JPH09318935A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device which is free from their degradation in its display grade and has high reliability even when the surface of the liquid crystal display device is irradiated with strong light. SOLUTION: Light shielding layers 20 consisting of three films are formed in the positions corresponding to thin-film transistors 18 on a substrate 14. The metallic film 20a is a metal, for example, aluminum, having high reflectivity. The metallic film 20b is a metal, for example, molybdenum, having the reflectivity lower than the reflectivity of metallic film 20a. The multilayered films 20c are multilayered films formed by alternately laminating films of, for example, titanium oxide, having a high refractive index and films of, for example, silicon dioxide, having a low refractive index in two layers.

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 to which, for example, a thin film transistor is added.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view of a typical conventional liquid crystal display device. A signal line 4 and a scanning line 5, which are formed in a matrix, semiconductor switching elements such as a thin film transistor 6 and a pixel electrode 7, are provided on one substrate 1 which is an active matrix substrate. A voltage is applied from the signal line 4 via 6.

A light-shielding layer 8 is provided at a position corresponding to the thin film transistor 6 on the other substrate 2 which is an opposite substrate. On the surface of the substrate 2 other than the light shielding layer 8 and the light shielding layer 8, a flat counter electrode 9 is formed.

A substrate 1 which is an active matrix substrate and a substrate 2 which is a counter substrate are bonded to each other, and liquid crystal 3 is filled between the substrates to manufacture a liquid crystal display device.

The light shielding layer 8 may be composed of a single metal film, or may be composed of two layers of a light shielding layer 8a and a light shielding layer 8b as shown in FIG. Here, the case where the number of the light shielding layers 8 is two will be described.

When the light shielding layer 8 is composed of two layers, the light shielding layer 8a is made of a metal film, for example, a film made of chromium. A metal oxide film, for example, a film made of chromium oxide is used for the light shielding layer 8b. The light-shielding layer 8b functions as an antireflection film, and its film thickness is selected so that the reflectance of the light-shielding layer 8 becomes low due to interference.

As shown in FIG. 3, when light of high intensity enters from the substrate 2 side of the liquid crystal display device as shown by 10, the incident light 10 is blocked by the light shielding layer 8a, and the incident light 10 is blocked. Are prevented from being directly irradiated on the thin film transistor 6.

A part of the incident light 10 is absorbed by the light shielding layer 8a. Due to this light absorption, the temperature of the light shielding layer 8 rises, and as a result, the liquid crystal 3 and the thin film transistor 6 rise in temperature. As a result, the reliability of the liquid crystal 3 is lowered due to the temperature rise and the characteristics of the thin film transistor 6 are deteriorated.

A part of the light applied to the liquid crystal display device enters the inside of the liquid crystal display device as indicated by 11, and a part of the light is reflected by one of the substrates 1 to be applied to the light shielding layer 8b. . When this light is further reflected again by the light shielding layer 8b and applied to the thin film transistor 6, the characteristics of the thin film transistor 6 deteriorate due to the light irradiation.

As indicated by reference numeral 12, the liquid crystal display device enters the inside of the liquid crystal display device and is partially reflected by one of the substrates 1.
When the light re-reflected by the light-shielding layer 8b is emitted to the substrate 1 side through the space between the picture element electrodes 7, the display contrast is lowered.

As a means for preventing the temperature increase due to light absorption in the light shielding layer 8a, the reflectance of the light shielding layer 8a on the side in contact with the substrate 2 is increased. As a result, a part of the incident light 10 is reflected by the light shielding layer 8a, so that the temperature rise due to light absorption can be suppressed.

As a means for preventing re-reflection on the light-shielding layer 8b, the light-shielding layer 8b on the side in contact with the counter electrode 9 has a low reflectance. As a result, the incident lights 11 and 12 are absorbed by the light-shielding layer 8b, so that it is possible to reduce the amount of light that is applied to the thin film transistor 6 or that is emitted to the substrate 1 side through between the pixel electrodes 7.

[0013]

In the prior art, since the light shielding layer 8 is formed of only one metal layer or two layers of metal and metal oxide, the reflectance of the light shielding layer 8 on the substrate 2 side. Cannot be made sufficiently high and the reflectance on the counter electrode 9 side cannot be made sufficiently low.

