JP2007249248A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display, wherein alignability of a liquid crystal can be maintained and the optimum display state can be obtained, even if the height of a protrusion is reduced. <P>SOLUTION: The liquid crystal display includes a first substrate 1 on which a pixel electrode 4 is disposed in a matrix shape; a slit 6 formed at the pixel electrode 4; a second substrate 8 on which a transparent electrode 11 is formed; a belt like protrusion 12 formed on a groove like step part which is formed at a part of the transparent electrode 11, corresponding to the slit 6; alignment layers 7 and 13, laminated on both substrates and subjected to vertical alignment treatment; a liquid crystal layer 14, interposed between both substrates and having negative dielectric anisotropy; a first polarizing plate 15 disposed on the outer side of the first substrate 1; and a second polarizing plate 16, disposed on the outer side of the second substrate 8 and having a transmission axis orthogonal to the transmission axis of the first polarizing plate 15. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a wide viewing angle liquid crystal display device in which a plurality of domains are provided in one pixel.

In general, liquid crystal display devices are characterized by thinness, light weight and low power consumption, and are widely used from portable terminals to large televisions. As this liquid crystal display device, a TN liquid crystal display device is often used, and high performance and quality are maintained as the display device.

However, the TN liquid crystal display device has a problem such as a large viewing angle dependency. Therefore, a VA (vertically aligned) liquid crystal display device having a wider viewing angle than the TN type has been proposed. In the case of a VA liquid crystal display device, a liquid crystal having negative dielectric anisotropy is sealed between a pair of glass substrates, a pixel electrode is disposed on one glass substrate, and a common electrode is disposed on the other glass substrate. A vertical alignment film is laminated on both glass substrates, and a pair of polarizing plates are arranged outside the both glass substrates so that the transmission axis directions thereof are orthogonal to each other. When no electric field is generated between the two electrodes, the liquid crystal molecules are regulated by the vertical alignment film and vertically aligned, and the linearly polarized transmitted light that has passed through one polarizing plate passes through the liquid crystal layer as it is and is transmitted by the other polarizing plate. Blocked. When an electric field is generated between the electrodes, the liquid crystal molecules between the glass substrates are horizontally aligned with an inclination to the electric field, so that the linearly polarized light passing through one polarizing plate passes through the liquid crystal layer. When this occurs, the light is birefringent and becomes elliptically polarized light, and passes through the other polarizing plate.

In order to further improve the viewing angle of this VA type liquid crystal display device, a protrusion or a groove is provided in the pixel.
An MVA (Multi-domain vertically aligned) method for forming a plurality of domains in a pixel has been proposed. This is described in Patent Document 1, for example.

The pixel configuration of this conventional MVA liquid crystal display device will be described. Of a pair of glass substrates arranged in parallel and opposite to each other, a pixel electrode, a scanning line, a signal line, and a TFT are formed on one glass substrate, and a color filter, a common electrode, and a protrusion are formed on the other glass substrate. . A plurality of scanning lines and signal lines are wired in a matrix on a glass substrate, TFTs are arranged at intersections thereof, and pixel electrodes are arranged in a region surrounded by the scanning lines and signal lines. The gate electrode of the TFT is connected to the scanning line, the source electrode is connected to the signal line, and the drain electrode is connected to the pixel electrode. The slit formed in the pixel electrode has a plurality of projections formed in a zigzag shape when viewed from the normal direction of the glass substrate, and the slit is located between the plurality of projections and formed substantially parallel to the adjacent projections. Has been. The liquid crystal molecules incline in a 90 ° direction with respect to the protrusions and the slits, and incline in the opposite direction with the protrusions and the slits as a boundary. A pair of crossed Nicols polarizing plates are arranged outside the pair of glass substrates, and the angle formed between the transmission axis of the polarizing plate and the direction of the protrusion is set to 45 °, as viewed from the normal direction of the polarizing plate. The angle between the tilted liquid crystal molecules and the transmission axis of the polarizing plate is set to 45 °. When the angle between the tilted liquid crystal molecules and the transmission axis of the polarizing plate is 45 °, the transmitted light can be most efficiently obtained from the polarizing plate.

