JPH0695159A - Liquid crystal display - Google Patents

Abstract

(57) [Abstract] [Purpose] Compared with the one using a TFT, the number of steps is small, the minimum size of the device is relatively large, and defects such as dust are less likely to occur, and further the weight is reduced. (EN) A liquid crystal display device that has all of the above features, has a fast response speed, has a small viewing angle dependency, and can easily be formed into a large screen panel. A varistor element and pixel electrodes are arranged in a matrix-array on a transparent insulating substrate, and scanning electrodes are provided in the column direction of the pixel electrodes, while another transparent insulating film facing the transparent insulating substrate is provided. In a liquid crystal display device in which transparent data signal electrodes are arranged in stripes in the row direction of the pixel electrodes on a flexible substrate and a liquid crystal layer is provided in the gap between the pair of transparent insulating substrates, a polymer dispersed in the liquid crystal layer. A liquid crystal is used, and a flexible film is used as the other transparent insulating substrate facing each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image (including character) display device using a so-called liquid crystal, such as a liquid crystal display for a liquid crystal television or an office automation equipment, and particularly to an active matrix liquid crystal display device (hereinafter (Referred to as AMLCD).

[0002]

2. Description of the Related Art In the recent field of liquid crystal display devices, development of high-definition display elements with a lot of image information has been actively carried out.

When displaying an image having a large amount of image information, an AMLCD having a switching element for each liquid crystal pixel is provided.
However, it has excellent characteristics regarding image quality such as contrast and response speed. In particular, many active matrix (hereinafter referred to as AM) elements using thin film transistors have been commercialized.

Characteristic features of using the AM element are 1) large-capacity display, 2) fast response speed, and 3) relatively wide viewing angle. While it has many great advantages, it also has some serious drawbacks.

That is, in the manufacturing process of the thin film transistor, a very advanced fine processing technique must be used, and a process of stacking thin films of at least 5 layers or more is performed. Even in the normal case, it is a photolithography process using six or more photomasks. This process is complicated, and the cleanliness of the manufacturing environment must be the same as in the semiconductor memory device manufacturing process. Has become. Besides, in the semiconductor memory, one chip has a size of several millimeters square at the maximum,
The size of a substrate for use in a computer is several hundreds of millimeters square, which means it is several thousand times to tens of thousands times the area of a semiconductor memory, causing serious problems such as poor dimensional accuracy and defects such as dust. It's easy to do. Furthermore, in the case of a semiconductor memory, even if there is a defect, if the defective portion is not used as an element, the region other than that portion can be sufficiently used as a semiconductor memory as a whole. On the other hand, in the case of AMLCD, since the entire display area is used as a whole, the existence of defects is usually not allowed (except when allowed by the product standard). Further, as a problem of the structure of the thin film transistor itself, there are many wirings composed of thin films intersecting on the same substrate, and the structure is apt to cause defects in terms of disconnection and insulation. For example, if the insulation between the wirings is not maintained, a remarkable defect occurs in which line defects appear on the display screen when displayed.

Considering only the problem of cost reduction,
Simple matrix type (that is, AM element is not used)
A large number of liquid crystal display devices using STN liquid crystal are used in word processors, notebook computers, and the like. Regarding the response speed, although it is still in the research stage, it is reported that it is about the same as that using an AM device. However, as a liquid crystal display device, which has a production technology that is profitable as a product and can sufficiently satisfy the response speed and the viewing angle dependency, it has not yet been completed.

In addition, a liquid crystal display device having a light weight is also desired due to a demand for portability, weight reduction and cost reduction in the case of a large screen, and a thin glass substrate is considered. It is starting. However, it is technically difficult to handle large and thin glass substrates.
Considering cost, it is a big negative factor.

Due to the above-mentioned reasons, there is a big problem that the yield of the product is extremely low in the manufacturing process and the improvement is very difficult. Therefore, it is desired to develop an AM device having a structure that the process is simple, the number of steps is small, the risk of defects caused by dust is small, and the cost is low.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to reduce the number of steps and the minimum size of a device as compared with a device using a thin film transistor. We provide an AMLCD that is relatively large, is less likely to cause defects such as dust, and is lighter in weight, has a faster response speed, has a wider viewing angle, and can easily be made into a large-screen panel. To do.

[0010]

Means provided by the present invention for solving the above-mentioned problems are as follows: varistor elements and pixel electrodes are arranged in a matrix-array pattern on at least a transparent insulating substrate, and scanning is performed. Electrodes are provided in the column direction of the pixel electrodes, while transparent data signal electrodes are arranged in stripes in the row direction of the pixel electrodes on another transparent insulating substrate facing the transparent insulating substrate. In a liquid crystal display device in which a liquid crystal layer is provided in a space between the pair of transparent insulating substrates, a polymer-dispersed liquid crystal is used for at least the liquid crystal layer, and a flexible film is used for the other transparent insulating substrates facing each other. It is a liquid crystal display device characterized by using.

