JP3795178B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device. More specifically, the present invention relates to a liquid crystal display device including a switching element such as a thin film transistor that improves the visual characteristics and display characteristics of a display screen and enables display comparable to a CRT.
[0002]
[Prior art]
Conventionally, liquid crystal display devices using nematic liquid crystal display elements have been widely used in numerical segment type liquid crystal display devices such as watches and calculators. Recently, it has been used as a display including a word processor, a computer and a navigation system.
[0003]
Among the liquid crystal display devices described above, an active matrix type liquid crystal display device in which active elements such as TFTs are used as switching elements and pixels are arranged in a matrix is known as one that is used particularly frequently. Since the liquid crystal display device has advantages such as that the thickness (depth) can be remarkably reduced, power consumption is small, and full color can be easily obtained, compared with a CRT display device. Demand is growing in a wide range of fields such as mobile TVs and cameras. However, since it is still inferior in terms of luminance and color reproducibility as compared with a CRT display device, improvement is strongly desired.
[0004]
The active matrix liquid crystal display device includes a light-transmitting substrate (active matrix substrate), and a plurality of substrates for applying a voltage to the liquid crystal layer are provided on the substrate, as shown in FIG. Pixel electrodes 51 are formed in a matrix. As active elements which are switching means for selectively driving the pixel electrodes 51, thin film transistors (hereinafter referred to as TFTs) 52 are formed on the substrate and connected to the pixel electrodes 51. Further, in the case of performing color display, although not shown, in addition to the above configuration, color filter layers such as red, green, and blue are provided on the substrate.
[0005]
The scanning electrodes 53 are connected to the gate electrodes of the TFTs 52, and the signal lines 54 are connected to the source electrodes. The scanning lines 53 and the signal lines 54 are disposed so as to pass through the periphery of the pixel electrodes 51 arranged in a matrix and to be orthogonal to each other. When the gate signal is input by the scanning lines 53, the TFTs 52 are driven and controlled. Further, when the TFTs 52 are driven by the signal lines 54, data signals (display signals) are input to the pixel electrodes 51 through the TFTs 52.
[0006]
Further, pixel electrodes 51 and additional capacitors 55 are connected to the drain electrodes of the TFTs 52. The counter electrodes of the additional capacitors 55 are connected to common wirings 56, respectively. The additional capacitors 55 are used for holding a voltage applied to the liquid crystal layer.
[0007]
In an active matrix liquid crystal display device, a liquid crystal layer is sandwiched between the active matrix substrate and a counter substrate facing the active matrix substrate. That is, the liquid crystal layer is sandwiched between the pixel electrodes 51... Formed on the active matrix substrate and the counter electrode formed on the counter substrate to form a liquid crystal capacitor. The additional capacitors 55 are connected in parallel with the liquid crystal capacitors.
[0008]
The TFT 52 will be described in more detail. As shown in FIG. 9, a gate electrode 62 is formed on a transparent insulating substrate 61, and a gate insulating film 63 is formed so as to cover it. A semiconductor thin film 64 is formed on the gate electrode 62 via a gate insulating film 63. A channel protective layer 65 is formed on the central portion of the semiconductor thin film 64. N on the source side of the channel protective layer 65 and the semiconductor thin film 64.⁺A source electrode 66a made of a silicon layer is formed, and n⁺A drain electrode 66b made of a silicon layer is formed.
[0009]
A metal layer 67a serving as a source wiring is connected to the source electrode 66a, and a metal layer 67b serving as a drain wiring is connected to the drain electrode 66b. The surface of the TFT 52 is covered with an interlayer insulating film 68, and a transparent conductive film to be the pixel electrode 51 is further formed thereon. The pixel electrode 51 is connected to a metal layer 67 b serving as a drain wiring of the TFT 52 through a contact hole 69. Although not shown, an alignment film for aligning the liquid crystal over the entire surface including the periphery is formed on the pixel electrode 51.
[0010]
As described above, since the interlayer insulating film 68 is formed between the scanning line 53 and the signal line 54 and the transparent conductive film to be the pixel electrode 51, the above-described liquid crystal display device has the scanning line 53 and the signal line. The pixel electrode 51 can be stacked on the 54. Such a structure is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-172585, thereby improving the aperture ratio of the pixel in the liquid crystal display device, and applying an electric field caused by the signal line 54 or the like to the interlayer insulating film 68. Shielding can prevent liquid crystal alignment defects (disclination).
[0011]
Conventionally, an inorganic thin film such as SiN is used as the interlayer insulating film 68. The SiN film can be formed to a thickness of about 500 nm by using, for example, a CVD method.
[0012]
Here, the liquid crystal molecules used as the liquid crystal layer have a refractive index anisotropy Δn, and further, the liquid crystal molecules are compared to the substrate (active matrix substrate and counter substrate) sandwiching the liquid crystal molecules. Since it may be inclined and oriented, the contrast of the display image changes depending on the viewing direction and angle of the viewer, resulting in a problem that the viewing angle dependency increases.
[0013]
Regarding the above problem, a twisted nematic (TN) type liquid crystal display system that is often used in a nematic type liquid crystal display device will be described. For example, as shown in FIG. 10, when a halftone display voltage is applied to the TN liquid crystal display element 71, the liquid crystal molecules 72 are slightly raised. At this time, in the liquid crystal display element 71, the linearly polarized light 75 that passes through the normal direction of the surfaces of the substrates 73 and 74, and the linearly polarized light 76 and 77 that passes through the normal direction with an inclination, The intersecting angles will be different. Since the liquid crystal molecules 72 have the refractive index anisotropy Δn as described above, normal light and abnormal light are generated when the linearly polarized light 75, 76, 77 in each direction passes through the liquid crystal molecules 72. Along with the phase difference between the normal light and the abnormal light, the linearly polarized light 75, 76, and 77 are converted into elliptically polarized light, respectively, and this becomes a generation source of viewing angle dependency.
[0014]
Further, in the actual liquid crystal layer, the liquid crystal molecules 72 have different tilt angles between the vicinity of the intermediate portion between the substrate 73 and the substrate 74 and the substrate 73 or the vicinity of the substrate 74, and the liquid crystal molecules 72 have the normal direction as an axis. The molecule 72 is in a state of being twisted by 90 °. As described above, the linearly polarized light 75, 76, and 77 that pass through the liquid crystal layer are subjected to various birefringence effects depending on their directions and angles, and exhibit complicated viewing angle dependency.
[0015]
Specifically, as the viewing angle dependency, when the viewing angle is tilted from the normal direction of the screen to the normal viewing angle direction which is the lower direction of the screen, the display image is colored at a certain angle or more (hereinafter referred to as “coloring phenomenon”). Or a phenomenon that black and white are reversed (hereinafter referred to as “inversion phenomenon”). Further, when the viewing angle is tilted in the anti-viewing angle direction, which is the upward direction of the screen, the contrast rapidly decreases.
[0016]
In addition, the liquid crystal display device has a problem that the viewing angle becomes narrower as the display screen becomes larger. When a large liquid crystal display screen is viewed from the front at a close distance, the colors displayed at the upper and lower portions of the screen may differ due to the effect of viewing angle dependency. This is because the prospective angle for viewing the entire screen is increased, which is the same as viewing the liquid crystal display screen from a more oblique direction.
[0017]
In order to improve such viewing angle dependency, it has been proposed to insert a retardation plate (retardation film) as an optical element having optical anisotropy between a liquid crystal display element and one polarizing plate. (For example, see Japanese Patent Laid-Open Nos. 55-000600 and 56-0907318).
