JPH0682822A - Liquid crystal display element and its production - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display element having an excellent picture element potential holding characteristic, large opening rate and high display grade and the process for production thereof. CONSTITUTION:Anodically oxidized films 4a, 4b respectively varying in film thicknesses are formed on gate electrodes 2 and electrodes 3 for additive capacitors. A dielectric substance layer consisting of the anodically oxidized film 4b and insulating film 5 is interposed between pixel electrodes 11 and the electrodes 3 for additive capacitors. The additive capacitors are formed in parallel with the capacitors by picture elements. The characteristic to hold the picture element potentials is improved by the capacitor characteristics thereof. The anodically oxidized films 4a, 4b are formed respectively at the film thicknesses optimum for TFTs 14 and the film thicknesses optimum for the additive capacitors and, therefore, the change in the characteristics of the TFTs 14 does not arise and the additive capacity is sufficiently increased while the large opening rate is maintained.

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 element using a thin film transistor (hereinafter referred to as TFT) as a switching element and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display element is a cathode ray tube (C
It is used in various fields because it has an advantage that the thickness (depth) can be remarkably reduced as compared with RT) and that power consumption during driving can be reduced.

In recent years, an active matrix type liquid crystal display device has been widely used which can display a high quality image in color even when the number of scanning lines is increased as in a television or a computer.

3 and 4 are diagrams showing a conventional active matrix type liquid crystal display device. In the liquid crystal display device, a plurality of gate bus lines 12 and 12 and a plurality of source bus lines 16 and 16 are provided vertically and horizontally on the insulating substrate 1. A pixel electrode 11 is formed in each region surrounded by the gate bus lines 12 and 12 and the source bus lines 16 and 16. On this picture element electrode 11, a liquid crystal cell (not shown) in which a liquid crystal is sealed is arranged as a picture element. A TFT 14 is formed to drive each picture element. The gate electrode 2 of the TFT 14 is formed on the substrate 1 as a part of the gate bus line 12. Below the pixel electrode 11, an additional capacitance electrode 3 made of the same material as the gate electrode 2 is formed on the same plane as the gate electrode 2.
An anodic oxide film 4 and an insulating film 5 are formed on the gate electrode 2 and the additional dual-purpose electrode 3.

A method of forming the anodic oxide film 4 will be described with reference to FIG. First, the insulating substrate 1 on which the gate electrode 2 and the additional capacitance electrode 3 are formed and the electrode substrate such as Pt are immersed in an electrolytic solution such as ammonium borate, ammonium phosphate, or ammonium tartrate. Then, the gate electrode 2 and the additional capacitance electrode 3 serve as an anode, and the electrode substrate is wired so as to serve as a cathode, and an electrolytic treatment is performed to form an anodic oxide film on the gate electrode 2 and the additional capacitance electrode 3. 4 is formed.

A semiconductor film 8 made of amorphous silicon (a-Si) is formed on the insulating film 5 above the gate electrode 2.
Insulating film 9, n ⁺ -amorphous silicon (n ⁺ -a-S
The contact film 10 made of i), the source electrode 6 and the drain electrode 7 are laminated to form a TFT 14. The source electrode 6 and the drain electrode 7 are the source bus line 16
Made of the same material as, and formed at the same time. Further, a pixel electrode 11 is laminated so as to be electrically connected to the drain electrode 7. A protective insulating film 13 is laminated on the pixel electrode 11 and the TFT 14.

In the above structure, a dielectric layer consisting of the anodic oxide film 4 and the gate insulating film 5 is interposed between the pixel electrode 11 and the additional capacitance electrode 3. Therefore, the pixel electrode 11
And the additional capacitance electrode 3 form an additional capacitance for charge storage. This additional capacitance is formed in parallel with the capacitance of the picture element, and the picture element potential holding characteristic is improved.

