Patent Abstract:
A liquid crystal display device capable of canceling out effects of signal charges, even when a columnar spacer bears signal charges, and preventing disturbance in a transverse electric field, includes pairs of columnar spacers that are disposed in two unit pixels adjacent to each other in a row direction or in a column direction. Each pair of columnar spacers is spaced from all other pairs of columnar spacers by at least two pixels of a row or a column.

Full Description:
The present application claims priority of Japanese Patent Application No. 2000-342163 filed on Nov. 9, 2000, which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display device and a method for manufacturing the liquid crystal display device and a CF (Color Filter) subtrate and more particularly to the liquid crystal display device in which a columnar spacer used to secure a cell gap between the CF substrate on which a colored layer is formed and a TFT (Thin Film Transistor) substrate on which the TFTs are formed, and to the method for manufacturing the liquid crystal display device and the CF substrate. 
     2. Description of the Related Art 
     The liquid crystal display device is widely used as a display device of various kinds of information devices or a like. In general the liquid crystal display device is so configured that a liquid crystal is put into a cell gap, in a hermetically sealed manner, between a CF substrate on which a colored layer having a plurality of one set of pixels made up of three kinds of unit pixels including a unit pixel for a red (R) color, a unit pixel for a green (G) color, and a unit pixel for a blue (B) color is formed; and a TFT substrate on which TFTs are adapted to operate as switching elements is formed on a face being opposite to the colored layer. Such the liquid crystal display device is roughly classified into two types, one being a TN (Twisted Nematic)—type liquid crystal display device and another being an IPS (In-Plane Switching)—type liquid crystal display device, depending on its display method. 
       FIG. 17  is a cross-sectional view schematically showing configurations of a conventional TN-type liquid crystal display device. As shown in  FIG. 17 , a liquid crystal  71  (liquid crystal molecule) is put into a cell gap  70 , in a hermetically sealed manner between, between a TFT substrate  51  and a CF substrate  61 . Moreover, the TFT substrate  51  includes a first transparent substrate  52  made up of glass or a like, a first polarizer  53  formed on a rear of the first transparent substrate  52 , a pixel electrode  54  formed on a surface of the first transparent substrate  52 , an interlayer dielectric  55  formed in a manner that it covers the pixel electrode  54 , a drain wiring  56  formed on the interlayer dielectric  55 , a passivation film  57  formed in a manner that it covers the drain wiring  56 , and a first oriented film  58  formed on the passivation film  57 . 
     The CF substrate  61  includes a second transparent substrate  62  made up of glass or a like, a second polarizer  63  formed on a rear of the second transparent substrate  62 , a common electrode  64  formed on a surface of the second transparent substrate  62  and a BM (Black Matrix) layer  65  formed on the surface of the second transparent substrate  62 , a colored layer  66  covering the common electrode  64  and the BM layer  65 , an OC (Over Coat) layer  67  covering the BM layer  65  and the colored layer  66 , and a second oriented film  68  formed on the OC layer  67 . 
     In the TN-type liquid crystal display device described above, by applying a driving voltage between the pixel electrode  54  of the TFT substrate  51  and the common electrode  64  of the CF substrate  61 , an electric field in a longitudinal direction relative to both the TFT substrate  51  and the CF substrate  61 , is produced, as indicated by arrows  72 . 
       FIG. 18  is a cross-sectional view schematically showing configurations of a conventional IPS-type liquid crystal display device. The configurations of the IPS-type liquid crystal display device shown in  FIG. 18  differ from those in the TN-type liquid crystal display device described above in that the pixel electrode  54  and the common electrode  64  are formed on the first transparent substrate  52  in the TFT substrate  51  so that the pixel electrode  54  and the common electrode  64  are insulated from each other with the interlayer dielectric  55  being interposed between the pixel electrode  54  and the common electrode  64 . 
     In such the IPS-type liquid crystal display device as described above, by applying a driving voltage between the pixel electrode  54  and the common electrode  64  formed on the TFT substrate  51 , an electric field in a horizontal direction relative to the TFT substrate  51 , is produced, as indicated by arrows  73 . By configuring above, in the case of the IPS-type liquid crystal display device, a direction of the liquid crystal molecule  71  along the surface of the TFT substrate  51  is determined, which can provide a wider viewing angle compared with the case of the TN-type liquid crystal display device. Therefore, the IPS-type liquid crystal display device (hereinafter, referred to simply as an LCD) is mainly and increasingly used. 
