Patent Document

RELATED APPLICATIONS 
     The present patent document is a Divisional of application Ser. No. 11/126,958, filed May 10, 2005, which claims the benefit of Korean Application No. 2004-32746 filed on May 10, 2004. Both of the foregoing applications are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an in-plane switching mode (IPS) liquid crystal display (LCD) device, and more particularly, to an in-plane switching mode LCD device capable of improving a contrast ratio by preventing light leakage through an alignment defective region resulting from a column spacer when rubbing an alignment layer by aligning the column spacer and a data line. 
     BACKGROUND OF THE INVENTION 
     With the development of various portable electronic devices such as mobile phones, PDAs and notebook computers, the demand for a light, thin and small flat panel display device is recently increasing. Research is actively being conducted for flat panel display devices such as an LCD (Liquid Crystal Display), a PDP (Plasma Display Panel), an FED (Field Emission Display), a VFD (Vacuum Fluorescent Display), or the like. Of them, the LCD device receives much attention due to its simple mass-production technique, easy driving system and high picture quality. 
     The LCD device has various display modes according to the arrangements of liquid crystal molecules. A TN-mode (Twisted Nematic Mode) LCD device has widely been used due to such advantages as high contrast ratio, rapid response time and low driving voltage. In such a TN mode LCD device, when a voltage is applied to liquid crystal molecules horizontally aligned with two substrates, the liquid crystal molecules rotate and then are almost vertically aligned with the two substrates. Accordingly, when a voltage is applied, the viewing angle of the TN mode LCD device becomes narrow due to a refractive anisotropy of the liquid crystal molecules. 
     To solve such a narrow viewing angle problem, various kinds of modes of the LCD device having a wide viewing angle have recently been proposed. Among them, an IPS-mode (In-Plane Switching Mode) LCD device is actually being mass-produced. The IPS-mode LCD device aligns liquid crystal molecules on a plane by forming at least a pair of electrodes in parallel with each other in a pixel and then forming a horizontal electric field substantially parallel with the surface of the substrate between the two electrodes. 
       FIG. 1  illustrates a structure of the above-described IPS-mode LCD device. As shown in  FIG. 1 , an IPS-mode LCD has a structure that electrodes disposed in one pixel and forming a horizontal electric field are bent. The electrodes are bent to divide a pixel into two domains, thereby improving a viewing angle characteristic. 
     As shown in  FIG. 1 , a gate line  3  and a data line  4  disposed vertically and horizontally define a pixel of an liquid crystal panel  1 . Although only one pixel, (n, m) th  pixel, is illustrated in  FIG. 1 , the liquid crystal panel  1  has ‘N(&gt;n)’ number of the gate lines  3  and ‘M(&gt;m)’ number of the data lines  4 , and thus has ‘N×M’ number of pixels. At this time, the data line  4  is bent at a certain angle and symmetrically arranged with respect to the center of the pixel. 
     A thin film transistor  10  is formed near the crossing of the gate line  3  and the data line  4 . The thin film transistor  10  includes: a gate electrode  11  to which a scan signal from the gate line  3  is applied; a semiconductor layer  12  formed on the gate electrode  11  and forming a channel layer, which is activated when the scan signal is applied; a source electrode  13  and a drain electrode  14  formed on the semiconductor layer  12 , to which an image signal inputted from the outside is applied through the data line  4 . 
     A Common electrode  5  and a pixel electrode  7  formed in a zigzag shape and arranged substantially parallel with the data line  4  are disposed in the pixel. In addition, a common line  16  connected to the common electrode  5  is disposed at an upper part of the pixel, and a pixel electrode line  17  connected to the pixel electrode  7  is disposed on the common line  16  and overlaps the common line  16 . 
     A column spacer  18  for maintaining a uniform cell gap of the liquid crystal panel is formed on the gate line  3  on the left side of the data line  4 . 
