Patent Publication Number: US-11644718-B2

Title: Liquid crystal display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/537,701, filed on Nov. 30, 2021, which, in turn, is a continuation of U.S. patent application Ser. No. 16/929,610, filed on Jul. 15, 2020 (now U.S. Pat. No. 11,215,878), which, in turn, is a continuation of U.S. patent application Ser. No. 16/662,128, filed on Oct. 24, 2019 (now U.S. Pat. No. 10,761,381), which, in turn, is a continuation of U.S. patent application Ser. No. 16/286,767, filed on Feb. 27, 2019 (now U.S. Pat. No. 10,495,929), which, in turn, is a continuation of U.S. patent application Ser. No. 16/114,350 (now U.S. Pat. No. 10,261,366), filed on Aug. 28, 2018, which, in turn, is a continuation of U.S. patent application Ser. No. 15/844,825 (now U.S. Pat. No. 10,088,713), filed on Dec. 18, 2017, which, in turn, is a continuation of U.S. patent application Ser. No. 15/606,531 (now U.S. Pat. No. 9,874,785), filed on May 26, 2017, which, in turn, is a continuation of U.S. patent application Ser. No. 14/817,520 (now U.S. Pat. No. 9,696,592), filed on Aug. 4, 2015. Further, this application claims priority from Japanese Patent Application No. 2014-160415 filed on Aug. 6, 2014, the entire contents of which are hereby incorporated by reference into this application. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The invention relates to a display device and particularly, to a liquid crystal display device capable of avoiding black unevenness generated in a display area. 
     (2) Description of the Related Art 
     A liquid crystal display device is formed by a TFT substrate with pixels including pixel electrodes and thin film transistors (TFT) formed in a matrix shape, an opposite substrate facing the TFT substrate, and a liquid crystal interposed between the TFT substrate and the opposite substrate. Then, an image is formed by controlling the transmittance of light through liquid crystal molecules in every pixel. 
     In a liquid crystal display device, there sometimes occurs black unevenness especially in the periphery of a display area. This may be affected by the water entering into the liquid crystal. In order to avoid the water from entering inside, various structures have been developed. On the other hand, there is another way of, even if water enters into the liquid crystal display device, adsorbing the water entered inside in order to suppress the affect on the liquid crystal. 
     Japanese Patent Publication Laid-Open No. 2008-191265 discloses a structure in which an adsorbent layer for adsorbing the water is arranged in a seal portion for sealing the TFT substrate and the opposite substrate. Japanese Patent Publication Laid-Open No. 2012-150290 discloses a structure in which an adsorbent layer for adsorbing the water is arranged between a display area and a seal portion. 
     SUMMARY OF THE INVENTION 
     The both structures described in Japanese Patent Publication Laid-Open No. 2008-191265 and Japanese Patent Publication Laid-Open No. 2012-150290 are to arrange an adsorption layer for adsorbing the water entered inside a liquid crystal display device; then, as the adsorption layer, a material which is not used usually for the liquid crystal display device is used. In other words, something other than the essential material for the operation of the liquid crystal display device is used as another component. This conventional method has the following problems: 
     (1) The other component is arranged in the different process; therefore, the manufacturing cost is increased according to an increase in the component cost and the process. (2) The material other than the essential material for the operation of the liquid crystal display device is used; therefore, it is necessary to check whether the display performance is affected by the material when the liquid crystal display device is operated for a long time. 
     An object of the invention is to solve the above problems and to avoid black unevenness from occurring in a liquid crystal display device by effectively adsorbing water entered into a liquid crystal display panel, without increasing the manufacturing cost and without deteriorating reliability. 
     The invention is to solve the above problems and the concrete means are as follows. 
     (1) A liquid crystal display device including a display area and a terminal portion, in which a TFT substrate with an organic passivation film formed there and an opposite substrate are adhered to each other by a seal portion and a liquid crystal is enclosed there, wherein in the seal portion of the TFT substrate, a groove-shaped through-hole is formed in the organic passivation film to surround the display area, a water absorption layer formed of the same material in the same process as that of the organic passivation film is formed within the groove-shaped through-hole, and the water absorption layer is not covered with the inorganic insulating film. 
     (2) The device according to the above (1), wherein the water absorption layer is continuously formed along the whole periphery to surround the display area. 
     (3) The device according to the above (1), wherein the water absorption layer is formed discontinuously to surround the display area. 
     (4) The device according to the above (1), wherein the water absorption layer is formed only in the corner portions of the display area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a top plan view of a liquid crystal display device according to the invention. 
