JP2015219249A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of obtaining a desired chromaticity in the case that a Red, Green and Blue (RGB) pixel is displayed by adopting a Fringe Field Switching (FFS) mode.SOLUTION: A liquid crystal display device controls a liquid crystal with a pixel structure in which a red pixel, a green pixel, and a blue pixel are represented as base units. Voltage-transmittance characteristics of the liquid crystal corresponding to the blue pixel are different from voltage-transmittance characteristics of the liquid crystal corresponding to each of the red pixel and the green pixel.

Description

  The present invention relates to a liquid crystal display device driven by a horizontal electric field method.

  Generally, in a liquid crystal display device, a thin film transistor array substrate (hereinafter referred to as a TFT substrate) in which a plurality of thin film transistors (hereinafter referred to as TFTs) are disposed on a transparent substrate, and a color filter are disposed on the transparent substrate. A liquid crystal panel in which liquid crystal is sealed between a color filter substrate (hereinafter referred to as a CF substrate) is used.

  On the TFT substrate, TFTs (switching elements) and liquid crystal drive electrodes connected to the TFTs are arranged in a matrix array. Further, the CF substrate is arranged between a pixel (hereinafter referred to as an RGB pixel) including red (Red, R), green (Green, G), and blue (Blue, B) colored layers and a colored layer of each color. The provided light shielding layer (black matrix) is disposed so as to correspond to each TFT.

  Conventionally, a twisted nematic mode (hereinafter referred to as TN mode) has been adopted as a driving method for a typical liquid crystal display device. In the TN mode, the direction of the electric field applied to the liquid crystal sealed between the TFT substrate and the CF substrate is set to a direction substantially perpendicular to the substrate, and the molecules of the liquid crystal layer aligned in the horizontal direction (hereinafter, referred to as the TN mode). The liquid crystal molecules are operated in the vertical direction by an electric field. However, the TN mode has a predetermined angle with respect to the substrate when the liquid crystal molecules are aligned in the vertical direction by an electric field, so that the brightness varies depending on the direction in which the display screen is viewed and the viewing angle cannot be widened. There is.

  As a countermeasure against this problem, In-Plane Switching, which controls the light transmittance by generating a horizontal electric field with a comb electrode formed on one substrate and rotating liquid crystal molecules in the plane, There is a liquid crystal display device that is driven in a mode (hereinafter referred to as a horizontal electric field mode). In the liquid crystal display device driven in the transverse electric field mode, the major axis of the liquid crystal molecules is substantially parallel to the substrate surface, and the liquid crystal molecules do not rise in the direction perpendicular to the substrate. Therefore, the change in brightness when the viewing direction is changed is small and there is almost no viewing angle dependency. As described above, it is known that the horizontal electric field mode is employed in a liquid crystal display device for a monitor that has a much wider viewing angle than the TN mode and has excellent display quality.

  In the liquid crystal display device driven in the transverse electric field mode, no transverse electric field is generated on the comb-teeth electrode, so that the liquid crystal molecules on the comb-teeth electrode are always in a non-transmissive state without responding to the applied voltage. As described above, the liquid crystal display device driven in the horizontal electric field mode has a problem that the transmittance is low.

  In order to solve the above problems in the transverse electric field mode, conventionally, light transmittance is generated by generating a fringe electric field between two electrodes having a slit formed on one substrate and rotating liquid crystal molecules in the plane. Has been disclosed (see Patent Document 1). Such a drive mode is called fringe field switching (hereinafter referred to as FFS mode). Note that a liquid crystal display device driven in the FFS mode can be obtained even if the electrode disposed on the lower layer side of the two electrodes is an electrode having no slit.

Japanese Patent No. 3498163

  In the FFS mode liquid crystal display device as in Patent Document 1, the change in chromaticity is large when a voltage is applied to the liquid crystal and the transmittance is changed. There is.

  The present invention has been made to solve such a problem, and provides a liquid crystal display device capable of obtaining a desired chromaticity when an RGB pixel is displayed by employing the FFS mode. With the goal.

