JPH10123547A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image display device enabling a multi-level display by forming a continuous change in electric field intensity by control of an applied voltage with a simple electrode shape. SOLUTION: A projecting part 25 making a section consisting of minute areas a half spherical shape is provided on the surface of a side that at least one side substrate 10a out of the substrates 10 holding a liquid crystal 30 in between is in contact with the liquid crystal. The projecting part 25 of the half spherical shape is provided with the top 25C with the highest height from the substrate, and its height is reduced gradually in the direction of a bottom edge part 25A, and the layer thickness of the liquid crystal layer 30 is changed. When the voltage is applied between electrodes, the continuous change in the electric field intensity making the effective applied voltage of the central part of the half spherical shape projecting part 25 maximum, and gradually reducing the effective applied voltage toward the terminal edge is formed, and the multi- level display is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device, and more particularly to an image display device using a liquid crystal.

[0002]

2. Description of the Related Art Conventionally, as a method of performing multi-gradation display of a liquid crystal display, there have been a method based on driving waveform control and a method based on pixel division driving. The driving waveform control method has a problem that the driving system is complicated, and the pixel division driving method requires high-definition patterning to obtain multiple gradations.

As a method of solving these problems, a step is formed on a substrate or an ITO electrode to form a step in the thickness of a liquid crystal layer in a pixel, and the electric field intensity applied to the liquid crystal layer is changed by the step to obtain an effective effect. There has been proposed a method of driving at different threshold voltages. However, in this method, the thickness of the liquid crystal layer is greatly different between a portion having a step and a portion having no step, so that the transmittance in the liquid crystal layer is different, and the contrast is lowered. As an invention in consideration of the problem of the decrease in contrast, Japanese Patent Application Laid-Open No. 3-48819 has been proposed.
Japanese Patent Application Laid-Open Publication No. H11-163873 proposes a liquid crystal display device in which “a convex portion or a concave portion formed of a minute region is provided on the surface of at least one of the two substrates constituting the display in contact with the liquid crystal”.

However, since the steps in the present invention are formed by convex or concave protrusions, the electric field strength between the electrodes sandwiching the liquid crystal layer partially and steeply differs within the pixel, and the multi-gradation display is performed. However, there has been a problem that a continuous change in the electric field intensity required in the method cannot be obtained.

[0005]

SUMMARY OF THE INVENTION Therefore, the present invention provides a method of reducing the density gradation by forming a continuous change in the electric field intensity without the electric field intensity between the electrodes in the pixel being partially steep. Accordingly, an object of the present invention is to provide an electrode structure that enables multi-tone display.

[0006]

According to the present invention, there is provided a display device having a liquid crystal disposed between two substrates, wherein at least one of the substrates sandwiching the liquid crystal has a hemispherical surface on a surface in contact with the liquid crystal.
Alternatively, it basically has a configuration having a projection in the shape of a kamaboko. The protruding portion of the substrate has a vertex having the highest height from the substrate, and gradually lowers its height in the hem portion direction. A configuration is provided in which the effective applied voltage at the central portion is maximized for each pixel and a continuous change in the electric field intensity is gradually reduced toward the edge for each pixel. The protruding portions are formed of the same material as the substrate or the same material as the electrode material.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the image display device of the present invention will be described with reference to the drawings. 1 and 2 show schematic cross sections of a liquid crystal display according to the present invention. The liquid crystal display 1 includes two glass substrates, a first glass substrate 10a, a second glass substrate 10b, a first ITO electrode 20a disposed on the first glass substrate 10a, and a second glass substrate 10.
b, a second ITO electrode 20b provided on the substrate b, and a liquid crystal layer 30 provided between the two substrates. Of the two glass substrates 10a and 10b sandwiching the liquid crystal layer 30, the ITO electrode 20a disposed on the first glass substrate 10a side has an ITO electrode 2a.
An electrode 25 formed of ITO, which is the same material as Oa, and having a mountain-shaped cross section is formed.

