JPH03113426A - Active matrix display device - Google Patents

Abstract

PURPOSE:To reduce the generation rate of a disconnection without deteriorating a numerical aperture of a display screen by providing an electrode for additional capacity opposed through a dielectric layer to a picture element electrode arranged like a matrix on the inside surface of one of a pair of substrates and forming this electrode for additional capacity like a mesh. CONSTITUTION:On a gate insulating film 6 of the side of a TFT 2, a picture element electrode 1 is brought to pattern formation, and the picture element electrode 1 is connected to a drain electrode 16. The end part of the opposite side to the TFT 2 of the picture element electrode 1 is superposed to an electrode 22 for additional capacity through an anodically oxized film 11 and the gate insulating film 6. In such a way, an additional capacity 27 is formed by the end part of the picture element electrode 1 and the electrode 22 for additional capacity. In this case, since the electrode 22 for additional capacity is like a mesh, a leakage electric field exists a great deal in the outside of an area in which the electrode 22 for additional capacity and the picture element electrode 1 are opposed to each other. In such a way, the additional capacity can be increased without causing the deterioration of a numerical aperture, and also, the generation of a disconnection of the electrode for additional capacity is reduced, and a display device having a high image quality is obtained with high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an active matrix display device with additional capacitance.

(Prior art) A matrix display device using liquid crystal or the like as a display medium is
It has been put to practical use in displays such as portable televisions, word processors, and personal convenience computers. Active matrix drive systems are often used in matrix display devices used in these devices. Active matrix display devices have the advantage of being able to display fine details.

FIG. 3 shows a plan view of an active matrix substrate used in a conventional display device. Figure 4 shows the TV in Figure 3.
A cross-sectional view taken along the rV line is shown. Picture element electrodes 1 are arranged in a matrix on an insulating substrate 5. Between the picture element electrodes 1, a source bus line 3 parallel to one direction and a gate bus line 4 orthogonal to the source bus line 3 are provided. There is an inverted staggered TFT on the gate bus wiring 4.
(Thin Film Transistor) 2 is formed. A source electrode 15 of the TFT 2 is connected to the source bus wiring 3, and a drain electrode 16 is connected to the picture element electrode 1.

A part of the gate bus wiring 4 functions as a gate electrode 4a of the TFT 2.

An additional capacitance electrode 12 is provided below the picture element electrode l in parallel to the gate bus wiring 4. Gate bus wiring 4
A gate insulating film 6, which will be described later, is formed over the entire surface between the additional capacitance electrode 12 and the picture element electrode 1. An additional capacitor 17 is formed between the picture element electrode 1 and the additional capacitor electrode 12.

The cross-sectional configuration of the TFT 2 and the additional capacitor 17 will be explained with reference to FIG. Gate bus wiring 4 on insulating substrate S
And an additional capacitance electrode 12 is patterned. An anodic oxide film 11 is formed on the additional capacitance electrode 12 . A gate insulating film 6 is formed on the entire surface, covering the gate bus wiring 4 and the additional capacitance electrode 12.

A semiconductor film 7 made of an intrinsic semiconductor amorphous silicon (hereinafter referred to as ra-3i(f)J) is formed on the portion of the gate bus wiring 4 functioning as the gate electrode 4a with a gate insulating film 6 interposed therebetween. There is. Semiconductor film 7
An insulating layer 8 is provided at the upper center. Furthermore, n-type amorphous silicon (hereinafter [
A contact layer 9.9 of a-Si(n″') is formed. A source electrode 15 and a drain electrode I6 are formed on the contact layer 9.9, respectively.

A picture element electrode 1 is patterned on the gate insulating film 6 on the side of the TFT 2 . Picture element electrode 1 is drain electrode 1
6. The end of the picture element electrode 1 on the opposite side from the TFT 2 is overlapped with the additional capacitance electrode 12 via the anodic oxide film 11 and the gate insulating film 6. As described above, the additional capacitor 17 is formed by the end of the picture element electrode 1 and the additional capacitor electrode 12. A protective film 10 is deposited over the entire surface, covering the TFT 2, the picture element electrode 1, and the additional capacitor 17.

