JP2009276435A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which is little in the change of chromaticity between black display and white display. <P>SOLUTION: A specific angle θ1 of ≤1° is set between a counter substrate side liquid crystal alignment axis of a red pixel and a counter substrate side liquid crystal alignment axis of a green pixel and a blue pixel, and thereby the transmission of the red pixel is made to be shifted to a long wavelength side in the black display. At the same time, with a green pixel and a blue pixel, the transmission in the black display shifts to a short wavelength side. The transmission characteristics of the green pixel and the blue pixel in the black display and the transmission characteristics of the red pixel cancel each other, thereby the difference between the chromaticity in the black display and that in the white display can be made small. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a display device, and more particularly to a liquid crystal display device capable of realizing a high-quality image with little change in chromaticity over a wide luminance range from white display to black display.

  Since the liquid crystal display device is flat and lightweight, the application is expanding in various fields such as a large display device such as a TV, a mobile phone, and a DSC (Digital Still Camera).

  In a liquid crystal display device, there are a TFT substrate in which pixel electrodes and thin film transistors (TFTs) are formed in a matrix, and a counter substrate in which color filters are formed at locations corresponding to the pixel electrodes of the TFT substrate, facing the TFT substrate. The liquid crystal is sandwiched between the TFT substrate and the counter substrate. An image is formed by controlling the light transmittance of the liquid crystal molecules for each pixel.

  A color image is formed by associating different color filters such as red, green, and blue for each pixel, and controlling light transmitted through the pixel corresponding to each color. The light passing through the liquid crystal layer is controlled by the refractive index anisotropy Δn of the liquid crystal and the thickness of the liquid crystal layer, that is, the product Δn · d of the gap d between the TFT substrate and the counter substrate, and the voltage applied to the liquid crystal layer. The

  By the way, the optimum value of Δn · d differs for each wavelength of light, that is, for each color. In other words, assuming that Δn · d is the same for each color, the transmittance characteristics of the liquid crystal are different for each color, so the chromaticity for white display and the chromaticity for black display are different. Therefore, if the same transmittance is to be realized for each color under the same voltage application condition, the gap d between the TFT substrate and the counter substrate is changed for each color, or the rotation or twist angle of the liquid crystal molecules is changed for each color. There is a need.

  In “Patent Document 1”, in a TN (Twisted Nematic) type liquid crystal display device, by changing the initial twist angle of the liquid crystal for each color, there is little change in chromaticity in white display and black display. The structure of is described.

Japanese Patent Laid-Open No. 08-304757

  In a liquid crystal display device, in order to ensure accurate color reproducibility, it is necessary to change the gap d between the TFT substrate and the counter substrate for each color, or change the rotation angle or twist angle of liquid crystal molecules for each color. . However, in the configuration in which the gap d between the TFT substrate and the counter substrate is changed for each color, the thickness of the color filter formed on the counter substrate needs to be changed for each color, and the process becomes complicated.

  On the other hand, in the liquid crystal display device described in “Patent Document 1”, the twist angle of the liquid crystal is optimized for each color to prevent a change in chromaticity between white display and black display. In order to realize this, in “Patent Document 1”, the alignment film has a two-layer structure, and the first layer and the second layer have different twists in the liquid crystal for different colors by changing the direction of the alignment axis. The corner is set.

  However, in the technique of “Patent Document 1”, in order to set an alignment axis for each pixel, it is necessary to pattern two alignment films by photolithography and perform rubbing twice for each alignment film. Therefore, the process becomes complicated and the manufacturing cost increases.

  An object of the present invention is to perform an optimal liquid crystal alignment for each color by setting an alignment axis for each color by a single alignment film, and to suppress a change in chromaticity in white display and black display. .

  The present invention overcomes the above problems, and specific means are as follows.

  (1) A liquid crystal display device in which liquid crystal is sandwiched between a TFT substrate, a counter substrate, and the TFT substrate and the counter substrate, wherein the TFT substrate includes a first pixel having a TFT and a pixel electrode. A second pixel having a TFT and a pixel electrode and a third pixel having a TFT and a pixel electrode are formed, and the first substrate displays a first color corresponding to the first pixel. A first color filter; a second color filter that displays a second color corresponding to the second pixel; and a third color that displays a third color corresponding to the third pixel. A filter is formed, a liquid crystal is sandwiched between the TFT substrate and the counter substrate, a TFT substrate side alignment film having a TFT substrate side liquid crystal alignment axis is formed on the TFT substrate, Opposing group having substrate-side liquid crystal alignment axis A side alignment film is formed, and the TFT substrate side liquid crystal alignment axis and the counter substrate side liquid crystal alignment axis are set by photo alignment, and the first pixel, the second pixel, or the third pixel The orientation of the counter substrate side liquid crystal alignment axis or the TFT substrate side liquid crystal alignment axis of any of the pixels is the same as that of the other pixels in the first pixel, the second pixel, or the third pixel. A liquid crystal display device having a specific angle with respect to the liquid crystal alignment axis of the counter substrate side or the liquid crystal alignment axis of the TFT substrate side.

  (2) The direction of the counter substrate side liquid crystal alignment axis or the TFT substrate side liquid crystal alignment axis of the other pixels in the first pixel, the second pixel, or the third pixel is the same. The liquid crystal display device according to (1), which is characterized.

  The orientations of the counter substrate side liquid crystal alignment axis and the TFT substrate side liquid crystal alignment axis of any one of the first pixel, the second pixel, and the third pixel are the first pixel, The direction of the counter substrate side liquid crystal alignment axis and the TFT substrate side liquid crystal alignment axis of the second pixel or the other pixels of the third pixel has a specific angle. A liquid crystal display device according to 1).

  (4) The liquid crystal display device according to (1) or (2), wherein the specific angle is 1 degree or less.

  (5) The liquid crystal display device according to (1), wherein the liquid crystal display device is an IPS system.

  (6) The liquid crystal display device according to (1), wherein the liquid crystal display device is a TN system.

