventional photolithography process.

Enhancing the Brightness of Parallax Barrier Based 3D Flat Panel Mobile Displays Without Compromising Power Consumption

This paper presents an alternative approach for achieving higher optical efficiency in conventional parallax barrier 3D mobile displays. The method entails modifying and enhancing the protrusion structure of conventional multi-domain vertical alignment (MVA) pixel arrays plus the storage capacitors (Cst) of the pixel circuitry which increase effective pixel transmission area by a factor of 1.07. Hiding the modified storage capacitor under the parallax barrier strip increases the barrier gap or slit size by a factor of 1.52. The result is a structure that enhances mobile displays' optical efficiency by a compounded factor slightly over 60% without compromising power consumption.