[0008]

In the above active matrix type liquid crystal display device, the anodic oxide film 4 is
Since it is formed on the gate electrode 2 and the additional capacitance electrode 3 at the same time, the gate electrode 2 and the additional capacitance electrode 3 have the same film thickness. This film thickness is a film thickness suitable for performing an operation as a gate insulating film together with the insulating film 5, and T
Since the film thickness is suitable for FT14, the film thickness is not always suitable as the dielectric layer for the additional capacitance. The thickness of the anodic oxide film 4 on the additional capacitance electrode 3 needs to be determined in consideration of increasing the additional capacitance. For example,
The anodic oxide film 4 on the gate electrode 2 is made of Ta ₂ O ₅ and Al ₂ O ₃ and has a film thickness of 2000 Å, and the gate insulating film 5 is made of Si ₃ N ₄ and SiO ₂ and has a film thickness of 20.
When the thickness is from 00 to 5000 Å, the film thickness for forming the dielectric layer for the additional capacitance is too large, and the obtained additional capacitance becomes small.

In order to increase the additional capacitance, it is necessary to reduce the film thickness of the anodic oxide film 4 and / or the insulating film 5 forming the dielectric layer or to increase the area of the additional capacitance electrode 3. There is. However, when the area of the additional capacitance electrode 3 is increased, the aperture ratio (ratio of the amount of light extracted on the emission side to the amount of light incident on the liquid crystal panel) decreases,
This is not preferable because it deteriorates the display quality of the liquid crystal display element. Further, when the film thickness of the insulating film 5 is made thin, it is not possible to sufficiently complement the defect portion generated in the anodic oxide film.

There is also a method of separately laminating the gate insulating film 5 on the gate electrode 2 and the additional capacitance electrode 3 in order to obtain the optimum film thickness of the dielectric layer for each of the TFT and the additional capacitance. There is also a method of selectively using two types of films having different dielectric constants. However, in this case, the number of steps increases, which is not preferable.

The present invention has been made in order to solve the above problems, and provides a liquid crystal display device having excellent display potential holding characteristics, a large aperture ratio, and high display quality, and a manufacturing method thereof. The purpose is to

[0012]

A liquid crystal display element according to the present invention comprises a pixel electrode provided on an insulating substrate, a thin film transistor for switching a voltage applied to the pixel electrode, the substrate and the pixel. A liquid crystal display device having an additional capacitance electrode made of the same material as the gate electrode of the thin film transistor, which is provided between the thin film transistor and the thin film transistor, wherein an anodic oxide film is provided on the gate electrode and the additional capacitance electrode. The anodic oxide film provided on the gate electrode and the anodic oxide film provided on the additional capacitance electrode have different film thicknesses, whereby the above object is achieved.

According to the method of manufacturing a liquid crystal display device of the present invention, a pixel electrode provided on an insulating substrate, a thin film transistor for switching a voltage applied to the pixel electrode, the substrate and the pixel electrode. In a liquid crystal display element having a gate electrode of the thin film transistor and an electrode for additional capacitance provided between the thin film transistors, different potentials are applied to the gate electrode and the electrode for additional capacitance, or different time is applied. A potential is applied to form an anodic oxide film, whereby the above object is achieved.

[0014]

In the present invention, the film thickness of the anodic oxide film on the electrode for the additional capacitance and the film thickness of the anodic oxide film on the gate electrode can be changed, so that the degree of freedom in designing the additional capacitor is widened. For example, if the thickness of the anodic oxide film on the gate electrode is TF,
The film thickness of the anodic oxide film on the electrode for additional capacitance can be reduced while keeping the film thickness optimum for T. Therefore, the additional capacitance can be increased without increasing the area of the additional capacitance electrode and lowering the aperture ratio.

As a result, a liquid crystal display element having excellent pixel potential holding characteristics and a large aperture ratio can be obtained.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment) FIG. 1 is a plan view showing an embodiment of the liquid crystal display device of the present invention, and FIG. 2 is a sectional view taken along line XX of FIG.

In this liquid crystal display element, the gate electrode 2
Further, the anodic oxide films 4a and 4b having different film thicknesses are formed on the electrode 3 for additional capacitance.

This liquid crystal display device is manufactured as follows.

