JPH0593921A - Active matrix type liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide the active matrix type liquid crystal display element which does not degrade specific resistance and does not generate the image quality defect occurring in the degradation in the specific resistance even if an oriented film is partly peeled by rubbing. CONSTITUTION:Signal lines 21 and the electrode surface on the liquid crystal 17 side of thin-film transistors 13 are coated with the same material as the material of display picture element electrodes 14. Even if the oriented film 32 is partly peeled by rubbing, the peeled film does not come into direct contact with the signal lines 21 and the liquid crystal 17 and the same material as the material of the display picture element electrodes comes into contact with the liquid crystal. The material of the display picture element electrodes 14 is ITO (Indium Tin Oxide) and is extremely chemically stable. The metallic components of this material do not intrude into the liquid crystal 17 in spite of direct contact with the liquid crystal. The specific resistance near the peeled film does not degrade and the degradation in the image quality occurring in the degradation in the specific resistance is obviated even if the oriented film 32 is partly peeled.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a thin film transistor (Th
in Film Transistor, TFT) as a switching element,
The present invention relates to an active matrix type liquid crystal display element which constitutes a display pixel electrode array.

[0002]

2. Description of the Related Art In recent years, as a display element using a liquid crystal, a large-capacity and high-density active matrix type liquid crystal display element directed to a television display or a graphic display has been actively developed and put into practical use. In such a display element, a semiconductor switch is used as a drive control unit of each pixel so that high-contrast display without crosstalk can be performed.

As this semiconductor switch, a transmissive display is possible, and it is easy to increase the area.
A thin film transistor is used and is formed on an insulating substrate.

FIG. 3 shows a schematic sectional structure disclosed in Japanese Patent Application Laid-Open No. 56-162793 as an example of the above-mentioned liquid crystal display element. In FIG. 3, reference numerals 11 and 12 denote transparent insulating substrates made of glass or the like, and a plurality of thin film transistors 13 and display pixel electrodes 14 made of a transparent electrode film are arranged in a matrix on one main surface of one insulating substrate 11. It is configured. A counter electrode 15 made of a transparent conductive film is formed on the entire main surface of the other insulating substrate 12. The two insulating substrates 11 and 12 are arranged with a gap so that the main surfaces of the insulating substrates 11 and 12 face each other. The periphery of this gap is sealed with a sealing agent 16, and a liquid crystal 17 is sealed inside.

Next, an electric circuit for one pixel of a display pixel electrode array including a thin film transistor will be described with reference to FIG. In FIG. 4, 21 is a signal line, 22 is a scanning line, and a plurality of these signal lines 21 and scanning lines 22 are crossed on one main surface of the insulating substrate 11 and are insulated from each other. It is arranged. A thin film transistor 13 is provided at each intersection of the signal line 21 and the scanning line 22. The gate of each thin film transistor 13 is connected to the scanning line 22 in each row, and the drain is connected to the signal line 21 in each column. Further, the source is connected to the display pixel electrode 14. The display pixel electrode 14 faces the counter electrode 15 via the liquid crystal 17 as described above, and the counter electrode 15 is connected to the positive electrode side of the DC power supply 24.

Next, a method of driving one pixel by the circuit configuration will be described.

When a video signal is applied from the signal line 21 to the drain during a period in which the scanning line selection voltage is applied to the gate of the thin film transistor 13 from the scanning line 22, that is, a switching period, the display pixel electrode 14 connected to the source is connected. Is set to the same potential as the video signal potential. Further, the display pixel electrode 14 holds this potential while the scanning line non-selection voltage is applied to the gate. As a result, a potential difference according to the video signal voltage is applied to the liquid crystal 17 sandwiched between the display pixel electrode 14 and the counter electrode 15 set to a predetermined potential. Then, the arrangement state of the liquid crystal 17 changes in accordance with the potential difference, so that the light transmittance of the portion of the liquid crystal in which the potential difference occurs changes, and an image is displayed.

