JP3096098B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art One of the techniques for performing display using liquid crystal is a method of forming a transparent electrode pattern on a transparent substrate, installing a light source on the back surface, and recognizing a display image using the transmitted light. is there. However, this display method requires a lighting device,
Moreover, since it is usually used in a TN mode or an STN mode in which two polarizers are installed, the display tends to be dark, so it is necessary to make the illumination extremely bright, and it is very difficult to reduce the power consumption and the thickness. There was a disadvantage. or,
The same drawbacks as described above also exist in a method of providing a TFT (Thin Film Transistor) corresponding to each pixel as a liquid crystal driving element and installing a color filter and realizing a color display by light from a light source installed on the back surface. .
On the other hand, in recent years, polymer-dispersed liquid crystal display devices in which liquid crystal is dispersed in a polymer matrix have been proposed, but these are hardly affected by the thickness of a liquid crystal layer, can have a large area, and have a polarizing plate. It has attracted attention because it has features such as not requiring. Further, Japanese Patent Application Laid-Open No. 1-241520 discloses a technique for performing color display using this polymer dispersed liquid crystal in correspondence with a color filter. However, the method described in this publication also has the following disadvantages. That is, the state in which the liquid crystal transmits light is referred to as “O
N ”and“ O ”to turn off the light scattering state.
Even at the time of “FF”, light incident from the front side (display surface side) is scattered by the liquid crystal layer and transmitted through the color filter, so that it is difficult to obtain sufficient blackness in “black” display, and a sufficient contrast ratio is obtained. In the case of a structure using a light source from the back surface, the contrast ratio can be improved to some extent by increasing the luminance of the light source, but the display of “black” becomes whitish. In the case of using a structure using reflected light without using a light source from the back surface, the contrast ratio becomes particularly small. By using a polymer network type liquid crystal in which liquid crystal is dispersed in a three-dimensional network structure as the liquid crystal layer of the display element, advantages such as low voltage driving and excellent steepness can be obtained. In addition, JAPAN Display '89, p572-
At 575, the encapsulated liquid crystal is driven by the TFT,
Although a technique for performing display using lighting means has been disclosed,
These methods also have the following problems. That is, in the polymer network type and the encapsulated liquid crystal type (these are called PDLC), it is necessary to uniformly control the size of the network or the capsule in order to obtain a sufficient contrast ratio. Further, in order to reduce the applied voltage at the time of driving, it is necessary to uniformly control the size of the network or the capsule, and the size is appropriately about 2 to 3 μm. Further, in order to reduce the driving voltage, it is desirable to reduce the thickness of the liquid crystal layer. However, such control is difficult in practice, and causes considerable variation. Therefore, in order to obtain a certain contrast ratio, the film thickness is increased, and thus the driving voltage is increased. In addition, in these methods, a solvent used when forming a composite of liquid crystal and a polymer, an unreacted prepolymer, and impurities generated by decomposition of the liquid crystal or the prepolymer by ultraviolet rays are taken into the liquid crystal layer. In particular, there are concerns about reliability. In addition, since a number of polymer layers other than the liquid crystal are formed between the upper and lower electrodes, the voltage actually applied to the liquid crystal layer is reduced, and the driving voltage is increased.

[0003]

【Purpose】 . In order to reduce the applied voltage during driving, the thinner the liquid crystal layer, the better. In order to improve the scattering efficiency of incident light when no driving voltage is applied, it is better that the liquid crystal layer is thicker. If the thickness of the liquid crystal layer is different or the size of the liquid crystal layer is different, the difference in the thickness and size of the liquid crystal layer will cause a difference in the voltage required to enter the light transmitting state.
In order to solve at once the problem that the steepness when measuring the voltage-transmittance characteristics is deteriorated, the present invention controls the thickness and the size of the liquid crystal layer, thereby increasing the contrast ratio and increasing the steepness. It is an object of the present invention to provide a liquid crystal display device having a low driving voltage.

