Abstract:
A liquid crystal display (LCD) device is disclosed, which comprises a protrusion, and a column spacer being partially overlapped with the protrusion to thereby prevent a cell gap defect. The LCD device includes first and second substrates facing each other and gate and data line crossing each other to define a unit pixel region. In addition a thin film transistor formed adjacent to a crossing of the gate and data lines is included. The protrusions formed on the first substrate correspond with predetermined portions of the gate line. The column spacers are formed on the second substrate with a predetermined portion overlapped with some portion of one of the protrusions. A liquid crystal layer is formed between the first and second substrates.

Description:
[0001]     This application claims the benefit of the Korean Patent Application No. P2005-56120, filed on Jun. 28, 2005, which is hereby incorporated by reference as if fully set forth herein.  
       BACKGROUND  
     Discussion of the Related Art  
       [0002]     Demands for various display devices have increased with development of an information society. Accordingly, many efforts have been made to research and develop various flat display devices such as liquid crystal display (“LCD”), plasma display panel (“PDP”), electroluminescent display (“ELD”), and vacuum fluorescent display (“VFD”). Some species of flat display devices have already been applied to displays for various equipment.  
         [0003]     Among the various flat display devices, liquid crystal display (“LCD”) devices have been most widely used due to their thin profile, light weight, and low power consumption, whereby the LCD devices may provide a substitute for a Cathode Ray Tube (“CRT”). In addition to mobile type LCD devices such as a display for a notebook computer, LCD devices have been developed for computer monitors and televisions to receive and display broadcasting signals.  
         [0004]     Despite various technical developments in the LCD technology having applications in different fields, research in enhancing the picture quality of the LCD device has been, in some respects, slower as compared to other features and advantages of the LCD device. In order to use LCD devices in various environments as a general purpose display, a high quality picture may be required. High resolution and high luminance with a large-sized screen should be achieved, while still maintaining a light weight, thin profile, and low power consumption.  
         [0005]     Generally, a related art LCD device includes first and second substrates bonded to each other at a predetermined interval, and a liquid crystal layer formed between the first and second substrates. Specifically, the first substrate includes a plurality of gate and data lines, a plurality of pixel electrodes, and a plurality of thin film transistors T. The plurality of gate lines are formed on the first substrate at fixed intervals, and the plurality of data lines are formed perpendicular to the plurality of gate lines at fixed intervals. The plurality of pixel electrodes, which are arranged in a matrix-type configuration, are respectively formed in pixel regions defined by the plurality of gate and data lines crossing each other. The plurality of thin film transistors T are formed adjacent to crossings of the gate and data lines, and are switched according to signals of the gate lines for transmitting signals of the data lines to the respective pixel electrodes.  
         [0006]     The second substrate includes a black matrix layer that excludes light from regions except the pixel regions P of the first substrate, R/G/B color filter layer displaying various colors in correspondence with the pixel regions, and a common electrode to display the picture image. The liquid crystal layer is formed between the first and second substrates. The LCD device is driven according to an electric field generated between the pixel electrode and the common electrode. Thus, it is possible to control the amount of light passing through the liquid crystal layer according to the alignment of the liquid crystal layer, thereby displaying the images. This is referred to as a Twisted Nematic (“TN”) mode, which has the disadvantage of a narrow viewing angle. In order to overcome the disadvantage of the TN mode LCD device, an In-Plane Switching (“IPS”) mode LCD device has been developed.  
         [0007]     In case of the IPS mode LCD device, both pixel and common electrodes are formed at a predetermined interval in a pixel region of a first substrate, thereby generating an IPS mode electric field (transverse electric field). That is, a liquid crystal layer is driven with the transverse electric field. Spacers are formed between the first and second substrates, so as to maintain the predetermined gap between the first and second substrates. The spacers are classified as either ball spacers or column spacers.  
         [0008]     The ball spacers are formed in the shape of a sphere, and are scattered on the first or second substrate. Even after the attachment of the first and second substrates, the ball spacers may move freely, and the ball spacers have a small contact area with the first and second substrates.  