Therefore, a part of the incident light 10 is absorbed by the light shielding layer 8, and the temperature rise due to the light absorption, that is, the temperature rise of the liquid crystal 3 and the thin film transistor 6 occurs. Due to this temperature increase, the reliability of the liquid crystal 3 is deteriorated and the characteristics of the thin film transistor 6 are deteriorated.

A part of the incident light 11 is reflected by the light shielding layer 8 and is applied to the thin film transistor 6. This light irradiation causes deterioration of the characteristics of the thin film transistor 6. Further, since a part of the incident light 12 reflected by the light shielding layer 8 is emitted to the substrate 1 side through the space between the pixel electrodes 7, the display contrast is lowered.

An object of the present invention is to solve such problems and to provide a liquid crystal display device with a surface irradiated with strong light.
An object of the present invention is to provide a highly reliable liquid crystal display device which does not deteriorate the display quality.

[0017]

According to the present invention, a semiconductor switching element and a pixel electrode to which a potential is applied via the semiconductor switching element are formed on one substrate, and a counter electrode and a semiconductor switching element are provided on the other substrate. In a liquid crystal display device in which a light-shielding layer is formed in a corresponding portion and liquid crystal is filled between the both substrates, the light-shielding layer is sequentially formed from the substrate surface.
It is composed of three layers of a first metal film, a second metal film, and an antireflection film, and the first metal film and the second metal film have different reflectances.

Further, the antireflection film of the light-shielding layer of the present invention is characterized in that it is a multilayer film in which films having different refractive indexes are alternately laminated.

Further, the antireflection film of the light shielding layer of the present invention is a semiconductor film.

Hereinafter, the operation of the present invention will be described.

According to the present invention, the light-shielding layer can sufficiently increase the reflectance on the surface on the counter substrate side, and can sufficiently reduce the reflectance on the liquid crystal-side surface of the light-shielding layer.

Therefore, most of the incident light is reflected on the surface of the light-shielding layer, so that the temperature rise due to the light absorption of the light-shielding layer, that is, the temperature rise of the liquid crystal and the thin film transistor can be suppressed to a level without a problem. As a result, it is possible to prevent the characteristics of the switching element from being deteriorated and the reliability of the liquid crystal to be lowered due to the temperature increase.

Most of the incident light is reflected on the surface of the light shielding layer, part of it is incident on the liquid crystal display device, and the light reflected on the active matrix substrate side is absorbed by the antireflection film of the light shielding layer. Therefore, the light that has entered the light-shielding layer is not emitted to the switching element or emitted to the one substrate side through the space between the picture elements. As a result, it is possible to prevent the deterioration of the characteristics of the switching element and the reduction of the display contrast due to the light irradiation.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

(Embodiment 1) FIG. 1 is a sectional view of a liquid crystal display device according to Embodiment 1 of the present invention, and FIG. 2 is a plan view thereof. In this liquid crystal display device, liquid crystal 15 is filled between a pair of translucent substrates 13 and 14 made of glass or the like. Signal lines 16 and scanning lines 17, semiconductor switching elements such as thin film transistors 18 and pixel electrodes 19 arranged in a matrix are provided on one substrate 13 which is an active matrix substrate. A voltage is applied from the signal line 16 via 18.

A light-shielding layer 20 is formed at a position corresponding to the thin film transistor 18 on the other substrate 14 serving as a counter substrate.

Due to the relationship between the steps and the like, as shown in FIG. 2, the light shielding layer 20 is not only at the position corresponding to the thin film transistor 18 but also at portions other than the pixel electrode 19 including the signal line 16 and the scanning line 17. Also to form.

The light shielding layer 20 and the light shielding layer 2 of this substrate 14
A planar counter electrode 21 is formed on the surface other than 0.

The light shielding layer 20 is made of a metal film 20a, 2
0b and a multilayer film 20c serving as an antireflection film.

The metal film 20a is made of a metal having a high reflectance, such as aluminum (having a reflectance of 80% or more for visible light).
It is formed with a film thickness of about 100 nm. The metal film 20a has a role of increasing the reflectance of the light shielding layer 20 on the substrate 14 side.

