JP4523083B2 - Liquid crystal display - Google Patents

Abstract

A liquid crystal device comprises two electrodes 30,40 parallel to each other formed on one 10 of two substrates 10,20, homeotropic alignment films 90 formed on the substrates and a liquid crystal material 70 having positive dielectric anisotropy injected between the substrates. When a voltage V is applied to the two electrodes, a parabolic electric field between the electrodes drives the liquid crystal molecules. Since the generated electric field is symmetrical with respect to the boundary-plane equidistant from each of the two electrodes, the liquid crystal molecules 80 are symmetrically aligned with respect to the boundary-plane, and the optical characteristic is compensated in both regions divided by the boundary-plane, thereby obtaining a wide viewing angle. The electric field does not exert any influence on the liquid crystal molecules on the boundary-plane since the electric field on the boundary-plane is parallel to the substrate and perpendicular to the two electrodes; and thus, it is perpendicular to the liquid crystal molecules. The device also comprises means for varying directions of long axes of molecules of the liquid crystal layer, wherein the layer has at least two adjacent regions, the molecules of any one region being aligned in the same direction, and the molecules of two regions are aligned symmetrically with respect to the plane-boundary of the regions. The parallel electrodes in each pixel unit may be bent, and in adjacent pixels may be in different directions.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device.
[0002]
[Prior art]
In general, a liquid crystal display device has a structure in which liquid crystal is injected between two substrates on which electrodes are formed, and the amount of light transmission is adjusted by adjusting the strength of a voltage applied to the electrodes.
Hereinafter, a conventional liquid crystal display device will be described in detail with reference to the accompanying drawings.
[0003]
1A and 1B are cross-sectional views schematically showing the structure of a TN (twisted-nematic) type liquid crystal display device according to the prior art.
As shown in FIG. 1A and FIG. 1B, a TN liquid crystal display device includes a pair of transparent glass substrates 1, 2, two transparent electrodes 3, 4 formed on the inner surface, respectively. A liquid crystal layer 7 between the glass substrates 1 and 2 is included, and two polarizing plates 5 and 6 for polarizing light are attached to the outer surfaces of the glass substrates 1 and 2. Here, the electrode 3 of the lower substrate 1 is a pixel electrode, the electrode 4 of the upper substrate 2 is a common electrode, and the dielectric anisotropy Δε of the liquid crystal layer 7 is larger than zero.
[0004]
When no electric field is applied, as shown in FIG. 1A, the liquid crystal molecules 8 of the liquid crystal layer 7 packed between the two substrates 1 and 2 have their major axis directions on the two substrates 1 and 2. They are arranged in parallel and have a helically twisted structure from one substrate to the other.
[0005]
When a power source V is connected to the two electrodes 3 and 4 to form a sufficiently large electric field in the liquid crystal layer 7 in the direction of the arrow in FIG. 1B, as shown in FIG. The long axis of the molecule 8 is parallel to the direction of the electric field.
[0006]
[Problems to be solved by the invention]
However, such a TN liquid crystal display device has a problem that the viewing angle is narrow and gradation inversion occurs.
[0007]
Accordingly, the present invention is to solve the above-described conventional problems, and an object thereof is to provide a new type liquid crystal display device having a wide viewing angle.
[0008]
[Means for Solving the Problems]
In the liquid crystal display device according to the present invention for achieving the above object, a liquid crystal material having dielectric anisotropy is injected between the first substrate and the second substrate, and the liquid crystal molecules are distributed between the two substrates. Are arranged vertically. A first electrode and a second electrode parallel to each other are formed on one of the two substrates.
[0009]
The first and second substrates are obtained by forming an alignment film for vertically aligning the molecular axis of the liquid crystal substance, and the alignment film may or may not be rubbed.
[0010]
Furthermore, it can further include parallel plates respectively attached to the outside of the two substrates, and the transmission axes of the parallel plates can be arranged to be parallel or orthogonal to each other.
[0011]
Here, the dielectric anisotropy of the liquid crystal material can be either positive or negative, and any of pure nematic liquid crystal, chiral nematic liquid crystal, or nematic liquid crystal containing an additive may be used.
[0012]
When a voltage is applied to two electrodes of such a liquid crystal display device, a parabolic electric field is formed between the two electrodes, and liquid crystal molecules are driven by this electric field.
Here, a liquid crystal display device to which such a driving method is applied is referred to as an EOC (electrically-induced optidal compensation) type liquid crystal display device.
[0013]
In such an EOC-type liquid crystal display device, the arrangement of liquid crystal molecules on both sides is symmetrically formed with reference to the central portion of the region between the two electrodes. Accordingly, a phase retardation with respect to the transmitted light is also generated symmetrically, and a wide viewing angle can be obtained.
[0014]
The structure and arrangement of the electrodes in the liquid crystal display device as described above are different in the alignment direction of the liquid crystal molecules on both sides of the portion where the electrodes are bent, by forming the electrodes in a form that is bent in units of pixels or inside the pixels. Since the optical delay can be compensated for each other, a wider viewing angle can be obtained.
