JPH06194645A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To prevent whity display at the time of inclining the visual angle of a liquid crystal display element obtaining the display of wide visual field by dividing an area into plural. CONSTITUTION:At least one compensating plate or composite compensating plate 1 is added to a liquid crystal element 2 having the area whose oriented direction is different. The compensating plate 1 hardly has the anisotropy of refractive index on a plane in a direction parallel with the surface of the compensating plate and the refractive index in a direction perpendicular to the surface of the compensating plate is smaller than the refractive index on the plane, so that the plate 1 has the anisotropy of the negative refractive index, and the anisotropy of the refractive index of a polarity possessed by the element 2 part at the time of impressing voltage is compensated.

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 device.

[0002]

2. Description of the Related Art As a conventional liquid crystal display device which realizes a wide viewing angle by dividing an area into a plurality of areas and applying an alignment regulating force in different alignment directions between adjacent areas, for example, Japanese Patent Laid-Open No. 63-106624. There is one shown in.
Here, this will be described as an example. FIG. 6 shows a plan view of this liquid crystal display element. FIG. 7 shows a sectional view of this liquid crystal display element (a sectional view taken along the line CC ′ of FIG. 6). Furthermore, a schematic diagram of the rubbing direction is shown in FIG. On one glass substrate 23, a display transparent electrode 25 for each pixel, an alignment film 10 and a thin film transistor 13 for driving the transparent electrode 25 are formed. A display transparent electrode 24 and an alignment film 10 are formed on the other glass substrate 22. The alignment film 10 is
It is made of polyimide. Opposing transparent electrodes 24,
Pixels B formed between 25 are, for example, squares of 200 μm in length and width, and are arranged in a matrix.
A band-shaped spacer 21 made of polyimide is provided at the center of the display transparent electrode forming the pixel B.
As a result, each pixel B is divided into regions I and II by the strip spacer 21. These divided regions I and II
Are typically formed as shown in FIG. That is, the above-described area division is performed on the other glass substrate 22 facing the one glass substrate 23. This glass substrate 2
The alignment films 3 and 22 on the liquid crystal surface are rubbed in the directions of the arrows shown in FIG.

A liquid crystal display device before this conventional example, for example,
TN in which the liquid crystal orientation is twisted in a 90 ° spiral between the upper and lower substrates
In the (twisted nematic) type liquid crystal display element, the viewing angle dependency of the display appears when the viewing angle direction, that is, the viewing direction, is inclined from the substrate vertical direction of the display element. And
Particularly, when the viewing angle direction is tilted during gradation display, a phenomenon called gradation inversion occurs in which the magnitude of the transmittance of each gradation is reversed. In this conventional example, the liquid crystal alignment in each of the divided regions has the same spiral twist direction but different angles with respect to the substrate surface. Since the rising directions of the liquid crystal molecules are different when a voltage is applied due to the difference in the angle with respect to the substrate surface, the respective regions compensate each other for optical characteristics when light is incident from an oblique direction inclined from the vertical direction with respect to the substrate. As a result, the viewing angle dependency when a voltage is applied is canceled by the regions of different orientations between the upper and lower substrates, and optical characteristics with little viewing angle dependency are obtained. In particular, the phenomenon of gradation inversion is no longer observed even when the viewing angle is changed during gradation display.

[0004]

However, when the viewing angle direction is changed in the liquid crystal display device having the conventional structure, the gradation inversion phenomenon is not seen up to a viewing angle of ± 40 degrees, but the entire display is within the viewing angle range. However, there is a drawback in that the phenomenon in which the display changes and the display floats white. This phenomenon of whitening occurs due to the following reasons. In the liquid crystal display element having the conventional structure, the characteristics of each other are mutually compensated by coexisting the orientations having different orientation directions. As a result, the characteristics are averaged in the upper and lower viewing angle directions.
Since the viewing angle dependency of the transmittance of black display in the N-type liquid crystal display element is too large, the change in transmittance of black display becomes large even if the average is averaged. In other words, in order to suppress the whitening phenomenon, it is necessary to suppress the change in the transmittance of black display, in particular, the increase in the transmittance. The cause of this increase in transmittance is the occurrence of positive optical anisotropy possessed by the liquid crystal alignment that rises due to voltage application.

