Patent Publication Number: US-2005128382-A1

Title: Color filter substrate, fabrication method thereof and liquid crystal display panel having the same

Description:
This application claims the benefit of Korean Patent Application No. 90284/2003, filed on Dec. 11, 2003, which is hereby incorporated by reference for all purposes as if fully set forth herein.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a color filter substrate, a fabricating method thereof and a liquid crystal display panel having the same. More particularly, the present invention relates to a color filter substrate, a fabricating method thereof and a liquid crystal display panel capable of preventing defects in alignment of liquid crystal molecules from occurring due to column spacers on a pixel region of a first mother substrate and a second mother substrate which are bonded to maintain a uniform cell-gap by the column spacers.  
      2. Discussion of the Related Art  
      A liquid crystal display device displays desired images by individually providing data signals to pixels arranged in a matrix form according to image information to thereby control the light transmittance of the pixels.  
      Accordingly, the liquid crystal display device is provided with a liquid crystal display panel on which pixels are arranged in a matrix form and a driving circuit for driving the pixels.  
      The liquid crystal display panel includes a thin film transistor array substrate and a color filter substrate which face each other and are bonded together to maintain a uniform cell-gap, and a liquid crystal layer formed at an interval between the color filter substrate and the thin film transistor array substrate.  
      In addition, the thin film transistor array substrate and the color filter substrate are bonded by a seal pattern formed at an outer edge of an effective image display unit. A spacer is formed on the thin film transistor array substrate or the color filter substrate, and maintains a uniform cell-gap of the bonded thin film transistor array substrate and color filter substrate.  
      A polarizing plate and a phase retardation plate may be provided to outer surfaces of the thin film transistor array substrate and the color filter substrate. Including components like the polarizing plate and phase retardation plate, a liquid crystal display panel which has high brightness and contrast characteristics is constructed by changing a state that light proceeds or the index of refraction.  
      A common electrode and a pixel electrode are formed on the liquid crystal display panel in which the thin transistor array substrate and the color filter substrate face each other and are bonded. The common electrode and the pixel electrode apply the electric field to the liquid crystal layer. That is, by controlling a voltage applied to the pixel electrode in a state that the voltage is applied to the common electrode, the light transmittance of unit pixels can be individually controlled. To control the voltage applied to the pixel electrode according to each unit pixel, a thin film transistor may be used as a switching device for each unit pixel.  
      An alignment layer is formed on a surface where the thin film transistor array substrate and the color filter substrate face each other, and rubbing is performed to arrange liquid crystal of the liquid crystal layer in a certain direction.  
      The liquid crystal display device is generally classified as a twisted nematic (TN) mode liquid crystal display panel and an in-plane switching (IPS) mode liquid crystal display panel.  
      In the TN mode liquid crystal display panel, the pixel electrode is formed on the thin film transistor array substrate according to each unit pixel, and the common electrode is formed on an entire surface of the color filter substrate.  
      Accordingly, the liquid crystal layer is driven by the electric field formed between the pixel electrode formed on the thin film transistor array substrate and the common electrode formed on the color filter substrate.  
      In the IPS mode liquid crystal display panel, the pixel electrode and the common electrode are predeterminedly separated from the thin film transistor array substrate. Therefore, the liquid crystal layer is driven by the lateral electric field between the pixel electrode formed on the thin film transistor array substrate and the common electrode.  
      Here, red, green and blue color filters are predeterminedly separated to correspond to a pixel region and are arranged in a matrix form. A black matrix is formed in a net shape on a region where the red, green and blue color filters are separated.  
      Column spacers arranged together with the red color filters, the green color filters and the blue color filters are formed on the black matrix in which the red color filters, the green color filters and the blue color filters are disposed adjacent to each other in a vertical direction. The column spacers allow a uniform cell-gap to be maintained when bonding the color filter substrate and the thin film transistor array substrate.  
