JPH08160453A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To prevent obstruction for visibility and decrease in the contrast ratio and to improve display quality by suppressing reflection due to a light- shielding layer of a liquid crystal display device. CONSTITUTION: A Cr light-shielding layer 11 and an ITO auxiliary capacitance electrode 12 are formed on a substrate 10, and the substrate 10 in this state is baked to form a CrOX film having low reflectance used as an antireflection film 11ox on the interface between the light-shielding layer 11 and the auxiliary capacitance electrode 12. By this method, reflection of ambient light made incident from the upper side can be suppressed. Thus, obstruction for visibility by the reflected light or leaking in a TFT caused by the light which is reflected between substrates and enters α-Si layer 15 is prevented, and decrease in the contrast ratio is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device which suppresses reflected light which hinders good visual recognition.

[0002]

2. Description of the Related Art Liquid crystal display devices are characterized by thinness, light weight and low power consumption, and are being put to practical use in the fields of OA equipment, AV equipment and the like. In particular, the active matrix type using a thin film transistor (hereinafter abbreviated as TFT) as a switching element can perform static driving with a duty ratio of 100% in a multiplexed manner in principle, and has a large screen and a high-definition moving image display. Is used for.

In an active matrix type liquid crystal display device, display pixels are arranged in a matrix so that a desired voltage can be applied to a pixel capacitance in which liquid crystal is loaded between transparent electrodes arranged opposite to each other. The transparent electrodes are each supported by a transparent substrate, one is a pixel electrode formed in a matrix, and the other is a common electrode formed over the entire surface. A thin film transistor (TFT: Thin Film Transistor) is connected to each pixel electrode,
The input signal voltage is selected. Each TFT is selected by line-sequential scanning and turned on simultaneously for the same row, and a data signal voltage synchronized with this is applied to each pixel electrode. A voltage is also set to the common electrode, and the voltage applied to the pixel capacitance is held by the OFF resistance of the TFT until it is rewritten in the next field, and a constant electric field is formed in the liquid crystal layer.
The liquid crystal reacts electrostatically to change its optical state and modulate the transmitted light. The light thus modulated for each pixel is combined, visually recognized, and observed as a display image.

A conventional example of a liquid crystal display device using a positive stagger type in which a gate is disposed above a semiconductor layer as a TFT will be described. FIG. 4 is a plan view (a) of the unit pixel portion and a cross-sectional view (b) taken along the line BB.
A light shielding layer (51) made of Cr is formed on a substrate (50) such as glass. Indium tin oxide (ITO) is formed on the entire surface covering the light shielding layer (51).
An auxiliary capacitance electrode (52) made of a transparent conductive material of (de) is formed. An interlayer insulating layer (53) is formed on the auxiliary capacitance electrode (52), and the pixel electrode (54P), the drain line (54L), the source electrode (54S) of the TFT, and the TFT are formed on the interlayer insulating layer (53). The drain electrode (54D)
It is made of ITO. On the source electrode (54S) and the drain electrode (54D), an a-Si layer (55),
The gate insulating layer (56) and the gate electrode (57G) are laminated in the same pattern to form a TFT. The gate line (57) has the same structure as the TFT part, and is a
It is composed of a laminated body in which a -Si layer (55) and a gate insulating layer (56) are arranged. The pixel electrode (54P) is two-dimensionally located in a region surrounded by the gate line (57L) and the drain line (54L), and the light-shielding layer (51) is provided around the pixel electrode (54P) and the TFT. It is formed in the arranged region, functions as a black matrix (BM), blocks unmodulated light around the pixel electrode (54P), and improves the contrast ratio.

