JPH05134236A - Display device - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display device which uniformalizes a gradation display within picture elements and improves display quality. CONSTITUTION:At least either 1 of the electrode substrate surfaces facing each other of the matrix display device which clamps a ferroelectric liquid crystal between the electrode substrates and drives the ferroelectric liquid crystal by the electric field impressed via the electrodes provided on the electrode substrates have plural pieces of projections 2 or dents disposed periodically along the two directions within the plane.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Regarding a display element using a ferroelectric liquid crystal (hereinafter, also referred to as FLC), as shown in Japanese Patent Laid-Open No. 61-94023, two transparent electrodes are formed and oriented. Is known in which a ferroelectric liquid crystal is injected into a liquid crystal cell constituted by facing the glass substrates of (1) to (3) with a cell gap of about 1 to 3 μm maintained. The characteristics of the display device using the ferroelectric liquid crystal are that the coupling force between the spontaneous polarization of the ferroelectric liquid crystal and an external electric field can be used for switching, and that the long-axis direction of the ferroelectric liquid crystal molecule is the polarization direction of the spontaneous polarization. Since there is a one-to-one correspondence, switching can be performed depending on the polarity of the external electric field. As a ferroelectric liquid crystal, a chiral smectic liquid crystal (SmC) is generally used.
*, SmH *) is used, so that the long axis of the liquid crystal molecule exhibits twisted alignment in the bulk state.
The disposition of the long axis of the liquid crystal molecule can be eliminated by arranging the cell in a cell having a cell gap of the order of microns (NA. CLARK et al, MCLC (198).
3, Vo1.94, P213-P234)). An actual ferroelectric liquid crystal cell is constructed using, for example, a simple matrix substrate as shown in FIG. FIG. 3A is a cross-sectional view of the cell, in which 41 is a glass substrate, 42 is an ITO stripe electrode formed on the glass substrate 41, and 43.
Is an insulating film of silicon dioxide formed on the stripe electrode 42, 44 is an alignment film of polyimide formed on the insulating film 43, 45 is a sealing member, and 46 is a sealing member 4
5, which is a ferroelectric liquid crystal sealed in the cell. FIG. 3B is a plan view schematically showing the state of the stripe electrodes 42 formed on the substrate 41.

As a gradation display method using FLC, a pixel is divided and driven independently (dither method), and a potential gradient is generated in the pixel to divide a display area (potential gradient method). ), A method of applying a unidirectional electric field to the liquid crystal in a monostable state and controlling the displacement in the long axis direction of the liquid crystal molecule by the strength of the electric field, or by changing the thickness of the liquid crystal layer in the pixel. There has been proposed a method of performing gradation display by changing the electric field intensity applied to.

Regarding the method of changing the thickness of the liquid crystal layer in particular, the applicant has proposed a driving method, a shape of the electrode substrate, and a technique of aligning molecules.

That is, in a ferroelectric liquid crystal device in which a ferroelectric liquid crystal is sandwiched between electrode substrates, and the ferroelectric liquid crystal is driven by an electric field applied through electrodes provided on the electrode substrates, the opposing electrode substrate surfaces At least one of which has a stripe-like ridge-like shape periodically, whereby the cross section thereof is uneven, and the liquid crystal molecule is projected on the electrode substrate surface, and the liquid crystal layer normal is a stripe-like ridge. It is oriented so as to be orthogonal to the direction.

[0006]

However, in the above conventional example, since the ridge structure of the electrode substrate has a stripe shape as shown in FIG. 10, the pixel interior is reset to the black state as shown in FIG. When the tonal display is performed, the written areas are continuous in a stripe shape, and the stripes remarkably appear, thus deteriorating the display quality.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a liquid crystal display device in which gradation display in pixels is made uniform to improve display quality.