      An alignment layer (not shown) is formed on the surface of the color filter substrate having the red, green and blue color filters, the black matrix and the column spacers, and then rubbing is performed. At this time, in the rubbing process, a polymer chain on a surface of the alignment layer is aligned in a certain direction by rubbing the surface of the alignment layer with a rubbing cloth under a uniform pressure and at a uniform rate.  
      Accordingly, when forming a liquid crystal layer at the cell-gap after bonding the color filter substrate and the thin film transistor array substrate by the column spacers to maintain uniform the cell-gap, liquid crystal molecules are arranged in a certain direction by the alignment layer.  
      As described, the column spacers are formed on a region where the red color filters, the green color filters and the blue color filters are disposed adjacent to each other in the vertical direction of the black matrix. Therefore, when rubbing the alignment layer, rubbing defects occur on the pixel region along the rubbing direction.  
      That is, in the case that the column spacers are formed on the region where the red color filters, the green color filters and the blue color filters are disposed adjacent to each other in the vertical direction of the black matrix and that rubbing is performed by driving a rubbing roll from top to bottom by rotating the rubbing roll, in which the rubbing cloth is rolled, at a high speed, the rubbing cloth gets damaged by the height of the column spacer. Therefore, the rubbing defects are generated from top to bottom of the pixel region on which the red, green and blue color filters are formed.  
      The color filter substrate of the related art liquid crystal display panel deteriorates picture quality of the liquid crystal display device since the rubbing defects are generated, and produces defects which decrease the yield.  
      In particular, since the liquid crystal display device is mass-produced, the same rubbing defect is repeatedly generated on the liquid crystal display device of the same model. As a result, there is a problem that picture quality and yield deteriorations of the liquid crystal display device are continuously generated.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is directed to a color filter substrate, fabrication method thereof and liquid crystal display panel having the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.  
      An advantage of the present invention is to provide a color filter substrate, a method thereof and a liquid crystal display panel having the same capable of preventing defects in alignment of liquid crystal molecules from occurring due to column spacers in a pixel region of a first mother substrate and a second mother substrate which are bonded to maintain a uniform cell-gap by the column spacers.  
      In addition, another advantage of the present invention is to provide a color filter substrate, a method thereof and a liquid crystal display panel having the same capable of preventing continuous generation of picture quality and yield deteriorations of a liquid crystal display device by preventing the same rubbing defect from repeatedly generating in the liquid crystal display device which is mass-produced, with the same model.  
      To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, a color filter substrate comprises red, green and blue color filters corresponding to a pixel region; a black matrix on a region where the red, green and blue color filters are separated in a horizontal direction and in a vertical direction; and column spacers on the horizontal and vertical intersections of the black matrix, and  
      In another aspect, a method of fabricating a color filter substrate comprises forming a black matrix on a substrate to separate pixel regions of the substrate; forming red, green and blue color filters on the pixel regions of the substrate; forming column spacers on horizontal and vertical intersections of the black matrix; and forming an alignment layer on a surface of the substrate.  
      In another aspect, a liquid crystal display panel comprises a plurality of gate and data lines on a first substrate, the gate and data lines crossing each other to define pixel regions; switching devices at the crossing of the gate and data lines; at least one pair of a common electrode and a pixel electrode on the pixel region; a color filter layer on a second substrate, the color filter layer corresponding to the pixel regions; a black matrix layer on a separated region of the color filter layer in horizontal and vertical regions; a column spacer on a crossing portion of horizontal and vertical regions of the black matrix layer; and a liquid crystal layer between the first and second substrates.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     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 an exemplary view showing a plan structure of a color filter substrate of a liquid crystal display panel in accordance with the present invention;  
       FIG. 2  is an exemplary view showing a sectional structure of the color filter substrate cut along line I-I in  FIG. 1 ;  
       FIG. 3  is an exemplary view showing rubbing defects are not generated when performing the rubbing on the color filter substrate in  FIG. 2 ;  
       FIG. 4  is an exemplary view showing a plan structure of a unit pixel of a related art IPS mode liquid crystal display panel; and  
       FIG. 5  is an exemplary view showing a plan structure of the unit pixel of the IPS mode liquid crystal display panel in which a common electrode and a pixel electrode are arranged in a zigzag pattern.  