[0004]

A first aspect of the present invention has a structure in which a liquid crystal layer is sandwiched between a pair of substrates provided with liquid crystal driving electrodes, and the liquid crystal layer emits light depending on whether or not a voltage is applied. In a liquid crystal display device utilizing change to a state of scattering and a state of transmitting light, the liquid crystal layer is embedded in a layer of a fine uneven structure formed on at least one substrate with electrodes, A nonlinear switching element is provided corresponding to each pixel, and the nonlinear element corresponding to each pixel is provided on a substrate opposite to a substrate on which a fine uneven structure for controlling the thickness of a liquid crystal layer is formed. The present invention relates to a liquid crystal display device characterized by the following. A second aspect of the present invention has a structure in which a liquid crystal layer is sandwiched between a pair of substrates provided with liquid crystal driving electrodes, and the liquid crystal layer scatters light when a voltage is applied and when no voltage is applied. In a liquid crystal display device utilizing the change to a state where light is transmitted, the liquid crystal layer is embedded in a layer having a fine uneven structure formed on at least one substrate with electrodes, and each pixel has A non-linear switching element is provided correspondingly, and a fine concavo-convex structure for controlling the thickness of the liquid crystal layer is formed on at least one substrate. Which also serves as a flattening layer or a protective layer for a color filter. FIG. 1 is a diagram schematically showing a basic operation of a scattering type LCD used in the present invention. This liquid crystal display device has a structure in which a pair of substrates on which electrodes are formed are spaced apart and opposed to each other, and a liquid crystal layer is provided between them. The liquid crystal layer is formed of a polymer-dispersed liquid crystal in which liquid crystals are dispersed in a polymer matrix, or a film formed of a polymer network-type liquid crystal in which liquid crystals are dispersed in a three-dimensional network structure formed of a polymer, that is, a polymer network. .
In FIG. 1, reference numerals 1 and 2 denote substrates on which electrodes are formed, 3 denotes a switch, 4 denotes liquid crystal particles or liquid crystals in a network, and 5 denotes liquid crystal molecules. In the figure, 6 is incident light to the liquid crystal display device, and 6 'is transmitted light when the liquid crystal display device is in the ON state. FIG. 3A shows the state when no voltage is applied (off), and FIG. 3B shows the state when voltage is applied (on). In the present invention, the thickness of the liquid crystal layer showing the state of light scattering and light transmission is controlled by the fine concavo-convex structure formed on the substrate with electrodes, and the alignment state of liquid crystal molecules is also controlled by this fine concavo-convex structure. It has one feature. This is shown in FIG.
The liquid crystal molecules embedded in the concave portions of the fine uneven structure show the same behavior as the liquid crystal molecules in the capsule or the network in FIG. The "alignment" in the present invention does not uniformly align the whole like the alignment in the STN type liquid crystal display. When no voltage is applied, the liquid crystal molecules are oriented in random directions so that the incident light is irregularly reflected. By applying a voltage to the liquid crystal molecules, the liquid crystal molecules are aligned and the incident light is transmitted so that the light is transmitted. In order to utilize the operation as a shutter, the “control of the alignment state” in the present invention aims to realize the following two points. (I) In the state where no voltage is applied, incident light is sufficiently diffused and reflected. (Ii) The light transmission state is sufficiently and uniformly achieved with a low applied voltage. Therefore, the concave portion of the fine uneven structure becomes the thickness of the liquid crystal layer. In FIG. 1, the liquid crystal molecules are represented as spheres,
This is only a model, and in fact, a part of the liquid crystal layer exhibits the same behavior, and the liquid crystal molecules need not necessarily be confined in a closed space. FIG. 3 shows the shape and distribution of the fine uneven structure layer. The width of the portion holding the liquid crystal molecules is 2 to 5 μm, preferably 2 to 3 μm.
By setting m, the light scattering efficiency of liquid crystal molecules can be improved. That is, by making the alignment direction different for each region of about 2 to 5 μm, a light scattering structure is obtained when no voltage is applied. In particular, the arrangement pattern of the protrusions is more preferably as shown in FIG. 3A than in FIG. 3A, and a structure in which the width of the protrusion is smaller than the width of the recess is desirable. The drive voltage can be reduced by setting the thickness of the liquid crystal layer to 2 to 5 μm. In order to control the thickness of the liquid crystal layer only, the fine concavo-convex structure only needs to provide columnar portions in some places (FIG. 5A). It can be controlled by adjusting the existing interval. In addition, in order to further enhance the controllability of the alignment state, it is preferable that the underlying portion is made of the same alignment material, and therefore, the shape is as shown in FIG. 5B. The layer having the fine uneven structure may be provided only on one substrate side, but it is more effective to provide the layer on both sides. The fine concavo-convex structure can be provided in an arbitrary shape such as an island shape or a stripe shape, but an island shape as shown in FIG. 3 is more effective than a stripe shape. The shape of the convex portion does not hinder any of the shapes such as A, B, and C in FIG. Actually, A
In many cases, when the design is made in the form of B, it is often finished in the form of B.
Usually, the depth of the unevenness is about 2-5 μm, preferably 2-3 μm.