  (7) A liquid crystal display device in which liquid crystal is sandwiched between a TFT substrate, a counter substrate, and the TFT substrate and the counter substrate, wherein the TFT substrate includes a first pixel having a TFT and a pixel electrode. And a second pixel having a TFT and a pixel electrode, and a third pixel having a TFT and a pixel electrode, and a color filter for displaying red corresponding to the first pixel on the counter substrate, A color filter displaying green corresponding to the second pixel and a third color filter displaying blue corresponding to the third pixel are formed between the TFT substrate and the counter substrate. The TFT substrate is provided with a TFT substrate side alignment film having a TFT substrate side liquid crystal alignment axis, and the counter substrate is formed with a counter substrate side alignment film having a counter substrate side liquid crystal alignment axis. ,in front The TFT substrate side liquid crystal alignment axis and the counter substrate side liquid crystal alignment axis are set by photo-alignment, and the direction of the counter substrate side liquid crystal alignment axis or the TFT substrate side liquid crystal alignment axis of the first pixel is the first direction. 2. The liquid crystal display device according to claim 1, wherein the counter substrate side liquid crystal alignment axis or the TFT substrate side liquid crystal alignment axis of the second pixel or the third pixel has a specific angle.

  (8) The liquid crystal display according to (7), wherein the second pixel and the second pixel have the same orientation of the counter substrate side liquid crystal alignment axis or the TFT substrate side liquid crystal alignment axis. apparatus.

  (9) The liquid crystal display device according to (6) or (7), wherein the specific angle is 1 degree or less.

(10) A liquid crystal display device in which liquid crystal is sandwiched between a TFT substrate, a counter substrate, and the TFT substrate and the counter substrate, wherein the TFT substrate includes a first pixel having a TFT and a pixel electrode A second pixel having a TFT and a pixel electrode and a third pixel having a TFT and a pixel electrode are formed, and the first substrate displays a first color corresponding to the first pixel. A first color filter; a second color filter that displays a second color corresponding to the second pixel; and a third color that displays a third color corresponding to the third pixel. A filter is formed, a liquid crystal is sandwiched between the TFT substrate and the counter substrate, and a first alignment control protrusion is formed on the counter substrate corresponding to the first pixel of the TFT substrate; For second orientation control corresponding to the second pixel Kiga is formed, the third orientation control projection in response to the third pixel is formed,
Any of the first alignment control protrusion, the second alignment control protrusion, and the third alignment control protrusion is the first alignment control protrusion, the second alignment control protrusion, or the third alignment. A liquid crystal display device having a height higher than other protrusions of the control protrusions.

  (11) The height of the other protrusions of the first alignment control protrusion, the second alignment control protrusion, and the third alignment control protrusion is the same. Liquid crystal display device.

  (12) The liquid crystal according to (10), wherein the first color filter is a red filter, the second color filter is a green filter, and the third color filter is a blue filter. Display device.

  According to the present invention, in the IPS mode or TN mode liquid crystal display mode, the TFT substrate side liquid crystal alignment axis of a pixel of a specific color or the counter substrate side liquid crystal alignment axis and the TFT substrate side liquid crystal alignment axis of a pixel of another color or By setting a specific angle between the liquid crystal alignment axis on the counter substrate side, a shift in chromaticity in white display and black display can be suppressed, so that a liquid crystal display device with good color reproducibility can be realized.

  According to the present invention, a configuration that suppresses a color shift in white display and black display can be realized by a single alignment film on both the TFT substrate-side alignment film and the counter substrate-side alignment film, so that color reproduction can be achieved without complicating the process. A liquid crystal display device with good characteristics can be realized.

  According to the present invention, in the VA liquid crystal display device, by increasing the height of the alignment control protrusion in the pixel of a specific color, it is possible to suppress a chromaticity shift in white display and black display, which is excellent. A VA liquid crystal display device having color reproducibility can be realized.

  Hereinafter, the contents of the present invention will be described in detail according to examples.

  In this embodiment, an example in which the present invention is applied to an IPS liquid crystal display device will be described. The IPS system controls the amount of light transmitted through the liquid crystal layer 300 by rotating the liquid crystal with an electric field component parallel to the TFT substrate 100 or the counter substrate 200, and has excellent viewing angle characteristics.

  FIG. 1 is a cross-sectional view showing a structure in a display region of an IPS liquid crystal display device. Various electrode structures of IPS liquid crystal display devices have been proposed and put into practical use. The structure shown in FIG. 1 is a structure that is widely used at present. To put it simply, a comb-like pixel electrode 110 is formed on a counter electrode 108 formed of a flat solid with an insulating film interposed therebetween. Yes. Then, an image is formed by controlling the light transmittance of the liquid crystal layer 300 for each pixel by rotating the liquid crystal molecules 301 by the voltage between the pixel electrode 110 and the counter electrode 108. The structure of FIG. 1 will be described in detail below. Although the present invention will be described by taking the configuration of FIG. 1 as an example, it can also be applied to IPS type liquid crystal display devices other than FIG.

  In FIG. 1, a gate electrode 101 is formed on a TFT substrate 100 made of glass. The gate electrode 101 is formed in the same layer as the scanning line. The gate electrode 101 has a MoCr alloy laminated on an AlNd alloy.

  A gate insulating film 102 is formed of SiN so as to cover the gate electrode 101. A semiconductor layer 103 is formed of an a-Si film on the gate insulating film 102 at a position facing the gate electrode 101. The a-Si film is formed by plasma CVD. The a-Si film forms the channel portion of the TFT, and the source electrode 104 and the drain electrode 105 are formed on the a-Si film with the channel portion interposed therebetween. Note that an n + Si layer (not shown) is formed between the a-Si film and the source electrode 104 or the drain electrode 105. This is for making ohmic contact between the semiconductor layer and the source electrode 104 or the drain electrode 105.