The metal film 20b is made of a metal having a lower reflectance than that of the metal film 20a, such as molybdenum (having a reflectance of about 60% for visible light) and a thickness of about 50 nm.
It is formed on top of 0a.

As a film forming method, aluminum and then molybdenum are formed on the substrate 14 by a sputtering method, and then patterned into a predetermined shape to form a metal film 20a made of aluminum and a metal film 20b made of molybdenum.
Is formed.

In the case of aluminum, since the reflectance is high, an antireflection film that is sufficiently effective against this is used as the metal film 2.
It is difficult to form several transparent films on top of 0a, but by providing the metal film 20b, the reflectance on the surface of the metal film 20b can be lowered, and a multilayer film which is an antireflection film provided on the metal film 20b. The effect of 20c can be improved.

When the metal film 20a is formed of aluminum, the metal film 20b also serves as a protective film against aluminum and prevents damage such as corrosion to aluminum that occurs in the process of manufacturing a liquid crystal display device. You can

The multilayer film 20c is a multilayer film in which a film having a high refractive index, such as titanium oxide, and a film having a low refractive index, such as silicon dioxide, are alternately laminated by vacuum evaporation or the like. The refractive index of titanium oxide is 2.2 to 2.7, and its film thickness is about 40 nm. The refractive index of silicon dioxide is 1.46, and its film thickness is about 100 nm.

In the first embodiment, the multilayer film 20c has two layers, but it may be formed in two or more layers depending on the materials of the films to be laminated and the refractive index thereof.

That is, by controlling the number of layers of the multilayer film 20c, the film thickness of each layer, the refractive index, and utilizing interference, the multilayer film 20c functions as an antireflection film.

By making the light-shielding layer 20 have the above-described structure, the surface of the light-shielding layer 20 on the substrate 14 side has a sufficiently high reflectance in the entire visible light range, for example, the reflectance is 80% or more. In addition, the reflectance on the surface of the liquid crystal 15 side can be made sufficiently low in the entire visible light range, for example, the reflectance can be 5% or less.

The liquid crystal display device having such a configuration is used in a device in which intense light is emitted from the substrate 14 side, for example, a projection device.

Light of high intensity is emitted from the substrate 1 of the liquid crystal display device.
When the light enters from the 4 side as shown by 22 in FIG. 1, the incident light 22 is blocked by the metal film 20a, and the thin film transistor 18 is prevented from being directly irradiated with the incident light. Since the reflectance of the metal film 20a on the substrate 14 side is as high as 80% or more, most of the incident light 22 is reflected by the surface of the metal film 20a.

Therefore, the temperature rise due to the light absorption of the light shielding layer 20, that is, the temperature rise of the liquid crystal 15 and the thin film transistor 18 can be suppressed to a level at which there is no problem. As a result, it is possible to prevent the characteristics of the thin film transistor 18 from deteriorating and the reliability of the liquid crystal 7 to decrease due to the temperature increase.

A part of the light applied to the liquid crystal display device enters the inside of the liquid crystal display device as shown by 23 in FIG. 1, is reflected by the substrate 13 and is applied to the light shielding layer 20. However, since the reflectance of the metal film 20b on the liquid crystal 15 side is sufficiently low and 5% or less, the incident light 23 is not reflected by the metal film 20b.
Is mostly absorbed by.

Therefore, the thin film transistor 18 is not irradiated by the reflection on the light shielding layer 20. This can prevent deterioration of the characteristics of the thin film transistor 18 caused by light irradiation.

Further, as shown at 24 in FIG. 1, most of the light that enters the inside of the liquid crystal display device, is reflected by the substrate 13 and is applied to the light shielding layer 20 is absorbed by the multilayer film 20c. , Is not emitted to the substrate 13 side through the space between the pixel electrodes 19. Thereby, it is possible to prevent a decrease in display contrast.

The material of the metal film 20a may be silver, platinum, palladium or the like other than aluminum as described above. The visible light reflectance of the metal film 20a is about 80%.
The above is desirable.

The material of the metal film 20b may be tantalum, titanium, tungsten, etc., in addition to the above molybdenum. The reflectance of visible light of the metal film 20b is preferably about 60% or less.