m, the pitch is preferably about 1 to 10 μm, preferably 4 to 6 μm, and the pitch is [(depth of unevenness) +
(The size of the convex portion)], and the size of the convex portion is preferably substantially the same as the depth of the unevenness. Generally, in a liquid crystal display device, a non-linear switching element or a color filter may be provided for each pixel. The non-linear switching element may be provided on a flattening layer having a function of flattening the element or a protective layer for protecting the non-linear switching element from liquid crystal.
In the liquid crystal display device of the present invention, a non-linear switching element or a color filter may be provided corresponding to each pixel as in the prior art. In this case, by providing a fine uneven structure layer on the flattening layer or the protective layer of the nonlinear switching element provided for each pixel, or on the flattening layer or the protective layer of the color filter, these layers and the fine uneven structure are provided. Layer can also be used. Then, as shown in FIG. 4, in the present invention, a layer having a fine uneven structure is provided on the substrate side where no nonlinear switching element is provided. A display method using light scattering of a liquid crystal layer includes a PC type (Phase Change:
Phase transition), DS type (Dynamic Scatteri)
ng), thermosetting type, or PDLC (polymer dispersion type liquid crystal and polymer network type liquid crystal are collectively described as follows) are known. When PDLC is used, rubbing for aligning liquid crystal molecules is performed. And other steps are not required, so that stable display quality can be easily obtained. But PD
Since LC has poor steepness as compared with a conventional STN type liquid crystal or the like, the duty ratio is 1/60 to 1 when a simple matrix drive such as an STN type liquid crystal display is performed.
The limit is about / 100, and it is considered difficult to increase the size of the display. Therefore, each pixel has a TFT,
If a non-linear element such as a TFD or MIM is used, the steepness as described above is not necessary, so that stable display quality, large screen, and high definition screen can be realized. As the TFT, normal stagger type or reverse stagger type amorphous silicon or polycrystalline silicon can be used. As a specific method for producing a layer having a fine uneven structure for controlling the thickness and alignment state of the liquid crystal layer, there is a method of forming a predetermined structure by etching a thin film formed on a substrate with electrodes.
Ultraviolet (light) is used as a material for forming the fine uneven structure.
By using a photolithography technique using a curable resin, a fine uneven structure can be similarly formed. Furthermore, a fine uneven structure can be formed using a stamper in which predetermined unevenness is formed on the surface of another substrate such as a metal plate by etching or the like. By controlling the thickness and alignment state of the liquid crystal layer by the fine uneven structure formed by such a method, the prepolymer and impurities of the liquid crystal layer may be concerned in a so-called polymer dispersion type or polymer matrix type liquid crystal. It is possible to provide a liquid crystal display device that is uniform, has high scattering efficiency, and is excellent in reliability without mixing. As the substrate, glass or a transparent polymer such as polyethylene terephthalate, polycarbonate, polyether sulfone, polyarylate, or the like can be used. In the case of a transmission type, a transparent electrode needs to be used as an electrode provided on the substrate, but in the case of a reflection type, one electrode does not need to be transparent. For example, when a non-linear switching element such as a TFT is formed on the substrate 2 side as in this embodiment, the electrode 4 on the substrate 2 does not need to be transparent, for example, Cr, Al, Ta, Ta / M.
Metal electrodes such as o and Cu can be used. As the liquid crystal, a normal nematic liquid crystal such as a cyanobiphenyl-based nematic liquid crystal or an ester-based, pyrimidine-based, or a mixture thereof can be used. As a material for forming the layer 5 having the fine uneven structure, besides an ultraviolet curing resin such as PMMA, an epoxy resin, an acrylic resin, polystyrene, polycarbonate, polyvinyl alcohol, a polymer compound such as siloxane or ester, polyimide, Ordinary polymer compounds such as polyamide can be used.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments. Embodiment 1 FIG. 4 shows a color liquid crystal display device according to an embodiment of the present invention. Glass was used as the substrate 1. The electrodes 7 and 8 on the substrates 1 and 2 are formed by patterning a transparent electrode (ITO) formed by sputtering by photolithography. A TFT 10 is formed for each pixel on the substrate 2 and performs a switching operation of a pixel electrode according to input data. In this embodiment, the TFT 10
The reverse stagger type using amorphous silicon was adopted. The fine concave-convex structure 9 for controlling the thickness and orientation state of the liquid crystal layer is formed by applying an ultraviolet-curable polymethyl methacrylate resin (PMMA) to the electrode side of the electrode-attached substrate 1 in a thickness of 2 μm, and then applying a metal stamper. Formed. The depth of the unevenness was 2.5 μm, the pitch was 5 μm, and the shape of the projection was a square prism having a base of 2 × 2 μm and a height of 2.5 μm. In this embodiment, a cyanobiphenyl nematic liquid crystal is used as the liquid crystal. As a result, the driving voltage can be made lower than that of the conventional device, and the steepness can be improved. Example 2 A photosensitive polyimide was used as a material for forming a microstructure 5 for controlling the thickness and alignment state of a liquid crystal layer. This was applied to the substrate 1 and then patterned to obtain a microstructure. Otherwise, a liquid crystal display device was manufactured in the same manner as in Example 1. In this example, the metal stamper was not used, but was manufactured by photolithography.

