Patent Publication Number: US-11650467-B2

Title: Liquid crystal display device

Description:
CLAIM OF PRIORITY 
     The present application claims priority from Japanese Patent Application JP 2013-254205 filed on Dec. 9, 2013, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display device. The invention more particularly relates to a liquid crystal display device in which reduction in transmissivity is small even in a case where the screen is a high-definition screen, the liquid crystal display device having few pixel defects in the high-definition screen. 
     2. Description of the Related Art 
     In a liquid crystal display device, a thin film transistor (TFT) substrate in which pixels each including a pixel electrode, a TFT, and the like are formed like a matrix, a counter substrate facing the TFT substrate and having color filters formed at positions in facing relation to the pixel electrodes on the TFT substrate are arranged, and liquid crystal is sandwiched between the TFT substrate and the counter substrate. The liquid crystal display device forms images by controlling light transmissivity of liquid crystal molecules at each pixel. 
     The liquid crystal display device is flat and lightweight. Thus, the application of the liquid crystal display device has been extended in various fields. A small liquid crystal display device has widely been used in portable information terminals, such as mobile phones, smartphones, and Digital Still Cameras (DSCs). A viewing angle characteristic is a key issue in liquid crystal display devices. The viewing angle characteristic relates to a phenomenon that brightness or chromaticity changes between cases where a screen of the liquid crystal display device is viewed from front and where the screen is viewed from an oblique direction. An In-Plane Switching (IPS, which is a registered trademark of Japan Display Inc.) system causing a horizontal electric field to operate liquid crystal molecules has an excellent viewing angle characteristic. 
     Although various IPS systems exist, e.g., a system in which a common electrode is formed in a planar and solid manner and in which a comb-teeth pixel electrode is arranged above the common electrode so as to sandwich an insulating film between the pixel electrode and the common electrode, and to cause an electric field generated between the common electrode and the pixel electrode to rotate liquid crystal molecules. This system can increase the transmissivity. Accordingly, this system is currently a mainstream. The common electrode and an interlayer insulating film are formed on an organic passivation film serving also as a planarizing film. 
     Meanwhile, if a pixel size is reduced by providing the liquid crystal display device with a high-definition screen, a ratio of a radial cross-sectional area of a through-hole connecting between a pixel electrode and a source electrode of the TFT is increased. 
     In the above IPS liquid crystal display device, if the ratio of the radial cross-sectional area of the through-hole to the pixel size increases, an adhesion strength between the organic passivation film and the interlayer insulating film formed thereon decreases. Thus, a problem occurs, in which the interlayer insulating film peels off. JP-2011-59314-A describes a device which reduces stress on the interlayer insulating film and which prevents peeling-off of the interlayer insulating film by forming the interlayer insulating film not in the through-hole but only on the organic passivation film. 
     If a diameter of the through-hole is reduced as the pixel size is reduced by provision of the high-definition screen, a taper angle of a wall portion of the through-hole (hereinafter sometimes referred to also as a taper angle of the through-hole) should be increased. On the other hand, an alignment film is used to initially align the liquid crystal. A material of the alignment film, which is initially in a liquid state, is applied by flexographic printing, inkjet printing, or the like. 
     If the taper angle of the through-hole is increased, applying the material of the alignment film may cause a phenomenon that the material of the alignment film does not go into the through-hole. Then, a display defect, such as a luminance unevenness, occurs due to a fact that no alignment film exists in the through-hole, or to a thickness unevenness of the alignment film in a periphery of the through-hole. JP-2007-322563-A describes a device that varies a height at a periphery of the through-hole thereby to facilitate the alignment film to flow into the through-hole. 
     If the pixel size is reduced, a ratio of a pixel electrode to each pixel is relatively reduced, so that a transmissivity at each pixel is decreased. According to photoalignment of the alignment film initially aligning the liquid crystal, an alignment treatment can be performed on an inner wall portion of the through-hole. Thus, the inner wall portion of the through-hole can be used as a display area. JP-2013-140386-A describes a device that increases the transmissivity at each pixel by utilizing photoalignment to utilize an inside of the through-hole as a display area. 
