JPS6060059B2 - Multilayer twisted nematic liquid crystal display - Google Patents

Description

Detailed Description of the Invention The present invention provides a so-called twisted nematic liquid crystal in which the helical axis is perpendicular to the two substrates and the long axis of the liquid crystal molecules is twisted substantially by 900 degrees between the substrates. The present invention relates to a multilayer twisted nematic liquid crystal display device in which liquid crystal display cells are inserted into multiple layers.

Twisted nematic liquid crystal display devices exhibit strong anisotropy, that is, visual dependence, in display contrast when an effective voltage is applied within three times the threshold voltage for optical effects when driving the liquid crystal. Known (Funada, Kamide/Wakuni, ΞTO; applied physics,
..., 86den 1975).

This visual dependence is determined by the twist direction (chirality) of the liquid crystal molecules and the slight tilt direction (tilt angle) of the liquid crystal molecules with respect to the substrate surface. Therefore, within the same liquid crystal cell, all liquid crystal molecules are aligned with the same chirality and tail angle, and the best contrast region resulting from this alignment is most often aligned with the direction in which the liquid crystal cell is observed. It is being This is important in manufacturing twisted nematic liquid crystal display devices to obtain high-quality display (Special Publication No. 1973-
258 hours). A driver circuit that multilayers the liquid crystal cells of the twisted nematic liquid crystal display device as described above, configures an electrode structure for partially applying an electric field to each liquid crystal layer, and applies a set voltage to each electrode. A multi-layer twisted nematic liquid crystal liquid crystal display device comprising a multi-layer twisted nematic liquid crystal display device has already been proposed in the specification of ``JP-A-50-794''.

The advantages of this type of multilayer twisted nematic liquid crystal display device, compared to a single layer device, include the following points. 1 Display designs can be diversified.

2 electro-optical logic circuits can be formed.

3. When displaying by multiplex driving, the number of picture elements can be increased by the number of layers if the voltage application time (duty factor) applied to each picture element is kept constant.

On the other hand, however, there is also the problem of deterioration in display quality, such as splitting of the display screen caused by multi-layering, which has been a major obstacle to practical use as a display device.

In view of the above-mentioned drawbacks of the present invention, by making full use of technical means, a new and useful display device having a characteristic electrode arrangement that does not cause the above-mentioned deterioration of display function even when the twisted nematic liquid crystal display cell is multilayered has been created. The purpose is to provide

FIG. 1 is a cross-sectional view showing the structure of a liquid crystal display device in which a conventionally commonly used twisted nematic liquid crystal cell has, for example, a two-layer structure. Three transparent substrates 1a, 1b, 1c made of glass or the like are arranged facing each other, and a nematic liquid crystal layer (or a cholestect liquid crystal layer with a long pitch) 2 is placed in the gap between each transparent substrate 1a, 1b, 1c.
a and 2b are interposed.

In addition, in order to apply a driving voltage to the liquid crystal layers 2a and 2b, 1n
Transparent electrodes 3a, 3b, 3c, 3d made of 203, etc. are formed on the transparent substrates 1a, 1b, 1c, and the transparent electrodes 3
a and 3b are connected to a voltage source 4a to drive the liquid crystal layer 2a, and transparent electrodes 3c and 3d are connected to a voltage source 4b to drive the liquid crystal layer 2b. Transparent electrodes 3a, 3b, 3c, 3d
And on the surfaces of the transparent substrates 1a, 1b, 1c facing the liquid crystal, alignment layers 5a, 5b are subjected to preferential alignment treatment to determine the molecular alignment of the liquid crystal by a wrapping method, an oblique evaporation method, etc.
, 5c, and 5d are coated. Transparent substrates 1a, 1b,
The periphery of 1c is sealed with sealing materials 6a and 6b made of epoxy resin, frit glass, etc., thereby forming a liquid crystal cell. Linear polarizing filters 7a, 7b such as yaws type or polyene type are provided on the outer surfaces of the transparent substrates 1a and 1c, and a scattering reflector plate 8 is placed on the back side of the liquid crystal cell. The polarizing filters 7a and 7b are used to visualize the display based on the orientation change of liquid crystal molecules. Transparent electrode 3
By applying a voltage to a, 3b, 3c, and 3d, a display is performed to the observer 9 through the optical effect based on the orientation change of the liquid crystal layers 2a, 2b. In particular, FIG. 2 schematically shows the divisions of the display area by taking out the electrode arrangement state in order to understand this conventional device in more detail.

