KR101689319B1 - Liquid crystal display device - Google Patents

Abstract

A liquid crystal display device includes a red pixel having a first area, a green pixel having a second area, and a third pixel having a second area, wherein the red, green, and blue pixel areas have different pixel areas, Wherein the second area of the green pixel is larger than the first area of the red pixel and the third area of the blue pixel is smaller than the first area of the red pixel, Area.

Liquid crystal display, luminance, color coordinates, asymmetry, area ratio

Description

[0001] Liquid crystal display device [0002]

The present invention relates to a liquid crystal display device which improves the contrast ratio characteristics by making the pixel areas of red, green and blue different from each other.

In general, a liquid crystal display device is driven by using optical anisotropy and polarization properties of a liquid crystal. Since liquid crystal has a long structure, it has directionality in the arrangement of molecules, and the direction of the molecular arrangement can be controlled by artificially applying an electric field to the liquid crystal. Therefore, when the molecular alignment direction of the liquid crystal is arbitrarily adjusted, the molecular arrangement of the liquid crystal is changed, and light is refracted in the molecular alignment direction of the liquid crystal by optical anisotropy, so that image information can be expressed.

The active matrix liquid crystal display (AM-LCD), in which the thin film transistors and the pixel electrodes connected to the thin film transistors are arranged in a matrix manner, I have been receiving.

Modern liquid crystal display devices employ a normal black mode in order to realize a wide viewing angle mode and an excellent contrast ratio characteristic and realize a desired gradation characteristic by using birefringence of a liquid crystal. In order to realize a high luminance characteristic in such a liquid crystal display device, a liquid crystal layer phase difference? N * d of an appropriate level or higher is required. The phase difference of the liquid crystal layer is determined by the refractive index (n) of the liquid crystal and the cell gap. Generally, a retardation of 300 nm or more is used in a liquid crystal display device of a transverse electric field mode and a vertical electric field mode. This is because, when a retardation of 300 nm or less is used, a problem of luminance drop occurs in a full white gradation.

In the normal black mode, since the electric field is not applied to the liquid crystal, the direction of the liquid crystal depends purely on the free energy received by the liquid crystal in the pixel. Therefore, a deviation of the free energy received by the liquid crystal occurs, and a deviation of the free energy results in non-uniformity of the liquid crystal director. Specifically, the non-uniformity of the liquid crystal director is caused by the non-uniformity of the rubbing direction in the transverse electric field mode, and by the unevenness of the pretilt angle of the liquid crystal in the vertical electric field mode. Such non-uniformity of the liquid crystal director causes light leakage in the black mode and is displayed with undesired brightness, resulting in degradation of the black characteristic. Particularly, in the transverse electric field mode, the unevenness of the liquid crystal directors is larger than in the vertical electric field mode, resulting in lowering of the control ratio characteristics.

In order to improve the black characteristic of the normal black mode as described above, it is possible to improve the vertical transmittance of the polarizing plate, the scattering property of the liquid crystal, and the degree of convergence of the light source. Among these techniques, it is well known that the elasticity and the refractive index of the liquid crystal can be improved by improving the scattering property of the liquid crystal. Equation (1) expresses a calculation expression for the scattering index (Slc) of the liquid crystal.

Equation 1

K is the elastic constant that averages the spray (K11), twist (K22), and bend (K33), and Δn is the refractive index anisotropy of the liquid crystal. And, n _e and n _o mean an extraordinary ray refraction index and an image ray refraction index of a liquid crystal layer, respectively, and d means a cell gap. The smaller the value of the scattering index (Slc), the smaller the scattering and the better the control ratio.

Referring to Equation (1), it is possible to improve the contrast ratio by improving the scattering characteristic of the liquid crystal through an increase in the elastic modulus of the liquid crystal, a decrease in the absolute refractive index of the liquid crystal, and a decrease in the cell gap.

In order to improve the black characteristic of the normal black mode, a method of increasing the modulus of elasticity of the liquid crystal is widely used in the increase of the elastic modulus of the liquid crystal, the absolute refractive index of the liquid crystal, and the decrease of the cell gap. However, when the elastic modulus is increased, there arises a problem that it is difficult to improve the scattering characteristics over a certain level due to the limitation of the liquid crystal as well as the driving voltage.

Alternatively, a method of reducing the absolute refractive index and the cell gap can be considered. However, this method is not applied to commercial liquid crystal display devices because it involves a decrease in luminance characteristics due to a lack of a refractive index for realizing white luminance.

In order to solve the above problems, the present invention provides a liquid crystal display device capable of reducing a phase difference of a liquid crystal layer and simultaneously designing red, green, and blue pixel areas different from each other to improve color temperature and brightness without deteriorating a color- And a display device.

