JP3049022B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a thin film transistor (T) as a switching element.
The present invention relates to a liquid crystal display device using FT) and forming an auxiliary capacitance between a pixel electrode and a gate wiring.

[0002]

2. Description of the Related Art A so-called gate storage type liquid crystal display device in which a thin film transistor (TFT) is used as a switching element and an auxiliary capacitance is formed between a pixel electrode and a gate line is conventionally known as a top view of FIG. A- in FIG.
As shown in the cross-sectional views of FIG. 5 along the line A ′, an auxiliary capacitance is formed by the gate wiring 3 and the pixel electrode 4. The pixel electrode 4 is formed on the gate wiring 3 on the glass substrate 7 via a gate insulating film 6 composed of a multilayer film of silicon nitride (SiN _x ) and silicon dioxide (SiO ₂ ). The drain wiring 1 is formed so that the longitudinal direction is orthogonal to the gate wiring 3, and the source electrode 5 is connected to the pixel electrode 4 via the island 2.

In this case, a large number of pixel electrodes 4 are arranged in a matrix, and a large number of TFTs are arranged correspondingly.
As one of the recent technological development trends in the liquid crystal display having such a configuration, there is a tendency to further increase the number of the pixel electrodes 4 (the number of pixels) to demand higher definition.

[0004]

However, in order to realize high definition, it is necessary to solve the following problems.

(1) The area of one pixel decreases in inverse proportion to the increase in the number of pixels.

(2) When the gate wiring and the drain wiring are made narrower in proportion to the pixel size, the wiring resistance increases and hinders the driving. Therefore, when the wiring width is made conventional, the aperture ratio decreases.

(3) As the pixel size decreases, the capacity for holding the potential decreases correspondingly, and a larger auxiliary capacity is required to compensate for this.

As described above, the aperture ratio of a pixel (= effective display area of one pixel / area of one pixel) is synergistically affected and greatly reduced due to high definition.

[0009] To show a specific example, the current number of pixels is 640x4.
For 80 VGA class liquid crystal display devices, generally 70%
Although an aperture ratio of the order of magnitude can be obtained, the S × 800 × 600 pixels
In the case of the VGA class, about 65%, and in the case of the XGA class with 769 × 1024 pixels, only an aperture ratio of about 60% can be obtained, and the brightness is reduced accordingly.

Therefore, as a countermeasure against the above, a method of increasing the luminance of a surface light source provided on the back of the pixel electrode can be considered. This countermeasure can have a certain improvement effect, but the power consumption increases. It is not preferable for portable use. In addition, there is a disadvantage that the leakage current is increased due to the TFT characteristics, and it is hard to say that this is an appropriate method.

A liquid crystal display device in which the aperture ratio is improved by forming the gate wiring and the source wiring with an opaque metal film having a reduced width and a transparent wiring portion, respectively, is also conventionally known (Japanese Unexamined Patent Application Publication No. Hei 8 (1996)). 69909 publication). However, in this conventional liquid crystal display device, since the gate wiring and the source wiring each have a two-layer structure, the number of PRs (the number of steps)
Will increase.

The present invention has been made in view of the above points,
It is an object of the present invention to provide a liquid crystal display device capable of improving an aperture ratio and achieving high definition without deteriorating other performances such as electric characteristics.

[0013]

In order to achieve the above object, the present invention provides a so-called gate storage type liquid crystal which uses a thin film transistor as a switching element and forms an auxiliary capacitance between a pixel electrode and a gate wiring. In a display device, a metal film in which a gate wiring is partially cut out only in a portion where an auxiliary capacitance is formed between the gate electrode and a pixel electrode,
Of the metal film
Is a transparent conductive film formed all over the bottom.
It has a two-layer structure .

According to the present invention, a portion of the metal film constituting the gate line forming the storage capacitor between the pixel electrode and the pixel electrode is cut away so as to cover at least the cut portion. Since the transparent conductive film is formed, an auxiliary capacitance can be secured between the pixel electrode and the metal film that is not cut, and light can be transmitted through the transparent conductive film.