         [0009]     Likewise, the column spacers are formed in an array process of the first or second substrate. The column spacers are fixedly formed in the shape of a column. Accordingly, the column spacers have a larger contact area with the first and second substrates as compared with the ball spacers.  
         [0010]      FIG. 1  illustrates a cross sectional view of a related art LCD device having column spacers. As shown in  FIG. 1 , the LCD device having the column spacers is provided with first and second substrates  30  and  40  facing each other, the column spacers formed between the first and second substrates  30  and  40 , and a liquid crystal layer (not shown) formed between the first and second substrates  30  and  40 .  
         [0011]     The first substrate  30  includes a plurality of gate lines  31  and data lines (not shown) crossing each other to define respective pixel regions. Also, each thin film transistor TFT is formed adjacent to the crossing area of the gate and data lines, and a pixel electrode (not shown) is formed in each of the pixel regions.  
         [0012]     The second substrate  40  includes a black matrix layer  41  that excludes light from regions except the pixel regions P of the first substrate, R/G/B color filter layer  42  displaying various colors in correspondence with the pixel regions, and a common electrode or an overcoat layer  43  formed on an entire surface thereof.  
         [0013]     The column spacer  20  is formed on the first substrate corresponding to a predetermined portion of the gate line  31 . Also, a gate insulating layer  36  is formed on the surface of the first substrate  30  including the gate line  31 , and a passivation layer  37  is formed on the gate insulating layer  36 .  
         [0014]      FIG. 2A  illustrates a plan view of a touch defect generated in a related art LCD device having column spacers.  FIG. 2B  illustrates a cross sectional view of a touch defect generated in a related art LCD device having column spacers. As shown in  FIG. 2A  and  FIG. 2B , if a surface of an LCD panel  10  having column spacer according to the related art is touched by hand or finger at a predetermined direction, spots are generated on the touched portion of the surface of the LCD panel  10 . The spots are referred to as the touch defect.  
         [0015]     In the case of an LCD device having column spacers as shown in  FIG. 2B , the column spacers  20  are in contact with lower and upper substrates  1 ,  2 . The contact between the column spacer and the substrate causes increased frictional force between the column spacers  20  and the two opposing substrates  1 ,  2 . Thus, the liquid crystal molecules between the column spacers are not restored to the original state, thereby generating the spots on the screen. Also, when the LCD panel  10  is touched along a predetermined direction as shown in  FIG. 2B , the liquid crystal molecules  3  gather to the region around the touch portion, thereby causing the region around the touch portion to protrude. In this case, a cell gap h 1  corresponding to a protruding portion is higher than a cell gap h 2  of the remaining portions, thereby generating light leakage. Accordingly, it is impossible to obtain the uniform luminance  
         [0016]     In the case of the LCD device having the column spacers, the column spacers have a large contact area with the opposing substrates, generating great friction. As shown in  FIG. 2B , the column spacer  20  is in contact with the large area of the first substrate. Thus, after the first and second substrates are shifted by touch, it takes a long time to return to the original state of the opposing substrates, thereby causing the touch defect.  
       SUMMARY  
       [0017]     Accordingly, the present disclosure is directed to a liquid crystal display (“LCD”) device, which obviates one or more problems due to limitations or disadvantages of the related art.  
         [0018]     In a first aspect, a liquid crystal device (“LCD”) device includes a first substrate and a second substrate. The first substrate faces the second substrate. The LCD device further includes gate lines and data lines. The gate lines cross the data lines to define a unit pixel region, which is formed on the first substrate. A thin film transistor formed adjacent to the crossing of the gate lines and the data lines. Protrusions are formed on the first substrate corresponding to predetermined portions of at least one of the gate lines. Column spacers are formed on the second substrate with a predetermined portion overlapping with a portion in a corresponding one of the protrusions. The overlapped portions are variable. The LCD device further includes a liquid crystal layer formed between the first and second substrates.  
         [0019]     In a second aspect, a liquid crystal display (“LCD”) device includes a first substrate and a second substrate. The LCD device further includes gate and data lines crossing each other to define a unit pixel region, formed on the first substrate, a thin film transistor formed adjacent to a crossing of the gate and data lines, a plurality of protrusions formed on the first substrate corresponding to predetermined portions of the gate line, a plurality of column spacers formed on the second substrate, wherein each of the column spacers has a predetermined portion overlapped with some portion in each of the protrusions, and the overlapped portions are variable in position and a liquid crystal layer formed between the first and second substrates.  
