Patent Publication Number: US-6707524-B2

Title: Fringe field switching mode liquid crystal display, and fabrication method therefor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fringe field switching (FFS) mode liquid crystal display (LCD), and in particular to an FFS mode LCD and a fabrication method therefor which can improve an image quality by separately aligning one pixel so that pixel voltages can offset each other to be a zero voltage. 
     2. Description of the Background Art 
     A conventional thin film LCD is used as an information display device such as an information display window of a portable terminal, a screen display of a notebook computer, and a monitor of a laptop computer. 
     Especially, the LCD can replace a general cathode ray tube type monitor (CRT), which has high industrial applicability. 
     In the conventional LCD is generated a remaining image of a previous frame for a few seconds. Even though a fixed image pattern is applied to the liquid crystal for a predetermined time and the image pattern is removed, the image pattern remains weakly for a predetermined time. 
     In an in plane switching (IPS) mode or a fringe field switching (FFS) mode for embodying a field angle wider than a general TN mode, the remaining image is maintained for a long time. 
     Ions are moved in one direction due to DC voltage elements transmitted in driving the liquid crystal, and thus a signal voltage is distorted to generate the remaining image. 
     Such a remaining image is frequently generated in the IPS mode LCD for driving the liquid crystal by forming electrodes on one substrate, as compared with the TN mode LCD for driving the liquid crystal by forming electrodes on upper and lower substrates. 
     The conventional FFS mode LCD will now be explained with reference to FIGS. 1 and 2. 
     FIG. 1 is a cross-sectional view illustrating a pixel structure of the conventional FFS mode LCD. 
     FIG. 2 is a plan view illustrating the pixel structure of the conventional FFS mode LCD. 
     The conventional FFS mode LCD forms a first transparent electrode Vcom;  4  on a glass substrate  2 , and forms an insulating film  6  thereon. 
     A second transparent electrode Vdd;  8  is formed on the insulating film. 
     A plus frame voltage and a minus frame voltage are applied to the pixel electrode  8 . Accordingly, the voltages offset each other, and an average voltage becomes zero. 
     However, slight DC elements are generally applied between the plug frame and the minus frame due to parasitic capacitance. Here, reference numeral  10  denotes gate lines, and  12  denotes data lines. 
     As described above, positive ions are moved in a cathode direction due to the DC elements, and fixed to a rear film in the cathode direction. 
     As a result, the signal voltage is distorted by the ions fixed to the rear film of the cathode electrode region. In the case of negative ions, the ions are moved in an anode direction, to cause the remaining image. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a fringe field switching mode liquid crystal display and a fabrication method therefor which can remove a remaining image due to a residual DC voltage, by dividing a fringe field switching mode pixel into at least two, and enabling the adjacent pixels to have opposite polarities, so that the voltages applied to the pixel has a zero voltage state. 
     In order to achieve the above-described object of the invention, there is provided a fringe field switching mode liquid crystal display, including: gate lines and data lines aligned on a transparent insulating substrate to vertically cross each other; common electrode lines aligned horizontally to the gate lines; a pixel region defined in a space formed by the gate lines and data lines; a first transparent electrode formed in the pixel region, and divided into at least two regions; and a second transparent electrode insulated from the first transparent electrode, and divided on the first transparent electrode as many as the first transparent electrode, a data voltage being applied to the second transparent electrode in a first region and to the first transparent electrode in a second region, a sum of the voltages applied to the pixel region having a zero voltage. 
