JPH08220558A - Thin film transistor and active matrix type liquid crystal display device using thin film transistor - Google Patents

Abstract

PURPOSE: To reduce the photoexcited current and to stabilize the display characteristic by providing a shading film having an overlap amount with a gate electrode under the gate electrode through an insulating film. CONSTITUTION: On an array substrate 1 which consists of a glass plate, a shading film 10 is formed by forming a metal such as chromium in a film and patterning. Then an insulating film 11 which consists of a silicon nitride and the like is formed in a film, and furthermore, a chromium or the like is formed in a film on the insulating film 11, and a patterning is applied in a photographic process and an etching to form a gate electrode 12. In this case, the positional relation of the gate electrode 12 and the shading film 10 is important, and when the overlap amount B of the gate electrode 12 and the shading film 10 is large, the capacity between the gate electrode 12 and the shading film 10 is made larger so as to render the deterioration of the display property, and on the other hand, when the overlap amount B is small, the shielding effect of the back side light is reduced so as to fail to prevent the photoexcited current of the TFT. Consequently, the estimate of the overlap amount B is carried out in consideration of the superposing slippage in the photographic processing and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor and an active matrix type liquid crystal display device using the same, and more particularly to suppression of leak current due to light in the thin film transistor.

[0002]

2. Description of the Related Art Flat panel displays, particularly active matrix type liquid crystal display devices, are expected as one of the core devices in the advanced information society and the age of multimedia.

The active matrix type liquid crystal display device is
Pixels are formed at the intersections of the source electrode lines and the gate electrode lines arranged in a grid pattern, and each pixel is driven by a switching element such as a thin film transistor (hereinafter referred to as TFT), so that good pixel contrast can be obtained. There is.

FIG. 7 is a plan view (a) and a sectional view (b) showing a general structure of an active matrix type liquid crystal display device.
Is. 1 is an array substrate made of a glass plate, 2 is a source electrode line, 3 is a gate electrode line, 4 is a TFT, 5 is a pixel, 7
Is a counter substrate on which the transparent electrodes 6 facing the array substrate are formed, 8 is a liquid crystal sandwiched between the array substrate 1 and the counter substrate 7, and 9 is a backlight for irradiating light from the array substrate 1 side.

The charge accumulated between the pixel 5 and the transparent electrode 6 is controlled by turning on / off the TFT 4 to change the orientation of the liquid crystal, and the back light emitted from the backlight 9 is transmitted to display a screen. I do.

FIG. 8 is a plan view (a) showing one pixel and a part of the pixel adjacent thereto and a sectional view taken along the line AA of the TFT portion (b).
Is.

In the figure, 3 is a gate electrode line, 2 is a source electrode line, 12 is a gate electrode formed integrally with the gate electrode line 3, 13 is a source electrode formed integrally with the source electrode line 2, and 14 is a source electrode. Drain electrode, 15 is drain electrode 1
4 is a pixel electrode electrically connected to 4; 16 is a storage capacitor electrode electrically connected to the gate electrode line 10; 17 is a gate insulating film covering the gate electrode 12; 18 is an amorphous silicon i layer serving as a channel; Is a channel protective film, 20
Is an amorphous silicon n ⁺ layer doped with phosphorus, 1
Is an array substrate made of glass for forming the above 10 to 20.

The manufacturing method will be described with reference to the sectional views showing the manufacturing steps of the TFT shown in FIGS. First,
As shown in FIG. 9A, a chromium (Cr) film, which is a low resistance and high melting point metal, is deposited on the array substrate 1 made of a glass plate by a sputtering method, and patterning is performed by photolithography and etching, and a gate is formed. The electrode 12 is formed.

Next, as shown in FIG. 9B, a silicon nitride film is deposited by a plasma CVD method to form a gate insulating film 1.
Form 7.

Next, as shown in FIG. 9C, an intrinsic amorphous silicon film and a silicon nitride film are continuously deposited by a plasma CVD method, and the silicon nitride film is patterned by photolithography and etching. Then, a channel protective film 19 serving as an etching stopper and an amorphous silicon i layer 18 serving as a channel are formed.

Next, as shown in FIG. 9 (d), an n ⁺ amorphous silicon film doped with phosphorus is plasma-enhanced.
Then, the amorphous silicon n ⁺ layer 20 serving as the source and the drain is formed by patterning by the method.