     SUMMARY OF THE INVENTION 
     Recently, even a small liquid crystal display device requires a high-definition screen such as a Video Graphics Array (VGA) screen using 640×480 dots. Incidentally, a dot is a set of three pixels, i.e., a red pixel, a green pixel, and a blue pixel. Therefore, the VGA screen uses pixels the number of which is 1920×480. To enable VGA on a 3-inch screen, the shorter diameter of each pixel is set to be very small, e.g., 32 μm. Further, another high-definition screen has been developed, in which the shorter diameter of each pixel is less than 30 μm. 
     Even if each pixel is reduced in size, in order to maintain a predetermined transmissivity, it is necessary to arrange the TFT, the through-hole, and the like in a small area, and to increase the ratio of the area of the pixel electrode to the pixel as much as possible. If the radial cross-sectional area of the through-hole is reduced, the taper angle of the through-hole is increased. Thus the material of the alignment film becomes difficult to flow into the through-hole. Consequently, a display defect, such as a luminance unevenness, occurs. 
     If a height difference is provided among upper surrounding portions of the through-hole like the device described in JP-2007-322563-A, what is called an organic passivation film cannot be used. This is because of the following reasons. That is, the organic passivation film is formed thick to have a thickness of 2 μm to 4 μm. Thus, a surface of the organic passivation film is flat. Consequently, it is difficult to form a height difference among the surrounding portions of the through-hole. 
     On the other hand, to meet demands for uniformizing a thickness of the liquid crystal layer, some types of the liquid crystal display devices need to use an organic passivation film. Since the organic passivation film is formed thick to have a thickness of 2 μm to 4 μm, a problem of increasing the radial cross-sectional area of the through-hole becomes increasingly serious if a through-hole is formed in the organic passivation film. 
       FIG.  14    is a perspective view illustrating the above problem of an IPS liquid crystal display device.  FIG.  15    is a cross-sectional view taken along line I-I shown in  FIG.  14   . In  FIG.  14   , a pixel electrode  107  having a slit  1071  provided therein is connected through a through-hole to a source electrode  102 . An interlayer insulating film (not shown) exists under the pixel electrode  107 . Under the interlayer insulating film, a common electrode (not shown) exists. 
       FIG.  15    is a cross-sectional view illustrating a through-hole  109  and a neighborhood thereof. In  FIG.  15   , a gate insulating film  101  is formed on a TFT substrate  100 . On the gate insulating film  101 , a source electrode  102  extending from a TFT is formed. An inorganic passivation film  103  is formed on the source electrode  102  and the gate insulating film  101 . An organic passivation film  104  is formed on the inorganic passivation film  103 . A common electrode  105  is formed on the organic passivation film  104 . An interlayer insulating film  106  is formed so as to cover the common electrode  105 . A pixel electrode  107  having a slit is formed on the interlayer insulating film  106 . This structure may be configured without providing an inorganic passivation film under the organic passivation. 
     In  FIG.  15   , a counter substrate  200  is arranged opposite to the TFT substrate  100 . A liquid crystal layer  300  is sandwiched between the TFT substrate  100  and the counter substrate  200 . A black matrix  202  is formed on part of the counter substrate  200  in facing relation to the through-hole  100 . A color filter  201  is formed on part of the counter substrate  200  in facing relation to the pixel electrode  107 . An overcoat film  203  is formed so as to cover the black matrix  202  and the color filter  201 . An alignment film  108  is formed on the overcoat film  203 . 
     At the side of the TFT substrate  100 , the pixel electrode  107  is connected to the source electrode  102  via the through-hole  109  formed in the inorganic passivation film  103 , the organic passivation film  104 , and the interlayer insulating film  106 . If the screen is changed to a high-definition screen so as to reduce the area of each pixel, in order to ensure a transmissivity at each pixel, it is necessary to increase the taper angle of the inner wall of the through-hole  109  and to reduce the radial cross-sectional area of the through-hole  109 . 