First, Ta, Al, etc. are laminated on the insulating substrate 1 by sputtering, and this is patterned by photoetching to form the gate electrode 2 and the additional capacitance electrode 3 of the TFT 14 on the same plane at a constant pitch. Form.

Next, the Ta or Al surface on the gate electrode 2 and the additional capacitance electrode 3 is oxidized by an anodic oxidation method to obtain a film thickness of tantalum pentoxide (Ta ₂ O ₅ ) or Al ₂ O _3. Different anodic oxide films 4a and 4b are formed.

As a method of forming the anodic oxide films 4a and 4b having different film thicknesses on the gate electrode 2 and the additional capacitance electrode 3, for example, the following method can be mentioned. First,
As shown in FIG. 5, the insulating substrate 1 on which the gate electrode 2 and the additional capacitance electrode 3 are formed and the electrode substrate such as Pt are immersed in an electrolytic solution such as ammonium borate, ammonium phosphate, or ammonium tartrate. Next, wiring is performed so that the gate electrode 2 and the additional capacitance electrode 3 serve as an anode and the electrode substrate serves as a cathode. At this time, the voltage applied to the gate electrode 2 and the additional capacitance electrode 3 can be changed. Since the film thickness of the anodic oxide film is determined by the voltage applied to the electrodes, the film thickness of the anodic oxide films 4a and 4b can be changed. Therefore, the anodic oxide film 4a is formed on the TFT 14
The anodic oxide film 4b can be formed to have different film thicknesses, and the anodic oxide film 4b can be formed to have different film thicknesses as the optimum dielectric layer for the additional capacitance.

In the above, instead of controlling the voltage,
The same effect can be obtained by controlling the anodic oxidation time.

After that, the gate insulating film 5 is subjected to plasma CVD.
It is formed by the method. Further, the semiconductor film 8 and the insulating film 9 are successively laminated. This is patterned by photo etching to form the patterned semiconductor film 8 and insulating film 9 on the gate electrode 2. Next, plasma CV
The semiconductor contact film 10 for ohmic contact is formed by the D method, and patterned by photoetching to form the patterned semiconductor contact film 10 that contacts the source electrode 6 and the drain electrode 7. Next, a source electrode 6 and a drain electrode 7 are formed by stacking Ti, Mo, W, etc. by a sputtering method or an electron beam evaporation method and patterning them by photoetching. As described above, the switching TFT 14 is manufactured.

Next, a transparent conductive film containing indium oxide as a main component is laminated by a sputtering method or an electron beam evaporation method. This is patterned by photo-etching to form a rectangular pixel electrode 11 having one end connected to the drain electrode 7 and the other end extending above the additional capacitance electrode 3. Further, a protective film 13 is laminated on this by the plasma CVD method. As described above, one cell substrate of the active matrix type liquid crystal display device in which the anodic oxide films 4a and 4b having different film thicknesses are formed on the gate electrode 2 and the additional capacitance electrode 3 on the insulating substrate 1 is manufactured. To be done.

Next, the electrode substrate on which the counter electrode for applying a voltage to the liquid crystal is formed together with the pixel electrode 11 is used as the other cell substrate and is integrally bonded to each other through a gap, and the liquid crystal is sealed in this gap. By performing twisted nematic alignment, an active matrix type liquid crystal display device can be obtained.

The operation of this liquid crystal display device is as follows. By applying a voltage to the picture element electrode 11 and the counter electrode via the TFT, a matrix display for each picture element unit is executed. At this time, a dielectric layer composed of the anodic oxide film 4b and the insulating film 5 is interposed between the picture element electrode 11 and the additional capacitance electrode 3, and the additional capacitance is formed in parallel with the capacitance of the picture element. It Due to this capacitor characteristic, the voltage determined by the time constant is applied to the liquid crystal even if the TFT 14 is turned off and the voltage application to the pixel electrode 11 is cut off. As a result, the voltage decrease due to the leak current of the liquid crystal is compensated, and the pixel potential holding characteristic is improved.

The details of this embodiment are as follows.