[0006]

(1) It is possible to accurately control the thickness of the liquid crystal layer, reduce the occurrence of display unevenness of the liquid crystal display element, and improve the display quality. (2) Compared with a polymer network type liquid crystal display device or a polymer dispersion type liquid crystal display device, it is possible to precisely control the alignment state of liquid crystal molecules, to improve a contrast ratio and a response speed, and to perform display. Quality can be improved. (3) The size of the liquid crystal layer can be controlled, and as a result, the efficiency of scattering visible light can be improved, and the contrast ratio can be improved. (4) The non-linear element corresponding to each pixel is formed on a substrate opposite to the substrate on which the fine structure for controlling the thickness and orientation of the liquid crystal layer is formed, so that the non-linear element is contaminated when the fine structure is formed. And damage can be prevented, and the yield at the time of manufacturing the liquid crystal display device can be improved. (5) The fine structure for controlling the thickness and orientation of the liquid crystal layer is:
When a non-linear element corresponding to each pixel, or a flattening layer of a color filter or a protective layer is also used, an increase in the number of steps for forming a fine structure can be suppressed to a minimum. Lowering of the yield can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a basic operation of a scattering type liquid crystal display device used in the present invention.

FIG. 2 is a sectional view showing one specific example of the liquid crystal display device of the present invention.

FIG. 3 shows (a) two specific examples of the fine concavo-convex structure of the present invention.
It is a figure shown to (b).

FIG. 4 is a cross-sectional view showing one specific example of the liquid crystal display device of the present invention when a TFT is used as a nonlinear switching element.

FIG. 5 is a sectional view showing two specific examples A and B of the fine uneven structure.

FIG. 6 shows a specific example A of the shape of the convex portion in the fine uneven structure.
It is sectional drawing which shows B and C.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Substrate 3 Switch 4 Liquid crystal 5 Liquid crystal molecule 6 Incident light 6 'Transmitted light 7 Electrode 8 Electrode 9 Fine unevenness part 10 TFT

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/1334 G02F 1/1335 505 G02F 1/1368

Claims (2)

(57) [Claims] 1. A structure in which a liquid crystal layer is sandwiched between a pair of substrates provided with liquid crystal driving electrodes. The liquid crystal layer scatters light when a voltage is applied and when no voltage is applied. In a liquid crystal display device utilizing the change to a state where light is transmitted, the liquid crystal layer is embedded in a layer of a fine uneven structure formed on at least one substrate with electrodes, and corresponds to each pixel. A non-linear switching element, and the non-linear element corresponding to each pixel is provided on a substrate on a side opposite to a substrate on which a fine uneven structure for controlling the thickness of a liquid crystal layer is formed. Display device. 2. A structure in which a liquid crystal layer is sandwiched between a pair of substrates provided with liquid crystal driving electrodes, wherein the liquid crystal layer scatters light when a voltage is applied and when no voltage is applied. In a liquid crystal display device utilizing the change to a state where light is transmitted, the liquid crystal layer is embedded in a layer of a fine uneven structure formed on at least one substrate with electrodes, and corresponds to each pixel. A non-linear switching element is provided, and a fine uneven structure for controlling the thickness of the liquid crystal layer is provided on at least one of the substrates. A liquid crystal display device, which also serves as a protective layer or a protective layer for a color filter.