JPH05224197A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To prevent the generation of a display defect by short circuiting by forming a light shielding mask of an oxide film formed by anodizing a metallic film under the conditions under which the metallic film is colored to a dark color over the entire thickness thereof. CONSTITUTION:The light shielding mask 20 to be provided on the substrate (TFT substrate) 1 formed with picture element electrodes 3 and thin-film transistors (TFTs) 4 of a pair of transparent substrates 1, 2 facing each other via a liquid crystal layer LC is formed of the oxide film formed by anodizing the metallic film under the conditions under which the metallic film is colored to the dark color over the entire thickness thereof. This light shielding mask 20 is formed on the picture element electrodes 3, the TFTs 4 and a transparent overcoat insulating film (SiN film, etc.) covering data line. The light shielding mask 20 is formed to a grid shape corresponding to the spacings between the rows and columns of the respective picture element electrodes 3, 3 in the same manner as with the conventional light shielding masks. The light shielding mask 10 has an insulating characteristic in such a case and the electrical short circuiting of the transparent electrodes 3, etc., on the substrate 1 provided with the light shielding mask with the light shielding mask 20 does not arise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a matrix type liquid crystal display device.

[0002]

2. Description of the Related Art In a matrix type liquid crystal display element, in order to prevent light leakage between pixels and improve display quality, one of a pair of transparent substrates facing each other with a liquid crystal layer interposed therebetween is formed on each of the transparent substrates. A light-shielding mask generally called a black mask is provided between the transparent electrodes.

FIG. 5 is a sectional view of a part of a conventional liquid crystal display device, and here, a liquid crystal display device of a TFT active matrix type is shown.

This liquid crystal display element includes a transparent pixel electrode 3 and its active element on one of a pair of transparent substrates (eg, glass plates) 1 and 2 facing each other across a liquid crystal layer LC. Thin film transistors (TFTs) 4 are arranged vertically and horizontally, a transparent counter electrode 7 that faces all pixel electrodes 3 is formed on the other substrate 2, and an alignment film 8 is formed on each of the substrates 1 and 2. 9 is formed, and the light shielding mask 10 is provided on the substrate 1 (hereinafter referred to as a TFT substrate) on which the pixel electrode 3 and the thin film transistor 4 are formed.

The thin film transistor 4 has an inverted stagger structure, and the thin film transistor 4 has a gate electrode G formed on the substrate 1 and Si N (silicon nitride) formed on the gate electrode G. A gate insulating film (transparent film) 5 made of, a semiconductor layer 6 made of a-Si (amorphous silicon) formed on the gate insulating film 5, and a source electrode S formed on the semiconductor layer 6. And a drain electrode D.

The gate electrode G of this thin film transistor 4
Is integrally formed with a gate line (not shown) wired on the substrate 1 so as to correspond to the rows of the pixel electrodes 3, and the gate insulating film 5 covers the gate electrode G and the gate line and covers almost the entire surface of the substrate 1. Has been formed. The pixel electrode 3 is formed on the gate insulating film 4, and one end of the pixel electrode 3 is connected to the source electrode S of the thin film transistor 4. Although not shown, data lines are provided on the gate insulating film 5 so as to correspond to the columns of the pixel electrodes 3, and the drain electrode D of the thin film transistor 4 is provided.
Is connected to the data line.

An overcoat insulating film (transparent film such as SiN) 11 is formed on the TFT substrate 1 to cover the pixel electrodes 3, the thin film transistors 4 and the data lines. It is formed on the film 11. The alignment film 8 on the TFT substrate 1 side
Are formed on the light-shielding mask 10.

The light-shielding mask 10 is generally made of a metal film which can be easily formed and patterned, and the light-shielding mask 10 is formed on the overcoat insulating film 11 with C.
It is formed by a method of forming a metal film of r (chrome) or the like and patterning the metal film into a lattice shape corresponding to the row and column of each pixel electrode 3, 3 by photolithography.