Insulating substrate 1: Glass substrate Gate electrode 2: Ta, Al, thickness 4000-8000 angstrom Additional capacitance electrode 3: Ta, Al, thickness 4000-800
0 angstrom anodic oxide film 4a: Ta ₂ O ₅ , thickness 2000 angstrom anodic oxide film 4b: Ta ₂ O ₅ , thickness 1000 angstrom gate insulating film 5: SiN _x , 2000 angstrom source electrode 6, drain electrode 7: Ti, Mo , W, thickness 3000 angstrom semiconductor film 8: amorphous silicon (a-Si), thickness 300 angstrom insulating film 9: SiN _x , thickness 2000 angstrom semiconductor contact film 10: n ⁺ -amorphous silicon (n ⁺ -a-Si), Thickness 400 Å Pixel electrode 11: Indium oxide, thickness 1000 Å Protective film 13: SiN _x , thickness 4000 Å In this liquid crystal display device, the area of the additional capacitance electrode 3 is increased to reduce the additional capacitance. It was possible to increase the amount and improve the retention characteristic of the pixel potential.

In the above embodiment, Ta was used as the material for the gate electrode 2 and the additional capacitance electrode 3, but Al, W,
Other anodizable metals can be used. In particular,
When Ta is used, since the dielectric constant of tantalum pentoxide is high, the additional capacitance can be made high. However,
Since Ta has a large specific resistance, the image quality may be deteriorated due to a gate wiring delay. Therefore, Cu or Al is laminated on the Ta wiring to reduce the resistance. As the insulating film, Si ₃ N ₄ , TiO ₂ , SiO ₂ , Y ₂ O ₃ can be used, and as the protective film, Si ₃ N ₄ , AlN, other nitride film or oxide film can be used. it can. Amorphous silicon or polysilicon may be used as the semiconductor film. The semiconductor film, the insulating film and the protective film may be formed by a vapor deposition method, a plasma CVD method or a sputtering method. Further, by overlapping a color filter layer on the pixel electrode 11 or the counter electrode, it can be used as a color display device.

[0031]

According to the present invention, since the additional capacitance is formed in parallel with the capacitance of the picture element, the retention characteristic of the picture element potential is improved. The thickness of the anodic oxide film on the gate electrode is TF.
Since the film thickness of the anodic oxide film on the electrode for the additional capacitance is formed to be the optimum film thickness for the additional capacitance T, the characteristics of the TFT are not changed and the aperture ratio is kept large. The additional capacity can be increased sufficiently. Therefore, a high-quality display image can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a liquid crystal display element of the present invention.

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

FIG. 3 is a plan view showing a conventional liquid crystal display element.

FIG. 4 is a sectional view taken along line XX of FIG.

FIG. 5 is a diagram showing an example of a method for forming an anodic oxide film of a liquid crystal display element of the present invention.

FIG. 6 is a diagram showing a conventional anodic oxidation method.

[Explanation of symbols]

 2 gate electrode 3 electrode for additional capacitance 4a anodic oxide film on gate electrode 4b anodic oxide film on electrode for additional capacitance

Claims (3)

[Claims] 1. A pixel electrode provided on an insulating substrate, a thin film transistor for switching a voltage applied to the pixel electrode, and a thin film transistor of the thin film transistor provided between the substrate and the pixel electrode. A liquid crystal display device having an electrode for additional capacitance made of the same material as the gate electrode, wherein an anodic oxide film is provided on the gate electrode and the electrode for additional capacitance, and the anodic oxidation film provided on the gate electrode is provided. A liquid crystal display element in which a film and an anodized film provided on the electrode for additional capacitance are different in film thickness. 2. The liquid crystal display element according to claim 1, wherein a film thickness of an anodized film provided on the electrode for additional capacitance is smaller than a film thickness of an anodized film provided on the gate electrode. 3. A pixel electrode provided on an insulating substrate, a thin film transistor for switching a voltage applied to the pixel electrode, and the thin film transistor provided between the substrate and the pixel electrode. An additional capacitance electrode made of the same material as the gate electrode, and a different potential is applied to the gate electrode and the additional capacitance electrode, or the potentials are applied for different times, A method for manufacturing a liquid crystal display device, which comprises forming an oxide film.