Regarding the material of the multilayer film 20c, a film having a high refractive index may be tantalum oxide, zinc oxide or the like in addition to the above-mentioned titanium oxide, and the refractive index range is 1.7 to.
In addition to the above-mentioned silicon dioxide, magnesium fluoride or the like may be used as the film having a low refractive index of about 2.7, and the range of the refractive index is about 1.3 to 1.7.

(Embodiment 2) As another embodiment, the light shielding layer 20 of Embodiment 2 is made of a metal film 20a, 20a.
b, three portions 20d made of a semiconductor film to be an antireflection film.

Since the second embodiment is different from the first embodiment only in the structure of the semiconductor film 20d which is the third layer,
The sectional view and the plan view will be described with reference to FIGS. 1 and 2 of the first embodiment.

In this liquid crystal display device, a liquid crystal 15 is filled between a pair of translucent substrates 13 and 14 made of glass or the like. Signal lines 16 and scanning lines 17, semiconductor switching elements such as thin film transistors 18 and pixel electrodes 19 arranged in a matrix are provided on one substrate 13 which is an active matrix substrate. A voltage is applied from the signal line 16 via 18.

A light shielding layer 20 is formed on the other substrate 14 serving as the counter substrate at a position corresponding to the thin film transistor 18.

Due to the process and the like, as shown in FIG. 2, the light-shielding layer 20 is not only at the position corresponding to the thin film transistor 18, but also at the portion other than the pixel electrode 19 including the signal line 16 and the scanning line 17. Also to form.

The light-shielding layer 20 and the light-shielding layer 2 of this substrate 14
A planar counter electrode 21 is formed on the surface other than 0.

The light shielding layer 20 is made of a metal film 20a, 2
0b and a semiconductor film 20d serving as an antireflection film.

As in the first embodiment, the metal film 20a is formed of a metal having a high reflectance, for example, aluminum (having a reflectance of 80% or more for visible light) with a thickness of about 100 nm.
The metal film 20a has a role of increasing the reflectance of the light shielding layer 20 on the substrate 14 side.

The metal film 20b is made of a metal having a reflectance lower than that of the metal film 20a, for example, molybdenum (reflectance of visible light is about 60%) with a thickness of about 50 nm.
It is formed on top of 0a.

As a film forming method, aluminum and then molybdenum are formed on the substrate 14 by a sputtering method and then patterned into a predetermined shape to form a metal film 20a made of aluminum and a metal film 20b made of molybdenum.
Is formed.

In the case of aluminum, since the reflectance is high, an antireflection film that is sufficiently effective against this is used as the metal film 2.
It is difficult to form several transparent films on top of 0a, but by providing the metal film 20b, the reflectance on the surface of the metal film 20b can be lowered, and a semiconductor film which is an antireflection film provided on the metal film 20b. The effect of 20d can be improved.

When the metal film 20a is formed of aluminum, the metal film 20b also serves as a protective film for aluminum and prevents damage such as corrosion of aluminum that occurs in the process of manufacturing a liquid crystal display device. You can

The semiconductor film 20d is made of a semiconductor such as amorphous silicon and has a refractive index of 3.5 to 4.0. By absorbing the amorphous silicon film and controlling the film thickness to utilize the interference, the semiconductor film 20d functions as an antireflection film, and the reflectance can be reduced to 5% or less in the entire visible light range. The amorphous silicon film used here is formed by a CVD method or the like and has a film thickness of 10 to 30.
It is about nm.

By making the light-shielding layer 20 have the above-described structure, the surface of the light-shielding layer 20 on the substrate 14 side has a sufficiently high reflectance in the entire visible light range, for example, the reflectance is 80% or more. In addition, the reflectance on the surface of the liquid crystal 15 side can be made sufficiently low in the entire visible light range, for example, the reflectance can be 5% or less.

The liquid crystal display device having such a configuration is used in a device, such as a projection device, in which intense light is emitted from the substrate 14 side.

Light of high intensity is emitted from the substrate 1 of the liquid crystal display device.
When the light enters from the 4 side as shown by 22 in FIG. 1, the incident light 22 is blocked by the metal film 20a, and the thin film transistor 18 is prevented from being directly irradiated with the incident light. Since the reflectance of the metal film 20a on the substrate 14 side is as high as 80% or more, most of the incident light 22 is reflected by the surface of the metal film 20a.