Next, as shown in FIG. 9 (e), a metal film containing aluminum (Al) as a main component is deposited by a sputtering method and patterned to form a source electrode 13 and a drain electrode 14, An inverted stagger type TFT is formed.

[0013]

As described above, the charge accumulated between the pixel 5 and the transparent electrode 6 is transferred to the TF.
The screen is displayed by controlling the ON / OFF of T4 to change the orientation of the liquid crystal and transmitting the back light emitted from the backlight 9. At this time, the back light emitted from the backlight 9 is also emitted to the TFT 4.

When the back light is applied to the TFT 4,
The amorphous silicon i layer 18 of 4 receives back light, carriers are excited by the back light, and a photoexcitation current flows even when the TFT 4 is in the OFF state. As a result, the electric charge accumulated between the liquid crystals 4 is reduced and the display characteristics are deteriorated.

The present invention has been made to solve the above problems, and an object of the present invention is to reduce the photoexcitation current and stabilize the display characteristics.

[0016]

The invention according to claim 1 is
A light-shielding film that sequentially shields light on a transparent insulating substrate, a gate electrode formed through the light-shielding film and the insulating film, a gate insulating film, a non-doped semiconductor layer that serves as a channel, and both sides of the non-doped semiconductor layer and the channel. Is a thin film transistor having a semiconductor layer for making ohmic contact with and / or a source electrode and a drain electrode made of metal.

According to a second aspect of the present invention, in the thin film transistor according to the first aspect, the light-shielding film is made of metal and is arranged so as to overlap only the peripheral portion of the gate electrode.

The invention according to claim 3 is the invention according to claim 1 or 2.
In the thin film transistor described above, the insulating film is made of silicon oxide.

According to a fourth aspect of the present invention, a light-shielding film made of a colored insulating material for shielding light, a gate electrode, a gate insulating film, a non-doped semiconductor layer serving as a channel, and a non-doped semiconductor layer are formed on a transparent insulating substrate. And a semiconductor layer for making ohmic contact on both sides of the above channel and /
Alternatively, the thin film transistor includes a source electrode and a drain electrode made of metal.

According to a fifth aspect of the invention, in the thin film transistor according to the fourth aspect, the colored insulator is milky white glass or colored glass.

The invention according to claim 6 is the invention according to claim 1 or 4.
In the thin film transistor described in, the non-doped semiconductor layer is made of i-type amorphous silicon, and the semiconductor layer for making ohmic contact is made of n ⁺ -type amorphous silicon.

According to a seventh aspect of the present invention, an array substrate is formed in which a plurality of gate signal lines and a plurality of source signal lines are intersected with each other, and thin film transistors are disposed at the intersections. A counter substrate provided with a second light-shielding film that shields light at a portion facing the thin film transistor, a liquid crystal sandwiched between the counter substrate and the array substrate, and a back for irradiating light from the array substrate side. It is an active matrix type liquid crystal display device equipped with a light.

According to an eighth aspect of the present invention, in the active matrix type liquid crystal display device according to the seventh aspect, the second light shielding film is made of metal.

According to a ninth aspect of the invention, in the active matrix type liquid crystal display device according to the seventh aspect, the second light shielding film is made of a colored insulator.

According to a tenth aspect of the present invention, in the active matrix liquid crystal display device according to the ninth aspect, the colored insulator is milky white glass or colored glass.

According to an eleventh aspect of the present invention, in the active matrix type liquid crystal display device according to the seventh aspect, the thin film transistors are sequentially formed on the array substrate by a light shielding film for shielding light, and the light shielding film and the insulating film are interposed therebetween. A gate electrode, a gate insulating film, a non-doped semiconductor layer to be a channel, a semiconductor layer for making ohmic contact with the non-doped semiconductor layer and / or both sides of the channel, and / or a source electrode and a drain electrode made of metal. is there.

According to a twelfth aspect of the present invention, in the active matrix type liquid crystal display device according to the eleventh aspect, the light-shielding film is made of metal and is arranged so as to overlap only with the peripheral portion of the gate electrode.

According to a thirteenth aspect of the present invention, in the active matrix type liquid crystal display device according to the eleventh or twelfth aspect, the insulating film is made of silicon oxide.

According to a fourteenth aspect of the present invention, in the active matrix type liquid crystal display device according to the seventh aspect, the thin film transistors are formed on the array substrate in sequence by a light shielding film made of a colored insulating material, a gate electrode and a gate. Insulation film,
A non-doped semiconductor layer to be a channel, a semiconductor layer for making ohmic contact with the non-doped semiconductor layer and both sides of the channel, and / or a source electrode and a drain electrode made of metal are provided.

According to a fifteenth aspect of the present invention, in the active matrix liquid crystal display device according to the fourteenth aspect, the colored insulator is milky white glass or colored glass.

According to a sixteenth aspect of the present invention, in the active matrix type liquid crystal display device according to the eleventh or fourteenth aspect, the non-doped semiconductor layer is made of i type amorphous silicon, and the semiconductor layer for making ohmic contact is an n ⁺ type. Of amorphous silicon.

[0032]

According to the inventions of claims 1 to 6, it is possible to prevent the photoexcitation current of the thin film transistor due to the light emitted from the transparent insulating substrate side.

According to the inventions of claims 2 and 12,
Since the light-shielding film overlaps only with the peripheral portion of the gate electrode, the capacitance between the light-shielding film and the gate electrode can be reduced.

According to the inventions of claims 3 and 13,
Since the insulating film is made of silicon oxide with a small relative permittivity,
The capacitance between the light shielding film and the gate electrode can be reduced.

According to the inventions of claims 4, 5, 14 and 15, since the light-shielding film is made of a colored insulator that shields light, an insulating film for insulating the gate electrode is not required, and the manufacture is easy. Become.

According to the inventions of claims 7 to 16, it is possible to prevent the photoexcitation current of the thin film transistor which is generated by the natural light incident from the counter substrate and deteriorates the display characteristics, and to obtain stable display characteristics.

According to the inventions of claims 11 to 16, it is possible to prevent the photoexcitation current of the thin film transistor which is generated by the light incident from the backlight and deteriorates the display characteristics, and to obtain stable display characteristics.

[0038]

【Example】

Example 1. FIG. 1 is a sectional view of a TFT portion formed in an active matrix type liquid crystal display device according to an embodiment of the present invention. In the figure, 1 is a transparent insulating substrate (array substrate) made of a transparent insulator such as a glass plate, 12 is a gate electrode, 13 is a source electrode, 14 is a drain electrode, 17 is a gate insulating film that covers the gate electrode 12, and 18 is Amorphous silicon i layer serving as a channel, 19 is a channel protective film,
20 is amorphous silicon n doped with phosphorus
⁺ Layer, 10 is a light-shielding film made of metal such as chromium (Cr),
Reference numeral 11 is an insulating film made of silicon nitride or the like which insulates the light shielding film 10 from the gate electrode 12.

2A to 2E show the TF shown in FIG.
FIG. 2 is a cross-sectional view showing the manufacturing process of T, and the manufacturing method will be described below with reference to FIG.

First, as shown in FIG. 2A, on the array substrate 1 made of a glass plate, a metal such as chromium or aluminum is formed into a film by a sputtering method and patterned to form a light shielding film 1.
Form 0.

Next, as shown in FIG. 2B, an insulating film 11 made of silicon nitride or the like is formed by a plasma CVD method, and then chromium is formed on the insulating film 11 by photolithography and etching. Gate electrode 12 after patterning
To form. At this time, the positional relationship between the gate electrode 12 and the light shielding film 10 is important, and if the overlap amount B between the gate electrode 12 and the light shielding film 10 shown in the figure is large, the gate electrode 12
On the other hand, the capacitance between the light shielding film 10 and the light shielding film 10 becomes large, resulting in deterioration of display characteristics. On the contrary, when the overlap amount B is small, the back light shielding effect is reduced and the photoexcitation current of the TFT cannot be prevented. Therefore, the estimation of the overlap amount B is made in consideration of misalignment and the like during photoengraving.

Next, as shown in FIGS. 2 (c) to 2 (e),
Gate insulating film 17, amorphous silicon i layer 18, channel protective film 19, amorphous silicon n ⁺ layer 20,
The source electrode 13 and the drain electrode 14 are sequentially formed in the same manner as in the conventional case to form a TFT.

According to this embodiment, since the light shielding film 10 having the overlap amount B with the gate electrode 12 is provided below the gate electrode 12 through the insulating film 11, the back light emitted from the backlight is shielded. As a result, it is possible to prevent the photoexcitation current of the TFT from being generated, and the display characteristics are stabilized.

