JPH04358127A - Thin film transistor type liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the electrostatic breakdown of a gate insulating film and a light leak near a drain electrode by providing a shield electrode among the drain electrode, the channel part of a TFT, and liquid crystal and applying nearly the same potential with a counter electrode. CONSTITUTION:A thin film transistor(TFT) substrate has a 1st insulating film 12, formed on a gate electrode 1, a 2nd insulating film 13 which is formed over the entire surface of the 1st insulating film except at the connection part between a source electrode 8 and a picture element electrode 4, and the shield electrode 11 which is formed over the entire surface of the 2nd insulating film except the connection part between the source electrode 8 and picture element electrode 4. Further, the substrate is equipped with a 3rd insulating film 14 which is formed over the entire surface of the shield electrode except at the connection part between the source electrode 8 and picture element electrode 4 and the picture element electrode 4 formed on the 3rd insulating film. In this case, a voltage inputted to the shield electrode 11 is nearly as high as a voltage inputted to the counter electrode of a counter electrode substrate. Then the shield electrode 11 and the electrode substrate which faces the TFT are electrically connected.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor type liquid crystal display device, and particularly to an electrode structure and pattern on a thin film transistor substrate thereof.

0002

[Prior Art] Conventionally, as a technology in this field, for example,
EID90-6, ED90-35, IE90-15, 1
The one described in ``Development of 0.4-inch color TFT-LCD'' is known. FIG. 5 is a partial cross-sectional view showing the structure of a thin film transistor (hereinafter referred to as "TFT") described in the above-mentioned literature.

Conventionally, thin film transistor type liquid crystal display devices (
The mainstream TFT structure in TFT-LCDs (hereinafter referred to as "TFT-LCD") has been an inverted staggered structure as shown in FIG. That is, the gate electrode 32 is formed at the bottom, and after the gate insulating film 34, semiconductor layer 35, and ohmic contact layer 36 are formed successively, the drain-source electrode 37 is formed.
, 38 are formed. Further, the pixel electrode 33 has drain-source electrodes 37 and 3 as shown in this figure.
There are some that are formed after 8 and others that are formed before 8, and either one is adopted. Finally, a passivation film 39 is provided.

0004

SUMMARY OF THE INVENTION However, these conventional TFT-LCD structures have several problems. First of all, in creating a TFT-LCD,
There is a process of applying an alignment film to the TFT substrate and rubbing it, but static electricity is likely to be generated during this process, resulting in shorting between the gate and drain electrodes or between the gate and source electrodes due to electrostatic breakdown of the gate insulating film. There was a problem with this.

Second, since the drain electrode is capacitively coupled to the liquid crystal layer above it, the drain signal enters the liquid crystal layer, causing light leakage near the drain electrode. An object of the present invention is to provide a TFT-LCD with excellent display quality by solving the above-mentioned problems of insulating film breakdown during rubbing and light leakage near the drain electrode.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a plurality of gate electrodes, a plurality of drain electrodes intersecting with the gate electrodes, a TFT provided at the intersection, and a TFT. In a TFT-LCD including a TFT substrate having a pixel electrode connected to a source electrode of the TFT substrate, and a counter electrode substrate facing the TFT substrate with a liquid crystal in between,
The TFT substrate includes a first insulating film formed on the gate electrode, a second insulating film formed on the first insulating film and on the entire surface other than the connecting portion between the source electrode and the pixel electrode, and 2. A shielding electrode formed on the insulating film and on the entire surface other than the connection portion between the source electrode and the pixel electrode; and and a pixel electrode formed on the third insulating film, and configured such that the voltage input to the shielding electrode is approximately the same as the voltage input to the counter electrode of the counter electrode substrate. .

[0007]

[Operation] According to the present invention, as described above, the TFT-LCD
, the voltage signal on the drain electrode is shielded by the shielding electrode and does not enter the liquid crystal layer. Furthermore, the storage capacitor formed between the shield electrode and the pixel electrode reduces downshifting of the pixel electrode voltage caused by the parasitic capacitance between the gate and source electrodes. Furthermore, a shielding electrode above the channel portion of the TFT prevents electrostatic breakdown of the gate insulating film.