     In fabrication of the LCD, in order to secure the cell gap  70 , into which the liquid crystal  71  is put in a hermetically sealed manner, between the CF substrate  61  and TFT substrate  51 , a columnar spacer (not shown) made up of an insulating material is disposed between the CF substrate  61  and the TFT substrate  51 . Though the liquid crystal  71  is put in a hermetically sealed manner between the CF substrate  61  and the TFT substrate  51 , the liquid crystal  71  expands or shrinks depending on a change in ambient temperatures. Therefore, the columnar spacer has to be disposed SO that a liquid crystal panel is formed in a manner that it is somewhat crushed at ordinary temperatures. Moreover, the columnar spacer has to be disposed so that the cell gap  70  is formed uniformly within faces being opposite to each other between both the CF substrate  61  and TFT substrate  51 . However, there is a “trade-off” between these two needs. To satisfy these two needs simultaneously, a columnar area ratio CA defined as below has to be set within a range, as a precondition. The columnar area ratio CA is defined as follows:
 
Columnar area ratio  CA =( Px )·( Py )/( Lx )·( Ly )
 
where Px denotes a horizontal length of the columnar spacer, Py denotes a longitudinal length of the columnar spacer, Lx denotes a horizontal length of each of the unit pixels including the unit pixel for the R color, unit pixel of the G color, and unit pixel for the B color, and Ly denotes a longitudinal length of each of the unit pixels including the R, G, and B color pixels. That is, the columnar area ratio CA is defined as a ratio of a cross sectional area of the columnar spacer to an area of each unit pixel.
 
     The applicant of the present invention has already found that the above two needs can be approximately satisfied by disposing the columnar spacer so that the above columnar area ratio CA is set within a range of 0.05% to 0.15% (refer to Japanese Laid-open Patent Application No. 2001-117103, published on Apr. 27, 2001 after the filing date of Japanese Patent Application No. 2000-342163 of which the present application claims priority) 
     On the other hand, to avoid reduction in an effective area of the liquid crystal panel, it is desirous that the number of the columnar spacers is small and its sizes, that is, its horizontal length Px and its longitudinal length Py are small. Size of the columnar spacer is determined depending on fabrication accuracy of photolithography. If the size is too small, it is unstable in terms of strength. Therefore, both the horizontal length Px and the longitudinal length Py are set at approximately 8 μm or more. Moreover, the columnar spacer is disposed on a gate electrode (gate bus line) of the TFT which can provide a uniformly wide and flat place on the TFT substrate  51  and the horizontal length Px and longitudinal length Py have to be set so that they are smaller than a width P(G) (approximately 13 μm) of the gate electrode (not shown). Furthermore, when the horizontal length Px and longitudinal length Py of the columnar spacer have to be determined, it is necessary to take into consideration a shift “n” (approximately 3 μm or more) in superposition of the TFT substrate  51  on the CF substrate  61 . 
     Also, when the columnar spacer is disposed, consideration has to be given to a column density. The column density is defined as a ratio of the number of columnar spacers to one set of pixels  75  made up of three kinds of unit pixels for R, G, and B colors. For example, as shown in  FIG. 13A , when one columnar spacer  76  is disposed at any one (for example, the unit pixel for G color) of the unit pixels contained in one set of pixels  75 , the column density is defined as “1/1”. Moreover, as shown in  FIG. 13B , when one columnar spacer  76  is arranged in two sets of the pixel  75 , the column density is defined as “1/2”. As shown in  FIG. 13C , when one columnar spacer  76  is arranged in three sets of the pixel  75 , the column density is defined as “1/3”. This means that, when the configuration shown in  FIG. 13A  having the column density being “1/1” is considered as a standard configuration, the columnar spacer  76  in the configuration shown in  FIG. 13B  having the column density being “1/2” is thinned out, that is, the number of the columnar spacers  76  is reduced by a half and in the configuration shown in  FIG. 13C  having the column density being “1/3”, the number of the column spacers  76  is reduced by one third. 
     If the horizontal length Lx and longitudinal length Ly of each of the unit pixels for the R, G, and B colors, and the horizontal length Px and longitudinal length Py of the columnar spacer  76  in  FIGS. 13A  to  13 C are set at values as shown in a lower part of  FIG. 13A , the columnar area ratio CA can be calculated by using the expression shown above and the following values can be obtained.
     {circle around (1)} In the case of the column density being “1/1”-&gt;Columnar area ratio≈0.19%   {circle around (2)} In the case of the column density being “1/2”-&gt;Columnar area ratio≈0.095%   {circle around (3)} In the case of the column density being “1/3”-&gt;Columnar area ratio≈0.063%   

     Therefore, when compared with the columnar area ratio CA used as the precondition described above, the values obtained in the above cases of {circle around (2)} and {circle around (3)} are within the optimum range (0.05% to 0.15%). However, since a value being close to a mean value of the optimum range is preferable in actual operations, it is desirous that the columnar spacer  76  is disposed so that the configuration having the column density being “1/2” (the case of {circle around (2)}) boxed by a frame  77  shown in  FIG. 13B  can be provided. 
       FIGS. 14A ,  14 B, and  14 C are also diagrams explaining the column density of the columnar spacer  76  in which the horizontal length Lx and longitudinal length Ly of each of the unit pixels remain the same as those in  FIGS. 13A  to  13 C and the horizontal length of Px and longitudinal length Py of the columnar spacer  76  are different from those in  FIGS. 13A  to  13 C. 