On the TFT array substrate having the above structure, a counter substrate having a common electrode via a liquid crystal layer of 5 to 10 μm is further arranged, and the liquid crystal layer and the common electrode are standardized by the pixel electrode (54P). The pixel capacitance is formed, and the liquid crystal display device is completed. In the liquid crystal display device having this structure, the auxiliary capacitance electrode (52) is formed over the entire surface of the substrate, and the auxiliary capacitance is formed in the entire area facing the pixel electrode (54P). Further, the light shielding layer (51) is formed on the substrate (50), and BM is formed on the TFT array substrate side to realize a so-called BM on TFT array substrate structure in which the aperture ratio is improved. That is, when the BM is formed on the counter substrate side, the bonding margin of 5 to 10 μm is eliminated in consideration of the bonding deviation, and the pixel electrode (54P) and the light shielding layer (51) are aligned on the TFT array substrate side. B with an alignment margin of 3 to 4 μm considering the deviation
The formation of M is achieved, and the aperture ratio is improved as a result of the advantages and disadvantages of these effective display areas.

[0006]

Cr, which is the material of the light shielding layer (51), has a high reflectance and B formed between pixel doses.
When ambient light is reflected by M, it hinders visual recognition or causes a reduction in contrast ratio, which causes a reduction in display quality. Especially, normally white
In the mode, even when the structure is observed from above the TFT array substrate, ambient light incident from the counter substrate side to the outside of the pixel capacitance region passes through the liquid crystal layer and the gate line (57
L) or through the ITO drain line (54L) and reflected by the light shielding layer (51),
Since it is emitted backwards in the same optical path, the visibility is reduced. Further, when observed from above the TFT array substrate, the ambient light is reflected in the entire area between the pixel capacitance regions, so that the visibility is further deteriorated.

When used in a system using a strong light source such as a projector, light is reflected between the substrates and scattered in the panel, so that the scattered light enters the a-Si layer (55) and is incident. If so, a light leak current is generated and the voltage holding ratio is lowered, which causes a reduction in the contrast ratio. On the other hand, in order to prevent such problems, CrO having a low reflectance is used.
There is one in which X is used to form a light-shielding layer having a CrOX / Cr laminated structure. That is, Cr with high light-shielding property is thickened to 100
By forming the film thickness to about 0Å and forming CrOx for reflection prevention on the side to be the display screen to a thickness of about 500Å, it is possible to prevent the deterioration of the visibility due to the reflected light. In such a CrOX / Cr laminated body, for example, in sputtering of Cr, oxygen is flowed into the chamber for a certain period of time so that a part of Cr is partially converted into CrO.
The film is made X. However, this method requires a system for inflowing O2 and a system for controlling this in addition to a system for inflowing Ar into the chamber, which requires a large scale film forming apparatus and a large cost burden. .

[0008]

The present invention has been made to solve this problem. First, a light-shielding layer formed on a part of a substrate, and a light-shielding layer entirely covering the light-shielding layer. An auxiliary capacitance electrode made of a transparent conductive material layer, an interlayer insulating layer formed on the auxiliary capacitance electrode, a plurality of pixel electrodes formed on the interlayer insulating layer, and a thin film transistor connected to each pixel electrode. In the liquid crystal display device including, a film in which the surface of the light shielding layer is oxidized is formed at the contact interface between the auxiliary capacitance electrode and the light shielding layer.

Secondly, in the first structure, the auxiliary capacitance electrode is formed of a transparent conductive material made of an oxide alloy of indium and tin, the light shielding layer is formed of Cr, and the surface of the light shielding layer is formed. The oxidized film was a Cr oxide film formed by heating.

[0010]

In the first structure, the surface oxide film of the light shielding layer is formed at the contact interface between the light shielding layer and the auxiliary capacitance electrode.
Regarding ambient light from above the substrate on which the thin film transistor is formed, the reflection on the surface of the light shielding layer is suppressed to prevent it from being disturbed from being visually recognized, and the light scattered by the reflection between the substrates is the semiconductor of the thin film transistor. It is prevented that the light wraps around the layer and is incident, and the display quality is improved.