In the above liquid crystal display element, the light shielding mask 10 is provided on the TFT substrate 1. The light shielding mask is provided on the substrate 2 on which the counter electrode 7 is formed. This is because there is a gap between one side edge of the light-shielding mask and the pixel electrode 3 due to the alignment error between the first and second electrodes, and light leakage occurs at this portion. However, even in this case, if the width of the light-shielding mask is made sufficiently larger than the interval between the pixel electrodes 3 and 3 adjacent to each other, the light-shielding mask can be provided between the pixel electrodes 3 and 3 even if there is an alignment error between the substrates 1 and 2. Although the light can be surely shielded from light, the overlapping width of the pixel electrode 3 and the light shielding mask becomes large, and the light transmission area of the pixel electrode 3 is restricted, so that the aperture ratio of the liquid crystal display element is reduced.

On the other hand, when the light-shielding mask 10 is provided on the TFT substrate 1, even if an error occurs in the formation position of the light-shielding mask 10, this error is caused when the metal film is patterned by the photolithography method. It is within the alignment error of the exposure mask, and therefore the light shielding mask 10
Since it can be formed with high precision, the light-shielding mask 10 can reliably shield light between the pixel electrodes 3 and 3 without increasing the width of the light-shielding mask.

[0011]

However, in the above-mentioned conventional liquid crystal display element, since the light-shielding mask 10 corresponding to each pixel electrode 3, 3 is formed of a metal film such as Cr, the pixel electrode 3 and the thin film transistor are thin film transistors. 4 and the overcoat insulating film 11 covering the data line has a defect such as a pinhole or a crack, the source and drain electrodes S and D of the pixel electrode 3 and the thin film transistor 4 and the data line are formed on the overcoat insulating film 11. There is a problem that the liquid crystal display element becomes a defective product having a display defect by being electrically short-circuited with the formed light shielding mask 10.

Although FIG. 5 shows a liquid crystal display element in which the light shielding mask 10 is provided on the pixel electrode 3, the thin film transistor 4 and the overcoat insulating film 11 which covers the data line, the liquid crystal display element includes electrodes and the light shielding mask. A display defect due to a short circuit is caused by scanning a TFT active matrix type liquid crystal display element in which a light shielding mask is formed on a substrate and a thin film transistor and a pixel electrode are formed on an insulating film covering the light shielding mask, or one substrate. A simple matrix type in which an electrode is formed, a signal electrode orthogonal to the scanning electrode is formed on the other substrate, and a light-shielding mask is provided above or below the electrode formation surface of either substrate via an insulating film. It also occurs in liquid crystal display devices.

An object of the present invention is to provide a light-shielding mask made of a metal film on one substrate, but the transparent electrode or the like on the substrate provided with this light-shielding mask is electrically short-circuited with the light-shielding mask. It is an object of the present invention to provide a liquid crystal display element which can prevent the occurrence of a display defect due to a short circuit between a transparent electrode and the like and a light-shielding mask and can improve the manufacturing yield.

[0014]

According to the present invention, a transparent electrode for displaying a pixel is formed on each of a pair of transparent substrates facing each other with a liquid crystal layer interposed therebetween, and one of the substrates is formed on this substrate. The present invention is intended for a matrix-type liquid crystal display element in which a light-shielding mask is provided correspondingly between the transparent electrodes, and the first invention is a condition for coloring the light-shielding mask in a dark color over the entire thickness of the metal film. It is characterized in that it is formed of an oxide film anodized in.

A second invention is that the light-shielding mask comprises:
It is characterized in that the metal film is anodized over the entire thickness thereof under the condition that it becomes a porous film, and that this porous film is formed by an oxide film dyed in a dark color.

[0016]

According to the present invention, the light-shielding mask is anodized under the condition that the metal film is anodized under the condition that the metal film is colored dark over the entire thickness, or under the condition that the metal film is a porous film over the entire thickness. This light-shielding mask (oxide film) is insulative because it is oxidized and the porous film is formed of a dark-colored oxide film. Therefore, the transparent electrode on the substrate on which the light-shielding mask is provided is a light-shielding mask. There is no electrical short circuit with.

