JP2002182247A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an aperture ratio by increasing auxiliary capacitance and also downsizing a capacitance electrode in an active matrix type liquid crystal display device. SOLUTION: The active matrix type liquid crystal display device comprises TFTs arranged in a matrix form and auxiliary capacitance, and the TFT is provided with a gate electrode on the substrate, a gate insulating film covering the gate electrode, an operating layer on the gate insulating film, a source electrode and a drain electrode on the operating layer, and a protective film covering the source electrode and the drain electrode, and is constituted of an auxiliary capacitance electrode made of the same material as the gate electrode, a pixel electrode connected with the source electrode in an area where the protective film on the source electrode is removed, and a dielectric made of the same material as the gate insulating film.

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 having a structure in which the number of manufacturing steps of an auxiliary capacitor is reduced. And a liquid crystal display device.

A liquid crystal display device includes a simple matrix type and an active matrix type, which are selectively used depending on the application. The active matrix type includes a thin film transistor in each pixel, and the transistor is used when a specific pixel is selected. Is turned on, otherwise O
Since the FF is set, crosstalk can be suppressed even when the number of scanning lines is large, and a high contrast ratio can be obtained.

[0003] Therefore, an active matrix type liquid crystal display device is suitable for large-area display, and its practical use is being promoted.

[0004]

2. Description of the Related Art FIG. 4 shows an equivalent circuit of an active matrix type liquid crystal display device, and FIG. 5 is a front view showing the arrangement of thin film transistors (TFTs), pixels and auxiliary capacitors.

That is, a plurality of gate buses 1 and a plurality of drain buses 2 are orthogonal to each other, and a thin film transistor (TFT) 3 is provided at an intersection of the gate buses 1 and a plurality of drain buses 2. Take a structure to arrange in.

That is, the source electrode 4 of the TFT is connected to the pixel 7
However, since the pixel 7 is configured by using the transparent electrode 8 as an electrode and interposing a liquid crystal between the transparent electrode 8 and a transparent electrode formed on another glass substrate, It has a capacitance and can be electrically shown as a capacitance 5.

However, there is a problem that the capacitance is insufficient with only the capacitance 5, and the switching operation of the TFT 3 causes flicker (flicker) and afterimage (burn-in) of the screen.

Therefore, it is necessary to add an auxiliary capacitor 5.
An auxiliary capacitance electrode 9 is formed on a glass substrate, and an auxiliary film 6 is formed by opposing an insulating film formed on the glass substrate to the dielectric and the transparent electrode 8.

FIG. 3 is a cross-sectional view showing a conventional structure of an inverted staggered TFT, a pixel and an auxiliary capacitor, which is manufactured by the following steps.

That is, a metal such as aluminum (Al) or tantalum (Ta) is formed to a thickness of about 100 nm on a glass substrate 11 made of borosilicate glass or the like and having a thickness of about 1 mm. Selective etching is performed using an etching technique (photolithography) to form a gate electrode 12 and an auxiliary capacitance electrode 13.

Next, an insulator such as silicon nitride (Si3 Nx) is coated to a thickness of about 400 nm by a plasma CVD method to form a gate insulating film 14.

Next, the plasma CVD is performed on the
An amorphous silicon film (hereinafter referred to as an a-Si film) serving as an operation layer 15 and a Si3Nx film are formed by a method or the like, and the Si3Nx film is patterned by using a photolithography technique to form a channel protective film 16.

Next, an amorphous silicon film (n + a-Si film) 17 to which an n-type impurity is added and a Ti film 18 and an Al film for assisting adhesion are formed by a plasma CVD method. Next, a drain electrode 19 and a source electrode 20 following a drain bus line (not shown) are formed by performing patterning using a photolithography technique.

Next, after a protective film 21 is formed thereon by plasma CVD, the protective film 21 in the pixel forming portion is etched to open a window, and tin oxide (SnO2) and indium oxide (I
After forming a transparent conductive film made of a solid solution (abbreviated as ITO) of n2O3) by sputtering or the like, patterning is performed using a photolithography technique, and the transparent electrode 8 is patterned to complete the pixel and auxiliary capacitance. I have.

Although a TFT is made in this way,
The auxiliary capacitance is formed on the glass substrate 11 at the same time as the gate electrode 12 by using the auxiliary capacitance electrode 13 as one electrode.
14 and the protective film 21 are made of a dielectric material, and the transparent electrode 8 is used as a counter electrode.

Here, as described above, it is desirable that the auxiliary capacitance is large in order to eliminate flicker and afterimage on the screen, but since the auxiliary capacitance electrode is formed below the pixel, Preferably, the electrodes are rather reduced.

[0017]

In an active matrix type liquid crystal display device using a TFT, TF
An auxiliary capacitor is provided below the pixel in order to eliminate the flickering of the screen and the afterimage generated at the time of the switching operation of T, but it is desirable that the electrostatic capacitance is larger than before.

On the other hand, from the viewpoint of image display, it is necessary to reduce the size of the auxiliary capacitance electrode to improve the effective display area (aperture ratio).

