JPH04362923A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To increase the contrast and reduce the irregularity by covering the outsides of insulating layers of an address conductor and a data conductor with conductive layers. CONSTITUTION:A thin film transistor substrate for an active matrix liquid crystal display element is manufactured. A pixel 1 and the conductors 3 and 4 are formed in a process similar to a normal active matrix. Then a chromium film of 100nm in thickness is further formed by sputtering and then the conductive layer of chromium is formed on a source conductor 3 (data line) and a gate conductor 4 (address line) by dry etching using photolithography. After the TFT substrate is thus manufactured, an LCD which has a color filter as a counter electrode is manufactured. Namely, a lateral electric field produced between the conductors 3 and 4 and pixel 1 or counter electrode is canceled by the electromagnetic shield effect of the conductive layer.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a liquid crystal display element.
In particular, it relates to a liquid crystal display element with less disclination within the display screen.

0002

BACKGROUND OF THE INVENTION A liquid crystal display (LCD) is composed of two glass plates facing each other with a liquid crystal layer of several micrometers in between.The inner surface of each glass plate is made of ITO (indium metal).
It is coated with a transparent electrode such as tin oxide). The transparent electrode within the display screen is divided into pixels of a shape and size depending on the display object, and each of these pixels is driven from the outside through wiring running on the glass surface.

[0003] Among liquid crystal display elements, active matrix type display elements, which are characterized by color display and high-quality display, are usually divided into pixels each having a size of several tens to hundreds of micrometers on one side of the glass. The pixels are driven by TFTs (thin film transistors) connected to each other.

A transparent electrode is formed integrally over the entire surface of the counter electrode, and in the case of color display, a color filter is further formed in contact with the transparent electrode. This T
In order to drive the FT, data wiring (source wiring) and address wiring (gate wiring) are installed on the TFT side substrate. By sequentially addressing the scanning lines using the address wiring and applying a predetermined voltage to the pixels using the data wiring, a predetermined voltage is written to all pixels. According to the voltage written in this way, the liquid crystal between each pixel and the counter electrode is driven, and the desired screen is displayed by changing the light transmittance of each pixel accordingly.

The active matrix method using such a driving method has advantages in image quality, such as fast response speed, good contrast, wide field of view, no crosstalk, and the ability to display halftones. There is. In addition, especially in color display, which has been attracting attention in recent years, the active matrix method has become mainstream because high image quality is required.

In order to control the light transmittance of pixels, the liquid crystal sandwiched between transparent electrodes must be oriented in a specific direction, and for this purpose, an alignment film is formed on the surface of the transparent electrodes. Ru. The alignment film is a thin film with a thickness of several tens to hundreds of μm formed of an organic polymer, an inorganic vapor deposited film, or the like, and recently polyimide is often used. Alignment films are processed to orient the liquid crystal in a predetermined direction, and in the case of polymer alignment films, rubbing is typical, and in the case of inorganic vapor-deposited films, control of the vapor deposition direction is typical. It is used as a method. Rubbing is an operation in which the polymer surface is rubbed in a specific direction with a material such as cloth, and the liquid crystal molecules are aligned in the rubbed direction parallel to the interface at the interface with the alignment film.

[0007] The alignment mode of the liquid crystal in the active matrix method is generally twisted nematic mode, and in this case, for example, the polyimide alignment film is arranged so that the pixel side and the counter electrode side are perpendicular to each other. Accordingly, the liquid crystal molecules are oriented parallel to the interface and perpendicular to each other on the pixel surface and the counter electrode surface, respectively, and in the middle of both surfaces, they are aligned continuously parallel to the interface. That direction will change. The liquid crystal molecules are oriented as described above when no voltage is applied between the pixel and the counter electrode, and as the voltage increases, they gradually become oriented in a direction perpendicular to the electrode plane.

[0008] When no voltage is applied, the polarized light that enters the liquid crystal is continuously rotated in accordance with the orientation of the liquid crystal molecules, and when it exits, it is rotated by 90 degrees with respect to the incident light. When a voltage is applied, the optical rotation of the emitted light decreases as the liquid crystal molecules become vertical, and when the voltage is sufficiently large, the polarization direction of the emitted light becomes the same as that of the incident light. By installing polarizing plates on both sides of the glass plate, the light transmittance can be controlled according to the magnitude of the applied voltage. Normally white mode is achieved when the optical axes of the polarizing plates are orthogonal to each other. - mode (white when no voltage is applied), and normally black mode (black when no voltage is applied) when parallel.

Note that FIG. 3 shows the TF of a conventional liquid crystal display element.
An enlarged view of the T-side pixel periphery is shown, where 1 is a pixel and 2 is a TFT. In addition, 7 is the source line and the gate.
This source line (data line) and gate line (address line) are both source lines with no conductive layer coating.
These are a gate line 9 without a conductive layer coating.