[0017]

【Example】

(Embodiment of the First Invention) An embodiment in which the first invention is applied to a TFT active matrix type liquid crystal display device will be described below with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view of a part of a liquid crystal display element, and FIG. 2 is a process drawing of a light-shielding mask provided on one of the substrates. 1 and 2
In FIG. 5, parts having the same configurations as those of the conventional liquid crystal display element shown in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted.

In the liquid crystal display element of this embodiment, as shown in FIG. 1, of a pair of transparent substrates 1 and 2 facing each other across a liquid crystal layer LC, a substrate (in which a pixel electrode 3 and a thin film transistor 4 are formed ( Hereinafter, the light-shielding mask 20 provided on the TFT substrate 1 is formed of an oxide film which is anodized under the condition that a metal film is colored in a dark color over the entire thickness thereof. And a transparent overcoat insulating film (SiN film or the like) 11 that covers the thin film transistor 4 and a data line (not shown). The light-shielding mask 20 is formed in a grid pattern corresponding to the row and column between the pixel electrodes 3 and 3, like the light-shielding mask in the conventional liquid crystal display element.

The light shielding mask 20 is formed by the following steps.

First, as shown in FIG. 2A, a pixel electrode 3, a thin film transistor 4 and a data line are formed on a substrate 1, and an overcoat insulating film 1 covering them is formed thereon.
1 is formed on the overcoat insulating film 11
Metal film 21 for light-shielding mask made of l (aluminum) or the like
Is formed by a sputtering apparatus.

Next, as shown in FIG. 2B, the light-shielding mask metal film 21 is patterned by photolithography to have a lattice shape corresponding to the rows and columns of the pixel electrodes 3 and 3.

Next, as shown in FIG. 2 (c), the patterned light-shielding mask metal film 21 is anodized over the entire thickness thereof under the condition that it is colored in a dark color, and the metal film 21 is colored in a dark color. The light-shielding mask (oxide film) 20 is colored.

The anodic oxidation of the metal film 21 for the light-shielding mask is performed by immersing the substrate 1 in an electrolytic solution so that the metal film 21 on the substrate 1 faces the counter electrode (platinum electrode) in the electrolytic solution. The film 21 is used as an anode and the counter electrode is used as a cathode, and a voltage is applied between both electrodes. Thus, when a voltage is applied between the metal film 21 and the counter electrode in the electrolytic solution, the metal film 21 as the anode undergoes a chemical conversion reaction in the electrolytic solution to be anodized. In this case, the metal film 21 is oxidized from the surface side thereof, but the oxidation depth is mainly determined by the applied voltage. Therefore, if the applied voltage is set in accordance with the film thickness of the metal film 21, the metal film 21 is formed. It can be oxidized over its entire thickness. Since the volume of the metal is increased by oxidizing the metal, the film thickness of the oxide film obtained by anodizing the metal film 21 becomes thicker than that before the oxidation.

The anodic oxidation of the light-shielding mask metal film 21 is carried out by using an electrolytic solution such that the oxide film produced becomes a darkly colored film. That is, for example, when the light-shielding mask metal film 21 is an Al film, its anodization is
A mixed solution of formaldehyde and boric acid or a mixed solution of 15% sulfosalicylic acid and 0.15% sulfuric acid is used as an electrolytic solution.

When the Al film is anodized using such an electrolytic solution, the resulting oxidized Al film becomes a colored film. In addition,
The color of this oxidized Al film is in the range from golden to black, but if the concentration of the electrolyte and the applied voltage are properly selected, a dark oxidized Al film of black or a color close to black can be produced. You can Also, this oxidized Al film has excellent light resistance,
Does not fade even when exposed to UV light for a long time.

In the above embodiment, the light shielding mask 20 is used.
Is formed of an oxide film which is anodized under the condition that the metal film 21 is colored in a dark color over the entire thickness thereof. Therefore, this light-shielding mask (oxide film) 20 is insulative, and therefore,
Even if the overcoat insulating film 11 covering the pixel electrode 3, the thin film transistor 4 and the data line has defects such as pinholes and cracks, the source and drain electrodes S and D of the pixel electrode 3 and the thin film transistor 4 and the data line are overcoated. Light-shielding mask 10 formed on insulating film 11
There is no electrical short circuit with.

