JPH08160409A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To suppress the reflection by the light shielding layer of a liquid crystal display device and to provide an easily visible screen without increasing a cost. CONSTITUTION: Low-reflection CrOX is formed at the contact boundary of a light shielding layer 21 consisting of Cr and a common electrode 22 consisting of ITO by executing baking in the state that the light shielding layer 21 and the common electrode layer 22 are formed on a substrate 20, by which an antireflection film 21ox is formed. As a result, the reflection of the ambient light entering from above is suppressed, the disturbance in visual recognition by reflected light is prevented and a display grade is improved. The addition of a baking stage is merely necessitated and there are no increase of special devices and other processes and there is no burden in terms of cost.

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.

The active matrix type liquid crystal display device is
Display pixels configured so that a desired voltage can be applied to a pixel capacitance in which liquid crystal is loaded are arranged in a matrix between transparent electrodes that are arranged to face each other between a pair of transparent substrates. The transparent electrodes are each supported by a transparent substrate, one of which is a pixel electrode formed in a matrix,
The other is a common electrode formed over the entire surface. Each pixel electrode has a thin film transistor (TFT).
ansistor) is connected and 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. The common electrode is also set to a predetermined voltage, the voltage applied to each 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. In this way, the transmitted light modulated for each pixel is synthesized and visually recognized,
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 below. 5 is a plan view of a unit pixel portion, and FIG. 6 is a sectional view taken along line BB of FIG. On a substrate (50) such as glass, a light shielding layer (51) made of Cr and an auxiliary capacitance electrode (5) for holding charges are provided.
2) is formed, and an interlayer insulating layer (53) is formed on the entire surface covering the light shielding layer (51) and the auxiliary capacitance electrode (52). A pixel electrode (54) is formed on the interlayer insulating layer (53).
P), the drain line (54L), the source electrode (54S) and the drain electrode (54D) of the TFT are formed of indium tin oxide (ITO). Source electrode (54S) and drain electrode (54
D) on the a-Si layer (5) via the N + a-Si layers (55N) formed in the source / drain regions, respectively.
5), gate insulating layer (56) and gate electrode (57G)
Are stacked in the same pattern to form a TFT.
The periphery of the pixel electrode (54P) and the drain line (54P
A gate line (57L) is arranged in a region intersecting L), and has a structure identical to that of the TFT part, and is composed of a laminated body in which an a-Si layer (55) and a gate insulating layer (56) are arranged as a lower layer.

The light-shielding layer (51) is arranged in a region covering the TFT portion, and light from below the substrate (50) is aS.
It blocks the incidence on the i layer (55) and prevents the OFF resistance of the TFT from decreasing and the voltage holding ratio from decreasing. The pixel electrode (54P) has a gate line (57P) in plan view.
L) and the drain line (54L), the auxiliary capacitance electrode (52) partially overlaps the pixel electrode (54P) to form an auxiliary capacitance for holding charges.

At a position facing the TFT array substrate having the above structure, a liquid crystal layer (70) is sandwiched, and Cr is provided on the substrate (60).
A light shielding layer (61) made of and a counter substrate having a common electrode (62) of ITO formed on the entire surface covering the light shielding layer (61) are arranged. The common electrode (62) is commonly opposed to each pixel electrode (54P) on the substrate (50) side with the liquid crystal sandwiched therebetween to form a pixel capacitance, and the light shielding layer (61) is arranged in the entire area between each pixel capacitance. To form a black matrix. That is, the liquid crystal layer (7
0) and the common electrode (62) are standardized to form a pixel capacitance which is a display pixel, and a light shielding layer (61) is arranged outside the region of the pixel capacitance to block light that is not modulated as a black matrix. The contrast ratio is improved by.