     The columnar area ratio CA of each of the cases is as follows.
     {circle around (1)} In the case of the column density being “1/1”-&gt;Columnar area ratio≈0.285%   {circle around (2)} In the case of the column density being “1/2”-&gt;Columnar area ratio≈0.142%   {circle around (3)} In the case of the column density being “1/3”-&gt;Columnar area ratio≈0.094%   

     Therefore, in the example, values obtained in the cases {circle around (2)} and {circle around (3)} are within the optimum range of the columnar area ratio CA used as the precondition. However, for the same reason as above, it is desirous that the columnar spacer  76  is disposed so that the configuration having the column density being “1/3” (the case of {circle around (3)}) boxed by a frame  77  shown in  FIG. 14C  can be provided. 
     As described above, by changing the horizontal length Px and longitudinal length Py of the columnar spacer  76 , the column density that can satisfy the precondition is changeable. By changing the horizontal length Lx and longitudinal length Ly of each of the unit pixels, the column density that can satisfy the precondition is also changeable. However, when the horizontal length Px and longitudinal length Py of the columnar spacer  76  are to be changed, the change must be within the range of constraints described above. 
       FIG. 15  is a top view schematically showing configurations of the conventional LCD in which the columnar spacer  76  is disposed so that the columnar area ratio CA is set within the optimum range used as the precondition and the column density becomes “1/2”. As shown in  FIG. 15 , the conventional LCD is so configured that two columnar spacers  76  are arranged in four sets of the pixel  75  indicated by broken lines (two sets along a row direction and two sets along a column direction), that is, one columnar spacer  76  is arranged in two sets of the pixel  75 . Here, the columnar spacer  76  is disposed in, for example, the same unit pixels for G color and also in every other set of pixels  75  in a staggered manner. Thus, by disposing the columnar spacer  76  so that the columnar area ratio CA can satisfy the precondition and the column density becomes “1/2”, an elastic compositional deformation of the columnar spacer  76  is well balanced, which enables the columnar spacer  76  to be adaptable to changes in a thickness of the cell gap  70  caused by ambient temperatures. 
     However, the conventional LCD has a problem. That is, in the conventional LCD, since the columnar spacer  76  is arranged in the unit pixels for a same color in every other set of pixels  75 , when the liquid crystal  71  is driven, all the columnar spacers  76  bear signal charges being the same in polarity, which causes disturbance in a transverse electric field caused by the signal charge being the same in polarity. 
     This problem in the conventional LCD will be explained below by referring to FIG.  16 .  FIG. 16  is a diagram explaining a method for driving the conventional LCD. The liquid crystal making up the LCD has a property that it is crushed by continued application of a voltage being the same in polarity (positive or negative). To avoid this, the liquid crystal  71  (not shown in  FIG. 16 ) in the conventional LCD is driven by a dot reverse driving method in which a voltage being opposite in polarity is always applied alternately to the same unit pixel. Therefore, as shown in  FIG. 16 , a positive signal charge or a negative signal charge is written alternately in every unit pixel being arranged along the row direction X and a negative signal charge or a positive signal charge is written alternately in every unit pixel being arranged along the column direction Y so that each of the unit pixels adjacent to each other bears the signal charge being opposite in polarity. The reason why the positive or negative voltage is applied alternately to the unit pixels being adjacent to each other is to prevent flicker in displaying. 
     If the columnar spacer  76  is disposed in the unit pixels for the same color, for example, the G and G color pixels, for every other set of pixels  75 , as in the case of the conventional LCD shown in  FIG. 15 , since the signal charge being the same in polarity is always written in every other unit having the columnar spacer  76  being arranged in the column direction Y, the signal charge causes the columnar spacer  76  to be electrically charged. That is, the columnar spacer  76  disposed in the unit pixel “G” bears the electrical charge being the same in polarity (positive or negative). As a result, the traverse electrical field is disturbed by influence of the signal charge being the same in polarity. In  FIG. 16 , there is shown a range  78  in which the traverse field is disturbed and shows that the range extends to an entire region in the column direction Y in which the columnar spacer  76  is arranged. On the other hand, since there is no object to be charged in the unit pixel having no columnar spacer  76 , no disturbance in the traverse field occurs. 
     In the case of the IPS-type LCD in particular, since a method is employed to decrease specific resistance of the liquid crystal  71  in order to inhibit image retention, when the columnar spacer  76  is electrically charged, the electric charge in the liquid crystal panel gathers and the local specific resistance of the liquid crystal  71  is changed. Therefore, in the conventional LCD whose liquid crystal  71  is driven by the dot reverse driving method, if the columnar spacer  76  is disposed so that it is charged only when the signal charge having one polarity is applied, only electric line of force of the pixel voltage having one polarity enters the columnar spacer  76  and, as a result, the specific resistance of the liquid crystal  71  existing near the columnar spacer  76  is changed, which causes a failure in displaying such as flicker even when the liquid crystal  71  of the LCD is driven by the dot reverse driving method. 