Here, 10 is a division of the display area formed by the electrode groups 3a and 3b, and similarly, 11 is a division of the display area formed by the electrode groups 3c and 3d. In this case, the electrode arrangement is as follows when viewed from the normal direction (z direction) of the substrate of the liquid crystal cell:
The distance between the sections of the display area that divides the x-axis direction (bi) and the distance between the same kind of sections that occur at the places where each liquid crystal layer touches each other (r
) are made to be equal. By the way, Figure 3A
, B, when the twisted nematic field effect display cell 12 is multiplex driven, the viewing angle region 13 with good display contrast is not in the normal direction, but in the normal direction.
Depending on the orientation direction of the liquid crystal molecules, the viewing angle region is limited to a specific z-axis direction. Viewing angle as shown in Figure 3 (
When observing the conventional device (cell) shown in FIGS. 1 and 2 from 0), it is obvious that the apparent distance R between the display areas 10 and 11 due to projection.

'' depends on the viewing angle θ since the optical thickness l of the substrate 1b is finite. For example, in FIG. 4, if -00<0, then R. In the case of R.
″=r, and when θ>0, RO″>r.
In addition, in the case of θ to θ1, sections 10 and 11 of the display area
The result is that the two are superimposed. In this way, when observing the conventional cell as shown in FIG. 4 with θ>0 and θ of the effective viewing angle area shown in FIG. Distance R. '' is RO''>r, which is a different value compared to the distance r in the X-axis direction between sections in the same display area, and is displayed as a ゜゜ line on the display surface, resulting in a significant deterioration of display quality. The present invention has been developed to solve this drawback, and when driving a multilayer twisted nematic liquid crystal display device, the contrast ratio approximately becomes RJ=r when observed in the most effective viewing angle region. The present invention provides a multilayer liquid crystal display device in which electrode groups are arranged in a similar manner to eliminate "lines" on the display surface and maintain good display quality.

Hereinafter, the present invention will be explained in detail according to embodiments with reference to the drawings.

FIG. 5 is a diagram illustrating the main part of a multilayer liquid crystal display device using an XY matrix electrode structure, showing one embodiment of the present invention.

In order to facilitate understanding of the features of the present invention, FIG. 5 is shown as a schematic diagram in comparison with FIG. 4 of the conventional structure.

Note that the liquid crystal cell structure other than the electrode arrangement is the same as the structure shown in FIG.
Sono~3T! The transparent electrodes 3a, 3b, 3c, and 3d are made of soda glass having a thickness of about 100 ml and are patterned by etching or the like in accordance with the display, and the alignment layer 5a is made of In2O3.
, 5b, 5c. 5d uses SiO2 formed into a thin film by electron beam evaporation and then wrapped in a certain direction with cloth or the like. The liquid crystal layers 2a and 2b have a layer thickness of about 7 μm, and are made of biphenyl liquid crystal RO゛Ame 403 (manufactured by ROche) containing a very small amount of cholesteryl nonanoate.
Adopt. The sealing materials 6a and 6b are made of epoxy resin used for screen printing, etc., and the polarizing filter 7a
, 7b uses L-83-18 type manufactured by Sanritsu Electric. Further, the scattering reflector plate 8 is made of a sandblasted aluminum plate. The transparent substrates 1a and 1b constitute a liquid crystal cell on the display side, and the transparent substrates 1b and 1c constitute a liquid crystal cell on the rear side. The liquid crystal cells on the display side and the back side are stacked in two layers, and in the cell on the display side, a matrix display area is formed by matrix-shaped transparent electrodes 3a and 3b arranged in the upper half of the figure, and on the back side. In the cell, a matrix display area is formed by matrix-shaped transparent electrodes 3c and 3d arranged in the lower half of the figure. One display screen is formed by the two matrix display areas on the display surface side and the back side.