[0007]

Cr constituting the light-shielding layer (61) has a high reflectance, and when the counter substrate side is used as a display screen, the light-shielding layer (61) in which ambient light is formed as a black matrix is used. The reflected light interferes with the visual recognition, resulting in deterioration of display quality. Also,
Even when the TFT array substrate side is used as the display screen, in the normally white mode, ambient light incident from the TFT array substrate side to the outside of the pixel region is accompanied by the auxiliary capacitance electrode (52) made of Cr and the gate line made of Al ( 57L), or it passes through the liquid crystal layer (70) from the drain line (54L) made of ITO, is reflected by the light shielding layer (61), and is emitted back through the same optical path. Will interfere with.

On the other hand, in order to solve such a problem,
There is a light-shielding layer (61) having a two-layer structure of Cr and CrOx having low reflection, and arranging the CrOx film on the display screen side to suppress reflection of ambient light and improve display quality. However, for forming a laminated body of Cr and CrO x, for example, Cr
In the sputtering, it is necessary to stack Cr having a high light-shielding property thickly and to introduce oxygen for a predetermined time in order to form CrOx for antireflection. Therefore, as a film forming apparatus, an apparatus for introducing oxygen and a control system for the same are required, and the cost is increased.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems. First, it is formed on one of opposing surfaces of a pair of substrates in which liquid crystal is hermetically bonded and used for driving a liquid crystal. A plurality of pixel electrodes forming one of the pixel capacitances, a thin film transistor connected to each of the pixel electrodes, and the other of the plurality of pixel capacitances entirely formed on the other of the facing surfaces and standardized by the pixel electrodes. In a liquid crystal display device having a common electrode integrally formed with and a light shielding layer formed outside the area of the pixel capacitance, the light shielding layer is formed on the same substrate as the common electrode, and the light shielding layer and the light shielding layer A liquid crystal display device, wherein a film in which the surface of the light shielding layer is oxidized is formed at the contact interface of the common electrode.

Secondly, in the first structure, the common electrode is formed 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 oxidized. The Cr oxide film is formed by heat treatment.

[0011]

With the first structure, by forming the surface oxide film of the light-shielding layer on the light-shielding layer, it is possible to prevent ambient light from being reflected on the surface of the light-shielding layer and hindering visual recognition, and to improve the display quality. improves. In the second configuration, a low-reflectance Cr oxide film is formed by heat treatment at the interface between Cr that forms the light-shielding layer and the indium-tin oxide alloy that forms the common electrode, and Reflection is suppressed and display quality is improved. Further, since the formation of the Cr oxide film is performed only by adding a heat treatment step, no special film forming apparatus is required.
Increased cost can be avoided.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. 1 is a plan view of a unit pixel portion of a liquid crystal display device according to a first embodiment of the present invention, and FIG.
It is a sectional view taken along the line A. On a transparent substrate (10) such as glass, a light shielding layer (11) is formed in the TFT region and an auxiliary capacitance electrode (12) is formed in the pixel capacitance region by Cr sputtering and photoetching.
SiO2 is deposited on the entire surface covering the light shielding layer (11) and the auxiliary capacitance electrode (12) by CVD to form an interlayer insulating layer (1
3) is formed. IT on the interlayer insulation layer (13)
A pixel electrode (14P) and a drain line (14L) are formed by O sputtering and photoetching, and the source electrode (14S) portion and the drain electrode (14L) are formed, respectively.
They are close to each other with part D). Source electrode (14S)
On the region where the drain electrode (14D) and the drain electrode (14D) are close to each other, a-Si, SiNX and Al are continuously formed through the N + a-Si layer (15N) on the source / drain region,
By etching with the same pattern, the a-Si layer (15), the gate insulating layer (16) and the gate electrode (17).
G) is laminated to form a TFT. Pixel electrode (1
4P), a gate line (17L) integrated with the gate electrode (17G) is formed in a region crossing the drain line (14L), and a-S is formed in the lower layer as in the TFT part.
It has a structure in which an i layer (15) and a gate insulating layer (16) are arranged. The N + a-Si layer (15N) is formed by CVD and photoetching, or is formed by a-Si plasma CVD of phosphorus contained in ITO forming the source / drain wiring (14) during sputtering. By reacting inside, an N + type thin film is formed at the interface.