Here, when the liquid crystal 17 is driven by direct current, the liquid crystal is deteriorated by the electrolysis of molecules and the life is shortened, so that the liquid crystal is driven by alternating current. Generally, AC drive is performed by setting the potential of the counter electrode 15 to a DC potential and setting the video signal voltage symmetrically with respect to this counter electrode potential in even and odd frames. That is, the video signal voltage is a sum of a predetermined DC voltage and a positive / negative symmetrical AC voltage corresponding to the video signal.

5 and 6 are cross-sectional views of one pixel of a display pixel electrode array provided with a thin film transistor. FIG. 5 shows a thin film transistor 13 portion and FIG. 6 shows a signal line 21 portion.

First, the thin film transistor 13 portion will be described with reference to FIG. In FIG. 5, reference numeral 13G is a gate electrode, and this gate electrode 13G is one of the insulating substrates 11 to be the array substrate 27.
It is formed above and electrically connected to a scan line (not shown).
Surface of this gate electrode 13G and insulating substrate 11 including it
The surface of is covered with a gate insulating film 28. A semiconductor layer 29 is formed in a portion facing the upper surface of the gate electrode 13G with the gate insulating film 28 interposed therebetween.
An insulator layer 30 is formed in the center of the upper portion of 29.

Further, 13S is a source electrode, and this source electrode 13S is formed on the left half of the semiconductor layer 29 and the insulator layer 30 in the figure with an ohmic layer 31a interposed therebetween. 13D is a drain electrode, and this drain electrode 13D is formed on the right half of the semiconductor layer 29 and the insulator layer 30 in the drawing with an ohmic layer 31b interposed therebetween. The display pixel electrode 14 is the drain electrode 13D.
Is formed on the gate insulating film 28 so as to be conductively connected so as to overlap one end of the. The whole of these is covered with the alignment film 32.

The counter substrate 34 for the array substrate 27 is, as described above, the counter electrode 15 over the entire one main surface of the insulating substrate 12.
Further, an alignment film 35 is formed on the entire upper surface of the counter substrate 34. The liquid crystal 17 is held in the gap between the array substrate 27 and the counter substrate 34.

Next, the signal line 21 portion will be described with reference to FIG. As described above, the gate insulating film 28 is formed on the insulating substrate 11, and the signal line 21 is formed at a position avoiding the display pixel electrode 14 of each pixel. The signal line 21 is also covered with the alignment film 32 as described above.

By the way, in the liquid crystal display device having such a structure, as shown in the drawing, the drain electrode 13D, the source electrode 13S and the signal line 21 of the thin film transistor 13 are convex with respect to the display pixel electrode 14. In the manufacturing process of the liquid crystal display element, there is a so-called rubbing process in which the entire alignment film 32 is subjected to liquid crystal alignment processing by a roller. In this case, as described above, the drain electrode 13D, the source electrode 13S and the signal line 21
Has a convex shape with respect to the display pixel electrode 14, the alignment film 32 in these portions is rubbed more strongly than the alignment film 32 in the display pixel electrode 14 portion. Therefore, these drain electrodes 13D
, The source electrode 13S and the alignment film 32 in the signal line 21 portion are liable to peel off during rubbing, and if peeling occurs, even if the thickness of the alignment film 32 is about several μm, these electrodes and wiring portions Will be in direct contact with the liquid crystal 17.

Here, a chemically active low resistance metal such as aluminum is often used as the material of the signal line 21, but when these metals come into direct contact with the liquid crystal 17, a metal component is contained in the liquid crystal 17. When mixed, the specific resistance of the liquid crystal in the vicinity decreases. Therefore, during the period when the scanning line non-selection voltage is applied to the scanning line 22, the charge to be held by the display pixel electrode 14 leaks through the liquid crystal 17, so that the contrast is lowered and the gradation display capability is lowered. , Causing poor image quality.