[0015]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a top view of one embodiment of a liquid crystal display device according to the present invention, and FIG. 2 is a cross-sectional view taken along line BB 'in FIG. As in the conventional case, an auxiliary capacitance is formed by the gate line 8 and the pixel electrode 4. Note that silicon nitride (Si) is formed on the gate wiring 8 on the glass substrate 7.
The pixel electrode 4 is formed via a gate insulating film 6 composed of a multilayer film of N _x ) and silicon dioxide (SiO ₂ ).
Further, as shown in FIG. 1, the drain wiring 1 is formed so that the longitudinal direction is orthogonal to the gate wiring 8, and the source electrode 5 is connected to the pixel electrode 4 via the island 2. Further, an ITO film (storage ITO film) 8 which is a transparent conductive film is formed on the gate wiring 8.

Next, the manufacturing method of this embodiment will be described. First, as shown in FIG. 2, an amorphous-TFT is formed on a glass substrate 7 which is a transparent substrate. A gate film is formed on the glass substrate 7 by a sputtering method, and a gate wiring 8 is formed by etching the gate film using a row-shaped wiring pattern as a mask.
In the gate wiring 8, a portion forming an auxiliary capacitance is cut out in a concave shape.

That is, in the figure shown by 11 in FIG. 1, the side end of the pixel electrode 4 and the gate wiring 8 thereunder are conventionally formed with a certain width from the pixel electrode 4 as shown by 3 in FIG. However, in this embodiment, FIG.
2 is cut out (notched in a concave shape in the top view of FIG. 1) to reduce the width overlapping with the pixel electrode 4. The gate wiring 8 is usually made of chromium (Cr), but is notched in a concave shape, so that the width is narrow and the wiring resistance is high. Therefore, aluminum (Al) can also be used.

Next, as shown in FIGS. 1 and 2, an ITO film (storage ITO) is
A film 9 is formed. However, the gate electrode part is excluded. After the storage ITO film 9 is formed by a sputtering method, it is formed by etching using a row-shaped wiring pattern as a mask. The pattern of the ITO film 9 has a width which covers the concave portion (12 in FIG. 2) of the gate wiring 8,
In addition, it is formed on the entire surface of the gate wiring 8. The performance does not change whether the gate wiring 8 is formed on the upper layer or the lower layer. When the amorphous TFT is of a channel etch type, after forming a gate wiring 8 of Cr and a storage ITO film 9,
An SiO ₂ oxide film is formed by a sputtering method.

Next, in order to form an island 2 of a-Si, a two-layer structure is formed by using SiN having good interface characteristics with a-Si. This SiN film is formed on the island 2
Like (a-Si), a film is formed by a plasma CVD method. The island 2 (a-Si) has an i-layer (i-a-S
i) and an n-layer (n ⁺ a-Si) are formed. Next, the source electrode 5 and the drain wiring 1 made of a metal film are formed on the island 2 (a-Si). The drain wiring 1 is formed by forming a Cr film by a sputtering method and etching using a line-shaped wiring pattern as a mask. Subsequently, the source electrode 5 is formed by etching the ITO film formed by the sputtering method using the pixel electrode pattern as a mask.

As described above, in this embodiment, the gate wiring 8 is formed by connecting the storage film I with the metal film of the row wiring pattern.
By forming a two-layer structure with the TO film 9 and extending the pixel electrode 4 on the upper layer of the two-layer structure, an auxiliary capacitance is formed at a portion where the pixel electrode 4 overlaps with the gate wiring 8, so that an auxiliary capacitance is formed. Capacitance can be secured with almost no loss compared to the conventional structure, and since the metal film of the gate wiring 8 is concave, a cutout portion where the gate wiring 8 does not exist is transmitted even when irradiated with light, Pixel electrode 4 is storage I
Since the portion overlapping the TO film 9 can also be an effective display area, the aperture ratio can be improved.