It is an object of the present invention to provide a liquid crystal display device having a wide range of viewing angle characteristics, which is free from the phenomenon of grayscale inversion due to changes in viewing angle and whitening.

[0006]

The present invention provides a liquid crystal display device in which a liquid crystal substance is sandwiched between two supporting substrates and which has one or more compensating plates for compensating for optical characteristics. Having a plurality of regions having different liquid crystal orientations between the supporting substrates, and with respect to the refractive index of at least one compensating plate, there is almost no anisotropy of the in-plane refractive index in the direction parallel to the compensating plate surface, Further, at least one compensating plate having a refractive index in the direction perpendicular to the compensating plate surface is smaller than the in-plane refractive index, or by combining the compensating plates, a surface in the direction perpendicular to the combined compensating plate surface is provided. And at least one combination compensator configured so that the refractive index in the direction perpendicular to the plane of the combination compensator is smaller than the in-plane index of refraction. .

[0007]

1 is a sectional view of the liquid crystal display device of the present invention.
In the liquid crystal display element of the present invention, the liquid crystal substance 5 is sandwiched between two supporting substrates 4, and a plurality of regions having different liquid crystal alignment directions are provided between the supporting substrates. The characteristics of the respective regions are averaged by the alignment direction of the liquid crystal in the liquid crystal element 2 part. Further, such a structure has a positive refractive index anisotropy when a voltage is applied. The compensating plate or the combined compensating plate 1 according to the present invention has almost no anisotropy in the in-plane refractive index in the direction parallel to the compensating plate surface 8, and the in-plane refractive index in the direction perpendicular to the compensating plate surface. Since it is smaller than the refractive index, it has negative refractive index anisotropy in the direction perpendicular to the compensating plate surface. Compensation plate 1 when voltage is applied
A schematic view of the refractive index ellipsoid of the liquid crystal element 2 is shown in FIG. It can be seen that in the refractive index ellipsoid 6 of the liquid crystal element 2, the ellipsoids in the respective regions compensate each other. Further, the compensating plate or the combination compensating plate 1 has a negative refractive index anisotropy so as to compensate the positive optical anisotropy generated in the direction perpendicular to the substrate surface. As a result, good visual characteristics can be obtained regardless of the oblique direction of the viewing angle.

[0008]

Embodiments of the present invention will be described with reference to FIGS. FIG. 3 is a sectional view showing the first embodiment of the present invention. In this example, a thin film transistor made of amorphous silicon was used as an active element, and the size of one unit pixel was 100 μm square. The scanning electrode lines and the signal electrode lines were made of chromium (Cr) formed by a sputtering method and had a thickness of 10 μm. Silicon nitride (SiNx) was used for the gate insulating film 11. The pixel electrode 12 was formed by sputtering using ITO (indium tin oxide) which is a transparent electrode. The glass substrate on which the thin film transistors were formed in an array in this manner was used as a first supporting substrate. Further, on the second supporting substrate on the opposite side, color filters were formed in an array by a dyeing method, a protective layer using silica was provided on the upper surface, and a transparent electrode using ITO was further formed.

An alignment film 10 made of polyimide was applied on the first supporting substrate. A positive type resist was applied to the surface of the alignment film, and a mask on a stripe was used to divide a region between the center lines of adjacent pixels into a region for masking and a region for exposing. After developing the resist in the exposed area, rubbing treatment was performed. Furthermore, the resist is applied again, the mask area is reversed from the previous time, exposed and developed to remove the resist on the surface of the alignment film in the unrubbed area, and the surface is different from the previous rubbing direction by 180 °. Rubbing treatment. The second support substrate was also subjected to the alignment treatment in the same manner as the first support substrate, but the rubbing direction was twisted by 90 °. The two substrates were bonded together with an adhesive via a spacer made of silica particles, and nematic liquid crystal was injected as shown in the figure.

As the liquid crystal material, the main refractive index, that is, the refractive index for ordinary light is 1.486 and the refractive index anisotropy is 0.07.
6 was used, and the gap of the liquid crystal cell was 6.2 μm. At this time, the product of the refractive index anisotropy of the liquid crystal element and the thickness (Δ
n · d) was 471 nm.