An active matrix substrate having such a configuration,
A display medium such as a liquid crystal is sealed between the substrate and the counter substrate to form an active matrix display device.

The additional capacitor 17 is connected until the next gate-on signal is applied to the gate electrode 4a after a gate-on signal is input to the gate electrode 4a and a voltage is applied to the picture element electrode 1 via the source electrode 15. It is provided to maintain the potential of the picture element electrode 1.

Further, the additional capacitor 17 also plays the role of reducing a shift in the potential of the picture element electrode 1 caused by the overlapping capacitance between the gate electrode 4a and the drain electrode 16.

(Problem to be solved by the invention) In such a conventional active matrix display device,
In order to obtain a sufficient potential holding function of the additional capacitor 17, the area of the additional capacitor electrode 12 may be increased or the thickness of the gate insulating film 6 between the picture element electrode 1 and the additional capacitor electrode 12 may be reduced. was being carried out. However, when the area of the additional capacitance electrode 12 is increased, a problem arises in that the aperture ratio decreases in a transmissive display device. When the aperture ratio decreases, the amount of light transmitted becomes significantly small, resulting in a decrease in image quality. Therefore, in order to obtain sufficient image quality, it is necessary to make the backlight extremely strong, which requires a large amount of power. On the other hand, when the thickness of the gate insulating film 6 is reduced, a problem arises in that leakage is likely to occur between the picture element electrode 1 and the additional capacitance electrode 12. Furthermore, display devices equipped with an additional capacitor have fundamental problems such as foreign matter mixed in during the formation of the additional capacitor electrode 12 and breakage of the additional capacitor electrode 12 due to cracks or the like.

The present invention solves these problems, and an object of the present invention is to provide an additional capacitor that has sufficient potential retention characteristics, does not reduce the aperture ratio of a display screen, and has a low probability of disconnection. An object of the present invention is to provide an active matrix display device having electrodes for use in the present invention.

(Means for Solving the Problems) The active matrix display device of the present invention includes a pair of insulating substrates, pixel electrodes arranged in a matrix on the inner surface of one of the pair of substrates, and An active matrix display device comprising an electrode for additional capacitance facing an element electrode with a dielectric layer interposed therebetween, the electrode for additional capacitance forming a mesh shape, whereby the above object is achieved. .

Further, the shape of the additional capacitance electrode may be other than the mesh shape described above, and may be a shape in which a large number of narrow electrode elements are combined.

(Function) In the active matrix display device of the present invention, since the additional capacitor electrode has a mesh shape, a large leakage electric field is formed outside the area where the additional capacitor electrode and the pixel electrode face each other. Ru. This leak? The stray capacitance caused by the S electric field increases the additional capacitance compared to a conventional display device having the same additional capacitance electrode area.

FIG. 5 shows an example of the shape of the mesh-like additional capacitance electrode 22 used in the active matrix display device of the present invention. VI-VI of a display device using the substrate of FIG. 5 in FIG.
A cross-sectional view of the additional capacitor 27 along the line is shown. FIG. 7 shows the shape of the additional capacitance electrode 12 used in a conventional active matrix display device. FIG. 8 shows a sectional view of the additional capacitor 17 taken along line 1--2 of the display device using the substrate shown in FIG.

The areas of the additional capacitance electrodes 12 and 22 in FIGS. 5 and 7 facing the picture element electrode 1 are made equal.

As shown in FIG. 8, in the conventional display device, in the direction parallel to the extending direction of the additional capacitor electrode 12, the additional capacitor electrode 1
An electric field is formed in parallel between the pixel electrode 2 and the picture element electrode l.

On the other hand, as shown in FIG.
2, a leakage electric field is formed outside the region where the additional capacitance electrode 22 and the picture element electrode 1 face each other. Due to the stray capacitance caused by such a leakage electric field, the capacitance value of the additional capacitor 27 becomes larger than that of the additional capacitor 17. When comparing the additional capacitor electrodes having the same area in this way, the additional capacitor 27 having the mesh-like additional capacitor electrode 22 has a larger capacitance value than the conventional additional capacitor 17.