[0018]
This method allows the light converted from linearly polarized light to elliptically polarized light as described above to pass through a phase difference plate interposed on one or both sides of the liquid crystal layer, thereby causing a phase difference between normal light and abnormal light generated at the viewing angle. Is compensated and re-converted into linearly polarized light, and the viewing angle dependency can be improved. Therefore, in this method, it is necessary to set not only the retardation plate but also the characteristics of the liquid crystal layer, that is, the liquid crystal display element.
[0019]
Therefore, in order to further improve the viewing angle dependency, the retardation plate is one in which one main refractive index direction in the refractive index ellipsoid is parallel to the normal direction of the surface of the retardation plate. On the other hand, the liquid crystal display element has a configuration in which the value of retardation Δn · d, which is the product of the refractive index anisotropy Δn of the liquid crystal material and the thickness d of the liquid crystal layer, is in the range of 200 nm to 500 nm. And a liquid crystal display device in which the above-described retardation plate is interposed between the liquid crystal display element and the polarizing plate has been proposed (Japanese Patent Laid-Open No. 5-313159).
[0020]
This method not only sets the characteristics of the retardation plate and the liquid crystal display element, but also determines the rubbing direction of the alignment film forming the liquid crystal display element, the slow axis direction of the retardation plate, and the transmission axis direction of the polarizing plate. Each of them is configured to be parallel to each other, thereby making it possible to further improve the viewing angle dependency.
[0021]
Further, a method using the above-described retardation plate in which the main refractive index direction of the refractive index ellipsoid is inclined with respect to the normal direction of the surface of the retardation plate has been proposed (Japanese Patent Laid-Open No. 6-75116). Publication). In this method, the following two types of retardation plates are used.
[0022]
One of the three main refractive indexes of the refractive index ellipsoid is that the direction of the minimum main refractive index is parallel to the surface, and one of the remaining two main refractive indexes is the surface of the retardation plate. The other direction is also inclined at an angle of θ with respect to the normal direction of the retardation plate surface, and the value of θ satisfies 20 ° ≦ θ ≦ 70 °. It is a phase difference plate.
[0023]
The other is that there is no refractive index anisotropy in the surface of the phase difference plate, the main refractive index nb in the surface normal direction of the phase difference plate and the main refractive indexes na and nc parallel to the surface of the phase difference plate, satisfying the relationship of na = nc> nb, that is, having negative uniaxiality, and further having main refraction with one of the main refractive indexes na and nc parallel to the surface of the retardation plate as an axis The refractive index ellipsoid is tilted by rotating the refractive index nb clockwise or counterclockwise from the state parallel to the normal direction to the surface of the phase difference plate.
[0024]
As for the above-described two types of retardation plates, the former can be uniaxial and biaxial. The latter not only uses one retardation plate, but also combines two retardation plates so that the inclination directions of the main refractive indexes nb in the normal direction of the surface of the retardation plate are 90 ° to each other. It is possible to use what is set to make.
[0025]
In a liquid crystal display device configured by interposing at least one such retardation plate between a liquid crystal display element and a polarizing plate, the viewing angle dependency can be improved to some extent.
[0026]
[Problems to be solved by the invention]
However, in the method disclosed in Japanese Patent Laid-Open No. 58-172585, the interlayer insulating film 68 is SiN, which is a transparent insulating film._X, SiO₂, TaO_XWhen the film is formed by CVD or sputtering, irregularities on the surface of the underlying metal layers 67a and 67b and the channel protective layer 65 are reflected on the interlayer insulating film 68. For this reason, when the pixel electrodes 51 are formed on the interlayer insulating film 68, a larger step is formed based on the steps of various films serving as a base. Nation) is caused.
[0027]
Further, in the case where an organic film such as polyimide is applied to form a pixel portion, the contact hole for electrically connecting the pixel electrodes 51 and the drain electrodes 66b is formed. It is necessary to add a process to form. Specifically, photo-patterning is performed on an organic film such as polyimide using a mask material, a contact hole is processed by etching, and finally a step of removing unnecessary photoresist is added. There is a need.
[0028]
In addition, in order to shorten the etching and peeling process, a method using a photosensitive polyimide film may be considered, but in this case, the resin after forming the interlayer insulating film 68 appears to be colored. . For this reason, in the liquid crystal display device in which high translucency and transparency are required, there is a problem that it cannot be used as the interlayer insulating film 68.
[0029]
Further, in the above conventional method, when the interlayer insulating film 68 is formed and the pixel electrodes 51 are stacked on the scanning lines 53... And the signal lines 54. 53 and the signal lines 54 and the pixel electrodes 51 are increased in electric capacity.
[0030]
Specifically, since the inorganic thin film such as the SiN film has a high relative dielectric constant of 8, and the film thickness is reduced to about 500 nm in order to form the inorganic thin film using the CVD method, the scanning line 53 .. And the signal capacitance between the signal lines 54 and the pixel electrodes 51 are greatly increased. For this reason, the following problems (1) and (2) are introduced.
[0031]
{Circle around (1)} When the signal lines 54 and the pixel electrodes 51 are stacked, the signal transmittance is increased by increasing the electric capacity between the signal lines 54 and the pixel electrodes 51. For this reason, the data signal held in the pixel electrodes 51 during the signal holding period is subject to fluctuation by the potential of the data signal. For this reason, when the pixel electrodes 51 apply a voltage to the liquid crystal, the effective value (effective voltage) of the voltage fluctuates, and in the actually obtained display screen, in particular, adjacent pixels in the vertical direction. However, there arises a problem that vertical crosstalk is invited.
[0032]
As one method for reducing the influence of the electric capacitance between the signal lines 54 and the pixel electrodes 51 on the display screen, for example, Japanese Patent Laid-Open No. 6-230422 corresponds to each signal line. A driving method for inverting the polarity of a data signal input to a pixel has been proposed. This driving method can provide an effective effect for a liquid crystal display device having a high correlation with the display of adjacent pixels, for example, a monochrome display liquid crystal display device.
[0033]
However, in a liquid crystal display device in which pixel electrodes are arranged in a vertical stripe shape, such as a normal notebook type personal computer, adjacent pixels connected to one signal line 54 have different display colors. Become. In particular, when color display is performed, for example, three pixel electrodes 51 corresponding to three colors of red (R), green (G), and blue (B) in one pixel area having a square shape. However, they are arranged in a vertically long rectangular shape in this order (the arrangement of the pixel electrodes 51... Is hereinafter referred to as a vertical stripe shape).
[0034]
In the case of a general color display having such an array of pixels in the form of vertical stripes, the effect of reducing vertical crosstalk is insufficient if the polarity inversion driving is performed for each signal line 54. Become.
[0035]
(2) When the scanning lines 53 and the pixel electrodes 51 are stacked, the electric capacity between the scanning lines 53 and the pixel electrodes 51 becomes large, which is caused by a switching signal for controlling the TFTs 52. Thus, there is a problem that the field through of the write voltage to the pixel electrode 51 becomes large.
[0036]
Note that an increase in electric capacity can be suppressed by forming the inorganic thin film to a thickness of 500 nm or more. However, when the thickness of the inorganic thin film is increased, there is a problem that it takes too much time in the manufacturing process.
[0037]
In addition, the method disclosed in Japanese Patent Laid-Open No. 5-313159 can improve the viewing angle dependency of the display screen with respect to a specific direction, but cannot improve all directions and has a problem that there is a limit. Has occurred.