According to an aspect of the present invention, there is provided a liquid crystal display device including a red pixel having a first area, a green pixel having a second area, and a blue pixel having a third area, The second area of the pixel is larger than the first area of the red pixel and the third area of the blue pixel is smaller than the first area of the red pixel.

The ratio of the second area of the green pixel to the first area of the red pixel is 1.2 to 1.5, and the ratio of the second area of the red pixel to the second area of the red pixel Is in the range of 0.8 to 0.5.

In the liquid crystal display device as described above, the red pixel, the green pixel, and the blue pixel are arranged horizontally or vertically.

In the above-described liquid crystal display device, a plurality of red pixels, green pixels, and blue pixels are sequentially arranged in this order.

In the above-described liquid crystal display device, the green pixel and the blue pixel are alternately arranged in the vertical direction.

In the above-described liquid crystal display device, it is preferable that a first difference between the second area of the green pixel and the first area of the red pixel and a first difference between the third area of the blue pixel and the first area of the red pixel And the second difference is the same.

The liquid crystal display device according to the present invention can reduce the phase difference of the liquid crystal layer and simultaneously design the RGB pixel areas to be different from each other so that the color temperature and the luminance can be improved without decreasing the color reproduction rate. In particular, it is possible to optimize the white luminance, the variation range of the color coordinates, and the contrast ratio by making the green pixel larger than the red pixel and making the blue pixel smaller than the red pixel based on the red pixel.

By arranging the RBG pixel regions horizontally or vertically successively, the present invention can be easily applied to a liquid crystal display device of a transverse electric field mode. When the RGB pixel regions are arranged vertically and consecutively, by arranging the green pixels and the blue pixels alternately, the RGB pixel regions can be arranged in a balanced manner as a whole.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

1 is a schematic view of a liquid crystal display device according to an embodiment of the present invention.

As an example of the present invention, Fig. 1 shows a liquid crystal display device 110 in a transverse electric field mode. The present invention can be applied to all liquid crystal display devices including a vertical mode as well as a transverse electric field mode. 1, the liquid crystal display device 110 of the present invention includes upper and lower substrates 112 and 114 and a liquid crystal layer 116 between the upper and lower substrates 112 and 114, .

Although not shown in the drawing, a plurality of gate lines and a plurality of data lines are orthogonal to each other to form a plurality of pixel regions. In a plurality of pixel regions, a red pixel 130a, a green pixel 130b, and a blue pixel 130c are sequentially arranged. Particularly, according to the present invention, the green pixel 130b is designed to have a larger area than the red pixel 130a, and the blue pixel 130c is designed to have an area smaller than that of the red pixel 130a do.

A pixel electrode 162 connected to the thin film transistor 160 and the thin film transistor 160 and a common electrode 164 for generating a horizontal electric field together with the pixel electrode 162 are formed on the lower substrate 114. The thin film transistor 160 includes a gate electrode 166 formed on the lower substrate 112, a gate insulating layer 168 stacked on the lower substrate 112 on which the gate electrode 166 is formed, a gate electrode 166, And an active layer 170 located on the gate insulating layer 168 corresponding to the active layer 170 and source and drain electrodes 172a and 172b connected to both ends of the active layer 170. [ The pixel electrode 162 is connected to the drain electrode 172b. The thin film transistor 160, the pixel electrode 162, and the common electrode 164 are formed in each of the plurality of pixel regions.

The common electrode 164 is formed simultaneously with the gate electrode 166. A gate insulating layer 168 is formed between the common electrode 164 and the pixel electrode 162. Although not shown in the drawings, the common electrode 164 and the pixel electrode 162 may be formed on the same plane. The common electrode 164 and the pixel electrode 162 are spaced apart from each other by a predetermined distance and generate a horizontal electric field for driving the liquid crystal layer 116 by application of a potential. A protective layer 174 is formed on the gate insulating layer 168 including the thin film transistor 160 and the pixel electrode 162. [

A black matrix 176 is formed on the upper substrate 114 in contact with the liquid crystal layer 116 at a position corresponding to the thin film transistor 160. The black matrix 176 has openings that expose corresponding portions of the pixel regions. A color filter layer 178 is formed in the opening of the black matrix 176. The color filter layer 178 includes red, green, and blue color filters 178a, 178b, and 178c.

The black matrix 176 functions to block light in a portion excluding the pixel region where the pixel electrode 162 is located. An overcoat layer 180 is formed on the color filter layer 178 and the black matrix 176. The overcoat layer 180 protects the color filter layer 178 and prevents the material of the color filter layer 178 from being eluted.

Although not shown in FIG. 1, the liquid crystal display device 110 includes a backlight unit as a light modulation device for supplying light at a lower portion of the lower substrate 114.

