A Liquid Crystal Mode with Combined Fringe and In-Plane Switching Fields by Using a Bottom Floating Electrode Seong-Hyeon Yoo 1 , Min-Kyu Park 2 , Dong-Jin Lee 1, 3 , Cheolho Lee 2 , Gyu Yeop Shim 2 , Kyoung Ho Park 3 , Joun-Ho Lee 3 , Hyunchul Choi 3 , Byeong Koo Kim 3 , and Hak-Rin Kim 1, 2 1 Department of Sensor and Display Engineering, Kyungpook National University, Daegu, Korea 2 School of Electronics Engineering, Kyungpook National University, Daegu, Korea 3 LG Display Co., Ltd., Kyungsangbook-do, Korea Abstract We demonstrate a liquid crystal (LC) mode switched by combined fringe and in-plane switching (IPS) fields, which are self-adjusted by adopting a bottom floating electrode for enhanced electro-optical properties. In our LC mode structure, conventional IPS electrodes are formed as pixel electrodes and common electrodes on an insulating layer, and floating electrodes that are patterned per the sub-pixels are formed under the insulating layer. When the areas of the pixel and common electrodes are same, the voltage of the bottom floating electrode is spontaneously determined to be half the value of the pixel voltage, which ideally generates symmetric fringe fields with both pixel and common electrodes. Due to the in-plane fields additionally generated between the pixel and common electrodes, the proposed LC structure shows higher transmittance than fringe-field switching (FFS) and IPS LC modes. Transmittance of the conventional FFS and IPS LC modes is highly sensitive to the in-plane electrode’s width and spacing condition, but the proposed LC mode shows good transmittance without degradation under large variation condition of the in-plane electrode’s spacing-to-width ratio. Author Keywords liquid crystal; liquid crystal mode; fringe field; in-plane field; floating electrode 1. Introduction Liquid crystal (LC) has been applied to various display applications like as televisions (TVs), desktop monitors, tablet computers, and mobile phones due to the enhancement of electro-optical properties via developments of operating modes. First, twisted nematic (TN) LC mode was widely used in LC display (LCD) application because of its high transmittance property [1]. However, the viewing angle property of TN mode which is important property in LC display is very bad due to its twisted LC configuration. In order to develop a wide viewing angle LCD, many LC modes has been proposed, such as multi-domain vertical alignment (MVA) mode [2], in-plane switching (IPS) mode [3], and fringe field switching (FFS) mode [4]. In the MVA mode, wide viewing angle property is achieved thorough patterned pre-tilt angle of the LCs by the surface geometry, but the disclination line formed at the boundary of the domain decreases the transmittance. In the IPS mode, the viewing angle property is improved because the LC directors are reoriented in plane by in- plane fields formed between patterned pixel electrodes and patterned common electrodes. However, the transmittance above the pixel electrodes and common electrodes is very low because the horizontal field barely exists above the electrodes. Also, the IPS mode needs additional storage capacitors to keep the gray scale level during a flame, which cause the decrease of the aperture ratio [5]. In the FFS mode, the LCs at the region in the electrode edge is sufficiently rotated by the fringe field, which induces the LCs rotation at the region in the middle of electrode and then improves the transmittance above the electrodes. But, the transmittance of the FFS mode at the region in between the electrodes is relatively low compare with the IPS mode, and the high transmittance property in the FFS mode is shown only when the width and gap of electrode is narrow, but it is hard to fabricate the narrow width and gap of electrode in large panel display. Recently, Lee et al [6] proposed fringe in-plane switching (FIS) mode using the combination of the in-plane field and the fringe field through the in-plane electrode and the bottom plane electrode. Here, the transmittance of the FIS mode was improved than the FFS mode and the operating voltage was lower than the FFS mode, while keeping a wide viewing angle property. But, the FIS mode needs additional data lines and transistors, which decreases the aperture area. Therefore, the actual transmittance of the FIS mode is decreased. In this work, we demonstrate a LC mode switched by mixed electric fields of an in-plane and a fringe field using an in-plane electrode and a bottom floating electrode to enhance electro- optical properties. In the proposed LC mode, the fringe field as well as the in-plane field formed by in-plane electrode is formed via the bottom floating electrode without additional data input, where the voltage of the floating electrode is spontaneously determined to be a half value of the potential of the pixel electrode when the area of pixel and common electrodes are same. Keeping a wide viewing angle property, the proposed LC mode shows a high transmittance property than the fringe field switching (FFS) and the transmittance property according to the electrode gap is robust, which facilitates a fabrication process and enhances an electrode design margin. 2. Operation principle of the proposed LC mode Fig. 1. (a) Cross-sectional view of the proposed LC mode showing electric field lines in sub-pixel scale. (b) Equivalent circuit of the proposed LC mode. Fig. 1(a) shows a cross-sectional view of the proposed LC mode structure showing the electrode structure and electric field distributions. In the proposed LC mode structure, the comb- P-114 / S.-H. Yoo 1410 • SID 2014 DIGEST ISSN 0097-966X/14/4503-1410-$1.00 © 2014 SID