Sang-Ho Yoon

17.2: Invited Paper: Improved PVA Mode with High Transmittance and Aperture Ratio

In this paper, we propose a cell structure which has high aperture ratio and transmittance with chevron-shaped electrode. As an exemplary cell, we selected PVA (Patterned Vertical Alignment) mode. Optical transmittance and aperture ratio were calculated with 3D-FEM numerical solver, TechWiz LCD, which is commercially available. The simulation results exhibited 4.8% improvement in aperture ratio and 11.3 % improvement in optical transmission.

Effect of surface anchoring energy on electro-optic characteristics of a fringe-field switching liquid crystal cell

Surface anchoring strength of the alignment layer on liquid crystal (LC) determines electro-optic characteristics in the LC devices. This paper investigates how azimuthal and polar anchoring strength affects the electro-optic performance of a fringe-field switching (FFS) mode associated with electrode structure, cell gap and dielectric anisotropy of the LC by numerical simulation. Our important findings in the FFS mode are that both azimuthal and polar anchoring energy can considerably affect the operating voltage and also maximum transmittance when using a LC with positive dielectric anisotropy; however, when using a LC with negative dielectric anisotropy only azimuthal anchoring energy affects electro-optic characteristics. The study proposes an optimal design of an alignment layer for maximizing transmittance in the FFS mode.

MODELING AND SIMULATION OF PARASITIC CAPACITANCES FOR ACTIVE MATRIX LIQUID CRYSTAL DISPLAYS (AMLCDs)

In this paper, we present a compact approach for modeling a parasitic capacitance in active matrix liquid crystal displays (AMLCDs) as a function of voltage applied at pixel electrodes. The director distribution as well as the potential distribution is estimated from a three-dimensional finite element method (FEM), while the parasitic capacitance within a liquid crystal cell is calculated with an energy moment method. Furthermore, we applied our proposed approach on the VA (vertical alignment) mode LC cell with a chevron-type electrode structure in order to understand the dynamic behavior of the cell.

The Influence of the Data Signal on Transmission Characteristics of LCD Cells

In this paper, we report our preliminary study about the influence of data signal on the optical properties of LCD cell which is operated at vertical alignment (VA) mode. The VA cell employed in this study has a size of 88 × 264 μm2 with a cell gap of 4 μm. In order to analyze the optical crosstalk between the data signals, we employed finite element method (FEM) for calculating the LC director distributions and 2 × 2 extended Jones method for optical transmission. Our simulation revealed that the voltage discrepancy between data signal and pixel electrode voltage is the main cause for the reduction of brightness as well as the generation of flickers.

THREE-DIMENSIONAL NUMERICAL SIMULATION FOR UNDERSTANDING THE FRINGE-FIELD EFFECT ON THE DYNAMIC BEHAVIOR OF LIQUID CRYSTAL

A three-dimensional numerical study for understanding the fringe-field effect on the dynamic behavior of liquid crystal is presented. Our three-dimensional numerical simulator (TechWiz LCD) is based on the FEM (finite element method) formulation of Ericksen-Leslie equation, flow equation, and Laplace equation. Since our FEM solver has a fully unstructured mesh generator, it is possible to investigate the dynamic performance of any mode of LC cell with an arbitrarily shaped electrode structure including a chevron-type LC cell. In this paper, we report our preliminary result on the simulation of the dynamic behavior of the fringe-filed switching (FFS) mode LC cell that is designed for the fast response and wide viewing angle. The simulated dynamic response of the director distribution for the FFS-mode LC cell is also compared with experimental observations. The simulation reveals that most of the directors over the LC cell experience horizontal rotations despite the existence of both the vertical and the horizontal electric fields in the LC cell.

A mesh generation algorithm for complex geometry [semiconductor process modelling]

A mesh generation algorithm for a curved surface is proposed to investigate a complex structure on a semiconductor substrate. This algorithm relies on the advancing front method with scattered data interpolation through a NURBS (nonuniform rational B-spline) surface. This algorithm has been applied to a cell-based simulation and a level set simulation. The NURBS mesh according to our algorithm excellently represented the surface evolution of the topography.

Three-dimensional modeling of the TED due to implantation damage

In this paper, we report the three-dimensional simulation result of the transient enhanced diffusion (TED) of dopants in the ion implanted silicon by employing our 3D semiconductor process simulator, INPROS system. In order to simulate three-dimensional TED redistribution of dopants in the silicon, the defect distributions after ion implantation was calculated by plus one model, followed by finite element numerical solver for thermal annealing. Our three-dimensional TED simulation could successfully interpret the pile-up phenomena by modifying the diffusion model to the pair-diffusion model. Excellent agreement between the simulated 3D profile and the SIMS data has been obtained.

Implementation of

In this paper, we report the first successful implementation, to the best of our knowledge of a Q-tensor model in a full three-dimensional (3-D) finite element method (FEM) simulator. Our FEM simulation code is based on the Landau–de Gennes Q-tensor model as well as the models of Dickmann and Nakagawa. The Oseen–Frank free-energy representation was formulated into a 3-D FEM code wherein tensor-order parameters as well as scalar-order parameters were employed for handling the defects and topological transitions such as splay-to-bend transition for the optically compensated bend (OCB) mode. The accuracy of our FEM simulator was verified using our simulation results with Moris simulation data for the OCB mode. Splay-to-bend transition voltage was calculated to be 4 V according to the Q-tensor-model-based simulation while the conventional vector-model-based FEM solver showed 8 V. Our comparative study revealed that the vector model overestimates splay-to-bend voltage for the OCB mode.

Q

In this paper, we propose a novel simulation scheme, which we call “block image simulation,” for the image analysis of a full thin film transistor liquid crystal display (TFT-LCD) panel. The proposed approach makes it possible to estimate viewable image for varying conditions as well as electrical characteristics of a TFT-LCD panel covering all the pixels. We also propose a compact circuit model for a TFT-LCD pixel, which accounts for the parasitic capacitors present between the neighboring gate and data lines and voltage-dependent liquid crystal (LC) pixel capacitance. In this work, we also report our successful simulation study on an exemplary 32 inch HDTV (1366 × 768) LCD panel in terms of crosstalk, shading, and gray scale error.

-Tensor Model in Three-Dimensional Finite Element Method Simulator

In this paper, we report a novel compact SPICE model for circuit simulation of LCD-TVs. In this work, we generated a SPICE model for a unit cell of TFT-LCD by taking all of parasitic capacitances and resistances into account. In order to extract circuit model from a unit cell, an electrical connectivity of resistors and capacitors was generated through the pattern analysis data including electrode and port data, followed by the calculation of the parasitics using a finite element method (FEM). Moreover, we employed a piecewise linear voltage-controlled capacitor model with calculated values in order to take voltage dependency of LC capacitance into account. Consequently, we generated a new kickback model which considers the influence of adjacent bus lines.