  In order to solve the above-described problems, a liquid crystal display device according to the present invention is a liquid crystal display device that controls liquid crystal with a pixel structure having red pixels, green pixels, and blue pixels as basic units, and corresponds to blue pixels. The voltage-transmittance characteristic of the liquid crystal is different from the voltage-transmittance characteristic of the liquid crystal corresponding to each of the red pixel and the green pixel.

  According to the present invention, a liquid crystal display device that controls liquid crystal with a pixel structure having red, green, and blue pixels as a basic unit, the voltage-transmittance characteristics of the liquid crystal corresponding to the blue pixels are Since the voltage-transmittance characteristics of the liquid crystal corresponding to each of the green pixels are different, it is possible to obtain desired chromaticity when the RGB pixels are displayed using the FFS mode.

It is a figure which shows an example of a structure of each pixel in the liquid crystal display device by embodiment of this invention. It is a figure which shows an example of a structure of the light shielding layer by embodiment of this invention. It is a figure which shows an example of the voltage-transmittance characteristic of a liquid crystal when the angle of the slit of the slit electrode by embodiment of this invention is changed. It is a figure which shows an example of the chromaticity change in the white display by embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment>
FIG. 1 is a diagram showing an example of the configuration of each pixel in a liquid crystal display device according to an embodiment of the present invention. Note that FIG. 1 shows a liquid crystal display device that controls liquid crystal with a pixel structure in which an RGB pixel is one picture element (basic unit, one-dot chain line in the figure). The liquid crystal display device is driven in an FFS mode in which the alignment of the liquid crystal is changed by a fringe electric field.

  As shown in FIG. 1, the blue slit electrode 1, the red slit electrode 3, and the green slit electrode 5 are provided on the TFT substrate on which the TFT 10 connected to the source wiring 8 and the gate wiring 9 is disposed.

The blue slit electrode 1 is provided corresponding to the blue pixel, and has a plurality of slits 2 that generate a fringe electric field when a voltage is applied. Each slit 2, the longitudinal direction of the slits 2, a liquid crystal angle between orientation axis 7 forms a (not shown) is formed so that theta _B.

The red slit electrode 3 is provided corresponding to the red pixel, and has a plurality of slits 4 that generate a fringe electric field when a voltage is applied. Each slit 4, the longitudinal direction of the slits 4, the angle and the orientation axis 7 forms a liquid crystal are formed so that theta _R.

The green slit electrode 5 is provided corresponding to the green pixel, and has a plurality of slits 6 that generate a fringe electric field when a voltage is applied. Each slit 6 has longitudinal direction, angle and orientation axis 7 forms a liquid crystal of each of the slits 6 are formed such that theta _G.

In the above configuration, the angle θ _{B of the} slit 2 formed by the blue slit electrode 1, the angle θ _{R of the} slit 4 formed by the red slit electrode 3, and the slit 6 formed by the green slit electrode 5 It is different from the angle θ _G.

  There are roughly two types of pixel configurations in the liquid crystal display device driven in the FFS mode. That is, there are a type in which the pixel electrode connected to the TFT is disposed in the upper layer, a common electrode to which a common potential is supplied is disposed in the lower layer, and a type in which the common electrode is disposed in the upper layer and the pixel electrode is disposed in the lower layer. . In this embodiment, in any of the above types, the electrode disposed in the upper layer may have the same configuration as the slit electrode as shown in FIG. 1, and the electrode disposed in the lower layer may be planar. .

  FIG. 2 is a diagram showing an example of the configuration of the light shielding layer 11 according to the embodiment of the present invention.

  A light shielding layer 11 is disposed on the CF substrate on the display surface side with respect to the liquid crystal.

  As shown in FIG. 2, the light shielding layer 11 is formed corresponding to the blue opening 12 formed corresponding to the blue pixel, the red opening 13 formed corresponding to the red pixel, and the green pixel. It has a green opening 14. A plurality of blue openings 12, red openings 13, and green openings 14 are arranged in the vertical direction of the light shielding layer 11 for each picture element (one-dot chain line in the figure).