[0038]
Furthermore, in the method disclosed in Japanese Patent Laid-Open No. Hei 6-75116, as described above, the condition of the retardation plate is set so that the refractive index ellipsoid is inclined. On the other hand, as for the liquid crystal display element, as an example, a liquid crystal display element in which the refractive index anisotropy Δn of the liquid crystal material is 0.08 and the thickness d of the liquid crystal layer is 4.5 μm, that is, the retardation Δn of the liquid crystal layer. -It is shown that the liquid crystal display element in case the value of d is 360 nm is used. However, no further mention is made regarding the condition of what kind of liquid crystal display element and the polarizing plate should interpose the retardation plate.
[0039]
In the method of improving the viewing angle dependency by interposing the retardation plate between the liquid crystal display element and the polarizing plate, it is necessary to set not only the retardation plate but also the characteristics of the liquid crystal display element. Therefore, in the case of the above method, in order to most effectively compensate for the phase difference, it is necessary to combine the above phase difference plate and the liquid crystal display element in which the value of Δn · d is in the range. It is not clear. For this reason, there is a problem that improvement of the viewing angle dependency of the liquid crystal display device using the retardation plate is still insufficient.
[0040]
The present invention solves the above-described conventional problems, and can improve the aperture ratio of the liquid crystal display and suppress the alignment failure (disclination) of the liquid crystal by overlapping the flat pixel electrode and each wiring. In addition, it is possible to obtain a good display by further reducing the influence of the crosstalk etc. given to the display by the capacitance component between each wiring and the pixel electrode. Improved phenomenon, high brightness, low power consumption, high definition, excellent color reproducibility, vivid image quality, especially in a wide viewing angle region with a viewing angle of 70 ° or more, vivid like a CRT centering on white and red An object of the present invention is to provide a liquid crystal display device that realizes color image quality.
[0041]
[Means for Solving the Problems]
  In order to solve the above problems, a liquid crystal display device according to claim 1 of the present invention includes a liquid crystal display element having at least a counter substrate, a pixel substrate, and a liquid crystal layer, and a pair disposed on both sides of the liquid crystal display element. A polarizer, and at least one retardation plate interposed between the liquid crystal display element and the polarizer, the counter substrate includes a common electrode and a plurality of color filters, and the pixel substrate includes: Scan lines and signal lines, switching elements provided in the vicinity of intersections of the scan lines and signal lines, interlayer insulating films provided above the scan lines, signal lines, and switching elements, and the switching elements And a pixel electrode provided on the interlayer insulating film, wherein the interlayer insulating film has a transmittance of light of a peak wavelength in the vicinity of the color wavelength band of the color filter of approximately 95% or more. AMade of positive photosensitive acrylic resinThe liquid crystal layer is composed of an organic film, and is interposed between the counter substrate and the pixel substrate, and has a refractive index anisotropy Δn (450) for light having a wavelength of 450 nm and a refractive index anisotropy Δn (for light having a wavelength of 650 nm. 650) is set in a range of 0 to 0.01, and the phase retardation plate has at least three representative refractive indexes of a refractive index ellipsoid in the representative layer. na, nb, and nc have a relationship of na = nc> nb, and one of the main refractive indexes na and nc is parallel to the surface of the retardation plate, and the direction of the main refractive index that is parallel to the axis is an axis. The refractive index ellipsoid is inclined by rotating the main refractive index nb clockwise or counterclockwise from a state parallel to the normal direction of the surface of the retardation plate to an inclined state. It is said.
[0042]
According to the first aspect of the present invention, when the wiring and the pixel electrode are stacked with the interlayer insulating film and the aperture ratio is improved, the interlayer insulating film made of an organic material is formed, thereby forming the pixel portion. The portion that becomes can be further flattened. For this reason, the alignment defect (disclination) of a liquid crystal can be suppressed. Further, since the interlayer insulating film has a relative dielectric constant lower than that of the conventional inorganic thin film, the electric capacity between the wiring and the pixel electrode is reduced and the signal transmittance is also suppressed. For this reason, it is possible to further reduce the influence such as crosstalk that the capacitance between the wiring and the pixel electrode has on display, and to reduce the field-through of the write voltage to the pixel electrode. In addition, since the interlayer insulating film can obtain a high-quality and highly transparent film with high productivity, it is possible to increase the film thickness and reduce an increase in electric capacity.
[0043]
The interlayer insulating film has high transparency, and the transmittance of light having a peak wavelength when the light source transmits the color filter is 95% or more. For this reason, the light from the light source can be used efficiently (that is, with low power consumption). For this reason, even if the light amount of the light source is slightly reduced and the power consumption is reduced, a display with high brightness and a bright appearance can be obtained, and a liquid crystal display device which is a display screen having a better, brighter and beautiful hue can be obtained. .
[0044]
Here, optical elements such as a retardation plate and a polarizing plate usually have a problem that the refractive index anisotropy with respect to the wavelength of light is different. For example, in many of those currently used as retardation plates, the refractive index anisotropy is small on the short wavelength side and large on the high wavelength side. However, by using a liquid crystal having a small difference between the refractive index anisotropy on the short wavelength side and the refractive index anisotropy on the high wavelength side in combination with the retardation plate, normal light and abnormal light generated depending on the viewing angle can be obtained. This phase difference can be compensated more effectively than before.
[0045]
In particular, in the present invention, by combining the liquid crystal and the retardation plate as described above, it is possible to convert elliptically polarized light into linearly polarized light in a wide range of viewing angles. That is, the combination of the liquid crystal and the retardation plate described above can eliminate the coloring phenomenon and the reversal phenomenon associated with the change in viewing angle at a viewing angle of about 70 ° as a limit value. Therefore, the viewing angle dependency can be reduced as compared with the conventional liquid crystal display device, and the image quality of the CRT display device is not inferior. Especially, the liquid crystal display in which white and red are bright even in a wide viewing angle region of 70 ° or more. A device can be obtained.
[0046]
In order to solve the above-described problems, the liquid crystal display device according to claim 2 of the present invention has the above-described configuration of claim 1,A drain electrode connected to the pixel electrode;A connection electrode connecting the pixel electrode and the drain electrode; and the interlayer insulating film is provided on the switching element, the scanning line, the signal line, and the connection electrode. The pixel electrode is provided so as to partially overlap at least one of the scanning line and the signal line, and the connection electrode and the pixel electrode are connected through a contact hole penetrating the interlayer insulating film. It is characterized by being.
[0047]
According to the second aspect of the present invention, when the pixel electrode is connected to the drain electrode of the switching element via the connection electrode, a contact hole having smooth side walls without unevenness is formed even when the switching element is small. Can do. Further, by burying a conductive material in the interlayer insulating film, the connection electrode can be easily made with a high yield with less disconnection.
[0048]
Furthermore, when the connection electrode is formed as a transparent conductive film planarly overlapped with the pixel electrode via an interlayer insulating film, the aperture ratio of the pixel can be further improved.
[0049]
In order to solve the above problems, a liquid crystal display device according to claim 3 of the present invention has an additional capacitor for holding a voltage applied to the liquid crystal layer in addition to the configuration of claim 2.do itIt is characterized by being.
[0051]
In order to solve the above problems, a liquid crystal display device according to a fourth aspect of the present invention has a refractive index anisotropy Δn (435 for light having a wavelength of 435 nm in addition to the configuration according to the first, second, or third aspect. ) And a refractive index anisotropy Δn (610) difference Δn (435) −Δn (610) with respect to light having a wavelength of 610 nm is characterized by using a liquid crystal set in a range of 0.00875 or less.
[0052]
According to the configuration described in claim 4 above, since the light transmission between the liquid crystal layer and the color filter is balanced, the light can be used efficiently (low power consumption) and viewed from an oblique direction. Thus, a liquid crystal display device with improved display quality can be obtained.