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS  
      Hereinafter, description will now be made in detail to a color filter substrate, a method thereof and a liquid crystal display panel having the same in accordance with the present invention with reference to the accompanying drawings.  
       FIG. 1  is an exemplary view showing a plan structure of a color filter substrate of a liquid crystal display panel in accordance with the present invention.  
      In  FIG. 1 , red, green and blue color filters (R, G and B) are predeterminedly separated in a vertical direction and in a horizontal direction in order that they can correspond to a pixel region, and are arranged in a matrix form. A black matrix  120  is formed in a net shape on a region where the red, green and blue color filters (R, G and B) are separated vertically and horizontally.  
      As described, in a case of a TN mode liquid crystal display panel in which a pixel electrode is formed on a thin film transistor array substrate and a common electrode is formed on the color filter substrate  110 , the common electrode can be additionally formed on an entire surface of the color filter substrate  110 . On the other hand, in a case of an IPS mode liquid crystal display panel in which the pixel electrode and the common electrode are formed on the thin film transistor array substrate, the common electrode is not formed on the color filter substrate  110 .  
      Additionally, an over-coat layer for planarization of the surface may be formed on an entire surface of the color filter substrate  110  on which the red, green and blue color filters (R, G and B) and the black matrix  120  are formed.  
      Column spacers may be formed on horizontal and vertical intersections of the net-shaped black matrix  120 . When bonding the color filter substrate  110  and the above-described thin film transistor array substrate, the column spacers allow a uniform cell-gap to be maintained. The column spacers  130  can be formed on all the horizontal and vertical intersections of the net-shaped black matrix  120 , or can be formed on some of the horizontal and vertical intersections of the net-shaped black matrix  120 .  
      An alignment layer (not shown) having polyimide material is formed on the surface of the color filter substrate  110  having the red, green and blue color filters (R, G and B), the black matrix  120  and the column spacers  130 . Then, an alignment process is performed. In the alignment process, a polymer chain on a surface of the alignment layer is arranged in a certain direction by rubbing the surface of the alignment layer with a cloth under a uniform pressure and at a uniform rate.  
      Accordingly, after bonding the color filter substrate  110  and the thin film transistor array substrate using the column spacers  130  to maintain a uniform cell-gap, when forming a liquid crystal layer on the cell-gap, liquid crystal molecules are arranged by the alignment layer in a certain direction.  
      A fabrication method of a color filter substrate of a liquid crystal display panel in accordance with the present invention will be described with reference to the accompanying drawings.  
       FIG. 2  is an exemplary view showing a sectional structure of the color filter substrate  110  along line I-I in  FIG. 1 .  
       FIG. 3  is an exemplary view showing rubbing defects are not generated when performing the rubbing on the color filter substrate in  FIG. 2 .  
      With reference to  FIG. 2 , the black matrix  120  is predeterminedly separated on a glass substrate  111 . At this time, the black matrix  120  is formed in a net shape in order that the black matrix can separate pixel regions on the glass substrate  111 .  
      Thereafter, red, green and blue color filters (R, G and B) filters are formed on a region where the black matrix  120  is separated. The red, green and blue color filters (R, G and B) are predeterminedly separated in the vertical direction and in the horizontal direction so as to correspond to the pixel region on the glass substrate  111 , and therefore they are arranged in a matrix form.  