  The opening ratio (area) of the blue opening 12 is larger than the opening ratio of the red opening 13 and the green opening 14. These aperture ratios may be adjusted so that the shape or area of each pixel electrode provided on the TFT substrate side differs for each color. However, in this embodiment, the shape or area of each pixel electrode is not changed. Further, the area of the opening corresponding to each color formed in the light shielding layer 11 is adjusted to be different.

  In the vicinity of the red opening 13 and the green opening 14, by adjusting the aperture ratio of the red opening 13 and the green opening 14, a light shielding portion (light shielding region) in the light shielding layer 11 is widely formed. A columnar spacer 15 is arranged.

In a liquid crystal display device driven in the FFS mode, in order to prevent a color shift within the viewing angle range, the slit angle (angle θ) in each slit electrode (blue slit electrode 1, red slit electrode 3, green slit electrode 5). _In many cases, _{B 1} , angle θ _R , and angle θ _G ) are alternately arranged so as to be line symmetric with respect to the row direction or the column direction of each pixel as an axis of symmetry. In the present embodiment, as shown in FIG. 2, the angle of each slit is varied for each row of each pixel so that the line is symmetrical with respect to the row direction (the horizontal direction on the paper). Also in this case, the slit electrodes arranged on the upper and lower sides with respect to the symmetry axis may be configured similarly to the slit electrodes as shown in FIG.

  Further, as another method for preventing color shift within the viewing angle range, a boundary line divided in the vertical direction at the center of each pixel is used as a symmetry axis, and the shape is symmetrical with respect to the symmetry axis. Although the case where a slit electrode is arrange | positioned is considered, the slit electrode arrange | positioned at each of the upper and lower sides with respect to an axis of symmetry should just be set as the structure similar to a slit electrode as shown in FIG.

FIG. 3 is a diagram illustrating an example of voltage-transmittance characteristics of the liquid crystal when the slit angle of the slit electrode is changed. In FIG. 3, the horizontal axis indicates the voltage (V) applied between the electrodes disposed on the upper layer and the lower layer (the upper layer is a slit electrode as shown in FIG. 1), and the horizontal axis indicates the relative transmittance of the liquid crystal. Yes. FIG. 3 shows voltage-transmittance characteristics when the angles (angle θ _B , angle θ _R , angle θ _G ) are 5 °, 10 °, and 15 °.

  In the FFS mode, the voltage-transmittance characteristic (VT characteristic) of the liquid crystal changes depending on the angle of the slit in the slit electrode. As shown in FIG. 2, it can be seen that the smaller the slit angle, the more the voltage-transmittance characteristic shifts to the low voltage side.

  FIG. 4 is a diagram illustrating an example of chromaticity change in white display.

  As shown in FIG. 4, when a voltage is applied between the electrodes arranged in the upper layer and the lower layer (the upper layer is a slit electrode as shown in FIG. 1), the chromaticity is shifted to the yellow side as the relative transmittance increases. Then, it shifts slightly to the blue side (shifts along the arrow shown in FIG. 4). Thus, it can be seen that chromaticity can be controlled under a certain voltage by changing the voltage-transmittance characteristics because the chromaticity changes according to the applied voltage.

Specifically, the voltage-transmittance characteristics can be changed by changing the angle of the slit in the slit electrode as described above. Accordingly, the angle θ _B of the slit 2 in the blue slit electrode 1 is made larger than the angle θ _R of the slit 4 in the red slit electrode 3 and the angle θ _G of the slit 6 in the green slit electrode 5, thereby reducing the blue pixel. The transmittance from the gradation to the middle gradation can be increased. That is, yellow coloring near the halftone can be prevented.

In addition, as shown in FIG. 2, it can be seen that the transmittance on the high voltage side decreases as the angle of the slit in the slit electrode increases. That is, by making the angle θ _B of the slit 2 in the blue slit electrode 1 larger than the angle θ _R of the slit 4 in the red slit electrode 3 and the angle θ _G of the slit 6 in the green slit electrode 5, On the adjustment side, the transmittance decreases.