In the above second structure, Cr constituting the light shielding layer
By forming an oxide film of Cr having low reflection by heat treatment on the interface between the layer and the oxide alloy of indium and tin that form the auxiliary capacitance electrode, light incident from above the substrate on which the thin film transistor is formed is prevented. Reflection by the light-shielding layer is suppressed, and display quality is improved. Further, since the Cr oxide film is formed only by adding the step of heat treatment,
No special device is required, and increase in cost is avoided.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a plan view of a unit pixel,
FIG. 2 is a sectional view taken along the line AA of FIG. On the transparent substrate (10), Cr is formed in the inter-pixel capacitance region by sputtering and photoetching, and the light shielding layer (11) which is BM is formed. By ITO metal mask sputtering on the entire surface covering the light shielding layer (11),
The auxiliary capacitance electrode (12) is formed over the entire display screen area, and Cr is oxidized at the interface between the light shielding layer (11) and the auxiliary capacitance electrode (12) by baking, so that CrO of low reflection is obtained.
X is generated and is used as an antireflection film (11ox).

Here, the sputtering of Cr is performed at a pressure of 0.40 p in a chamber equipped with a Cr target.
a, with the temperature set to 200 ° C., an electric field was formed by direct current discharge of 1.30 kw, and Ar gas was added at 80 sccm.
Is introduced at a flow rate of 2,000 Å to form a film with a thickness of 2000 Å. For ITO sputtering, a metal mask is applied to the peripheral area of the display screen in a chamber equipped with a target of indium and tin, and the pressure is set to 0.75 pa.
With the temperature set at 285 ° C., an electric field was formed by direct current discharge of 0.55 kw, Ar gas at 200 sccm,
O2 gas is introduced at a flow rate of 2.0 sccm to form a film having a thickness of 1400Å.

The baking for producing CrOX is
It is performed at 400 ° C. for 30 minutes after coating the ITO auxiliary capacitance electrode (12) on the pattern of the light shielding layer (11) made of Cr, whereby Cr is oxidized by oxygen in the ITO, and the contact interface is formed. A thin film of CrOx is formed. The entire surface covering the light-shielding layer (11), the antireflection film (11ox) and the auxiliary capacitance electrode (12) is coated with SiO 2 by CVD.
An interlayer insulating layer (13) is formed by stacking two layers, and the pixel electrode (14P) and the drain line (1) are formed on the interlayer insulating layer (13) by sputtering ITO and photoetching.
4L) is formed, and the source electrode (14S) part and the drain electrode (14D) part are close to each other. On the region where the source electrode (14S) and the drain electrode (14D) are close to each other, N + a-S on the source / drain region is formed.
a-Si, SiNX and Al through the i layer (15N)
Are continuously formed and etched in the same pattern to form a TFT by laminating the a-Si layer (15), the gate insulating layer (16) and the gate electrode (17G). Around the pixel electrode (14P) and the drain line (1
4L), a gate line (17L) integrated with the gate electrode (17G) is formed in a region intersecting the 4L), and like the TFT part, the a-Si layer (15) and the gate insulating layer (16) are formed in the lower layer.
The structure is arranged. N + a-Si layer (15
N) is film formation by CVD and photoetching, or
Phosphorus contained in ITO forming the source / drain wiring (14) at the time of sputtering is plasma CV of a-Si.
By reacting during the film formation by D, an N + type thin film is formed at the interface.