     However, as illustrated in  FIG.  15   , if the taper angle of the through-hole  109  is large, the alignment film material  108 , which is initially liquid, is difficult to flow into the through-hole  109  from a top face  1091  (see  FIG.  17   ) of the through-hole  109 . Thus, a problem occurs, in which no alignment film is formed in the through-hole. In addition, another problem occurs, in which the thickness of the alignment film  108  is increased on the periphery of the through-hole  109 , so that the thickness unevenness of the alignment film  108  occurs. Then, display defects, such as a luminance unevenness, occur due to absence of an alignment film in the through-hole  109 , or due to the thickness unevenness of the alignment film in the periphery of the through-hole  109 . 
     The reason why thus the alignment film does not flow into the through-hole  109  is considered as follows.  FIGS.  16 A and  16 B  illustrate a contact angle of the alignment film material  108 .  FIG.  16 A  illustrates a case where the alignment film material  108  is dropped onto the planar pixel electrode  107  formed of ITO. In this case, the contact angle is θ.  FIG.  16 B  illustrates a contact angle in a case where the alignment film material  108  of a liquid form exists and is near the top face  1091  of the through-hole  109  having a taper angle α. 
     In  FIG.  16 B , the contact angle in vicinity of the top face of the through-hole  109  is β which is larger than θ. That is, it can be said that the alignment film material  108  is more difficult to wet and spread at the top face of the through-hole  109  than on the pixel which is flat. Here, assuming that “α” denotes the taper angle of the through-hole  109 , that “β” denotes the contact angle of the alignment film material  108  at the top face of the through-hole  109 , and that “θ” denotes the contact angle of the alignment film material  108  on the planar pixel electrode  107  shown in  FIG.  16 A , a relationship among α, β, and θ is given by the following expression.
 
θ≤β≤α+θ
 
     Accordingly, the alignment film material  108  spreads over the pixel electrode  107  formed of ITO in vicinity of the through-hole  109  without going into the through-hole  109 . That is, as illustrated in  FIG.  15   , the alignment film material  108  is formed thick on the periphery of the through-hole  109 . 
     An object of the present invention is to provide liquid crystal display device using an organic passivation film in a TFT substrate, which is configured to facilitate each alignment film material to go into a through-hole even in a case where the area of each pixel is reduced using a high-definition screen, and where the radial cross-sectional area of the through-hole is limited. 
     The present invention is accomplished to overcome the above problems. Specific means according to the present invention are as follows. 
     (1) A liquid crystal display device includes: a TFT substrate having pixels each having a common electrode formed on an organic passivation film, an interlayer insulating film formed so as to cover the common electrode, a pixel electrode having a slit and formed on the interlayer insulating film, a through-hole formed in the organic passivation film and the interlayer insulating film, and a source electrode electrically conducted to the pixel electrode via the through-hole; a counter substrate having color filters formed in facing relation to the pixels, and a black matrix formed among the color filters; and liquid crystal sandwiched between the TFT substrate and the counter substrate. When the through-hole formed in the organic passivation film assumes a cross-section in which a top face is defined on the side of the counter substrate and a bottom face is defined on the side of the source electrode, the top face has a diameter larger than that of the bottom face, and the through-hole has a depth of D, then, a taper angle at a depth of D/2 of the through-hole is equal to or more than 50 degrees. The common electrode covers part of a side wall of the through-hole but does not cover the remaining part of the side wall of the through-hole. 