      In a case of a TN mode liquid crystal display panel in which a pixel electrode is formed on a thin film transistor array substrate and a common electrode is formed on the color filter substrate  110 , the common electrode can be additionally formed on a surface of the glass substrate  111  on which the black matrix  120  and the red, green and blue color filters (R, G and B) are formed. On the other hand, in a case of an IPS mode liquid crystal display panel in which the pixel electrode and the common electrode are formed on the thin film transistor array substrate, the common electrode is not formed on the glass substrate  111 .  
      Additionally, an overcoat layer for planarization of the surface may be formed on an entire surface of the color filter substrate  110  on which the red, green and blue color filters (R, G and B) and the black matrix  120  are formed.  
      Subsequently, column spacers  130  which are aligned on the black matrix  120  are formed. At this time, as shown in  FIG. 1 , the column spacers  130  may be formed on the horizontal and vertical intersections of the net-shaped black matrix  120 . The column spacers  130  may be formed on all the horizontal and vertical intersections of the net-shaped black matrix  120 . Or, the column spacers may be formed on some of the horizontal and vertical intersections of the net-shaped black matrix  120 .  
      Thereafter, an alignment layer  140  having polyimide material is formed on the surface of the glass substrate  111  having the black matrix  120 , the red, green and blue color filters (R, G and B) and the column spacers  130 , and then an alignment process is performed from top to bottom as shown in  FIG. 1  or from bottom to top. At this time, in the alignment process, a polymer chain on a surface of the alignment layer  140  is arranged in a certain direction by rubbing the surface of the alignment layer  140  with a cloth under a uniform pressure and at a uniform rate.  
      Accordingly, when forming a liquid crystal layer on the cell-gap after bonding the color filter substrate and the thin film transistor array substrate by the column spacers to maintain uniform cell-gap, liquid crystal molecules are arranged by the alignment layer  140  in a certain direction.  
      As described, in the color filter substrate, the method thereof and the liquid crystal display panel having the same in accordance with the present invention, as the column spacers  130  are formed on all the horizontal and vertical intersections or on some of the horizontal and vertical intersections of the net-shaped black matrix  120 , generation of rubbing defects on the pixel region can be prevented when the alignment layer  140  is rubbed from top to bottom as shown in  FIG. 1  or from bottom to top.  
      That is, as shown in  FIG. 3 , in a case in which the column spacers  130  are formed on the horizontal and vertical intersections of the net-shaped black matrix  120  and that rubbing is performed by driving a rubbing roll  160  from top to bottom as shown in the drawing by rotating the rubbing roll  160  in which a rubbing cloth  150  is rolled, the rubbing cloth  150  may be damaged  151  due to the height of the column spacer  130 . In spite of the damage, since rubbing defects  152  are generated along the black matrix  130  from top to bottom as shown in the drawing, the pixel region on which the red, green and blue color filters (R, G and B) are formed is not affected.  
      Meanwhile, as shown in  FIG. 3 , the IPS mode liquid crystal display panel can be used as the liquid crystal display panel in which rubbing is performed from top to bottom or from bottom to top.  
       FIG. 4  is an exemplary view showing a plan structure of a unit pixel of a IPS mode liquid crystal display panel.  
      With reference to  FIG. 4 , in the IPS mode liquid crystal display device, gate lines  201  and data lines  203  are disposed vertically and horizontally, respectively, to thereby define pixel regions. In a practical liquid crystal panel, the ‘N’ number of gate lines  201  and the ‘M’ number of data lines  203  cross each other to thereby define the ‘N×M’ number of pixel regions.  
      Here, a thin film transistor  209  made up of a gate electrode  201 A, a semiconductor layer  205 , a source electrode  202 A and a drain electrode  202 B are disposed in a region where the gate lines  201  and the data lines  203  cross each other. The gate electrode  201 A is connected to the gate line  201 , and the source electrode  202 A is connected to the data lines  203 .  
      In addition, common lines  204  are disposed parallel to the gate lines  201 , and at least a pair of a common electrode  206  and a pixel electrode  207  for applying the electric field to liquid crystal molecules are arranged parallel to the data lines  203 .  
