Patterned Vertical Alignment Research Articles

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.

Fast Turn-Off Switching of Vertically-Aligned Negative Liquid Crystals by Fine Patterning of Pixel Electrodes

We investigated the two-dimensional (2D) confinement effect on the switching of vertically-aligned negative liquid crystals (LCs) by an electric field applied between the top and bottom patterned electrodes. When an electric field is applied to a patterned vertical alignment (PVA) cell, virtual walls form in the middle of the gaps between and at the center of the patterned electrodes. These virtual walls formed in a PVA cell results in the turn-off time being dependent on the pitch of the patterned electrodes as well as the cell gap. We found that a short response time can be achieved by the fine patterning of pixel electrodes with little decrease in the transmittance. The obtained numerical results agree well with the model based on the 2D confinement effect of LCs.

Temperature-Dependent Behavioral Model of Active-Matrix Liquid Crystal Displays for All Types of Liquid Crystals

This paper proposes a temperature-dependent behavioral circuit model to predict optical characteristics of an active-matrix liquid crystal display with twisted-nematic (TN), patterned vertical alignment (PVA), and fringe-field switching (FFS) modes. The optical responses of liquid crystal displays (LCDs) are strongly affected by ambient temperature. We optimized time-constant parameters that describe the movement of liquid crystal molecules so that simulated optical responses of TN, PVA, and FFS LCDs best fit to the measured ones depending over the temperature range from 0 to 50 °C. We found that the time-constant parameters have a linear relationship with the ambient temperature, which enables us to anticipate the optical responses at any given temperature. The simulation results of the transient responses show excellent matches with the measurement ones regardless of ambient temperature.

Behavioral Model of Patterned Vertical Alignment Pixel in Active-Matrix Liquid Crystal Displays

This paper proposes a more accurate behavioral circuit model to predict transient responses of an active-matrix liquid crystal display (AMLCD) with a patterned vertical alignment (PVA) mode. In the case of the PVA mode, we observed that simulation errors increase when the conventional circuit model is directly applied to overdriven static and dynamic data transitions. To overcome this issue, we investigate the actual behavior of the liquid crystal (LC) molecules in the PVA AMLCD pixel using a high-speed camera attached to a microscope. We discovered that the behavior of the LC molecules is significantly dependent on their proximity to the edges of transparent electrodes. Based on this investigation, we propose a first-order circuit model that has two LC groups with two different response characteristics. The proposed model is embedded in a circuit simulator using an analog hardware description language. Simulation results show that the transient optical responses are considerably more accurate than the conventional responses for any data transitions, including overdriven transitions.

P.102: Improvement of Gamma Curve Distortion in VA LCD by using Optical Film Patterned Retarder

AbstractIn this paper, we improved the γ‐curve distortion at off‐axis direction in a 4‐domain (4‐D) patterned vertical alignment (PVA) liquid crystal (LC) cell by applying a pair of the film patterned retarder (FPR) system with the A‐film property at the conventional wide‐view (WV) PVA LC cell. In order to achieve the excellent γ‐curve in the 4‐domain LC cell, we optimized the parameter of the pair of the patterned A‐film by using the two‐dimensional parameter space method, which calculates the polarization difference between the normal direction and the all viewing directions under voltage applied state. As a result, we confirmed that the gamma distortion index (GDI) of the proposed optical structure is reduced to over 80% without any loss of the optical luminance and the contrast ratio in the dark state.

A Behavioral Circuit Model of Active-Matrix Liquid Crystal Displays for Optical Response Simulation

We propose a behavioral circuit model to precisely predict optical responses of an active-matrix liquid crystal (LC) display (LCD) using a patterned vertical alignment (PVA) mode. To get more accurate simulation results, we propose two LC groups with different time constants for a pixel after observing the LCD pixels by using a high-speed camera. In addition, we include a time-delay concept into our behavioral model for brightening or rising transitions. We describe the behavior of the PVA-LCD by using the analog hardware description language Verilog-A. We simulate the PVA-LCD panel by importing the behavioral circuit model in the circuit simulator SmartSPICE. The simulation results of the transient optical responses show excellent matches with the measurement ones.

Optimization of electrode structure to control liquid crystal director nearby domain boundary in a Z-shape patterned vertical alignment mode

Various pixel structures have been proposed in the patterned vertical alignment (PVA) mode to improve transmittance and response time because collisions of the liquid crystal directors are inevitable near domain boundary region. One of them is well known as Z-shape structure, which shows multi-domain characteristic but low transmittance due to forming disclination lines at the domain boundary. This characteristic comes from the LC director that cannot tilt down to 45° with respect to the transmissive axis of crossed polarizers. In order to overcome this problem, we proposed a new pixel structure which improves transmittance while keeping the number of masks same as before. Consequently, the proposed structure improved transmittance up to 18% compared with conventional Z-shape structure.