Therefore, the temperature rise due to the light absorption of the light shielding layer 20, that is, the temperature rise of the liquid crystal 15 and the thin film transistor 18 can be suppressed to a level at which there is no problem. As a result, it is possible to prevent the characteristics of the thin film transistor 18 from deteriorating and the reliability of the liquid crystal 7 to decrease due to the temperature increase.

A part of the light applied to the liquid crystal display device enters the inside of the liquid crystal display device as shown by 23 in FIG. 1, is reflected by the substrate 13 and is applied to the light shielding layer 20. However, since the reflectance of the metal film 20b on the liquid crystal 15 side is sufficiently low and 5% or less, the incident light 23 is not reflected by the metal film 20b.
Is mostly absorbed by.

Therefore, the thin film transistor 18 is not irradiated by the reflection on the light shielding layer 20. This can prevent deterioration of the characteristics of the thin film transistor 18 caused by light irradiation.

Further, as shown by 24 in FIG. 1, most of the light that enters the inside of the liquid crystal display device, is reflected by the substrate 13 and is applied to the light shielding layer 20 is absorbed by the semiconductor film 20d. , Is not emitted to the substrate 13 side through the space between the pixel electrodes 19. Thereby, it is possible to prevent a decrease in display contrast.

The material of the semiconductor film 20d may be a semiconductor having a large refractive index in the visible region, such as germanium, in addition to the above amorphous silicon. The refractive index of germanium is 4.0.

Since these have a large refractive index in the visible region,
Even a single layer effectively functions as an antireflection film for metal.

In Embodiments 1 and 2, the multilayer film 20c and the semiconductor film 20d, which are antireflection films, are replaced by the metal film 2.
The multilayer film 2 which is an antireflection film is provided only on the upper part of 0b.
0c and the semiconductor film 20d are transparent to visible light, they may be provided on the entire surface of the substrate 14.

[0071]

As described above, according to the present invention, the light shielding layer can have a sufficiently high reflectance on the surface on the counter substrate side, and the reflectance on the liquid crystal side surface of the light shielding layer. Can be low enough.

Therefore, most of the incident light is reflected by the surface of the light shielding layer, so that the temperature rise due to the light absorption of the light shielding layer, that is, the temperature of the liquid crystal and the thin film transistor can be suppressed to a level without any problem. As a result, it is possible to prevent the characteristics of the switching element from being deteriorated and the reliability of the liquid crystal to be lowered due to the temperature increase.

Most of the incident light is reflected by the surface of the light shielding layer, part of it is incident on the liquid crystal display device, and the light reflected by the active matrix substrate side is absorbed by the antireflection film of the light shielding layer. Therefore, the light that has entered the light-shielding layer is not emitted to the switching element or emitted to the one substrate side through the space between the picture elements. As a result, it is possible to prevent the deterioration of the characteristics of the switching element and the reduction of the display contrast due to the light irradiation.

[Brief description of drawings]

FIG. 1 is a sectional view of a liquid crystal display device of the present invention.

FIG. 2 is a plan view of a liquid crystal display device of the present invention.

FIG. 3 is a sectional view of a conventional liquid crystal display device.

[Explanation of symbols]

 13 14 substrate 15 liquid crystal 16 signal line 17 scanning line 18 thin film transistor 19 picture element electrode 20 light-shielding layer 20a 20b metal film 20c multilayer film 20d semiconductor film 21 counter electrode 22 23 24 incident light

Claims (3)

[Claims] 1. A semiconductor switching element and a pixel electrode to which a potential is applied through the substrate are formed on one substrate, and a light-shielding layer is formed on a portion corresponding to the counter electrode and the semiconductor switching element on the other substrate. In the liquid crystal display device in which liquid crystal is filled between the both substrates, the light shielding layer is composed of three layers including a first metal film, a second metal film, and an antireflection film in order from the substrate surface, A liquid crystal display device, wherein the first metal film and the second metal film have different reflectances. 2. The liquid crystal display device according to claim 1, wherein the antireflection film of the light shielding layer is a multilayer film in which films having different refractive indexes are alternately laminated. 3. The liquid crystal display device according to claim 1, wherein the antireflection film of the light shielding layer is a semiconductor film.