JP2000075324A - Active matrix type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active matrix type liquid crystal display device which is free from the occurrence of image quality defects even if alignment layers are partly peeled without adversely affecting its characteristics. SOLUTION: Even if a disconnection arises in the wiring portion of a signal line of aluminum, the wiring of a protective layer 14a of ITO exists in the disconnected portion and, therefore, the disconnection does not occur. The degradation in the yield occurring in the disconnection of the signal line may be suppressed. At the time of forming a source electrode 13S and a drain electrode 13D and the protective layer 14a on these source electrode 13S and drain electrode 13D, the layer may be used as an etching stopper. Even if minor mask alignment occurs, the simultaneous patterning of the source electrode 13S, the drain electrode 13D and the protective layer 14a is made possible and, therefore, the source electrode 13S and the drain electrode 13D may be surely coated by the protective layer 14a. The self-alignment by the protective layer 14a is possible as well. The characteristics of a thin-film transistor is thus made constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device comprising a display pixel electrode array using thin film transistors as switching elements.

[0002]

2. Description of the Related Art In recent years, large-capacity, high-density active matrix type liquid crystal display devices for television display, graphic display, and the like have been developed and put into practical use as display devices using liquid crystal. In such a display device, a semiconductor switch is used as drive control means for each pixel so that high-contrast display can be performed without crosstalk.

As this semiconductor switch, a thin film transistor (Thin Film Transistor: TF) can be used because it is capable of transmissive display and is easy to increase in area.
T) is used and is formed on an insulating substrate.

FIG. 3 shows a schematic cross-sectional structure disclosed in Japanese Patent Application Laid-Open No. 56-162793 as an example of the above-mentioned liquid crystal display device. In this FIG.
Reference numeral 12 denotes a transparent insulating substrate such as glass, and one of the insulating substrates 11
On one main surface, a plurality of thin film transistors 13 and display pixel electrodes 14 made of a transparent electrode film are arranged in a matrix. Also, on one main surface of the other insulating substrate 12,
A counter electrode 15 of a transparent conductive film is formed on the entire surface. These two insulating substrates 11 and 12 are arranged with a gap therebetween so that one main surface of each of the two insulating substrates 11 and 12 faces 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 having a thin film transistor will be described with reference to FIG. In FIG. 4, reference numeral 21 denotes a signal line, 22 denotes a scanning line, and the signal line 21 and the scanning line 22 cross each other 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 a scanning line for each row.
The drain is connected to the signal line 21 for each column. Further, the source is connected to the display pixel electrode 14. The display pixel electrode 14 is connected to the liquid crystal 17 as described above.
Opposing the counter electrode 15 through the
Is connected to the positive electrode side of the DC power supply 24.

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

When a video signal is applied from the signal line 21 to the drain during a period in which a scanning line selection voltage is applied from the scanning line 22 to the gate of the thin film transistor 13, that is, during a switching period, the display pixel electrode 14 connected to the source is Is set to the same potential as the video signal potential. The display pixel electrode 14 keeps this potential during the period when the scanning line non-selection voltage is applied to the gate. As a result, a potential difference corresponding 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. When the arrangement state of the liquid crystal 17 changes according to the potential difference, the light transmittance of the liquid crystal portion where the potential difference occurs changes, and an image is displayed.

Here, when the liquid crystal 17 is driven by a direct current, the liquid crystal is degraded by electrolysis of molecules and the life is shortened, so that the liquid crystal 17 is driven by an alternating current. Generally, AC driving is performed by setting the potential of the counter electrode 15 to a DC potential, and setting the video signal voltage to the opposite electrode potential in a positive / negative symmetric manner in an even-odd frame. That is, the video signal voltage is obtained by adding a predetermined DC voltage and a positive / negative symmetric 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 will be described with reference to FIG. In FIG. 5, 13G is a gate electrode, and this gate electrode 13G is one of the insulating substrates 11 to be an array substrate 27.
It is formed above and is conductively 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 at a portion facing the upper surface of the gate electrode 13G via the gate insulating film 28, and an insulator layer 30 is formed at the upper center of the semiconductor layer 29.

