Abstract:
A liquid crystal display device minimizing touch inferiority and a press inferiority defects is provided. The device includes first and second substrates, a liquid crystal layer interposed therebetween, gap spacers between the first and second substrates for maintaining a cell gap, and pressure spacers between the first and second substrates configured to contact the first and second substrates when pressure is applied to the first or second substrate, wherein a spatial density of the gap spacers or a spatial density of the pressure spacers varies at different positions across the first and second substrates.

Description:
PRIORITY CLAIM  
       [0001]     This application claims the benefit of priority to Korean Patent Applications No. 136115/2005, filed on Dec. 30, 2005 and No. 43314/2006, filed on May 15, 2006, herein incorporated by reference.  
       TECHNICAL FIELD  
       [0002]     The present invention relates to a liquid crystal display (LCD) device, more particularly, to an LCD device which is capable of preventing a touch inferiority and a press inferiority by adjusting a density of both gap spacer and pressure spacer according to a position of an LCD panel.  
       BACKGROUND  
       [0003]     In view of their compact construction, light weight, and low power-consumption, flat panel display devices are being widely developed. Flat panel displays include liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and vacuum fluorescent displays (VFDs). Owing to the ease with which they are driven, and to their superior ability to display images, LCDs are becoming increasingly popular.  
         [0004]      FIG. 1  is a schematic diagram illustrating a section of a typical LCD panel. As illustrated in  FIG. 1 , an LCD panel  1  generally comprises a lower substrate  5 , an upper substrate  3  and a liquid crystal layer  7  disposed therebetween. The lower substrate  5  (also known as the driving device array substrate) includes a plurality of pixels (not shown), in which each pixel includes a driving device or thin film transistor (TFT). The upper substrate  3 , also known as the color filter substrate, includes a color filter layer to provide color. The lower and upper substrates  5  and  3  further include pixel electrodes and common electrodes, respectively. An alignment layer is formed on the lower and upper substrates  5  and  3  to align liquid crystal molecules from the liquid crystal layer  7 .  
         [0005]     The lower substrate  5  and the upper substrate  3  are bonded to one another by a sealant  6  at peripheral regions thereof. A spacer  8  is interposed between the lower and upper substrates  5  and  3  to maintain a constant cell-gap therebetween. Images are displayed as the driving devices in the lower substrate  5  control light transmittance through the liquid crystal layer  7  via the liquid crystal molecules disposed between the lower and upper substrates  5  and  3 .  
         [0006]     An LCD panel may be fabricated using a driving device array substrate forming process to form driving devices in the lower substrate  5  and a color filter substrate forming process to form the color filter in the upper substrate  3 . A spacer and sealant forming process may be employed to complete the fabrication process.  
         [0007]     The driving device array substrate forming process typically includes forming a plurality of gate and data lines arranged on the lower substrate  5  to define pixel regions, forming thin film transistors (TFTs) (i.e., the driving devices) in each pixel region with each TFT being connected to a gate and data line, and forming pixel electrodes for driving the liquid crystal layer  7  when signals are applied through the TFTs. The color filter substrate forming process includes forming a black matrix on the upper substrate  3 , forming a color filter on the formed black matrix, and forming a common electrode.  
         [0008]     The spacer  8  can be a column spacer or a ball spacer. It is difficult to evenly distribute ball spacers on a substrate and maintain a uniform cell gap without reducing the aperture ratio in an LCD panel. Column spacers may be better suited for maintaining a constant cell gap and for preserving the aperture ratio, since they can be formed at predetermined positions throughout the LCD panel.  
         [0009]     However, column spacers have their own share of problems. First, they may be unable to prevent a touch inferiority defect at the surface of the LCD device. For example, when a surface portion of an LCD device is swept away, non-uniform brightness at the swept portion may generate a stain. Secondly, a press inferiority defect may occur when the surface of an LCD device is pressed under constant strength. In this case, the color filter substrate or the TFT substrate may be altered so that a corresponding stain is generated.  
       SUMMARY  
       [0010]     In an embodiment, a liquid crystal display device includes first and second substrates and a liquid crystal layer between the first and second substrates. Column spacers reside between the first and second substrates to maintain a cell gap and protrusions contact corresponding column spacers where the spatial density of the protrusions varies at different positions across the first or second substrates.  
         [0011]     In another embodiment, a liquid crystal display device includes first column spacers contacting the first and second substrates and second column spacers on one of the first and second substrates and spaced apart from the other of the first and second substrates. The spatial density of the first column spacers varies across the first and second substrates, such that the spatial density in a center portion is less than an outer periphery portion.  