     SUMMARY OF THE INVENTION 
     In view of the above, it is an object of the present invention to provide an LCD which is capable of canceling out effects of signal charges even when a columnar spacer bears the signal charges and preventing disturbance in a traverse electric field, a method for manufacturing the LCD and a CF substrate. 
     According to a first aspect of the present invention, there is provided a liquid crystal display device including: 
     a columnar spacer being interposed between a CF substrate and a TFT substrate; and 
     wherein a column density of the columnar spacer is smaller than 1 (one) and wherein the columnar spacer is disposed in two unit pixels being adjacent to each other and each bearing a signal charge being opposite in polarity. 
     In the foregoing, a preferable mode is one wherein a liquid crystal in the liquid crystal display device is driven by a gate line reverse driving method or a dot reverse driving method. 
     According to a second aspect of the present invention, there is provided a liquid crystal display device including: 
     a CF substrate on which a colored layer is formed so that unit pixels are arranged in a matrix form; 
     a TFT substrate on which TFTs are formed at a place being opposite to the colored layer; 
     a columnar spacer formed to secure a cell gap being disposed between the CF substrate and TFT substrate; and 
     wherein a liquid crystal is put into the cell gap in a hermetically sealed manner and wherein a columnar area ratio being a ratio of a cross sectional area of the columnar spacer to an area of the unit pixel is set within a range of 0.05% to 0.15% and each columnar spacer making up a pair of the columnar spacers is disposed in each of two unit pixels being arranged in a matrix form and being adjacent to each other at an arbitrary place along a row direction or column direction. 
     In the foregoing, a preferable mode is one wherein the unit pixel is driven by a dot reverse driving method when the columnar spacers are arranged along the column direction and wherein the unit pixel is driven by a gate line reverse driving method when the columnar spacers are arranged along the row direction. 
     According to a third aspect of the present invention, there is provided a liquid crystal display device including: 
     a CF substrate on which a colored layer is formed so that sets of pixels each set being made up of three kinds of unit pixels including a unit pixel for a red (R) color, a unit pixel for a green (G) color, and a unit pixel for a blue (B) color are arranged in a matrix form; 
     a TFT substrate on which TFTs are formed at a place being opposite to the colored layer; 
     a columnar spacer formed to secure a cell gap being disposed between the CF substrate and TFT substrate; and 
     wherein a liquid crystal is put into the cell gap in a hermetically sealed manner and wherein a columnar area ratio being a ratio of a cross sectional area of the columnar spacer to an area of each unit pixel is set within a range of 0.05% to 0.15% and the columnar spacer is disposed both in one unit pixel making up an arbitrary one set of pixels and in another unit pixel exhibiting a same color as exhibited by the unit pixel in another set of pixels being adjacent to the above one set of pixels along a column direction. 
     In the foregoing, a preferable mode is one wherein the unit pixel is driven by a dot reverse driving method. 
     According to a fourth aspect of the present invention, there is provided a liquid crystal display device including: 
     a CF substrate on which a colored layer is formed so that sets of pixels each being made up of three kinds of unit pixels including a unit pixel for a red (R) color, a unit pixel for a green (G) color, and a unit pixel for a blue (B) color are arranged in a matrix form; 
     a TFT substrate on which TFTs are formed at a place being opposite to the colored layer; 
     a columnar spacer formed to secure a cell gap being disposed between the CF substrate and the TFT substrate; and 
     wherein a liquid crystal is put into the cell gap in a hermetically sealed manner and wherein a columnar area ratio being a ratio of a cross sectional area of the columnar spacer to an area of each unit pixel is set within a range of 0.05% to 0.15% and the columnar spacer is arranged both in one unit pixel making up an arbitrary one set of pixels and in another unit pixel being adjacent to the unit pixel along a row direction. 
     In the foregoing, a preferable mode is one wherein the unit pixel is driven by a gate line reverse driving method. 
     Also, a preferable mode is one wherein the columnar spacer is disposed on a gate electrode of the TFT formed on the TFT substrate. 
     Also, a preferable mode is one wherein a pixel electrode and a common electrode are formed on the TFT substrate in a manner that the pixel electrode and the common electrode are insulated from each other. 
     Also, a preferable mode is one wherein, when one columnar spacer is disposed in any one in one set of pixels made up of three kinds of unit pixels including the unit pixel for the R color, the unit pixel for the G color, and the unit pixel for the B color, a column density is defined as 1/1 and wherein the columnar spacer is arranged so as to lower the column density, even when a plurality of sets of pixels is disposed in a manner that the sets of pixels are adjacent to each other, by reducing the number of the columnar spacers within a range in which the columnar area ratio is satisfied. 
     Also, a preferable mode is one wherein the columnar spacer is disposed in a plurality of sets of pixels so that the column density becomes 1/2. 