[0015]
When the polarizing plate is mounted in a direction in which the transmission axes are perpendicular to each other, the transmission axis of the polarizing plate can be mounted in all directions except when it is parallel or perpendicular to a part of the electrode. Most preferably, the angle formed by the electrode and the electrode is 45 °.
And the angle of the folded part of the electrode can have a range between 0 ° and 180 °, most preferably 90 °.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIGS. 2A to 2C and FIGS. 3A to 3C are schematic views showing the principle of the EOC type liquid crystal display device according to the first and second embodiments of the present invention.
As can be seen from the drawing, the pair of transparent glass substrates 10 and 20 on which the alignment films 90 are respectively formed face each other. Two linear electrodes 30 and 40 are formed in parallel to each other on the inner surface of the lower substrate 10 of the two substrates 10 and 20. A liquid crystal material is injected between the two glass substrates 10 and 20 to form the liquid crystal layer 70, and the liquid crystal molecules 80 of the liquid crystal layer 70 are aligned perpendicular to the two substrates 10 and 20. Here, the liquid crystal molecules 80 can be configured to have a tip tilt angle with respect to the substrates 10 and 20, and the two electrodes 30 and 40 can be configured of a transparent or opaque conductive material. Two polarizing plates 50 and 60 for polarizing light passing therethrough are attached to the outer surfaces of the glass substrates 10 and 20, respectively.
[0017]
In general, one of the two electrodes 30 and 40 is a pixel electrode for applying a different data signal to each unit pixel, and the other one is for applying a signal common to all unit pixels. It is a common electrode. Each pixel electrode is connected to one terminal of a switching element such as a thin film transistor formed in each pixel.
[0018]
At this time, the liquid crystal material of the liquid crystal layer 70 preferably has a dielectric anisotropy Δε larger than zero, but the dielectric anisotropy Δε may be smaller than zero. The liquid crystal material may be nematic, chiral nematic, or nematic liquid crystal mixed with a levorotatory or dextrorotatory chiral additive.
[0019]
In addition, each alignment layer 90 can be rubbed on all of the liquid crystal molecules 80 so as to have a direction when the liquid crystal molecules 80 lie down, or can be selectively rubbed on only one, or all rubbed. It is also possible not to process. When the rubbing process is performed, the rubbing direction can be set to an arbitrary direction with respect to the two electrodes 30 and 40. When the rubbing process is performed on all the alignment films 90 of the two substrates 10 and 20, the rubbing process is performed. The directions are preferably opposite to each other, and one of the two rubbing directions is preferably perpendicular to the electrode.
[0020]
Here, the transmission axes of the two polarizing plates 50 and 60 can be arranged parallel or perpendicular to each other.
[0021]
The widths of the two electrodes 30 and 40 are in the range of 1 to 10 μm, the distance between the two electrodes 30 and 40 is in the range of 2 to 20 μm, and the thickness of the liquid crystal layer 70 is in the range of 1 to 15 μm. preferable.
[0022]
2A to 2C show the case of pure nematic liquid crystal in which the dielectric anisotropy of the liquid crystal material is positive, and FIGS. 3A to 3C show the chiral additive of the liquid crystal material. This is a case of a mixed nematic liquid crystal having a positive dielectric anisotropy or a chiral nematic liquid crystal having a positive dielectric anisotropy.
As shown in FIGS. 2A and 3A, when no electric field is applied, the liquid crystal molecules 80 of the liquid crystal layer 70 are aligned perpendicularly to the two substrates 10 and 20 by the alignment force of the alignment film 90. It has a structure.
[0023]
At this time, the light passing through the polarizing plate 50 attached to the lower substrate 10 passes through the liquid crystal layer 70 without changing the polarization direction. Here, if the transmission axes of the two polarizing plates 50 and 60 are parallel, the light passes through the polarizing plate 60 attached to the upper substrate 2, so that a bright state is realized. When the transmission axes of the two polarizing plates 50 and 60 are orthogonal to each other, the light passing through the polarizing plate 50 of the lower substrate 10 is blocked by the polarizing plate 60 of the upper substrate 20 and thus becomes dark.
[0024]
2 (B) and 3 (B) show a case where an electric field is sufficiently applied, and FIGS. 2 (C) and 3 (C) respectively show FIGS. 2 (B) and 3 (B). It is the figure looked down from the upper board | substrate side.
At this time, the electric field is essentially parallel to the substrates 10 and 20 in the central portion of the region between the two electrodes 30 and 40, perpendicular to the electrodes 30 and 40, and approaches the electrodes 30 and 40. It becomes a parabolic shape distorted downward.
[0025]
At this time, since the nematic liquid crystal material has a positive dielectric anisotropy, the major axis of the liquid crystal molecules 80 tends to be aligned along the direction of the electric field, but in the portion adjacent to the two substrates 10 and 20. Since the alignment force of the alignment film 90 is stronger than the force due to the applied electric field, the liquid crystal molecules 80 maintain the original state of being aligned vertically. Therefore, when a pure nematic liquid crystal material is used, the liquid crystal director continuously changes so that the force by the electric field and the alignment force are balanced.