         [0012]     In yet another embodiment, a liquid crystal display device includes a plurality of pixels. First column spacers contact first and second substrates and second column spacers reside on one of the first and second substrates and are spaced apart from the other of the first and second substrates. The number of the first column spacers in the plurality of pixels varies across the first and second substrates, such that the number of first column spacers in the pixels in a center portion of the display is less than the number of first column spacers in the pixels in a periphery portion.  
         [0013]     In still another embodiment, a liquid crystal display device includes first column spacers contacting first and second substrates. A plurality of pixels include gate lines and data lines. Second column spacers reside on one of the first and second substrates and are spaced apart from the other of the first and second substrates. The number of second column spacers between the first column spacers increases along the data and gate lines from a peripheral portion of the display toward a center portion of the display.  
         [0014]     In a further embodiment, a liquid crystal display device includes first and second substrates and a liquid crystal layer between the first and second substrates. Column spacers reside between the first and second substrates to maintain a cell gap. Protrusions contact corresponding column spacers and the distance between the protrusions increases in a direction from a periphery of the display toward a center of the first or second substrates.  
         [0015]     In a still further embodiment, a method for making a liquid crystal display device includes forming first and second substrates and forming column spacers between the first and second substrates to maintain a cell gap. Protrusions are formed contacting corresponding column spacers, where a spatial density of the protrusions varies at different positions across the first or second substrates. A liquid crystal layer is disposed between the first and second substrates. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a sectional view schematically illustrating an LCD panel;  
         [0017]      FIG. 2  is a sectional view illustrating an LCD panel according to one aspect of the disclosure;  
         [0018]      FIG. 3  is a plan view illustrating an LCD panel according to the invention.  
         [0019]      FIGS. 4A and 4B  are partial sectional views along line I-I′ of  FIG. 3 ;  
         [0020]      FIGS. 5A and 5B  schematically illustrate density differences in gap spacer and pressure spacer localization according to position on an LCD panel;  
         [0021]      FIGS. 6A-6C  are graphs illustrating the density of the protrusions in the LCD panel according to the present invention; and  
         [0022]      FIGS. 7A-7C  are views illustrating the LCD panel having the protrusions and the column spacers according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0023]     Touch inferiority may be generated on an LCD device due to contact between column spacers and substrates during touching. That is, contact between a column spacer and a substrate may generate a frictional force therebetween. If the substrate is negatively impacted by these frictional forces, the liquid crystal molecules may not recover their original state and a stain may be generated in the touched portion. The touch inferiority can be minimized or prevented by reducing the number of column spacers in contact with the substrates.  
         [0024]     Press inferiority may be generated when pressure is applied to the substrates so as to produce changes in the color filter substrate and/or the thin film transistor (TFT) substrate. Press inferiority can be minimized or prevented by maximizing the number of column spacers so that when the pressure is applied, changes to the color filter substrate and/or the TFT substrate are prevented.  
         [0025]     Touch inferiority and press inferiority operate by opposing principles. When the spatial density of column spacers is increased, the contact areas between the column spacers and substrates is increased, thereby resulting in increased touch inferiority. However, as the application of pressure to the substrates increases, press inferiority is reduced. On the other hand, when the spatial density of column spacers is reduced, the contact areas between the column spacers and substrates is decreased, thereby resulting in reduced touch inferiority. However, as the application of pressure to the substrates increases, the substrates may be altered, increasing press inferiority.  
         [0026]     In view of the contrary principles underlying touch inferiority and press inferiority, it is difficult to simultaneously reduce or prevent both phenomena. In other words, one cannot simply adjust the number of column spacers or their spatial density to simultaneously reduce both touch inferiority and press inferiority.  
         [0027]     The present invention provides column spacers to minimize touch inferiority and press inferiority. The column spacers are illustrated in  FIG. 2 .  
         [0028]     As shown in  FIG. 2 , a sealant  106  is used to bond a lower substrate  105  with driving device arrays such as TFTs to an upper substrate  103  having a color filter. A liquid crystal layer  107  is interposed between the lower and upper substrate  105  and  103 . On the upper substrate  103 , a plurality of first column spacers  108  and second column spacers  109  are formed. At this time, the first column spacers  108  and the second column spacers  109  are spaced from the lower substrate  105  in a predetermined distance. On the lower substrate  105 , a plurality of protrusions  118  are formed at the corresponding region to the first column spacers  108 . As shown in  FIG. 2 , the first column spacers are contacted with the protrusions  118 , but the second column spacers  109  are separated from the lower substrate  105 .  