         [0020]     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     The accompanying drawings, which are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the disclosure. In the drawings:  
         [0022]      FIG. 1  is a cross sectional view of illustrating an LCD device having column spacers according to the related art;  
         [0023]      FIG. 2A  is a plan view illustrating a touch defect generated in a related art LCD device having column spacers;  
         [0024]      FIG. 2B  is a cross sectional view of illustrating a touch defect generated in a related art LCD device having column spacers;  
         [0025]      FIG. 3  is an illustration of a cross sectional view of an LCD device having a protrusion;  
         [0026]      FIG. 4  is an illustration of a plan view of a column spacer and a corresponding protrusion of  FIG. 3 ;  
         [0027]      FIG. 5  is an illustration of a plan view of a position of an upper substrate, a column spacer and a protrusion of an LCD device according to one embodiment;  
         [0028]      FIG. 6  is an illustration of a plan view of adjacent column spacers and corresponding protrusions of  FIG. 5 ;  
         [0029]      FIG. 7  is a cross sectional view along I-I′ of  FIG. 6 ;  
         [0030]      FIG. 8  is an illustration of a plan view of an IPS mode LCD device according to one embodiment; and  
         [0031]      FIG. 9  is a cross sectional view along II-II′ of  FIG. 8 . 
     
    
     DETAILED DESCRIPTION  
       [0032]     Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Hereinafter, an LCD device according to one embodiment of the present disclosure will be described with reference to the accompanying drawings.  
         [0033]      FIG. 5  is an illustration of a plan view of a position of a first substrate, an upper substrate, a column spacer and a protrusion of an LCD device according to one embodiment. In an LCD device as shown in  FIG. 5 , a plurality of column spacers  110  are formed at fixed intervals on a first substrate  100 , and a plurality of protrusions  210  are formed corresponding to the column spacers. Each protrusion  210  is partially overlapped with each column spacer  110 . Also, the plurality of protrusions  210  of a similar size are formed at fixed intervals. Further, each protrusion  210  is formed in correspondence with a line formation portion. For example, a portion may be formed on a gate line, a data line or a common line. Specifically, in the embodiment shown in  FIG. 5 , the protrusions  210  are formed every six sub-pixels along the ‘A’ direction, and are formed every two sub-pixels along the ‘B’ direction.  
         [0034]     Each protrusion  210  is formed corresponding to each column spacer  110 . When the column spacers  110  are partially overlapped with the protrusions  210 , the overlapped portions are variable in position. In this case, a total area of the overlapped portions between the column spacers  110  and the protrusions  210  corresponds to a total area of the overlapped portions between column spacers and protrusions shown in  FIGS. 3 and 4 .  
         [0035]     For example, as shown in  FIG. 5 , when forming an imaginary diamond shape with the adjacent four protrusions  210   a - 210   d , the four protrusions have the different portions overlapped with the column spacers  110   a - 110   d . If the first protrusion  210   a  is positioned in the upper side of the imaginary diamond shape, the lower portion of the first protrusion  210   a  is overlapped with the first column spacer  110   a . In the case of the second protrusion  210   b  which is positioned in the right side of the imaginary diamond shape, the right portion of the second protrusion  210   b  is overlapped with the second column spacer  110   b . In the case of the third protrusion  210   c  which is positioned in the lower side of the imaginary diamond shape, the upper portion of the third protrusion  210   c  is overlapped with the third column spacer  110   c . In the case of the fourth protrusion  210   d  which is positioned in the left side of the imaginary diamond shape, the left portion of the fourth protrusion  210   d  is overlapped with the fourth column spacer  110   d.    