[0053]
According to a fifth aspect of the present invention, in order to solve the above-described problem, in addition to the configuration according to any one of the first to fourth aspects, the color filter is incident through the pixel substrate. The transmitted light has a light transmittance of at least one peak wavelength of 85% or more.
[0054]
According to the configuration of the fifth aspect, it is possible to obtain a liquid crystal display device that can use light more efficiently (low power consumption) and that has improved display quality.
[0055]
In order to solve the above-described problems, a liquid crystal display device according to a sixth aspect of the present invention has a configuration in which the retardation plate includes a discotic structural unit in addition to the configuration according to any one of the first to fifth aspects. And a tilt angle formed by the disc surface of the discotic structural unit and the surface of the phase difference plate changes continuously or discontinuously in the depth direction of the phase difference plate. It is said.
[0056]
According to the configuration described in claim 6, the retardation plate can be easily manufactured at a low cost by the coating method as compared with the conventional manufacturing method such as the stretch manufacturing method type, and even if it is large in size. A phase difference plate with little quality variation can be obtained. Therefore, a liquid crystal display device having a large display screen on which a visual angle difference is easily recognized on the display screen, particularly a liquid crystal display device having a screen size of 20 ″ or more to about 40 ″, a high-definition display screen. Can be realized.
[0057]
Further, at this time, the inclination angle of the optical anisotropic axis in the retardation plate can be easily changed in the thickness direction of the retardation plate by appropriately selecting the orientation treatment or material of the base. For this reason, it is easy to optimize the characteristics matching between the liquid crystal display element and the phase difference plate. In addition, the retardation plate can easily obtain an optimum structure according to characteristics such as the refractive index of the liquid crystal layer on the inner side (liquid crystal side) and the outer side (atmosphere side) of the liquid crystal display element.
[0058]
In order to solve the above problems, the liquid crystal display device according to claim 7 of the present invention is characterized in that, in addition to the configuration according to claim 6, the average value of the tilt angles is 15 ° to 75 °. It is said.
[0059]
According to the configuration of the seventh aspect, the effects of the retardation plate and the liquid crystal are more reliably exhibited, and a liquid crystal display device with higher quality display can be obtained.
[0060]
In order to solve the above problems, a liquid crystal display device according to an eighth aspect of the present invention, in addition to the configuration according to any one of the first to seventh aspects, has a liquid crystal layer with a liquid crystal layer. It is oriented in a 90 ° twisted state, and its display method is a normally white method.
[0061]
According to the configuration described in claim 8, the liquid crystal is oriented in a twisted state of 90 °, and the display method of the display screen, the color reproducibility, and the viewing angle are adopted by adopting the normally white display method. A display screen with improved dependency can be obtained. In particular, in the normally white system, from the above viewpoint, it is possible to obtain a display screen that is whiter and clearer than the normally black system that is another system.
[0062]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to FIGS. Note that the present invention is not limited thereby.
[0063]
As shown in FIG. 1A, the liquid crystal display device 1 of the present invention includes a liquid crystal display element 5, a retardation plate 2a disposed on one side of the liquid crystal display element 5, and a position disposed on the other side. The liquid crystal display element 5 and the polarizing plates 3 and 4 as a pair of polarizers sandwiching the liquid crystal display element 5 and the phase difference plates 2a and 2b are provided.
[0064]
In the liquid crystal display element 5, a liquid crystal layer 12 is sealed with a sealing material 13 between a glass substrate 6 as a counter substrate and a glass substrate 7 as a pixel substrate. On the surface of the glass substrate 6, a transparent electrode layer 8 as a common electrode made of ITO (indium tin oxide), an alignment film 10 made of polyimide, polyvinyl alcohol, or the like, and divided for each pixel (not shown) are arranged. A plurality of color filters are formed.
[0065]
Similarly, a plurality of transparent electrode layers 9 as pixel electrodes made of ITO or the like and an alignment film 11 made of polyimide or the like are also formed on the surface of the glass substrate 7. The transparent electrode layers 9 are usually arranged in units of several hundreds, and are formed at positions corresponding to the plurality of color filters.
[0066]
As the glass substrates 6 and 7, alkali-free glass is used. As the liquid crystal used for the liquid crystal layer 12, nematic liquid crystal is used in the present embodiment. Further, as the sealing material 13, a thermosetting resin, an ultraviolet curable resin, or the like is used. In addition, each said member is not limited to these.
[0067]
Further, in the liquid crystal display device 1, for example, a light source 14 having an elongated cylindrical shape and light emitted from the light source 14 are applied to the liquid crystal display element 5 at a position on the back surface side when viewed from the transparent electrode layer 9. A light guide 15 for guiding light is disposed. The light source 14 and the light guide 15 form one backlight unit, and the backlight unit irradiates light from the light source 14 to the entire area corresponding to the display screen in the liquid crystal display device 1. Can do.
[0068]
Each surface of the alignment films 10 and 11 is rubbed in advance so that the intervening liquid crystal molecules are twisted and aligned by about 90 °. Specifically, as shown in FIG. 3, in the liquid crystal display element 5, in the case of the alignment film 10 on the glass substrate 6, the rubbing process is performed in the direction of the arrow 21. In the case of the upper alignment film 11, the rubbing process is performed so as to be in the direction of the arrow 22 orthogonal to the arrow 21. The arrows 21 and 22 are hereinafter referred to as a rubbing direction 21 and a rubbing direction 22.
[0069]
In the liquid crystal display device 1 of the present invention, as shown in FIG. 4, the polarizing plates 3 and 4 are arranged so that the absorption axes 23 and 24 thereof are orthogonal to each other. Therefore, when a voltage is not applied to the liquid crystal layer 12 of the liquid crystal display element 5, the liquid crystal display device 1 is a normally white display system in which the liquid crystal layer 12 transmits light and performs white display. At this time, the absorption axis 23 of the polarizing plate 3 and the rubbing direction 21 of the alignment film 10 are set to be parallel to each other. Similarly, the absorption axis 24 of the polarizing plate 4 and the rubbing direction 22 of the alignment film 11 are set to be parallel to each other.
[0070]
Here, in the phase difference plates 2a and 2b, the direction of the main refractive index nb that is inclined in the direction giving anisotropy to the phase difference plates 2a and 2b is projected onto the surface of the phase difference plates 2a and 2b. Are defined as 25a and 25b, respectively. At this time, in the liquid crystal display device 1, as shown in FIG. 4, the direction 25a of the phase difference plate 2a and the rubbing direction 21 are set to be parallel to each other and opposite to each other. The direction 25b of the phase difference plate 2b and the rubbing direction 22 are set to be parallel to each other and to be in the same direction.
[0071]
If at least one of the retardation plates 2a and 2b is interposed between the polarizing plate 3 and the polarizing plate 4, the phase difference can be compensated. Further, two or more retardation plates 2 a or 2 b may be interposed between the polarizing plate 3 and the liquid crystal display element 5 or between the polarizing plate 4 and the liquid crystal display element 5. In addition, two or more retardation plates 2a and 2b may be interposed between the liquid crystal display element 5 and both polarizing plates 3 and 4, respectively.