[0026]
In this case, as described above, since the electric field between the two electrodes 30 and 40 is formed in a parabolic shape as a whole, the left and right liquid crystals are referenced with respect to the center plane of the region between the two electrodes 30 and 40. The molecules 80 are arranged symmetrically.
[0027]
At this time, as seen in FIGS. 2B and 2C, the viewing angle in the direction perpendicular to the electrodes 30 and 40 is symmetric with respect to the center plane in the direction of the major axis of the liquid crystal molecules 80. As a result, the effect of symmetrically compensating the phase retardation with respect to the light passing through the liquid crystal layer 70 is generated, and the viewing angle is widened. Further, since the refractive index change rate is small in the minor axis direction of the liquid crystal molecules 80, that is, in the horizontal direction with respect to the electrodes 30 and 40, the viewing angle is expanded.
[0028]
On the other hand, in the central part of the region between the two electrodes 30, 40, the electric field is parallel to the substrate. Therefore, since the force by the electric field is perpendicular to the liquid crystal molecules 80 arranged perpendicular to the substrate, a discontinuous surface where the liquid crystal molecules 80 do not move is formed at the center of the two electrodes 30 and 40. Is done.
[0029]
Next, as shown in FIGS. 3B and 3C, the case where the liquid crystal material is a chiral nematic liquid crystal or a nematic liquid crystal mixed with a chiral additive is different from a pure nematic liquid crystal. is there.
The discontinuous surface in which the liquid crystal molecules 80 do not move is generated in the central portion of the region between the two electrodes 30 and 40, as in FIGS. 2B and 2C. However, the long axis of the liquid crystal molecules 80 is not only changed by the electric field force and the alignment force in the other portions, but is twisted by the chirality to be the central plane in the region between the two electrodes 30, 40. The arrangement of the liquid crystal molecules 80 in the regions on both sides of the film is not completely symmetric.
[0030]
That is, in FIG. 2C, when viewed from the upper substrate, the liquid crystal molecules 80 and the major axis are both arranged perpendicular to the electrodes 30 and 40, but in FIG. The liquid crystal molecules 80 on both sides of the center plane are rotated counterclockwise. Of course, the rotation direction of the liquid crystal molecules 80 may be opposite. In this case, the viewing angle is wide not only in the direction perpendicular to the electrodes 30 and 40 but also in the parallel direction.
[0031]
In the state as described above, the polarization of the light polarized through the polarizing plate 50 attached to the lower substrate 10 rotates along the twist of the liquid crystal director while passing through the liquid crystal layer 70. In the above two cases, the polarization can be rotated by 90 ° by adjusting the dielectric anisotropy, the distance between the two substrates 10 and 20, the pitch of the liquid crystal molecules 80, and the like. In this case, when the transmission axes of the two polarizing plates 50 and 60 are arranged in parallel to each other, this light is blocked by the polarizing plate 60 attached to the upper substrate 20, so that a dark state is realized. When the transmission axes of the two polarizing plates 50 and 60 are arranged so as to be orthogonal to each other, the light that has passed through the polarizing plate 50 of the lower substrate 10 passes through the polarizing plate 60 of the upper substrate 20, so that it becomes bright.
[0032]
In other words, in the EOC liquid crystal display device according to the present invention, the liquid crystal molecules 80 are arranged symmetrically with respect to the center plane between the two electrodes 30 and 40. As a result, in FIG. 2B and FIG. 3B, the light transmitted in the A direction and the light transmitted in the B direction are transmitted through a similar path of the liquid crystal molecules 80. Therefore, the delay with respect to the light passing therethrough is formed substantially the same, so that a wide viewing angle can be obtained.
[0033]
In such a liquid crystal display device, the structure and arrangement of the electrodes can be variously changed, and can be formed as shown in FIGS. This will be described in detail below.
As shown in FIGS. 4 and 5, the gate line 100 is formed horizontally, and the data line 200 orthogonal to the gate line 100 is formed vertically to define the pixel. A first electrode line 32 that is a common electrode line is formed in parallel with the gate line 100, and a second electrode line 42 that is a pixel electrode is formed in each pixel so as to face in parallel with the first electrode line 32. ing. A thin film transistor TFT, which is a switching element, is formed near the intersection of the gate line 100 and the data line 300. The first terminal of the thin film transistor TFT is the gate line 100, the second terminal is the data line 300, and the third terminal is the first terminal. The two electrode lines 42 are connected to each other.