[0008] skirt 25 electrode 25 to the lowest top 25C for highest its height H _1, the height H ₃
A, consisting of progressively inclined portion 25B which forms a curved shape to lower the height H ₂ toward the hem portion 25A from the top 25C. A protruding ITO electrode 25 is provided on the first ITO electrode 20a.
Of the liquid crystal layer 30 where the substrate is formed has a thickness A (A region) between the substrates 10a and 10b, and a thickness C (C at the top 25C).
Area), and assuming that the thickness at a certain point of the inclined portion 25B which is an intermediate portion between the top and the hem is B (area B), the liquid crystal layer thickness is A
>B> C.

As described above, in the image display device, the portion where the protruding ITO electrode 25 is formed on the first substrate 10a has a different thickness of the liquid crystal layer at each location of the electrode 25. Gently changes and decreases due to the interposition of the inclined portion 25B having The difference in the thickness of the liquid crystal layer makes it possible to make a difference in the effective voltage in the A region, the B region, and the C region, for example.

[0010] Between the substrates thus configured, the first and second substrates
When a voltage is applied between the upper and lower electrodes 20a and 20b, the effective applied voltage is high in the region C where the liquid crystal layer is thinned, and the effective applied voltage is reduced as the thickness of the liquid crystal layer is increased. The polarization inversion always occurs from the region where the effective applied voltage is high. In other words, inversion starts gradually from a region C having a thickness C where the thickness of the liquid crystal is reduced, a region B where the thickness of the liquid crystal layer is gradually increased, the inversion region gradually spreads, and a thickness A having the largest thickness. Region A having the polarity is inverted. By this operation, the image display device in which the protruding electrode 25 having the curved section is formed can obtain a gradation display.

Next, another embodiment of the present invention will be described with reference to FIG. This image display apparatus has two glass substrates, a first glass substrate 10a, and a second glass substrate 10a.
b, and a first IT provided on the first glass substrate 10a.
It has an O electrode 200a, a second ITO electrode 200b disposed on the second glass substrate 10b, and a hemispherical projection 250 formed of a transparent material of the same material as the substrate.

The protrusion 250 is formed on the first glass substrate 10a, and the first ITO electrode 200a is formed on the first glass substrate 10a.
It is arranged above. Protrusion 250 is formed by a glass substrate of the same material, without a mountain-sectional shape, the skirt portion 250A of the height highest dimension h ₁ from the substrate 10a to the top portion 250C, to the lowest height dimension H ₃ And a slope 250B that forms a curved surface whose height is gradually reduced from the top 250C toward the hem 250A. The thickness of the liquid crystal layer 30 between the two electrodes at the portion where the protruding portion 250 is formed on the first substrate 10a is determined by the first substrate 10a and the second substrate 10b.
Assuming that the thickness between them is thickness A, the thickness C at the top 250C, and the thickness of the inclined portion 250B, which is an intermediate portion between the top and the hem, is B, the liquid crystal layer thickness has the relationship of A>B> C. Is shown. In the image display device according to the present embodiment configured as described above, the portion where the protrusion 250 is formed on the first substrate 10a has a different thickness of the liquid crystal layer at each position between the upper and lower electrodes 200a and 200b. These thicknesses gradually change and decrease due to the interposition of the inclined portion 250B having a curved cross section. Due to the difference in the thickness of the liquid crystal layer, the effective voltage in the A region, the B region, and the C region can be different. Then, between the first and second upper and lower electrodes 200a, 2
When a voltage is applied to the liquid crystal layer 00b, the thickness of the liquid crystal layer is reduced.
In the region, the effective applied voltage is high, and polarization inversion occurs first. Then, as the thickness of the liquid crystal layer increases, the inversion gradually spreads to the B region where the effective applied voltage decreases, and the A region having the thickest thickness A undergoes polarization inversion.

The image display device of this embodiment also has a
A gradation display can be obtained by the electrode 200a formed on the 50. Further, the image display device described in the above embodiment,
By changing the shape and height of the electrode and the projection, and the area within the pixel, an optimum gradation state can be obtained. According to the present invention, continuous gradation can be easily displayed by gradually changing the thickness of the liquid crystal layer provided between the two substrates. In this embodiment, the projecting portion is formed on one of the substrates sandwiching the liquid crystal.
The effect can be expected.