     (2) A liquid crystal display device includes: a TFT substrate having pixels each having a common electrode formed on an organic passivation film, an interlayer insulating film formed so as to cover the common electrode, a pixel electrode having a slit and formed on the interlayer insulating film, a through-hole formed in the organic passivation film and the interlayer insulating film, and a source electrode electrically conducted to the pixel electrode via the through-hole; a counter substrate having color filters formed in facing relation to the pixels, and a black matrix formed among the color filters; and liquid crystal sandwiched between the TFT substrate and the counter substrate. When the through-hole formed in the organic passivation film assumes a cross-section in which a top face is defined on the side of the counter substrate and a bottom face is defined on the side of the source electrode, the top face a diameter larger than that of the bottom face, and the through-hole has a depth of D, then, a taper angle at a depth of D/2 of the through-hole is equal to or more than 50 degrees, and the slit of the pixel electrode extends to a depth of 1 μm or more from a top surface of the organic passivation film or to a depth of D/4 or more from the top surface of the organic passivation film. 
     According to the present invention, a liquid crystal display device using a high-definition screen to thereby reduce the area of each pixel and also using an organic passivation film in a TFT substrate is provided, which can stably form an alignment film in a through-hole, even if a through-hole diameter is reduced. Accordingly, the liquid crystal display device according to the present invention can prevent a display defect such as a luminance unevenness due to absence of the alignment film or due to the thickness unevenness of the alignment film in the periphery of the through-hole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a plan view of a pixel of a liquid crystal display device to which the present invention is applied; 
         FIG.  2    is a perspective view illustrating a pixel electrode and a through-hole according to a first embodiment; 
         FIG.  3    is a cross-sectional view taken on line A-A shown in  FIG.  2   ; 
         FIG.  4    illustrates a definition of a taper angle of the through-hole; 
         FIG.  5    illustrates an example of a planar shape of the through-hole; 
         FIG.  6    is a perspective view illustrating a pixel electrode and a through-hole according to a second embodiment; 
         FIG.  7    is a cross-sectional view taken on line E-E shown in  FIG.  6   ; 
         FIG.  8    is a perspective view illustrating a pixel electrode and a through-hole of another configuration of the second embodiment; 
         FIG.  9    is a cross-sectional view taken on line F-F shown in  FIG.  8   ; 
         FIG.  10    is a perspective view illustrating a common electrode and a through-hole according to a third embodiment; 
         FIG.  11    is a cross-sectional view taken on line G-G shown in  FIG.  10   ; 
         FIG.  12    is a perspective view illustrating a common electrode and a through-hole according to a fourth embodiment; 
         FIG.  13    is a cross-sectional view taken on line H-H shown in  FIG.  12   ; 
         FIG.  14    is a perspective view illustrating a pixel electrode and a through-hole according to the related art; 
         FIG.  15    is a cross-sectional view taken on line I-I shown in  FIG.  14   ; 
         FIGS.  16 A and  16 B  illustrate a definition of a contact angle; and 
         FIG.  17    is a perspective view illustrating a moving direction of a material of an alignment film according to the related art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the present invention is described in detail with reference to embodiments. 
     First Embodiment 
       FIG.  1    is a plan view of a pixel in a TFT substrate of a liquid crystal display device to which the present invention is applied.  FIG.  1    illustrates an example of an IPS liquid crystal display device. In  FIG.  1   , scanning lines  10  extend in a lateral direction and are arranged in a longitudinal direction at a predetermined pitch PY. Video signal lines  20  extend in the longitudinal direction and are arranged in the lateral direction at a predetermined pitch PX. Each region surrounded by the scanning line  10  and the video signal line  20  is a pixel. 
     In  FIG.  1   , a gate electrode  11  branches from the scanning line  10 . A semiconductor layer  30  is formed on the gate electrode  11 . On the other hand, a source electrode  102  is formed on the semiconductor layer  30 . The source electrode  102  extends in the direction of a pixel electrode  107  and increases in width at part thereof overlapping with a pixel electrode  106  and under a through-hole  109 . The source electrode  102  serves also as a light shielding film preventing occurrence of light leakage in the through-hole  109 . 
     In  FIG.  1   , the pixel electrode  107  having a slit  1071  is formed like a rectangle. An interlayer insulating film is formed under the pixel electrode  107 . A planar common electrode is formed under the interlayer insulating film. Lines of electric force from the pixel electrode  107  are formed so as to pass through a slit  1071  toward the common electrode. 