         FIG.  2    is a cross-sectional view taken along the line A-A of FIG.  1 . 
         FIG.  3    is an enlarged top plan view corresponding to  FIG.  2   . 
         FIG.  4    is an enlarged cross-sectional view of a seal portion of  FIG.  2   . 
         FIG.  5    is an enlarged cross-sectional view of another example of the seal portion of  FIG.  2   . 
         FIG.  6    is a schematic plan view illustrating the invention. 
         FIG.  7    is a schematic plan view illustrating another example of the invention. 
         FIG.  8    is a schematic plan view illustrating further another example of the invention. 
         FIG.  9    is a cross-sectional view illustrating the structure of the seal portion of the liquid crystal display device used together with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before describing the embodiment of the invention, a structure for avoiding water from entering into a liquid crystal layer, which is used together with the invention, will be described.  FIG.  9    is a cross-sectional view in the vicinity of a seal portion of a liquid crystal display device. In  FIG.  9   , a TFT substrate  100  and an opposite substrate  200  are adhered to each other by a sealing material  20 . An organic passivation film  4  serving also as a flattening film is formed on the TFT substrate  100 . This organic passivation film  104  is formed of acrylate resin; therefore, the above film absorbs water and transmits the water easily. Further, the organic passivation film  104  also serves as the flattening film and formed thick with 1 to 4 μm, generally with 2 to 3 μm; therefore, the above film easily transmits the water. 
     The organic passivation film is provided with a groove-shaped through-hole along the end portion of the TFT substrate  100  in a way of surrounding a display area. The water absorbed by the organic passivation film  104 , coming from the end portion of the substrate inwardly, is shut out by the groove-shaped through-hole  1041  and does not arrive at a liquid crystal layer  300 . In the groove-shaped through-hole  1041 , the organic passivation film  104  is covered with the insulating film  105  formed of SiN; therefore, it takes a long time for the entered water to pass the groove-shaped through-hole  1041 , hence to prolong a lifetime of the liquid crystal display device as much. 
     In the structure as illustrated in  FIG.  9   , however, once the water passes the insulating film  105 , the water easily arrives at the liquid crystal layer  300 . According to the structure as illustrated in  FIG.  9   , there is a limit to a long life of the liquid crystal display device. 
     In the opposite substrate  200  in  FIG.  9   , a black matrix  201  is formed extensively in the end portion of the substrate. The black matrix  201  is formed of an organic material in many cases. When the black matrix is formed of the organic material, water easily enters from the end portion. In order to shut down the water entered through the black matrix  201 , a black matrix groove  2011  is formed. The black matrix is not so thick as the organic passivation film  104  in the TFT substrate  100  and therefore, the entered amount of the water is smaller than that on the side of the TFT substrate. The contents of the invention will be described in detail using the following embodiments. 
     First Embodiment 
       FIG.  1    is a top plan view of a liquid crystal display device to which the invention is applied. In  FIG.  1   , the TFT substrate  100  and the opposite substrate  200  are adhered to each other by the sealing material  20 , with the liquid crystal interposed between the TFT substrate  100  and the opposite substrate  200 . The TFT substrate  100  is formed larger than the opposite substrate  200 , and a portion of only one sheet of the TFT substrate  100  is a terminal portion  150 . In the terminal portion  150 , an IC driver  160  for driving a liquid crystal display panel and terminals for connecting a flexible wiring substrate for supplying power, video signals, and scanning signals to the liquid crystal display panel are formed. 
     In  FIG.  1   , in a display area  500 , scanning lines  30  respectively extend in a horizontal direction and are aligned in a vertical direction. Further, video signal lines  40  respectively extend in the vertical direction and are aligned in the horizontal direction. An area surrounded by the scanning line  30  and the video signal line  40  is a pixel  35 . In a narrow frame, a distance w between the end portion of the display area  500  and the end portion of the liquid crystal display device is small with about 1 mm. In this case, the width of the sealing material becomes smaller and if so, the outside water gets easily reach the liquid crystal layer in the display area. This easily causes a so-called black unevenness easily, affected by the water. 