When the luminance is the same as that of the conventional device, the density of pixels can be increased by an amount corresponding to the improvement of the aperture ratio, and a liquid crystal display device with high resolution can be realized.

Next, another embodiment of the present invention will be described. FIG. 3 shows a top view of another embodiment of the liquid crystal display device according to the present invention. In the figure, the same components as those of FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, the point that an amorphous-TFT is formed on a glass substrate 7 and the point that the gate wiring 8 forms a storage capacitor between the pixel electrode 4 and the storage capacitor is cut out in a concave shape are shown in FIGS. This embodiment is the same as the embodiment, except that the gate wiring 8
1 and 2 is that a storage ITO film 13 is formed in a portion excluding a gate electrode portion so as to cover only a concave portion of FIG.
This embodiment is different from the above embodiment.

In this embodiment, the storage ITO film 13 does not cover the entire surface of the gate wiring 8 but only the recessed portion of the gate wiring 8. The possibility of defective defects is reduced. The aperture ratio of this embodiment is shown in FIG.
2 is secured in the same manner as in the embodiment of FIG. Pixel electrode 4
This is because a portion overlapping with the storage ITO film 13 can also be an effective display area.

[0024]

As described above, according to the present invention,
A part of a metal film forming a gate wiring forming an auxiliary capacitance between the pixel electrode and the pixel electrode is cut away,
A transparent conductive film is formed so as to cover at least the notched portion, an auxiliary capacitance is secured between the pixel electrode and the uncut metal film, and light is transmitted through the transparent conductive film. In addition, the pixel electrode portion overlapping with the transparent conductive film can also be an effective display area, so that the aperture ratio can be increased and the luminance can be improved.

Further, according to the present invention, since the metal film and the transparent conductive film constitute a redundant wiring, even if one of the metal film and the transparent conductive film is disconnected, it can be replaced by the other which is not disconnected. effective.

Further, according to the present invention, when the luminance is the same as the conventional one, the density of pixels can be increased by an amount corresponding to the improvement of the aperture ratio, and a liquid crystal display device with high resolution can be realized.

[Brief description of the drawings]

FIG. 1 is a top view of one embodiment of the present invention.

FIG. 2 is a sectional view taken along the line B-B 'in FIG.

FIG. 3 is a top view of another embodiment of the present invention.

FIG. 4 is a top view of an example of the related art.

FIG. 5 is a sectional view taken along line A-A 'in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Drain electrode 2 Island 3 and 8 Gate electrode 4 Pixel electrode 5 Source electrode 6 Gate insulating film 9 and 13 Storage ITO film

Claims (5)

(57) [Claims] In a so-called gate storage type liquid crystal display device, wherein a thin film transistor is used as a switching element and an auxiliary capacitance is formed between a pixel electrode and a gate line, the gate line is connected to the pixel electrode. A metal film partially cut out only in a portion forming the auxiliary capacitance,
Covers the notched part of the film and partially covers the metal film
Transparent conductive film formed over the entire surface of the part or lower part
A liquid crystal display device having a two-layer structure . Wherein the metal film of the gate wiring, a liquid crystal display device according to claim 1, characterized in that it is made of aluminum or chromium. 3. A thin film transistor as a switching element.
And use an auxiliary capacitor between the pixel electrode and the gate wiring.
So-called gate storage type liquid crystal display that forms an amount
In the device, the gate line may be formed by forming a metal film partially cut out only at a portion where the storage capacitor is formed between the pixel electrode and the pixel electrode, and a cutout portion and the cutout portion of the metal film. corresponding liquid crystal display device is characterized in that the more becomes two-layered structure with a transparent conductive film formed only on the top or bottom of the metal film. 4. The liquid crystal display device according to claim 3, wherein the metal film of the gate wiring is made of aluminum or chromium. 5. The transparent conductive film is formed by a sputtering method so as to cover a notched portion of a metal film constituting the gate wiring, and then has a row-shaped wiring pattern having the same longitudinal direction as the gate wiring. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is formed by etching using a mask as a mask.