However, in the conventional MVA type liquid crystal display device, the actual display state of the liquid crystal molecules is not ideal, so that the optimum display state cannot be obtained. As a countermeasure, for example, in Patent Document 2, the transmittance is increased by optimizing the cross-sectional shape of the protrusion.
Japanese Patent No. 2947350 JP 2000-267102 A

However, in Patent Document 1 and Patent Document 2, when spherical spacers dispersed in the liquid crystal are present in the protrusions, the liquid crystal layer around the spacers becomes thick, resulting in unevenness in the cell gap and uneven brightness in the protrusions. To do. From this point, the unevenness of the cell gap is reduced by making the protrusions as low as possible. However, by making the protrusions low, the orientation of the liquid crystal deteriorates, and problems such as afterimages arise. Therefore, conventionally, the height of the protrusion is determined within a range where the occurrence of uneven brightness and the afterimage can be compromised.

In view of the above problems, an object of the present invention is to provide a liquid crystal display device that maintains the orientation of liquid crystal even when the height of the protrusions is lowered and can obtain an optimal display state.

In order to achieve the above object, the present invention forms a transparent electrode by forming a first substrate in which pixel electrodes are arranged in a matrix, and an alignment film subjected to a vertical alignment process is laminated on the pixel electrode. A second substrate on which an alignment film subjected to a vertical alignment film treatment covering the electrode is stacked; and a liquid crystal layer sandwiched between the two substrates, and the liquid crystal molecules are vertically aligned when no electric field is applied to the liquid crystal layer. In a liquid crystal display device in which liquid crystal molecules are aligned in a direction regulated by the electric field when an electric field is applied to the liquid crystal layer, a groove-shaped step is provided on the transparent electrode, A dielectric material is disposed between the step portion and the alignment film.

In order to achieve the above object, the present invention provides a first substrate in which pixel electrodes are arranged in a matrix, an alignment film subjected to vertical alignment treatment is laminated on the pixel electrode, and a transparent electrode. A second substrate on which an alignment film subjected to a vertical alignment film treatment covering the transparent electrode is laminated, and a liquid crystal layer sandwiched between the two substrates, and when no electric field is applied to the liquid crystal layer, the liquid crystal molecules In a liquid crystal display device in which liquid crystal molecules are aligned vertically and arranged in a direction regulated by the electric field when an electric field is applied to the liquid crystal layer, a groove-shaped step is provided in the transparent electrode. The equipotential surface is generated in accordance with the shape of the groove-shaped step portion, and a dielectric material is disposed between the groove-shaped step portion and the alignment film.

According to this configuration, the equipotential surface is formed along the groove by the action of the groove, and the dielectric material is disposed between the groove and the alignment film, so that the action of physically tilting the liquid crystal molecules is weakened. However, the orientation of the liquid crystal can be maintained and an optimal display state can be obtained.

Further, a color filter having a hole portion may be provided on the second substrate side, and the groove-shaped step portion may be provided by forming the transparent electrode in the hole portion.

According to this configuration, it is not necessary to separately provide a layer for forming the groove-shaped step portion, and the liquid crystal can be aligned by the groove-shaped step portion formed in the color filter.

Embodiments of the present invention will be described below with reference to the drawings. 1 is a plan view of the liquid crystal display device, and FIG. 2 is a cross-sectional view taken along line AA of FIG.

Reference numeral 1 denotes a transparent first substrate such as a glass substrate, on which scanning lines 2 and signal lines 3 are wired in a matrix. A region surrounded by the scanning line 2 and the signal line 3 corresponds to one pixel, a pixel electrode 4 is disposed in this region, and a switching element connected to the pixel electrode 4 is disposed at an intersection of the scanning line 2 and the signal line 3. A certain TFT 5 is formed. A part of the pixel electrode 4 overlaps the adjacent scanning line 2 with an insulating film interposed therebetween, and this part functions as a storage capacitor. Pixel electrode 4
A plurality of slits 6 to be described later are formed. Reference numeral 7 denotes an alignment film that covers the pixel electrode 4 and is subjected to vertical alignment processing. In FIG. 2, the insulating film existing below the pixel electrode 4 is omitted.

Reference numeral 8 denotes a transparent second substrate such as a glass substrate. A black matrix 9 is formed on the second substrate 8 so as to divide each pixel, and a color filter 10 is laminated. A transparent electrode 11 such as ITO (Indium Tin Oxide) is laminated on the color filter 10, and a projection 12 having a predetermined pattern is formed on the transparent electrode 11, and the transparent electrode 11 and the projection 12 are subjected to a vertical alignment process. The alignment film 13 is covered.