0010

[Problems to be Solved by the Invention] Active matrix liquid crystal display elements (AM-LCDs) have T
Address lines and data lines are arranged on the FT side, and
A write voltage remains in the pixel, and furthermore, a common electrode is formed over the entire surface of the opposing electrode. Voltages of different levels are applied to these electrodes, and therefore, an electric field corresponding to the voltage and electrode shape is formed between each of these electrodes. Among these electric fields, the electric field perpendicular to the pixel plane (vertical electric field) formed between the pixel and counter electrode is originally intended to drive liquid crystal molecules, but other electric fields teeth,
This has nothing to do with driving liquid crystal molecules.

As shown in FIG. 3, the width of the address line and data line is considerably narrower than the width of the pixel, so the area of the electric field generated from them should be a small ratio to the pixel surface. . However, due to the relatively large voltage level of the address line and the complicated shapes of the pixels and TFTs, the electric field actually formed within the pixel becomes complicated. Sometimes a directional vector component parallel to the pixel plane is added to the electric field vector (transverse electric field).

[0012] When such a transverse electric field is formed, a force is applied to the liquid crystal molecules to cause them to align laterally, resulting in a portion of the liquid crystal where the alignment direction of the liquid crystal molecules changes significantly. Places where such fluctuations in molecular orientation are extremely large often appear as a continuous line with a width of several μm, and within a display pixel, for example, in normally white mode, when all lights are on, Appears as a bright line when the surrounding area is black.

[0013] The bright line caused by such a large change in orientation will be tentatively referred to as disclination. In the original meaning of the theory of liquid crystal physical properties, disclination refers to a completely discontinuous line in the liquid crystal alignment layer, but in the present invention, the term "emission line" refers to the difference between the original disclination and the liquid crystal alignment layer. We will refer to both as large disturbances in orientation.

[0014] The brightness of the display screen changes due to the occurrence of disclination. For example, when a black screen is displayed in normally white mode, the part of the screen where disclination exists is darker than the original black. The screen becomes brighter, and as a result, phenomena such as a decrease in contrast and unevenness of the screen appear. This phenomenon is a major drawback to the image quality of LCDs.

[0015] As a result of intensive research aimed at suppressing the occurrence of disclination, the inventors of the present invention found that conventional liquid crystal display elements do not have a conductive layer coating.
The present invention was completed based on the knowledge that the above-mentioned disclination occurs because the gate wire 9 (see FIG. 3) is not coated with a conductive layer or conductive layer. be.

That is, an object of the present invention is to provide a liquid crystal display element that suppresses the occurrence of the above-mentioned disclination, or a liquid crystal display element that has extremely little disclination within the display screen.

[0017]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides electrical conductivity on the outside of the insulating layer of the address wiring and data wiring, which is the cause of the above-mentioned disclination. It is characterized by being covered with a layer of.

[0018]

[Operation] Due to the presence of such a conductive layer formed outside the wiring, the transverse electric field formed between the wiring and the pixel or counter electrode is canceled by the electromagnetic shielding effect of the conductive layer.

The material used for such a conductive layer may have a volume resistivity of 100 Ω·cm or less, and examples of such material include chromium,
Examples include metal materials such as tantalum, aluminum, and tungsten, and oxide conductors such as indium tin oxide (ITO) and tin antimony oxide (NESA).

[0020] The thickness of such a conductive layer is sufficient to be within the gap distance of the LCD (usually about several μm), and for example, it is sufficient to have a thickness of several tens to hundreds of layers, which is equivalent to the thickness of a wiring layer or a pixel layer. A sufficient disclination suppressing effect can be exhibited with a thickness of about nm. Therefore, the film for the conductive layer of the present invention can be formed by a process common to that for forming wiring and pixel films. The most commonly used such process is sputtering. The conductive layer thus formed is patterned by the same process as wiring and pixels. The most common means of such a process is
Photolithography processes such as wet etching and dry etching.

The conductive layer of the present invention and the wiring layer must be insulated, and in order to achieve this purpose, the existing insulation layer, which is formed outside the wiring layer in the conventional method, must be insulated. Using an insulating layer satisfactorily achieves this purpose.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to FIGS. 1 and 2 (enlarged views of the periphery of pixels on the TFT side of a liquid crystal display element according to an embodiment of the present invention).

(Embodiment 1) FIG. 1 is an enlarged view of the periphery of a pixel on the TFT side of a liquid crystal display element according to an embodiment of the present invention. In the figure, 1 is a pixel, 2 is a TFT, and 3 is a , a source line on which a chromium conductive layer is formed, 4 a gate line on which a chromium conductive layer is formed, and 7 an intersection between the source line and the gate line. .