  The source electrode 104 is also used as a video signal line, and the drain electrode 105 is connected to the pixel electrode 110. The source electrode 104 and the drain electrode 105 are simultaneously formed in the same layer. In this embodiment, the source electrode 104 or the drain electrode 105 is made of a MoCr alloy. In order to reduce the electrical resistance of the source electrode 104 or the drain electrode 105, for example, an electrode structure in which an AlNd alloy is sandwiched between MoCr alloys is used.

  An inorganic passivation film 106 is formed of SiN so as to cover the TFT. The inorganic passivation film 106 protects the TFT, particularly the channel portion, from the impurities 401. An organic passivation film 107 is formed on the inorganic passivation film 106. The organic passivation film 107 has a role of flattening the surface at the same time as protecting the TFT, and thus is formed thick. The thickness is 1 μm to 4 μm.

  A photosensitive acrylic resin, silicon resin, polyimide resin, or the like is used for the organic passivation film 107. In the organic passivation film 107, it is necessary to form a through hole 111 at a portion where the pixel electrode 110 and the drain electrode 105 are connected. However, since the organic passivation film 107 is photosensitive, the organic passivation film 107 is not used without using a photoresist. The through hole 111 can be formed by exposing and developing itself.

  A counter electrode 108 is formed on the organic passivation film 107. The counter electrode 108 is formed by sputtering ITO (Indium Tin Oxide), which is a transparent conductive film, over the entire display region. That is, the counter electrode 108 is formed in a planar shape. After the counter electrode 108 is formed on the entire surface by sputtering, the counter electrode 108 is removed by etching only in the through hole 111 portion for conducting the pixel electrode 110 and the drain electrode 105.

  An upper insulating film 109 is formed of SiN so as to cover the counter electrode 108. After the upper electrode is formed, a through hole 111 is formed by etching. The through hole 111 is formed by etching the inorganic passivation film 106 using the upper insulating film 109 as a resist. Thereafter, ITO that will be the pixel electrode 110 is deposited so as to cover the upper insulating film 109 and the through hole 111. The pixel electrode 110 is formed by patterning the deposited ITO. ITO serving as the pixel electrode 110 is also deposited on the through hole 111. In the through hole 111, the drain electrode 105 extending from the TFT and the pixel electrode 110 become conductive, and a video signal is supplied to the pixel electrode 110.

  FIG. 2 shows an example of the pixel electrode 110. The pixel electrode 110 is a comb-like electrode with both ends closed. A slit 112 is formed between the comb teeth. A planar counter electrode (not shown in FIG. 2) is formed below the pixel electrode 110. When a video signal is applied to the pixel electrode 110, the liquid crystal molecules 301 are rotated by electric lines of force generated between the counter electrode 108 through the slit 112. As a result, light passing through the liquid crystal layer 300 is controlled to form an image.

  FIG. 1 illustrates this as a cross-sectional view. A slit 112 shown in FIG. 1 is formed between the comb-shaped electrode and the comb-shaped electrode. A constant voltage is applied to the counter electrode 108, and a voltage based on a video signal is applied to the pixel electrode 110. When a voltage is applied to the pixel electrode 110, as shown in FIG. 1, the lines of electric force are generated, and the liquid crystal molecules 301 are rotated in the direction of the lines of electric force to control the transmission of light from the backlight. Since transmission from the backlight is controlled for each pixel, an image is formed. A TFT substrate-side alignment film 113 for aligning the liquid crystal molecules 301 is formed on the pixel electrode 110. In FIG. 1, the TFT substrate side alignment film 113 is a single layer. In the present invention, the direction of the TFT substrate side liquid crystal alignment axis in the green pixel and the blue pixel may be slightly different from the direction of the TFT substrate side liquid crystal alignment axis in the red pixel.

  In the example of FIG. 1, a counter electrode 108 formed in a planar shape is disposed on the organic passivation film 107, and a comb electrode 110 is disposed on the upper insulating film 109. However, conversely, the pixel electrode 110 formed in a planar shape may be disposed on the organic passivation film 107, and the comb-like counter electrode 108 may be disposed on the upper insulating film 109.

  In FIG. 1, a counter substrate 200 is provided with a liquid crystal layer 300 interposed therebetween. A color filter 201 is formed inside the counter substrate 200. The color filter 201 is formed with red, green, and blue color filters 201 for each pixel, and a color image is formed. A light shielding film 202 is formed between the color filters 201 and the contrast of the image is improved. The light shielding film 202 has a role as a light shielding film of the TFT, and prevents a photocurrent from flowing through the TFT.

  An overcoat film 203 is formed to cover the color filter 201 and the light shielding film 202. Since the surfaces of the color filter 201 and the light shielding film 202 are uneven, the surface is flattened by the overcoat film 203. On the overcoat film 203, a counter substrate-side alignment film 213 for determining the initial alignment of the liquid crystal is formed. In FIG. 1, the counter substrate side alignment film 213 is a single layer. In the present invention, the direction of the counter substrate side liquid crystal alignment axis in the green pixel and the blue pixel may be slightly different from the direction of the counter substrate side liquid crystal alignment axis in the red pixel.

  Since FIG. 1 shows IPS, the counter electrode 108 is formed on the TFT substrate 100 side, and is not formed on the counter substrate 200 side. Thus, in IPS, the conductive film is not formed inside the counter substrate 200. Then, the potential of the counter substrate 200 becomes unstable. Further, external electromagnetic noise enters the liquid crystal layer 300 and affects the image. In order to eliminate such a problem, a surface conductive film 210 is formed outside the counter substrate 200. The surface conductive film 210 is formed by sputtering ITO, which is a transparent conductive film.

  The configuration formed as described above is referred to as a liquid crystal cell. The lower polarizing plate 150 is attached to the lower side of the TFT substrate 100 of such a liquid crystal cell, and the upper polarizing plate 250 is attached to the upper side of the counter substrate 200 to form a liquid crystal display panel. By the lower polarizing plate polarizing axis or the upper polarizing plate polarizing axis, the TFT substrate side liquid crystal alignment axis formed on the TFT substrate side alignment film 113, or the counter substrate side alignment axis formed on the counter substrate side alignment film 213, A display mode such as normally white or normally black is set.