[0072]
As shown in FIG. 2, the phase difference plate 2a used in the liquid crystal display device 1 has three main refractive indexes na of average refractive index ellipsoids at least in the representative layer or as a whole of the phase difference plate 2a. Nb · nc has a relationship of na = nc> nb, that is, a relationship in which the refractive index anisotropy is negative. Thereby, the phase difference plate 2a has uniaxiality in which only one optical axis exists. In addition, when an orthogonal coordinate system xyz is defined in which the surface of the retardation plate 2a is the xy plane, the direction of the main refractive index nb is the direction of the arrow A with respect to the normal direction z-axis of the surface of the retardation plate 2a. Is inclined at an angle θ. Further, the main refractive index nc is also inclined at an angle θ in the direction of arrow B with respect to the x-axis direction parallel to the surface of the retardation film 2a.
[0073]
That is, in the retardation film 2a, as a whole, the refractive index ellipsoid is inclined at an angle θ counterclockwise about the direction of the main refractive index na. The inclination of the refractive index ellipsoid may be inclined clockwise about the direction of the main refractive index na. The phase difference plate 2b has the same configuration as that of the phase difference plate 2a, and a description thereof will be omitted.
[0074]
In the present embodiment, as the retardation plates 2a and 2b, the inclination of the main refractive index nb is such that the angle θ is about 20 °. At this time, the main refractive index nc similarly has the angle θ of about 20 °. That is, the refractive index ellipsoid is inclined 20 ° counterclockwise about the direction of the main refractive index na.
[0075]
By setting different retardation values for the retardation plates 2a and 2b, a phase difference compensation function can be reliably obtained. The retardation value includes a first retardation value and a second retardation value. The first retardation value is the difference between the main refractive index nc and the main refractive index nb as a whole of the retardation plates 2a and 2b, and the retardation plate 2a.・ Thickness d of 2b_fProduct (nc−na) × d_fIt is. On the other hand, the second retardation value includes the difference between the main refractive index nc and the main refractive index nb, and the thickness d of the phase difference plates 2a and 2b._fProduct (nc−nb) × d_fIt is.
[0076]
In the present embodiment, as the retardation plates 2a and 2b, specifically, a discotic liquid crystal is applied to a transparent support (for example, triacetyl cellulose (TAC)), and the discotic liquid crystal is tilted and aligned. The first retardation value is 0 nm, and the second retardation value is 100 nm.
[0077]
The discotic liquid crystal tilted and aligned on the retardation plates 2a and 2b forms a layer with a discotic structure that is a disc shape in liquid crystal molecules as one structural unit. The inclination angle formed by the disk surface in one unit of the discotic structure and the surfaces of the phase difference plates 2a and 2b changes continuously or discontinuously in the depth direction of the phase difference plates 2a and 2b. At this time, it is preferable that an average value of the inclination angle is 15 ° to 75 °.
[0078]
Since the discotic liquid crystal layer can be formed by a coating method as compared with a conventional manufacturing method such as a stretch manufacturing method, the retardation plates 2a and 2b can be easily manufactured at low cost. it can. Furthermore, since the manufacturing method is easy and the cost is low, the phase difference plates 2a and 2b can be made larger than the conventional ones, and higher quality phase difference plates 2a and 2b can be obtained. .
[0079]
Here, the conventional liquid crystal display device has a problem that the larger the display screen is, the larger the left-right viewing angle difference is on the display screen. In particular, in a display screen having a screen size of 20 ″ or more, the viewer is moved from the position where the viewer is 50 cm away from the display screen at a vertical distance and the viewing angle is 70 ° or more with respect to the center of the display screen. When viewed, a noticeable coloring phenomenon was observed at the end on the side far from the viewer.
[0080]
However, in the retardation plate that forms the discotic liquid crystal as described above, the retardation plate can be increased in size, and quality variations associated with the increase in size are reduced. For this reason, higher quality phase difference plates 2a and 2b can be obtained. Therefore, in the liquid crystal display device of the present invention, a liquid crystal display device having a large display screen on which a visual angle difference is easily recognized on the display screen, in particular, as a monitor for home use or business use, OA, has recently been required. In addition, even a liquid crystal display device having a screen size of 20 ″ or more to about 40 ″ being developed can realize a display screen of high quality display.
[0081]
Further, at this time, the inclination angle of the optical anisotropic axis in the retardation plates 2a and 2b can be easily changed in the thickness direction of the retardation plates 2a and 2b by appropriately selecting a base alignment treatment or material. Can do. For this reason, it is easy to optimize the characteristic matching between the liquid crystal display element 5 and the phase difference plates 2a and 2b. In addition, the retardation plates 2a and 2b can easily have an optimum structure according to the characteristics such as the refractive index of the liquid crystal layer 12 on the inner side (liquid crystal side) and the outer side (atmosphere side) of the liquid crystal display element 5. Can get to.
[0082]
When the above-described retardation plates 2a and 2b are used for the liquid crystal display device 1 and the display screen is visually confirmed from the left and right and the upper 50 ° directions, neither color nor inversion is seen, and a beautiful display is obtained. It was observed.
[0083]
Further, as the retardation plates 2a and 2b, a discotic liquid crystal is applied to a transparent support and the discotic liquid crystal is hybrid-aligned, and the first retardation value is 0 nm, Those having a retardation value of 100 nm were also used in the liquid crystal display device 1 in the same manner as described above.
[0084]
Even in this case, when the display screen of the liquid crystal display device 1 was visually confirmed from the left and right and from the direction of 50 ° to 70 ° above, no coloration or inversion was seen in any of the conditions, and a beautiful display was seen.
[0085]
By using the phase difference plates 2a and 2b, the phase difference between the normal light and the extraordinary light generated according to the viewing angle is compensated, so that it can be converted into linearly polarized light over a wide range of viewing angles. Since the coloring phenomenon and the inversion phenomenon associated with the change can be eliminated, the liquid crystal display device 1 with less viewing angle dependency can be obtained.
[0086]
In the liquid crystal display device 1 of the present invention, the refractive index anisotropy Δn (450) for light with a wavelength of 450 nm and the refractive index anisotropy Δn (650 for light with a wavelength of 650 nm are used as the liquid crystal layer 12 together with the retardation plates 2a and 2b. It is preferable to use a liquid crystal in which the difference Δn (450) −Δn (650) is set in the range of 0 or more and 0.01 or less (hereinafter, this setting condition is referred to as condition (1)).
[0087]
Further, in addition to the above condition (1), the difference Δn (435) −Δn (610) between the refractive index anisotropy Δn (435) for light with a wavelength of 435 nm and the refractive index anisotropy Δn (610) for light with a wavelength of 610 nm. However, it is more preferable to use a liquid crystal set in a range of 0.00875 or less (hereinafter, this setting condition is referred to as condition (2)).
[0088]
In the optical elements such as the retardation plates 2a and 2b and the polarizers 3 and 4, the refractive index anisotropy with respect to the wavelength of light is usually different in each part of the optical element. For example, most of the presently used retardation plates 2a and 2b have a refractive index anisotropy that is small on the short wavelength side and large on the high wavelength side. Therefore, normal light generated according to the viewing angle is obtained by using a liquid crystal having a small difference between the refractive index anisotropy on the short wavelength side and the refractive index anisotropy on the high wavelength side in combination with the retardation plates 2a and 2b. And the extraordinary light can be compensated more effectively than in the past.
[0089]
In particular, in the present invention, by combining the liquid crystal layer 12 and the retardation plates 2a and 2b as described above, even if the viewer views the display screen with a larger viewing angle, that is, Even when the viewing angle is in a wider range, it is possible to convert elliptically polarized light into linearly polarized light, and it is possible to obtain the liquid crystal display device 1 having a display screen with less viewing angle dependency and improved coloring and inversion phenomena.
