JP2791998B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display.
More specifically, the present invention relates to an improved structure of a liquid crystal display device using a voltage-controlled birefringent liquid crystal and provided with a black mask for improving contrast.

[0002]

2. Description of the Related Art FIG. 6 shows a structure of a voltage controlled birefringent liquid crystal display cell. The configuration shown in FIG. 6 is composed of a so-called homeotropically aligned liquid crystal cell in which the major axis direction of the liquid crystal molecules is oriented substantially perpendicular to the electrode surface.

In FIG. 6, a liquid crystal cell 20 is composed of two transparent glass substrates 21 and 2 which are opposed to each other at a predetermined interval.
5, transparent electrodes 22 and 24 formed on the opposing surfaces of the glass substrates 21 and 25, and a light-shielding film 26 called a black mask for preventing light transmission outside the pixel display section and improving contrast. And a liquid crystal 23 interposed between transparent electrodes. Polarizing plates 10 and 30 whose polarization directions are orthogonal to each other are arranged above and below the liquid crystal cell 20.

The z-axis in FIG. 6 is the optical axis, and the polarizers 10 and 3
Arrows A and B shown above 0 indicate the directions of the polarization axes, respectively. The liquid crystal molecules 23 are aligned (homeotropic) with their major axis directions substantially aligned with the optical axis z, but are aligned with a slight inclination (pretilt) to improve the response.

The direction of the pretilt of the liquid crystal molecules 23 is the y direction in FIG.
Form a degree angle. FIG. 7 shows the pretilt direction of the liquid crystal molecules 23 as viewed from the z-axis direction.

In the state shown in FIG. 6, when light is incident along the optical axis z from above the polarizing plate 10, for example, the incident light is
As a result, the light becomes linearly polarized light in the A direction, and enters the liquid crystal cell 20. If the pretilt amount is neglected, the liquid crystal molecules 23 are substantially z
Since the light is oriented perpendicular to the axis, the linearly polarized light in the A-axis direction passes through as it is, and transmission is blocked by the polarizing plate 30 having a B-axis polarization axis orthogonal to the A-axis, and the display is in a dark state.

When a voltage exceeding a predetermined threshold voltage is applied between the electrodes 22 and 24, the alignment of the liquid crystal molecules 23 is tilted by the electric field, and forms a predetermined angle with respect to the optical axis z. Accordingly, the linearly polarized light incident on the liquid crystal cell 20 is birefringent into two components orthogonal to each other, and the polarized light having a component parallel to the B-axis direction is transmitted through the polarizing plate 30 to display a bright state.

[0008]

FIG. 8 shows an alignment state near the threshold voltage of the liquid crystal molecules 23 (below) as viewed from the optical axis z direction. The dotted and solid lines in FIG.
2 and the position of the common electrode 24 are shown. In FIG. 8, the black dot of the liquid crystal molecule 23 indicates one head of the long axis, and indicates the tilt direction of the molecule.

That is, near the threshold voltage, the liquid crystal molecules at the center are oriented in the optical axis direction, but the liquid crystal molecules around the electrodes are already inclined with respect to the optical axis. This indicates that light transmission has already occurred near the black mask before reaching the threshold voltage.

FIGS. 9 and 10 show the sectional structure of a liquid crystal cell and the state of an electric field. FIG. 9 shows a sectional structure of a liquid crystal cell of a monochrome liquid crystal display device. In FIG. 9, 41 and 45 are transparent glass substrates, 42 and 44 are transparent electrodes made of ITO,
3 is a liquid crystal layer and 46 is a black mask.

The arrows shown by the dotted lines represent the electric field. In the center of the liquid crystal cell in FIG.
Since the electric field is aligned substantially parallel by the electrodes, the liquid crystal molecules 431 do not tilt below the threshold voltage and remain in a vertical alignment.

However, the lower electrode 44 is cut off at the portion where the black mask 46 is disposed, and the black mask 46 is a non-conductive material. Occurs.

Therefore, the liquid crystal molecules 4 in the oblique electric field portion
32 starts to slope even at a low voltage equal to or lower than the threshold voltage. This inclination direction is at an angle of 45 ° to the polarization direction of the polarizing plate. For this reason, even when an OFF voltage (dark state) equal to or less than the threshold is applied, light leakage occurs in the periphery of the pixel, that is, in the vicinity of the black mask, and as a result, the contrast is reduced.

FIG. 10 shows a sectional structure of a liquid crystal cell of a color liquid crystal display device. 10, 51 and 56 are transparent glass substrates, 52, 54 and 55 are transparent electrodes made of ITO,
53 is a liquid crystal layer, 57 is a black mask, and 58 is a color filter. The relationship between the electric field and the liquid crystal molecules in this case is the same as in the case of FIG. 9, and light leakage occurs around the pixel.

An object of the present invention is to provide a voltage-controlled birefringent liquid crystal display device which eliminates light leakage around the above-mentioned light-shielding film, that is, around the black mask, and has a high contrast.

