JP4993879B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to the structure of a FFS (Fringe Field Switching) mode liquid crystal display device.

  In recent years, in the field of flat panel display (FPD), a liquid crystal display (LCD), a plasma display (PDP), a field emission display (FED), a vacuum fluorescent display (VFD) and the like have been actively researched. Currently, liquid crystal display devices (hereinafter referred to as “LCD”) are in the spotlight because of mass production technology, ease of driving means and high image quality. An LCD is a device that displays information on a screen using the refractive index anisotropy of liquid crystal.

  LCDs that are driven in various modes such as a TN (twisted nematic) mode, an STN (super twisted nematic) mode, and an IPS (in-plane switching) mode have been developed. Among these, the IPS mode is a mode in which liquid crystal molecules are always switched to be horizontal with respect to the substrate of the liquid crystal panel, and is switched by using a horizontal electric field in the horizontal direction with respect to the substrate. . Therefore, it is known that the liquid crystal molecules do not stand up obliquely and the change in optical characteristics depending on the viewing angle is small, so that a wider viewing angle can be obtained than in the TN mode or STN mode.

  In recent years, an FFS mode, which is a mode in which switching is performed using a horizontal electric field in the horizontal direction with respect to a substrate, has been developed as in the IPS mode. The FFS mode LCD includes a pixel electrode and a common electrode made of transparent electrodes, and forms a fringe field by making the distance between the pixel electrode and the common electrode narrower than the cell gap between the upper and lower substrates of the liquid crystal panel. Since the liquid crystal molecules of the liquid crystal layer are operated by the electric field generated in the fringe field, it is known that the aperture ratio and the transmittance are higher than those of the IPS mode LCD (see, for example, Patent Document 1).

In order to further widen the viewing angle, a dual domain mode has been developed. The dual domain mode is a method of widening the viewing angle by dividing the alignment direction of the liquid crystal molecules of the liquid crystal layer in one unit pixel in the liquid crystal panel into two directions. An application in which this dual domain mode is applied to an LCD driven in the FFS mode has also been developed (see, for example, Patent Document 2). A method in which the alignment direction of liquid crystal molecules applied to a conventional general LCD is unidirectional is called a single domain mode.
JP 2005-107535 A JP 2002-182230 A

  A conventional FFS mode LCD will be described below with reference to FIG. FIG. 8 is a front view showing the structure of a unit pixel in a liquid crystal panel of a single domain mode LCD driven in the FFS mode. The unit pixel 80 includes a data line 81, a gate line 82, a thin film transistor (hereinafter referred to as “TFT”) 83 provided at a portion where the data line 81 and the gate line 82 intersect, and a common electrode (also referred to as “common electrode”). .) 84, the pixel electrode 85, and the common line 92 that supplies a voltage to the common electrode 84. The source electrode of the TFT 83 is connected to the data line 81 and the drain electrode is connected to the pixel electrode 85. The gate electrode of the TFT 83 is connected to the gate line 82.

  Next, the operation of liquid crystal molecules when an electric field is applied to the unit pixel 80 will be described with reference to FIGS. 9A and 9B. 9A and 9B are enlarged views of a partial region 87 of the unit pixel 80 of FIG. 8, where FIG. 9A shows the alignment state of the liquid crystal molecules 88 when no electric field is applied, and FIG. 9B shows the application of voltage. This shows the alignment state of the liquid crystal molecules 88 at the time.

As shown in FIG. 9A, all liquid crystal molecules 88 are aligned in the rubbing direction 89 when no electric field is applied. At this time, the liquid crystal molecules 88 have a rubbing angle of an angle θ ₉ (for example, 15 degrees) with respect to the X direction. When an electric field is applied in this state, the liquid crystal molecules 88 are rotated counterclockwise so that the major axis is parallel to the Y direction. This is because an electric field in the Y direction is generated when an electric field is applied.