     Referring to  FIG. 2 , the IPS-mode LCD device having such a structure will be described in more detail. As shown in  FIG. 2 , the gate electrode  11  is formed on a first substrate  20  and a gate insulating layer  22  is formed on the gate electrode  11 . The semiconductor layer  12  is formed on the gate insulating layer  22 , and the source electrode  13  and the drain electrode  14  are formed on the semiconductor layer  12 . A passivation layer  24  is formed over the first substrate  20 . 
     The common electrode  5  is disposed on the first substrate  20  and the pixel electrode  7  is disposed on the gate insulating layer  22 , so that a horizontal electric field is generated between the common electrode  5  and the pixel electrode  7 . 
     A black matrix  32  and a color filter layer  34  are formed on a second substrate  30 . The black matrix  32  where liquid crystal molecules do not operate is provided to prevent light leakage, and is mainly formed on the thin film transistor  10  region and between the pixels (i.e., regions of gate lines and data lines). The color filter layer  34  including R (Red), B (Blue) and G (Green) color filters is provided to display colors. In addition, the column spacer  18  is formed between the first substrate  20  and the second substrate  30  to maintain a uniform cell gap of the liquid crystal panel  1 . 
     In general, a ball spacer having a ball shape is widely used as a spacer. The ball spacers are distributed by being dispersed onto the substrate. When the spacers are dispersed, it is difficult to uniformly distribute the ball spacers on the substrate, and besides a precise cell gap cannot be maintained if the ball spacers are lumped. In addition, since the ball spacers themselves diffuse light which transmits a liquid crystal layer, they result in deterioration of image quality of an LCD device. To solve such a problem, the above-described column spacer is used. However, the column spacer  18  may cause the following problems. 
     Though not shown in  FIG. 2 , an alignment layer is applied to the first substrate  20  and the second substrate  30 . The alignment layer has an align direction by a rubbing process. In the rubbing process, the align direction is determined by rubbing a rubbing roll having a rubbing cloth against the alignment layer to thereby form grooves on the alignment layer. Accordingly, a region where grooves are not formed by the rubbing is formed around the column spacer  18  which has almost the same height as the cell gap of the liquid crystal panel  1 . In such a region, liquid crystal molecules are arranged in an irregular direction (i.e., alignment defective region) and light leakage occurs in a normally black mode. 
     Meanwhile, as shown in  FIG. 1 , when the common electrode  5  and the pixel electrode  7  are arranged at a certain angle with respect to a direction of the Y-axis and are symmetric in the pixel, the rubbing is performed along the direction of the Y-axis of the data line  4 . Accordingly, when the column spacer  18  is arranged on the left side of the data line  4 , a light leakage region in a band shape occurs on the left side of the data line  4  in the direction of the Y-axis, resulting in deterioration of an LCD display. 
     SUMMARY OF THE INVENTION 
     An in-plane mode (IPS) display device presented that is capable of improving a contrast ration by preventing light leakage occurring through an alignment defective region by disposing a column spacer along a black matrix. 
     By way of introduction only, as embodied and broadly described herein, in one aspect of the present invention, an in-plane mode display device comprises: a first substrate; a plurality of data lines substantially perpendicularly crossing the gate lines to define a plurality of pixels; a switching device at each pixel in a set of pixels; at one pair of electrodes in each pixel in the set of pixels to form a horizontal electric field substantially parallel with a surface of the first substrate; and a plurality of column spacers between the first substrate and the second substrate, column spacers of the set of pixels aligned in columns substantially perpendicular to the gate lines such that each column formed by the column spacers overlaps at least a portion of the data line most proximate to the column. 
     In another embodiment, an in-plane switching mode display device comprises a first substrate and a second substrate of a plurality of gate lines on the first substrate to define a plurality of pixels. At each pixel is disposed: a switching device; at least one first electrode and at least one second electrode disposed substantially parallel each other to form a horizontal electric field substantially parallel each other to form a horizontal electric field substantially parallel with a surface of the first substrate; and a column spacer disposed between the first substrate and the second substrate. The data line most proximate to the data line is bent at least once and the column spacer is disposed adjacent to the data line in an area where a bent portion of the data line is convex. 