[0090]
In the present embodiment, specifically, a liquid crystal material having a refractive index anisotropy Δn (550) of 0.070, 0.080, and 0.095 for light having a wavelength of 550 nm is used as the liquid crystal layer 12. . The liquid crystal material described above can obtain the liquid crystal layer 12 that satisfies the above conditions (1) and (2). At this time, the cell thickness of the liquid crystal display element 5 is set to about 5 μm.
[0091]
By combining the liquid crystal layer 12 using the liquid crystal and the retardation plates 2a and 2b, the coloring phenomenon and the inversion phenomenon associated with the change in the viewing angle in the liquid crystal display element 5 can be eliminated up to a viewing angle of about 70 ° as a limit value. It can be confirmed by visual inspection. Therefore, the viewing angle dependency can be reduced as compared with the conventional liquid crystal display device, and the CRT display device has an image quality comparable to that of the liquid crystal display device. In particular, the white and red liquid crystals are vivid in a wide viewing angle region of about 70 ° or more. A display device can be obtained.
[0092]
Further, in the configuration of FIG. 4, in the liquid crystal layer 12, the liquid crystal is aligned in a state twisted by 90 °. In addition, since the normally white display method is adopted, the display screen display contrast, color reproducibility, and viewing angle dependency can be further improved. In particular, the normally white method is more preferable than the normally black method because the white can have a clearer white display screen.
[0093]
Next, the structure of the pixel substrate used in the liquid crystal display device 1 of the present invention will be described below.
The glass substrate 7 used as a pixel substrate in the liquid crystal display element 5 of the present invention has a plurality of TFTs 31 as switching elements formed on the glass substrate 7, as shown in part in FIG. A plurality of transparent electrode layers (pixel electrodes) 9 are formed thereon (in FIG. 6, only one TFT 31 is shown, and the pixel electrode 9 includes a pixel electrode 9a). And a pixel electrode 9b).
[0094]
More specifically, one TFT 31 for controlling the pixel electrode 9a is formed on the gate electrode 32 formed on the glass substrate 7 via a gate insulating film 33 formed so as to cover the gate electrode 32. The semiconductor thin film 34, the source electrode 35 formed in the source part of the semiconductor thin film 34, and the drain electrode 36 also formed in the drain part.
[0095]
A signal line 37a is connected to the source electrode 35 of the TFT 31, and a connection electrode 38 to the pixel electrode 9a is connected to the drain electrode 36. An interlayer insulating film 40 is formed so as to cover the TFT 31, the signal line 37 a and the connection electrode 38. The connection electrode 38 is further connected to the pixel electrode 9 a through the contact hole 39.
[0096]
As the interlayer insulating film 40, an acrylic photosensitive resin, a resin such as benzocyclobutene or transparent photosensitive polyimide is used. These photosensitive resins have high transparency and excellent translucency. In the present embodiment, specifically, a positive photosensitive acrylic resin obtained by mixing a naphthoquinonediazide-based positive photosensitive material with a base polymer made of a copolymer of methacrylic acid and glycidyl methacrylate. The insulating film 40 is used.
[0097]
In the interlayer insulating film 40 using the above material, as shown in the graph 40a of FIG. 5, before development, absorption due to coloring derived from the unreacted photosensitive material or the like is observed in a low wavelength region of 380 nm to 540 nm. It is done. After the development of the interlayer insulating film 40, as shown in a graph 40b of FIG. 5, for example, by irradiation with ultraviolet light such as i-line (365 nm), absorption due to coloring observed in the graph 40a disappears. In addition, the transmittance of light having a peak wavelength in the light emitted from the light source 14 is approximately 95% or more, and the interlayer insulating film 40 is further improved in transmittance. For example, in the present embodiment, the blue light peak spectrum of light from the light source 14 is 435 nm. At this time, the transmittance of the interlayer insulating film 40 is approximately 95%.
[0098]
For this reason, the light from the light source 14 can be utilized efficiently (that is, with low power consumption). For this reason, even if the light amount of the light source 14 is slightly reduced and the power consumption is reduced, a high-brightness and bright display can be obtained, and the liquid crystal display device 1 which is a display screen having a better, brighter and beautiful hue can be obtained. Can do.
[0099]
In addition, as shown in FIG. 6, the pixel electrode 9a is partially stacked on the signal line 37b connected to the TFT 31 (not shown) in the adjacent pixel electrode 9 (not shown). The adjacent pixel electrode 9b is partially stacked on the signal line 37a for inputting an image signal to the pixel electrode 9a (in FIG. 6, the stacked portion is indicated as C ′). Further, as shown in FIG. 1B, the interlayer insulating film 40 has a planar region including the gate electrode 32 and the additional capacitor 41 as a lower layer region and a planar region including the pixel electrode 9 as shown in FIG. Each region can be partially stacked as the upper layer region (in FIG. 1B, the stacked portion of the gate electrode 32 is indicated as D and the stacked portion of the additional capacitor 41 is indicated as E).
[0100]
Thereby, the aperture ratio of the pixel can be further improved. In addition, since the pixel portion can be flattened as compared with the case of forming an inorganic thin film, liquid crystal alignment defects can be suppressed, and the tilt of the liquid crystal can be controlled more uniformly than in the past to display multiple gradations. Therefore, the color sense of the viewer with respect to the display screen can be further improved.
[0101]
Further, since the relative dielectric constant is lower than that of the conventional inorganic thin film, the use of the interlayer insulating film 40 reduces the electric capacity between the signal line 37 and the gate electrode 32 and the pixel electrode 9, thereby providing a signal. The transmittance is also suppressed. For this reason, it is possible to further reduce the influence of the electric capacitance on the display screen, such as crosstalk, and to reduce the field-through of the write voltage to the pixel electrode 9. In addition, since the interlayer insulating film 40 can obtain a high-quality and highly transparent film with high productivity, it is possible to increase the film thickness and further reduce the increase in electric capacity.
[0102]
In FIG. 6, the drain electrode 36 and the pixel electrode 9a are connected in the vicinity of the TFT 31, but the connection electrode 38 is connected to the upper part of the adjacent gate electrode 32 and additional capacitor 41 (not shown in FIG. 6). The extension may be formed by extending. Alternatively, the gate electrode 32 may be connected to the pixel electrode 9a by forming a contact hole at the tip of the extension. The connection electrode 38 may be the same material as the drain electrode 36 or may be a different material. The material of the connection electrode 38 can be easily selected from the structure of the glass substrate 7, the manufacturing process, restrictions on the manufacturing line, and the like.
[0103]
By using the connection electrode 38 described above, even when the TFT 31 is small, the contact hole 39 having a smooth side wall without unevenness can be formed. Further, the connection electrode 38 can be easily formed with a high yield with less disconnection by embedding a conductive material in the interlayer insulating film 40.
[0104]
Although not shown in the drawings, the connection electrode 38 may be formed as a transparent conductive film that is superimposed on the pixel electrode 9 via the interlayer insulating film 40 in the case where the extension is formed as described above. Good. By forming the connection electrode 38 in this way, the aperture ratio of the pixel can be further improved.
[0105]
As shown in FIG. 6, the contact hole 39 is provided on a light-shielding connection electrode 38 or on a light-shielding wiring connected to an additional capacitor (not shown). Thus, by providing the contact hole 39 on the light shielding portion such as a light shielding wiring, it is possible to hide the light leakage due to the disorder of the alignment of the liquid crystal. For this reason, contrast reduction does not occur in the obtained display screen. In addition, since the contact hole 39 can be formed on the same glass substrate 7 as the light shielding portion, the positional accuracy of the light shielding portion and the contact hole 39 can be improved. For this reason, the aperture ratio of the pixel can be further improved.