     In  FIG.  1   , the pixel electrode  107  is connected to the source electrode  102  via the through-hole  109 . The through-hole  109  is formed in an organic passivation film whose thickness is large. Thus, the through-hole  109  has a taper so as to have a larger-diameter top face  1091  and a smaller-diameter bottom face  1092 . According to the present embodiment, the source electrode  102  is formed so as to be slightly larger than the through-hole  109 , and serves also as a light shielding film for the through-hole  109 . The source electrode  102  may be shaped cross-sectionally like a circle corresponding to a shape of the through-hole  109 . To obtain a desired transmissivity, the pixel may be configured so that part of the top face  1091  or the bottom face  1092  of the through-hole  109  protrudes from the source electrode  102 . 
       FIG.  2    is a perspective view illustrating a relationship between the pixel electrode  107  and the through-hole  109 . In  FIG.  2   , the pixel electrode  107  having the slit  1071  covers the through-hole  109  and is electrically conducted to the source electrode  102 . However, according to the present embodiment, the pixel electrode  107  does not cover the entire inner wall of the through-hole  109 . In an outside of the pixel electrode  107 , the pixel electrode  107  does not cover the inner wall and the periphery of the top face of the through-hole  109 . 
     In a configuration illustrated in  FIG.  2   , when an alignment film material  108  of a liquid form is applied, the alignment film material  108  spreads over a SiN film configuring the interlayer insulating film  106  from an ITO film configuring the pixel electrode  107 . Thus, the alignment film material  108  flows into the through-hole  109 , starting from a boundary portion of a step-like part, which is about 50 nm, of the ITO film. Further, since the alignment film material  108  is easier to wet and spread on the SiN film than on the ITO film, the alignment film material  108  can flow into the through-hole  109  via the interlayer insulating film  106  made of SiN. 
     Accordingly, as illustrated in  FIG.  3   , the alignment film material  108  flows into the through-hole  109 . Even in a periphery of the through-hole  109 , the alignment film  108  can be formed so as to have a uniform thickness.  FIG.  3    is a cross-sectional view of the liquid crystal display device, which corresponds to a cross-section taken along line A-A shown in  FIG.  2   . Description of configurations of each of the TFT substrate  100  and the counter substrate  200  illustrated in  FIG.  3   , which have been described with reference to  FIG.  15   , is omitted here. 
     A main difference between the configurations illustrated in  FIGS.  3  and  15    is that the pixel electrode  107  in the configuration illustrated in  FIG.  3    is not completely formed on the entire through-hole  109 . The pixel electrode  107  is formed on a left-side periphery and a left-side inner wall of the through-hole  109 , as viewed in  FIG.  3   . However, the pixel electrode  107  is not formed on a right-side periphery and a right-side inner wall of the through-hole  109 , as viewed in  FIG.  3   . That is, the alignment film material  108  illustrated in  FIG.  3    flows into the through-hole  109  from the right side of the through-hole  109 , as viewed in  FIG.  3   . With this configuration, even if a taper angle of the through-hole  109  is large, the alignment film material  108  can stably flow into the through-hole  109 . 
     Incidentally, if the taper angle of the through-hole  109  is about 50 degrees in the conventional configuration, at a certain frequency, a phenomenon occurs, in which the alignment film material  108  does not flow into the through-hole  109 . Further, if the taper angle of the through-hole  109  is equal to or more than 60 degrees, the alignment film material  108  hardly flows into the through-hole  109 . Accordingly, a display unevenness occurs over a wide range of the screen. 
     Meanwhile, as illustrated in  FIG.  3   , because an organic passivation film  104  serves as a planarizing film, the organic passivation film  104  is formed thick, e.g., a thickness of 2 μm to 4 μm. That is, the organic passivation film  104  is very thick, as compared with other films. Therefore, it can be considered that the shape of the through-hole  109  is determined by the shape of the through-hole formed in the organic passivation film  104 . That is, the taper angle of the inner wall of the organic passivation  109  can be considered as the taper angle of the through-hole formed in the organic passivation film  104 . 