The compensator 1 uses polycarbonate as a material, and has almost no refractive index anisotropy in the film plane by biaxial stretching, and the refractive index in the direction perpendicular to the film plane has an in-plane refractive index. The smaller one was produced. At this time, the product (Δn · d) of the refractive index anisotropy of the compensator and the cell gap is about 3
It was set to 50 nm. This condition is set so that the black display has the lowest transmittance when observed from a 60 ° viewing angle, that is, the black whitening is minimized. The vertical viewing angle dependence of the transmittance and the contrast ratio of the liquid crystal display device according to this example and the conventional liquid crystal display device not using the compensation plate are shown in FIGS. 4 and 9, respectively. The transmittance on the front side was 100%, 50% and 0%, the contrast ratio was 100% and 0%, and the contrast ratio was 50% and 0%. In the conventional liquid crystal display device, the transmissivity is symmetrical, and the viewing angle dependency is small, but the transmissivity of 0% is greatly increased. On the other hand, in the liquid crystal display device of the present invention, the rate of increase in the transmittance of 0% is much smaller than that in the conventional case. Further, it can be seen that the contrast ratio becomes high as a whole, and the contrast is obtained over a wide viewing angle range.

Further, as a second embodiment of the present invention, the liquid crystal panel section is manufactured in the same manner as in the first embodiment, and the product (Δn · d) of the refractive index anisotropy of the compensator and the cell gap is approximately. 235n
A product having a thickness of m was produced. In this embodiment, the increase in the transmittance of black display is larger than that in the first embodiment, but the conditions are such that the ratio of the difference in transmittance between gradations is maintained. FIG. 5 and FIG. 10 show changes in contrast ratio between the present embodiment and the conventional device and the difference in transmittance between gradations depending on the viewing angle. The ratio of the difference in transmittance between gradations is 100%
The value obtained by subtracting the transmittance of 50% from the transmittance of No. 1 was divided by the value of the transmittance of 50% minus 0%. In the conventional device, the ratio between the gradations is maintained only up to a viewing angle of about 30 °. On the other hand, in the device of this example,
Even if the viewing angle is tilted up to 60 °, the ratio of the transmittance between the gradations is kept at the value at the front, which shows that the gradation can be recognized correctly. As described above, by setting the conditions of the compensator, it is possible to correctly recognize the gradation over a wide viewing angle range.

Further, as a third embodiment of the present invention, an example in which a liquid crystal panel section is manufactured in the same manner as in the first embodiment and a combination compensating plate is used is shown. The combined compensator is a combination of two optically compensating biaxial compensators, and as a whole, there is almost no refractive index anisotropy in the plane of the combined compensator and refraction in the direction perpendicular to the combined compensator plane. The refractive index is smaller than the in-plane refractive index. At this time, the product (Δn · d) of the refractive index anisotropy of the compensator and the cell gap was set to about 350 nm as in the first embodiment. The combined compensating plate according to this embodiment showed almost the same characteristics as the compensating plate according to the first embodiment. Furthermore, as a fourth embodiment of the present invention, a liquid crystal panel section is manufactured in the same manner as in the first embodiment, two uniaxial films are arranged as a combination compensating plate, and an optical axis of each uniaxial film or the like is provided. An example using a combination compensating plate in which is arranged in a direction forming an angle of 90 ° is shown. At this time,
Product of refractive index anisotropy of compensator and cell gap (Δn · d)
Is about 350 nm as in the first embodiment. The combined compensating plate according to this embodiment exhibited almost the same characteristics as the compensating plate according to the first embodiment. As the combination compensator, in addition to the third and fourth embodiments described above, it is also possible to fabricate a set of combination compensators with three or more compensators.

Furthermore, as another embodiment, the value of the product of the refractive index anisotropy and the thickness of the compensating plate when the liquid crystal material is changed and the same conditions as those of the first and second embodiments are provided is shown. Table 1 below
Shown in.

[0015]

[Table 1]

Under any of the conditions, good display intended under each condition was obtained.