     According to a fifth aspect of the present invention, there is provided a method for manufacturing a liquid crystal display device including a CF substrate on which a colored layer is formed so that unit pixels are arranged in a matrix form, a TFT substrate on which TFTs are formed at a place being opposite to the colored layer and a columnar spacer formed to secure a cell gap being disposed between the CF substrate and the TFT substrate wherein a liquid crystal is put into the cell gap in a hermetically sealed manner and, the method including: 
     a process of forming the TFT substrate by incorporating at least one TFT in a surface of a first transparent insulating substrate; 
     a process of forming the CF substrate by first forming at least one colored layer on a surface of a second transparent insulating substrate being opposite to the TFT and then by forming the columnar spacer on the colored layer; and 
     a process of putting the liquid crystal into the cell gap secured by the columnar spacer disposed between the TFT substrate and the CF substrate, in the hermetically sealed manner. 
     In the foregoing, a preferable mode is one wherein the process of forming the CF substrate includes a process of first applying a photosensitive resin in a manner so as to cover the colored layer and then performing patterning on the photosensitive resin to form the columnar spacer. 
     According to a sixth aspect of the present invention, there is provided a CF substrate for being disposed opposite to a TFT substrate on which TFTs are formed, thereby forming a cell gap between the TFT substrate and the CF substrate, wherein a liquid crystal is put into the cell gap in a hermetically sealed manner, the CF substrate including: 
     a colored layer formed on a transparent substrate so that unit pixels are arranged in a matrix form; and 
     a columnar spacer is formed on the colored layer. 
     In the foregoing, a preferable mode is one wherein the columnar spacer is made up of photosensitive resins. 
     With the above configurations, each columnar spacer making up a pair of columnar spacers is disposed in each of two unit pixels being arranged in a matrix manner and being adjacent to each other along a row direction or a column direction at an arbitrary place in a plurality of places where unit pixels are arranged and each columnar spacer making up the pair of the columnar spacers bears a charge being opposite in polarity and therefore effects by a signal charge can be cancelled out. Moreover, when the columnar spacer is incorporated into the CF substrate, lithography technology is employed and therefore easy formation of the columnar spacer is made possible. In configurations of the CF substrate, the columnar spacer is formed on the colored layer and therefore the columnar spacer can be disposed easily at an arbitrary place. As a result, even when the columnar spacer bears the signal charge, the effects by the signal charge can be cancelled out and a disturbance of a traverse electric field can be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages, and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a top view showing configurations of an LCD according to a first embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of the LCD of  FIG. 1  taken along a line A—A; 
         FIG. 3  is a cross-sectional view of the LCD of  FIG. 1  taken along a line B—B; 
         FIGS. 4A ,  4 B, and  4   c  are process diagrams illustrating a method of manufacturing a CF substrate making up main components of the LCD, in order of processes, according to the first embodiment of the present invention; 
         FIG. 5  is a top view schematically showing configurations of the LCD according to the first embodiment of the present invention; 
         FIG. 6  is a diagram showing a method for driving the LCD according to the first embodiment of the present invention; 
         FIG. 7  is a top view schematically showing configurations of an LCD according to a second embodiment of the present invention; 
         FIG. 8  is a top view schematically showing configurations of an LCD according to a third embodiment of the present invention; 
         FIG. 9  is a top view schematically showing configurations of an LCD according to a fourth embodiment of the present invention; 
         FIG. 10  is a top view schematically showing configurations of an LCD according to a fifth embodiment of the present invention; 
         FIG. 11  is a diagram showing an equivalent circuit of a part of the LCD according to the present invention; 
         FIG. 12  is a diagram showing an equivalent circuit of an entire LCD which embodiment of the present invention; 
         FIGS. 13A ,  13 B, and  13 C are diagrams explaining column density of a columnar spacer employed in a conventional LCD; 
         FIG. 14A ,  14 B, and  14 C are also diagrams explaining column density of a columnar spacer employed in another conventional LCD; 
         FIG. 15  is a top view of showing schematic configurations of the conventional LCD; 
         FIG. 16  is a diagram explaining a method for driving the conventional LCD; 
         FIG. 17  is a cross-sectional view schematically showing configurations of a conventional TN-type liquid crystal display device; and 
         FIG. 18  is a cross-sectional view schematically showing configurations of a conventional IPS-type liquid crystal display device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Best modes of carrying out the present invention will be described in further detail using various embodiments with reference to the accompanying drawings. 
     In the embodiments, as described later in detail, a CF substrate and a TFT substrate are formed with columnar spacers being interposed between these two substrates in a manner that these two substrates face each other. A column density of the columnar spacer is set to be smaller than 1 (one). The columnar spacers in a pair are so arranged that they are adjacent to each other. Each columnar spacer making up the pair of the columnar spacers is disposed in each of two unit pixels being adjacent to each other, to each of which signals having polarity being opposite to each other are applied. 
     First Embodiment 
       FIG. 1  is a top view showing configurations of an LCD according to a first embodiment of the present invention.  FIG. 2  is a cross-sectional view of the LCD of  FIG. 1  taken along a line A—A.  FIG. 3  is a cross-sectional view of the LCD of  FIG. 1  taken along a line B—B.  FIGS. 4A  to  4 C are process diagrams illustrating main processes in a method for manufacturing the LCD according to the first embodiment. 