[0008]

In order to achieve the above object, in the present invention, a ferroelectric liquid crystal is sandwiched between electrode substrates, and a strong electric field is applied by an electric field applied through electrodes provided on the electrode substrates. In a matrix display device in which a dielectric liquid crystal is driven, at least one of opposing electrode substrate surfaces has a plurality of protrusions or depressions arranged periodically along two directions in a plane in a pixel. With this configuration, a plurality of domains serving as the cores of the writing area are scattered in the pixel, and the grayscale display appears to be uniform in the pixel.

[0009]

FIG. 1 shows the shape of one pixel of one electrode substrate of a liquid crystal device according to the first embodiment of the present invention. The same figure (a) is a perspective view, (b) is a top view and sectional drawing.
When a flat electrode substrate having no unevenness is used as the opposing electrodes, the display state in the pixel is as shown in FIG. As described above, when the conventional electrode substrate having a striped ridge-like shape is used, the display state is as shown in FIG. When the same gradation is displayed in a wide range of the display portion, stripes are conspicuous in the conventional example, but in the present embodiment, since the cores of the domains are dispersed, the gradation display looks uniform. Even in the conventional example, the same effect as that of this example can be expected by making the stripe interval invisible so as to be invisible. However, the point that a fine stripe is formed with high precision and the liquid crystal is stably aligned with the invisible fine stripe. It is difficult to realize it.

When analog gray scale is displayed by changing the electric field strength applied to the liquid crystal layer by changing the thickness of the liquid crystal layer in the pixel, the VT curve (transmittance with respect to the applied voltage V) is displayed. It is important that the change curve of T) be continuous and linear.

First, in order to be continuous, it is necessary that the opposing electrode substrates do not include planes parallel to each other in the pixel. For example, as shown in FIGS. 1 and 3, the pixel is entirely filled with irregularities. Further, in order to match the inclination of the VT curve for each pixel, it is desirable to form the unevenness in a cycle that matches the pixel size.

Next, in order to be linear, it is required that the amount of change in light quantity depending on the voltage ratio is always equal. In the Clark-Lagaval type SSFLC, one of the bistable states is aligned with the absorption axis on one side of two polarizers arranged in crossed Nicols. If this state is a dark state, the amount of transmitted light in the bright state is as shown in the following mathematical formula,
It largely depends on the cell thickness d.

[0013]

[Equation 1] Therefore, even in the bright state, the transmittance is greatly different between the thick cell portion and the thin cell portion. For example, the cell thickness is 1.0 μm
Assuming that the transmitted light amount at the location of 1 is 1, the transmitted light amount at the cell thickness of 1.5 μm is about 1.6. Therefore, in order to equalize the change in the light amount due to the voltage ratio, the transmittance for the same voltage ratio change It is desirable that a large area in the pixel is switched at a low area, and a small area is switched at a high transmittance area.

As a result of considering the above, in the present invention, the shape of one pixel portion of one electrode substrate 1 is formed as shown in FIG. That is, it has a shape in which four projections 2 having a square bottom surface and a ridge line being a parabola are arranged in the X direction and four in the Y direction. Figure 1
When a quadrangular pyramid is arranged instead of the protrusion 2, the amount of change in transmittance differs for the same change in voltage ratio, so it is necessary to correct the applied voltage before driving.

In this embodiment, the cell thickness is set to 2.0 μm at the thickest part of the liquid crystal layer and 1.5 μm at the thinnest part.

FIG. 5 shows a display device according to an embodiment of the present invention. This device includes a liquid crystal display unit 101 having a matrix electrode composed of a scanning electrode 201 and an information electrode 202 shown in FIG. 6, an information signal applying circuit 103 for applying an information signal to liquid crystal through the information electrode 202, and a scanning signal. A scanning signal applying circuit 102 for applying the liquid crystal to the liquid crystal through the scanning electrode 201, a scanning signal control circuit 104, an information signal control circuit 106, and a drive control circuit 105. Ferroelectric liquid crystal is arranged between the scanning electrode 201 and the information electrode 202. Reference numeral 107 denotes a graphic controller, and the data transmitted from this is the drive control circuit 105.
Through the scanning signal control circuit 104 and the information signal control circuit 1
It is input to 06 and converted into address data and display data, respectively. The scanning signal applying circuit 102 generates a scanning signal according to the address data, and the scanning signal is applied to the liquid crystal display unit 1.
01 to the scan electrode 201. Further, the information signal application circuit 103 generates an information signal according to the display data and applies it to the information electrode 202 of the liquid crystal display unit 101.