[0019]

An object of the present invention is to provide a liquid crystal display device in which a thin film transistor and a pixel portion having an auxiliary capacitance are arranged in a matrix on a substrate, wherein the thin film transistor has a gate on the substrate. An electrode, a gate insulating film covering the gate electrode, an operating layer on the gate insulating film, a source electrode and a drain electrode on the operating layer, and a protective film covering the source electrode and the drain electrode. An auxiliary capacitor electrode made of the same material as the electrode, a pixel electrode connected to the source electrode in a region on the source electrode from which the protective film has been removed, and a dielectric made of the same material as the gate insulating film. The auxiliary capacitance electrode made of the same material as the gate electrode or the auxiliary capacitance electrode made of the same material as the gate electrode, The problem is solved by a liquid crystal display device configured to have a pixel electrode connected to a storage electrode, and an auxiliary capacitor composed of a dielectric made of an oxide film obtained by electrolytically oxidizing the surface of the auxiliary capacitor electrode. be able to.

[0020]

As described above, in the active matrix type liquid crystal display device, it is necessary to add an auxiliary capacitance for high image quality, and the required capacitance is determined by the gate capacitance and the pixel capacitance of the TFT. Can be

For example, the gate length is 10 μm and the gate width is 20 μm.
When the size of the pixel electrode is set to 255.times.90 .mu.m using an m.sup.m TFT, a storage capacitor electrode having a pattern of about 50.times.90 .mu.m is used under the pixel.

Here, the conventional storage capacitor dielectric has a two-layer structure of a gate insulating film 14 and a protective film 21 as shown in FIG. 3, and is formed using Si3 Nx having a thickness of about 700 nm. I have.

Therefore, the present inventors employ one of the following methods to reduce the storage capacity of the storage capacitor by reducing the thickness of the dielectric. The dielectric of the storage capacitor is formed only of the gate insulating film. An auxiliary capacitance electrode is formed of Al, and an aluminum oxide film obtained by electrolytically oxidizing Al is used as a dielectric.

The present invention has been made in view of the fact that the auxiliary capacitance does not necessarily require a high breakdown voltage because the TFT is driven at a low voltage, thereby reducing the size of the auxiliary capacitance electrode. can do.

[0025]

Embodiment 1 (Related to Claim 1, Corresponding to FIG. 1) FIG. 1 shows one embodiment of the present invention, and is a sectional view of an auxiliary capacitor and a TFT according to the present invention.

That is, after Al is formed to a thickness of 100 nm on a glass substrate 11 by a sputtering method, the gate electrode 12 is formed to have a gate length of 10 μm and a gate width of 20 using a photolithography technique.
The auxiliary capacitance electrode 13 was formed into a pattern having a width of 25 μm and a length of 90 μm.

Next, Si3Nx was formed to a thickness of 350 nm as a gate insulating film 14 on the substrate including these patterns by a high-temperature plasma CVD method keeping the substrate temperature at 350.degree. Next, as before, an active layer 15 made of an a-Si film, a channel protective film 16, an n + a-Si film 17, a Ti film 18, and an Al film are sequentially formed, and the gate is formed by using a photolithography technique. Dry etching is performed on the insulating film 14 to pattern-form the drain electrode 19, the source electrode 20, and a bus line (not shown).

Next, Si3Nx was placed on the substrate at a substrate temperature of 200
The protective film 21 is formed to have a thickness of 350 nm by a low-temperature plasma CVD method kept at a temperature of ° C. The steps so far are not different from the conventional steps.

That is, in the pixel forming portion, an auxiliary capacitance electrode 13 is provided on a glass substrate 11, on which a gate insulating film 14 made of Si3Nx and a protective film 21 are laminated.

Next, after covering the entire region of the substrate with the resist, only the pixel electrode forming region is opened, and plasma etching is performed under the following conditions to form only the protective film 21 which is formed at a low temperature and is easily etched. Removed.

Etchant: CF4 and O2 (composition ratio 1: 0.1) Total flow rate: 500 sccm Gas pressure: 20 Pa Microwave power: 800 W Next, ITO is formed to a thickness of 100 nm by a sputtering method, and photolithography is performed. Was used to form a transparent electrode 8.

That is, the thickness of the conventional auxiliary capacitor is 700 nm.
Therefore, an area of 50 × 90 μm was required for the auxiliary capacitance electrode 13, but the area was reduced to 25% by halving the film thickness.
The size could be reduced to × 90 μm. As a result, the aperture ratio can be improved.

Instead of forming the gate insulating film as a single film as in this example, a composite film, for example, Si 3 N 4 / SiO 2
In some cases. In that case, it is effective to remove the upper layer of the gate insulating film at the same time as removing the protective film 21.

Embodiment 2 (Related to Claim 2, Corresponding to FIG. 2) FIG. 2 shows another embodiment of the present invention, and is a cross-sectional view of another auxiliary capacitor and a TFT according to the present invention.

That is, after Al is formed to a thickness of 500 nm on a glass substrate 11 by a sputtering method, a photolithography technique is used to form a gate electrode 12 having a gate length of 10 μm and a gate width of 20 μm.
m, and the auxiliary capacitance electrode 13 has a width of 5 μm and a length of 90 μm.
A pattern was formed to a size of μm.