In all of the above embodiments, the same effect can be obtained even if the product of the thickness of the compensating plate or the combination compensating plate and the refractive index anisotropy is about 5 to 8 times the value shown here. However, the thickness of the compensator was significantly increased, which caused some trouble in practical use. Further, the product of the thickness of the compensating plate or the combination compensating plate and the refractive index anisotropy (Δn ·
When d) is equal to or twice the product of the thickness of the liquid crystal layer and its refractive index anisotropy, a significant decrease in transmittance of 100% occurs, and a transmittance of 100% and 50%. Phenomena such as inversion of the transmittance value occurred, and good viewing angle characteristics could not be obtained. Therefore, it is desired that the product (Δn · d) of the thickness of the compensator and the refractive index anisotropy is smaller than the product of the thickness of the liquid crystal layer and the refractive index anisotropy as used in the above-mentioned examples.

Further, in this embodiment, the compensating plate is arranged above the liquid crystal element part, but it may be arranged below the liquid crystal element part or divided into a plurality of compensating plates and arranged above and below the liquid crystal element part. However, the same effect was obtained. However, since there is an optimum value for the product of the thickness of the compensating plate or the combination compensating plate and the refractive index anisotropy, there is an optimum value, so some changes are necessary.

Further, in the above-mentioned embodiment, the normally white constitution is adopted in which the absorption axes of the polarizing plates arranged outside are orthogonal to each other, but the same effect is obtained in the normally black constitution in which the absorption axes of the polarizing plates are parallel. was gotten.

[0020]

According to the present invention, when the alignment direction of the liquid crystal is changed depending on the strength of the voltage application, the liquid crystal molecules are optically compensated within the pixel, and the positive refractive index difference caused by the voltage application is compensated. Since the compensator having negative anisotropy in the vertical direction compensates for the directionality, it is possible to obtain a liquid crystal display element having a wide viewing angle characteristic with no viewing angle dependency in both monochrome display and gradation display.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display element of the present invention.

FIG. 2 is a schematic view showing a state of a refractive index ellipsoid of a constituent element of the liquid crystal display element of the present invention when a voltage is applied.

FIG. 3 is a sectional view showing an embodiment of a liquid crystal display device according to the present invention.

FIG. 4 is a diagram showing the measurement results of the viewing angle dependence of the transmittance and the contrast ratio in the vertical direction during gradation display in the first embodiment of the liquid crystal display device according to the present invention.

FIG. 5 shows the results of measurement of the viewing angle dependence of the ratio of the difference in transmittance between gray scales in the vertical direction during gray scale display of the second embodiment of the liquid crystal display device according to the present invention. It is a figure.

FIG. 6 is a plan view of a conventional liquid crystal display element.

7 is a cross-sectional view taken along the line CC ′ of FIG.

FIG. 8 is a schematic diagram of a rubbing direction of a conventional liquid crystal display element.

FIG. 9 is a diagram showing measurement results of viewing angle dependence of transmittance and contrast ratio in the vertical direction during gradation display of a conventional liquid crystal display device.

FIG. 10 is a diagram showing a measurement result of a viewing angle dependence of a ratio of a difference in transmittance between gray scales in a vertical direction and a contrast ratio when displaying a gray scale of a conventional liquid crystal display element.

[Explanation of symbols]

1 Compensation plate or combination compensation plate 2 Liquid crystal element having regions having different alignment directions 3 Polarizing plate 4 Supporting substrate 5 Liquid crystal substance 6 Elliptic index ellipse of a liquid crystal device having regions having different alignment directions when voltage is applied Body 7 Compensation plate or refractive index ellipsoid of combination compensator 8 Compensation plate surface 9 Counter electrode 10 Alignment film 11 Insulating film 12 Pixel electrode 13 Thin film transistor

Claims (1)

[Claims] 1. A liquid crystal display device having a liquid crystal substance sandwiched between two supporting substrates and having one or more compensating plates for compensating for optical characteristics, wherein alignment of liquid crystals is provided between the supporting substrates. There are a plurality of regions having different directions, and with respect to the refractive index of at least one compensating plate, there is almost no anisotropy of the in-plane refractive index in the direction parallel to the compensating plate surface, and
There is at least one compensating plate whose refractive index in the direction perpendicular to the compensating plate surface is smaller than the in-plane refractive index, or by combining compensating plates, it is possible to combine A liquid crystal display device having almost no refractive index and having at least one combination compensating plate configured such that the refractive index in the direction perpendicular to the surface of the combination compensating plate is smaller than the in-plane refractive index.