1, in order to improve the black characteristic in the normal black mode, the retardation? N (n) of the liquid crystal layer, which is a value obtained by multiplying the refractive index? N of the liquid crystal layer 116 by the cell gap d between the upper and lower substrates 112 and 114 * d) is designed to have a thickness of 250 to 300 nm.

Reducing the retardation of the liquid crystal layer 116 accompanies an increase in the color temperature due to the fluctuation of the wavelength dispersion of the liquid crystal layer as well as the decrease in the luminance characteristic. Here, the degradation of the luminance characteristic can be improved by reducing the color temperature to a certain level. On the other hand, there is a method of changing the color reproduction rate of the color filter 178 in order to reduce the color temperature. However, such a change in the color reproduction rate leads to a change in the color coordinates, and therefore, In the present invention, a method of adjusting the color temperature by designing different areas of the red, green, and blue pixels to prevent the problem of the luminance lowering is proposed.

Table 1 is a table in which the area ratio of the RGB pixel region is fixed at 1: 1: 1 and the luminance and color coordinate characteristics according to the phase difference change of the liquid crystal layer are expressed by numerical values.

Table 1

No Δn The interval (d) Δn * d RGB area ratio White luminance Wx Wy CR One 0.1002 3.1 0.31062 1: 1: 1 100% ref. ref. 100% 2 0.095 3.1 0.2945 1: 1: 1 90% -0.08 -0.1 110% 3 0.093 3.1 0.2883 1: 1: 1 86% -0.16 -0.2 126% 4 0.091 3.1 0.2821 1: 1: 1 82% -0.24 -0.3 134% 5 0.089 3.1 0.2759 1: 1: 1 79% -0.32 -0.4 140% 6 0.087 3.1 0.2697 1: 1: 1 75% 0.4 -0.5 145%

When the area ratio of the RGB pixel region is fixed at 1: 1: 1 and the phase difference (n * d) of the liquid crystal layer is changed as shown in Table 1, the contrast ratio (CR) But the white luminance decreases proportionally. Then, it can be seen that the color coordinate is varied by a very large width. Therefore, when the phase difference (n * d) of the liquid crystal layer is changed while the area ratio of the RGB pixel region is fixed at 1: 1: 1, it can be understood that the desired color gamut is not obtained.

Table 2 shows numerical values of the luminance and color coordinate characteristics when the area ratio of the RGB pixel region and the phase difference of the liquid crystal layer are changed.

Table 2

No Δn The interval (d) Δn * d RGB area ratio White luminance Wx Wy CR One 0.1002 3.1 0.31062 1: 1: 1 100% ref. ref. 100% 2 0.095 3.1 0.2945 1: 1.1: 0.9 99% -0.01 +0.02 114% 3 0.093 3.1 0.2883 1: 1.2: 0.8 101% +0.01 +0.01 130% 4 0.091 3.1 0.2821 1: 1.3: 0.7 102% +0.04 +0.03 137% 5 0.089 3.1 0.2759 1: 1.4: 0.8 101% +0.03 +0.02 142% 6 0.087 3.1 0.2697 1: 1.5: 0.5 102% +0.05 +0.03 149%

As shown in Table 2, when the area ratio of the RGB pixel region and the phase difference (n * d) of the liquid crystal layer are changed, the contrast ratio CR linearly increases in the direction in which the phase difference of the liquid crystal layer decreases, Is maintained at a substantially constant level.

It can be seen that the color coordinates are very small compared to Table 1. At this time, the area ratio of the RGB pixel region sequentially increases the green pixel area and sequentially reduces the blue pixel area in a state where the red pixel area is fixed. In Table 2, the first difference between the red pixel area and the green pixel area is the same as the second difference between the red pixel area and the blue pixel area.

The ratio of the area of the green pixel to the area of the red pixel is 1.2 to 1.5 and the ratio of the area of the blue pixel to the area of the red pixel is 0.8 to 0.5 and the retardation of the liquid crystal layer is approximately 250 to 300 nm The optimum white luminance, the contrast ratio, and the minimum fluctuation range of the color coordinates can be obtained. The difference in position of the liquid crystal layer is preferably 0.2697 to 0.2883 as shown in Table 2.

In the liquid crystal display device of the vertical field mode, the pixel electrodes and the common electrode are formed on the lower and upper substrates, respectively, so that the areas of the RGB pixel regions can be easily designed differently. However, in the case of the liquid crystal display device of the transverse electric field mode shown in Fig. 1, since the pixel electrode and the common electrode are both formed on the lower substrate, the area of the RGB pixel region It is difficult to design differently. In order to solve such a problem, the present invention proposes a method of asymmetrically designing the horizontal direction or the vertical direction of the RGB pixel region.

2 is a layout diagram of RGB pixels of horizontal asymmetry in the liquid crystal display of the present invention.