Reference numeral 13S denotes a source electrode, which is formed on the left half of the semiconductor layer 29 and the insulator layer 30 via an ohmic layer 31a. 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 figure via an ohmic layer 31b. The display pixel electrode 14 is connected to the drain electrode 13D.
And is formed on the gate insulating film 28 so as to overlap with one end of the gate insulating film 28. These components are entirely covered with an alignment film 32.

As described above, the counter substrate 34 with respect to the array substrate 27 is provided over the entirety of one main surface of the insulating substrate 12.
Are formed, and an alignment film 35 is formed on the entire surface of the counter substrate 34 over the entire surface. The liquid crystal 17 is interposed between the array substrate 27 and the opposing substrate.

Next, the signal line 21 will be described with reference to FIG. The gate insulating film 28 is formed on the insulating substrate 11 as described above, and the signal line 21 is formed at a position avoiding the display pixel electrode 14 for 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 configuration, as shown, 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 device, there is a so-called rubbing process in which the entire alignment film 32 is subjected to a liquid crystal alignment process using a roller. In this case, as described above, the drain electrode 13D, the source electrode 13S and the signal line 21
Are convex 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. Therefore, these drain electrodes 13D
In the rubbing, the source electrode 13S and the alignment film 32 of the signal line 21 are likely to peel off. If the peeling occurs, even if the thickness of the alignment film 32 is about several μm, the drain electrode 13D and the source The electrode 13S and the signal line 21 are in direct contact with the liquid crystal 17.

Here, a chemically active low-resistance metal such as aluminum is often used as a 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. And the specific resistance of the liquid crystal 17 in the vicinity is lowered. For this reason, during the period in which the scanning line non-selection voltage is applied to the scanning line 22, the electric charge to be held by the display pixel electrode 14 leaks through the liquid crystal 17, so that the contrast and the gradation display capability are reduced. Causes poor image quality.

As described above, in the active matrix type liquid crystal display device using the thin film transistor 13 as the semiconductor switch, the rubbing is likely to occur in the alignment film of the electrode and the wiring portion during the rubbing, and the peeling may cause poor image quality.

As a configuration for preventing a metal component from being mixed with a metal in contact with a liquid crystal as described above, for example, a configuration described in JP-A-2-188720 is known.

Japanese Patent Application Laid-Open No. 2-188720 discloses that
IT wider than this signal line on aluminum signal line
O, and the ITO is brought into contact with the liquid crystal. Also, even if the ITO is displaced by the mask, the signal lines are surely covered, and the liquid crystal and the aluminum of the signal lines are prevented from coming into contact with each other.

[0019]

However, in the case of the configuration described in Japanese Patent Application Laid-Open No. Hei 2-188720, even if ITO having a width wider than that of the signal line is used, a large problem does not easily occur in the structure. In addition, when the thin film transistor is to be formed on the drain electrode and the source electrode, if the area where the drain electrode and the source electrode are in contact with the semiconductor layer is changed, the characteristics of the thin film transistor are greatly different.

The present invention has been made in view of the above problems. Even if a part of the alignment film is peeled off by rubbing without deteriorating the characteristics, the specific resistance may be reduced in the vicinity thereof. It is another object of the present invention to provide an active matrix type liquid crystal display device that does not cause image quality failure due to a decrease in specific resistance.

[0021]

According to the present invention, there is provided an insulating substrate, a plurality of scanning lines and signal lines arranged crossing each other on one principal surface of the insulating substrate, and a gate electrode connected to the scanning lines. An insulating film disposed on the gate electrode, a semiconductor film disposed on the insulating film, an insulating film provided at a predetermined position of the semiconductor film, electrically connected to the semiconductor film and the signal line. A thin film transistor having a source electrode and a drain electrode electrically connected to the semiconductor film and arranged near each intersection of the scanning line and the signal line;
A display pixel electrode connected to the drain electrode of the thin film transistor and connected to the scanning line and the signal line via the thin film transistor; and the same material as that of the display pixel electrode, on the signal line, the source electrode, and the drain electrode. An array substrate provided with a protective layer disposed thereon, a counter substrate facing the array substrate, and a liquid crystal disposed between the array substrate and the counter substrate.