  The present invention prevents changes in chromaticity in white display and black display by changing the TFT substrate side liquid crystal alignment axis and the counter substrate side liquid crystal alignment axis for each color. FIG. 3 contrasts the conventional configuration of the lower polarizing plate polarization axis, TFT substrate side liquid crystal alignment axis, counter substrate side liquid crystal alignment axis, and upper polarizing plate polarization axis in the normally black display mode with the configuration of the present invention. It is described. The arrow in FIG. 3 represents the polarization axis or the alignment axis.

  In FIG. 3, the lower polarizing plate 150, the TFT substrate side alignment film 113, the counter substrate side alignment film 213, and the upper polarizing plate 250 are arranged in this order from the bottom, and the light from the backlight passes in this order. Become. In FIG. 3, the lower polarizing plate polarization axis, the TFT substrate side liquid crystal alignment axis, the counter substrate side liquid crystal alignment axis, and the upper polarizing plate polarization axis are the same in green and blue pixels indicated by G and B. (A) in FIG. 3 is the lower polarizing plate polarization axis, the TFT substrate side liquid crystal alignment axis, the counter substrate side liquid crystal alignment axis, and the upper polarizing plate polarization axis in the conventional example. Conventionally, the lower polarizing plate polarization axis, the TFT substrate side liquid crystal alignment axis, the counter substrate side liquid crystal alignment axis, and the upper polarizing plate polarization axis in the red pixel are the same as the green pixel or the blue pixel.

  In this case, the conventional example has a problem as shown in FIG. In FIG. 4, the horizontal axis represents the wavelength λ of light, and the vertical axis represents the transmittance TR of the liquid crystal cell. FIG. 4 shows the transmittance of the liquid crystal display panel in black display. In FIG. 4, the layer thickness d of the liquid crystal is 4 μm, and the refractive index anisotropy Δn is 0.08.

  In the conventional example of FIG. 3, light is not transmitted if the polarization axis of the polarizing plate or the alignment axis of the alignment film is exactly as shown by the arrow. However, in reality, an error of about 0.1 degree occurs with respect to the direction of the arrow shown in FIG. 3 due to an alignment axis formation error in the alignment film, a polarizing plate attaching error, and the like. For example, if the TFT substrate side liquid crystal alignment axis and the counter substrate side liquid crystal alignment axis are shifted by 0.1 degrees in the opposite direction, a twist of 0.2 degrees is generated in the liquid crystal layer. Such light leakage due to misalignment of the alignment axis occurs frequently on the short wavelength side as shown by the curve A in FIG. Therefore, the screen is bluish on the black display side. On the other hand, since a specific color temperature is set on the white display side, the chromaticity differs between the white display and the black display. This means that accurate color reproducibility cannot be achieved.

  Returning to FIG. 3, in the present invention, the alignment axes of the alignment films of the green pixel and the blue pixel are the same, and the alignment axes of the alignment film of the red pixel are a slight angle between the TFT substrate 100 side and the counter substrate 200 side. Just set the angle to twist the LCD in advance. In FIG. 3, (B) shows that in the present invention, the TFT substrate side liquid crystal alignment axis is set to the same alignment axis direction for the green pixel, blue pixel, and red pixel. On the other hand, the counter substrate side liquid crystal alignment axis of the red pixel is shifted counterclockwise by θ1 with respect to the counter substrate side liquid crystal alignment axis of the green pixel or blue pixel.

  Then, in the R pixel, light leakage in black display is larger on the long wavelength side than on the short wavelength side. Therefore, light leakage on the short wavelength side in the green pixel and the blue pixel is canceled out by the red pixel, and a change in chromaticity near the black display can be reduced. A curve B in FIG. 4 is an example in which the counter substrate side liquid crystal alignment axis in the red pixel is shifted by 0.1 degree with respect to the counter substrate side liquid crystal alignment axis in the green pixel and the blue pixel. FIG. 4 shows that the light leakage in the black display in the green pixel and the blue pixel is the curve B, so that the light leakage in the red pixel and the light leakage in the green pixel and the blue pixel cancel each other.

  (C) in FIG. 3 shows that in the present invention, the TFT substrate side liquid crystal alignment axis of the red pixel is shifted by θ2 clockwise from the TFT substrate side liquid crystal alignment axis of the green pixel and the blue pixel. Further, the counter substrate side liquid crystal alignment axis of the red pixel is shifted by θ1 counterclockwise from the counter substrate side liquid crystal alignment axis of the green pixel and blue pixel. Therefore, in the red pixel, the liquid crystal is twisted by θ1 + θ2. In this case, the light leakage in red shifts to the longer wavelength side, and is in the direction of more correcting the change in chromaticity due to the light leakage in the green pixel and the blue pixel.

  Whether one of the TFT substrate side liquid crystal alignment axis and the counter substrate side liquid crystal alignment axis is shifted or both may be determined depending on the degree of color correction. However, as the magnitude of θ1 + θ2 increases, the absolute value of light leakage increases and causes a decrease in contrast. Therefore, it is preferable to suppress θ1 or θ2 to 1 degree or less. Here, when only the orientation axis of one substrate is shifted, θ1 or θ2 becomes zero.

  FIG. 5 is a diagram showing the effect of the present invention. In FIG. 5, the horizontal axis represents the x coordinate in the chromaticity diagram in the CIE color system, and the vertical axis represents the y coordinate. In the liquid crystal display device, the transmittance of each color is set so that the color temperature of white display becomes a specific value. On the other hand, in black display, it is ideal that light is completely stopped, but slight light leakage occurs due to the transmittance characteristics of the liquid crystal or the setting error of the alignment film alignment axis and polarizing plate polarization axis.

