JP4854152B2 - Liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the contrast compatible with the response speed in a liquid crystal display device. SOLUTION: If the distance d between the longitudinal side 42 of a display electrode and the straight line part 51 of an alignment controlling window 50 is shortened, the response speed of a liquid crystal is made higher. If the alignment controlling window 50 is enlarged (equivalent to shortening of the distance d), the contrast is unfavorably lowered. If the distance d is <=25 &mu;m-30 &mu;m, the effect of the enhancement of the response speed is reduced. Thereby, the distance d is favorably specified to be 25 &mu;m-30 &mu;m. The width of the alignment controlling window 50 is favorably about 7 &mu;m.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display (LCD) that performs display using the electro-optical anisotropy of liquid crystal, and more particularly to the structure of an electrode thereof.
[0002]
[Prior art]
LCDs have advantages such as small size, thinness, and low power consumption, and are being put to practical use in fields such as OA equipment and AV equipment. In particular, an active matrix LCD using a thin film transistor (hereinafter abbreviated as TFT) as a switching element can in principle perform a static drive with a duty ratio of 100% in a multiplexed manner, with a large screen and high-definition video. Used for display.
[0003]
The liquid crystal layer is sandwiched between a common electrode common to a plurality of pixels and a display electrode driven by the TFT. The display electrode formation region corresponds to one pixel region. A slit is formed in the common electrode corresponding to one pixel or a color region of one pixel. This slit is called an alignment control window and has a function of making the tilt direction of liquid crystal molecules constant. Examples of the shape of the orientation control window include a shape having a linear slit and a V-shaped slit coupled so as to branch to both ends of the linear slit.
[0004]
[Problems to be solved by the invention]
The shape of the orientation control window and the arrangement with respect to the display electrode need to be determined in consideration of the aperture ratio, response speed, and the like.
[0005]
An object of the present invention is to optimize the arrangement of alignment control windows and display electrodes.
[Means for Solving the Problems]
In order to achieve the above object, in the liquid crystal display device according to the present invention, the distance or interval on the display plane between the alignment control window and the display electrode is 25 μm to 30 μm at the longest place.
[0006]
When the interval is 30 μm or more, the response speed tends to be faster as the interval is shorter. However, it was confirmed that the response speed hardly changes even when the interval is shorter than 30 μm, particularly less than 25 μm. On the other hand, the reduction in the interval leads to a reduction in displayable area per pixel, and this reduction in area tends to cause a decrease in aperture ratio and contrast. Therefore, it is preferable that the interval is 30 μm or less and as close to 30 μm as possible.
[0007]
Further, by setting the width of the alignment control window to about 7 μm, it is possible to prevent a decrease in the pixel display area while sufficiently exhibiting the alignment division function.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings. FIG. 1 and FIG. 2 are diagrams showing in detail the structure of a part of the liquid crystal display device of this embodiment, particularly for one pixel. FIG. 1 is a schematic plan view of a first substrate side on which a TFT is formed among a pair of substrates constituting the liquid crystal display device, and FIG. 2 is a liquid crystal display device at a position along the line AA in FIG. FIG. A gate electrode 11 made of a metal such as Cr, Ta, or Mo is formed on an insulating substrate 10 such as glass, and a gate insulating film 12 made of one or both of SiNx and SiO ₂ is formed so as to cover the gate electrode 11. Has been. A polycrystalline silicon (p-Si) layer 13 patterned so as to straddle the gate electrode 11 is formed on the gate insulating film 12, and an SiO 2 patterned in the same shape as the gate electrode 11 is formed thereon. using the injection stopper 14 such as _2, P, contained in low concentration impurities such as As (N-) low density (LD: Lightly doped) region LD, contained a high concentration of the same impurity on the outside ( N +) source region S and drain region D are formed. Immediately below the implantation stopper 14 is an intrinsic layer that is substantially free of impurities, and serves as a channel region CH. An interlayer insulating film 15 made of SiNx or the like is formed so as to cover the p-Si layer 13 having these regions. A source electrode 16 and a drain electrode 17 made of Al, Mo or the like are formed on the interlayer insulating film 15, and are connected to the source region S and the drain region D through contact holes opened in each interlayer insulating film 15. Has been.
[0009]
A planarization insulating film 18 such as SOG (SPIN ON GLASS), BPSG (BORO-PHOSPHO SILICATE GLASS), acrylic resin or the like is formed so as to cover the entire surface of the TFT obtained by the above configuration. A display electrode 19 for driving a liquid crystal made of a transparent conductive film such as ITO (indium tin oxide) is formed on the planarizing insulating film 18, and the source electrode 16 is connected through a contact hole opened in the planarizing insulating film 18. It is connected to the.