[0106]
Further, as shown in FIG. 7A, the light source 14 used in the present embodiment emits light having a peak spectrum in three colors of blue (B), green (G), and red (R). It is. The light from the light source 14 passes through the interlayer insulating film 40 described above, reaches the plurality of pixel electrodes 9, and further passes through the color filter formed thereon. As shown in FIG. 7B, the color filter used in the present embodiment transmits light having the spectrum shown in FIG. 7A with a higher transmittance than the conventional color filter. It has become.
[0107]
Specifically, the graph shown by the solid line in FIG. 7B is the transmittance of the conventional dyeing color filter 42b, and the graph shown by the broken line is the transmission of the high-transmitting dyeing color filter 42a used in the present embodiment. Rate. The high-transmission dyeing color filter 42a has an overall high transmittance as compared with the conventional dyeing color filter 42b. In particular, the peak value of red light shows a transmittance of 85% or more. Yes. In addition, since the interlayer insulating film 40 also has a high transmittance as described above, it is possible to display a vivid color and to efficiently use light from the light source 14. For this reason, it is possible to obtain a liquid crystal display device 1 that is a display screen having a higher brightness and a brighter appearance and a better, brighter and beautiful hue.
[0108]
As described above, the liquid crystal display device of the present invention has an additional capacitor for holding a voltage applied to the liquid crystal layer, and the contact hole is an electrode connected to the additional capacitor or the scanning line. It is the structure provided so that it may be located in the upper part.
Therefore, in the above configuration, by providing the contact hole on the light-shielding portion, for example, the light-shielding wiring connected to the additional capacitor or the scanning line, light leakage due to the disorder of the liquid crystal orientation can be hidden. Therefore, the contrast of the display screen does not decrease. In addition, since the contact hole can be formed on the same substrate, the positional accuracy of the light shielding material and the contact hole is improved, so that the aperture ratio of the pixel can be further improved. For this reason, the liquid crystal display device having a bright and low power consumption display screen can be obtained.
As described above, since the liquid crystal display device of the present invention has the above-described configurations, it further improves the visual dependency on the display screen and adversely affects the display screen due to the structure of the pixel substrate. Can be further suppressed. Therefore, the liquid crystal display device of the present invention can be suitably used in a wide range of fields as a display including a word processor, a computer, and a navigation system in order to enable display comparable to that of a CRT.
[0109]
【The invention's effect】
  As described above, the liquid crystal display device according to claim 1 of the present invention includes a liquid crystal display element having at least a counter substrate, a pixel substrate, and a liquid crystal layer, and a pair of polarizers disposed on both sides of the liquid crystal display element. A phase difference plate interposed between the liquid crystal display element and the polarizer, the counter substrate includes a common electrode and a plurality of color filters, and the pixel substrate includes a scanning line and a signal. A line, a switching element provided in the vicinity of the intersection of the scanning line and the signal line, an interlayer insulating film provided on the scanning line, the signal line and the switching element, and the switching element, The interlayer insulating film has a transmittance of light of a peak wavelength of about 95% or more in the vicinity of the color wavelength band of the color filter.Made of positive photosensitive acrylic resinThe liquid crystal layer is composed of an organic film, and is interposed between the counter substrate and the pixel substrate, and has a refractive index anisotropy Δn (450) for light having a wavelength of 450 nm and a refractive index anisotropy Δn (for light having a wavelength of 650 nm. 650) is set in a range of 0 to 0.01, and the phase retardation plate has at least three representative refractive indexes of a refractive index ellipsoid in the representative layer. na, nb, and nc have a relationship of na = nc> nb, and one of the main refractive indexes na and nc is parallel to the surface of the retardation plate, and the direction of the main refractive index that is parallel to the axis is an axis. The refractive index ellipsoid is inclined by rotating the main refractive index nb clockwise or counterclockwise from a state parallel to the normal direction of the surface of the retardation plate to an inclined state. .
[0110]
Therefore, in the above configuration, when the wiring and the pixel electrode are stacked with an interlayer insulating film and the aperture ratio is improved, an interlayer insulating film made of an organic material is formed, so that a portion to be a pixel portion is more formed. It can be flattened. For this reason, the alignment defect (disclination) of a liquid crystal can be suppressed. Further, since the interlayer insulating film has a relative dielectric constant lower than that of the conventional inorganic thin film, the electric capacity between the wiring and the pixel electrode is reduced and the signal transmittance is also suppressed. For this reason, it is possible to further reduce the influence such as crosstalk that the capacitance between the wiring and the pixel electrode has on display, and to reduce the field-through of the write voltage to the pixel electrode. In addition, since the interlayer insulating film can obtain a high-quality and highly transparent film with high productivity, it is possible to increase the film thickness and reduce an increase in electric capacity.
[0111]
The interlayer insulating film has high transparency, and the transmittance of light having a peak wavelength when the light source transmits the color filter is 95% or more. For this reason, the light from the light source can be used efficiently (that is, with low power consumption). For this reason, even if the light amount of the light source is slightly reduced and the power consumption is reduced, a display with high brightness and a bright appearance can be obtained, and a liquid crystal display device which is a display screen having a better, brighter and beautiful hue can be obtained. .
[0112]
Furthermore, in the present invention, by combining the liquid crystal and the retardation plate as described above, it becomes possible to convert elliptically polarized light into linearly polarized light in a wide range of viewing angles. For this reason, it is possible to obtain a liquid crystal display device that can be less dependent on the viewing angle than the conventional liquid crystal display device and has the same image quality as that of a CRT display device, and particularly bright in white and red even in a wide viewing angle region of 70 ° or more. There is an effect that can be done.
[0113]
The liquid crystal display device according to claim 2 of the present invention, as described above, in addition to the configuration of claim 1 above,A drain electrode connected to the pixel electrode;A connection electrode connecting the pixel electrode and the drain electrode; and the interlayer insulating film is provided on the switching element, the scanning line, the signal line, and the connection electrode. The pixel electrode is provided so as to partially overlap at least one of the scanning line and the signal line, and the connection electrode and the pixel electrode are connected through a contact hole penetrating the interlayer insulating film. It is the structure which is done.
[0114]
Therefore, in the above configuration, when the pixel electrode is connected to the drain electrode of the switching element via the connection electrode, a contact hole having a smooth sidewall without unevenness can be formed even when the switching element is small. Further, by burying a conductive material in the interlayer insulating film, the connection electrode can be easily made with a high yield with less disconnection. In addition, when the connection electrode is formed as a transparent conductive film that is planarly overlapped with the pixel electrode via an interlayer insulating film, there is an effect that the aperture ratio of the pixel can be further improved.
[0117]
The liquid crystal display device according to claim 4 of the present invention has a refractive index anisotropy Δn (435) and a wavelength of 610 nm with respect to light having a wavelength of 435 nm, in addition to the configuration described in claim 1, 2 or 3 as described above. The difference is Δn (435) −Δn (610) in the refractive index anisotropy Δn (610) with respect to the light of the liquid crystal, and the liquid crystal is used in the range of 0.00875 or less.
[0118]
Therefore, in the above configuration, the light transmission balance between the liquid crystal layer and the color filter is balanced, so that the light can be used efficiently (low power consumption) and the coloring when viewed from an oblique direction is further improved. The liquid crystal display device with improved display quality can be obtained.
[0119]
In the liquid crystal display device according to claim 5 of the present invention, as described above, in addition to the configuration according to any one of claims 1 to 4, the color filter in the light incident through the pixel substrate. The light transmittance of at least one peak wavelength is 85% or more.