       FIG.  4    is a cross-sectional view for defining the taper angle of the through-hole  109 . The through-hole  109  in this case is the through-hole  109  formed in the organic passivation film  104 . As illustrated in  FIG.  4   , assuming that a depth of the through-hole  109  formed in the organic passivation film  104  is D, a taper angle α of the through-hole  109  is defined as an angle formed by a tangent line to the wall at a depth of D/2, i.e., half the depth of the through-hole  109 , and a line connecting between cross-sections of top surfaces of the organic passivation  104 . 
     A cross-section of the through-hole  109  varies depending on a planar shape of the through-hole  109  or at what part of the through-hole  109  is cut to form the cross-section.  FIGS.  5 A to  5 C  illustrate definitions of a cross-section in various cases of the planar shape of the through-hole  109 .  FIG.  5 A  corresponds to a case where the planar shape of the through-hole  109  is a circle. In this case, a cross-section taken along line B-B passing through the center of the circle corresponds to  FIG.  4   .  FIG.  5 B  corresponds to a case where the planar shape of the through-hole  109  is a square. In this case, a cross-section taken along line C-C on an axis of the square corresponds to  FIG.  4   .  FIG.  5 C  corresponds to a case where the planar shape of the top face of the through-hole  109  is a rectangle. In this case, a cross-section taken along line D-D on a short axis of the through-hole  109  corresponds to  FIG.  4   . That is, in a case where a plan view of the top face of the through-hole  109  has a long axis and a short axis, the taper angle of the through-hole  109  is defined by the taper angle α on a short-axis cross-section, which is illustrated in  FIG.  4   . 
     In a conventional structure, if the angle α illustrated in  FIG.  4    is about 50 degrees, at a certain frequency, the phenomenon occurs, in which the alignment film material  108  does not flow into the through-hole  109 . If the angle α is equal to or larger than 60 degrees, the phenomenon occurs, in which the alignment film material  108  hardly flows into the through-hole  109 . However, according to the present embodiment, even in a case where the angle α is equal to or larger than 50 degrees, the alignment film material  108  can flow into the through-holes  109  formed in all pixels. In addition, according to the present embodiment, even in a case where the angle α is equal to or larger than 60 degrees, the alignment film material  108  can flow into the through-holes  109  formed in all pixels. Accordingly, according to the present embodiment, display defects due to a thickness failure of the alignment film can be resolved. 
     Second Embodiment 
       FIG.  6    is a perspective view illustrating a relationship between a pixel electrode  107  and a through-hole  109  according to a second embodiment of the present invention. In  FIG.  6   , a slit  1071  formed in a pixel electrode  10  extends in a through-hole  109 . In the slit  1071 , a surface thereof is formed of SiN configuring an interlayer insulating film  106 , instead of ITO. Thus, an alignment film material  108  of a liquid form can flow into the through-hole  109 , starting from a boundary portion of a step-like part of the ITO film. Further, because the surface is formed of the SiN film in the slit  1071 , the alignment film material  108  is easier to wet and spread in this case than a case of using the ITO film. Thus, also from this aspect, the alignment film material  108  is easier to flow into the through-hole  109 . 
       FIG.  7    is a cross-sectional view of a liquid crystal display device, which corresponds to a cross-section taken on line E-E shown in  FIG.  6   .  FIG.  7    is similar to  FIG.  3    illustrating the first embodiment, except for a configuration of the pixel electrode  107 . In  FIG.  7   , the pixel electrode  107  extends in the through-hole  109  from the right side of the through-hole  109 , and is connected to a source electrode  102 . On the other hand, at the left side of the through-hole  107  shown in  FIG.  7   , the slit  1071  is formed, so that the pixel electrode  107  does not exist. Surfaces of an inner wall of the through-hole  109  and a periphery of a top face thereof are formed of SiN configuring the interlayer insulting film  106 . Accordingly, the alignment film material  108  flows into the through-hole  109  from the left side of the through-hole  109 , which corresponds to the slit  1071 . 