[0034]
As shown in FIG. 4, the first and second horizontal electrode lines 32 and 42 facing each other in parallel are formed horizontally on each pixel. Of the four pixels shown in the figure, two pixels arranged in the diagonal direction are connected to the first and second horizontal electrode lines 32 and 42, respectively, and the first and second pixels extending in the vertical direction from the first and second horizontal electrode lines 32 and 42, respectively. The second electrodes 33 and 43 are alternately formed in parallel with each other. Also, the first and second horizontal electrode lines 32 are connected to the other two adjacent pixels, respectively, and the first and second vertical electrode lines 31 and 41 are vertically extended from opposite ends thereof. Is formed. A first electrode 30 extending from the first horizontal electrode line 32 and the first vertical electrode line 31 and forming a certain angle with these is formed, and a second horizontal electrode line 42 is formed between the first electrodes 30. The second electrodes 30 and 40 extended from the second vertical electrode line 41 are formed in parallel with the first electrode 30. That is, the first and second electrodes 33 and 43 of one pixel are formed so as to have a certain angle without being parallel to the first and second electrodes 30 and 40 of adjacent pixels.
[0035]
As shown in FIG. 5, the first and second horizontal electrode lines 32 and 42 facing each other in parallel are formed in each pixel in the horizontal direction, and the first and second horizontal electrode lines 32 and 42 are mutually connected. First and second vertical electrode lines 31 and 41 extending in the vertical direction from opposite ends are formed. The first portion 34 of the first electrode 36 connected to the first horizontal electrode line 32 extends in the vertical direction, and the second portion 35 of the first electrode 36 connected to the first portion 34 is inclined. It is formed as follows. Here, a part of the first vertical electrode line 31 serves as the first portion 34 of the first electrode 36, and a number of branches 37 extending from the first vertical electrode line 31 are connected to the second portion 35. They are formed in parallel. Further, between the second portion 35 of the first electrode 36, the first portion 44 of the second electrode 46 extended from the second horizontal electrode line 42 and the second vertical electrode line 41 is the second portion of the first electrode 36. The second portion of the second electrode 46 extending from the first portion 44 of the second electrode 46 is formed in parallel with the first portion 34 of the first electrode 36. Here, a part of the second vertical electrode line 41 serves as the second portion 45 of the second electrode 46. In other words, the first and second electrodes formed in parallel with each other are formed in a bent shape inside each pixel.
[0036]
As described above, a wide viewing angle can be realized by arranging the liquid crystal molecules at various angles by forming the direction of the electrodes in one substrate on one substrate or in one or more directions inside the pixel.
[0037]
Hereinafter, the result of manufacturing and testing an EOC-type liquid crystal display device according to the present invention will be described.
Experimental example 1
In Experimental Example 1, when a nematic liquid crystal in which a chiral additive is mixed in the liquid crystal layer 70 and a pure nematic liquid crystal are used, the viewing angle is measured for each.
[0038]
Here, the refractive index anisotropy Δn of the liquid crystal layer 70 is 0.09, the thickness d of the liquid crystal layer 70 is 4.5 μm, and the alignment film 90 is not subjected to the rubbing treatment. The two electrodes 30 and 40 are formed in the horizontal direction, and the transmission axes of the polarizing plates 50 and 60 attached to the outer surfaces of the two substrates 10 and 20 are arranged so as to be 90 ° with respect to each other. One is arranged so that the transmission axis is 45 ° with respect to the two electrodes 30 and 40 and the other one is 135 ° with respect to the transmission axis. Here, the angle is set based on the right side of the horizontal direction set to 0 °.
[0039]
FIG. 6 shows the result of measuring the viewing angle by mixing 0.1% of a chiral additive with pure nematic liquid crystal, and FIG. 7 is a graph showing the result of measuring the viewing angle without using the additive.
As shown in FIG. 6, when a chiral additive was used, a viewing angle of about 80 ° in the horizontal direction and about 76 ° in the vertical direction was measured based on a contrast ratio of 10.
[0040]
When no additive was used, a viewing angle of about 76 ° in the horizontal direction and about 76 ° in the vertical direction was measured with reference to a contrast ratio of 10, as shown in FIG.
In the diagonal direction, a viewing angle of 120 ° or more was measured in both cases based on a contrast ratio of 60.
[0041]
Experimental example 2
In Experimental Example 2, the alignment film 90 formed on the two substrates 10 and 20 was rubbed, and the viewing angle was measured for each.
FIG. 8 is a result of measuring the viewing angle by rubbing the alignment film 90 formed on the upper substrate 20 at 135 ° and the alignment film 90 formed on the lower substrate 10 at 315 °. The alignment film 90 formed on the upper substrate 20 is 45 ° and the alignment film 90 formed on the lower substrate 10 is rubbed at 225 °, and the viewing angle is measured. The remaining conditions are the same as in Experimental Example 1.
[0042]
As shown in FIGS. 8 and 9, the rubbing can reduce the difference between the horizontal and vertical viewing angles and the diagonal viewing angles, so that a more uniform viewing angle can be obtained in all directions. can get.
[0043]
Experimental example 3
In Experimental Example 3, the viewing angle was measured with different arrangements of the polarizing plates 50 and 60 attached to the outer surfaces of the two substrates 10 and 20.