Next, as a gate insulating film 14 on the substrate including these patterns, Si3Nx is formed to a thickness of 350 nm by a high-temperature plasma CVD method in which the substrate temperature is maintained at 350.degree.
Next, as in the conventional case, an active layer 15 composed of an a-Si film, a channel protective film 16, an n + a-Si film 17, a Ti film 18, and an Al film are sequentially formed, and the gate insulating film is formed by using a photolithography technique. Dry etching is performed on the film 14, and the drain electrode 19 and the source electrode 20 are formed.
Then, a bus line (not shown) is patterned.

Next, Si3Nx was placed on the substrate at a substrate temperature of 200
The protective film 21 is formed to have a thickness of 350 nm by a low-temperature plasma CVD method which is maintained at a temperature of ° C. The steps so far are not different from the conventional steps.

That is, in the pixel forming portion, an auxiliary capacitance electrode 13 is provided on a glass substrate 11, on which a gate insulating film 14 made of Si3Nx and a protective film 21 are laminated.

Next, after the entire area on the substrate is coated with the resist, only the pixel electrode formation area is opened, and reactive ion etching (abbreviated as RIE) is performed under the following conditions to form the protective film 21 and the gate insulating film 14. , The auxiliary capacitance electrode 13 made of Al was exposed.

Etchant: SF6 Flow rate: 200 sccm Gas pressure: 2.6 Pa Power: 800 W Next, a 3% aqueous solution of ammonium borate: (NH 4) 3 BO 3 was used as an electrolyte, the exposed Al was used as an anode, and platinum (Pt) was used. ) The plate was used as a cathode, the voltage was increased to 150 V by constant current formation, and the voltage was maintained at that voltage for 10 minutes, and the surface of the auxiliary capacitance electrode 13 made of Al was made of aluminum oxide (γ'Al203) 23.
Was converted to

Since the growth rate of aluminum oxide 23 is about 14 ° / V, an Al oxide film having a thickness of 200 nm is grown. Since the relative dielectric constant is about 9, the capacitance is equivalent to that of a conventional Si3Nx having a thickness of 700 nm and a storage capacitor electrode having a size of 50 × 90 μm.

That is, the size of the auxiliary capacitance electrode can be reduced to 1/10 and the aperture ratio can be improved.

As a method of improving the aperture ratio, it has recently been proposed to use a part of a gate bus line as an auxiliary capacitance electrode. In this case, this method can be similarly applied.

[0044]

According to the present invention, it is possible to realize an active matrix type liquid crystal display device having a structure in which the auxiliary capacitor is reduced in size to improve the aperture ratio by reducing the number of manufacturing steps of the auxiliary capacitor.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a storage capacitor and a TFT according to the present invention.

FIG. 2 is a sectional view of another auxiliary capacitor and a TFT according to the present invention.

FIG. 3 is a sectional view showing a conventional structure of a TFT, a pixel, and an auxiliary capacitor.

FIG. 4 is an equivalent circuit of an active matrix type liquid crystal display device.

FIG. 5 is a front view showing the arrangement of TFTs, pixels, and auxiliary capacitors.

[Explanation of symbols]

 Reference Signs List 3 TFT 4 Source electrode 6 Auxiliary capacitance 7 Pixel 8 Transparent electrode 9, 13 Auxiliary capacitance electrode 11 Glass substrate 12 Gate electrode 14 Gate insulating film 21 Protective film 23 Aluminum oxide

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H092 JA26 JA34 JB63 JB66 KA05 MA05 MA08 MA13 MA17 MA24 NA07 NA27 5F110 AA30 BB01 CC07 DD02 EE03 EE44 FF02 FF03 FF09 FF30 GG02 GG15 GG28 GG29 GG45 HK03 HK18 HK04 HK03 HK04 NN24 NN35 NN72 NN73 QQ04

Claims (2)

[Claims] 1. A liquid crystal display device comprising a thin film transistor and an auxiliary capacitor arranged in a matrix on a substrate, wherein the thin film transistor includes a gate electrode on the substrate, a gate insulating film covering the gate electrode, and the gate. An operation layer on an insulating film, a source electrode and a drain electrode on the operation layer, and a protective film covering the source electrode and the drain electrode; an auxiliary capacitance electrode made of the same material as the gate electrode; A liquid crystal display device comprising: a pixel electrode connected to the source electrode in a region where the protective film is removed; and an auxiliary capacitance formed of a dielectric made of the same material as the gate insulating film. . 2. A liquid crystal display device comprising a thin film transistor and an auxiliary capacitor arranged in a matrix on a substrate, wherein the thin film transistor comprises a gate electrode on the substrate, a gate insulating film covering the gate electrode, and the gate. An operation layer on an insulating film, a source electrode and a drain electrode on the operation layer, and a protective film covering the source electrode and the drain electrode; an auxiliary capacitance electrode made of the same material as the gate electrode; A pixel electrode connected to the source electrode in a region where the protective film is removed, and an auxiliary capacitor formed of a dielectric made of an oxide film obtained by electrolytically oxidizing the surface of the auxiliary capacitor electrode. A liquid crystal display device comprising: