Byeong-Koo Kim

Recoverable Residual Image Induced by Hysteresis of Thin Film Transistors in Active Matrix Organic Light Emitting Diode Displays

A recoverable residual image is observed and analyzed in voltage driven active matrix organic light emitting diode (AMOLED) displays of which pixel circuits consist of two thin film transistors (TFTs) and one capacitor. The cause of the residual image is proven to be the hysteresis of the driving TFT in the pixel. The hysteresis of the p-channel TFT can be explained by hole trapping and de-trapping at the interface region of the channel. The recovery time of the residual image also strongly depends on the hysteresis level. We have found that the residual image can be eliminated by reducing the hysteresis level of TFTs.

Fast response time of fringe-field switching liquid crystal mode devices with reactive mesogens in a planar alignment layer

We report the response time of fringe-field switching (FFS) liquid crystal (LC) mode devices using an ultraviolet-curable reactive mesogen (RM) mixed in a planar alignment layer. The RM polymers within the alignment layer increase the surface azimuthal anchoring energy and the order parameter of the LC molecules. As a result, the falling time and the rising time in the FFS mode are improved by the enhanced azimuthal anchoring energy and the increased dielectric torque induced by higher order parameter of LCs.

Retardation Free In-plane Switching Liquid Crystal Display with High Speed and Wide-view Angle

In this paper, we propose an in-plane switching (IPS) mode for liquid crystal displays (LCDs) that, in principle, is free of retardation of the LC cell. Basically, the optical configuration of the LC cell consists of an A-plate and an LC layer for switching between the dark and bright states. We could achieve a fast response time compared with the conventional in-plane LC cell because the free retardation condition of the proposed LC cell enables us to reduce the cell gap even by quarter-wave retardation without any change of the optimized LC material in the transmissive mode. Experiments for verification of the proposed in-plane switching LC cells have shown a significant reduction of the rising time and falling time simultaneously due to the small cell gap. Furthermore, we also proposed an optical configuration for wide viewing property of the retardation free IPS LCD by applying the optical films. We proved the wide-view property of the retardation free IPS LCD by comparing its optical luminance with the calculated optical property of the conventional IPS LCD.

Highly Robust Integrated Gate-Driver for In-Cell Touch TFT-LCD Driven in Time Division Driving Method

This paper proposes a gate driver circuit for in-cell touch thin-film transistor (TFT) liquid crystal displays (LCDs) in which display and touch are driven at separate times to avoid cross-talk between display signals and touch signals. In the conventional gate driver circuit, transistors are connected between the gate node of pull-up transistor Q node and the low DC supply voltage V GL to reset the Q node. In the proposed gate driver gate driver circuit, these transistors are instead connected to the Touch Enable signal. During the display operation, the Touch Enable signal voltage is V GL to operate the proposed gate driver circuit in the same way as the conventional circuit. During touch operations, the Touch Enable signal changes to the high DC supply voltage V GH to keep the voltage at the Q node constant without leakage. In simulations and experiments, the proposed gate driver circuit prevented display failures caused by the interval during which the display pauses in the middle of a frame time for touch operation. The fabricated low temperature poly-silicon (LTPS) TFT-LCD has good multi-touch functionality without any ghost touches, and achieved 40-dB SNR and 120 Hz touch report rate.

Source Driver Channel Reduction Schemes Employing Corresponding Pixel Alignments for Current Programming Active-Matrix Organic Light-Emitting Diode Displays

We propose two types of novel scheme for reducing the number of output channels of driver-integrated circuit (D-IC) for the current programming compensation pixel structures of active-matrix organic light-emitting diodes (AMOLEDs). One is a 2:1 data demultiplexing technique that can reduce the number of output channels of D-IC by half. The proposed second scheme is a vertically aligned red (R), green (G), and blue (B) subpixel scheme instead of a horizontally aligned R–G–B subpixel one, which is regarded as the conventional pixel alignment scheme. We have also successfully implemented these schemes in a 2.4-in.-sized QCIF + (176 × RGB × 220) AMOLED using p-type excimer laser annealing (ELA) low-temperature polycrystalline silicon (LTPS) technology and evaluated key performance characteristics.

Effect of Rising Edge during Dynamic Stress With Duty Ratio in Amorphous InGaZnO Thin Film Transistors

We investigated the effects of rising edge during positive unipolar dynamic stress and bipolar dynamic stress under darkness and illumination with duty ratio D of dynamic stress from 1 to 50%. Threshold voltage shift ΔVth increased with effective time teff as the product of stress duration and D. ΔVth was higher during bipolar stress than during positive unipolar stress and under low D than at high D. Degradation of amorphous InGaZnO thin film transistor is related to the number and amplitude of rising edges. We suggest that an additional degradation under dynamic stress is originated from high electric field in channel region at rising edge.

Driving Method Compensating for the Hysteresis of Polycrystalline Silicon Thin-Film Transistors for Active-Matrix Organic Light-Emitting Diode Displays

A new driving method for active-matrix organic light-emitting diode displays is proposed and evaluated. The pixel structure of the proposed driving method is composed of three thin-film transistors (TFTs) and one capacitor. It inserts black data into display images to reset driving TFTs for the purpose of maintaining constant electrical characteristics of driving TFTs. The proposed driving scheme is less sensitive to the hysteresis of low-temperature polycrystalline silicon (LTPS) TFTs than the conventional pixel structure with two TFTs and one capacitor, and this scheme can virtually eliminate the recoverable residual image that occurs owing to the hysteresis characteristics of LTPS TFTs. In the proposed driving scheme, black data are inserted into displayed images so that the motion image quality is improved.

69.4: High Speed In-Plane Switching LCD with Free Retardation

We propose a high speed In-Plane Switching (IPS) liquid crystal display (LCD) with free retardation and wide view property. The proposed IPS mode can considerably reduce the response time of the LC cell. The optical configuration of the proposed IPS LC cell is composed of an A-plate and LC layer. We could achieve a fast response time without any change of an LC material in transmissive mode. The calculated and experimental results for an optical response of the proposed LC cell have shown a significant reduction of the falling time. Also, we investigated an optical configuration for wide viewing angle property of the high speed IPS LCD and compared iso-luminance with the conventional IPS LC cell.

52.1: A Study of Electrostatic Mura Specified for IPS LCD

In order to protect from the electrostatic damage it is common to deposit ITO thin layer on the rear side of CF substrate for the IPS based LCDs. But some polarizer assay of an IPS cell was found losing its protection ability as stored in the humid environment at relatively high temperature while the cell itself did not show the significant change. We clarified the root-cause and found the quality control factors.

A Transflective Liquid Crystal Display Driven by the Fringe Field Using a Liquid Crystal with a Negative Dielectric Anisotropy

Copyright uf0a92010 KIEEME. All rights reserved. http://www.transeem.org 134 † Author to whom all correspondence should be addressed: E-mail: lsh1@chonbuk.ac.kr