[0016]

As described above, in the active matrix type liquid crystal display element using the thin film transistor 13 as the semiconductor switch, the alignment film of the electrodes and the wiring portion is liable to peel off during rubbing, and this peeling may cause a defective image quality. The problem arises.

The object of the present invention is that even if a part of the alignment film is peeled off by rubbing, the specific resistance is not lowered in the vicinity thereof, and the image quality is not deteriorated due to the decrease in the specific resistance. An object is to provide an active matrix type liquid crystal display device.

[0018]

In the active matrix type liquid crystal display device according to the present invention, a plurality of scanning lines and signal lines are intersected with each other on one main surface of an insulating substrate, and a thin film transistor and a thin film transistor are provided near each intersection. An array substrate formed by arranging one pixel composed of a display pixel electrode connected to and connecting the one pixel to the scanning line and the signal line,
A counter substrate in which a counter electrode is disposed on one main surface of another insulating substrate; and a liquid crystal sandwiched in a gap obtained by combining the array substrate and the counter substrate so that their one main surface sides face each other. The signal lines and the electrode surfaces of the thin film transistors on the liquid crystal side are covered with the same material as the display pixel electrodes.

[0019]

In the present invention, even if a part of the alignment film is peeled off by rubbing, the signal lines and electrode surfaces do not come into direct contact with the liquid crystal, and are the same as the display pixel electrodes formed on the liquid crystal side surface. The material comes into contact with the liquid crystal. In general, the material of the display pixel electrode is ITO (Indium Tin Oxide).
Is used. Since this ITO is an oxide and is chemically very stable, the ITO component does not mix into the liquid crystal even when it comes into direct contact with the liquid crystal, and therefore the specific resistance in the vicinity where the peeling of the alignment film occurs. Does not decrease,
Image quality deterioration due to the decrease in the specific resistance does not occur.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

1 and 2 are cross-sectional views of one pixel of a display pixel electrode array provided with a thin film transistor. FIG. 1 shows a thin film transistor 13 portion and FIG. 2 shows a signal line 21 portion.
Since these configurations have many parts in common with the conventional configuration shown in FIGS. 5 and 6, common parts will be described with the same reference numerals.

First, the thin film transistor 13 portion will be described with reference to FIG.

The gate electrode 13G is formed on one insulating substrate 11 which will be the array substrate 27, and is electrically connected to a scanning line (not shown). The surface of the gate electrode 13G and the surface of the insulating substrate 11 including the gate electrode 13G are covered with a gate insulating film 28. A semiconductor layer 29 is formed in a portion facing the upper surface of the gate electrode 13G via the gate insulating film 28, and an insulator layer 30 is formed in the upper center of the semiconductor layer 29.

The source electrode 13S is formed on a part of the semiconductor layer 29 and the insulator layer 30 via the ohmic layer 31a, and the drain electrode 13D is formed on the semiconductor layer 29 and the insulator layer 30. It is partially formed via the ohmic layer 31b. The display pixel electrode 14 is conductively connected so as to overlap with one end of the drain electrode 13D, and has a gate insulating film 28.
Formed on.

Furthermore, the surface of the source electrode 13S and the drain electrode 13D, that is, the surface on the liquid crystal 17 side sandwiched between the counter electrode 34 and the counter electrode 34, is made of the same material as that of the display pixel electrode 14, for example, ITO (Indium Tin Oxide). ) Is covered by. Further, the whole of them is covered with the alignment film 32.

Deflection plates 36 and 37 are formed on both outer sides of the insulating substrates 11 and 12 of the array substrate 27 and the counter substrate 34.

The counter substrate 34 with respect to the array substrate 27
5 is the same as that shown in FIG. 5 and FIG. 6, the counter electrode 15 is formed over the entire one main surface of the insulating substrate 12, and the alignment film 35 is entirely formed on the upper surface of the insulating substrate 12. It is formed across.