FIG. 9 shows a cross-sectional view of a parallel plate capacitor for explaining the influence of a leakage electric field on additional capacitance. One electrode 30 of this capacitor corresponds to a picture element electrode, and has a disk shape for simplicity. The electrode 31 is also disk-shaped, and its diameter is d. The electrode 31 corresponds to a part of the additional capacitance electrode. A ring-shaped electrode 32 is provided on the outer periphery of the electrode 31 with a gap g therebetween. The electrode 32 also corresponds to a part of the additional capacitance electrode. Therefore, the electrodes 31 and 32 correspond to portions of adjacent additional capacitance electrodes, respectively. The distance between the electrodes 31 and 32 and the electrode 30 is t. In such a parallel plate capacitor, the capacitance Cv formed between the electrodes 31 and 30 is expressed by the following equation in vacuum, assuming that g is sufficiently smaller than d.

π(d×Bg)2 Cv=0. 08854 t Here, B is a correction coefficient regarding the gap g between the electrodes 31 and 32. The units of dlt and g are cm.

The unit of Cv is pp. As can be seen from the above equation, electrode 3
The capacitance Cv between the electrode 1 and the electrode 30 increases as the gap g increases. That is, as the electrodes 31 and 32 are separated and the leakage electric field of the electrode 31 increases, it becomes larger. On the contrary, the gap g
As Cv approaches 0, Cv becomes smaller. That is, electrodes 31 and 3
2 become close to each other and the electric fields between the electrodes 31 and 30 become parallel, the leakage electric field almost disappears and Cv becomes small.

Furthermore, since the additional capacitance electrode has a mesh shape, it is possible to reduce the incidence of breakage of the additional capacitance electrode due to foreign matter mixed in during formation of the additional capacitance electrode or cracks.

(Example) The invention will now be described with reference to examples.

FIG. 1 shows a plan view of an active matrix substrate used in an active matrix display device of the present invention. Second
The figure shows a sectional view taken along line nn in FIG. 1. Picture element electrodes 1 are arranged in a matrix on an insulating substrate 5.

Between the picture element electrodes 1, a source bus line 3 parallel to one direction and a gate bus line 4 orthogonal to the source bus line 3 are provided. An inverted staggered TFT 2 is formed on the gate bus wiring 4 . Source electrode 15 of TPT2
is connected to the source bus wiring 3, and the drain electrode 16 is connected to the picture element electrode 1. A part of the gate bus wiring 4 functions as a gate electrode 4a of the TPT2.

An additional capacitance electrode 22 is formed below the picture element electrode 1 . The additional capacitance electrode 22 is formed simultaneously with the gate bus wiring 4. Eight openings are provided in the additional capacitor electrode 22, so that the additional capacitor electrode 22 has a mesh shape. A gate insulating film 6, which will be described later, is formed over the entire surface between the gate bus wiring 4 and the additional capacitance electrode 22 and the picture element electrode 1. Picture element electrode l and additional capacitance electrode 22
An additional capacitor 27 is formed between the two.

The cross-sectional configuration of the TPT 2 and the additional capacitor 27 will be explained with reference to FIG. Gate bus wiring 4 on insulating substrate 5
Further, the additional capacitance electrode 22 is formed into a notch.

The additional capacitance electrode 22 is formed in a mesh shape as described above. An anodic oxide film 11 is formed on the additional capacitance electrode 22 . Gate bus wiring 4 and additional capacitance electrode 22
A gate insulating film 6 is formed over the entire surface.

A semiconductor film 7 made of a -3j(i) is formed on the portion of the gate bus wiring 4 that functions as the gate electrode 4a with a gate insulating film 6 interposed therebetween.

An insulating layer 8 is provided at the center of the semiconductor film 7 .