In addition to the above-mentioned chromium and aluminum, various metals such as tantalum and molybdenum can be used for the light-shielding film 10 of this embodiment.

Further, it can be applied to thin film transistors using various semiconductor layers in place of the non-doped amorphous silicon i layer 18 and the amorphous silicon n ⁺ layer 20.

Further, as shown in the sectional view of another embodiment of the present invention in FIG. 3, by using milk white glass or colored glass as an insulating material for the light shielding film 10, the insulating layer 1
Since it is not necessary to take 1 into consideration and it is not necessary to consider the problem of capacitance, it can be formed so as to overlap with the entire surface of the gate electrode 12.

Example 2. In the first embodiment, an example is shown in which silicon nitride is used for the insulating film 11 between the gate electrode 12 and the light shielding film 10. However, silicon nitride has a relative dielectric constant of 7 to
It is as large as 7.5, and the capacitance between the gate electrode 12 and the light shielding film 10 becomes large.

FIG. 4 is a sectional view showing a TFT according to another embodiment of the present invention, in which silicon oxide is used for the insulating film 11.

Since the relative permittivity of silicon oxide is about 3.5, the capacitance can be reduced by half as compared with the case where silicon nitride is used.

Example 3. In Examples 1 and 2, the light shielding film 10 was used.
Although the structure for shielding the back light is provided on the array substrate 1, the counter substrate 7 side shown in FIG. 7 is exposed to the natural light, so that the photoexcitation current is generated when the natural light is incident on the TFT.

FIG. 5 is a sectional view showing an embodiment of the active matrix type liquid crystal display device of the present invention, showing one pixel. In the figure, 1 is a circle T
FT, an array substrate on which a pixel electrode 15 connected to the TFT, a storage capacitor electrode 16, and a protective film 22 are formed, 7 is a counter substrate on which a transparent electrode is formed, 8 is a liquid crystal, 9 is a backlight, and the counter substrate 7 The light-shielding film 23 made of a metal film such as chromium or aluminum in a portion corresponding to the upper part of the TFT of
Are formed.

The light-shielding film 23 prevents natural light incident from the counter substrate 7 side from entering the TFT.
It is possible to prevent photoexcitation current from being generated in
As shown in (1), the back light of the backlight can also be shielded by forming the light shielding film 10 in the TFT portion together.

FIG. 6 is a cross-sectional view showing another embodiment of the active matrix type liquid crystal display device of the present invention, in which the peripheral portion of the light shielding film 23 is thicker than the central portion thereof and the natural light incident obliquely is shielded. The effect can be further increased.

In addition to the above metals, many metals such as tantalum, molybdenum, and titanium can be used for the light shielding film 23 of the present embodiment, and milky white glass or colored glass can also be used.

[0055]

According to the inventions of claims 1 to 6, it is possible to prevent the photoexcitation current of the thin film transistor due to the light emitted from the transparent insulating substrate side.

According to the inventions of claims 2 and 12,
Since the light-shielding film overlaps only with the peripheral portion of the gate electrode, the capacitance between the light-shielding film and the gate electrode can be reduced.

According to the inventions of claims 3 and 13,
Since the insulating film is made of silicon oxide with a small relative permittivity,
The capacitance between the light shielding film and the gate electrode can be reduced.

According to the inventions of claims 4, 5, 14 and 15, since the light-shielding film is made of a colored insulator which shields light, an insulating film for insulating the gate electrode is not required, and the manufacture is easy. Become.

According to the inventions of claims 7 to 16, it is possible to prevent the photoexcitation current of the thin film transistor which is generated by the natural light incident from the counter substrate and deteriorates the display characteristics, and to obtain stable display characteristics.

According to the eleventh to sixteenth aspects of the invention, it is possible to prevent the photoexcitation current of the thin film transistor which is generated by the light incident from the backlight and deteriorates the display characteristics, and to obtain stable display characteristics.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a TFT portion formed in an active matrix type liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a manufacturing process of the TFT shown in FIG.

FIG. 3 is a sectional view showing a TFT according to another embodiment of the present invention.

FIG. 4 is a sectional view showing a TFT according to another embodiment of the present invention.

FIG. 5 is a sectional view showing an embodiment of an active matrix type liquid crystal display device of the present invention.

FIG. 6 is a sectional view showing another embodiment of the active matrix type liquid crystal display device of the present invention.

FIG. 7 is a plan view (a) and a sectional view (b) showing a general structure of an active matrix liquid crystal display device.