  The light leaking in the black display is shifted in the blue direction as described with reference to FIGS. That is, in the chromaticity coordinates, light in a direction in which the x coordinate and the y coordinate are smaller in black display than in white display leaks. In FIG. 5, the chromaticity coordinates for white display are indicated by white rhombuses, and the chromaticity coordinates for black display in the conventional example are indicated by black rhombuses. On the other hand, the chromaticity coordinates for black display in the present invention are indicated by black circles.

  In the present invention, since the transmittance on the low wavelength side in the red pixel is suppressed in the vicinity of the black display, the shift to the blue direction is suppressed as the entire black display, approaching the chromaticity in the white display. . Therefore, in the present invention, the change in chromaticity can be suppressed in a wide luminance range, and the reproducibility of the image is improved.

  Another effect of the present invention is that the light transmittance in black display can be lowered, so that the contrast of the image can be raised. FIG. 6 shows this state. In FIG. 6, the vertical axis BT represents the transmittance for black display when the wavelength λ is around 570 nm, A on the horizontal axis represents the case of the conventional example, and B represents the case of the present invention. In FIG. 6, it can be seen that the black display transmittance is lower in the present invention than in the conventional example.

  This is because, as shown in FIG. 4, in the present invention, the transmittance in the red pixel is smaller than that in the green pixel and the blue pixel in the vicinity of the wavelength of 570 nm. That is, in the conventional example, the red pixel, the green pixel, and the blue pixel all show the transmittance characteristics of the curve A in FIG. 4, but in the present invention, the transmittance characteristics of the curve B in FIG. Therefore, the transmittance in black display of the entire pixel is lowered. Therefore, in the present invention, an image having a higher contrast than the conventional example can be obtained.

  In the present invention, the above characteristics are realized by setting the alignment axis of the alignment film to a specific value. In the present invention, the direction of the alignment axis must be controlled for each pixel. Below, the setting method of the orientation axis | shaft of an oriented film for implement | achieving this invention is demonstrated.

  Conventionally, a rubbing method has been widely used for setting an alignment axis of an alignment film. In the rubbing method, the alignment axis is set by rubbing the surface of the alignment film with a cloth-like material in a specific direction. On the other hand, another alignment axis setting method is a method based on photo-alignment.

FIG. 7 is a schematic diagram showing the principle of photo-alignment. The alignment film is formed of a polymer material, but when formed, the alignment film has a network-like molecular structure as shown in FIG. For example, when the structure shown in FIG. 7A is irradiated with UV light polarized in the horizontal direction, the structure in the vertical direction in FIG. 7A is destroyed. The energy of the polarized ultraviolet rays irradiated at this time is, for example, 6 J / cm ² . With respect to the alignment film thus formed, the liquid crystal molecules 301 are aligned as shown in FIG. Thus, the direction of the alignment axis of the alignment film can be controlled by the polarization direction of the irradiated ultraviolet light.

  Generally, in the IPS system, the interface tilt with the substrate surface is not necessary in principle, and the smaller the interface tilt angle, the better the viewing angle characteristics. In particular, by setting the tilt angle to 1 degree or less, it is effective because the color change and the brightness change depending on the viewing angle of the liquid crystal display device can be made below the allowable limit. In order to realize the configuration of the present invention, in this embodiment, photo-alignment is used for setting the alignment axis of the alignment film.

  FIG. 8 shows a flow of a photo-alignment process for realizing the configuration of the present invention. The alignment film is formed on both the TFT substrate 100 side and the counter substrate 200 side, but the process of FIG. 8 can be applied to any alignment film. In FIG. 8, an alignment film material is first applied onto a substrate by a spinner or rod coating. Thereafter, the applied alignment film is baked and solidified.

  With respect to the fired alignment film, first, an alignment axis is set using ultraviolet light polarized in a specific direction with respect to the green pixel and the blue pixel, using the first mask. Thereafter, using the second mask, the direction of the orientation axis is set using ultraviolet light polarized in a specific direction so that the direction of the polarization axis is slightly different from that of the green pixel or the blue pixel with respect to the red pixel. .

  The difference between the orientation axes of the green and blue pixels and the orientation axis of the red pixels is 1 degree or less. Such a direction of the alignment axis is set by rotating a substrate on which an alignment film is formed while fixing a light source that generates ultraviolet rays.

  As described above, according to the present invention, by using photo-alignment, the direction of the alignment axis can be set for each pixel by a single alignment film.

  In the first embodiment, the case where the present invention is applied to an IPS liquid crystal display device has been described. The present invention can be applied not only to the IPS system but also to a TN liquid crystal display device. In the TN mode, liquid crystal molecules are controlled by an electric field formed between the pixel electrode 110 formed on the TFT substrate 100 and the pixel electrode 110 formed on the counter substrate 200.

  FIG. 9 is a cross-sectional view of a TN liquid crystal display device. In FIG. 9, the TFT substrate 100 side is the same as that in FIG. 1 until the organic passivation film 107 is formed. However, in FIG. 9, an n + Si layer 1031 is illustrated between the semiconductor layer and the drain electrode or the source electrode in the drawing. In FIG. 9, the pixel electrode 110 is formed on the organic passivation film 107, and the TFT substrate side alignment film 113 is formed thereon. The liquid crystal is aligned by the TFT substrate side liquid crystal alignment axis formed on the TFT substrate side alignment film 113.

  In the counter substrate 200 of FIG. 9, the structure up to the overcoat film 203 is the same as that of FIG. On the overcoat film 203, a counter electrode 108 formed of a flat solid is formed of ITO. A counter substrate side alignment film 213 is formed on the counter electrode 108, and the liquid crystal is aligned by the counter substrate side liquid crystal alignment axis formed on the counter substrate side alignment film 213. In the TN system, the surface conductive film does not exist outside the counter substrate. This is because the counter electrode 108 in the counter substrate also serves as a shield against an external electric field.

  Although the liquid crystal layer 300 is homogeneously oriented, the liquid crystal molecules are inclined in the vertical direction due to the vertical electric field component between the pixel electrode 110 on the TFT substrate 100 side and the counter electrode 108 on the counter substrate 200 side. Light passing through the layer 300 is controlled. The light from the backlight is polarized in a specific direction by the lower polarizing plate 150, modulated by the liquid crystal layer 300, then polarized (analyzed) again by the upper polarizing plate 250 and visually recognized.

  Also in the TN system, the value of Δn of the transmitted light in the red pixel, the green pixel, and the blue pixel is different, so the problem that the chromaticity is different between white display and black display is the same. The present invention for preventing a change in chromaticity in white display and black display is also applied to a TN liquid crystal display device by changing the TFT substrate side liquid crystal alignment axis and the counter substrate side liquid crystal alignment axis for each color. I can do it. FIG. 10 compares the conventional configuration of the lower polarizing plate polarization axis, the TFT substrate side liquid crystal alignment axis, the counter substrate side liquid crystal alignment axis, and the upper polarizing plate polarization axis in the normally black display mode with the configuration of the present invention. It is described.

  In FIG. 10, the lower polarizing plate 150, the TFT substrate side alignment film 113, the counter substrate side alignment film 213, and the upper polarizing plate 250 are arranged in this order from the bottom, and light from the backlight passes in this order. Become. In the TN system, the directions of the TFT substrate side liquid crystal alignment axis and the counter substrate side liquid crystal alignment axis are 90 degrees. The lower polarizing plate polarization axis and the TFT substrate side liquid crystal alignment axis are in the same direction, and the counter substrate side liquid crystal alignment axis and the upper polarizing plate polarization axis are in the same direction. In this case, since the polarization axis of the lower polarizing plate 150 and the polarization axis of the upper polarizing plate 250 are 90 degrees, the display mode is normally black.

  In FIG. 10, the lower polarizing plate polarization axis, the TFT substrate-side liquid crystal alignment axis, the counter substrate-side liquid crystal alignment axis, and the upper polarizing plate polarization axis are the same for the green and blue pixels indicated by G and B. (A) in FIG. 10 is a lower polarizing plate polarization axis, a TFT substrate side liquid crystal alignment axis, a counter substrate side liquid crystal alignment axis, and an upper polarizing plate polarization axis in a red pixel in the conventional example. Conventionally, the lower polarizing plate polarization axis, the TFT substrate side liquid crystal alignment axis, the counter substrate side liquid crystal alignment axis, and the upper polarizing plate polarization axis in the red pixel are the same as the green pixel or the blue pixel.

  Also in the TN system, conventionally, when variations occur in the alignment axis of the alignment film, the polarization axis of the polarizing plate, etc., as in the case of the IPS system shown in FIG. 4, light on the short wavelength side leaks on the black display side. That was the phenomenon. Therefore, there has been a problem that the chromaticity of the white display and the black display is different.

  In the present invention in FIG. 10B, the alignment axis directions of the alignment films in the green pixel and the blue pixel are the same, and the TFT substrate side liquid crystal alignment axis of the red pixel is shifted by θ1. Then, the twist angle of the liquid crystal is shifted from 90 degrees by θ1 only in the red pixel, and the light transmission characteristic in the red pixel is different from the light transmission characteristic in the green pixel or the blue pixel. .

  By selecting θ1 so that the difference in the transmission characteristics is larger in the red pixel than in the short wavelength side in the red pixel, the light leakage on the short wavelength side in the green pixel and the blue pixel is reduced in red. It can be canceled out with pixels. Thereby, a change in chromaticity near the black display can be reduced.

  (C) in FIG. 10 shows that in the present invention, the TFT substrate side liquid crystal alignment axis of the red pixel is shifted by θ2 with respect to the TFT substrate side liquid crystal alignment axis of the green pixel and the blue pixel. The counter substrate side liquid crystal alignment axis of the red pixel is shifted by θ1 with respect to the counter substrate side liquid crystal alignment axis of the green pixel and the blue pixel. As a result, light leakage on the short wavelength side near the black display in the red pixel can be reduced, and the change in chromaticity near the black display can be reduced.

  As in the case of the IPS system, the overall contrast is improved by reducing the amount of light leakage on the short wavelength side in the black display of the red pixel. Even in the TN system, the shift amount θ1 or θ2 of the TFT substrate side liquid crystal alignment axis or the counter substrate side liquid crystal alignment axis with respect to the green pixel or the blue pixel of the red pixel is preferably set to 1 degree or less. This is because if the shift angle of the polarization axis is too large, the contrast is lowered.

  As described above, according to the present invention, even in a TN liquid crystal display device, a change in chromaticity between white display and black display can be reduced, and at the same time, contrast can be improved.

  Example 1 is an example in which the present invention is applied to an IPS liquid crystal display device, and Example 2 is an example in which the present invention is applied to a TN liquid crystal display device. The problem that the chromaticity in the black display deviates from the chromaticity in the white display occurs not only in the IPS system or the TN system but also in a VA (Vertical Alignment) liquid crystal display device.

  By controlling the alignment state of the liquid crystal for each pixel color, the present invention in which the spectrum of transmitted light near the black display is controlled to bring the chromaticity near the black display close to the chromaticity near the white display. The method can also be applied. However, the method of controlling transmitted light for each pixel is different.

  In VA, the initial alignment of liquid crystal molecules is perpendicular to the substrate, and by applying a voltage between the substrates, the light transmitted through the liquid crystal layer 300 is controlled by tilting the liquid crystal molecules. In order to determine in advance the direction in which the liquid crystal is tilted when a voltage is applied, an alignment control protrusion 260 is formed on the counter substrate 200.

  Conventionally, the shape of the alignment control protrusion 260 is the same for all of the red, green, and blue pixels. In this case, light leakage near the black display is more on the short wavelength side. Then, the chromaticity shifts in the blue direction, and the chromaticity when displaying white and the chromaticity when displaying black are different.