Therefore, according to the liquid crystal display element of the above-mentioned embodiment, the TFT substrate 1 is provided with the light-shielding mask 20 made of the metal film 21 which can be easily formed and patterned. The production yield can be improved by eliminating the occurrence of a display defect due to a short circuit between the upper pixel electrode 3 and the light shielding mask 20.

(Embodiment of the Second Invention) Next, an embodiment of the second invention will be described with reference to FIGS. Figure 3
FIG. 4 is a cross-sectional view of a part of the liquid crystal display element, and FIG. 4 is a process drawing of a light-shielding mask provided on one of the substrates. Since the liquid crystal display element of this embodiment is also of the TFT active matrix type, the same components as those of the conventional liquid crystal display element shown in FIG. 5 are designated by the same reference numerals and their description is omitted. To do.

As shown in FIG. 3, the liquid crystal display element of this embodiment is a TFT substrate in which a pixel electrode 3 and a thin film transistor 4 are formed among a pair of transparent substrates 1 and 2 facing each other across a liquid crystal layer LC. 1. The light-shielding mask 30 provided on 1 is formed by anodizing a metal film over the entire thickness thereof under the condition that the film is a porous film, and at the same time, forming an oxide film of this porous film dyed in a dark color. , Pixel electrode 3
And a transparent overcoat insulating film 11 covering the thin film transistor 4 and a data line (not shown). The light-shielding mask 30 is formed in a grid pattern corresponding to the row-to-row and column-to-column correspondence of the pixel electrodes 3 and 3, like the light-shielding mask in the conventional liquid crystal display element.

The light shielding mask 30 is formed by the following steps.

First, as shown in FIG. 4A, the pixel electrode 3, the thin film transistor 4 and the data line are formed on the substrate 1, and the overcoat insulating film 1 covering them is formed thereon.
1 is formed on the overcoat insulating film 11
Metal film 31 for light-shielding mask made of l (aluminum) or the like
Is formed by a sputtering apparatus.

Next, as shown in FIG. 4B, the light shielding mask metal film 21 is patterned by photolithography into a lattice shape corresponding to the rows and columns of the pixel electrodes 3 and 3.

Next, as shown in FIG. 4C, the patterned light-shielding mask metal film 31 is anodized under the condition that it becomes a porous film over its entire thickness, and the metal film 31 is porous-oxidized. The film 31a is used.

For the anodic oxidation of the metal film 31 for the light-shielding mask, a 10 to 20% sulfuric acid solution is used as an electrolytic solution, and in this electrolytic solution, the metal film 31 is subjected to the same chemical conversion as that of the first embodiment of the invention described above. It is carried out by a method of causing a reaction. Also in this case, if the applied voltage is set according to the film thickness of the metal film 31,
The metal film 31 can be a porous oxide film 31a over its entire thickness.

Next, the substrate 1 in which the metal film 31 for the light-shielding mask is made into a porous oxide film 31a by anodic oxidation is immersed in a dyeing bath in which a dye of black or a color close to black is dissolved to immerse the porous oxide film in the porous oxide film. As shown in FIG. 4D, 31a is dyed in a dark color, and this porous oxide film 31a is used as a light shielding mask 30.

As the dye, for example, anthraquinone dye, monoazo dye, and zanthene dye are used. Since these dyes have excellent dyeing property to the porous oxide film 31a and have good light resistance, they do not fade even when irradiated with ultraviolet rays for a long time.

That is, in this embodiment, the light shielding mask 30 is used.
Is anodized under the condition that the metal film 31 is a porous film over the entire thickness thereof, and the porous film 31a is formed of an oxide film dyed in a dark color. The light shielding mask (oxide film) 30 is also insulated. Therefore, even if the overcoat insulating film 11 covering the pixel electrode 3 and the thin film transistor 4 and the data line has a defect such as a pinhole or a crack, the source and drain electrodes S and D of the pixel electrode 3 and the thin film transistor 4 and The data line is not electrically short-circuited with the light shielding mask 10 formed on the overcoat insulating film 11.