The present invention uses a varistor element, which is a two-terminal element, which has a simpler structure as an AM element than a thin film transistor, and uses a printing method which is easy to manufacture. After patterning the AM element by means of firing, a varistor element is obtained as a sintered body by firing. In addition, the liquid crystal display device uses a light and flexible film instead of the glass substrate which occupies most of the volume and weight among the components of the AMLCD.

[0012]

According to the present invention, since the sintered varistor element obtained by firing after patterning by the printing method is used as the AM element for the switching element for each pixel, compared to the case where the AM element is formed by using the thin film transistor. The number of steps is small, the yield can be improved, and the cost can be reduced. (FIG. 3) and (FIG. 4) show a manufacturing process diagram of the varistor element and a manufacturing process diagram of the thin film transistor, respectively. Further, since a film (PET film or the like) is used instead of the glass substrate as the opposing transparent insulating substrate, the weight can be reduced. Further, since cracks and chips are less likely to occur as compared with the glass substrate, there is an advantage that it is easy to handle.

By the way, the amorphous silicon thin film transistor used in combination with the TN liquid crystal these days is a switching element of a pixel for a liquid crystal display device due to problems such as deterioration of current value with time and shift of threshold voltage at the beginning of development. Was thought to be poorly adaptable. However, because the driving voltage of the liquid crystal used is low,
The anxieties have been gradually found to be overcome to some extent, and have reached the present. On the other hand, the polymer-dispersed liquid crystal (also known as polymer liquid crystal, polymer-dispersed liquid crystal, etc.) described in the present invention generally has a higher driving voltage than the TN liquid crystal. That is, a voltage higher than the operating voltage of the thin film transistor used in combination with the TN liquid crystal is required. It has been known that when the thin film transistor is used at a higher voltage than usual, the operating life of the thin film transistor is impaired. Therefore, the varistor element is suitable because it operates without problems even at a higher voltage than the thin film transistor and is suitable for driving the polymer dispersed liquid crystal.

[0014]

Embodiments of the present invention will be described in more detail with reference to the drawings.

(FIG. 1) and (FIG. 2) show an outline of a liquid crystal display device in which a varistor element is used and a PET film is used as an opposing transparent insulating substrate, as an embodiment of the present invention. FIG.

FIG. 3 is a flow chart showing an outline of a manufacturing process of a liquid crystal display device using a varistor element as one embodiment of the present invention. In addition, (FIG. 4) is a flowchart showing an outline of a conventional manufacturing process of a liquid crystal display device using a thin film transistor. Note that (FIG. 5) shows a schematic flowchart of the photolithography process repeatedly performed during the manufacturing process.

As shown in FIG. 2, the liquid crystal display device shown in this embodiment has a scanning electrode 11, a pixel electrode 12, and a varistor element 13 as an AM element on a glass substrate on the AM element side as a transparent insulating substrate 10. Is provided. Then, the data signal electrode 15 and the color filter 16, R (red), G
Polymer dispersion as a liquid crystal is provided between the opposing color filter side film substrate as the opposing transparent insulating substrate 18 provided with (green), B (blue) and BM (black matrix) 17 and the AM element side glass substrate. The mold liquid crystal 14 is filled. The polymer-dispersed liquid crystal 14 was applied with a blade coater to a constant film thickness and cured to secure a cell gap. Moreover, since the polymer-dispersed liquid crystal is used,
Alignment films for aligning the liquid crystal between the AM element side glass substrate and the liquid crystal 14 layer and between the counter color filter side film substrate and the liquid crystal 14 layer are not necessary. Also, A
This configuration does not require orthogonal polarizing plates on the outside of the M element side glass substrate and the opposing color filter side film substrate.

The manufacturing process will be described below. First, a metal Cr thin film is formed to a thickness of 0.1 μm on a glass substrate on the AM element side, which is the transparent insulating substrate 10, using a magnetron sputtering device, and a resist pattern is formed on this by a photolithography process. The scanning electrode 11 is formed with an etching solution. Next, a so-called ITO film (Indium Tin Oxide film) is formed using a magnetron sputtering device.
Is formed into a film having a thickness of 0.11 μm, a resist pattern is formed on the film with a photolithography process, and the ITO on the scanning electrode is formed by etching using an etching solution having a composition ratio of ferric chloride: hydrochloric acid = 1: 3. The electrode 19 and the pixel electrode 12 are formed.

Next, the varistor paste was transferred onto the AM element side glass substrate by a printing method using a 325 mesh screen plate. The varistor paste used here is mainly composed of varistor particles and polymethylmethacrylate. More specifically, 20 parts of varistor particles are used for 15 parts of polymethylmethacrylate, and 5 parts of ethyl carbitol as a solvent. The mixture was used. The varistor particles are formed on the surface of the ZnO single crystal particles by M
It is covered with an inorganic insulating film of an oxide such as n or Co.

The AM element side glass substrate to which the varistor paste has been transferred is baked by heating in the air at a temperature of 420 ° C. for 1 hour to remove polymethylmethacrylate and ethylcarbitol, as shown in FIG. Like A
The varistor particles 13 were fixed on the M element side glass substrate.