     As shown in  FIG. 1  to  FIG. 3 , in the LCD of the embodiment of the present invention, a liquid crystal  21  (liquid crystal molecule) is put into a cell gap  20 , in a hermetically sealed manner, between a TFT substrate  1  and a CF substrate  11 . The TFT substrate  1  includes a first transparent substrate  2  made up of glass or a like, a first polarizer  3  formed on a rear of the first transparent substrate  2 , a gate electrode (gate bus line)  10  formed on a part of a surface of the first transparent substrate  2 , a common electrode  14  formed on an other portion of the surface of the first transparent substrate  2 , hereby the gate electrode  10  and the common electrode  14  constituting a same layer, an interlayer dielectric  5  formed in a manner so as to cover both the common electrode  14  and the gate electrode  10 , a pixel electrode  4  formed on the interlayer dielectric  5 , a drain electrode  6  formed also on the interlayer dielectric  5 , a data line  22  formed also on the interlayer dielectric  5 , a passivation film  7  formed in a manner so as to cover the pixel electrode  4 , drain electrode  6  and data line  22 , and a first oriented film  8  formed on the passivation film  7 . 
     Thus, in an IPS-type LCD, the pixel electrode  4  and the common electrode  14  are formed on the first transparent substrate  2  in the TFT substrate  1  in a manner that they are insulated from each other with the interlayer dielectric  5  being interposed between the pixel electrode  4  and the common electrode  14 . A TFT  30  includes the drain electrode  6 , a source electrode  9 , gate the electrode  10 , and a semiconductor layer  24 . A rubbing direction of the liquid crystal  21  is indicated by a reference number  29 . 
     The CF substrate  11  includes a second transparent substrate  12 , a second polarizer  13  formed on a rear of the second transparent substrate  12  with a conductive layer  23  being interposed between the second transparent substrate  12  and the second polarizer  13 , a BM layer  15  formed on a surface of the second transparent substrate  12 , a colored layer  16  covering the BM layer  15 , an OC layer  17  covering the BM layer  15  and colored layer  16 , a columnar spacer  26  formed on a part of the OC layer  17 , and a second oriented film  18  formed so as to cover the columnar spacer  26 . The columnar spacer  26  is disposed on a surface of the gate electrode (gate bus line)  10  of the TFT  30 . The surface of the gate electrode  10  has a uniformly wide and flat surface on the TFT substrate  1 . The columnar spacer  26  is adapted to secure the cell gap  20 . That is, the cell gap  20  in which the liquid crystal  21  is put in the hermetically sealed manner, exists in space being surrounded by the second oriented film  18  covering the columnar spacer  26  and the first oriented film  8 , between the CF substrate  11  and the TFT substrate  1 . 
     Next, the method for manufacturing the CF substrate  11  making up main components of the LCD will be described, in order of processes, by referring to  FIGS. 4A  to  4 C. 
     As shown in  FIG. 4A , first, on the surface of the second transparent substrate  12  made up of glass or a like are formed, in order, the BM layer  15 , the colored layer  16  and the OC layer  17 . Then, by using a photolithography method, a photosensitive resin  28  such as a positive resist is applied on all surfaces of the OC layer  17 . 
     Next, as shown in  FIG. 4B , after having covered the photosensitive resin  28  with a photo mask  31  having a light shielding portion  31 A and a light transmitting portion  31 B, exposure treatment (that is, radiation with ultraviolet rays UV) is performed. Then, as shown in  FIG. 4C , by carrying out development treatment, patterning operations are performed on the photosensitive resin  28 . As a result, a part of the photosensitive resin  28  is removed by the exposure to the ultraviolet rays UV applied through the light transmitting portion  31 B of the photo mask  31  and the columnar spacer  26  is formed on the CF substrate  11 . In the embodiment, the columnar spacer  26  is formed at a place corresponding to the gate electrode (gate bus line)  10  on the TFT substrate  1 . The columnar spacer  26  acts so as to secure the cell gap  20 , into which the liquid crystal  21  is to be put in the hermetically sealed manner, between the CF substrate  11  and the TFT substrate  1 . The columnar spacer  26  is formed so as to have a height of 4 μm to 7 μm. Moreover, after the liquid crystal  21  has been put, in the hermetically sealed manner, into the cell gap  20  secured by the columnar spacer  26 , a second polarizer  13  is formed on a rear of the CF substrate  11  with the conductive layer  23  interposed between the second polarizer  13  and the CF substrate  11 . 
     Then, as shown in FIG, to  FIG. 3 , by using the TFT substrate  1  into which the TFT  30  fabricated in separate processes is incorporated, the liquid crystal  21  is put into the cell gap  20  secured by the columnar spacer  26  between the CF substrate  11  and the TFT substrate  1 , in the hermetically sealed manner, and the LCD is now completed. 