Referring to FIG. 2, in the liquid crystal display of the present invention, each of the red pixel 130a, the green pixel 130b, and the blue pixel 130c has a first area, a second area, and a third area. The first area of the red pixel 130a is set to "1", the second area of the green pixel 130a is made larger than "1", and the third area of the blue pixel 130c is made smaller than "1" . In Fig. 2, the red pixel 130a, the green pixel 130b, and the blue pixel 130c are horizontally arranged in succession.

2, when the red pixel 130a, the green pixel 130b and the blue pixel 130c are arranged in a horizontal asymmetry, the optimum area ratios of the red pixels 130a, The area ratio of the second area of the green pixel 130b compared with the first area is 1.2 to 1.5 and the ratio of the area of the third area of the blue pixel 130c to the first area of the red pixel 130a is 0.8 to The optimum white luminance, the contrast ratio, and the minimum fluctuation range of the color coordinates can be obtained when the retardation (n * d) of the liquid crystal layer is approximately 250 to 300 nm when the retardation value is 0.5.

3 is a vertical-asymmetric RGB pixel layout in the liquid crystal display of the present invention.

Referring to FIG. 3, in the liquid crystal display of the present invention, each of the red pixel 130a, the green pixel 130b, and the blue pixel 130c has a first area, a second area, and a third area. The first area of the red pixel 130a is set to "1", the second area of the green pixel 130a is made larger than "1", and the third area of the blue pixel 130c is made smaller than "1".

The first area difference between the green pixel 130b and the red pixel 130a is the same as the second area difference between the blue pixel 130c and the red pixel 130a. Accordingly, the green pixel 130b and the blue pixel 130c can be arranged alternately in the vertical direction. The red pixel 130a, the green pixel 130b and the blue pixel 130c in the order of the red pixel 130a, the green pixel 130c, (130b). The red pixel 130a, the green pixel 130b, and the blue pixel 130c are arranged in this order in the same manner as the first column.

The red pixel 130a, the green pixel 130b and the blue pixel 130c can be arranged in a balanced manner by arranging the green pixel 130b and the blue pixel 130c alternately in the vertical direction. 3, when the red pixel 130a, the green pixel 130b, and the blue pixel 130c are vertically asymmetrically arranged, the optimal area ratio of each of the red pixels 130a, The area ratio of the second area of the green pixel 130b compared with the first area is 1.2 to 1.5 and the area ratio of the third area of the blue pixel 130c compared to the first area of the red pixel 130a is 0.8 The optimum white luminance, contrast ratio, and minimum fluctuation range of the color coordinates can be obtained when the retardation (n * d) of the liquid crystal layer is approximately 250 to 300 nm.

As shown in FIGS. 2 and 3, when the phase difference of the lower liquid crystal layer is used by the asymmetric arrangement of the RGB pixel areas in the horizontal direction or the vertical direction, the rise of the color temperature and the luminance can be effectively improved.

The present invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit of the present invention.

1 is a schematic view of a liquid crystal display device according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating a horizontal asymmetric RGB pixel layout of a liquid crystal display of the present invention

FIG. 3 is a graph showing the vertical asymmetric RGB pixel layout of the liquid crystal display of the present invention

Claims (7)

A liquid crystal display comprising a liquid crystal layer between an upper and a lower substrate on which a red pixel having a first area, a green pixel having a second area and a blue pixel having a third area are arranged, and a liquid crystal layer between the upper and lower substrates, Wherein the liquid crystal layer has a retardation of 300 nm or less, Wherein the second area of the green pixel is larger than the first area of the red pixel and the third area of the blue pixel is smaller than the first area of the red pixel. The method according to claim 1, Wherein a ratio of the second area of the green pixel to the first area of the red pixel is 1.2 to 1.5 and a ratio of the third area of the blue pixel to the first area of the red pixel is 0.8 to & 0.5. ≪ / RTI > The method according to claim 1, Wherein the red pixel, the green pixel, and the blue pixel are arranged in a horizontal direction or a vertical direction. The method of claim 3, Wherein the red, green, and blue pixels are sequentially arranged in the order of the red pixel, the green pixel, and the blue pixel. The method of claim 3, And the green pixel and the blue pixel are alternately arranged in the vertical direction. The method according to claim 1, The first difference between the second area of the green pixel and the first area of the red pixel and the second difference between the third area of the blue pixel and the first area of the red pixel are the same. Liquid crystal display device. A liquid crystal display device in which a red pixel having a first area, a green pixel having a second area, and a blue pixel having a third area are arranged, Wherein the second area of the green pixel is larger than the first area of the red pixel and the third area of the blue pixel is smaller than the first area of the red pixel, The red pixel, the green pixel, and the blue pixel in the horizontal direction or in the order of the red pixel, the blue pixel, and the green pixel, And the green pixel and the blue pixel are alternately arranged in a vertical direction.

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