[0014]

Embodiment 1 Hereinafter, the present invention will be specifically described based on examples and comparative examples. FIG. 3 is a sectional view showing a main part of one embodiment of a liquid crystal substrate used in the image display device of the present invention, and FIG. 4 is a top view of the liquid crystal substrate. The liquid crystal substrate 100 has an upper glass substrate 100a, a lower glass substrate 100b, an upper electrode 80, a lower electrode 85, and a liquid crystal layer 130 disposed between upper and lower electrodes. An upper ITO electrode 80 is disposed on the upper glass substrate 100a. Then, a hemispherical protruding electrode 90 made of the same material as the upper ITO electrode 80 and having a hemispherical protruding portion having a curved cross section is provided for each pixel G. The hemispherical protruding electrode 90 is arranged at the center in the pixel G. Also, the alignment film 110 is formed so as to cover them.
a is arranged.

A lower glass substrate 100b is provided so as to face the upper glass substrate 100a. Lower glass substrate 100b
A lower ITO electrode 85 is arranged on the upper side so as to be orthogonal to the upper electrode 80. Further, an alignment film 110b is arranged so as to cover the lower ITO electrode 85. These upper and lower substrates 100
a and 100b are bonded via a spacer 120 so that the upper ITO electrode 80 and the lower electrode 85 face each other. A sealing material 140 is provided on the edge of the substrate, and the liquid crystal is sealed between the alignment films 110a and 110b so that the liquid crystal layer 13 is formed.
0 is formed. Furthermore, the liquid crystal layer 1 of the upper and lower electrodes 80 and 85
Polarizing plates 150a, 150a are provided on the surface opposite to the surface in contact with 30.
0b is provided to form a liquid crystal substrate.

The gradation display state when a voltage is applied to the upper and lower electrodes in the liquid crystal substrate 100 thus configured will be described. (2 × 2) pixels G on the liquid crystal substrate 100
FIG. 5 shows a gradation display state in the region. FIG. 6 shows the effective applied voltage between the ITO electrodes on the upper and lower substrates forming the respective states.

FIG. 5A: State in which no voltage is applied Since no polarization inversion occurs, the brightest display is performed. 5 (b) to 5 (d)... State in which the voltage is gradually increased. The domain inversion D occurs from the projection of the mountain-shaped projection electrode provided in the center of the pixel G, and the range of the domain inversion D gradually increases. Becomes larger. FIG. 5 (e)... State in which the voltage is increased The entire surface of the pixel G is inverted.

The reason why the domain-inverted region in the pixel G differs depending on the applied voltage will be described with reference to FIG. The graph of FIG. 6 shows a change in state from light to dark in each portion in the pixel region with respect to the voltage between the upper and lower ITO electrodes. In the respective portions indicated by S, T, Q, and R, S is the range of the tops 25C and 250 of the hemispherical electrode, T and Q are the ranges from the inclined portions 25B and 250B to the hem 25A and 250A, and R is This is a portion where no projection is provided. That is, the thickness of the liquid crystal is changed by the hemispherical electrode, and a difference is generated in the effective applied voltage between the electrodes in each part from the top to the bottom of the hemispherical electrode. Therefore, the state of the liquid crystal in each portion from S to R will be described by comparing the range S at the top of the hemispherical electrode where the largest difference occurs and the range R where no protrusion is provided.

At the apex of the hemispherical protruding electrode, the effective applied voltage between the upper and lower ITO electrodes is higher than in other regions in the pixel because the distance between the electrodes is shorter. Therefore, polarization inversion of the liquid crystal occurs first. And
By increasing the applied voltage to increase the distance between the electrodes, the slopes 25B, 250B are removed from the skirts 25A, 250B.
Polarization reversal of the liquid crystal occurs in the range of the portions T and Q to A. As described above, the polarization reversal gradually occurs from the apex of the hemispherical projection electrode having a high effective applied voltage. Also,
Since the protrusion for causing partial polarization inversion is hemispherical, the domain of domain inversion gradually expands concentrically with an increase in applied voltage. Therefore, continuous gradation can be generated by appropriate control of the voltage.