     In another embodiment, an in-planes switching mode device comprises a first substrate and a second substrate and a plurality of gate lines and a plurality of data lines formed on the first substrate to define a plurality of pixels. At each pixel is disposed: a switching device; at least one pair of electrodes to form a horizontal electric field substantially parallel with a surface of the first substrate; and a column spacer at the crossing of the gate line and the data line. 
     In another embodiment, an in-plane switching mode display device comprises a first substrate and a second substrate and plurality of gate lines and a plurality of data lines on the first substrate to define a plurality of pixels. At each pixel is disposed; a switching device; at least one pair of electrodes at the pixel forms a horizontal electric field substantially parallel with a surface of the first substrate; a black matrix on the second substrate that blocks light; and a column spacer between the first substrate and the second substrate, the column spacer being aligned with the black matrix. 
     In another embodiment, an in-plane switching mode display device comprises a first substrate and a second substrate and a plurality of gate lines and a plurality of data lines on the first substrate substantially perpendicularly crossing to define a plurality of pixels. At each pixel is disposed: a switching device; at least one pair of electrodes to form a horizontal electric field substantially parallel with a surface of the first substrate; and a column spacer between the first substrate and the second substrate. Each data line has a bent portion and the column spacer is aligned with the bent portion. 
     The foregoing and other features and aspects of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
       In the drawings: 
         FIG. 1  is a plane view illustrating a structure of an in-plane switching mode in accordance with a related art; 
         FIG. 2  is a cross-sectional view taken along the line I-I′ of  FIG. 1 ; 
         FIG. 3  is a plane view illustrating a structure of an in-plane switching mode in accordance with one embodiment of the present invention; 
         FIG. 4A  and  FIG. 4B  are cross-sectional views taken along the line II-II′ of  FIG. 3 ; 
         FIG. 5  is a plane view illustrating a structure of an in-plane mode liquid crystal display device in accordance with another embodiment of the present invention; 
         FIG. 6  is a plane view illustrating a structure of an in-plane mode liquid crystal display device in accordance with yet another embodiment of the present invention; 
         FIG. 7  is view illustrating a large-area glass substrate on which a plurality of IPS-mode liquid crystal panels are formed; and 
         FIG. 8  is an enlarged view of an A part of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     Improving the contrast ratio is reduced when using the column spacers improves the quality of large-area IPS-mode liquid crystal display devices. However, there are realistically few methods for effectively removing a region where the rubbing is incompletely performed because of the column spacers. The most efficient method is that an incomplete rubbing region (alignment defective region), that is, a region where light leakage occurs, is located at a region where a black matrix is formed. Since such a method can eliminate the alignment defective region by simply blocking the inferior alignment region without changing a structure or a process (because the alignment defective region exists in the pixel), the contrast ratio can be improved without a cost increase or yield deterioration. In addition, since an additional black matrix is not formed but the already formed black matrix blocks the alignment defective region, the contrast ratio can be improved without reducing an aperture ratio. 
     By changing a location where a column spacer is formed or by changing a shape of a data line, the column spacer is aligned with a black matrix formed along the column spacer to thereby prevent light leakage. In addition, light leakage is prevented by aligning column spacers which are formed not inside a pixel but outside an liquid crystal panel with column spacers inside the pixel, that is, with the black matrix formed along the data line. 
     Hereinafter, with reference to the accompanying drawings, the present invention will be described in more detail. 
       FIG. 3  is a view illustrating a structure of an IPS-mode liquid crystal display device in accordance with one embodiment of the present invention. As shown in  FIG. 3 , an IPS-mode liquid crystal display device of the present invention includes a plurality of pixels defined by a plurality of gate lines  103  and a plurality of data lines  104 . A thin film transistor  110  which includes a gate electrode  111 , a semiconductor layer  112  formed on the gate electrode  111  and forming a channel layer, which is activated when a scan signal is applied, and a source electrode  113  and a drain electrode  114  formed on the semiconductor layer  112  is disposed on the crossing of the gate line  103  and the data line  104  in the pixel. 