Fast Eight-Domain Patterned Vertical Alignment Mode with Reactive Mesogen for a Single-Transistor-Driving

We proposed a wide-viewing patterned vertical alignment (PVA) mode with eight-domains driven by a single transistor. The eight-domain PVA mode was fabricated by introducing two different pretilt angles in a pixel using polymerized reactive mesogens (RMs) within alignment layer. The pretilt angles are simply controlled by an applied voltage during illumination of ultraviolet light for polymerization of the RMs. In addition, the polymerized RMs give rise to defect-free transition in our advanced PVA mode and thus fast response can be achieved over whole grey level.

Patterned Vertically Aligned Mode with a Single Cell Gap for Transflective Operation

In this paper, we propose a novel patterned vertical alignment (PVA) architecture with a single cell gap for transflective operation of an LC cell. The proposed architecture has a feature wherein a chevron-shaped electrode is rotated by 90 degree in the counterclockwise manner in an effort to significantly improve the aperture ratio. Since the data line is located under the pixel electrode, we can efficiently eliminate the space between the data line and the pixel electrode. Our numerical simulation revealed that the aperture ratio of the proposed transflective PVA cell improves approximately by 4.8% over the conventional transmissive PVA cell.

Surface-controlled patterned vertical alignment mode with reactive mesogen

We proposed a patterned vertical alignment (PVA) mode controlled by a modified surface with ultraviolet (UV) curable reactive mesogen (RM) mixed with vertical alignment material for a liquid crystal display (LCD) with fast response time. In the surface-controlled PVA (SC-PVA) mode, the RM monomers in the alignment layer are polymerized along the LC directors by UV exposure under an applied voltage. The polymerized RMs produce a pretilt against the substrate normal depending on the applied field direction in the patterned electrode configuration. In such SC-PVA mode, fast response time was achieved at whole grey levels with the predetermined rotational preference of the LC directors governed by the pretilt direction.

45.1 Fabrication of Fast Switchable Patterned Vertical Alignment Mode Using Modified Surface with Reactive Mesogen

AbstractWe proposed a new fast switchable patterned vertical alignment (PVA) mode using UV curable reactive mesogen (RM) which was mixed with vertical alignment layer. In this mixed alignment layer, the pretilt angle was controlled according to an applied voltage during UV exposure for curing the RM. As a result, the response time was dramatically improved at the whole grey levels by controlling the pretilt angle in conventional PVA mode.

Surface-Modification on Vertical Alignment Layer Using UV-Curable Reactive Mesogens

The patterned vertical alignment (PVA) liquid crystal (LC) mode shows a wide viewing angle and a perfect dark state at a normal direction. However, it is inevitable to avoid the formation of disclinations and the movement of defect points during stabilization of LC's reorientation. It is due to fact that the LC directors tilt downward in different directions with collisions between them by the fringe-electric field. Consequently, the transmittance decreases and the response time gets slower. In order to overcome this barrier, the pretilt angles in four different directions are introduced on the substrates utilizing UV-curable reactive mesogen (RM) monomers. According to our studies, concentration of RM, UV curing condition, and applied voltage to the cell are critical to achieve an optimized surface-modified PVA mode which provides the well-defined reorientation of the LCs with respect to an electric field. Moreover, morphological behaviors on surface of substrate depending on curing conditions were investigated in order to confirm the existence of the stabilized polymer.

Effect of the electrode edge on the viewing angle property of a patterned vertical alignment liquid crystal cell

This paper investigates the effect of the electrode edge of a patterned vertical alignment (PVA) liquid crystal (LC) device on the viewing angle characteristics. In general, a transmissive LCD applies an LC layer with half‐wave retardation for a bright state and with zero retardation for a dark state. The retardation of the LC layer would be distorted in each point, however, when a voltage is applied because of the non‐uniform voltage distribution in the electrode edge effect. In this paper, the feasibility of the full effect of the electrode edge on the viewing angle property is considered, and the optical viewing angles of the VA LCD with a uniform half‐wave LC layer and the PVA LCD with a practical non‐uniform LC layer are compared.

Control of liquid crystal director near signal lines and reduction of load of signal lines by optimized pattern of common electrode in the patterned vertical alignment mode

Abstract This study examined the electro-optical characteristics and stability of a liquid crystal director depending on the electrode patterning of a common electrode on the top substrate in patterned vertical alignment (PVA) mode. The new type of common electrode pattern suggests that the dark state of the device is improved by reducing the interfering electrical field caused by the signal lines, which can help to improve the aperture ratio and also the load-on signal lines were reduced, resulting in a decrease in power consumption.