In FIG. 6, 222 is a scanning electrode 201.
A pixel, which is a display unit, is formed by the intersection of the information electrode 202 and the information electrode 202.

FIG. 7 is a partial sectional view of the liquid crystal display section 101. In the figure, 301 is an analyzer and 309 is a polarizer, which are arranged in crossed Nicols. 302 and 308 are glass substrates, and 303 and 3
Reference numeral 07 is an insulating film, 304 and 306 are alignment films, 305 is a ferroelectric liquid crystal, and 310 is a seal member.

The ferroelectric liquid crystal used in this example contains a pyrimidine component and has the characteristics shown in the following table.

[0020]

[Table 1] FIG. 3 shows the shape of one pixel of one electrode substrate 1 of the display device according to the second embodiment of the present invention. The same figure (a) is a perspective view, (b) is a top view and sectional drawing. The feature is that the projections 2 and the depressions 3 are arranged in a checkered pattern. As the electrodes facing each other, a flat electrode substrate without irregularities is used on the other side. With such a configuration, the display state in the pixel is as shown in FIG.
become that way. Compared with FIG. 2, the vertical and horizontal stripes are not conspicuous even in the case of 90% gradation display, and the display quality is further improved.

In each of the above embodiments, it is desirable that the height of the protrusion or the depth of the recess or the height difference between the protrusion and the recess is 1/6 to 1/3 of the thickness of the liquid crystal layer.

[0022]

As described above, in the present invention, the ferroelectric liquid crystal is sandwiched between the electrode substrates, and the ferroelectric liquid crystal is driven by the electric field applied through the electrodes provided on the electrode substrates. In a display device, at least one of opposing electrode substrate surfaces has a plurality of protrusions or depressions periodically arranged in two directions in a plane, so that a domain serving as a core of a writing region in the pixel is formed. There are a plurality of dots, and the gradation display is apparently uniform in the pixel, and the display quality is improved.

[Brief description of drawings]

1A and 1B are shape explanatory views showing an electrode substrate on one side according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of gradation display according to the first embodiment.

3 (a) and 3 (b) are shape explanatory views showing an electrode substrate on one side according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of gradation display according to a second embodiment.

FIG. 5 is a configuration diagram of a display device according to the present invention.

FIG. 6 is an enlarged view of a liquid crystal display unit of the display device according to the present invention.

FIG. 7 is a cross-sectional view of a liquid crystal display unit of the display device according to the present invention.

8A and 8B are waveform explanatory diagrams showing drive signals of the display device according to the present invention.

9A and 9B are explanatory views of a conventional technique.

FIG. 10 is a perspective view of a conventional electrode substrate.

FIG. 11 is an explanatory diagram of conventional gradation display.

[Explanation of symbols]

1; electrode substrate, 2; protrusion, 3; recess, 201, 20
2, electrodes.

Claims (5)

[Claims] 1. A matrix display device in which a ferroelectric liquid crystal is sandwiched between electrode substrates, and the ferroelectric liquid crystal is driven by an electric field applied through electrodes provided on the electrode substrates. At least one of the display devices has a plurality of protrusions or depressions in a pixel, which are periodically arranged along two directions in a plane. 2. The height of the protrusion or the depression is 1/6 to 1/3 of the thickness of the liquid crystal layer.
Display device. 3. The display device according to claim 1, wherein the projection has a rectangular bottom surface and the projection has a curved surface. 4. The recess is rectangular when viewed from above,
The display device according to claim 1, wherein the concave portion has a curved surface. 5. The display device according to claim 3, wherein the projections and the depressions are provided alternately along two directions orthogonal to each other.