     The data line  104  is bent in a zigzag shape to divide a pixel into two domains. That is, the pixel is bent at a certain angle on the basis of the center of the pixel and therefore is symmetric, so that the pixel is divided into two domains which compensate a main viewing angle. The data line  104  has a bending direction opposite to the data line of the related art IPS-mode liquid crystal display device illustrated in  FIG. 1 . That is, in the related art IPS-mode liquid crystal display device, a bent portion of the data line is convex toward a region where the thin film transistor is formed (i.e., the right region of the data line), while in the present invention, a bent portion of the data line  14  is convex toward a region where the thin film transistor  110  is not formed (i.e., the left region of the data line). In other words, the bending direction of the data line  104  in the present invention is opposite to that of the data line in the related art IPS-mode liquid crystal display device illustrated in  FIG. 1 . 
     A common electrode  105  and a pixel electrode  107  substantially parallel with the data line  104  is disposed in the pixel. Like the data line  104 , the common electrode  105  and the pixel electrode  107  are also bent to be convex toward the region where the thin film transistor  110  is not formed. In addition, a common line  116  connected to the common electrode  105  is disposed at an upper portion of the pixel. A pixel electrode line  117  connected to the pixel electrode  107  is disposed on the common line  116 , so that an accumulated capacity is formed between the common line  116  and the pixel electrode line  117 . 
     As shown in  FIG. 3 , a column spacer  118  is formed on the gate line  103  on the left of the data line  104 . That is, the column spacer  118  is formed on the gate line  103  where the thin film transistor  110  is not formed. Since the column spacer  118  is formed at each pixel, the column spacers are arranged in a line along a direction of the Y-axis on the left side of the data line  104  over the liquid crystal panel  101 . The column spacer  118  is formed of a thermosetting resin. The thermosetting resin and the like is applied and then patterned to form the column spacer  118 . Formed by the patterning, the column spacer  118  is also referred to as a patterned spacer. At this time, the column spacer  118  may be formed on the first substrate where the thin film transistor  110  is formed or on the second substrate  130  where the black matrix  132  and the color filter layer  134  are formed. 
     When the liquid crystal panel  101  is rubbed, a region where the rubbing is incompletely performed (i.e., an alignment defective region) is formed on the left side of the data line  104  along a direction where the column spacer  118  is arranged. As a result, light leakage occurs on the liquid crystal panel through the alignment defective region and therefore a light leakage region  119  in a band shape is formed on the left side of the data line  104  in the direction of the Y-axis. 
     Meanwhile, the common electrodes  105  are arranged adjacent to both sides of the data line  104 . The common electrode  105  prevents distortion of a horizontal electric field generated between the common electrode  105  and the pixel electrode  107  by shielding an electric field generated therebetween. Accordingly, since a black matrix (not shown) formed on the data line  104  region blocks not only light transmitted through the data line  104  region but also light transmitted through the common electrode  105  regions disposed at both side surfaces of the data line  104 , the black matrix should be formed to cover the common electrodes  105  formed at both side surfaces of the data line  104  as well as the data line  104 . 
     As shown in  FIG. 3 , the light leakage region  119  is arranged along the data line  104  and the common electrode  105  disposed on the left side of the data line  104 . The light leakage region  119  is arranged by the data line  104  whose bent portion protrudes toward the left region (i.e., a region where the thin film transistor is not formed). Such an arrangement of the light leakage region  119  will be clearly shown in comparison with the IPS-mode LCD device in the related art. As the light leakage region  119  is arranged along the data line  104  and the common electrode  105  on the left side of the data line  104 , the light leakage region  119  is arranged substantially along the black matrix. Thus, the black matrix blocks light which leaks outside the liquid crystal panel  101 . 
     Meanwhile, the IPS-mode LCD device in accordance with the present invention has almost the same structure of the IPS-mode LCD device illustrated in  FIG. 2 , other than a planar structure of the data line  104 , the common electrode  105 , and the pixel electrode  107 . However, the IPS-mode LCD device of the present invention is not limited to such a structure. As shown in  FIG. 4   a , in the IPS-mode liquid crystal display device of the present invention, the common electrode  105  may be formed on a first substrate  120  by the same process as the gate electrode  111  of the thin film transistor, and the pixel electrode  107  formed of a transparent conductive material such as ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide) may be formed on the passivation layer  124 . 