       FIG.  8    illustrates another configuration of the present embodiment. In  FIG.  8   , the slit  1071  of the pixel electrode  107  is not formed to a bottom face of the through-hole  109 .  FIG.  9    is a cross-sectional view of the liquid crystal display device, which corresponds to a cross-section taken on line F-F shown in  FIG.  8   .  FIG.  9    is similar to  FIG.  7   , except for a configuration of the pixel electrode  107 . 
     In  FIG.  8   , in a left-side vicinity of a top face of the through-hole  109 , and a portion extending from the top face to a position at a depth X thereof, the slit  1071  is formed, and no ITO film configuring the pixel electrode  107  exists. In  FIG.  8   , assuming that a depth of the through-hole  109  is D, part in which no ITO exists extends from the top face of the through-hole  109  to the position at the depth of X thereof. Under this part, an ITO film configuring the pixel electrode  107  exists. 
     Incidentally, a value of X is equal to or larger than a smaller one of D/4 and 1 μm. That is, if a portion where the SiN film configuring the interlayer insulating film  106  is exposed is smaller than X shown in  FIG.  9   , effects of causing the alignment film material  108  to flow into the through-hole  109  are small. Incidentally, the depth D of the through-hole  109  shown in  FIG.  9    corresponds to a range from a top surface of the interlayer insulating film  106  to a top surface of the pixel electrode  107  provided in the through-hole  109 . The depth X is determined with reference to a top surface of the interlayer insulating film  106 . Since the thickness of the insulating film and the ITO film is small in comparison with the thickness of the organic passivation film, similar effects can be obtained even if the depth of D of the through-hole  109  shown in  FIG.  9    is changed to the depth of D of the through-hole  109  formed in the organic passivation film  104  shown in  FIG.  4   , and if the value of X is changed to represent a value from the top surface of the organic passivation film  104 . 
     Thus, even according to the present embodiment, the alignment film material  108  can preferably flow into the through-hole  109 . According to the present embodiment, even in a case where the angle α is equal to or larger than 50 degrees, the alignment film material  108  can flow into the through-holes  109  respectively formed in all pixels. In addition, according to the present embodiment, even in a case where the angle α is equal to or larger than 60 degrees, the alignment film material  108  can flow into the through-holes  109  formed in all pixels. Accordingly, display defects due to a thickness failure of the alignment film  108  can be resolved by the present embodiment. 
     Third Embodiment 
     A third embodiment is an IPS liquid crystal display device configured so that a pixel electrode  107  formed in a planar and solid manner is arranged on a lower side, and that a common electrode  105  having a slit  1051  is provided on an upper side via an interlayer insulating film  106 , contrary to the first embodiment. 
       FIG.  10    is a perspective view illustrating a relationship between a common electrode  105  and a through-hole  109  according to the third embodiment. In  FIG.  10   , the common electrode  105  having the slit  1051  does not cover the entire inner wall of the through-hole  109 . In an outside of the common electrode  105 , the common electrode  105  does not cover the inner wall and the periphery of the top face of the through-hole  109 . 
       FIG.  11    is a cross-sectional view of the liquid crystal display device, which corresponds to the cross-section taken on line G-G shown in  FIG.  10   . The common electrode  105  is formed on a left-side periphery and a left-side inner wall of the through-hole  109 , as viewed in  FIG.  11   . However, the common electrode  105  is not formed on a right-side periphery and a right-side inner wall of the through-hole  109 . 
     When an alignment film material  108  of a liquid form is applied in such a configuration, the alignment film material  108  spreads over a Sill film configuring the interlayer insulating film  106  from an ITO film configuring the common electrode  105 , similarly to the first embodiment in which surface condition is approximately same to that of the third embodiment. As illustrated in  FIG.  11   , the alignment film material  108  flows into the through-hole  109 , so that the thickness of the alignment film  108  can be uniformized even in a periphery of the through-hole  109 . 