         [0029]     The first column spacers  108  are contacted with the protrusions on the lower substrate  105  to maintain a constant cell gap between the upper and second substrates  103  and  105 . Thus, the combination of the first column spacers  108  the protrusion  118  function as a gap spacer to maintain the constant cell gap.  
         [0030]     Since the second column spacers  109  are spaced from the lower substrate  105  at a predetermined distance, the second column spacers  109  are not in contact with the lower substrate  105 . When the upper substrate  103  and the lower substrates  105  are pressed, however, the second column spacers  109  are brought in contact with the lower substrate  105  so that the distortion of the upper substrate  103  and the lower substrate  105  is prevented. Thus, the second column spacer  109  function as pressure spacers.  
         [0031]     The first column spacers  108  and the second column spacers  109  are formed on the upper substrate  103  by the same material such as an organic material in the same process, and the protrusions  118  are formed on the lower substrate  105  by a different process from that of the column spacers  108  and  109 . That is, the first and second column spacers  108  and  109  have substantially same structure. Thus, both first and second column spacer  108  and  109  are arranged in the same spatial configuration as conventional the column spacers.  
         [0032]     In accordance with an embodiment of the invention, only the first column spacers  108  contact the protrusions  118 , such that the first column spacers  108  maintain the cell gap of the liquid crystal display panel  101 . Since the number of the protrusions  118  is smaller than the total number of the first and second column spacers  108  and  109 , however, the number of the gap spacers (that is, the combination of the first column spacers  108  and the protrusions  118 ) to maintain the cell gap is smaller than the number of the prior art gap spacers (that is, the conventional column spacers of the prior art). Therefore, the number of the column spacers in contact with the lower substrate is decreased compared with the prior art column spacers, so that the contact area between the column spacers and the lower substrate is decrease.  
         [0033]     Further, as shown in  FIG. 2 , since the section area of the protrusions  118  is smaller than that of the first column spacers  108 , the contact area between the column spacers and the lower substrate  105  is further decreased compared with the contact area of prior art column spacers. In the liquid crystal panel of this invention, accordingly, the touch inferiority may be effectively prevented.  
         [0034]     Further, since the second column spacers  109  are then brought in contacted with the lower substrate  105  and function as pressure spacers when the first and second substrates  103  and  105  are pressed, the press inferiority caused by the pressure may be effectively prevented.  
         [0035]     When pressure is not applied to the upper substrate  103  and the lower substrate  105 , in accordance with the illustrated embodiment only the first column spacers  108  are in contact with the protrusions  118  to maintain the cell gap of the liquid crystal display panel  101 . Comparing with the prior art, thus, the number of the column spacers in contact with the lower substrate is decreased so that the touch inferiority may be prevented. Further, when pressure is applied to the upper substrate  103  and the lower substrate  105 , the first column spacers  108  are also in contact with the protrusions  118  and the second column spacers  109  are also in contact with the lower substrate  105 , so that press inferiority may be prevented. In other word, since all column spacers  108  and  109  are in contact with the lower substrate  105  when pressure is graded to the upper and lower substrate the press inferiority may be prevented.  
         [0036]      FIG. 3  is a plan view of a liquid crystal display device having the column spacers  108  and  109  of this invention. Although an in-plane switching mode liquid crystal display device is shown in figure as one example of the invention, other types liquid crystal display devices such as a Twisted Nematic mode and a Vertical Alignment mode liquid crystal display device, and the like, may be adapted to the invention.  
         [0037]     As shown in the illustrated embodiment of  FIG. 3 , the liquid crystal display device includes a plurality of pixels defined by a plurality of gate lines  130  and data lines  135  and a thin film transistor  150  is disposed at each pixel.  
         [0038]     The thin film transistor  150  includes a gate electrode  151  connected to the gate line  130  to which a scan signal is applied, a semiconductor layer  152  on the gate electrode  130  to be activated by the scan signal applied to the gate electrode  130  to form a channel layer, and a source and drain electrodes  153  and  154  on the semiconductor layer  152  to transmit the image signal from the data line  135  to the pixel.  
         [0039]     At least one common electrode  162  and pixel electrode  164  are parallel disposed in the pixel to generate an electric field parallel to the surface of the substrate. A common line  137  connected to the common electrode  162  and a pixel electrode line  138  connected to the pixel electrode  164  are disposed in the pixel. The common line  137  and the pixel electrode line  138  overlap to generate a storage capacitance.  
         [0040]     A plurality of column spacers  108  and  109  are formed over the gate line  130 . Although only one column spacer is formed in each pixel in  FIG. 3 , alternatively two column spacers may be formed in each pixel or only one column spacer may be formed in at least two pixels.  