[0008]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a plan view showing the electrode pattern of a TFT substrate in an embodiment of the present invention, and FIG. 2 is a part of the TFT substrate in an embodiment of the present invention (A-A' in FIG. 1).
FIG. First, as shown in FIGS. 1 and 2, the basic structure of the electrode pattern of the TFT substrate in this example is that a transistor with the semiconductor layer 3 as a channel is formed at the intersection of the gate electrode 1 and the drain electrode 2, and the source The electrode 8 and the pixel electrode 4 are electrically connected through the first through hole 6.

As shown in FIG. 2, a first insulating film 12 functioning as a gate insulating film is formed over the entire surface of the gate electrode 1 formed at the bottom. In this embodiment, the surface of the gate electrode 1 is anodized, and a gate anodic oxide film 9 is formed to prevent short circuit between the gate and drain electrodes 1 and 2. This first insulating film 1
A semiconductor layer 3 is formed on the semiconductor layer 2 in the pattern shown in FIG. The semiconductor layer 3 only needs to be provided in the channel portion of the transistor, but this pattern is used to reduce short circuits between the gate and drain electrodes 1 and 2.

[0010] There is an ohmic contact layer 10 on this semiconductor layer 3, and its pattern is formed in a portion where the drain electrode 2, the source electrode 8, and the semiconductor layer 3 overlap. The ohmic contact layer 10 also does not need to have this pattern,
This pattern is used for the same reason as above. On this ohmic contact layer 10, drain-source electrodes 2, 8
are formed in a pattern as shown in FIG. This pattern is quite common.

[0011] On the drain-source electrodes 2 and 8, a second
As shown in FIG.
It is formed on the entire surface except for. This second insulating film 13 is necessary to electrically disconnect the shielding electrode 11 and the drain-source electrodes 2 and 8, which will be formed later. On this second insulating film 13, a shielding electrode 11 made of a transparent material such as ITO is installed in the first and second through holes 6, 7.
1, and is shown as a shield electrode opening 5 in FIG. It can be seen that by adopting such a structure, the signal on the drain electrode 2 is shielded by the shielding electrode 11. Further, since the shield electrode 11 is also provided on the channel portion of the transistor, the channel portion of the transistor is electrically protected. Note that if the shield electrode 11 is formed on the gate electrode 1 except for the channel part of the transistor, a capacitance will be generated between the gate and the shield electrodes 1 and 11, and the gate voltage pulse will be distorted.
is not formed.

A third insulating film 14 is formed on the shielding electrode 11 except for the second through hole 7, and further, a pixel electrode 4 is formed on the third insulating film 14. Furthermore, the pixel electrode 4 is electrically connected to the source electrode 8 through first and second through holes 6 and 7. By forming the shield electrode 11 in this manner, the pattern of the pixel electrode 4 can be extended to the extent that it overlaps with the drain electrode 2. Furthermore, between the pixel electrode 4 and the shielding electrode 11, the pixel
Capacitance between shield electrodes can be provided.

FIG. 3 shows a TFT-L according to an embodiment of the present invention.
It is an equivalent circuit diagram per pixel of CD. As shown in this figure, a transistor 15 is arranged at a location where gate electrode 1 and drain electrode 2 intersect. Here, since the source electrode is electrically connected to the pixel electrode 4 through the first and second through holes, they are collectively shown as the pixel electrode 4. This pixel electrode 4 and the counter electrode 1 on the counter electrode substrate
7, there is a liquid crystal layer 16 between them. On the other hand, the shield electrode 11 has a pixel-shield electrode capacitance 19 made of the third insulating film in the overlapped portion with the pixel electrode 4, and
It also has a shield-drain electrode capacitance 20 made of the second insulating film.

