JPH0754387B2 - Liquid crystal display active matrix substrate - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display active matrix substrate composed of a plurality of X, Y matrix electrodes and thin film transistors driven at intersections thereof.

2. Description of the Related Art The active matrix display method in which a thin film transistor applies a potential to each picture element on a glass substrate of a conventional liquid crystal display device or EL display device, etc. Has been done.
In the future, as the area becomes larger and the definition becomes higher, the length and number of X, Y electrode busbars will increase, the probability of occurrence of electrode busbar disconnection will increase, and the yield will tend to decrease. As a countermeasure against the disconnection of the electrode bus bar, a redundant configuration in which a plurality of electrodes are wired has been considered. However, in the method of arranging a plurality of wirings on the substrate plane, the proportion of the electrode busbars on the substrate increases, the area of the pixel electrode decreases, and the aperture ratio decreases. On the other hand, it has been proposed to form the electrode bus bar with a multilayer structure in which materials having different etching resistance and resistance are laminated. This method has a redundant configuration without lowering the aperture ratio.

Problems to be Solved by the Invention In the above-described configuration, for example, in the configuration in which the electrode wiring is a multilayer film of a transparent electrode and a metal, etching is performed using a photoresist pattern with the same mask at the time of pattern formation. As shown in FIG. 3A, it is difficult to form the transparent electrode 31 on the substrate 30 in a structure having a width larger than that of the metal layer 32. Further, in the case of dry etching, the structure has a large step difference as shown in FIG. 3 (b), and in the case of etching with a solution, the structure has under-etching as shown in FIG. 3 (c). Cheap. When a thin film transistor is formed on the gate electrode formed as shown in FIGS. 3B and 3C, an insulating film defect is likely to occur, and the gate electrode and the source or drain electrode (not shown) are short-circuited. The probability was high.

On the other hand, when the transparent electrode and the metal are patterned by different masks to obtain a multilayer structure as shown in FIG. 3 (a), considering the mask alignment accuracy, the width of one layer is The gate structure as shown in FIG. 4 is extremely smaller than the width of the other layer, and the insulating layer 33, the semiconductor layer 34, and the semiconductor layer 34 are formed on the gate electrode including the transparent electrode 31 and the metal layer 32.
When the source electrode 35 and the drain electrode 36 are formed to form a thin film transistor having a channel length as short as possible, the semiconductor layer 34 of the channel portion has a structure that covers the step of the gate electrode. Is not uniform, and good transistor characteristics cannot be obtained.

The present invention solves the above-mentioned problems and can reduce the probability of short circuit between the gate electrode and the source or drain electrode due to the step of the gate electrode while the electrode busbar has a multi-layered structure and the occurrence of disconnection is less likely to occur. An object of the present invention is to provide a liquid crystal display active matrix substrate.

Means for Solving the Problems In order to solve the above problems, the present invention provides an active matrix substrate having a thin film transistor arranged at a portion where first and second electrode bus lines orthogonal to each other cross each other. An electrode busbar connected to the gate is composed of a multilayer structure of a transparent conductive film and a metal layer, a part of this metal layer is formed overhanging on an insulating substrate, and this overhanging part is formed as the gate of the thin film transistor channel part. Is.

With the above configuration, since the electrode bus bar has a multilayer structure,
The probability of disconnection is extremely low, and the gate of the thin film transistor channel part can be formed on the flat part because it is composed of the metal layer of the electrode bus line overhanging the insulating substrate, and the channel part covers the step of the gate electrode. Since it is not necessary to have a structure, the probability of short circuit between the gate electrode and the source electrode or the drain electrode is reduced, and good transistor characteristics can be maintained.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