Since a protective layer made of the same material as that of the display pixel electrode is provided on the signal line, the source electrode, and the drain electrode, the source electrode and the drain electrode do not come into direct contact with the liquid crystal. Prevents image quality defects such as reduced contrast and reduced gradation display capability due to changes in the liquid crystal caused by the direct contact of the signal line, source electrode, and drain electrode in the liquid crystal. A film is provided, and the area of the source electrode and the drain electrode in contact with the semiconductor film is defined by the insulating film. Therefore, the area of the source electrode and the drain electrode in contact with the semiconductor becomes constant. It can also be matched.

The signal line, the source electrode, and the drain electrode are made of aluminum. Since the metal of the signal line, the source electrode, and the drain electrode is covered with the protective layer, the metal does not come into direct contact with the liquid crystal. Further, it is possible to prevent image quality defects such as a decrease in contrast and a decrease in gradation display capability due to a decrease in resistance of the liquid crystal.

Further, the array substrate has an alignment film directly disposed on the display pixel electrode and the protective layer. Even if the alignment film is peeled off, the signal line, the source electrode and the drain electrode are connected to the display pixel electrode. Covered with a protective layer of the same material as the electrodes, the signal lines, source and drain electrodes can be prevented from directly contacting the liquid crystal without forming a passivation film. An image quality defect such as a decrease in contrast and a decrease in gradation display capability due to a change in liquid crystal caused by direct contact between a signal line, a source electrode, and a drain electrode is prevented.

[0025]

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

FIGS. 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. Note that these configurations have many parts in common with the conventional configuration shown in FIGS. 5 and 6, and therefore, the common parts will be described with the same reference numerals.

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

As shown in FIG. 1, the gate electrode 13G is formed on one of the insulating substrates 11 to be the array substrate 27, and is conductively connected to a scanning line (not shown). The surface of the gate electrode 13G and the insulating substrate including the gate electrode 13G
The surface of 11 is covered with a gate insulating film 28. A semiconductor layer 29 as a semiconductor film 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 the semiconductor layer 29 and a part of 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 formed on the other part of the substrate 30 via the ohmic layer 31b. The display pixel electrode 14 is conductively connected so as to overlap one end of the drain electrode 13D, and is formed on the gate insulating film 28.

Further, the surface side of the source electrode 13S and the drain electrode 13D and the signal line 21, that is, the surface of the liquid crystal 17 sandwiched between the counter substrate 34 is made of the same material as the display pixel electrode 14, for example. It is covered with a protective layer 14a of ITO (Indium Tin Oxide). Furthermore, these display pixel electrodes
14 and the protective layer 14a are directly covered by the alignment film 32.

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

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

The signal line 21 is, as shown in FIG.
Display pixel electrode for each pixel on the gate insulating film 28 on 11
It is formed in a state avoiding 14. And this signal line
21 is also covered with the same material as the display pixel electrode 14, for example, the protective layer 14a of ITO, and then covered with the alignment film 32 as described above. The thin film transistor 13 is provided at the intersection of the signal line 21 and the scanning line 22.

In the above structure, the same material is generally used for the drain electrode 13D, the source electrode 13S and the signal line 21 of the thin film transistor 13, and the display pixel electrode 14
Is convex. Therefore, during the rubbing, the alignment film 32 of the drain electrode 13D, the source electrode 13S, and the signal line 21 is rubbed more strongly than the alignment film of the display pixel electrode 14, and the alignment film of these portions may peel off. is there.

Here, a part of the alignment film 32, for example, a signal line
If the alignment film in the portion 21 is completely or partially peeled off, the signal line 21 is made of ITO, which is the same material as the display pixel electrode 14, in a portion in contact with the liquid crystal 17 on the surface of aluminum, which is a signal line material. Since the protective layer 14a is formed, the aluminum signal line 21 does not directly contact the liquid crystal 17. 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 17 in the vicinity is reduced, and the image quality defect such as a decrease in contrast and a decrease in gradation display capability does not occur. The protective film 14
The ITO of a is an oxide and is chemically very stable. Even if the protective film 14a itself comes into direct contact with the liquid crystal 17, no ITO component is mixed into the liquid crystal 17, and therefore, the orientation film 32 The specific resistance in the vicinity of the peeling does not decrease, and the image quality does not deteriorate due to the decrease in the specific resistance. Furthermore, the drain electrode of the thin film transistor 13
The same applies to a case where a part of the alignment film 32 on the surface of the source electrode 13S is removed.