Further, a contact layer 9.9 made of a-8i(n'') is formed on the semiconductor film 7. Contact layer 9.9
On top of these are a source electrode 15 and a drain electrode 16, respectively.
is formed.

Contact layer 9.9 is provided for making ohmic contact between semiconductor layer 7 and source electrode 15 and drain electrode 16. Further, the insulating layer 8 includes a contact layer 9.9,
It is provided to protect the semiconductor layer 7 from the chemical agent used when patterning the source electrode 15 and drain electrode 16.

A picture element electrode 1 is patterned on the gate insulating film 6 on the side of the TFT 2 . Picture element electrode 1 is drain electrode 1
6. The end of the picture element electrode 1 on the opposite side from the TFT 2 is overlapped with the additional capacitance electrode 22 via the anodic oxide film 11 and the gate insulating film 6. As aforementioned,
An additional capacitor 27 is formed by the end of the picture element electrode 1 and the additional capacitor electrode 22. A protective film 10 is deposited over the entire surface, covering the TFT 2, the picture element electrode 1, and the additional capacitor 27.

An active matrix substrate having such a configuration,
A display medium such as a liquid crystal is sealed between the display medium and a counter substrate provided with a counter electrode, thereby forming an active matrix display device.

In this embodiment, since the additional capacitor electrode 22 has a mesh shape, a large amount of leakage electric field exists outside the region where the additional capacitor electrode 22 and the picture element electrode 1 face each other. Additional capacitance increases due to stray capacitance caused by this leakage electric field.

In this way, in this embodiment, a larger value of additional capacitance than the conventional one can be obtained by using the additional capacitor electrode having the same area as the conventional one. Therefore, an active matrix display device can be obtained which can maintain the potential of the picture element electrode 1 more fully than in the past with the same aperture ratio as in the past.

Furthermore, in this embodiment, the additional capacitance electrode 22 has a mesh shape as shown in FIG. The incidence of wire breaks is reduced. Therefore, the shape of the additional capacitance electrode 22 of this embodiment helps to improve the yield of the display device.

(Effects of the Invention) In the active matrix display device of the present invention, additional capacitance can be increased without reducing the aperture ratio. Moreover, the occurrence of disconnection of the additional capacitance electrode is also reduced. Therefore, according to the present invention, a display device having high image quality can be obtained with high yield.

4. Don't worry! ■ Figure 1 is a plan view of an active matrix substrate used in one embodiment of the active matrix display device of the present invention;
2 is a sectional view taken along the line ntt in FIG. 1, FIG. 3 is a plan view of a conventional active matrix substrate, and FIG. 4 is a sectional view taken along the line IV-IV in FIG. FIG. 5 is a plan view showing an example of the additional capacitance electrode used in the display device of the present invention, and FIG. 6 is a plan view of the display device using the additional capacitance electrode shown in FIG. 7 is a plan view of an electrode for additional capacitance used in a conventional display device, and FIG. 8 is a cross-sectional view of a display device using the electrode for additional capacitance shown in FIG. FIG. 9 is a cross-sectional view of a parallel plate capacitor for explaining the effect that the shape of the additional capacitance electrode has on the electric field.

DESCRIPTION OF SYMBOLS 1... Picture element electrode, 2... TFT, 3... Source bus wiring, 4... Gate bus wiring, 4a... Gate electrode, 5... Insulating substrate, 6... Gate Insulating film, 7.
... Semiconductor layer, 8... Insulating layer, 9... Contact layer, 10... Protective film, 11... Anodic oxide film, 15...
- Source electrode, 16... Drain electrode, 22... Electrode for additional capacitance, 27... Additional capacitor, 30. 31.
32...electrode.

that's all

Claims (1)

[Claims] 1. A pair of insulating substrates, pixel electrodes arranged in a matrix on the inner surface of one of the pair of substrates, and facing the pixel electrodes with a dielectric layer interposed therebetween. an electrode for additional capacitance,
An active matrix display device having: an active matrix display device in which the additional capacitance electrode has a mesh shape.