         [0036]     In another embodiment, the upper portion of the first protrusion  210   a  may be overlapped with the first column spacer  110   a , the left portion of the second protrusion  210   b  may be overlapped with the second column spacer  110   b , the lower portion of the third protrusion  210   c  may be overlapped with the third column spacer  110   c , and the right portion of the fourth protrusion  210   d  is overlapped with the fourth column spacer  110   d . Accordingly, the overlapped portions of two protrusions are located in opposing positions on the y axis and the overlapped portions of two protrusions are located in opposing positions on the x axis. As shown in  FIG. 6  and will be discussed further below, protrusion  210   a  and protrusion  210   c  are located at opposing positions on the y axis and protrusions  210   b  and protrusion  210   d  are located at opposing positions on the x axis.  
         [0037]     The first substrate  100  is comprised of a black matrix layer  101 , a color filter layer  102 , and an overcoat layer (not shown). The black matrix layer  101  is formed corresponding to the other portions except for the pixel regions (gate and data lines). The color filter layer  102  is formed on the first substrate  100  including the black matrix layer  101 , and the overcoat layer (not shown) is formed above the black matrix layer  101  and the color filter layer  102 . The column spacers  110  are formed on the overcoat layer (not shown) corresponding to the black matrix layer  101  of the first substrate  100 .  
         [0038]      FIG. 6  is an illustration of a plan view of adjacent column spacers and corresponding protrusions as shown in  FIG. 5 .  FIG. 7  is a cross sectional view along I-I′ of  FIG. 6 .  
         [0039]     Referring to  FIGS. 6 and 7 , when providing a protrusion corresponding to the adjacent four column spacers, the opposite column spacers are in contact with the opposite portions of the respective protrusions. As shown in  FIG. 6 , in the case of the first and third protrusions  210   a  and  210   c  which are positioned opposite to each other along the y axis, the lower portion of the first protrusion  210   a  is overlapped with the upper portion of the first column spacer  110   a , and the upper portion of the third protrusion  210   c  is overlapped with the lower portion of the third column spacer  110   c . Also, in the case of the second and fourth protrusions  210   b  and  210   d  which are positioned opposite to each other along the x axis, the right portion of the second protrusion  210   b  is overlapped with the left portion of the second column spacer  110   b , and the left portion of the fourth protrusion  210   d  is overlapped with the right portion of the fourth column spacer  110   d . This embodiment will be further described in relation to  FIG. 7 .  
         [0040]      FIG. 7  is a cross sectional view along I-I′ of  FIG. 6 . Two column spacers  110   b ,  110   d , are shown overlapping two protrusions  210   b ,  210   d , respectively between a first substrate  100  and a second substrate  200 . The second column spacer  110   b  is overlapped with the second protrusion  210   b  at a width ‘a’, and the fourth column spacer  110   d  is overlapped with the fourth protrusion  210   d  at a width ‘b’.  FIG. 7  illustrates one embodiment for the overlap of a column spacer with a protrusion. The overlap may be varied in alternate embodiments.  
         [0041]     As shown in the embodiment of  FIG. 7 , protrusion  210   b  prevents the column spacer  110   b  from being shifted to the left on the x axis. Likewise, protrusion  210   d  prevents the column spacer  110   d  from being shifted to the right on the x axis. Likewise, protrusion  210   a  prevents column spacer  110   a  from being shifted upwards on the y axis and protrusion  210   c  prevents column spacer  110   c  from being shifted downwards along the y axis. This embodiment with four column spacers and corresponding protrusions prevents shifting of the column spacers in both the x and y axes, which thereby reduces the touch defect.  
         [0042]     In this embodiment, value ‘a’ is the distance of contact between the column spacer  110   b  and the protrusion  210   b . Value ‘b’ is the distance of contact between the column spacer  110   d  and the protrusion  210   d . The values of ‘a’ and ‘b’ are smaller than the width of the protrusions  210 . The width of the protrusion is also referred to as the critical value. Because the values of ‘a’ and ‘b’ are less than the critical value, the frictional force between the column spacer and the protrusion is reduced, thereby facilitating the easy return of the column spacer back to its original position.  
         [0043]      FIG. 8  is an illustration of a plan view of an In-Plane Switching (“IPS”) mode LCD device according to one embodiment.  FIG. 9  is a cross sectional view along II-II′ of  FIG. 8 .  