[0010]
A vertical alignment film 20 made of a polymer film such as polyimide is formed so as to cover all the above configurations. In the present embodiment, the vertical alignment film 20 is a rubbing-less type film. On the other hand, a second glass substrate 30 made of glass or the like that is paired with the substrate 10 is disposed at a position facing the substrate 10 with the liquid crystal layer interposed therebetween. On the glass substrate 30, the entire surface of the display unit is formed by ITO. A formed common electrode 31 is provided. An alignment film 33 such as polyimide is formed on the common electrode 31 in the same manner as the alignment film 20 on the first substrate 10 side.
[0011]
An alignment control window 50 is formed in the common electrode 31 as a slit that penetrates the thickness of the electrode. As shown by a broken line in FIG. 1, the planar shape of the orientation control window 50 is a shape in which a V-shaped portion 52 that is a V-shaped slit is coupled to both ends of a linear portion 51 that is a linear slit. Yes. In other words, both ends of the straight slit may be divided into two forks, and the divided portions may form a V shape. The straight line portion 51 of the orientation control window is disposed substantially in parallel with the long side 42 of the rectangular display electrode 19 and substantially at the center in the direction of the short side 43. The tip of the V-shaped portion 52 extends to a position of the common electrode 31 facing the rectangular vertex of the display electrode 19.
[0012]
As shown in FIG. 2, since there is no counter electrode immediately below the alignment control window 50, an electric field that tilts the liquid crystal molecules 41 is not generated, and the liquid crystal molecules 41 maintain the initial alignment state, and the electrode 19 , 31 is oriented in a substantially vertical direction. On the other hand, at the edge of the orientation control window 50, the orientation as shown by a broken line in FIG. 2, that is, from the common electrode on both sides of the orientation control window 50 to the portion immediately below the portion where no electrode exists (alignment control window 50). As described above, an electric field is then formed in a direction parallel to the display electrode. Here, in this embodiment, since the liquid crystal molecules 41 have negative dielectric anisotropy, the liquid crystal molecules 41 in the vicinity of the alignment control window 50 are arranged so that their major axes are orthogonal to the electric field when an electric field is generated. That is, as shown in FIG. 2, the orientation is controlled so that the liquid crystal molecules in the vicinity of the orientation control window 50 are positioned in a square shape. Similarly, since an electric field is formed obliquely toward the gap portion of the display electrode 19 at the edge of the display electrode 19, the orientation is controlled in an inverted C shape in FIG. 2. Due to the continuity of the liquid crystal, the tilt of the liquid crystal molecules 41 near the edges of the common electrode 31 and the display electrode 19 is transmitted to the internal liquid crystal. Therefore, the controlled alignment directions of the liquid crystal molecules 41 are a plurality of directions (here, four directions) as indicated by arrows in FIG. 1 with the alignment control window 50 as a boundary in the pixel.
[0013]
Consider an orthogonal projection of the display electrode 19 and the orientation control window 50 on the display plane of the present display device or a plane parallel thereto, that is, a plane parallel to the plane where the display electrode 19 or the common electrode 31 is disposed. The distance d between the projection long side 42 of the display electrode 19 and the projection edge of the alignment control window straight line portion 51 affects the response speed of the liquid crystal. When an electric field is applied, the liquid crystal molecules 41 are tilted from the normal direction of the plane so that the major axis is orthogonal to the electric field according to the strength of the electric field, but the direction of tilting is not determined by the electric field strength. . In the present embodiment, the tilting direction is determined by the tilting direction of the liquid crystal molecules 41 due to the oblique electric field generated near the edge of the alignment control window 50 and the edge of the display electrode 19 described above. That is, when the liquid crystal molecules 41 in the vicinity of the edge are inclined in a predetermined direction by an oblique electric field, this inclination is propagated to the inner portion of the electrode. Therefore, the shorter the propagation distance, the faster the response speed of the liquid crystal. That is, it is preferable that the length of the line connecting the long axes when the liquid crystal molecules 41 fall is short.