[0120]
Therefore, in the above configuration, there is an effect that it is possible to obtain a liquid crystal display device that can use light more efficiently (low power consumption) and can further improve display quality.
[0121]
In the liquid crystal display device according to claim 6 of the present invention, as described above, in addition to the structure according to any one of claims 1 to 5, the retardation plate is made of a compound having a discotic structural unit. And a tilt angle formed by the disc surface of the discotic structural unit and the surface of the phase difference plate changes continuously or discontinuously in the depth direction of the phase difference plate.
[0122]
Therefore, in the above configuration, the retardation plate can be easily manufactured at a low cost by the coating method as compared with a conventional manufacturing method such as a stretch manufacturing method type, and quality variation is small even if it is large. A phase difference plate can be obtained. Therefore, a liquid crystal display device having a large display screen on which a visual angle difference is easily recognized on the display screen, particularly a liquid crystal display device having a screen size of 20 ″ or more to about 40 ″, a high-definition display screen. Can be realized.
[0123]
Further, at this time, the inclination angle of the optical anisotropic axis in the retardation plate can be easily changed in the thickness direction of the retardation plate by appropriately selecting the orientation treatment or material of the base. For this reason, it is easy to optimize the characteristics matching between the liquid crystal display element and the phase difference plate. In addition, the retardation plate can easily obtain an optimum structure according to characteristics such as the refractive index of the liquid crystal layer on the inner side (liquid crystal side) and the outer side (atmosphere side) of the liquid crystal display element. There is an effect.
[0124]
As described above, the liquid crystal display device according to a seventh aspect of the present invention has a configuration in which the average value of the tilt angles is 15 ° to 75 ° in addition to the configuration according to the sixth aspect.
[0125]
Therefore, in the above configuration, the effects of the retardation plate and the liquid crystal are more reliably exhibited, and an effect is obtained that a liquid crystal display device with higher quality display can be obtained.
[0126]
In the liquid crystal display device according to claim 8 of the present invention, as described above, in addition to the configuration according to any one of claims 1 to 7, the liquid crystal display device twists the liquid crystal of the liquid crystal layer by 90 °. The display is oriented in a state and the display method is a normally white method.
[0127]
Therefore, with the above configuration, the display screen display contrast, color reproducibility, and viewing angle dependency are further improved by aligning the liquid crystal in a 90 ° twisted state and adopting a normally white display method. Display screen can be obtained. In particular, in the normally white system, from the above viewpoint, there is an effect that the white screen is more white and clear, which is superior to the normally black system which is another system.
[Brief description of the drawings]
1A is an exploded cross-sectional view showing a partially simplified configuration of a liquid crystal display device according to an embodiment of the present invention, and FIG. 1B is a pixel substrate in the liquid crystal display device of FIG. It is explanatory drawing which shows this structure.
FIG. 2 is a perspective view showing a main refractive index in a retardation plate of the liquid crystal display device.
FIG. 3 is an explanatory diagram showing an alignment relationship between a rubbing direction and a normal visual direction of an alignment film in the liquid crystal display device.
FIG. 4 is an exploded perspective view showing an optical arrangement of polarizing plates and retardation plates in the liquid crystal display device.
FIG. 5 is a graph showing light transmittance of an interlayer insulating film used in the liquid crystal display device.
FIG. 6 is a cross-sectional view of a pixel substrate in the liquid crystal display device.
7A is a graph showing a spectrum of light emitted from a light source used in the liquid crystal display device, and FIG. 7B is a transmission characteristic of two types of color filters used in the liquid crystal display device. It is a graph which shows.
FIG. 8 is a circuit diagram showing a configuration of a conventional transmissive liquid crystal display device including an active matrix substrate.
FIG. 9 is a cross-sectional view of a TFT portion of an active matrix substrate in a conventional liquid crystal display device.
FIG. 10 is a schematic diagram showing twisted alignment of liquid crystal molecules in a TN liquid crystal display element.
[Explanation of symbols]
1 Liquid crystal display device
2a retardation plate
2b retardation plate
3 Polarizing plate
4 Polarizing plate
5 Liquid crystal display elements
7 Glass substrate (pixel substrate)
9 Transparent electrode layer (pixel electrode)
11 Alignment film
12 Liquid crystal layer
31 TFT
36 Drain electrode
37 signal lines
38 connection electrode
39 Contact hole
40 Interlayer insulation film

Claims (8)

A liquid crystal display element having at least a counter substrate, a pixel substrate, and a liquid crystal layer;
A pair of polarizers disposed on both sides of the liquid crystal display element;
Comprising at least one retardation plate interposed between the liquid crystal display element and the polarizer,
The counter substrate includes a common electrode and a plurality of color filters,
The pixel substrate includes a scanning line and a signal line, a switching element provided in the vicinity of the intersection of the scanning line and the signal line, an interlayer insulating film provided above the scanning line, the signal line, and the switching element, A pixel electrode connected to the switching element and provided on the interlayer insulating film;
The interlayer insulating film is made of an organic film made of a positive photosensitive acrylic resin having a light transmittance of a peak wavelength in the vicinity of the color wavelength band of the color filter of approximately 95% or more,
The liquid crystal layer is interposed between the counter substrate and the pixel substrate, and a difference Δn between a refractive index anisotropy Δn (450) for light having a wavelength of 450 nm and a refractive index anisotropy Δn (650) for light having a wavelength of 650 nm. (450) −Δn (650) is set in the range of 0 to 0.01,
In the retardation plate, the three main refractive indexes na, nb, and nc of the refractive index ellipsoid in at least the representative layer have a relationship of na = nc> nb, and one of the main refractive indexes na and nc is the retardation plate. The main refractive index nb is clockwise or counterclockwise from the state parallel to the normal direction of the surface of the retardation plate to the inclined state with the direction of the main refractive index parallel to the surface of A liquid crystal display device characterized in that the refractive index ellipsoid is inclined by rotating it around. A drain electrode connected to the pixel electrode;
A connection electrode connecting the pixel electrode and the drain electrode; and the interlayer insulating film is provided on the switching element, the scanning line, the signal line, and the connection electrode.
On the interlayer insulating film, the pixel electrode is provided so as to partially overlap at least one of the scanning line and the signal line,
The liquid crystal display device according to claim 1, wherein the connection electrode and the pixel electrode are connected through a contact hole that penetrates the interlayer insulating film.   3. The liquid crystal display device according to claim 2, further comprising an additional capacitor for holding a voltage applied to the liquid crystal layer.   The difference Δn (435) −Δn (610) between the refractive index anisotropy Δn (435) for light with a wavelength of 435 nm and the refractive index anisotropy Δn (610) for light with a wavelength of 610 nm is set within a range of 0.00875 or less. The liquid crystal display device according to claim 1, wherein the liquid crystal is used.   5. The liquid crystal display according to claim 1, wherein the color filter has a transmittance of light of at least one peak wavelength in light incident through the pixel substrate of 85% or more. 6. apparatus.   The retardation plate includes a layer made of a compound having a discotic structural unit, and an inclination angle formed by the disc surface of the discotic structural unit and the surface of the retardation plate is a depth direction of the retardation plate The liquid crystal display device according to claim 1, wherein the liquid crystal display device changes continuously or discontinuously.   The liquid crystal display device according to claim 6, wherein an average value of the tilt angles is 15 ° to 75 °.   8. The liquid crystal display device according to claim 1, wherein the liquid crystal of the liquid crystal layer is aligned in a state twisted by 90 °, and the display system is a normally white system. 2. A liquid crystal display device according to item 1.

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