A transparent substrate (20) is arranged at a position facing the TFT array substrate having electrodes formed as described above with a liquid crystal layer (30) interposed therebetween, and on the inner side of the substrate (20),
The light-shielding layer (21) is formed in the inter-pixel capacitance region by sputtering of Cr and photoetching to form a black matrix. By the metal mask sputtering of ITO on the entire area that covers the inner side of the light shielding layer (21),
A common electrode (22) is formed over the entire display screen area, and Cr is oxidized by baking at the interface between the light-shielding layer (21) and the common electrode (22) to generate CrOX with low reflection, and an antireflection film ( 21 ox).

Here, the Cr sputtering is performed in a chamber equipped with a Cr target at a pressure of 0.40 p.
a, with the temperature set to 200 ° C., an electric field is formed by a direct current discharge of 1.00 kw, and Ar gas is set to 80 sccm.
Is carried out at a flow rate of 1, and a film is formed to a thickness of 1500Å. In addition, ITO sputtering is performed in a chamber equipped with a target of indium and tin by applying a metal mask to the peripheral area of the display screen at a pressure of 0.75.
0.55 kW with pa and temperature set to 200 ° C
An electric field is formed by the direct current discharge of Ar gas at 200 sc
cm, O2 gas is introduced at a flow rate of 2.0 sccm to form a film having a thickness of 1400Å.

Further, the baking for producing CrOX is
After forming the ITO auxiliary capacitance electrode (22) on the pattern of the light shielding layer (21) made of Cr, the temperature is set to 400 ° C. for 3
This is performed for 0 minutes, whereby Cr is oxidized by oxygen in ITO and a thin film of CrOx is formed at the contact interface. In FIG. 3, Cr and ITO are baked by baking as described above.
The reflectance of CrOx formed at the interface of No. 2 is shown, and as a comparative example, the reflectance of CrOx formed by the conventional film forming method of stacking 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%, which adversely affects the display, but CrOx is suppressed to 20% or less in the visible region and good visibility is obtained. Also,
Comparing (a) and (b), the characteristics of CrOx according to the present invention are more stable than those of the conventional CrOX. this is,
At the interface between Cr and ITO by heat treatment, the film forming method of the present invention, which promotes oxidation of Cr by oxygen in ITO,
It is shown that a film with better quality can be obtained as compared with the conventional film forming method in which Cr is sputtered while introducing oxygen.

In the present invention, as shown in FIG. 2, the structure in which the antireflection film (21ox) made of CrOx is interposed inside the light shielding layer (21) suppresses the reflection of light incident from the TFT array substrate side. Therefore, especially in the normally white mode, ambient light incident on the inter-pixel capacitance region from the TFT array substrate side passes through the liquid crystal layer (30) from the drain line (14L) made of ITO, and the light shielding layer (21). Since the optical path that is reflected by and returns to the same path is blocked, it is possible to prevent visual interference due to reflected light. Therefore, the liquid crystal display device shown in FIG. 1 and FIG. 2 has a structure in which the TFT array substrate side is used as the display screen, whereby a display screen having excellent visibility and good display quality can be obtained.

Further, since reflection is suppressed inside the light-shielding layer (21), light is reflected between the substrates and scattered in the panel to enter the a-Si layer (15), causing leakage and holding voltage. Since it is possible to prevent the rate from being lowered, it is particularly suitable for applications such as a projector having a high light source intensity. Then, such a liquid crystal display device of the present invention is manufactured only by adding a baking step after patterning Cr and forming an ITO film. That is, a special sputtering device for forming CrO2 is unnecessary, which is advantageous in terms of cost.