         [0044]     As shown in either  FIG. 8  or  9 , an LCD device is comprised of a first substrate  100 , a second substrate  200 , a plurality of protrusions  210 , and a plurality of column spacers  110 . As shown in  FIG. 9 , the first substrate  100  is opposite to the second substrate  200 . Also, the plurality of protrusions  210  are formed on predetermined portions of the second substrate  200 . The plurality of column spacers  110  are formed on the first substrate  100 , and each of the column spacers  110  corresponding to each of the protrusions  210  is partially overlapped with each of the protrusions  210 .  
         [0045]     As shown in  FIGS. 8 and 9 , the second substrate  200  includes a gate line  201  having a gate electrode  201   a , a gate insulating layer  206 , a semiconductor layer (not shown), a data line  202 , a thin film transistor TFT, a passivation layer  208 , a pixel electrode  203 , and a common electrode  207 . The gate insulating layer  206  is formed on an entire surface of the second substrate  200  including the gate line  201 , and the semiconductor layer (not shown) covering the gate electrode  201   a  is formed on the gate insulating layer  206 . The data line  202  having a source electrode  202   a  is formed perpendicular to the gate line  201  on the gate insulating layer  206 . The thin film transistor TFT is formed adjacent to a crossing of the gate and data lines  201  and  202 . The passivation layer  208  is formed on the surface of the second substrate  200  including the data line  202 . The pixel electrode  203  and the common electrode  207  are alternately formed on pixel regions of the passivation layer  208 . The common electrode  207  is extending from a common line  207   a  being adjacent to the gate line  201 .  
         [0046]     Referring to  FIG. 8 , a thin film transistor TFT is comprised of the gate electrode  201   a  protruding from the gate line  201 , the source electrode  202   a  of ‘U’ shape protruding from the data line  202 , a drain electrode  202   b  formed at a predetermined interval from the source electrode  202   a  and partially positioned inside the ‘U’ shape of the source electrode  202   a , and the semiconductor layer formed above the gate electrode  201   a  and overlapped with the source and drain electrodes  202   a  and  202   b . The semiconductor layer may be formed in a deposition structure comprising an amorphous silicon layer and an impurity layer, wherein the impurity layer of the semiconductor layer is partially removed corresponding to a portion between the source and drain electrodes  202   a  and  202   b . As explained above, the source electrode  202   a  may be formed in shape of ‘U’, or in shape of ‘-’. If the source electrode  202   a  is formed in a ‘U’ shape, it is possible to improve the efficiency of thin film transistor by increasing a channel area.  
         [0047]     As shown in  FIG. 9 , the LCD device according to one embodiment has a plurality of protrusions  210  provided on the predetermined portions corresponding to the gate line  201 . Each of the protrusions  210  may be formed in a single layer structure of a semiconductor layer pattern or a source/drain electrode layer, or may be formed in a deposition layer structure of the semiconductor layer pattern and the source/drain electrode layer. The semiconductor layer pattern  204   a  may be formed of a semiconductor layer material (deposition of amorphous silicon layer and impurity layer) when patterning the semiconductor layer  204 , and the source/drain electrode layer  202   c  may be formed of a metal material when patterning the data line  202  and the source/drain electrodes  202   a / 202   b . Accordingly, since the protrusion  210  is formed of the semiconductor pattern  204   a  or the source/drain electrode layer  202   c , the protrusion  210  is positioned above the gate insulating layer  206  and below the passivation layer  208 .  
         [0048]     Referring to  FIG. 8 , contact portion  205  corresponds to a contact portion between the drain electrode  202   b  and the pixel electrode  203 , from which the predetermined portion of the drain electrode  202   b  is exposed by removing the gate insulating layer  206  and the passivation layer  208 .  
         [0049]     Referring to  FIG. 9 , the first substrate  100  may include a black matrix layer  101 , a color filter layer  102 , and an overcoat layer  103 . The black matrix layer  101  is formed in a shape of shielding the other portions except the pixel regions (corresponding to the gate and data lines) and the thin film transistors (“TFTs”). The color filter layer  102  is formed on the first substrate  100  including the black matrix layer  101 , wherein the color filter layer is positioned in correspondence with the pixel regions. The overcoat layer  103  is formed on an entire surface of the first substrate  100  including the black matrix layer  101  and the color filter layer  102 . The plurality of column spacers  110  may be formed over the first substrate  100 , and each of the column spacers  110  corresponding to each of the protrusions  210  is partially overlapped with one of the protrusions  210  formed on the second substrate  200 .  