10 is similar to Experimental Example 1, the transmission axis of the polarizing plate 60 attached to the upper substrate 20 is 45 ° with respect to the direction of the two electrodes 30 and 40, and the polarizing plate 60 attached to the lower substrate 10 is used. FIG. 11 shows the result of measuring the viewing angle with the transmission axis of 135 ° being set to be 135 °. FIG. 11 shows that the transmission axis of the polarizing plate 60 attached to the upper substrate 20 is 30 ° and attached to the lower substrate 10. This is the result of measuring the viewing angle by arranging the transmission axis of the polarizing plate 60 to be 120 °. The remaining conditions are the same as in Experimental Example 1.
[0044]
As described in Experimental Example 1, FIG. 10 shows a viewing angle of 120 ° or more in the four diagonal directions based on the contrast ratio 60, and a field of view of about 80 ° in the vertical and horizontal directions based on the contrast ratio 10. Shows corners. Compared with FIG. 11, it can be seen that the viewing angle direction depends on the relative angle between the electrode direction and the transmission axis direction of the polarizing plate. Therefore, by realizing various electrode directions and the direction of the transmission axis of the polarizing plate, a substantially constant viewing angle can be obtained in all directions.
[0045]
Experimental Example 4
In Experimental Example 4, as shown in FIG. 12, the viewing angle was measured by attaching negative uniaxial compensation films 100 to the outer surfaces of the two substrates 10 and 20, respectively. This is because such a compensation film compensates for the residual phase difference with respect to the delay.
FIG. 13 shows a case where the viewing angle was measured without using the compensation film 100, and a viewing angle of about 80 ° was measured. FIG. 14 shows the result of measurement using the delay value of the compensation film 100 of 40 nm, and FIG. 15 shows the result of measurement of the viewing angle using the delay value of the compensation film 100 of 80 nm. 16 is the result of measuring the viewing angle using the compensation film 100 having a delay value of 120 nm. The remaining conditions are the same as in Experimental Example 1.
[0046]
As can be seen from FIGS. 14 to 16, when the compensation film 100 is used, the viewing angle is widened to 60 ° with reference to the contrast ratio of 10.
It can be seen that a viewing angle of 60 ° or more in all directions can be obtained by optimizing the distance between the two substrates 10 and 20 and the delay value of the compensation film 100 in accordance with such results. Here, the delay value of the compensation film is preferably in the range of 30 to 500 nm.
[0047]
In the experimental example of the present invention, a negative uniaxial compensation film was used, but a positive uniaxial compensation film, a biaxial compensation film, a compensation film having a hybrid structure, or a compensation film having a twist structure can also be used.
Moreover, although the compensation film 100 is attached to the two substrates 10 and 20, respectively, it can alternatively be attached to only one substrate.
[0048]
Experimental Example 5
In Experimental Example 5, electro-optical characteristics were measured.
Here, the nematic liquid crystal is used for the liquid crystal layer 70, the alignment film 90 is not subjected to the rubbing treatment, and the widths of the two electrodes 30 and 40 are 5 μm, respectively.
[0049]
FIG. 17 is a graph showing the relationship between the distance between the liquid crystal cells, the distance between the two electrodes, and the driving voltage.
Here, Vmax is a driving voltage for maximum transmittance, Tmax is maximum transmittance, ton is a reaction time of liquid crystal molecules when turned on, toff is a reaction time of liquid crystal molecules when turned off, ttot = ton + toff, V _Ten Is the drive voltage when the transmittance is 10% of the maximum value, V ₉₀ Is a drive voltage when the transmittance is 90% of the maximum value.
[0050]
As shown in FIG. 17, the result of measuring the driving voltage when the distance between the two substrates 10 and 20 is set to 3 to 6 μm and the distance between the two electrodes 30 and 40 is set to 8 or 10 μm and the transmittance is maximum. , Measured in the range of 6-30V.
Thus, the drive voltage can be lowered by appropriately adjusting the distance between the electrodes and the distance between the liquid crystal cells.
[0051]
In the EOC type liquid crystal display device according to the embodiment of the present invention, the structure and arrangement of the electrodes can be changed in various ways other than those described above. As shown in FIGS. Very good display characteristics can be obtained when a sawtooth shape is formed. This will be described in detail. As seen in FIGS. 18 and 19, the first electrode line 32 that is a common electrode line and the second electrode line 42 that is a pixel electrode are formed in each pixel so as to face each other in parallel.
[0052]
As shown in FIG. 18, in the embodiment of the present invention, first and second electrode lines 32 and 42 facing each other parallel to each pixel are alternately formed in the horizontal and vertical directions along the row of pixels. The pixels are formed in the same direction in the column direction. The first and second electrode lines 32 and 42 are connected to the first and second electrode lines 32 and 42, respectively, and the first and second electrode lines 32 and 42 extend perpendicularly to the first and second electrode lines 32 and 42, respectively. It is formed alternately.