In this embodiment, the hemispherical projection is
Although formed by TO, a similar effect can be obtained by forming it on a glass substrate with a glaze material or the like.

[0021]

[Embodiment 2] This embodiment shows a case in which the shape of the electrode of the projecting portion is a semi-cylindrical shape. FIG. 7 shows a top view of the liquid crystal substrate in this embodiment. In a liquid crystal substrate composed of an upper electrode 80a and a lower electrode 85a, a semi-cylindrical projection electrode 900 is formed on the lower electrode 85a for each pixel. A gradation display state when a voltage is applied to the upper and lower electrodes in the liquid crystal substrate 1000 thus configured will be described. FIG. 8 shows a gradation display state in a (2 × 2) pixel G region on the liquid crystal substrate 1000. FIG. 8 (a)... No voltage is applied. Since no polarization inversion occurs, the brightest display is performed. 8 (b) to 8 (d)... A state where the voltage is gradually increased. A bump-shaped projection electrode 900 provided at the center of the pixel G.
The domain inversion D is generated from the protruding portion of, and the range of the domain inversion D gradually increases. FIG. 8 (e)... State in which the voltage has been increased.

As described above, the domain-inverted region in the pixel G differs depending on the applied voltage, the inversion starts from the top of the semi-cylindrical electrode, and gradually decreases to the effective applied voltage between the electrodes in each portion until the edge side. Will occur.

[0023]

According to the liquid crystal display of the present invention, the thickness of the liquid crystal layer is gradually changed by disposing a protruding electrode having a curved cross-section at a portion for applying a voltage to the liquid crystal, thereby causing polarization inversion in the liquid crystal. The region gradually expands continuously according to the voltage applied between the upper and lower electrodes, and even when a ferroelectric liquid crystal having a steep threshold is used, it is possible to easily realize good gradation display. Can be.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an outline of the present invention.

FIG. 2 is a sectional view showing an outline of another embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a cross section of the liquid crystal display device of the embodiment.

FIG. 4 is a top view of the liquid crystal display device according to the first embodiment.

FIG. 5 is a drive explanatory diagram of the liquid crystal display device according to the first embodiment.

FIG. 6 is a graph illustrating a driving applied voltage and a transmittance of the liquid crystal display device of the example.

FIG. 7 is a top view of the liquid crystal display device according to the second embodiment.

FIG. 8 is a drive explanatory diagram of the liquid crystal display device according to the second embodiment.

[Explanation of symbols]

10,100 glass substrate, 20,80,85,20
0 ITO electrode, 25, 90, 250, 900 projecting electrode, 110 alignment film, 120 spacer, 140
Sealing material, 150 Upper polarizing plate, G pixel area.

Claims (7)

[Claims] A projection formed on a surface of at least one of the substrates sandwiching the liquid crystal, the surface being in contact with the liquid crystal;
In a display device having a difference in the thickness of a liquid crystal layer disposed between substrates, a protrusion formed on the substrate has a top portion having a height from the substrate and an inclined portion having a curved cross section from the top portion to a hem portion. When a voltage is applied between the substrates, the effective applied voltage becomes maximum near the top in the portion where the protruding portion is provided, and the effective applied voltage gradually decreases from the inclined portion to the skirt portion, and the continuous electric field intensity changes. An image display device formed with. 2. The projection provided on at least one of the substrates sandwiching the liquid crystal is provided for each pixel, and the top of the projection is located at a position passing through the center of each pixel. 2. The image display device according to claim 1, wherein the effective applied voltage at the central portion is maximized, and a continuous change in the electric field intensity is formed to gradually reduce the effective applied voltage toward the edge. 3. The image display device according to claim 1, wherein the protrusion is formed of the same material as the substrate. 4. The image display device according to claim 1, wherein the protrusion is formed of the same material as the electrode. 5. The image forming apparatus according to claim 1, wherein the projection has a hemispherical shape. 6. The image display device according to claim 5, wherein the liquid crystal disposed between the two substrates has a portion whose thickness dimension is gradually increased concentrically from a portion whose thickness dimension is reduced. 7. The image display device according to claim 1, wherein the projecting portion has a semi-cylindrical shape.