JOURNAL OF DISPLAY TECHNOLOGY, VOL. 6, NO. 4, APRIL 2010 115 Zigzag Electrodes for Suppressing the Color Shift of Kerr Effect-Based Liquid Crystal Displays Linghui Rao, Zhibing Ge, and Shin-Tson Wu, Fellow, IEEE Abstract—The electro-optic properties of Kerr effect based liquid crystal display (LCD) with zigzag electrode structure are studied using a three-dimensional simulator. The optimal bending angle of the zigzag in-plane switching (IPS) electrodes is found to be 90 , which is different from the conventional strip electrodes. Although the zigzag structure exhibits a slightly lower transmit- tance than the strip IPS electrodes, it significantly suppresses the color shift while providing a relatively wide viewing angle. Index Terms—Blue phase (BP), color shift, fast response time, in-plane switching, Kerr effect. I. INTRODUCTION L IQUID CRYSTAL displays (LCDs) are widely used nowadays for mobile devices, notebook computers, desktop monitors, and large screen TVs. For large screen LCD TVs, it is important to have fast response time, high contrast ratio, wide viewing angle as well as weak color shift. Recently, blue phase liquid crystal displays (BP LCDs) based on Kerr effect are emerging due to their attractive features, such as: 1) submillisecond response time which not only reduces motion picture image blurs but also enables color sequential operation; 2) isotropic dark state which leads to a wide and symmetric viewing angle, and 3) no need for alignment layers which greatly simplifies the fabrication processes [1]–[4]. However, till now almost all the ongoing research on BP LCDs focuses on in-plane switching (IPS) with strip electrodes [5], [6], and the color shift issue has not been addressed. In this paper, we investigated zigzag electrode structures for BP LCDs using a three-dimensional (3D) simulator developed in our group. These discussions apply equally well to the general Kerr effect-based LCDs, which include isotropic-to-anisotropic switching. The electro-optic properties of the zigzag structure under different bending angles, electrode width-to-spacing ra- tios were characterized by the voltage-dependent transmittance (VT) curve. We also found that IPS BP-LCD with zigzag elec- trode structure significantly suppresses the color shift while pre- serving a relatively wide viewing angle. The responsible phys- Manuscript received October 04, 2009; revised November 12, 2009 and De- cember 01, 2009. Current version published March 10, 2010. This work is sup- ported by Chi-Mei Optoelectronics Corporation (Taiwan). L. Rao and S.-T. Wu are with CREOL, The College of Optics and Photonics, University of Central Florida, Orlando, FL 32816 USA (e-mail: lrao@mail.ucf. edu; lrao@creol.ucf.edu; swu@mail.ucf.edu). Z. Ge was with CREOL, The College of Optics and Photonics, University of Central Florida, Orlando, FL 32816 USA. He is now with Apple, Inc., Cuper- tino, CA 95014 USA (e-mail: Zhibing@apple.com; zge@mail.ucf.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JDT.2009.2039463 ical mechanisms are discussed through the comparisons with conventional strip electrode IPS structure. II. DEVICE PHYSICS AND MODELING Blue phases exist in a narrow temperature range between the isotropic and helical cholesteric phase near the LC clearing temperature with cubic symmetry structure [7], [8]. These high speed electro-optical operations are mainly based on a local director reorientation within the unit lattice of the cubic blue phase structure [1]. Macroscopically, it appears as Kerr effect which is a second-order electro-optic effect occurred in opti- cally isotropic substances. When there is no voltage applied, the BPLC medium appears optically isotropic, and it becomes anisotropic when a strong electric field is applied. The induced birefringence can be expressed by [6], [9]: (1) where is the induced birefringence, is the wavelength, is the Kerr constant, is the maximum induced birefrin- gence, and the induced saturates at when the electric field E reaches a saturation field since cannot increase unlimitedly with the increasing electric field. Recently, our group has developed a device model for calcu- lating the electro-optic properties of the blue phase LCDs [10]. It consists of three steps: 1) calculate the potential distribution from solving the Poisson equation and then the distribution of electric field in the LC media; 2) calculate the induced birefringence by (1), limit it to be below the intrinsic of the LC/polymer composite and assign the local optic axis direction of each unit to be along the vector; and 3) calcu- late the voltage-dependent transmittance and other electro-optic properties with extended Jones matrix. III. ZIGZAG ELECTRODE STRUCTURE Current research of BPLC for display applications is con- ducted under the traditional strip electrode structure using IPS cells, as depicted in Fig. 1(a). The cell is placed between two crossed linear polarizers. The horizontal electric fields gener- ated from IPS electrodes induce phase retardation for the in- cident light. Here, represents the electrode width and is the spacing between the electrodes. Fig. 1(b) shows the zigzag elec- trode structure for blue phase LCDs, where stands for the bending angle of the electrodes. Our purpose is to compare the transmittance, viewing angle, and color shift between these two electrode configurations. 1551-319X/$26.00 © 2010 IEEE Authorized licensed use limited to: University of Central Florida. Downloaded on April 01,2010 at 16:19:14 EDT from IEEE Xplore. Restrictions apply.