[0053]
In the embodiment of the present invention shown in FIG. 19, the first and second electrode lines 32 and 42 facing each pixel parallel to each other are different from the embodiment of the present invention shown in FIG. It is formed in the horizontal and vertical directions alternately along the column. The first and second electrodes 33 and 43 that are connected to the first and second electrode lines 32 and 42 and extend perpendicularly to the first and second electrode lines 32 and 42, respectively, are alternately formed in parallel with each other. The same as the embodiment of the present invention shown in
[0054]
20 and 21 show an embodiment of the present invention in which the first electrode as the common electrode and the second electrode as the pixel electrode are formed in the diagonal direction of the pixel.
As shown in FIGS. 20 and 21, the first electrode line 32, which is a common electrode line, is formed on each side of each pixel around the vertex of the pixel to form a “┐” or “┌” shape. The second electrode line 42 is formed on both sides with the apex facing the diagonal direction as a center and forming a '└' shape or a '┘' shape.
[0055]
The first electrode 33 and the second electrode 43, which are connected to the first electrode line 32 and the second electrode line 42 and are alternately formed in parallel with each other, are formed in the diagonal direction of the pixel. As shown in FIG. 20, in the embodiment of the present invention, the first electrode 33 and the second electrode 43 are formed so that the directions of the first electrode 33 and the second electrode 43 are shifted from each other along the horizontal row of pixels. On the other hand, in the embodiment of the present invention shown in FIG. 21, the first electrode 33 and the second electrode 43 are formed so that the directions of the first electrode 33 and the second electrode 43 are shifted from each other along the horizontal and vertical columns of pixels.
[0056]
FIG. 22 shows an embodiment of the present invention consisting of a parallelogram whose pixel shape is inclined, unlike the case of FIGS.
As shown in FIG. 22, in each pixel, a first electrode line 32 that is a common electrode line and a second electrode line 42 that is a pixel electrode are formed so as to face each other in parallel. The first electrode 33 and the second electrode 43, which are connected to the first electrode line 32 and the second electrode line 42 and are alternately formed in parallel with each other, are connected to the first electrode line 32 and the second electrode line. 42 is formed in an inclined direction. Each pixel is formed of an inclined parallelogram, and the inclination directions of the pixels are formed opposite to each other along the column, so that the first electrode 33 and the second electrode 43 form a sawtooth shape along the column of pixels. Is formed.
[0057]
FIG. 23 shows an embodiment of the present invention in which the pixel itself has a sawtooth shape.
As shown in FIG. 23, each pixel is formed in a sawtooth shape with its center bent, and each of the sawtooth pixels has a first electrode line 32 that is a common electrode line and a second electrode that is a pixel electrode. The electrode lines 42 are formed so as to face each other in parallel. The first electrode line 32 and the second electrode line 42 are connected to each other, and the first electrode 33 and the second electrode 43 that are alternately formed in parallel to each other are formed. Here, the first electrode 33 and the second electrode 43 are bent from the center of the pixel to have a sawtooth shape.
[0058]
24 is an enlarged view of a portion (a) where the electrode is bent in the electrode structure shown in FIG.
As shown in FIG. 24, when a voltage is applied to the first electrode 33 and the second electrode 43, a parabolic electric field drives the liquid crystal molecules 80. At this time, the liquid crystal molecules 80 are arranged such that the direction in which the major axis is projected is perpendicular to the electrode, and the tilt direction is directed upward in the direction indicated by the arrow in FIG. That is, the alignment direction of the liquid crystal molecules is symmetric with respect to the center plane between the first electrode 33 and the second electrode 43. However, since the electrodes 33 and 43 are bent in a sawtooth shape, regions divided into two minute regions having arrangement directions that are symmetrical to each other with respect to the center plane of the electrode on both sides of the bent portion. Two sets are generated, and this has the same effect as that of four regions having different alignment directions of liquid crystal molecules.
[0059]
The polarizing plate attached to both outer side surfaces of the liquid crystal cell is in all directions except the direction in which the transmission axis is parallel or perpendicular to a part of the first and second electrodes bent in a sawtooth shape. Mounted. However, the best display performance is obtained when the angle between the transmission axis of the polarizing plate and the electrode is 45 °.
The angle at which the first and second electrodes formed in a sawtooth shape are bent may have a value between 0 ° and 180 °, which is related to the transmission axis direction of the polarizing plate. The best viewing angle characteristics are obtained when the angle between the transmission axis of the polarizing plate and the electrode is 45 °, but when the angle between the transmission axis of the polarizing plate and the electrode is 45 °, the electrode is folded. The angle formed must be 90 °.
[0060]
In order to compensate for the residual retardation with respect to the light delay, a retardation compensation film may be attached to the outside of the liquid crystal display device according to the embodiment of the present invention.
[0061]
FIG. 25 is an exploded perspective view of a liquid crystal display device according to an embodiment of the present invention to which a compensation film is attached.
As shown in FIG. 25, the compensation film 110 is attached between the liquid crystal cell 100 and the polarizing plates 50 and 60. In the liquid crystal display device shown in FIG. 25, one compensation film is attached between each side surface of the liquid crystal cell and the polarizing plate, but there is a gap between one surface of the liquid crystal cell and the polarizing plate. It is also possible to attach only two or more compensation films between each surface of the liquid crystal cell and the polarizing plate. At this time, as the compensation film, a uniaxial or biaxial compensation film can be used, and a uniaxial compensation film and a biaxial compensation film can also be used in combination.