      And, the common electrode  206  is formed simultaneously with the gate lines  201  and connected to the common line  204 . The pixel electrode  207  is formed simultaneously with the source and drain electrodes  202 A and  202 B and connected to the drain electrode  202 B of the thin film transistor  209 .  
      In addition, a pixel electrode line  214  connected to the pixel electrode  207  overlaps with the common line  204  and an insulating layer to thereby form a storage capacitor (Cst).  
      An alignment layer is formed on a surface of a thin film transistor array substrate  210  of the IPS mode liquid crystal display panel having such construction, and rubbing is carried out in a direction opposite to the rubbing direction of the color filter substrate  110  of  FIG. 3 .  
      The color filter substrate  110  and the thin film transistor array substrate  210  in which rubbing has respectively been performed are bonded, in which the red, green and blue color filters (R, G and B) of the color filter substrate  110  are aligned to correspond to the pixel region of the thin film transistor array substrate  210 .  
      Accordingly, the black matrix  120  formed on the color filter substrate  110  is aligned with the gate lines  201 , the data lines  203  and the thin film transistor  209  of the thin film transistor array substrate  210 . And, the column spacers  130  are formed on the horizontal and vertical intersections of the black matrix  120 , that is, on a region where the gate lines  201  and the data lines  203  cross each other so as to maintain the uniform cell-gap when bonding the color filter substrate  110  and the thin film transistor array substrate  210 .  
      Meanwhile,  FIG. 5  is an exemplary view showing a plan structure of the unit pixel of the IPS mode liquid crystal display panel in which the common electrode  206  and the pixel electrode  207  are arranged in a zigzag pattern.  
      With reference to  FIG. 5 , the unit pixel of the IPS mode liquid crystal display panel is substantially identical to that of the IPS mode liquid crystal display panel shown in  FIG. 4  except for the arrangement of the common electrode  206  and the pixel electrode  207  is a zigzag pattern.  
      When the common electrode  206  and the pixel electrode  207  are disposed in the zigzag pattern, a multi-domain can be induced because liquid crystal molecules can be arranged in different directions. In such a multi-domain structure, the abnormal light generated in each of domains due to birefringence characteristics of liquid crystals can be offset by each other so that a color shift phenomenon can be minimized.  
      In the present invention, by forming the column spacers on all the horizontal and vertical intersections or on some of the horizontal and vertical intersections of the net-shaped black, when rubbing is performed from top to bottom as shown in  FIG. 3  or from bottom to top, rubbing defects can be prevented from occurring on the pixel region.  
      The color filter substrate, the method thereof and the liquid crystal display panel having the same in accordance with the present invention in which the column spacers are formed on all the horizontal and vertical intersections or on some of the horizontal and vertical intersections of the net-shaped black matrix can be easily applied to various modes of liquid crystal display panels as well as the IPS mode liquid crystal display panel as shown in  FIGS. 4 and 5 . Those skilled in the art are able to modify and operate the present invention in fabricating various models of liquid crystal display devices using the concept of the present invention.  
      As described, in the color filter substrate, the method thereof and the liquid crystal display panel having the same in accordance with the present invention, the column spacers are formed on all the horizontal and vertical intersections or on some of the horizontal and vertical intersections of the net-shaped black matrix. Therefore, when rubbing of the alignment layer is performed from top to bottom or from bottom to top, rubbing defects may be prevented from occurring on the pixel region. Accordingly, deterioration of picture quality of the liquid crystal display device can be prevented and the manufacturing yield may be improved by minimizing defect factors of the liquid crystal display device.  
      In particular, as the same rubbing defects is prevented from repeatedly generated in liquid crystal display devices mass-produced with the same model, continuous deteriorations of picture quality and manufacturing yield of the liquid crystal display device can be prevented.  
      It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of the invention provided they come within the scope of the appended claims and their equivalents.