     Alternatively, as shown in  FIG. 4   b , both the common electrode of  105  and the pixel electrode of  107  formed of the transparent conductive material such as ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide) may be formed on the passivation layer  124 . The common electrode  105  and the pixel electrode  107  are formed of the transparent conductive material so as to improve brightness and aperture ratio of the IPS-mode LCD device. 
     As described, the IPS-mode LCD device in accordance with the present invention can block the light leakage region by the black matrix by allowing bending direction of the data line  104 , the common electrode  105  and the pixel electrode  107  to be opposite to that of the IPS-mode LCD device of the related art and aligning the column spacer  118  with the data line  104 . Thus, the IPS-mode LCD device in accordance with the present invention can improve the contrast ration of the liquid crystal panel  101 . 
     In terms of alignment of column spacer  118  and the data line  104 , when the column spacer is formed on the right side of the data line, not on the left side thereof, that is, when the column spacer is formed on a region where the thin film transistor is formed, the column spacer and the data line are also aligned with each other to thereby block the light leakage region effectively. The liquid crystal display device having this structure can be included as another embodiment of the present invention. 
     In addition, in terms of alignment of the data line and the column spacer, or alignment of the black matrix and the column spacer which are formed on the data line region, in which a column spacer  218  is formed at an intersection of a gate line  203  and a data line  204  is shown in  FIG. 5 . In such a structure, a black matrix formed along the data line  204  can block a light leakage region  219  because the light leakage region  219  formed by the column spacer  218  is disposed along the data line  204 . 
     Meanwhile, the IPS-mode LCD device of the present invention is not limited to a bent structure illustrated in  FIGS. 3 and 5 .  FIG. 6  shows an IPS-mode LCD device having a structure in which a data line  304 , a common electrode  305  and a pixel electrode  307  are not bent. Since a column spacer  318  is formed at the crossing of a gate line  303  and the data line  304  like the structure illustrated in  FIG. 5 , a rubbing defective region resulting from the column spacer  318  is formed along the data line  304 . Thus, the rubbing defective region is blocked by a black matrix formed long the data line  304 , thereby preventing a decrease of a contrast ratio which results from light leakage. 
     As described, the IPS-mode LCD device of the present invention may have various forms of a data line, a common electrode and a pixel electrode, and besides a column spacer may be disposed at various locations. In addition, the common electrode and the pixel electrode may be also formed on various locations (e.g.; a first substrate, a gate insulating layer or a passivation layer). The IPS-mode LCD device of the present invention, view in this light, is not limited to a specific structure illustrated in the drawings or described above. Though only the IPS-mode LCD device having a two-block (bock means a region where an image is substantially implemented) structure where two common electrodes and one pixel electrode are disposed in a pixel is illustrated in  FIGS. 3 ,  5  and  6 , a four-block IPS-mode LCD device where three common electrodes and two pixel electrodes are disposed or a six-block IPS-mode LCD device where four common electrodes and three pixel electrodes are disposed, or an IPS-mode LCD device having more blocks may be included in the present invention. 
     Meanwhile, processes for fabricating an IPS-mode LCD device is substantially performed on a glass substrate. That is, after a thin film transistor process and a color filter process are performed on the glass substrate where a plurality of liquid crystal panels are formed, the IPS-mode LCD device is completed by separating the glass substrate into unit panels. However, as the demand for a large-area LDC device increases, the glass substrate also increases in size and accordingly in weight. Thus, when processes are performed on a unit of the glass substrate, though the column spacer is formed on a panel region, it is hard to main a desired cell gap, because of the weight of the glass substrate. To solve such a problem, a uniform cell gap of the overall glass substrate, not of the liquid crystal panel, should be maintained by forming a column spacer on a dummy area where the liquid crystal panel is not formed. 