Here, at the boundary between the matrix display area on the display surface side and the matrix display area on the rear side, the transparent electrodes on the edges of both sides are arranged so as to overlap with each other, as shown in the figure. Twisted Nematetes! The viewing angle direction in which the contrast ratio of the liquid crystal display cell is highest is the direction that has an angle θ with respect to the normal direction of the display screen of the liquid crystal display cell.
Therefore, when observed from the direction of this angle θ, the matrix display areas on the display surface side and the back side appear to be spaced apart from each other, and this separation distance is determined by the arrangement pitch of the matrix electrodes. Almost corresponds. That is, r=-R
O''. With this arrangement, the display pattern displayed using different matrix display areas on the display surface side and the back side appears on the display screen as a continuous pattern, A display device with good display quality can be obtained.In this embodiment, the transparent electrodes 3a, 3b
, 3c, and 3d, and the liquid crystal cell is observed from a viewing angle area with good display contrast, the display areas of the two liquid crystal layers do not overlap each other, and there is no overlap between the display area sections. The distance R in the X-axis direction between the projections of the display area sections is compared with the distance r in the X-axis direction. The transparent electrodes 3a, 3b, 3c, 3
d group is arranged, each transparent electrode 3a, 3b, 3c,
A matrix type display corresponding to 3D selective voltage application is performed. By arranging the electrodes as in this example, when observing the liquid crystal cell from the effective viewing angle area, R
The condition J:r is satisfied, it becomes possible to prevent the appearance of ゜゜ lines on the display surface, and the display quality is improved. By the way, in the embodiment shown in FIG. 5, when observed from the normal direction and the 0<0 direction, the display area sections 10 and 11 overlap, but the twisted nematic field effect liquid crystal cell As for the optical properties of
Since the threshold voltage of the electro-optic effect in the region is high (see, for example, Oyoi Physics 43866 (1975)), the display contrast hardly or not changes at all even when superimposed, and there is no problem in practice.

As explained in detail above, according to the present invention, even if a twisted nematic liquid crystal display device is made of multiple layers, good display quality is maintained without deterioration of display function.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of a conventional multilayer twisted nematic liquid crystal display device. FIG. 2 is a schematic diagram illustrating the electrode arrangement state of FIG. 1. FIGS. 3A and 3B and FIG. 4 are explanatory diagrams illustrating the display form of the liquid crystal display device of FIG. 1. FIG. 5 is a schematic diagram showing one embodiment of the present invention. 1a, 1b, 1c...
・Transparent substrate, 2a, 2b...liquid crystal layer, 3a, 3b, 3
c, 3d...Transparent electrode.

Claims (1)

[Claims] 1 A plurality of liquid crystal display cells each containing a twisted nematic liquid crystal layer in which the long axes of liquid crystal molecules are oriented in a helical manner are stacked, and a matrix electrode that forms a display pattern is divided into each liquid crystal display cell, and each liquid crystal display In a multilayer twisted nematic liquid crystal display device in which matrix display areas formed for each cell are arranged in parallel to form one display screen, the display screen is oriented at an angle with respect to the normal direction that provides the best display contrast. The distance between each of the matrix display areas when observed from the direction of
A multilayer twisted nematic liquid crystal display device, characterized in that the matrix display area is arranged between each of the liquid crystal display cells at a position that is visually recognized to be approximately the arrangement pitch of the matrix electrodes.