       FIG.  2    is a detailed cross-sectional view of a seal portion corresponding to the cross section taken along the line A-A of  FIG.  1   . In the seal portion illustrated in  FIG.  2   , the TFT substrate  100  and the opposite substrate  200  are adhered to each other by the sealing material  20 . In  FIG.  2   , the liquid crystal  300  is charged inside the sealing material  20 . In  FIG.  2   , a first insulating film  101  is formed on the TFT substrate  100  formed of glass. The first insulating film  101  can be occasionally an undercoat film formed to prevent the impurities generated from the glass from contaminating the TFT semiconductor layer. A second insulating film  102  is formed on the first insulating film  101 . The second insulating film  102  can be occasionally a gate insulating film in the TFT. A scanning-line lead line  103  is formed on the second insulating film  102 . The scanning-line lead line  103  shown in a rectangular shape in  FIG.  2    is a cross section of the scanning-line lead line  103 , which is connected to the scanning line  30  in  FIG.  1   . 
     An organic passivation film  104  is formed to cover the scanning-line lead lines  103 . The organic passivation film  104  is formed thick with 2 to 3 μm, also serving as a flattening film. The organic passivation film  104  is formed of photosensitive resin, which does not need photoresist for patterning. 
     In the display area, it is necessary to connect a pixel electrode or a common electrode formed on the organic passivation film  104  to a source electrode of the TFT, which connection is performed through the through-hole formed on the organic passivation film  104 . The organic passivation film  104  is formed of resin such as acrylic resin. This film easily absorbs water and when the pixel electrode or the common electrode is formed directly on the organic passivation film  104 , the pixel electrode or the common electrode is exfoliated especially in the through-hole portion, due to the water absorbed by the organic passivation film  104 . In order to avoid this phenomenon, the conventional art has been designed in that the diameter of the through-hole is enlarged so that the inorganic insulating film  105  may cover the organic passivation film assuredly, also in the through-hole. In other words, in the conventional art, it has been essential that the organic passivation film  104  is covered with the inorganic insulating film  105 . 
     In  FIG.  2   , an interlayer insulting film  105  made of SiN is formed on the organic passivation film  104 . This interlayer insulting film  105  is an insulating film between a lower layer electrode formed flat and an upper layer electrode having a slit in the display area of the liquid crystal display device of the IPS method. In some cases, the lower electrode may be the common electrode and the upper layer electrode may be the pixel electrode and in other cases, it may be reversed; the lower layer electrode and the upper layer electrode are both formed of transparent oxide conductive film represented by Indium Tin Oxide (ITO). 
     Since the organic passivation film  104  easily transmits the water, as described in  FIG.  9   , the groove-shaped through-hole  1041  is formed in the organic passivation film  104  in order to shut out the water coming from the end portion through the organic passivation film  104 . The groove-shaped through-hole  1041  is formed around the whole periphery of the TFT substrate  100  to surround the display area within the seal portion. 
     The characteristic of the invention is that a water absorption layer  10  formed by the organic passivation film is formed in a shape of wall within the groove-shaped through-hole  1041 , not covered with the inorganic insulating material. This water absorption layer  10  is to absorb the water when water transmitted from the end portion of the TFT substrate  100  through the organic passivation film  104  further intends to pass the groove  1041  of the organic passivation film  104 . According to this, a time from the intrusion of the water into the liquid crystal display panel to the arrival at the liquid crystal layer  300  can be prolonged. As the result, a lifetime of the liquid crystal display device can be prolonged. 
     In  FIG.  2   , an alignment film  106  is formed on the interlayer insulting film  105 . The alignment film  106  is formed by applying an alignment film material that is originally liquid according to the flexography or inkjet, and three concave portions are formed on the organic passivation film  104  as a stopper so that the alignment film material does not arrive at the outer end portion of the seal portion. Further, the groove-shaped through-hole  1041  formed further outside of the concave portions also serves as the stopper against the alignment film material. In  FIG.  2   , the alignment film material passes over the three concave portions and stops in the final convex portion. 
     In  FIG.  2   , a black matrix  201  is formed on the side of the opposite substrate  200 . The black matrix  201  in  FIG.  2    is provided in order to avoid light from leaking from the seal portion. The black matrix  201  is formed of resin and a black matrix groove  2011  is formed in order to shut down the water transmitted through the resin. A color filter  202  is formed on the black matrix  201  in a stripe shape in a direction vertical to the paper surface. The color filter  202  is formed correspondingly to a first column spacer  210  formed on an overcoat film  203 . 
     The overcoat film  203  is formed on the color filter  202 . The overcoat film  203  is provided with a convex portion in correspondence with the portion of the color filter  202 . This convex portion is to avoid the alignment film material from spreading outside of the substrate when applying the alignment film material. The first spacer  210  is formed in the convex portion of the overcoat film  203 . The column spacer  210  is to define the space between the opposite substrate  200  and the TFT substrate  100  in the seal portion. 