[0014]
FIG. 3 shows the relationship between the interval d and the response speed. A graph indicated by a broken line is a case where the gap between the display electrode 19 and the common electrode 31, that is, a cell gap is 3.3 to 3.4 μm, and a graph indicated by a solid line is a cell gap of 3.5 to 3.6 μm. Is the case. As a general tendency, the response speed of the liquid crystal has a characteristic that it becomes faster as the cell gap of the liquid crystal display device is smaller, and in FIG. 3, the response speed of the liquid crystal is 3. The response speed of the liquid crystal at 3 to 3.4 μm is fast. However, as is apparent from FIG. 3, in the vertical alignment type liquid crystal display device of the present embodiment, not only such a general tendency, but also in any cell gap, the response speed tends to increase as the gap d becomes shorter. Further, it can be seen that the tendency is weakened when the distance d is 30 μm or less, and that the response speed can hardly be improved even when the distance d is shorter than 25 μm. The characteristics shown in FIG. 3 are negative type fluorinated liquid crystal as the liquid crystal, and the characteristics are: viscosity: 150 mPa · sec, optical anisotropy: Δn = 0.091, dielectric anisotropy: Δε = -3.8, NI point (temperature at which the liquid crystal changes to a liquid): 82 ° C. Of course, the liquid crystal that can be employed in the present embodiment is not limited to the liquid crystal having the above-mentioned characteristics, but in a liquid crystal that exhibits at least the same characteristics or the same kind of tendency, the window as shown in FIG. The relationship between the gap d with the display electrode side and the liquid crystal response speed is established. It can be seen that when the cell gap is 3.5 to 3.6 μm, the response speed is not shortened in the region where the distance d is 30 μm or less, and hardly changes at 25 μm or less. In addition, when the cell gap is 3.3 to 3.4 μm, the effect of shortening the response speed is dull when the distance d is 30 μm or less, and the effect at 25 μm or less is slight.
[0015]
On the other hand, the area where the orientation of the liquid crystal molecules can be controlled, that is, the area of the display electrode 19 excluding the alignment control window 50 is substantially equal to the substantial pixel display area. The distance d is preferably longer from the surface. Therefore, it is understood that the interval d should be made as long as possible within the range where the effect of shortening the response speed cannot be expected. Therefore, in the present embodiment, the interval d is set to 25 μm to 30 μm.
[0016]
Here, the width of the orientation control window 50 is preferably about 7 μm. As described above, the alignment control window 50 is formed by opening the common electrode 31 in a pattern as shown by the dotted line in FIG. 1, and since the electric field is hardly applied to the liquid crystal just below the window, the window area becomes a non-display area. For this reason, if the width of the window 50 is narrower than 7 μm, the pixel display area increases, but the alignment division function cannot be fully exhibited. On the other hand, even if it is larger than 7 μm, the alignment display function is hardly changed, but the pixel display area is reduced.
[0017]
FIG. 4 shows an example where the shape of the orientation control window is different. The display electrode 119 is substantially rectangular, and an orientation control window 150 having a width of approximately 7 μm is positioned as a substantially rectangular slit substantially parallel to the long side of the rectangle and at the center of the short side. The distance d between the edge of the orientation control window 150 and the long side of the display electrode 119 is 25 μm to 30 μm. It is also possible to provide an orientation control window parallel to the short side of the rectangular display electrode. In this case, the interval between the short sides is set to 25 μm to 30 μm.
[0018]
FIG. 5 shows another example of the arrangement of the orientation control window and the display electrode. The display electrode 219 is divided into three parts by a slit 260 that is cut into a rectangle, and an orientation control window 250 is provided for each of the divided parts. The shape of one orientation control window 250 is a shape in which both ends of one straight line portion are divided into two forks, similar to the orientation control window 50 shown in FIG. The distance d between the edge of the display electrode 219, that is, the edge 242 of the outer shape of the display electrode and the edge of the slit 260, and the edge of the linear portion of the orientation control window 250 is 25 μm to 30 μm. The width of the window 250 is about 7 μm, and the width of the slit 260 is also about 7 μm. The slit 260 is formed in the display electrode 219, and has an alignment division function similar to that of the window 250. The direction in which the liquid crystal is tilted with the slit 260 as a boundary is controlled to about 180 °.
[0019]
Thus, by providing a slit in the display electrode of one pixel and providing a plurality of alignment control windows per pixel, it is possible to deal with a pixel having a wider width Wp. When the interval d is 25 μm to 30 μm and the slit width Ws is 7 μm, when the display electrode of one pixel is divided into three as shown in FIG. 5, it can correspond to the pixel width Wp of 185 μm to 215 μm. Further, as shown in FIG. 1 or FIG. 4, when the display electrode of one pixel is not divided, it can correspond to a pixel width Wp of 57 μm to 67 μm. Further, by dividing the display electrode of one pixel into two, it is possible to cope with Wp 121 μm to 141 μm.
[0020]
In this way, according to the present invention, even for a pixel having a large pixel width Wp, the alignment direction can be reliably divided within the pixel, a high-speed response can be achieved, and the aperture ratio can be improved. By applying to a large LCD, a large LCD with excellent display quality can be realized.
