Ken Sumiyoshi

Molecular Orientation of Polyimide Films for Liquid Crystal Alignment Studied by Infrared Dichroism

An orientation structure of polyimide film, which is introduced by rubbing in liquid crystal device (LCD) fabrication, is clarified by polarized infrared spectroscopy. Samples rotated in-plane around the polarized incident beam reveal that the orientation direction of the rubbed polymer chain coincides with the rubbing direction. A sample-tilt measurement, in which the sample is tilted around the vertical axis, reveals that the polymer chains are tilted at an angle to the substrate surface. A simple model is proposed in order to estimate the thickness of the oriented layer of the rubbed film. In the model, the degree of dichroism of parallel and perpendicular polarized IR spectra is calculated as a function of polymer film thickness. Comparing the model with experimental data, it is determined that the thickness of the oriented layer is less than 14 nm.

A complementary TN‐LCD with wide‐viewing‐angle gray scale

— A complementary TN (C-TN) structure with two domains based on a simple fabrication process is proposed. To fabricate this C-TN cell, only one photolithography process and one rubbing process are added to conventional TN fabrication processes. This C-TN cell has symmetrical transmittance in the up and down directions. The gray-level order in the C-TN cell is maintained within a four-times-wider viewing angle than that in a conventional TN cell.

Light Leakage Analysis of In-Plane-Switching Liquid Crystal Displays

Light leakage in in-plane-switching liquid crystal displays (IPS LCDs) has been examined by image analysis and photon correlation measurement under a microscope. Static light leakage could be decomposed into a temperature-insensitive uniform part and a temperature-sensitive localized part. Nematic fluctuation effects in IPS LCDs are quantitatively clarified as follows. High-speed camera observation shows that dynamic fluctuation movements in a nematic layer modulate pixel images with static light leakage. The fluctuation level in the camera image is about 20% of the mean. However, spatial averaging over LCD pixel size suppresses fluctuation level into 3–5%. This result coincides with the photon correlation measurement results.

29.3: A 1450-ppi Field-Sequential System-on-Glass LCD Capable of Operating Over a Wide Temperature Range

We succeeded in developing a field-sequential color system-on-glass (SOG) LCD with a twisted-nematic mode using a novel material and novel driving method. We achieved a 4-ms response time and operation over a wide range of temperatures with a 2.1-μm cell gap. High optical efficiency was demonstrated with an aperture ratio of 59% and a 17.5-μm pixel pitch.

A two dimensional liquid crystal simulation for thin film transistor liquid crystal displays

Abstract A two-dimensional liquid crystal simulation, whose electrode configuration corresponds to that in a thin film transistor liquid crystal display (TFT-LCD), was carried out. Simulation results show that the lateral field between buslines and pixel electrode forms a reverse tilt domain. This reverse tilt domain leads to the disclination on the pixel electrode. The distance from the pixel electrode edge to this disclination location depends on the dielectric anisotropy and elastic constant for the liquid crystal. A small dielectric anisotropy or large elastic constant makes this distance small.

Improved Low-Temperature Response in Polymer-Stabilized Vertically-Aligned Cell

The longstanding weakness of liquid crystal displays (LCDs) is slow response at low temperature. We report that the in-cell polymer networks accelerate low-temperature response of vertically-aligned nematic cells. After refining the polymerization conditions of the LC and polymer, we succeed to improve from 143 ms to 31 ms in fall time at -20 °C.

Transflective IPS‐LCD with improved reflective contrast ratio

— In order to improve the reflective contrast ratio of transflective IPS-LCDs, a novel pixel design for a normally white reflective IPS has been proposed. In this design, the large-inter-electrode-spacing layout using a novel driving method and a double-layered electrode have effectively reduced the light leakage. By applying these two technologies, a transflective IPS-LCD has been successfully demonstrated with a high contrast ratio (15:1) in the reflective mode and a wide-viewing-angle characteristic in the transmissive mode.

22.2: RGB-Stacked Holographic Polymer Dispersed Liquid Crystal Device for Color Reflective Display

In stacking holographic PDLC devices, the parallax in the stack and the viewing angle should be considered. Based on a thin glass substrate (thickness = 0.1mm) assembly technique and an optical setup with a lenticular-lens array, RGB-stacked HPDLC devices with a low parallax and a large viewing angle (>15 degrees) have been developed.

Splayed TN Configuration Stability in Domain-Divided TN Mode

Abstract In the domain-divided TN mode for a wide-viewing-angle LCD, the LC directors are arranged in the splayed TN configuration by mismatching the pretilt directions on both substrates. For this mismatched pretilt alignment, the splayed TN configuration and the is shown that the reversely-twisted TN configuration are possible. It is more stable than the splayed TN in the high voltage range. The splayed TN stability proved to be evaluated by the balanced voltage, defined as voltage at which LC bulk energy becomes equal for two configurations in a simulation or voltage at which the boundary between two configurations is fixed in an experiment. Narrow twist angle, short chiral pitch and low pretilt angles raise the balanced voltage, i.e., stabilize the splayed TN configuration.

Transmittance Fluctuation from Nearly Extinct Nematic Cells

By introducing geometrical optics approximation (GOA) solutions to a nearly extinct homogeneous nematic director, the effects of assembly misalignment and director fluctuation on light leakage transmittance are studied. Transmittance expressions including fluctuation swing are obtained for three misoriented cases: misaligned homogeneous case, misaligned analyzer case, and mistwisted nematic case. Except for the misaligned homogeneous case with second-order fluctuation, all the other expressions have a linear contribution caused by their own misorientation. From these results, the transmittance variance from fluctuation at a misaligned situation is more enhanced than that in the extinction situation. After introducing thermal average statistics, expressions for the average and variance of transmittance with fluctuation are given. A numerical estimation for these expressions shows that in the misaligned homogeneous case by 1°, the standard deviation of transmittance is 20% of its average.