1 and 2 are a plan view and a sectional view of an active matrix substrate showing an embodiment of the present invention. First
In FIG. 2 and FIG. ₂ , 50% SnO ₂ was deposited on the glass substrate 1.
It is formed by the atmospheric pressure CVD method, and the gate electrode bus 2a and the pixel electrode 2b which are transparent electrodes are formed by photoetching. Next, 1000 Å Cr was formed by DC sputtering method, and this was photo-etched to form the gate electrode bus bar of the transparent electrode.
A gate electrode busbar 3a, which is a metal layer, is formed on 2a, and a gate portion is formed on the glass substrate 1 so as to project from the gate electrode busbar 3a, and this gate portion 3b is used as a gate of the thin film transistor channel portion. . Therefore,
Gate part that constitutes the gate of the transistor channel part
3b has only one layer of Cr. Further, a Ta ₂ O ₅ film 4 is formed on the entire surface by a reactive sputtering method to a thickness of 2000 liters. Next, plasma CVD
The SiNx film 5 and the a-Si film 6 are continuously deposited by 2000 Å and 2000 Å, respectively. Then, the a-Si film 6 is left in an island shape above the gate portion 3b by photoetching. Further, after removing the Ta ₂ O ₅ film 4 and the SiNx film 5 on the pixel electrode 2b by etching, the n ⁺ a-Si film 7 is 500 Å by plasma CVD method,
The MoSi ₂ film 8 and the Al film 9 are each sputtered to 500
Å and 7000Å were formed and divided by photo etching at a position above the a-Si film 6 to form a source electrode and a drain electrode.

By adopting the gate structure as described above, in the case of the Cr single layer, there were no gate disconnections of 5 to 10 out of 240. When a two-layer structure of the gate electrode bus 2a made of SnO ₂ and the gate electrode bus 3a made of Cr was formed by the same mask, 5-30 cross-shorts occurred between the source electrode bus and the gate electrode bus. And this was all gone. Further, when the gate structure as shown in FIG. 4 was used, the mobility of a-SiTET was 0.2 cm ² / V · sec, whereas in the structure of this example, 0.8 cm ² / V · sec. Mobility was obtained.

In addition, although the example of SnO ₂ is shown as the transparent electrode in the present embodiment, the same applies to ITO, CdO, and ZnO.

Effects of the Invention According to the present invention, since the gate of the channel portion of the thin film transistor can be formed in the flat portion, the probability of occurrence of short circuit between the electrode busbars can be reduced, and it is extremely effective in preventing the occurrence of gate disconnection. Can be held satisfactorily.

[Brief description of drawings]

FIG. 1 is a plan view of an essential part of a liquid crystal display active matrix substrate showing an embodiment of the present invention, and FIG. 2 is a line A- in FIG.
A'line sectional view, FIG. 3 is a sectional view for explaining the defect of the multi-layer gate formed by the same mask, and FIG. 4 is a cross-sectional view for explaining the defect of the thin film transistor using the multi-layer gate formed by different masks. FIG. 1 …… Glass substrate, 2a …… Transparent gate electrode busbar, 2b ……
Pixel electrode, 3a ... Metal gate electrode busbar, 3b ... Gate part (gate of thin film transistor channel part), 6 ... a
-Si film, 8 ... MoSi film, 9 ... Al film.

Front page continuation (72) Inventor Takao Kawaguchi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Seiichi Nagata 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (56) References JP-A-62-205390 (JP, A) JP-A-62-276526 (JP, A) JP-A-62-288882 (JP, A)

Claims (1)

[Claims] 1. A first and a second electrode busbar groups formed on an insulating substrate and orthogonal to each other, and a thin film transistor arranged at a portion where the first and second electrode busbars intersect.
An active matrix substrate in which the first electrode busbar is connected to the gate of the thin film transistor and the second electrode busbar is connected to the source or drain of the thin film transistor, respectively, and the first electrode busbar is connected to the insulating substrate. A transparent conductive film formed above and a metal layer formed on the transparent conductive film and a part of the conductive film overhanging the insulating substrate to form a multi-layered structure. A liquid crystal display active matrix substrate having an overhang portion as a gate of the thin film transistor channel portion.