  In order to solve this problem, the present invention changes the shape of the alignment control protrusion 260 formed on the counter substrate 200 for each pixel as shown in FIG. Thus, the chromaticity in the black display is brought close to the chromaticity in the white display. Specifically, by increasing the alignment control protrusion 260 of the red pixel, the initial alignment angle of the liquid crystal is further inclined near the alignment control protrusion 260.

  FIG. 11A shows the shape of the alignment control protrusion 260 and the initial alignment state of the liquid crystal in the green pixel and the blue pixel. FIG. 11B shows the shape of the alignment control protrusion 260 in the red pixel and the initial alignment state of the liquid crystal. This state is a black display state. Even in the black display, light leaks, and in the green pixel and blue pixel shown in FIG. In FIG. 11, the TFT on the TFT substrate 100 side, the pixel electrode 110, the color filter 201 on the counter substrate 200 side, the counter electrode 108, and the like are omitted.

  In FIG. 11, only in the red pixels shown in FIG. 11B, the inclination of the liquid crystal molecules in the vicinity of the alignment control protrusion 260 is large. By adopting such an alignment state, in black display in a red pixel, light leakage on the short wavelength side can be reduced and light leakage can be shifted to the long wavelength side. Therefore, according to the configuration of FIG. 11, the chromaticity shifted to the short wavelength side in the black display of the green pixel and the blue pixel can be canceled by the chromaticity shifted to the long wavelength side in the red pixel.

  Thus, according to this embodiment, even in the VA system, the difference between the chromaticity in the white display and the chromaticity in the black display can be reduced, and the color reproducibility of the image can be improved.

  In order to obtain the configuration as shown in FIG. 11, the height of the alignment control protrusion 260 formed on the counter substrate 200 must be changed for each pixel. 12 and 13 show an example of a process for changing the height of the alignment control protrusion 260 formed on the counter substrate 200 for each pixel. FIGS. 12 and 13 show a process for a configuration in which the heights of the alignment control protrusions 260 for the green pixel and the blue pixel are made the same, and only the heights of the alignment control protrusions 260 for the red pixel are changed.

  In FIG. 12, a photosensitive resin as a material for the orientation control protrusion 260 is coated on the substrate, and leveling is performed to obtain a uniform film thickness (COATING). The photosensitive resin has a feature that patterning can be performed without using a resist. The resin is a negative photosensitive resin. The negative photosensitive resin is cured and exposed to light when exposed to light.

  In FIG. 12, first, green pixels and blue pixels are exposed using a mask (EXPOSURE G, B). After that, the mask is replaced and the red pixel is exposed using the mask (EXPOSURE R). Since the negative photosensitive resin is developed and remains where the light hits, the larger the exposure amount, the more resin remains. That is, the height of the alignment control protrusion 260 is also increased.

  In FIG. 12, the height of the alignment control protrusion 260 formed on the red pixel can be increased by increasing the exposure amount for the red pixel rather than the exposure amount for the green pixel or the blue pixel. Thereafter, the substrate is baked to cure the alignment control protrusions 260 formed in each pixel (BAKING).

  FIG. 13 shows another process for forming the configuration of FIG. In FIG. 13, coating a photosensitive resin, which is a material for the orientation control protrusion 260, on the substrate and leveling it to obtain a uniform film thickness is the same as in FIG. 12 (COATING). The photosensitive resin in this case is also a negative type. The difference from FIG. 12 is that all red, green, and blue pixels are exposed simultaneously using a mask (EXPOSURE R, G, B).

  In order to make a difference in the height of the alignment control protrusion 260 between the red pixel and the green pixel or the blue pixel, a halftone exposure technique is used. That is, since the photosensitive resin is a negative type, in order to make the alignment control projection 260 of the red pixel higher than the alignment control projection 260 of the green pixel or the blue pixel, the exposure amount in the red pixel is set to the green pixel or There is a need to do more in blue pixels. Or it is necessary to make the exposure amount in a green pixel or a blue pixel smaller than the exposure amount in a red pixel.

  In FIG. 13, by reducing the transmittance of the mask in the green pixel or blue pixel, the exposure amount in the green pixel or blue pixel is made smaller than the exposure amount in the red pixel. As a method for reducing the transmittance of the mask, there are various methods such as periodically forming a pattern on a thin stripe on the mask. In this manner, the alignment control protrusion 260 is cured by baking the substrate on which the alignment control protrusion 260 is formed.

  The advantage of the process of FIG. 13 is that the alignment control protrusions 260 having different heights can be formed by a single exposure. Therefore, the process can be shortened and alignment errors associated with mask alignment do not occur.

  In FIGS. 12 and 13, a negative photosensitive resin is used, but a positive photosensitive resin can also be used. As described above, according to the present embodiment, the chromaticity shift problem in white display and black display can be solved even in the VA liquid crystal display device.

  In Example 1 and Example 2, the alignment axis of only the counter substrate side liquid crystal alignment axis is changed between the green pixel and the blue pixel by the red pixel, and the counter substrate side liquid crystal alignment axis and the TFT substrate side liquid crystal alignment Although the example in which both axes are changed with green pixels and red pixels with respect to blue pixels has been shown, the alignment axis of only the TFT substrate side liquid crystal alignment axis may be changed with green pixels and blue pixels with red pixels. .

  In the first to third embodiments, the transmission spectrum in the black display is changed with respect to the other color pixels only with the red pixels, but if necessary, the transmission spectrum is changed with respect to the other color pixels. Also good. In this case, the method of changing the spectrum of transmitted light at the time of black display in the red pixel described in the first to third embodiments may be used.