Therefore, even in the liquid crystal display element of the above embodiment, the TFT substrate 1 is provided with the light shielding mask 30 made of the metal film 31, but the pixel electrode 3 and the like on the TFT substrate 1 and the light shielding mask 30 are provided. It is possible to improve the production yield by eliminating the occurrence of display defects due to the short circuit with the.

Although the light-shielding masks 20 and 30 are provided on the overcoat insulating film 11 that covers the pixel electrodes 3, the thin film transistors 4 and the data lines in the above-described first and second embodiments, The light-shielding mask 20,
30 may be provided on the lower side of the pixel electrode 3 and the thin film transistor 4. In that case, the light shielding mask 20,
30 is formed, the transparent insulating film made of a SiN film or the like is formed thereon, and the thin film transistor 4 and the pixel electrode 3 are formed on the insulating film. However, the light-shielding mask 20,
Since 30 is an oxide film having an insulating property, the insulating film is not always necessary.

Further, the first and second inventions are not limited to the TFT active matrix type liquid crystal display element, but the scanning electrodes are formed on one substrate and the signal electrodes orthogonal to the scanning electrodes are formed on the other substrate. At the same time, it can be applied to a simple matrix type liquid crystal display element in which a light-shielding mask is provided above or below an electrode formation surface of either substrate with an insulating film interposed.

[0041]

According to the liquid crystal display element of the present invention, the light-shielding mask is an oxide film which is anodized under the condition that the metal film is colored in a dark color over the entire thickness, or the metal film is porous over the entire thickness. This light-shielding mask (oxide film) is insulative because it is anodized under the conditions that it becomes a film and this porous film is formed of a dark-colored oxide film, and therefore, on the substrate provided with the light-shielding mask. Since the transparent electrode does not electrically short-circuit with the light-shielding mask, even if one substrate is provided with a light-shielding mask made of a metal film, the display due to the short-circuiting between the transparent electrode and the light-shielding mask The production yield can be improved by eliminating the occurrence of defects.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a liquid crystal display element showing an embodiment of the first invention.

FIG. 2 is a process drawing of the same light-shielding mask.

FIG. 3 is a partial cross-sectional view of a liquid crystal display element showing an embodiment of the second invention.

FIG. 4 is a process drawing of similarly forming a light-shielding mask.

FIG. 5 is a partial cross-sectional view of a conventional liquid crystal display element.

[Explanation of symbols]

LC ... Liquid crystal layer, 1, 2 ... Substrate, 3 ... Pixel electrode, 4 ... Thin film transistor, G ... Gate electrode, 5 ... Gate insulating film, 6
... semiconductor layer, S ... source electrode, D ... drain electrode, 7 ...
Counter electrode, 8, 9 ... Alignment film, 11 ... Overcoat insulating layer, 20, 30 ... Shading mask 21, 31 ... Metal film, 3
1a ... Porous oxide film.

Claims (2)

[Claims] 1. A transparent electrode for displaying a pixel is formed on each of a pair of transparent substrates facing each other with a liquid crystal layer sandwiched therebetween, and one substrate is made to correspond to each transparent electrode formed on this substrate. In a matrix type liquid crystal display element provided with a light-shielding mask, the light-shielding mask is formed of an oxide film which is anodized under the condition that the metal film is colored in a dark color over the entire thickness thereof. 2. A transparent electrode for displaying a pixel is formed on each of a pair of transparent substrates facing each other with a liquid crystal layer interposed therebetween, and one substrate is provided between the transparent electrodes formed on this substrate. In a matrix-type liquid crystal display element provided with a light-shielding mask, the light-shielding mask is formed by anodizing a metal film over the entire thickness thereof under the condition that the film becomes a porous film, and the porous film is dyed in a dark color. A liquid crystal display device characterized by the above.