A liquid crystal layer 14 having a negative dielectric anisotropy is interposed between the substrates 1 and 8. When no electric field is generated between the pixel electrode 4 and the transparent electrode 11, the liquid crystal molecules are regulated vertically by the alignment films 7 and 13, and when an electric field is generated between the pixel electrode 4 and the transparent electrode 11, the liquid crystal is aligned. Molecules tilt horizontally. At this time, the liquid crystal molecules are regulated by the slits 6 and the protrusions 12 and tilted in a predetermined direction, so that a plurality of domains can be formed in one pixel.

A first polarizing plate 15 is disposed outside the first substrate 1, and a second polarizing plate 16 is disposed outside the second substrate 8. The first polarizing plate 15 and the second polarizing plate 16 have mutual transmission axes. It is set to be orthogonal. When observed from the normal direction of the second substrate 8, the transmitted light passes through the second polarizing plate 16 most efficiently when the transmission axis of the polarizing plates 15 and 16 and the tilt direction of the liquid crystal molecules form about 45 °. be able to. Since the liquid crystal molecules are inclined in the direction of about 90 ° with respect to the projections 12 and the slits 6, the extending direction of the slits 6 and the projections 12 in the pixel and the transmission axis of the second polarizing plate 16 are about 45 °.
Both polarizing plates 15 and 16 are arranged so as to form In this embodiment, the transmission axis of the first polarizing plate 15 is set to coincide with the extending direction of the scanning line 2, and the transmission axis of the second polarizing plate 16 is set to match the extending direction of the signal line 3.

When no electric field is generated between the pixel electrode 4 and the transparent electrode 11, the liquid crystal molecules are aligned vertically, so that the linearly polarized transmitted light that has passed through the first polarizing plate 15 passes through the liquid crystal layer 14 as linearly polarized light. It is blocked by the second polarizing plate 16 and becomes black. Further, when a predetermined voltage is applied to the pixel electrode 4 and an electric field is generated between the pixel electrode 4 and the transparent electrode 11, the liquid crystal molecules are inclined in the horizontal direction, so that the linearly polarized light transmitted through the first polarizing plate 15 is transmitted. Light becomes elliptically polarized light in the liquid crystal layer 14, passes through the second polarizing plate 16, and becomes white display.

Next, the shape of the protrusion 12 will be described. A long hole is formed in a portion of the color filter 10 where the protrusion is formed, and the transparent electrode 11 is formed so as to cover the surface of the color filter 10 and the long hole. That is, a groove-shaped step portion is formed on the transparent electrode 11. And the protrusion 12 is formed so that this groove-shaped step part may be filled. The protrusions 12 are formed in a predetermined pattern by a photolithography method using a resist made of, for example, an acrylic resin. Note that the transmittance is improved when the protrusion 12 is formed of a positive material rather than a negative material. This is because the surface of the protrusion 12 becomes smoother with the positive material, and the regulation force in the tilt direction with respect to the liquid crystal molecules is further improved. The relative dielectric constant of the protrusion can be 3-4.

In general, when the protrusions are made high (about 1.5 μm or more), the orientation of the liquid crystal is improved and it is difficult to produce an afterimage. However, when the spherical spacer is placed on the protrusions, the unevenness of the cell gap increases and the unevenness of brightness occurs. . On the other hand, when the protrusions are low (about 1 μm or less), the cell gap unevenness is reduced and the brightness unevenness is reduced, but conversely, the orientation of the liquid crystal is lowered and an afterimage or the like is likely to occur. Therefore, conventionally, the height of the protrusion has been set to about 1.2 μm in consideration of the occurrence of afterimages and the occurrence of luminance unevenness.

On the other hand, in the present invention, a groove-shaped step portion is formed in the transparent electrode 11. Thereby, an equipotential surface in the liquid crystal layer 14 is generated in accordance with the shape of the groove. FIG. 3 is a cross-sectional view of a liquid crystal display device illustrating equipotential surfaces and liquid crystal alignment. FIG. 3 schematically shows a state where an electric field is generated between the pixel electrode 4 and the transparent electrode 11. In the figure, a broken line indicates an equipotential surface. In the vicinity of the protrusion 12, the liquid crystal molecules 14a are inclined so as to be parallel to the equipotential surface. Under the influence, the surrounding liquid crystal molecules 14a are also tilted in the same direction.

Further, the protrusion 12 has a function of physically tilting the liquid crystal molecules 14a. Conventionally, the height of the protrusion is required to some extent in order not to reduce this physical action, and the protrusion cannot be lowered. However, according to the present invention, the groove-shaped step portion of the color filter 10 is not provided. Since the liquid crystal molecules 14a can be sufficiently tilted by the action, the height h of the projection 12 (from the flat portion other than the groove-shaped step portion of the transparent electrode 11 to the highest portion of the projection 12) is made lower than before. Is possible.