  However, the liquid crystal molecules 88 located in the region 86 shown in FIG. 8 and FIG. 9B operate with rotation in a different direction from the liquid crystal molecules 88 located in regions other than the region 86 as shown in FIG. 9B. This is because the pixel electrode 85 in the region 86 is provided in parallel to the Y direction, an electric field in the X direction is generated as shown in FIG. 10, and the liquid crystal molecules 88 located in the region 86 are in the major axis direction. Is rotated in parallel with the direction of the electric field, that is, in parallel with the X direction.

  In this way, the occurrence of disclination is induced by a part of the liquid crystal molecules 88 performing different operations. The occurrence of disclination causes a display trouble such as unevenness or burn-in on the display screen.

  The present invention has been made in view of the above problems, and has a high aperture ratio and high brightness as compared with conventional LCDs, prevents the occurrence of disclination, and / or burns in a display screen. An object of the present invention is to provide an LCD that can make it difficult to occur.

  In order to solve the above-described problems, the present invention provides a pair of transparent insulating substrates disposed at a predetermined interval and facing each other through a liquid crystal layer composed of a plurality of liquid crystal molecules, and a pair of transparent insulating substrates. A plurality of gate lines and data lines, which are formed on one of a pair of transparent insulating substrates and arranged in a matrix form so as to limit each unit pixel, and are arranged on each unit pixel. A common electrode made of a transparent conductor, and a pixel electrode made of a transparent conductor disposed in each unit pixel so as to form a fringe field together with the common electrode, the pixel electrode having a predetermined interval It is composed of a plurality of rod-shaped portions arranged and a connecting portion arranged so as to connect between the rod-shaped portions and intersect the rod-shaped portions, and both of the portions where the connecting portions do not intersect the rod-shaped portion. Is an opening portion, the connection portion and wherein the connecting at a predetermined angle with respect to the rod-shaped portion.

  The present invention also provides a pair of transparent insulating substrates disposed opposite to each other at a predetermined interval through a liquid crystal layer composed of a plurality of liquid crystal molecules, and an alignment film inside each of the pair of transparent insulating substrates. A plurality of gate lines and data lines which are formed on one substrate of a pair of transparent insulating substrates and arranged in a matrix form so as to limit each unit pixel, and each unit pixel is made of a transparent conductor. A pixel electrode made of a transparent conductor disposed in each unit pixel so as to form a fringe field together with the common electrode, and the pixel electrode includes a plurality of V electrodes arranged at a predetermined interval. A V-shaped portion and a connecting portion disposed on a central line connecting the V-shaped portions at the center and connecting the V-shaped portions. The connecting portion includes a central line and a V-shaped portion. Makes an acute angle Forms a central line at a predetermined angle in the same direction as the direction, characterized in that it is a line-symmetrical shape about the center line.

  The present invention has a pixel electrode having a characteristic structure described in detail below to form a unit pixel, thereby providing a high aperture ratio and high brightness as compared with a conventional LCD and generating disclination. It is possible to realize an LCD that can prevent the occurrence of image damage and / or make it difficult for image display burn-in to occur.

  Hereinafter, first to third embodiments to which the present invention is applied will be described with reference to the drawings. 1 to 3 correspond to the description of the first embodiment, FIGS. 4 to 5 correspond to the description of the second embodiment, and FIGS. 6 to 7B correspond to the description of the third embodiment.

<First embodiment>
FIG. 1 is a plan view showing the structure of a unit pixel in the first embodiment. As shown in FIG. 1, the unit pixel 100 in the FFS mode LCD according to the present invention includes the data line 9, the gate line 11, the TFT 7, the common electrode 2, the same as the conventional unit pixel 80 shown in FIG. The pixel electrodes 1 and 3 and the common line 12 are included. The unit pixel 100 of this embodiment is different from the conventional unit pixel 80 in the shape of the pixel electrodes 1 and 3.

  Although the TFT 7 shown in FIG. 1 is disposed on the upper portion of the unit pixel 100, it can be disposed on the lower portion in the present invention.