1 is a cross-sectional view of an IPS liquid crystal display device. It is a top view of the pixel electrode of FIG. FIG. 3 is a diagram illustrating the directions of a polarization axis and an alignment axis in Example 1. It is the light transmittance characteristic in black display. It is a figure which shows the difference in chromaticity in white display and black display. It is a comparison of the light transmittance in the black display of this invention and a prior art example. It is a schematic diagram which shows the principle of optical orientation. This is a photo-alignment process. 1 is a cross-sectional view of a TN liquid crystal display device. FIG. 6 is a diagram illustrating the directions of a polarization axis and an alignment axis in Example 2. 1 is a cross-sectional view of a VA liquid crystal display device to which the present invention is applied. It is the 1st process example of this invention in VA system. It is the 2nd process example of this invention in VA system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... TFT substrate 101 ... Gate electrode 102 ... Gate insulating film 103 ... Semiconductor layer 104 ... Source electrode 105 ... Drain electrode 106 ... Inorganic passivation film 107 ... Organic passivation film 108 ... Counter electrode 109 ... Upper insulating film, 110: pixel electrode, 111: through hole, 112: slit, 113: TFT substrate side alignment film, 150: lower polarizing plate, 200: counter substrate, 201: color filter, 202 ... light shielding film, 203 ... over Coat film, 210 ... surface conductive film, 213 ... counter substrate side alignment film, 250 ... upper polarizing plate, 260 ... alignment control protrusion, 300 ... liquid crystal layer, 301 ... liquid crystal molecule, 1131 ... n + Si layer, d ... liquid crystal layer thickness.

Claims (12)

A liquid crystal display device in which liquid crystal is sandwiched between a TFT substrate, a counter substrate, and the TFT substrate and the counter substrate,
A first pixel having a TFT and a pixel electrode, a second pixel having a TFT and a pixel electrode, and a third pixel having a TFT and a pixel electrode are formed on the TFT substrate. A first color filter that displays a first color corresponding to the first pixel; a second color filter that displays a second color corresponding to the second pixel; and A third color filter for displaying a third color corresponding to the pixel is formed;
Liquid crystal is sandwiched between the TFT substrate and the counter substrate, a TFT substrate side alignment film having a TFT substrate side liquid crystal alignment axis is formed on the TFT substrate, and the counter substrate side liquid crystal alignment axis is formed on the counter substrate. A counter substrate-side alignment film having
The TFT substrate side liquid crystal alignment axis and the counter substrate side liquid crystal alignment axis are set by photo-alignment,
The orientation of the counter substrate side liquid crystal alignment axis or the TFT substrate side liquid crystal alignment axis of any one of the first pixel, the second pixel, or the third pixel is the first pixel, The liquid crystal characterized by having a specific angle with the direction of the counter substrate side liquid crystal alignment axis or the TFT substrate side liquid crystal alignment axis of the second pixel or another pixel in the third pixel. Display device.   In the first pixel, the second pixel, or another pixel in the third pixel, the opposite substrate side liquid crystal alignment axis or the TFT substrate side liquid crystal alignment axis has the same direction. The liquid crystal display device according to claim 1.   The orientations of the counter substrate side liquid crystal alignment axis and the TFT substrate side liquid crystal alignment axis of any one of the first pixel, the second pixel, and the third pixel are the first pixel, The orientation of the counter substrate side liquid crystal alignment axis and the TFT substrate side liquid crystal alignment axis of the second pixel or other pixels of the third pixel has a specific angle. Item 2. A liquid crystal display device according to item 1.   The liquid crystal display device according to claim 1, wherein the specific angle is 1 degree or less.   The liquid crystal display device according to claim 1, wherein the liquid crystal display device is an IPS system.   The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a TN system. A liquid crystal display device in which liquid crystal is sandwiched between a TFT substrate, a counter substrate, and the TFT substrate and the counter substrate,
A first pixel having a TFT and a pixel electrode, a second pixel having a TFT and a pixel electrode, and a third pixel having a TFT and a pixel electrode are formed on the TFT substrate. A color filter that displays red corresponding to the first pixel, a color filter that displays green corresponding to the second pixel, and a third that displays blue corresponding to the third pixel A color filter is formed,
Liquid crystal is sandwiched between the TFT substrate and the counter substrate, a TFT substrate side alignment film having a TFT substrate side liquid crystal alignment axis is formed on the TFT substrate, and the counter substrate side liquid crystal alignment axis is formed on the counter substrate. A counter substrate-side alignment film having
The TFT substrate side liquid crystal alignment axis and the counter substrate side liquid crystal alignment axis are set by photo-alignment,
The direction of the counter substrate side liquid crystal alignment axis or the TFT substrate side liquid crystal alignment axis of the first pixel is the counter substrate side liquid crystal alignment axis of the second pixel or the third pixel or the TFT substrate side liquid crystal. A liquid crystal display device having a specific angle with respect to an orientation axis.   The liquid crystal display device according to claim 7, wherein the second pixel and the second pixel have the same orientation of the counter substrate side liquid crystal alignment axis or the TFT substrate side liquid crystal alignment axis.   The liquid crystal display device according to claim 6, wherein the specific angle is 1 degree or less. A liquid crystal display device in which liquid crystal is sandwiched between a TFT substrate, a counter substrate, and the TFT substrate and the counter substrate,
A first pixel having a TFT and a pixel electrode, a second pixel having a TFT and a pixel electrode, and a third pixel having a TFT and a pixel electrode are formed on the TFT substrate. A first color filter that displays a first color corresponding to the first pixel; a second color filter that displays a second color corresponding to the second pixel; and A third color filter for displaying a third color corresponding to the pixel is formed;
A liquid crystal is sandwiched between the TFT substrate and the counter substrate, and a first alignment control protrusion is formed on the counter substrate corresponding to the first pixel of the TFT substrate. The second pixel A second alignment control protrusion is formed corresponding to the third pixel, and a third alignment control protrusion is formed corresponding to the third pixel.
Any of the first alignment control protrusion, the second alignment control protrusion, and the third alignment control protrusion is the first alignment control protrusion, the second alignment control protrusion, or the third alignment. A liquid crystal display device having a height higher than other protrusions of the control protrusions.   11. The liquid crystal display according to claim 10, wherein other projections of the first alignment control projection, the second alignment control projection, and the third alignment control projection have the same height. apparatus.   The liquid crystal display device according to claim 10, wherein the first color filter is a red filter, the second color filter is a green filter, and the third color filter is a blue filter.

Images