     As shown in  FIG. 7 , a large-area glass substrate  400  where a plurality of liquid crystal panels  401  are formed is illustrated. Though only four liquid crystal panels  401  are formed on the glass substrate  400  in  FIG. 7  for the purpose of simplicity, two, six or more liquid crystal panels  401  may be formed on the glass substrate  400 . 
     As shown in  FIG. 7 , column spacers  458  are formed on a dummy area  450  where the liquid crystal panel  401  is not formed. The column spacers  458  of the dummy area  450  support the glass substrate of the dummy area  450  and maintain a cell gap of the overall glass substrate, thereby maintaining a uniform cell gap inside the liquid crystal panels  401 . A rubbing process carried out on an alignment layer formed on the liquid crystal panels  401  is performed by a unit of the glass substrate  400 , not by units of one liquid crystal panel  401 . In other words, an alignment direction of each liquid crystal panels  401  is determined by rubbing the overall glass substrate  400  by using a large-size rubbing roll. However, since the column spacers  458  are disposed on the dummy area  450  of the glass substrate  400 , an alignment defective region  419  is formed by the column spacers  458  during the rubbing. Since the alignment defective region  419  of the dummy area  450  which is formed by the column spacers  458  is formed on the entire glass substrate  400  along a rubbing direction, the liquid crystal panels  401  also has the alignment defective region  419 . Accordingly, since the column spacers  458  of the dummy area  450  cause the same problem as the column spacers disposed in the pixel, light leakage due to the column spacers disposed on the dummy area  450  of the glass substrate  400  should be eliminated in order to improve the IPS-mode LCD device in quality. 
       FIG. 8  is an enlarged view of an A area of  FIG. 7 . As shown in  FIG. 8 , a plurality of column spacers  458  are formed on the dummy area  450  of the glass substrate adjacent to the liquid crystal panel  401 . Although the liquid crystal panel has the structure illustrated in  FIG. 3 , it may have the structures illustrated in  FIGS. 5 and 6 . A column spacer  418  is arranged on the left side of a data line  403 , that is, on a gate line  404  where a thin film transistor  410  is not formed. The column spacer  458  of the dummy area  450  is also aligned with the column spacer  418  of the liquid crystal panel  401 . Accordingly, when a rubbing process is performed on the glass substrate, an alignment defective region resulting from the column spacer  418  of the liquid crystal panel  401  and an alignment defective region resulting from the column spacer  458  of the dummy area are formed on the same location  419  in the pixel. 
     Meanwhile, since the alignment defective region  419  is disposed along a black matrix formed along a data line  404  (a black matrix formed over the data line  404  and common electrodes  405  at both side surfaces of the data line  404 ), the black matrix blocks light leakage through the alignment defective region  419 . Consequently, a contrast ratio can be improved by removing the light leakage region. 
     As described, in the present invention, the light leakage region can be effectively eliminated by aligning the column spacer  458  formed on the dummy area  450  of the glass substrate with the column spacer  458  of the liquid crystal panel  401  (i.e., by aligning the column spacer  458  of the dummy area  450  with the black matrix of the liquid crystal panel  401 ). The column spacer  458  of the dummy area  450  may be formed at various locations according to a structure of the liquid crystal panel  401 . In other words, when the liquid crystal panel  401  is formed of the structure of  FIG. 5  or  6 , a location where the dummy area  450  is formed may change according to a location of the column spacer  418  formed on the panel having the corresponding structure. 
     Since the column spacer  418  formed on the liquid crystal panel  401  is aligned with the data line  404 , the column spacer  458  of the dummy area  450  which is aligned with the column spacer  418  may be considered to be aligned with the data line  404  of the liquid crystal panel  401 , strictly speaking, with the black matrix formed along the data line  404 . 
     As described so far, since a column spacer formed on a liquid crystal panel and a column spacer of a dummy area are aligned with a black matrix formed along a data line, a light leakage region resulting from an alignment defective region by the column spacer is blocked by the black matrix. As a result, light leakage occurring on a screen can be blocked in a normally black mode, thereby improving a contrast ratio of an IPS-mode LCD device. 
     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 embodiments are 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 equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.

Technology Category: 3