         [0041]     The protrusions  118  are formed over the gate line  130  to be contact with the first column spacers  108  in order to maintain the constant cell gap. Although only one protrusion  118  is disposed in every two pixels in  FIG. 3 , alternatively one protrusion  118  may be disposed in each pixel or at least two protrusions  118  may be formed in each pixel.  
         [0042]     The combination of the first column spacers  108  and the protrusions  118  act as the gap spacer and the second column spacers  109  which is not contacted with the protrusions  118  acts as pressure spacers.  
         [0043]     In one aspect of the illustrated embodiment, the gap spacers and the pressure spacers are alternatively disposed in the pixels. In the illustrated embodiment, the gap spacers and the pressure spacers are distributed in the whole area of the substrates  103  and  105  to maintain the constant cell gap and to prevent the touch inferiority and the press inferiority.  
         [0044]     Although the column spacers  108  and  109  and the protrusions  118  are formed over the gate line  130  in  FIG. 3 , alternatively the column spacers  108  and  109  and the protrusions  118  may be formed over the data line  135  or in the cross region of the gate line  130  and the data line  135 .  
         [0045]      FIGS. 4A and 4B  are sectional views along the I-I′ line of  FIG. 3  illustrating the structure of the column spacers  108  and  109  and the protrusions  118  of the LCD panel according to the illustrated embodiment. The upper substrate is a color filter substrate having a color filter (not shown); the lower substrate is a TFT substrate having a plurality of TFTs. The illustrated TFT includes a gate electrode  151  on the lower substrate  105 , a gate insulating layer  162  on the lower substrate  105 , a semiconductor layer  152  on the insulation layer  162 , and a source electrode  153  and a drain electrode  154  on the semiconductor layer  153 . Further, the protrusion  118  includes a semiconductor layer  118 A on the gate insulating layer  162  and a metal layer  118 B on the semiconductor layer  118 A. A passivation layer  164  is formed over the TFT and the protrusion  118 .  
         [0046]     The semiconductor layer  118 A of the protrusion  118  may be formed by the same process as the semiconductor layer  152  of the TFT. The metal layer  118 B may be formed by the same process as the source electrode  153  and the drain electrode  154  of the TFT. Though the semiconductor layer  118 A and the metal layer  118 B may be formed by different processes than the TFT, the protrusion  118  and the TFT may be formed by the same process. The protrusion  118  may be formed from semiconductor material or metallic material.  
         [0047]     The first column spacers  108  and the second column spacers  109  are formed on the upper substrate  103 . The first column spacers  108  and the second column spacers  109  are formed from organic material by common or separate processes.  
         [0048]     As shown in  FIG. 4B , the protrusion  118  may be formed on the passivation layer  164  of the lower substrate  105 . The protrusion  118  may be formed from organic or metallic materials. The first column spacers  108  may directly contact the lower substrate  105  without the protrusion  118 . In this case, the sectional area of the end portion contacting the lower substrate  105  may be reduced to decrease the frictional force between the surface of the lower substrate  105  and the first column spacers  108 .  
         [0049]     To simultaneously counteract touch inferiority and press inferiority in an LCD panel, an LCD panel may be configured so that the protrusions  118  are localized at different densities according to position on an LCD panel.  
         [0050]     The degree of the touch inferiority and the press inferiority is different at the central region and the edge region of the LCD panel. The touch inferiority is maximum at the central region of the LCD panel and decreases toward to the edge region of the LCD panel. Thus, the number (or density) of the gap spacers causing the touch inferiority is highest at the central region and decreases toward to the central region from the edge region to minimize the touch inferiority.  
         [0051]     Further, press inferiority is maximum at the central region of the LCD panel and decreases toward to the edge region of the LCD panel. Thus, the number (or density) of the pressure spacers to be contact with the substrates by the pressure inferiority is highest at the central region and decreases toward to the central region from the edge region to minimize the press inferiority.  
         [0052]     As described above, the gap spacers and the press spacers are formed to have different density (or number) according to the position on the LCD panel and thereby the touch inferiority and the press inferiority may be prevented. Meanwhile, the gap spacer and the press spacer are defined by the protrusions  118 . That is, the first column spacers  108  act as the gap spacer because they are contacting with protrusions  118  and the second column spacers  109  act as the press spacer because they are not contacted with the protrusions  118 . Since the column spacers  108  and  109  are uniformly distributed in the LCD panel, the density (or number) of the gap spacer and the press spacer are dependent upon the density (or number) of the protrusion  118 . In other word, the density (or number) of the protrusions  118  is decreased toward to the central region from the edge region and the density (or number) of the gap spacer is also decreased toward to the central region. Further, because there are fewer protrusions, the density (or number) of press spaces increases toward to the central region.  