[0021]
Further, for the pixel having the intermediate value width Wp as described above, the electrode configuration as shown in FIGS. 6 and 7 can be adopted. 6 is a plan view showing the display electrode 319 of one pixel and the alignment control windows 350a and 350b provided in the common electrode 331. FIG. 7 is a cross-sectional view of a plane orthogonal to the display electrode 319 and the common electrode 331. The display electrode 319 is divided into two portions 319a and 319b by a slit 360 that is substantially parallel to the orientation control windows 350a and 350b. The width Wp2 of the portion 319b is substantially half of the width Wp1 of the portion 319a, and the area is also substantially half.
[0022]
An alignment control window 350a is provided at a position corresponding to the vicinity of the center of the common electrode in the width Wp1 direction of the portion 319a. The distance d between the edge of the orientation control window 350a and two sides substantially parallel to the orientation control window of the display electrode portion 319a is 25 μm to 30 μm as in the above example. In addition, with respect to the other portion 319b of the display electrode, the orientation control window 350b is provided at a position facing the outer shape of the display electrode 319, that is, the side 342 serving as the outer shape of the pixel. The distance d between the edge of the orientation control window 350b and the edge of the slit 360 is also 25 μm to 30 μm.
[0023]
As shown by the broken line in the cross-sectional view of FIG. 7, an electric field is formed, and as shown in the drawing, the alignment directions of the liquid crystal molecules 41 are aligned in each of the three portions divided by the alignment control window 350a and the slit 360. In such a configuration, if the distance d is 25 μm to 30 μm, and the width of the slit and the alignment control window is 7 μm, the pixel width Wp can be 93 μm to 108 μm, and more various pixel widths can be handled. It becomes like this. A pixel width (for example, 68 μm to 92 μm) that cannot be realized even with such a configuration can be dealt with by expanding the width w of the slit and the alignment control window, although the aperture ratio is slightly reduced.
[0024]
【The invention's effect】
According to the present invention, it is possible to provide a liquid crystal display device having a large region in which the orientation of liquid crystal molecules can be controlled, that is, a large pixel contrast and a high response speed.
[Brief description of the drawings]
FIG. 1 is a plan view showing a structure of one pixel of a liquid crystal display device.
FIG. 2 is a cross-sectional view taken along line AA in FIG.
FIG. 3 is a diagram showing the relationship between the distance d on the display plane between the edge of the alignment control window straight line portion and the long side of the display electrode, and the response speed.
FIG. 4 is a diagram showing another example of the shape of the orientation control window.
FIG. 5 is a diagram showing another example of the shape of the display electrode and an example of the arrangement of orientation control windows corresponding to the display electrode.
FIG. 6 is a diagram showing still another example of the shape of the display electrode and an example of the arrangement of the alignment control windows corresponding to the display electrode.
7 is a cross-sectional view of a liquid crystal display device using the display electrode shown in FIG.
[Explanation of symbols]
19 display electrode, 31 common electrode (counter electrode), 40 liquid crystal, 41 liquid crystal molecule, 42 long side of display electrode, 50 alignment control window, 51 linear portion of alignment control window, 52 of alignment control window V-shaped part.

Claims (5)

A liquid crystal display device of a vertical alignment method in which a liquid crystal layer having liquid crystal molecules vertically aligned is provided between a plurality of display electrodes and a counter electrode, and the alignment of the liquid crystal molecules is controlled by an electric field,
The display electrode is divided into a plurality of parts by a linear cut, and the area of the end part located at the end of the divided part is smaller than the area of the other part,
The counter electrode has an alignment control window that is an opening having a shape having a linear portion substantially parallel to the notch, corresponding to the divided portion of the display electrode,
The edge that is the edge of the divided display electrode and the edge of the pixel overlaps with one of the alignment control windows, and the other edge of the portion and the straight portion of the alignment control window. The distance between the orthogonal projections on the display plane with the edge is 25 μm to 30 μm,
With respect to the other display electrode portion, the interval between the orthogonal projections on the display plane between the two sides parallel to the notch of the portion and the edge of the linear portion of the orientation control window substantially parallel to the notch is 25 μm. ~ 30 μm,
Liquid crystal display device. 2. The liquid crystal display device according to claim 1 , wherein the counter electrode includes an alignment control window including a straight portion and a portion that is bent and extends from an end portion of the straight portion.
Liquid crystal display device. 3. The liquid crystal display device according to claim 2 , wherein a tip of the alignment control window extends to a position facing the apex of the partitioned portion of the display electrode in the counter electrode.
Liquid crystal display device. 4. The liquid crystal display device according to claim 1 , wherein a width of the alignment control window is 7 μm.
Liquid crystal display 5. The liquid crystal display device according to claim 1 , wherein the dielectric constant of the liquid crystal is about −3.8.
Liquid crystal display device.

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