[0062]
The sawtooth electrode arrangement as shown in FIGS. 18 to 23 can be similarly applied to other modes in which the liquid crystal material is driven by two parallel electrodes. For example, a plane driving method (IPS mode (in-plane switching mode)) or two parallel electrodes are alternately formed on both substrates, and an EIMD method in which a liquid crystal material is driven by an electric field between these two electrodes. It can be applied to (electrical induced multi domain mode). This will be described in detail below.
[0063]
In the IPS liquid crystal display device, as in the above-described EOC mode, all two electrodes that are parallel and linear to each other are formed on one substrate. Here, the dielectric anisotropy Δε of the liquid crystal material is used regardless of whether it is larger or smaller than zero.
When no electric field is applied, the major axis of the liquid crystal molecules is arranged in parallel to the substrate and in a direction parallel to the electrode or at a certain angle, which is essential when a sufficiently large electric field is applied. In this way, an electric field parallel to the substrate is generated, whereby the long axes of the liquid crystal molecules located at the center of the liquid crystal layer are aligned parallel to the electric field. However, since the liquid crystal molecules in the vicinity of the substrate maintain the initial state by the alignment force, the liquid crystal molecules in the region from the substrate to the center have a helically twisted structure.
[0064]
In the EIMD type liquid crystal display device, a large number of first electrodes and second electrodes are formed so as to be arranged in parallel with each other and alternately on two substrates.
[0065]
26A and 26B are schematic views showing the principle of the EIMD type liquid crystal display device according to the embodiment of the present invention.
As shown in FIGS. 26A and 26B, the pair of transparent substrates 10 and 20 on which the alignment films 90 are respectively formed face each other, and are formed on the inner surfaces of the two substrates 10 and 20. Are alternately formed with first and second linear electrodes 30, 40 formed in parallel to each other. A liquid crystal material is injected between the two glass substrates 10 and 20 to form the liquid crystal layer 70, and the liquid crystal molecules 80 of the liquid crystal layer 70 are aligned perpendicular to the two substrates 10 and 20. Polarizing plates 50 and 60 are attached to the outer surfaces of the substrates 10 and 20, respectively.
[0066]
At this time, the liquid crystal material of the liquid crystal layer 70 preferably has a dielectric anisotropy Δε larger than zero, but the dielectric anisotropy Δε may be smaller than zero.
As shown in FIG. 26A, when no electric field is applied, the liquid crystal molecules 80 of the liquid crystal layer 70 have a structure that is aligned perpendicular to the two substrates 10 and 20 by the alignment force of the alignment film 90.
[0067]
FIG. 26B shows the case where a sufficient electric field is applied. When a sufficient voltage is applied to the two electrodes, the first and second electrodes 30 and 40 alternately disposed on the upper and lower substrates 10 and 20 have an inclination angle with respect to a direction perpendicular to the two substrates 10 and 20. A field is formed which is symmetrical with respect to a plane perpendicular to the two substrates 10, 20 or a central plane passing through the electrodes 30, 40. In the case of a nematic liquid crystal material having a positive dielectric anisotropy, the major axis of the liquid crystal molecules 80 is aligned along the direction of the electric field by the electric field in the tilt direction.
[0068]
In these two types of liquid crystal display devices, as in the EOC mode, the electrodes are formed in a sawtooth shape, and light is transmitted by regions where the tilt directions of the liquid crystal molecules are different from each other around the folded portion of the electrodes. A wide viewing angle can be obtained by compensating the delay.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing the structure of a twisted-nematic (TN) liquid crystal display device according to a conventional technique.
FIG. 2 is a schematic diagram showing a basic driving principle of an EOC (electrical induced optical compensation) type liquid crystal display device according to the first embodiment of the present invention;
FIG. 3 is a schematic diagram illustrating a basic driving principle of an EOC (electrical induced optical compensation) type liquid crystal display device according to a second embodiment of the present invention;
FIG. 4 is a plan view showing a structure of electrodes formed on a unit pixel in an EOC type liquid crystal display device according to a third embodiment of the present invention;
FIG. 5 is a plan view showing a structure of electrodes formed on a unit pixel in an EOC type liquid crystal display device according to a fourth embodiment of the present invention;
FIG. 6 is a graph showing a result of measuring a viewing angle of an EOC liquid crystal display device according to an embodiment of the present invention.
FIG. 7 is a graph showing a result of measuring a viewing angle of an EOC liquid crystal display device according to an embodiment of the present invention.
FIG. 8 is a graph showing a result of measuring a viewing angle of an EOC liquid crystal display device according to an embodiment of the present invention.
FIG. 9 is a graph showing a result of measuring a viewing angle of an EOC liquid crystal display device according to an embodiment of the present invention.
FIG. 10 is a graph showing a result of measuring a viewing angle of an EOC liquid crystal display device according to an embodiment of the present invention.