  The shape of the pixel electrodes 1 and 3 different from that of the conventional unit pixel 80 is provided with a plurality of pixel electrodes 1 parallel to the X direction, but the pixels parallel to the Y direction so as to form the region 86 of FIG. There is no electrode, and instead, a pixel electrode 3 is sewn between the pixel electrodes 1 in order to connect a plurality of pixel electrodes 1. However, the width in the Y direction of each pixel electrode 1 is set to be approximately equal to 4 μm (micrometer), which is the width of the conventional general pixel electrode, and the width of the pixel electrode 3 is adapted to the application and purpose. To be set selectively. For example, when importance is attached to the improvement of the aperture ratio, the width of the pixel electrode 3 is set to be narrower than that of a conventional general pixel electrode.

  As described above, since the pixel electrodes parallel to the Y direction forming the region 86 in FIG. 8 are eliminated, the openings 5 are provided in the regions at both ends between the pixel electrodes 1. By having the openings 5 in the regions at both ends between the pixel electrodes 1, the aperture ratio and the luminance can be improved as compared with the LCD adopting the conventional unit pixel 80 structure.

  Further, details of the feature of the shape of the pixel electrode 3 will be described below with reference to FIGS. 2A, 2B, and 3 which are enlarged views of the region 13 of FIG.

FIG. 2A is an enlarged view of the region 13 of FIG. 1 when no electric field is applied. As shown in FIG. 2A, when no electric field is applied, the liquid crystal molecules 15 constituting the liquid crystal layer sandwiched between the upper and lower substrates of the liquid crystal panel of the LCD are aligned in the rubbing direction 17 by the alignment film. By this rubbing, the rubbing angle of each liquid crystal molecule 15 is θ ₁ (for example, 15 degrees).

In this case, the shape of the pixel electrode 3, in which the rubbing direction 17 is the rotation in the same direction as the direction in which the theta ₁ rotates with respect to the X direction theta ₂ performed on the Y-direction. However, theta ₂ is a satisfying angle θ _2> θ _1. The reason why this condition needs to be satisfied will be described later.

  Next, FIG. 2B is an enlarged view of the region 13 of FIG. 1 when an electric field is applied. As shown in FIG. 2B, each liquid crystal molecule 15 aligned in the rubbing direction 17 in FIG. 2A is aligned in a direction parallel to the Y direction, which is the direction of the applied electric field. However, the liquid crystal molecules 15 located in the region 19 around the pixel electrode 3 are aligned in a different direction from the liquid crystal molecules 15 located in regions other than the region 19. This is because the direction of the electric field in the region 19 is different from the direction of the electric field in the region other than the region 19 and is not parallel to the Y direction.

FIG. 3 is a diagram for explaining the direction of the electric field in the region 19. As shown in FIG. 3, the direction 21 of the electric field around the pixel electrode 3 is a direction perpendicular to the pixel electrode 3. That is, the angle at which the electric field direction 21 is inclined with respect to the X direction is equal to the angle θ _{2 at} which the pixel electrode 3 is inclined with respect to the Y direction. At this time, the liquid crystal molecules 15 located in the region 19 operate so as to rotate in a direction (a direction indicated by an arrow 23 in the drawing) whose major axis is parallel to the direction 21 of the electric field.

  By the way, disclination is a phenomenon in which the alignment of liquid crystal molecules does not return to the state before applying the electric field after applying the electric field, and the rubbing trace becomes a tilt line and noise appears on the display screen. For this reason, in order to prevent disclination, the operation directions of the liquid crystal molecules when an electric field is applied should be matched so that the operations of the liquid crystal molecules do not vary.

In order not to cause variation in the operation of each liquid crystal molecule 15, the direction in which the liquid crystal molecules 15 located in the region 19 rotate is set to the same direction as the direction in which the liquid crystal molecules 15 located in regions other than the region 19 rotate. Good. For example, when the angle θ _{2 at} which the electric field direction 21 is inclined with respect to the X direction is smaller than the angle θ _{1 at} which the rubbing direction 17 is inclined with respect to the X direction, the liquid crystal molecules 15 located in the region 19 are oriented in the clockwise direction. Will work. This is in a direction opposite to the direction in which the liquid crystal molecules 15 located in a region other than the region 19 rotate. Conversely, when θ ₂ is larger than θ ₁ , the liquid crystal molecules 15 located in the region 19 also operate in the counterclockwise direction, so that the operations of the liquid crystal molecules 15 do not vary.