[0016]

In order to achieve the above object, in a liquid crystal display device according to the present invention, there are provided a first and a second transparent substrates, which are arranged opposite to each other at a predetermined interval, A first transparent electrode having a predetermined first electrode pattern disposed on a surface of the transparent substrate facing the second transparent substrate, and a first transparent electrode facing the second transparent substrate facing the first transparent substrate; A second transparent electrode disposed on a surface and having a predetermined second electrode pattern different from the first electrode pattern, and vertically arranged with respect to the first transparent substrate or the second transparent substrate. A non-conductive layer disposed on a surface of the second transparent substrate opposed to the first transparent substrate, the portion not having the second transparent electrode, and a birefringence control type liquid crystal layer having separated liquid crystal molecules. A second transparent substrate on the second transparent substrate. The liquid crystal layer disposed between a portion where no pole is formed and a first transparent electrode formed on the first transparent substrate applies a voltage lower than a threshold voltage between the two transparent electrodes. In this case, an inclination is caused by an oblique electric field, and the light shielding film is arranged so as to cover a peripheral edge of the adjacent second transparent electrode with a predetermined width.

[0017]

The peripheral edge of the adjacent transparent electrode is covered with a predetermined width by the light-shielding film, so that the oblique electric field at the electrode edge is suppressed and the liquid crystal molecules are hardly inclined. Furthermore, even if
Even if the liquid crystal molecules are slightly tilted at the edge of the electrode, the portion is covered by the black mask, so that light leakage is prevented.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a voltage controlled birefringent liquid crystal display device according to the present invention will be described with reference to FIGS.

FIG. 1 shows a cross-sectional structure of an embodiment of a monochrome liquid crystal cell in a voltage controlled birefringent liquid crystal display device according to the present invention, and the state of an electric field when an OFF voltage is applied near (or below) a threshold voltage.

In FIG. 1, 61 and 65 are transparent glass substrates, 62 and 64 are transparent electrodes made of ITO, 63 is a liquid crystal layer, and 66 is a black mask made of a material having a small dielectric constant. If the dielectric constant is large, a large voltage is applied to the liquid crystal layer. Therefore, a black mask material having a relative dielectric constant that is not so large as compared with the relative dielectric constant of the liquid crystal is used.

For example, a resin in which a metal oxide is dispersed and having a relative dielectric constant of about 3.0 is used. At this time, the relative permittivity of the liquid crystal is 2.5.

The arrows shown by the dotted lines represent the electric field. The difference from the liquid crystal cell according to the prior art shown in FIG. 9 is that the black mask 66 covers the edge of the adjacent ITO electrode 64 with the overlap 661.

In the central part of the liquid crystal cell in FIG. 1, the electric field is aligned almost in parallel by the upper and lower ITO electrodes, so that the liquid crystal molecules 631 do not tilt below the threshold voltage and remain vertical. However, the electric field bends at the edge of the electrode where the black mask 66 is arranged as shown in the figure, resulting in an oblique electric field. However, the overlapping portion 661 of the black mask having a small dielectric constant is arranged on the edge of the ITO electrode 61 and occupies the region where the electric field concentration is strongest.

Further, the voltage between the electrodes is divided by the liquid crystal layer and the black mask. As the dielectric constant of the black mask decreases, the capacitance of the black mask layer decreases, and the voltage applied to the black mask increases. Therefore, the voltage applied to the liquid crystal layer decreases. Since the liquid crystal responds to the voltage, the inclination of the liquid crystal molecules 632 due to the oblique electric field is reduced.

Further, since the electrode edge portion of the oblique electric field is shielded by the overlap portion 61, light leakage due to the tilt of the liquid crystal molecules 632 is prevented.

FIG. 2 shows a cross-sectional structure of an embodiment of a color display liquid crystal cell in a voltage controlled birefringent liquid crystal display device of the present invention, and a state of an electric field when an OFF voltage is applied near (or below) a threshold voltage.

In FIG. 2, 71 and 76 are transparent glass substrates, 72, 74 and 75 are ITO transparent electrodes, 73 is a liquid crystal layer, 77 is a black mask, and 78 is a color filter. The relationship between the electric field and the liquid crystal molecules in this case is shown in FIG.
The light leakage around the pixel at the edge of the electrode is prevented by the overlapping portion 771 of the black mask. It is preferable that the width of the overlap portion be equal to or larger than the cell gap, and be as small as possible so as not to reduce the aperture ratio. Of course, an alignment margin is required.

In each of the embodiments shown in FIGS. 1 and 2, when the pixel pattern width is 100 μm, the interval between adjacent pixel patterns is 20 μm, and the liquid crystal cell gap is 5 μm, the width of the overlap portion of the black mask is 10 μm. The degree is appropriate.

Next, a method of manufacturing a substrate for forming the lower black mask 66 in the liquid crystal cell having the structure shown in FIG. 1 will be described with reference to FIGS.

In the method of FIG. 3, first, as shown in FIG. 3A, a photosensitive light-shielding film 660 is applied on a glass substrate 65 on which an ITO transparent electrode 64 has been patterned by spin coating or the like. Next, using the photomask 80, the electrode 64
And the surrounding area is exposed.