Next, a metal thin film of Cr is formed to a thickness of 0.1 μm on the film substrate for the opposing color filter by a magnetron sputtering apparatus, and the black matrix 17 is formed by the photolithography method. Further, in order to prevent a short circuit between the black matrix 17 and the data signal electrode 15, an insulating layer 20 made of SiO ₂ is formed and laminated. Next, a color filter 16 of three colors of R, G, and B is formed using a color resist, and then an ITO film is formed to a thickness of 0.15 μm using a magnetron sputtering device. At this time, the sheet resistance of the ITO film was 100Ω / □. Further, this ITO film was formed into a predetermined shape by a photolithography method to obtain a data signal electrode 15.

Next, the AM element side glass substrate was coated with the polymer dispersion type liquid crystal 14 using a blade coater to a film thickness of 15 μm, and then naturally dried. Then, the color filter 16 is applied to the AM element side glass substrate on which the epoxy resin seal pattern is printed by a screen printing machine.
The film substrate for the counter color filter, which is provided with the data signal electrode 15 made of the ITO film and the ITO film, is aligned and bonded by the aligner, and the pressure is 0.01 to 0.03 k.
Adhesion was performed by pressing and heating at gf / cm ² and a temperature of 80 ° C. for 1 hour.

As a result, the number of manufacturing steps is smaller than that of the thin film transistor, and a varistor element as a switching element is provided for each liquid crystal pixel, so that a liquid crystal display device having a high response speed and a relatively wide viewing angle can be obtained. It was In the present invention, in order to reduce the wiring resistance, it is possible to use, as a part of the data electrode, a metal thin film having relatively high conductivity such as Al, Cr and Ta.

[0024]

According to the constitution of the liquid crystal display device of the present invention,
By using the varistor element as the AM element, a printing method with a simple manufacturing process can be used, the manufacturing process is simplified as compared with the case of the thin film transistor, and the image quality is as high as that of the thin film transistor. It is possible to reduce the cost of portable liquid crystal displays that are not required. In addition, the viewing angle is wider and the response speed is faster than in the case without the AM element. In addition, a polymer-dispersed liquid crystal that does not require the polarizing plate used in TN liquid crystal, does not require cell gap control that controls the thickness of the liquid crystal layer, and does not require a seal to prevent the liquid crystal from leaking from the panel. By using it, it was possible to realize a film of the opposing transparent substrate. The use of a polarizing plate (TN liquid crystal in which a liquid crystal panel (glass substrate-liquid crystal-glass substrate) needs to be sandwiched between two polarizing plates) and the glass substrate are required to be isotropic.
If a film substrate is used instead of a glass substrate,
Since an ordinary film substrate is not isotropic, the transmitted light exhibits wavelength dependence (that is, it seems to be colored), and it is difficult to use it as a liquid crystal display. Since it is difficult to produce an isotropic film from the viewpoint of productivity, it has become possible to use a film substrate for a liquid crystal display only by using a polymer-dispersed liquid crystal that does not use a polarizing plate. In addition, by using a light-weight film substrate that is easy to handle without fear of cracking and chipping, it was possible to reduce the weight of the display, simplify the manufacturing process, and reduce the cost.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of a liquid crystal display device according to the present invention in a sectional view.

FIG. 2 is an explanatory view showing an embodiment of a liquid crystal display device according to the present invention, particularly one pixel in a sectional view.

FIG. 3 is a flow chart showing a manufacturing process of an embodiment of the liquid crystal display device according to the present invention.

FIG. 4 is a flowchart showing an example of a manufacturing process of a liquid crystal display device using a conventional thin film transistor.

FIG. 5 is a flowchart showing an example of a conventional photolithography process.

FIG. 6 is a flowchart showing an example of a conventional liquid crystal display device (using a glass substrate and a TN liquid crystal) about its manufacturing process.

FIG. 7 is a flow chart showing a manufacturing process of an embodiment of the liquid crystal display device of the present invention.

[Explanation of symbols]

10 ... Transparent insulating substrate (AM element side glass substrate) 11 ... Scan electrode 12 ... Pixel electrode (made of ITO) 13 ... Varistor element (AM element) 14 ... Polymer dispersed liquid crystal 15・ ・ ・ Data signal electrode 16 ・ ・ ・ Color filter (RGB) 17 ・ ・ ・ BM (black matrix) 18 ・ ・ ・ Transparent insulating substrate (opposite side color filter side ・ P
ET film substrate) 19 ... ITO electrode on scanning electrode 20 ... Insulating layer (SiO ₂ )

Claims (1)

[Claims] 1. A varistor element and pixel electrodes are arranged in a matrix-array form on at least a transparent insulating substrate, and scanning electrodes are provided in a column direction of the pixel electrodes, while another facing the transparent insulating substrate. In the liquid crystal display device, in which transparent data signal electrodes are arranged in stripes in the row direction of the pixel electrodes on the transparent insulating substrate, and a liquid crystal layer is provided in the gap between the pair of transparent insulating substrates, A liquid crystal display device, characterized in that a polymer-dispersed liquid crystal is used for a liquid crystal layer, and a film having flexibility is used for another transparent insulating substrate facing the liquid crystal layer.