With respect to such a problem, in the present embodiment, the transmittance of the blue pixel is improved by making the aperture ratio of the blue aperture 12 larger than the aperture ratio of the red aperture 13 and the green aperture 14. ing. Thus, the angle θ _B of the slit 2 in the blue slit electrode 1 is changed to that in the red slit electrode 3 by making the aperture ratio of the blue opening 12 larger than the aperture ratio of the red opening 13 and the green opening 14. Increasing the angle θ _{R of the} slit 4 and the angle θ _G of the slit 6 in the green slit electrode 5 compensates for the decrease in the transmittance on the high gradation side of the blue pixel. Therefore, it is possible to prevent yellow coloring near the halftone by adjusting the angle of the slit in the slit electrode, and to prevent yellow coloring on the high gradation side by adjusting the aperture ratio of the opening in the light shielding layer. it can.

  In general, the contrast is lowered near the columnar spacer due to the disorder of the alignment of the liquid crystal. If a light shielding portion having a relatively large area is simply formed in the vicinity of the columnar spacer in order to prevent the decrease in the contrast, the transmission is reduced. Ratio and the opening ratio of the opening in the light-shielding portion are reduced, and the displayed image becomes dark or the power consumption of the liquid crystal display device increases.

  In order to deal with such a problem, in the present embodiment, the columnar spacers 15 are arranged by utilizing light shielding portions that are widely formed in the vicinity of the red openings 13 and the green openings 14. By adopting such a configuration, it is possible to conceal the alignment disorder of the liquid crystal that occurs in the vicinity of the columnar spacer 15, so that the contrast is improved and display unevenness can be reduced. In addition, as compared with the case where a light shielding portion that is formed widely is not used and a separate light shielding portion is provided in the vicinity of the columnar spacer as in the present embodiment, the transmittance and the aperture ratio of the opening portion are improved. The brightness of the image is improved or the power consumption of the liquid crystal display device is reduced.

  From the above, according to the present embodiment, it is possible to obtain a desired chromaticity when the RGB pixel is displayed by adopting the FFS mode.

  In the present invention, the embodiments can be appropriately modified and omitted within the scope of the invention.

  1 blue slit electrode, 2 slit, 3 red slit electrode, 4 slit, 5 green slit electrode, 6 slit, 7 orientation axis, 8 source wiring, 9 gate wiring, 10 TFT, 11 light shielding layer, 12 blue opening, 13 red Opening, 14 Green opening, 15 Columnar spacer.

Claims (5)

A liquid crystal display device that controls liquid crystal with a pixel structure having red pixels, green pixels, and blue pixels as basic units,
The liquid crystal display device, wherein a voltage-transmittance characteristic of the liquid crystal corresponding to the blue pixel is different from a voltage-transmittance characteristic of the liquid crystal corresponding to each of the red pixel and the green pixel. The liquid crystal display device is driven in an FFS (Fringe Field Switching) mode in which the alignment of the liquid crystal is changed by a fringe electric field,
Each of the red pixel, the green pixel, and the blue pixel includes a slit electrode having a plurality of slits that generate the fringe electric field when a voltage is applied,
The different degree of the voltage-transmittance characteristics of the liquid crystal depends on an angle formed by the alignment axis of the liquid crystal and the longitudinal direction of each slit in each of the red pixel, the green pixel, and the blue pixel. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is characterized. A light-shielding layer disposed on the display surface side of the liquid crystal;
The light shielding layer has an opening formed corresponding to each of the red pixel, the green pixel, and the blue pixel,
3. The liquid crystal display device according to claim 1, wherein an area of the opening corresponding to the blue pixel is different from an area of each opening corresponding to the red pixel and the green pixel.   The liquid crystal display device according to claim 3, wherein an area of the opening corresponding to the blue pixel is larger than an area of each opening corresponding to the red pixel and the green pixel. A columnar spacer for holding the liquid crystal;
5. The liquid crystal display device according to claim 4, wherein the columnar spacer is disposed in a light shielding region of the light shielding layer formed between the openings corresponding to the red pixel and the green pixel.

Images