FIG. 11 is a graph showing a result of measuring a viewing angle of an EOC liquid crystal display device according to an embodiment of the present invention.
FIG. 12 is a graph showing a result of measuring a viewing angle of an EOC liquid crystal display device according to an embodiment of the present invention.
FIG. 13 is a graph showing a result of measuring a viewing angle of an EOC liquid crystal display device according to an embodiment of the present invention.
FIG. 14 is a graph showing a result of measuring a viewing angle of an EOC liquid crystal display device according to an embodiment of the present invention.
FIG. 15 is a graph showing a result of measuring a viewing angle of an EOC liquid crystal display device according to an example of the present invention.
FIG. 16 is a graph showing a result of measuring a viewing angle of an EOC liquid crystal display device according to an embodiment of the present invention.
FIG. 17 is a graph showing the results of measuring electro-optical characteristics in an EOC liquid crystal display device according to an example of the present invention.
FIG. 18 is a plan view showing a structure of an electrode formed on a unit pixel in a liquid crystal display device according to an embodiment of the present invention.
FIG. 19 is a plan view showing a structure of an electrode formed in a unit pixel in a liquid crystal display device according to an embodiment of the present invention.
FIG. 20 is a plan view showing a structure of an electrode formed in a unit pixel in the liquid crystal display device according to the embodiment of the present invention.
FIG. 21 is a plan view showing a structure of an electrode formed in a unit pixel in the liquid crystal display device according to the embodiment of the present invention.
FIG. 22 is a plan view showing a structure of an electrode formed in a unit pixel in the liquid crystal display device according to the embodiment of the present invention.
FIG. 23 is a plan view showing a structure of an electrode formed in a unit pixel in a liquid crystal display device according to an embodiment of the present invention.
FIG. 24 is an enlarged view of a portion of FIG.
FIG. 25 is an exploded perspective view of a liquid crystal display device according to an embodiment of the present invention.
FIG. 26 is a schematic diagram illustrating a driving principle of an EIMD liquid crystal display device according to an embodiment of the present invention.
[Explanation of symbols]
10, 20 substrate
30, 40 electrodes
32, 42 First and second electrode lines
33, 43 first and second electrodes
50, 60 Polarizing plate
70 Liquid crystal layer
80 Liquid crystal molecules
90 Alignment film
100 compensation film

Claims (17)

A switching element made of a thin film transistor is formed in each pixel, and the liquid crystal display device drives each pixel by the switching element,
A first substrate and a second substrate facing each other;
A liquid crystal material layer injected between the first and second substrates and oriented perpendicular to the first and second substrates;
At least two electrodes formed on one of the first and second substrates and parallel to each other ;
Polarizing plates each having a transmission axis and attached to the outside of the first substrate and the second substrate,
Including
The two or more electrodes include first and second portions that are not parallel to each other, and are arranged at 45 degrees with respect to the transmission axis of the polarizing plate when an electric field is applied to the liquid crystal material layer. A liquid crystal display device, wherein four different liquid crystal domains are formed.   The liquid crystal display device according to claim 1, wherein the liquid crystal material layer has a positive dielectric anisotropy.   The liquid crystal display device according to claim 2, wherein the liquid crystal material layer includes one of a chiral nematic liquid crystal, a nematic liquid crystal, and a nematic liquid crystal mixed with a chiral additive. The liquid crystal display device according to claim 1 , wherein each of the first substrate and the second substrate further includes an alignment film that vertically aligns a liquid crystal molecular axis of the liquid crystal material layer. The liquid crystal display device according to claim 4 , wherein transmission axes of the polarizing plates are arranged perpendicularly or parallel to each other. The liquid crystal display device according to claim 5 , wherein the liquid crystal molecules of the liquid crystal material layer have a tip tilt angle.   The liquid crystal display device according to claim 1, wherein the electrodes are formed such that adjacent pixels face in different directions.   The liquid crystal display device according to claim 1, wherein the electrode is bent in a unit pixel. The liquid crystal display device according to claim 6 , wherein the electrode has a width of 1 to 10 μm. The liquid crystal display device according to claim 9 , wherein a distance between the plurality of electrodes is 2 to 20 μm. The liquid crystal display device according to claim 10 , wherein a distance between the first substrate and the second substrate is 1 to 15 μm. The liquid crystal display device according to claim 11 , wherein a distance between the first substrate and the second substrate is 3 to 10 μm. The liquid crystal display device according to claim 12 , wherein a distance between the first substrate and the second substrate is 3 to 6 μm. The liquid crystal display device according to claim 11 , wherein each of the first substrate and the second substrate includes an alignment film on which one or both are rubbed. The liquid crystal display device according to claim 1 , further comprising a compensation film attached to one or both of the first and second substrates and the polarizing plate. The liquid crystal display device according to claim 15 , wherein the compensation film has a positive uniaxial property, a negative uniaxial property, a biaxial property, a hybrid structure, or a twist structure. The liquid crystal display device according to claim 16 , wherein a delay value of the compensation film is in a range of 30 to 500 nm .

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