Therefore, in order to prevent the occurrence of disclination, it is necessary to satisfy the condition of θ ₂ > θ ₁ .

  As described above, in this embodiment, an LCD that can improve the aperture ratio and the luminance and prevent the occurrence of disclination by forming the unit pixel 100 having the structure of the pixel electrodes 1 and 3 described above. Can be configured.

<Second embodiment>
In the present embodiment, display is performed while taking advantage of having openings at both ends of the pixel electrode 1 parallel to the X direction, which is one of the features of the shape of the pixel electrodes 1 and 3 in the first embodiment. A unit pixel having a structure effective in preventing screen burn-in will be described. However, portions common to the first embodiment are denoted by the same reference numerals in the drawing and description thereof is omitted.

FIG. 4 is a plan view showing the structure of the unit pixel in this embodiment. As shown in FIG. 4, the unit pixel 200 is different from the unit pixel 100 of FIG. 1 in the pixel electrode 25 provided to connect the pixel electrodes 1. The angle θ _{3 at} which the pixel electrode 25 is inclined with respect to the Y direction needs to satisfy the condition of θ ₃ > θ _{1 for} the same reason as θ ₂ in the first embodiment.

  A feature of the pixel electrode 25 is that it is an electrode for two of the pixel electrodes 3 of the first embodiment. However, the electrode width of the pixel electrode 25 is the same as the conventional general electrode width of 4 μm. As a result, the area of the pixel electrode 25 can be made a little wider without affecting the aperture ratio.

  FIG. 5 is a cross-sectional view of the unit pixel 200 taken along the broken line II ′ of FIG. As shown in FIG. 5, the unit pixel 200 is formed by mounting an insulating film 29 on a common electrode 27 and forming pixel electrodes 1 and 25 on the insulating film 29. Here, the film thickness d of the pixel electrodes 1 and 25 is about 0.04 μm. This is a structure in which the film thickness of the pixel electrode of the unit pixel in the conventional LCD is half that of 0.08 μm.

  Thus, by making the film thickness of the pixel electrodes 1 and 25 thinner, an alignment film made of polyimide (PI) or the like applied thereon can be applied horizontally without unevenness. For this reason, the effect of preventing the burn-in of the display screen caused by the alignment failure due to the unevenness of the alignment film can be obtained. However, when the film thickness of the pixel electrode is reduced, the resistance in the unit pixel is increased, so that there is a problem that voltage distribution and disconnection are likely to occur.

  Therefore, as described above, the unit pixel 200 in this embodiment has a structure like the pixel electrode 25 in which the number of electrodes is increased as compared with the normal case. As the number of pixel electrodes is increased in this way, the resistance can be kept low. Therefore, even when the film thickness is reduced, the resistance does not become higher than usual. In the case of the fringe field, the common electrode 2 and the pixel electrode 25 are transparent electrodes made of ITO (indium-tin oxide) or the like and transmit light, so that the number of electrodes is increased compared to the normal case. Even in the structure like the electrode 25, the rate of decrease in luminance is small.

  Note that the pixel electrode 25 in the present embodiment may be increased to three conventional pixel electrodes. In this case, even if the film thickness of the pixel electrode used at this time is as thin as about 0.026 μm, which is one third of the film thickness of the conventional general pixel electrode, the increase in resistance can be suppressed. .

  As described above, in this embodiment, by forming the unit pixel 200 having the structure of the pixel electrodes 1 and 25 described above, it is possible to prevent the occurrence of disclination and to construct an LCD that hardly causes burn-in. Can do.