[0024] The manufacturing method of this liquid crystal display element will be explained as follows.
First, a TFT substrate for an active matrix LCD, which is shown in the enlarged view shown in FIG. 1, was manufactured. Here, the pixel 1 and each wiring 3, 4 are formed by a process similar to that of a normal active matrix. after that,
Furthermore, a chromium film with a thickness of 100 nm was formed by sputtering, and then a dry film was formed by photolithography.
A conductive layer was formed on the source wiring (data line) and the gate wiring (address line) by etching. In this embodiment, the chromium layer corresponds to the conductive layer.

After producing the TFT substrate in this way,
An LCD using a color filter as a counter electrode was manufactured. L
The CD manufacturing process was carried out in exactly the same manner as the conventional manufacturing process.

Next, this LCD was actually driven at 60° C. for 240 hours, then returned to room temperature, and the display screen was observed. When observed with the naked eye, this LCD showed no unevenness, and its contrast ratio was 170 at the highest point. Furthermore, when the display screen was observed under a microscope, only 6 disclinations per 100 pixels were observed near the edges of the pixels.

(Embodiment 2) FIG. 2 is an enlarged view of the TFT side pixel periphery of a liquid crystal display element according to another embodiment of the present invention. In the figure, 1, 2, and 7 are the same as in FIG. , indicates the pixel, TFT, and the intersection of the source line and the gate line, 5
is a source line on which an ITO conductive layer is formed,
Moreover, 6 is a gate line on which an ITO conductive layer is formed.

[0028] The manufacturing method of this liquid crystal display element will be explained as follows.
First, a TFT substrate for an active matrix LCD, which is shown in the enlarged view shown in FIG. 2, was manufactured. Here, the pixel 1 and each wiring 5, 6 are formed by a process similar to that of a normal active matrix. Then,
After forming ITO for pixels with a thickness of 140 nm by sputtering, an etching pattern was used that, unlike conventional etching patterns, left the upper part of the source wiring and the upper part of the gate wiring in addition to the pixel. Dry etching was performed using the pattern. In this example, the ITO layer corresponds to the conductive layer.

After producing the TFT substrate in this way,
An LCD using a color filter as a counter electrode was manufactured. L
The CD manufacturing process was carried out in exactly the same manner as the conventional manufacturing process.

Next, this LCD was actually driven at 60° C. for 240 hours, then returned to room temperature, and the display screen was observed. When observed with the naked eye, this LCD showed no unevenness, and its contrast ratio was 150 at the highest point. Furthermore, when the display screen was observed under a microscope, only 9 disclinations per 100 pixels were observed near the edges of the pixels.

(Comparative Example) For comparison, the above-mentioned conventional liquid crystal display element based on FIG. 3 will be explained. As mentioned above, 8 and 9 in FIG. and a gate line without conductive layer coating.

First, a TFT substrate for an active matrix LCD as shown in the enlarged view shown in FIG. 3 was fabricated. Here, the pixel 1 and each wiring 8, 9 are formed by the same process as a normal active matrix. After producing a TFT substrate in this manner, an LCD was produced using a color filter as a counter electrode. L.C.
The manufacturing process of D was carried out in exactly the same manner as the conventional manufacturing process.

Next, this LCD was actually driven at 60° C. for 240 hours, then returned to room temperature, and the display screen was observed. When observed with the naked eye, this LCD had an extremely large amount of unevenness, and its contrast ratio was 120 at the highest point. Furthermore, when the display screen was observed under a microscope, 94 disclinations per 100 pixels were observed at the edges or in the center of the pixels.

[0034]

As explained above, the liquid crystal display element of the present invention has a structure in which the outside of the insulating layer of the address wiring and data wiring is covered with a conductive layer. This produces an effect of providing a high-quality screen with extremely little lination, and therefore high contrast and little unevenness.

[Brief explanation of drawings]

FIG. 1 is an enlarged view of the TFT-side pixel periphery of a liquid crystal display element according to an embodiment of the present invention.

FIG. 2 is an enlarged view of the TFT-side pixel periphery of a liquid crystal display element according to another embodiment of the present invention.

FIG. 3 is an enlarged view of the vicinity of a pixel on the TFT side of a conventional liquid crystal display element.

[Explanation of symbols]

1 Pixel 2 TFT 3 Source line 4 on which a chromium conductive layer is formed
Gate line 5 with a chromium conductive layer formed on the top Source line 6 with an ITO conductive layer formed on the top ITO on the top
Gate line 7 with a conductive layer formed Intersection of source line and gate line 8 Source line without conductive layer coating 9 Gate line without conductive layer coating

Claims (4)

[Claims] 1. A liquid crystal display element characterized in that the outside of wiring within a display screen is coated with a conductive material. 2. The liquid crystal display element according to claim 1, wherein the conductive material is a metal material or an oxide conductor having a volume resistivity of 100 Ω·cm or less. [Claim 3]Claim 1, wherein the conductive material is chromium.
The liquid crystal display element described in . 4. The liquid crystal display element according to claim 1, wherein the conductive material is indium tin oxide.