         [0053]      FIGS. 5A and 5B  are views indicating conceptually the density of the protrusions  118 . The protrusions  118  are positioned at higher spatial densities “a” at the edge region and at decreasing spatial densities near the central region of the LCD panel as shown in  FIGS. 5A and 5B  (namely, a 1 &lt;a 2 &lt;a 3 &lt;a 4 , here, each of a 1 , a 2 , a 3  and a 4  denotes a protrusion density at regions I, II, III and IV divided in the LCD panel). The density regions may be defined by circular or square shapes as shown in  FIGS. 5A and 5B , respectively. Selection of the square or circular shapes may depend on the size of a fabricated LCD panel  101  or an aspect ratio. The density regions of the LCD panel  101  need not be limited to four regions, however; instead, they may be divided by essentially any plurality of density regions.  
         [0054]     By configuring the LCD panel to have different distributions of the protrusions  118  depending on LCD panel location to have different distributions of the gap spacers and the pressure spacers, it is possible to simultaneously reduce both touch inferiority and press inferiority in an LCD panel.  
         [0055]     The density of the protrusions  118  may be increasing in various configurations toward the edge region from the central region of the LCD panel. For example, the density of the protrusions  118  may be linearly or non-linearly varied.  
         [0056]     The variation of the density of the protrusions  118  in the LCD panel means a variation of the number of the protrusions  118  and a variation of the distance between the neighboring protrusions  118 . That is, the increase in density of the protrusions  118  at the edge region of the LCD panel means an increase in the number of the protrusions  118  and decrease in the distance between the neighboring protrusions at the corresponding region. Further, the decrease of density of the protrusions  118  at the central region of the LCD panel means a decrease in the number of the protrusions  118  and an increase in the distance between the neighboring protrusions at the corresponding region.  
         [0057]      FIGS. 6A-6C  are graphs illustrating the density of the protrusions  118  in an LCD panel arranged in accordance with an embodiment of the invention and  FIGS. 7A-7C  are views illustrating an LCD panel having the protrusions  118  and the column spacers  108  and  109 . For purposes of illustration, since the figures are drawn to describe conceptually the invention, only the pixels are drawn without the detail structure of the LCD panel. That is, the figures includes only the pixels arranged in the vertical and horizontal directions and the protrusions and the column spacers therein without the detailed structure.  
         [0058]     Though not shown in the figures, the LCD panel of this invention includes IPS mode, TN mode, and VA mode LCD panels. Further, though the column spacers  108  and  109  and the protrusions  118  are disposed within the pixels in figures, the column spacers  108  and  109  and the protrusions  118  can be disposed over the gate line, over the data line, and at the cross region of the gate line and the data line.  
         [0059]     As shown in  FIG. 6A , the density of the protrusions  118  may be linearly increased toward the edge region from the central region of the LCD panel (where the origin represents the center of the LCD panel). Accordingly, the density of the protrusions  118  is linearly increased, as the distance d from the central region is increased. The linear variation of the density of the protrusions  118  is shown in  FIG. 7A . In  FIG. 7A , the column spacers  108  and  109  are disposed in each pixel and the protrusions  118  are disposed in predetermined pixels to form the gap spacers. In this case, the distance between the neighboring protrusions  118  is linearly decreased and the number of the protrusions  118  is linearly increased toward to the edge region from the central region.  
         [0060]     Since the protrusions  118  are contacted with the first column spacers  108  to form the gap spacer, in the aspect of the gap spacer, the density of the gap spacers may be linearly increased toward to the edge region from the central region of the LCD panel.  
         [0061]     As shown in  FIG. 6B , in this invention the density of the protrusions  118  of this invention may exponentially increase toward the edge region from the central region of the LCD panel. The density of the protrusions  118  is exponentially increased, as the distance d from the central region is increased. As shown in  FIG. 7B , the distance between the neighboring protrusions  118  is exponentially decreased and the number of the protrusions  118  is exponentially increased toward to the edge region from the central region.  
         [0062]     As shown in  FIG. 6C , in a further aspect of the invention the density of the protrusions  118  may logarithmically increase toward the edge region from the central region of the LCD panel. The density of the protrusions  118  is logarithmically increased, as the distance d from the central region is increased. As shown in  FIG. 7C , the distance between the neighboring protrusions  118  is logarithmically decreased and the number of the protrusions  118  is logarithmically increased toward to the edge region from the central region.  
         [0063]     As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims. Therefore, changes and modifications that fall within the metes and bounds of the claims, or equivalents thereof are intended to be embraced by the appended claims.