<Third embodiment>
In the present embodiment, a dual domain that takes advantage of having openings at both ends of the pixel electrode 1 parallel to the X direction, which is one of the features of the shape of the pixel electrodes 1 and 3 in the first embodiment. A unit pixel in the mode LCD will be described. However, portions common to the first embodiment are denoted by the same reference numerals in the drawing and description thereof is omitted.

  FIG. 6 is a plan view showing the structure of the unit pixel in this embodiment. As shown in FIG. 6, the shape of the pixel electrode 31 is significantly different from the shape of the pixel electrodes 1 and 3 (see FIG. 1) in the first embodiment.

  Since the LCD in the present embodiment is in the dual domain mode, the first characteristic of the shape of the pixel electrode 31 is axisymmetric with respect to a central line L parallel to the Y direction that equally divides the unit pixel 300 into two. That is. With the shape having this characteristic, the liquid crystal molecules in the unit pixel are equally divided into two, and are oriented so as to be different from each other by 180 degrees. This characteristic liquid crystal orientation enables a wide viewing angle.

  Similar to the pixel electrodes 1 and 3 in the unit pixel 100 of the first embodiment, the pixel electrode 31 has openings 33 at both ends in the X direction. Due to the structure having the opening 33, a dual domain mode LCD having a high aperture ratio and high luminance can be realized.

  Further, the pixel electrode 31 has another characteristic shape 35. The characteristic shape 35 refers to a shape having a predetermined inclination with respect to the center line L. The characteristic shape 35 will be described in detail with reference to FIGS. 7A and 7B.

  FIG. 7A is a diagram for explaining the operation of liquid crystal molecules when an electric field is applied when the characteristic shape 35 has a predetermined inclination and is parallel to the Y direction. As shown in FIG. 7A, in the region 37 corresponding to the characteristic shape 35 of the present embodiment, the liquid crystal molecules 15 located in the region 37 rotate in a different direction from the liquid crystal molecules 15 located in regions other than the region 37. As a result, the operation of each liquid crystal molecule 15 varies and induces disclination. In this case, the rubbing is performed in a direction parallel to the X direction. However, in the conventional general rubbing process, a variation in the rubbing angle occurs within a range of ± 1 degree. At this time, since the direction of the electric field in the region 37 is parallel to the X direction, the influence of the variation in the rubbing angle is directly reflected.

FIG. 7B is a diagram for explaining the operation of liquid crystal molecules when an electric field is applied when the characteristic shape 35 is a shape having a predetermined inclination with respect to the center line L. As shown in FIG. 7B, the characteristic shape 35 has an inclination of an angle θ ₄ with respect to the center line L. At this time, the liquid crystal molecules 15 located in the region 37 are located in regions other than the region 37. Rotate in the same direction as the liquid crystal molecules 15 to be rotated.
In order not to directly reflect the influence of such a variation in the rubbing angle of ± 1 degree, the inclination angle θ ₄ of the characteristic shape 35 is set to ± 1 degree or more. Thereby, the direction of the electric field in the region 37 is the direction in which the rubbing direction is rotated in the direction in which the liquid crystal molecules 15 located in the region other than the region 37 rotate. Therefore, since all the liquid crystal molecules 15 in the unit pixel 300 rotate in the same direction, the operation of each liquid crystal molecule 15 does not vary.

  Note that the pixel electrode 31 illustrated in FIG. 6 may have a shape obtained by rotating the shape of the pixel electrode 31 by 180 degrees.

  As described above, in this embodiment, as described above, the unit pixel 300 is formed with the structure in which the pixel electrode 31 has the opening 33 and the characteristic shape 35, so that the aperture ratio is high and the brightness is high. A dual domain mode LCD can be constructed in which the occurrence of linations is suppressed.