Further, since the signal line 21 has a double structure in which the ITO of the protective layer 14a is formed on the surface of the aluminum, even if the wiring of the aluminum signal line 21 is disconnected, the disconnection of the ITO occurs in this disconnected portion. The presence of the wiring of the protective layer 14a does not cause a disconnection, the reduction in yield due to the disconnection of the signal line 21 can be suppressed, and the reliability of the liquid crystal display device itself can be improved. Further, by using the insulating layer 30, when forming the source electrode 13S and the drain electrode 13D and the protective layer 14a on the source electrode 13S and the drain electrode 13D, the insulating layer 30 can be used as an etching stopper layer. Even if a shift occurs, the source electrode 13S and the drain electrode 13D and the protective layer 14a can be patterned at the same time.
S and drain electrode 13D.
a, the area of the source electrode 13S and the drain electrode 13D in contact with the semiconductor layer 29 can be made a predetermined value, so that the characteristics of the thin film transistor 13 can be made constant. Since the manufacturing process itself is the same as before,
The effect can be expected without complicating the manufacturing process, which is a new factor for lowering the yield.

According to this embodiment, the protective film with ITO is formed on the aluminum of the signal line 21, but SnO ₂ (tin oxide) and In ₂ O ₃ (indium oxide) are used instead of ITO. Can also.

[0038]

According to the present invention, since the protective layer made of the same material as the display pixel electrode is provided on, for example, the signal line, the source electrode and the drain electrode, the source electrode and the drain electrode are in direct contact with the liquid crystal. This prevents image quality defects such as a decrease in contrast and a decrease in gradation display capability due to a change in the liquid crystal caused by direct contact of the signal line, the source electrode, and the drain electrode in the liquid crystal. The insulating film is provided at a predetermined position, and the area of the source electrode and the drain electrode in contact with the semiconductor film is defined by the insulating film. Therefore, the area of the source electrode and the drain electrode in contact with the semiconductor becomes constant, and The film can be self-aligned so as to provide a film, and the characteristics can be kept constant. It can be maintained.

[Brief description of the 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 device of the present invention.

FIG. 2 is a cross-sectional view showing a signal line part according to the first embodiment;

FIG. 3 is a sectional view showing the 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 liquid crystal display device shown in FIG.

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

FIG. 6 is a sectional view showing a signal line part according to the first embodiment;

[Explanation of symbols]

 11, 12 Insulating substrate 13 Thin film transistor 13D Drain electrode 13G Gate electrode 13S Source electrode 14 Display pixel electrode 14a Protective layer 17 Liquid crystal 21 Signal line 22 Scan line 27 Array substrate 28 Gate insulating film 29 Semiconductor layer as semiconductor film 32 Alignment film 34 substrate

Claims (3)

[Claims] An insulating substrate, a plurality of scanning lines and signal lines arranged on one main surface of the insulating substrate so as to cross each other;
A gate electrode connected to the scanning line, an insulating film disposed on the gate electrode, a semiconductor film disposed on the insulating film, an insulating film provided at a predetermined position on the semiconductor film, the semiconductor film, A thin film transistor having a source electrode electrically connected to the signal line and a drain electrode electrically connected to the semiconductor film, arranged near each intersection of the scanning line and the signal line; A display pixel electrode connected and connected to the scanning line and the signal line via the thin film transistor, and a protective layer provided on the signal line, the source electrode, and the drain electrode using the same material as the display pixel electrode An array substrate comprising: a counter substrate facing the array substrate; and a liquid crystal disposed between the array substrate and the counter substrate. Active matrix liquid crystal display device, characterized in that. 2. The active matrix type liquid crystal display device according to claim 1, wherein the signal line, the source electrode and the drain electrode are made of aluminum. 3. The active matrix liquid crystal display device according to claim 1, wherein the array substrate has an alignment film disposed directly on the display pixel electrode and the protective layer.