     According to the present embodiment, even when the angle α is equal to or larger than 50 degrees, the alignment film material  108  can flow into the through-holes  109  formed in all pixels. In addition, according to the present embodiment, even when the angle α is equal to or larger than 60 degrees, the alignment film material  108  can stably flow into the through-holes  109  formed in all pixels. Accordingly, display defects due to a thickness failure of the alignment film can be resolved by the present embodiment. 
     Fourth Embodiment 
     A fourth embodiment is an IPS liquid crystal display device configured so that a pixel electrode  107  formed in a planar and solid manner is arranged on a lower side, and that a common electrode  105  having a slit  1051  is provided on an upper side via an interlayer insulating film  106 , contrary to the second embodiment. 
       FIG.  12    is a perspective view illustrating a relationship between a common electrode  105  and a through-hole  109  according to the fourth embodiment. In  FIG.  12   , a slit  1051  formed in the common electrode  105  extends in the through-hole  109 . In an inner wall part of the slit  1051 , a surface thereof is formed of SiN configuring an interlayer insulating film  106 , instead of ITO, similarly to the second embodiment. Accordingly, via the slit  1051  formed in the common electrode  105 , the alignment film material  108  of a liquid form can flow into the through-hole  109 , starting from a boundary portion of a step-like part of the ITO film. 
       FIG.  13    is a cross-sectional view of the liquid crystal display device, which corresponds to a cross-section taken on line H-H shown in  FIG.  12   .  FIG.  13    is similar to  FIG.  11    illustrating the third embodiment, except for a configuration of the common electrode  105 . Since the slit  1051  is provided at the left side of the through-hole  109 , as viewed in  FIG.  13   , the common electrode  105  does not exist there. Surfaces of an inner wall and a periphery of a top face of the through-hole  109  are formed of SiN configuring the interlayer insulating film  106 . Thus, the alignment film material  108  easily flows into the through-hole  109  from the left side of the through-hole  109 , which corresponds to the slit  1051 . 
     In a case where the slit  1051  of an uppermost layer is not formed to a bottom face of the through-hole  109 , as shown in  FIG.  8    illustrating the second embodiment, similarly, assuming that the depth of the through-hole  109  is D, a slit is formed in a left-side vicinity of a top face of the through-hole  109 , and a portion extending from the top face to a position at a depth X thereof. Under this slit, an ITO film configuring the pixel electrode  107  exists. 
     Incidentally, a value of X is equal to or larger than a smaller one of D/4 and 1 μm. For example, in a case where the slit  1051  reaches a bottom face of the through-hole  109 , the value of X is equal to the value of D. According to the present embodiment, even in a case where the taper angle α is equal to or larger than 50 degrees, the alignment film material  108  can flow into the through-holes  109  formed in all pixels. Accordingly, according to the present embodiment, a display unevenness due to a thickness failure of the alignment film  108  can be resolved. 
     Incidentally, although it has been described that each of the pixel electrode and the common electrode is formed of an ITO film, the ITO film may be changed to a transparent electrically-conductive film, such as an IZO film. Further, in the second to fourth embodiments, the slit formed in the pixel electrode or in the common electrode extends in the through-hole. Thus, the liquid crystal can be driven in the through-hole. Therefore, the liquid crystal display device may have a structure in which the entire slit or part of the slit is exposed from the source electrode. 
     Incidentally, the present invention can be applied to an alignment film subjected to a photo-alignment treatment using polarized ultraviolet rays as well as the alignment film subjected to the alignment treatment using a rubbing method. 
     In the foregoing description, it has been described that the color filters are formed in the counter substrate. However, according to the present invention, the color filters may be formed in the TFT substrate. In this case, a color filter may be used instead of the organic passivation film. Alternatively, both of the organic passivation film and the color filter may be used. 
     In the foregoing description, a term “black matrix” is used. It is noted that “black matrix” includes the meaning of so called “black stripes” or its equivalent structures.