     According to the manufacturing method described above, since the columnar spacer  26  is incorporated in the CF substrate  11  by using photolithography technology, easy formation of the columnar spacer  26  is made possible. Moreover, since the CF substrate  11  already having the columnar spacer  26  therewith can be obtained, the columnar spacer  26  can be disposed easily at an arbitrary place between the CF substrate  11  and the TFT substrate  1 . 
     In the LCD of the embodiment, as shown in  FIG. 5 , the columnar spacer  26  is disposed so that a columnar area ratio CA is set within an optimum range used as a precondition described above and a column density becomes “1/2”. Moreover, each columnar spacer  26  making up a pair of the columnar spacers  26  is arranged in each of two unit pixels adjacent to each other in a column direction Y, for example, in a G and G color unit pixels, while the columnar spacer  26  is arranged in the unit pixel in every two unit pixels in a row direction X, for example, in the G color unit pixel, in a staggered manner. One set of pixels  25  is made up of three unit pixels including a unit pixel for an R color, a unit pixel for the G color and a unit pixel for a B color. 
     Next, a method for driving the LCD of the present invention will be explained by referring to FIG.  6 . As shown in  FIG. 6 , a positive signal charge or a negative signal charge is written alternately in every unit pixel being arranged along the row direction X and a negative signal charge or a positive signal charge is written alternately in every unit pixel being arranged along the column direction Y so that each of the unit pixels adjacent to each other bears the signal charge being opposite in polarity. Therefore, signal charges each being opposite in polarity are always written in each of the two unit pixels being adjacent to each other in the column direction Y, in each of which each columnar spacer  26  making up the pair of the columnar spacers  26  are disposed. As a result, even when the pair of the columnar spacers  26  is electrically charged, since each columnar spacer  26  making up the pair of the columnar spacers  26  bears the signal charge being opposite in polarity, each columnar spacer  26  making up the pair of the columnar spacers  26  can cancel out effects by the signal charge. Thus, even when the columnar spacer  26  is charged, no disturbance in a traverse electric field occurs, thereby preventing occurrence of a failure in displaying such as flicker. 
     As described above, according to the LCD of the first embodiment of the present invention, since the columnar spacer  26  is so disposed that the columnar area ratio CA is set within the optimum range used as the precondition, that each columnar spacer  26  making up the pair of columnar spacers  26  is arranged in each of two unit pixels being adjacent to each other, in order, in the column direction Y, for example, in the G and G color unit pixels, while it is arranged in the unit pixel in every two unit pixels and in a staggered manner in a row direction X, for example, in the G color unit pixel, even when the pair of the columnar spacers  26  is electrically charged, each columnar spacer  26  making up the pair of the columnar spacers  26  bears the signal charge being opposite in polarity and, therefore, the two columnar spacers  26  making up the pair of the columnar spacers  26  can cancel out the effects by the signal charge of each other. 
     Moreover, according to the method of manufacturing the LCD, the columnar spacer  26  is incorporated in the CF substrate  11  by performing photolithographic operations, the columnar spacer  26  can be easily formed. 
     Therefore, even if the columnar spacer  26  is electrically charged, the effects by the signal charges can be cancelled out and, as a result, the disturbance in the traverse electric field can be prevented. 
     Second Embodiment 
       FIG. 7  is a top view schematically showing configurations of an LCD according to a second embodiment of the present invention. Configurations in the second embodiment differ greatly from those in the first embodiment in that each columnar spacer  26  making up a pair of the columnar spacers  26  is arranged in each of two unit pixels being adjacent to each other in a row direction X. 
     That is, in the LCD of the second embodiment, as shown in  FIG. 7 , the columnar spacer  26  is disposed so that a columnar area ratio CA is set within an optimum range used as a precondition described above and a column density becomes “1/2”. Moreover, each columnar spacer  26  making up the pair of the columnar spacers  26  is arranged in each of two unit pixels adjacent to each other in the row direction X, for example, in the G and B color unit pixels, while each columnar spacer  26  making up the pair of the columnar spacers  26  is arranged in every two unit pixels in the row direction X and in a staggered manner, for example, in two unit pixels G and B being adjacent to each other. 
     The LCD of the second embodiment is driven by a dot reverse driving method as in a case of the first embodiment. Therefore, since approximately a same signal charge as that in the first embodiment is written, a disturbance in a traverse electric field can be prevented. However, in the LCD of the second embodiment, since each columnar spacer  26  making up the pair of the columnar spacers  26  is arranged in each of the two unit pixels being adjacent to each other along the row direction X, as the precondition, a colored layer  16  into which the columnar spacer  26  is incorporated has to be formed so that its thickness is the same in any portion. By forming the pair of the columnar spacers  26  having configurations as described above, a liquid crystal panel can be held in a stable manner. 
     Thus, according to the second embodiment, the same effects as obtained in the first embodiment can be achieved. 