Next, a second embodiment of the present invention will be described.
The planar structure is the same as that of the first embodiment shown in FIG. 1. In this embodiment, the sectional structure taken along the line AA of FIG. 1 is as shown in FIG. Hereinafter, the main points and differences will be described while omitting the description overlapping with that of the first embodiment. On the substrate (10) such as glass, the light shielding layer (11) made of Cr and the auxiliary capacitance electrode (12) are formed as in the first embodiment.
An interlayer insulating layer (13) is coated on these.
On the interlayer insulating layer (13), the pixel electrode (1
4P), drain line (14L), source electrode (14P)
S) and the drain electrode (14D) are formed. In the direction intersecting the drain line (14L), a
A gate line (17L) including the -Si layer (15) and the gate insulating layer (16) is formed, and a part of the gate line (17L) is formed.
4S) and the drain electrode (14D), respectively, via N + a-Si (15N) and a-Si.
(15), gate insulating layer (16) and gate electrode (17
G) is laminated to form a TFT.

On the other hand, the substrate (20) is arranged at opposite positions with the liquid crystal layer (30) interposed therebetween, and the common electrode (22) made of ITO is first formed on the inner side of the substrate (20). The light shielding layer (21) made of Cr is formed on the inner side of the common electrode (22) to form a black matrix. At the interface between the common electrode (22) and the light-shielding layer (21), Cr is oxidized by baking and low-reflecting CrOx is generated as described above, and the antireflection film (21ox) is formed.
It has been.

In this embodiment, since the antireflection film (21ox) is formed on the outer side of the black matrix, all the reflection of light from the counter substrate side can be suppressed. For this reason, the ambient light is not reflected and hinders visual recognition. Therefore, this structure is suitable for a direct-view type application in which the counter substrate side is used as a display screen.

[0021]

As is apparent from the above description, according to the present invention, the surface oxide film of the light shielding layer is formed at the contact interface between the light shielding layer forming the black matrix on the counter substrate side and the common electrode for driving the liquid crystal. The reflection of light was suppressed by. When the oxide film is formed on the liquid crystal layer side of the light shielding layer, the light reflection between the substrates is prevented and the light leak current is suppressed, so that the liquid crystal display device is suitable for the use of a strong light source such as a projector. it can. On the other hand, when the oxide film is formed on the substrate side of the light shielding layer, reflection of light from the counter substrate side can be suppressed. Therefore, by using the counter substrate side for the display screen, there is no reflection of ambient light and visibility is improved. It becomes an excellent liquid crystal display device. Further, since such an oxide film is selectively formed at the contact interface between the light shielding layer and the common electrode only by adding a heat treatment step, an increase in manufacturing 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 cross-sectional view of a unit pixel of the liquid crystal display device according to the first embodiment of the present invention.

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

FIG. 4 is a cross-sectional view of a unit pixel of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 5 is a plan view of a unit pixel of a conventional liquid crystal display device.

FIG. 6 is a cross-sectional view of a unit pixel of a conventional liquid crystal display device.

[Explanation of symbols]

 10, 20 Substrate 11, 21 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 22 Common electrode 30 Liquid crystal layer

Claims (2)

[Claims] 1. A plurality of pixel electrodes, which are formed on one of opposing surfaces of a pair of substrates in which liquid crystal is hermetically bonded and are formed inside, and which constitute one of pixel capacitances for driving liquid crystal, and are connected to the respective pixel electrodes. A thin film transistor, a common electrode that is formed entirely on the other of the facing surfaces and integrally forms the other of the plurality of pixel capacitors standardized by the pixel electrodes, and a light shielding layer formed between the regions of the pixel capacitor. In the liquid crystal display device, the light shielding layer is formed on the same substrate as the common electrode, and a film in which a surface of the light shielding layer is oxidized is formed at a contact interface between the light shielding layer and the common electrode. A liquid crystal display device characterized in that 2. The common 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 by heat treatment. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is an oxide film.