Next, when an unexposed portion is removed, FIG.
A black mask 66 as shown in FIG.
The black mask 66 has an overlap portion 661 extending on the transparent electrode 65 by a predetermined width.

In the method of FIG. 4, first, as shown in FIG. 4A, a resist layer 70 is applied on a glass substrate 65 on which an ITO transparent electrode 64 has been patterned, and as shown in FIG. A resist layer 70 patterned by a lithography process with a width smaller than the pattern width of the ITO electrode (to be narrowed by the width of the overlap portion) is formed.

Next, the substrate is baked at about 250 ° C. to change the patterned resist layer 70 into a light-shielding film.

Further, as shown in FIG. 4C, a photosensitive light-shielding film 660 is applied thereon by screen printing or the like.
As shown in FIG. 4D, the photosensitive light-shielding film 660 on the resist layer 70 is removed by exposure and development from the back surface of the glass.
A black mask 660 is formed, and finally, the remaining resist layer 70 is peeled off as shown in FIG.

In this way, a black mask covering the end of the electrode can be formed. The technique described in Japanese Patent Application No. 3-68896 can be used for the format and the like of the black mask.

FIG. 5 is a graph comparing the light transmittance vs. voltage characteristics between the liquid crystal cell according to the prior art and the liquid crystal cell according to the present invention.

The dotted line indicates the characteristics according to the prior art, and the solid line indicates the characteristics of the liquid crystal cell according to the embodiment of the present invention. As is clear from the characteristics shown in FIG. 5, the region according to the embodiment of the present invention has a wider area before the light transmittance rises due to the effect of the overlap portion of the black mask, and the transmittance-voltage characteristic becomes steeper. I have. Therefore, it can be seen that even when an OFF voltage near the threshold voltage is applied, the light is sufficiently shielded and the contrast can be improved.

[0038]

According to the present invention, the light-shielding film covers the edge of the adjacent transparent electrode with a predetermined width, thereby preventing the tilt of the liquid crystal molecules. For example, even if the liquid crystal molecules slightly tilt at the electrode edge. Since that portion is covered with a light shielding film, light leakage is prevented.

Further, by forming the light-shielding film with a material having a lower dielectric constant than the liquid crystal, the oblique electric field at the edge of the electrode is suppressed, and the liquid crystal molecules are hardly tilted.

Therefore, the contrast characteristics are improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure and a state of an electric field of a liquid crystal cell according to an embodiment of the present invention.

FIG. 2 is a diagram showing a cross-sectional structure and a state of an electric field of a liquid crystal cell according to another embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a method for manufacturing a liquid crystal cell according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating another example of a method for manufacturing a liquid crystal cell according to an embodiment of the present invention.

FIG. 5 is a graph comparing light transmittance versus voltage characteristics of liquid crystal cells according to the present invention and a conventional technique.

FIG. 6 is a diagram showing a cell structure of a homeotropically aligned voltage controlled birefringent liquid crystal display device.

FIG. 7 is a diagram showing directions of pretilt of liquid crystal molecules.

FIG. 8 is a view showing the orientation of liquid crystal molecules of a liquid crystal cell according to a conventional technique.

FIG. 9 is a diagram showing a cross-sectional structure and a state of an electric field of a liquid crystal cell according to a conventional technique.

FIG. 10 is a diagram showing a cross-sectional structure and a state of an electric field of another liquid crystal cell according to a conventional technique.

[Explanation of symbols]

10, 30 polarizing plate 20 liquid crystal cell 21, 25, 41, 45, 51, 56, 61, 65, 7
1,76 glass substrate 22,24,42,44,52,54,55,62,6
4, 72, 74, 75 Transparent electrode 23, 43, 53, 63, 73 Liquid crystal layer 26, 46, 57, 66, 77 Black mask (light shielding film) 661, 771 Overlap portion

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/1335 G02F 1/1343 G02F 1/137

Claims (2)

(57) [Claims] A first transparent substrate disposed at a predetermined distance from each other and a first transparent substrate disposed on a surface of the first transparent substrate facing the second transparent substrate; A first transparent electrode having a first electrode pattern; and a second electrode different from the first electrode pattern, the second electrode being disposed on a surface of the second transparent substrate facing the first transparent substrate. A second transparent electrode having a pattern; a birefringence control type liquid crystal layer having liquid crystal molecules arranged in a direction perpendicular to the first transparent substrate or the second transparent substrate; A non-conductive light-shielding film disposed on a surface facing the first transparent substrate so as to cover a portion without the second transparent electrode; and a second transparent electrode on the second transparent substrate. And the first transparent electrode formed on the first transparent substrate. The liquid crystal layer disposed between the two transparent electrodes, when a voltage lower than the threshold voltage is applied between the two transparent electrodes, shows an inclination due to an oblique electric field, the light-shielding film, the second transparent electrode of the adjacent A voltage-controlled birefringent liquid crystal display device, which is arranged so as to cover a peripheral edge with a predetermined width. 2. The voltage controlled birefringent liquid crystal display device according to claim 1, wherein the light shielding film is formed of a material having a dielectric constant lower than that of the liquid crystal molecules.