         [0050]     The embodiment shown in  FIG. 8  is formed in an In-Plane Switching (“IPS”) mode. Alternatively, the above structure of partially overlapping the column spacers and the protrusions may be applied to a Twisted Nematic (“TN”) mode. In the TN mode LCD device, a pixel electrode is formed in a unit pixel region on a second substrate, and a common electrode is formed on a surface of a first substrate. However, the TN mode LCD device is similar in structure to the IPS mode LCD device. In the TN mode LCD device, the plurality of protrusions  210  are formed corresponding to the plurality of column spacers  110 , and each of the protrusions  210  is partially overlapped with each of the column spacers  110 .  
         [0051]     Referring to  FIGS. 3 and 4 , when the protrusion  51  is overlapped with the central portion of the column spacer  50 , the pressing force is focused on the central portion of the column spacer  50 , to thereby cause the deformation of the column spacer  50 . Also, the protrusion  51  has a small size of a critical value, about 6 μm or less, so that it is difficult to uniformly form the protrusions when patterning. Thus, it may generate the variation on pressing the column spacers. In this case, a viewer can feel this variation upon pressing the column spacers.  
         [0052]     In the LCD device according to an embodiment, the protrusion  51  has an increasing critical value of about 10 μl, and each protrusion  51  is partially overlapped with each column spacer  50 . Accordingly, even though the protrusion  51  increases in size, the contact area between the protrusion  51  and the column spacer  50  is similar to that of the general protrusion structure, thereby preventing the touch defect. Also, since the predetermined portion of the protrusion  51  is partially overlapped with the column spacer  50 , the pressing force applied to the column spacer  50  is decreased owing to the division of force, to thereby minimize the deformation of the column spacer  50 .  
         [0053]     The contact area between the protrusion  51  and the column spacer  50  in the case of partially overlapping the predetermined portion of the protrusion with the column spacer is similar to that in the case of overlapping the protrusion with the central portion of the column spacer. In consideration of a bonding margin, the overlapped width between the protrusion  51  and the column spacer  50  is larger than the bonding margin. Thus, even though there is a misalignment, the protrusion  51  is partially overlapped with the column spacer  50 .  
         [0054]     In the structure of  FIGS. 3 and 4 , the protrusion  51  may have the small size of the critical value below 6 μm when overlapping with the central portion of the column spacer  50 , so that it is difficult to establish a uniform pattern due to the resolution margin. In the structure of partially overlapping the predetermined portion of the protrusion with the column spacer (as in  FIGS. 5-9 ), the protrusion may be formed in the critical value corresponding to or larger than the resolution of photo-process. Accordingly, it is possible to control the uniformity in size of the protrusions, to thereby improve the picture quality by minimizing the deformation of the column spacers and the cell gap defect.  
         [0055]     In the LCD device according to the present embodiments, each protrusion increases in size, and the overlapped portion between the protrusion and the column spacer is uniform, to thereby minimize the deformation of the column spacer and the cell gap defect. Specifically, the predetermined portion of the protrusion is partially overlapped with the predetermined portion of the column spacer, thereby decreasing the pressing power applied to the column spacer.  
         [0056]     If the cell gap is not uniform, especially, the cell gap defect of the adjacent portions is large, the picture quality is deteriorated. In the LCD device according to the present embodiments, the deformation of the column spacer is minimized owing to the decrease in pressing force applied to the column spacer, to thereby maintain the uniform cell gap in the entire panel of the LCD device.  
         [0057]     Furthermore, if an external shifting force by touch is applied to any one of the first and second substrates, the shift will be resisted by conformations of column spacers and protrusions. Based on the conformations at different edges of the corresponding column spacers on the respective protrusions, a shift between substrates will not occur, thereby preventing a touch defect.  
         [0058]     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.