In this way, capacitive coupling between the drain electrode 2 and the pixel electrode 4 is avoided by the shield electrode 11. Further, it is also possible to prevent signals on the drain electrode 2 from entering the liquid crystal layer 16. However, even in the present invention, the influence of the gate signal on the pixel electrode due to the existence of the capacitance 18 between the gate and source electrodes, that is, the shift down of the pixel electrode voltage remains, but the capacitance seen from the pixel electrode 4 is Since there is an intermediate capacity 19, the degree of downshifting is reduced, as is clear from the description in the above-mentioned document.

Here, it is necessary to prevent a potential difference greater than the threshold potential Vth for driving the liquid crystal from occurring between the shielding electrode 11 and the counter electrode 17. In this example, the shielding electrode 11 and the counter electrode 17 were electrically connected and the same signal was input. It is easy to make this electrical connection outside the TFT array because both the shielding electrode 11 and the counter electrode 17 are one solid electrode. In addition,
It is not necessary to input the same signal to the shielding electrode 11 and the counter electrode 17;
1, it is sufficient that the voltage is always below Vth in terms of direct current.

FIG. 4 shows a TFT-L according to an embodiment of the present invention.
FIG. 2 is an electrical block diagram of a CD. Gate driver, drain driver and counter electrode signal input are conventional TFT-L
This is also provided in the CD, and in this embodiment, it is only necessary to connect the counter electrode 17 and the shield electrode 11 and input a common signal from the input terminal 24, so the circuit is not complicated at all. There isn't.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0018]

As explained in detail above, according to the present invention, a shielding electrode is provided between the drain electrode, the channel portion of the TFT, and the liquid crystal, and a potential similar to that of the counter electrode is applied to the shielding electrode. It is possible to prevent electrostatic discharge damage to the insulating film at the time of use, and also to prevent light leakage near the drain electrode.

Furthermore, since a capacitor is provided between the pixel and the shield electrode, downshifting of the pixel electrode potential due to parasitic capacitance between the gate and source electrodes is reduced.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an electrode pattern of a TFT substrate in an example of the present invention.

FIG. 2 is a cross-sectional view (along line AA' in FIG. 1) of a portion of a TFT substrate in an embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram per pixel of a TFT-LCD according to an embodiment of the present invention.

FIG. 4 is an electrical block diagram of a TFT-LCD according to an embodiment of the present invention.

FIG. 5 is a partial cross-sectional view of a conventional TFT substrate.

[Explanation of symbols]

1 Gate electrode 2 Drain electrode 3 Semiconductor layer 4 Pixel electrode 5 Shield electrode opening 6 1st through hole 7 2nd through hole 8 Source electrode 11 Shielding electrode 12 First insulation film 13 Second insulating film 14 Third insulating film

Claims (2)

[Claims] 1. A thin film transistor substrate having a plurality of gate electrodes, a plurality of drain electrodes intersecting the gate electrodes, a thin film transistor provided at the intersection thereof, and a pixel electrode connected to the source electrode of the thin film transistor. , a thin film transistor type liquid crystal display device comprising a counter electrode substrate facing the thin film transistor substrate with a liquid crystal in between, the thin film transistor substrate comprising: (a) a first insulating film formed on the gate electrode; and (b) ) a second insulating film formed on the first insulating film and on the entire surface other than the connecting portion between the source electrode and the pixel electrode;
a shielding electrode formed on the second insulating film and on the entire surface other than the connecting portion between the source electrode and the pixel electrode;
) a third insulating film formed on the shielding electrode and on the entire surface other than the connecting portion between the source electrode and the pixel electrode;
e) the pixel electrode formed on the third insulating film, and the voltage input to the shielding electrode is made to be approximately the same as the voltage input to the counter electrode of the counter electrode substrate. Thin film transistor type liquid crystal display device. 2. The thin film transistor type liquid crystal display device according to claim 1, wherein the shield electrode and a counter electrode of an electrode substrate facing the thin film transistor are electrically connected.