The TFT array substrate on which the electrodes are formed as described above is bonded to the counter substrate having the common electrode with a predetermined gap so as to form a pixel capacitance by the pixel electrode (14P), and the liquid crystal is formed inside. By sealing
Completed as a liquid crystal display device. FIG. 3 shows the reflectance of CrOx formed on the interface between Cr and ITO by baking as described above. As a comparative example, the reflectance of CrOx formed by the conventional film forming method of laminating Cr while introducing oxygen. And the reflectance of the Cr single layer are shown. (A) is the reflectance of CrOX of the present invention, (b) is the conventional CrOX, and (c) is the reflectance of light having a wavelength of 400 nm to 600 nm for the Cr single layer. From the figure, it can be seen that the Cr single layer has a reflectance of about 60% and adversely affects the display, but CrOX is suppressed to 20% or less in the visible region, and good visibility is obtained. Further, comparing (a) and (b), the characteristics of CrOx according to the present invention are more stable than those of the conventional CrOx. This is because the film forming method of the present invention in which Cr is oxidized by oxygen in ITO at the interface between Cr and ITO by heat treatment has a better quality than the conventional film forming method in which Cr is sputtered while introducing oxygen. Is obtained.

In the present invention, as shown in FIG. 2, the reflection of the light incident from above the TFT array substrate is suppressed by the structure in which the antireflection film (11ox) made of CrOx is interposed on the upper side of the light shielding layer (11). For this reason, especially
In the white mode, ambient light incident from the counter substrate side in the inter-pixel capacitance region passes through the drain line (14L) made of ITO from the liquid crystal layer, is reflected by the light shielding layer (11), and is emitted along the same path. Since the optical path of the reflected light is blocked, it is possible to prevent the visual interference due to the reflected light. Therefore, a direct-view liquid crystal display device having excellent visibility and good display quality can be obtained by adopting a configuration in which the counter substrate side faces the viewer side.

Further, since the light is prevented from being reflected between the substrates and scattered in the panel, the scattered light goes around to the a-Si layer (15) to leak the TFT and the voltage holding ratio is lowered. Therefore, the problem of lowering the contrast ratio is prevented. Therefore, it is also suitable for applications such as projectors where the intensity of the light source is strong. And such a liquid crystal display device is manufactured only by adding a baking process after patterning Cr and forming an ITO film. That is, a special sputtering device for forming CrO2 is unnecessary, and an increase in cost can be avoided.

[0018]

As is clear from the above description, according to the present invention, since the reflection of incident light is prevented by interposing the low reflection oxide film on the upper surface of the light shielding layer, the light shielding layer having such a structure. By forming the black matrix made of, it is possible to prevent visual interference due to reflection of ambient light and improve the display quality. Further, since the reflection of light between the substrates is suppressed, it is possible to prevent scattered light in the panel from sneaking into the semiconductor layer, and to prevent the contrast ratio from decreasing due to leakage of the thin film transistor.

Further, since the liquid crystal display device in which the reflection on the light shielding layer is suppressed is manufactured only by adding the heat treatment step, a special film forming device for forming the oxide film is unnecessary. Yes, an increase in cost can be avoided.

[Brief description of drawings]

FIG. 1 is a plan view of a unit pixel of a liquid crystal display device according to an exemplary embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a characteristic diagram illustrating the function and effect of the present invention.

FIG. 4 is a plan view and a cross-sectional view of a conventional liquid crystal display device.

[Explanation of symbols]

 10 substrate 11 light shielding layer 12 auxiliary capacitance electrode 13 interlayer insulating layer 14 source / drain wiring 15 a-Si 16 gate insulating layer 17 gate wiring

Claims (2)

[Claims] 1. A light-shielding layer formed on a part of a substrate, an auxiliary capacitance electrode formed of a transparent conductive material layer entirely covering the light-shielding layer, and an auxiliary capacitance electrode formed on the auxiliary capacitance electrode. In a liquid crystal display device having an interlayer insulating layer, a plurality of pixel electrodes formed on the interlayer insulating layer, and a thin film transistor connected to each pixel electrode and formed above the light shielding layer, the auxiliary capacitance electrode and A liquid crystal display device, wherein a film in which a surface of the light shielding layer is oxidized is formed at a contact interface with the light shielding layer. 2. The auxiliary capacitance electrode is formed of an oxide alloy of indium and tin, the light shielding layer is formed of Cr, and the film in which the surface of the light shielding layer is oxidized is formed of Cr by heating. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is an oxide film.