The signal line 21 is an insulating substrate as shown in FIG.
Display pixel electrode for each pixel on the gate insulating film 28 on
It is formed in a state of avoiding 14. And this signal line
21 is also covered with the same material as the display pixel electrode 14, for example, ITO, and then covered with the alignment film 32 as described above.

In the above structure, the drain electrode 13D, the source electrode 13S and the signal line 21 of the thin film transistor 13 are generally made of the same material and, like the conventional one, have a convex shape with respect to the display pixel electrode 14. .. Therefore, during rubbing, the drain electrode 13D, the source electrode 13S, and the alignment film 32 in the signal line 21 are
It may be rubbed more strongly than the alignment film in the 14th part, and peeling may occur in the alignment film in these parts.

Here, a part of the alignment film 32, for example, the signal line 21.
When peeling occurs in a part of the alignment film, the signal line 21 has a two-layer structure with respect to the liquid crystal 17, as described above, of a signal line material such as aluminum and ITO which is the same material as the display pixel electrode 14. Therefore, aluminum does not come into direct contact with the liquid crystal. Therefore, unlike the conventional case, a metal component such as aluminum is mixed into the liquid crystal 17, the specific resistance of the liquid crystal in the vicinity thereof is lowered, and the image quality failure such as the reduction of the contrast and the gray scale display ability is not caused.

Further, since the signal line 21 has a two-layer structure of aluminum and ITO as described above, even if a disconnection occurs in the wiring part made of aluminum, the disconnection part is not affected by the IT.
The presence of the O wiring does not cause the disconnection, and it is possible to suppress a decrease in yield due to the disconnection of the signal line and improve the reliability of the liquid crystal display element itself. Furthermore, since the manufacturing process itself is the same as the conventional one, the above-mentioned effects can be expected without causing the manufacturing process to be complicated, which is a new factor of decreasing the yield.

According to the present embodiment, the signal line has a two-layer structure of aluminum and ITO, but SnO is used instead of ITO.
₂ (tin oxide) and In ₂ O ₃ (indium oxide) can also be used.

[0033]

As described above, according to the present invention, the liquid crystal side surface of the signal line and the electrode made of the same material as the signal line is covered with the same material as the display pixel electrode. Even if partial peeling occurs, the signal line material is in direct contact with the liquid crystal as in the past, and the metal component mixes in the liquid crystal to lower the specific resistance in the vicinity, resulting in a decrease in contrast and gradation display capability. Good image quality can always be maintained without causing image quality failure.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a thin film transistor portion showing an embodiment of an active matrix type liquid crystal display element of the present invention.

FIG. 2 is a sectional view showing a signal line portion of the above.

FIG. 3 is a cross-sectional view showing an internal structure of a conventional general active matrix type liquid crystal display device.

4 is an equivalent circuit diagram showing an electric circuit for one pixel of a display pixel electrode array in the active matrix type liquid crystal display element shown in FIG.

FIG. 5 is a cross-sectional view showing a thin film transistor portion of a conventional active matrix type liquid crystal display element.

FIG. 6 is a cross-sectional view showing a signal line portion of the above.

[Explanation of symbols]

 11, 12 Insulating substrate 13 Thin film transistor 14 Display pixel electrode 15 Counter electrode 17 Liquid crystal 21 Signal line 27 Array substrate 34 Counter substrate

Claims (1)

[Claims] 1. A plurality of scanning lines and signal lines intersect with each other on one main surface of an insulating substrate, and one pixel composed of a thin film transistor and a display pixel electrode connected to the thin film transistor is arranged near each intersection. The array substrate having the one pixel connected to the scanning line and the signal line, the counter substrate having the counter electrode arranged on one main surface of the other insulating substrate, and the array substrate and the counter substrate. In an active matrix type liquid crystal display element comprising a liquid crystal sandwiched in a gap obtained by combining so that one main surface side faces each other, the signal lines and the electrode surface on the liquid crystal layer side of the thin film transistor, An active matrix type liquid crystal display element, characterized by being covered with the same material as a display pixel electrode.