     In  FIG.  2   , a second column spacer  220  lower than the first column spacer  210  is formed nearer to the side of the display area than the first column spacer  210 . When a pressure is applied to the opposite substrate  200  from the outside, the second column spacer  220  is to avoid the space between the TFT substrate  100  and the opposite substrate  200  from narrowing excessively. 
     A wall spacer  250  is formed outside of the first column spacer. This wall spacer becomes the stopper against the alignment film. The wall spacer  250  is formed in two stages. The alignment film  106  is formed to cover the overcoat film  203 . The outer shape of this alignment film is partitioned by the wall spacer  250 . 
     A bank-shaped spacer  230  is formed in the end portion of the seal portion. Production of the individual liquid crystal display panels is inefficient; therefore, a plurality of liquid crystal display panels are formed on a mother substrate to produce the liquid crystal display panels at once. In the mother substrate with the plural liquid crystal display panels formed there, the bank-shaped spacer  230  is arranged in the boundary of the liquid crystal display panels, scribing is performed along the center of the bank-shaped spacer  230 , and then, the substrate is cut into individual pieces of liquid crystal display panels. When there is no bank-shaped spacer  230 , this portion is the sealing material  20  and when the sealing material  20  exists, even if scribing is performed, it cannot be cut. 
       FIG.  3    is a top plan view corresponding to the portion of  FIG.  2   . In  FIG.  3   , the sealing material  20  is formed inside the bank-shaped spacer  230 . In  FIG.  3   , the color filter  202  is formed in a stripe shape and the first column spacer  210  is arranged in the portion corresponding to the color filter  202 . In  FIG.  3   , the color filter  202  and the first column spacer  210  are shown, by way of example, for two lines. The wall spacer  250  is arranged between the first column spacer  210  and the first column spacer  210 . The sealing material  20  is formed extensively in the end portion of the bank-shaped spacer  230 . In  FIG.  3   , the water absorption layer  10  is formed between the bank-shaped spacer  230  and the color filter  202  on the side of the TFT substrate. 
       FIG.  4    is a cross-sectional view enlarging the portion of the water absorption layer  10  in  FIG.  2   . In  FIG.  4   , the water absorption layer  10  is formed in the portion of the groove-shaped through-hole  1041  of the organic passivation film  104 . This water absorption layer  10  is formed of the same material in the same process as that of the organic passivation film  104 ; as the result, there needs no additional material cost and process in order to form the water absorption layer. 
     The water absorption layer  10  is not covered with the inorganic insulating film  105 , differently from the organic passivation film  104  in the other portion. Therefore, after completion of the liquid crystal display device, it can absorb the water transmitted through the sealing material  20 . In  FIG.  4   , the width w 1  of the water absorption layer  10  is, for example, 30 μm and the height h is 2 to 3 μm. On the other hand, the width of the groove-shaped through-hole  1041  formed in the organic passivation film  104  is about 70 μm. Here, these numeric values can be adjusted according to the water absorption effect expected by the water absorption layer.  FIG.  5    is a cross-sectional view when the cross section of the water absorption layer  10  is trapezoid; when the water absorption layer  10  is in this shape, the width w of the water absorption layer  10  can be measured only by the bottom of the trapezoid. Here, in the embodiment, the water absorption layer is not covered with the inorganic insulating film, but a part thereof may be covered with the inorganic insulating film to expose the part from the inorganic insulating film. Further, according to the water entering amount, in a plan view, the area of the portion exposed from the inorganic insulating film may be partially various. 
       FIG.  6    is a top plan view only showing the shape of the water absorption layer  10  in the TFT substrate. As illustrated in  FIG.  6   , the water absorption layer  10  is generally formed in the whole periphery to surround the display area  500 . However, when the water absorption layer  10  cannot be formed continuously in the periphery with regard to the layer of the wiring, the above layer  10  may be formed discontinuously, as illustrated in  FIG.  7   . Especially, in the screen corners, when black unevenness occurs on the screen, the water absorption layer  10  may be formed only around the corners, as illustrated in  FIG.  8   . Further, in  FIGS.  6  to  8   , the water absorption layer  10  is formed in a linear shape in a plan view; however, it is not restricted to this but may be formed in a wave shape or a zigzag. 
     As mentioned above, according to the invention, the water absorption layer  10  can be formed in the same material in the same process as that of the organic passivation film  104 ; therefore, the black unevenness generated on the screen due to the water can be avoided without an increase in the manufacturing cost.