FIG. 8 is a plan view (a) showing one pixel and a part of a pixel adjacent to the pixel and an AA cross-sectional view (b) of a TFT portion.

FIG. 9 is a cross-sectional view showing a manufacturing process of a TFT.

[Explanation of symbols]

1 transparent insulating substrate (array substrate), 2 source electrode wire,
3 gate electrode lines, 4 thin film transistors (TFTs), 5
Pixels, 6 transparent electrodes, 7 counter substrate, 8 liquid crystal, 9 backlight, 10 and 23 light shielding film, 11 insulating film, 1
2 gate electrode, 13 source electrode, 14 drain electrode, 15 pixel electrode, 16 storage capacitor electrode, 17 gate insulating film, 18 amorphous silicon i layer, 19 channel protective film, 20 amorphous silicon n ⁺ layer, 2
2 protective film

Claims (16)

[Claims] 1. A light-shielding film that sequentially blocks light on a transparent insulating substrate, a gate electrode formed through this light-shielding film and an insulating film, a gate insulating film, a non-doped semiconductor layer that serves as a channel, and this non-doped semiconductor layer. And a semiconductor layer for making ohmic contact with both sides of the channel and / or a source electrode and a drain electrode made of metal, and a thin film transistor. 2. The thin film transistor according to claim 1, wherein the light-shielding film is made of metal and is arranged so as to overlap only a peripheral portion of the gate electrode. 3. The thin film transistor according to claim 1, wherein the insulating film is made of silicon oxide. 4. A light-shielding film made of a colored insulating material for blocking light, a gate electrode, a gate insulating film, a non-doped semiconductor layer to be a channel, and a non-doped semiconductor layer to be a channel, which are sequentially formed on a transparent insulating substrate. A thin film transistor comprising a semiconductor layer for making ohmic contact and / or a source electrode and a drain electrode made of metal. 5. The thin film transistor according to claim 4, wherein the colored insulator is milky white glass or colored glass. 6. The thin film transistor according to claim 1, wherein the non-doped semiconductor layer is made of i-type amorphous silicon, and the semiconductor layer for making ohmic contact is made of n ⁺ -type amorphous silicon. 7. An array substrate formed by intersecting a plurality of gate signal lines and a plurality of source signal lines and arranging thin film transistors at the intersections, and arranged to face the array substrate and face the thin film transistors. A counter substrate on which a second light-shielding film that shields light is formed in a region to be covered, a liquid crystal sandwiched between the counter substrate and the array substrate, and a backlight for irradiating light from the array substrate side is provided. Characteristic active matrix liquid crystal display device. 8. The active matrix type liquid crystal display device according to claim 7, wherein the second light shielding film is made of metal. 9. The active matrix liquid crystal display device according to claim 7, wherein the second light shielding film is made of a colored insulator. 10. The active matrix type liquid crystal display device according to claim 9, wherein the colored insulator is milky white glass or colored glass. 11. A thin film transistor comprises a light-shielding film that sequentially blocks light on an array substrate, a gate electrode formed through the light-shielding film and an insulating film, a gate insulating film, a non-doped semiconductor layer that serves as a channel, and the non-doped semiconductor. 8. An active matrix type liquid crystal display device according to claim 7, further comprising a semiconductor layer and / or a source electrode and a drain electrode made of metal for making ohmic contact with the layer on both sides of the channel. 12. The active matrix type liquid crystal display device according to claim 11, wherein the light shielding film is made of metal and is arranged so as to overlap only with the peripheral portion of the gate electrode. 13. The active matrix type liquid crystal display device according to claim 11, wherein the insulating film is made of silicon oxide. 14. A thin film transistor comprises a light-shielding film made of a colored insulating material for blocking light, a gate electrode, a gate insulating film, a non-doped semiconductor layer to be a channel, and both sides of the non-doped semiconductor layer and the channel, on the array substrate. 8. The active matrix type liquid crystal display device according to claim 7, further comprising a semiconductor layer and / or a source electrode and a drain electrode made of a metal for making ohmic contact with. 15. The active matrix liquid crystal display device according to claim 14, wherein the colored insulator is milky white glass or colored glass. 16. The active matrix type liquid crystal according to claim 11, wherein the non-doped semiconductor layer is made of i-type amorphous silicon, and the semiconductor layer for making ohmic contact is made of n ⁺ -type amorphous silicon. Display device.