     In addition, there is provided a method for fabricating a fringe field switching mode liquid crystal display having gate lines and data lines aligned on a transparent insulating substrate to vertically cross each other, common electrode lines aligned horizontally to the gate lines, a thin film transistor formed by a source and drain extended from the data line, and the gate line, and a pixel region defined in a space formed by the gate lines and data lines, including the steps of: forming a first transparent electrode in the pixel region to be divided into at least two regions; and forming a second transparent electrode to be insulated from the first transparent electrode and divided on the first transparent electrode as many as the first transparent electrode, a data voltage being applied to the second transparent electrode in a first region and to the first transparent electrode in a second region, a sum of the voltages applied to the pixel region having a zero voltage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become better understood with reference to the accompanying drawings which are given only by way of illustration and thus are not limitative of the present invention, wherein: 
     FIG. 1 is a side-sectional view illustrating a pixel structure of a conventional FFS mode LCD; 
     FIG. 2 is a plan view illustrating the pixel structure of the conventional FFS mode LCD; 
     FIG. 3 is a cross-sectional view illustrating a pixel structure of an FFS mode LCD in accordance with the present invention; and 
     FIG. 4 is a plan view illustrating the pixel structure of the FFS mode LCD in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A fringe field switching (FFS) mode liquid crystal display (LCD) in accordance with a preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. 
     FIG. 3 is a cross-sectional view illustrating a pixel structure of the FFS mode LCD in accordance with the present invention. 
     FIG. 4 is a plan view illustrating the pixel structure of the FFS mode LCD in accordance with the present invention. 
     In the FFS mode LCD of the present invention, one unit pixel (not shown) is divided into two regions, namely regions A and B. For example, a data voltage Vdd is transmitted to an upper ITO electrode  28   a  through a drain electrode (not shown) of a data line  34  in region A, and the data voltage Vdd is transmitted to a lower ITO electrode  24   b  in region B. Here, Vcom, namely a common electrode is formed oppositely to the data voltage Vdd. 
     The voltages applied to regions A and B have the opposite polarities, so that a sum of the whole voltages in one pixel can be a zero voltage. It is thus possible to remove the DC voltage causing a remaining image. 
     The LCD of the present invention for completely removing the DC voltage will now be explained in more detail with reference to FIGS. 3 and 4. 
     Referring to FIG. 3, the FFS mode LCD deposits a transparent electrode layer including ITO on a glass substrate  22 , and patterns the deposited layer to be divided into two regions, namely regions A and B, thereby forming first transparent electrodes  24   a  and  24   b . Here, region A including the first transparent electrode  24   a  is connected to a common electrode  30 , and region B including the first transparent electrode  24   b  is isolated. 
     Thereafter, a gate insulating film  26  is deposited on the whole structure including the first transparent electrodes  24   a  and  24   b , and selectively patterned to connect the first transparent electrode  24   b  of region B, thereby forming a contact hole (not shown). 
     A second transparent electrode layer (not shown) including ITO is deposited on the gate insulating film  26  having the contact hole (not shown), and selectively patterned to form second transparent electrodes  28   a  and  28   b . Here, the first transparent electrode  24   a  of region A and the second transparent electrode  28   b  of region B are connected to a common electrode  30 , namely Vcom electrode. 
     In addition, a thin film transistor (TFT, not shown) is formed on the gate line  32 , and a drain region of the TFT is connected to the second transparent region  28   a  of region A and the first transparent electrode  24   b  of region B. Therefore, an average voltage becomes a zero voltage. 
     In the FFS mode LCD, when the signal voltage Vdd of the data line  34  is applied through the TFT, the signal voltage Vdd is transmitted to the second transparent electrode  28   a  of region A and the first transparent electrode  24   b  of region B. 
     Here, the data voltage Vdd is applied to the second transparent electrode  28   a  positioned on region A in one first transparent electrode  24   a , and Vcom is transmitted to the second transparent electrode  28   b  positioned on region B in the other first transparent electrode  24   b.    
     Accordingly, when the data voltage Vdd is applied, the region A and the region B become the opposite polarities, and thus an average sum of the whole voltages in one pixel becomes zero. 
     As discussed earlier, in accordance with the present invention, the FFS mode LCD for removing the remaining image has the following advantages: 
     One FFS mode pixel is divided into two regions, and the voltages applied to both regions have the opposite polarities to offset each other, thereby removing the DC voltage to prevent the remaining image. Moreover, a contrast and image quality are improved by removing the DC voltage. 
     As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiment is not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalences of such metes and bounds are therefore intended to be embraced by the appended claims.