Therefore, an experiment for determining a specific height h of the protrusion 12 was performed. As a sample of the conventional example and the liquid crystal display device of the present invention, liquid crystal display devices each having a protrusion height of 0.6 to 1.2 μm were manufactured. And the brightness nonuniformity and the afterimage of each sample were measured.

The brightness unevenness depends on the cell gap unevenness, and in both the conventional example and the liquid crystal display device of the present invention, the brightness unevenness is similarly observed as the height of the protrusion is increased.
The case of μm or less was good. This indicates that the unevenness of the cell gap is caused by the spacers in the liquid crystal layer 14 being held between the protrusions, and thus depends on the height of the protrusions.

The occurrence of an afterimage depends on the orientation of the liquid crystal. In the conventional liquid crystal display device, the height of the protrusion is 1
. In the case of 2 μm, it was good, but in the case of 0.6 μm, it was not able to endure viewing. on the other hand,
In the liquid crystal display device of the present invention, when the height h of the protrusion is 0.9 to 1.2 μm, the afterimage is less than that of the conventional example, and when 0.8 μm, the afterimage at 1.2 μm of the conventional example is equivalent. Yes, 0.6-0
. In the case of 7 μm, the afterimage was slightly more than in the conventional example at 1.2 μm.

From the measurement results of the luminance unevenness and the afterimage, the height of the protrusion 12 of the liquid crystal display device of the present invention is preferably 1 μm or less where the luminance unevenness is good. It is more preferable that the thickness is 0.8 μm from the viewpoint of reduction.

Note that the liquid crystal display device of the present invention can be used for various devices having a display portion, such as a portable terminal and a large-sized television.

According to the present invention, a groove is formed in a part of the transparent electrode, and an equipotential surface is formed along the groove by the action of the groove, and the dielectric material is disposed between the groove and the alignment film. Therefore, the liquid crystal molecules can be sufficiently tilted, and even when the action of physically tilting the liquid crystal molecules is weakened, the orientation of the liquid crystal can be maintained and an optimal display state can be obtained.

According to the present invention, the color filter having a hole is provided on the second substrate side, and the groove can be provided by forming a transparent electrode along the hole, which is sufficient for aligning the liquid crystal. A deep groove can be obtained.

It is a top view of the liquid crystal display device of this invention. It is the sectional view on the AA line of FIG. It is sectional drawing of the liquid crystal display device explaining the equipotential surface of this invention, and the orientation of a liquid crystal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st board | substrate 4 Pixel electrode 6 Slit 7, 13 Orientation film 8 2nd board | substrate 10 Color filter 11 Transparent electrode 12 Projection 14 Liquid crystal layer

Claims (3)

A first substrate in which pixel electrodes are arranged in a matrix and an alignment film subjected to a vertical alignment process is stacked on the pixel electrodes;
Forming a transparent electrode, a second substrate on which an alignment film subjected to a vertical alignment film treatment covering the transparent electrode is laminated;
A liquid crystal layer sandwiched between the two substrates;
A liquid crystal display device in which liquid crystal molecules are aligned vertically when no electric field is applied to the liquid crystal layer, and liquid crystal molecules are aligned in a direction regulated by the electric field when an electric field is applied to the liquid crystal layer In
A liquid crystal display device, wherein a groove-shaped step portion is provided on the transparent electrode, and a dielectric material is disposed between the groove-shaped step portion and the alignment film. A first substrate in which pixel electrodes are arranged in a matrix and an alignment film subjected to a vertical alignment process is stacked on the pixel electrodes;
Forming a transparent electrode, a second substrate on which an alignment film subjected to a vertical alignment film treatment covering the transparent electrode is laminated;
A liquid crystal layer sandwiched between the two substrates;
A liquid crystal display device in which liquid crystal molecules are aligned vertically when no electric field is applied to the liquid crystal layer, and liquid crystal molecules are aligned in a direction regulated by the electric field when an electric field is applied to the liquid crystal layer In
A groove-shaped step portion is provided in the transparent electrode, and an equipotential surface in the liquid crystal is generated according to the shape of the groove-shaped step portion, and a dielectric is provided between the groove-shaped step portion and the alignment film. A liquid crystal display device comprising a material. The color filter having a hole is provided on the second substrate side, and the groove-shaped step is provided by forming the transparent electrode in the hole. A liquid crystal display device according to 1.

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