     Third Embodiment 
       FIG. 8  is a top view schematically showing configurations of an LCD according to a third embodiment of the present invention. Configurations in the third embodiment differ greatly from those in the first embodiment in that a liquid crystal  21  ( FIG. 2 ) of the third embodiment is driven by a gate line reverse driving method. That is, in the LCD of the embodiment, as shown in  FIG. 8 , an arrangement of a pair of columnar spacers  26  is the same as in a case of the first embodiment, however, since the liquid crystal  21  is driven by the gate line reverse driving method, a signal charge being the same in polarity is written in every row made up of unit pixels. Therefore, each of the unit pixels making up the two unit pixels being adjacent to each other in a column direction Y in which each columnar spacer making up the pair of the columnar spacers  26  is disposed, bears a signal charge being opposite in polarity, which enables effects by the signal charge to be cancelled out as in the case of the first embodiment. 
     Thus, according to the third embodiment, the same effects as obtained in the first embodiment can be achieved. 
     Fourth Embodiment 
       FIG. 9  is a top view schematically showing configurations of an LCD according to a fourth embodiment of the present invention. Configurations in the fourth embodiment differ greatly from those in the first embodiment in that a column density is changed to be “1/3” and each columnar spacer  26  making up a pair of the columnar spacers  26  is disposed in each of two unit pixels being adjacent to each other. That is, in the LCD of the fourth embodiment, as shown in  FIG. 9 , the columnar spacer  26  is disposed so that a columnar area ratio CA is set within an optimum range used as a precondition described above and the column density becomes “1/3”. Moreover, each columnar spacer  26  making up the pair of the columnar spacers  26  is arranged in each of two unit pixels adjacent to each other in a column direction Y, for example, in a G and G unit pixels, while the columnar spacers  26  are arranged in every two unit pixels in a direction X and in a staggered manner, for example, in the G and G unit pixels being adjacent to each other. 
     In the above configurations, though the number of the columnar spacers  26  is small, so long as the columnar area ratio CA is set within the range used as the precondition, there is no problem, that is, effects of a signal charge can be cancelled out. 
     Thus, according to the fourth embodiment, the same effects as obtained in the first embodiment can be achieved. 
     Fifth Embodiment 
       FIG. 10  is a top view schematically showing configurations of an LCD according to a fifth embodiment of the present invention. Configurations in the fifth embodiment differ greatly from those in the first embodiment in that a column density is changed to be “1/4” and each columnar spacer  26  making up a pair of the columnar spacers  26  is disposed in each of two unit pixels being adjacent to each other. That is, in the LCD of the fifth embodiment, as shown in  FIG. 10 , the columnar spacer  26  is disposed so that a columnar area ratio CA is set within an optimum range used as a precondition described above and the column density becomes “1/4”. Moreover, each columnar spacer  26  making up the pair of the columnar spacers  26  is arranged in each of two unit pixels adjacent to each other in a column direction Y, for example, in a G and G unit pixels, while the columnar spacers  26  are arranged in every two unit pixels in a direction X and in a staggered manner, for example, in the G and G unit pixels being adjacent to each other. 
     In the above configurations, though the number of the columnar spacers  26  is smaller than that in a case of the fourth embodiment, so long as the columnar area ratio CA is set within the range used as the precondition, there is no problem, that is, effects of a signal charge can be cancelled out. 
     Thus, according to the fifth embodiment, the same effects as obtained in the first embodiment can be achieved. 
       FIG. 11  is a diagram showing an equivalent circuit of a part of the LCD of the present invention. As shown in  FIG. 11 , to a gate electrode  10  of a TFT  30  making up each of unit pixels for R, G, and B colors is connected a gate voltage terminal  33  and to a drain electrode  6  of the TFT  30  is connected a drain voltage terminal  34 . Moreover, to a common electrode  14  is connected a common electrode voltage terminal  35 . Between a source electrode  9  of the TFT  30  and the common electrode  14  are connected a capacitor C 1  for a liquid crystal  21  (FIG.  2 ), a capacitor C 2  for the TFT substrate  1  made up of glass and a capacitor C 3  for a colored layer  16 .  FIG. 12  is a diagram showing an equivalent circuit of an entire LCD of the present invention. 
     It is apparent that the present invention is not limited to the above embodiments but may be changed and modified without departing from the scope and spirit of the invention. For example, in the above embodiments, the pair of the columnar spacers  26  is disposed in the unit pixel “G”, however, they may be arranged in other unit pixels such as an R or B unit pixel. A horizontal or longitudinal length of the columnar spacer  26  may be set arbitrarily so long as the columnar area ratio CA is set within the optimum range used as the precondition. Moreover, in the above embodiment, examples are shown in which the columnar spacers  26  are thinned out based on the optimum columnar area ratio CA. The arrangement in the unit pixel of the columnar spacers  26  employed when they are thinned out is not limited to the above example. The columnar spacers  26  may be arranged arbitrarily so long as they are disposed in unit pixels being adjacent to each other in the row direction X or column direction Y.

Technology Classification (CPC): 6