It is a top view which shows the structure of the unit pixel in 1st Example. It is an enlarged view of the area | region 13 of FIG. 1 at the time of no electric field application. It is an enlarged view of the area | region 13 of FIG. 1 at the time of an electric field application. It is a figure which shows the direction of the electric field in the area | region 19 of FIG. 2B. It is a top view which shows the structure of the unit pixel in 2nd Example. It is sectional drawing cut | disconnected along the broken line II 'of FIG. It is a top view which shows the structure of the unit pixel in 3rd Example. It is a figure for demonstrating the characteristic of the structure of the unit pixel of FIG. It is a figure for demonstrating the characteristic of the structure of the unit pixel of FIG. It is a top view which shows the structure of the unit pixel in the liquid crystal panel of the conventional liquid crystal display device. FIG. 9 is an enlarged view of a region 87 in FIG. 8 when no electric field is applied. It is an enlarged view of the area | region 87 of FIG. 8 at the time of an electric field application. It is a figure which shows the direction of the electric field in the area | region 86 of FIG. 9B.

Explanation of symbols

100, 200, 300 Unit pixel 1, 3, 25, 31 Pixel electrode 2 Common electrode 5 Opening 7 TFT
9 Data line 11 Gate line 12 Common line 15 Liquid crystal molecule

Claims (5)

A pair of transparent insulating substrates disposed opposite to each other at a predetermined interval through a liquid crystal layer composed of a plurality of liquid crystal molecules;
An alignment film inside each of the pair of transparent insulating substrates;
A plurality of gate lines and data lines formed on one of the pair of transparent insulating substrates and arranged in a matrix so as to limit each unit pixel;
A common electrode disposed on each unit pixel and made of a transparent conductor;
A pixel electrode made of a transparent conductor disposed in each unit pixel so as to form a fringe field together with the common electrode,
The pixel electrode includes a plurality of rod-like portions arranged at a predetermined interval, and a connection portion arranged so as to connect each rod-like portion and intersect the rod-like portion, and the connection portion is Both ends of the portion not intersecting with the rod-shaped portion are openings, and the connection portion is connected to the rod-shaped portion with a predetermined angle;
The angle at which the connection portion is inclined with respect to the direction parallel to the data line is formed larger than the rubbing angle of the liquid crystal molecules,
An FFS mode liquid crystal display device characterized in that, when an electric field is applied, the direction in which liquid crystal molecules located in the connection portion region rotate is the same as the direction in which liquid crystal molecules located in a region other than the connection portion region rotate. . The FFS mode liquid crystal display device according to claim 1,
The predetermined angle is not less than an angle obtained by adding 90 degrees to the rubbing angle of the liquid crystal molecules aligned by the alignment film of the substrate,
The FFS mode liquid crystal display device , wherein a rubbing angle of the liquid crystal molecules is an angle between a direction parallel to the rod-shaped portion and a rubbing direction of the liquid crystal molecules. The FFS mode liquid crystal display device according to claim 1 or 2,
An FFS mode liquid crystal display device, wherein a plurality of the connecting portions are arranged between the rod-like portions. The FFS mode liquid crystal display device according to claim 1 or 2,
The FFS mode liquid crystal display device, wherein the pixel electrode has a thickness of 0.04 μm or less. A pair of transparent insulating substrates disposed opposite to each other at a predetermined interval through a liquid crystal layer composed of a plurality of liquid crystal molecules;
An alignment film inside each of the pair of transparent insulating substrates;
A plurality of gate lines and data lines formed on one of the pair of transparent insulating substrates and arranged in a matrix so as to limit each unit pixel;
A common electrode disposed on each unit pixel and made of a transparent conductor;
A pixel electrode made of a transparent conductor disposed in each unit pixel so as to form a fringe field together with the common electrode,
The pixel electrode includes a plurality of V-shaped portions arranged at a predetermined interval and a connection disposed on a central line connecting the V-shaped portions at the center and connecting the V-shaped portions. The connecting portion has a predetermined angle with the central line in the same direction as the direction in which the central line and the V-shaped portion form an acute angle, and is symmetrical with respect to the central line. And
The predetermined angle is ± 1 degree or more,
An FFS mode liquid crystal display device characterized in that, when an electric field is applied, the direction in which liquid crystal molecules located in the connection portion region rotate is the same as the direction in which liquid crystal molecules located in a region other than the connection portion region rotate. .

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