28.2: The Molecular Orientation of Polyimide Alignment Layer used in TFT‐LCDs with NEXAFS Study

AbstractAromatic polyimide thin films are used as the alignment film in thin film transistor‐liquid crystal displays (TFT‐LCD's). The films play an important role in the initial alignment of the liquid crystal materials in LCD panels. Therefore, any structural or morphological deformation may lead to defect in the physical interactions thus malfunction of the display eventually. for example, an LCD is known to bear image sticking problem when it is assembled following 3 days or longer stagnancy in the process after main curing of the layer. In this paper, the molecular orientation of polyimide surfaces with respect to the stagnancy is investigated by means of surface sensitive Near Edge X‐ray Absorption Fine Structure (NEXAFS) spectroscopy. NEXAFS measurements clearly reveal preferred in‐plane and out‐of‐plane orientation of phenyl and C=O groups at the surface of the polyimide thin film in regard to the stagnancy after main curing. with longer stagnancy phenyl and C=O groups preferred in‐plane orientation. The preferred in‐plane orientation within the film can accelerate the image sticking problem in LCD's operating in PVA mode. Based on the result, vertical alignment of polyimide pendant group is found helpful for the better alignment of LC molecules in LCD's operating in the patterned vertical alignment (PVA) mode.

Viewing angle switching of patterned vertical alignment liquid crystal display

Viewing angle control of a patterned vertical alignment (PVA) liquid crystal display using only one panel is investigated. In conventional PVA modes, a vertically aligned liquid crystal (LC) director tilts down in four directions making 45° with respect to crossed polarizers to exhibit a wide viewing angle. In the viewing angle control device, one pixel was divided into two sub-pixels such that the LC director in the main pixel is controlled to be tilted down in multiple directions making an angle with the polarizer, playing the role of main display with the wide viewing angle, while the LC director in the sub-pixel is controlled to be tilted down to the polarizer axis, playing the role of sub-pixel to the viewing angle control for the narrow viewing angle. Using sub-pixel control, light leakage or any type of information such as characters and image can be generated in oblique viewing directions without distorting the image quality in the normal direction, which will prevent others from peeping at the displayed image by overlapping the displayed image with the made image.

Multidimensional Modeling of Liquid Crystal Director Field in the Patterned Vertical Aligned LC Cell Using the Fast Q-Tensor Method

In this article we model the liquid crystal director field in the Patterned Vertical Alignment (PVA) LC using the fast Q-tensor method, which can model multidimensional director configurations with defects in the liquid crystal director field. In this work we model the LC director field with same condition of the real cell using fast Q-tensor method. Different from the result of the 2 dimensional calculation, in case of 3 dimensional simulation result, the defect line from the phase transition on the slit is not occurred. Since the generated defects due to geometry of the slit disturbed the phase transition in the middle of slit. We modeled the defect nucleation from geometry of the slit and LC director field of the conventional PVA cell. As a result, we could calculate optical transmittance of the conventional PVA cell.

Multi-domain PVA LCD Cell: Pros and Cons

In this article, we report our comparative study on the electro-optical properties between the conventional patterned vertical alignment (PVA) cell and super-patterned vertical alignment (S-PVA) cell. Electro-optical properties of these cells are calculated with 3D FEM numerical solver, TechWiz LCD, which is commercially available in the market. Our simulation results implies that the color difference of S-PVA can be improved by more than 13% over the traditional PVA cell since S-PVA mode has twice as many domains as the conventional PVA mode.

Novel Patterned Vertical Alignment LCD for Mobile Application with High Transmittance and Reliability

We developed a novel Patterned Vertical Alignment (PVA) LCD for mobile application with high transmittance and reliability by optimizing the design rule, fabrication process and LC materials. Our new design rule enabled an increase of 36% aperture ratio (A/R) and better electro-optical performance compared with those of the conventional PVA structure. Image sticking and edge smudge level also were reduced by using newly developed alignment material and ultraviolet (UV) sealant.

Patterned Vertical Alignment Liquid Crystal Cell with Crossed Stripe-Electrode Patterns

We propose crossed stripe-electrode patterns for a vertically-aligned liquid crystal (LC) cell. The proposed electrode structure forms the radial LC distribution with the point singularity S = + 1 in the presence of the applied electric field, resulting in the wide viewing angle characteristics as well as the reduced color-shift compared to the conventional patterned vertical alignment (PVA) cell. Moreover, the radial LC distribution with the point singularity results in an increased transmittance compared to the conventional PVA cell, because the region with zero transmittance only occurs at the singular point.