JPH0843854A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the aperture rate of pixels of liquid crystal cells by forming auxiliary capacitors of a structure formed by holding insulating films with transparent conductive films consisting of the same material as the material of pixel electrodes. CONSTITUTION:This liquid crystal display device is constituted by forming the auxiliary capacitors with the transparent conductive films 4 and the transparent conductive films 5 at every pixel. The transparent conductive films 4 are used as the driving electrodes of the pixels for the pixel electrodes. Materials, such as ITO and SnO2, are used for the transparent conductive films 4. Interlayer films are used as the insulating films. PSG, SiO2, SiN, etc., are used for the material of the interlayer films. The regions of the auxiliary capacitors are formed of the structure obtd. by holding the interlayer films with the transparent conductive films 4 and the transparent conductive films 5 connected to the gate lines 2, by which the regions heretofore shielded of light by auxiliary capacitor lines 1 are diminished in the effective pixel regions corresponding to the pixels of liquid crystals while the additive capacitances are assured. Consequently, the opening rate of the pixels is improved.

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 in which a driving voltage according to information is applied through a pixel electrode connected to a liquid crystal cell corresponding to each pixel, and data is displayed using the plurality of liquid crystal cells. Regarding the device.

[0002]

2. Description of the Related Art Currently, thin film transistors for OA use.
Liquid Crystal Display (Thin Film Transistor-Liquid Crystal)
Disply: hereinafter referred to as TFT-LCD) is, for example, 640
× 480-pixel video graphics array (Video Gr
Those compatible with aphics Array (hereinafter referred to as VGA) have appeared on the market. Large screen compatible with XGA (eXtended Graphics Array) specifications and engineer workstation (EWS) specifications, which have upward compatibility with VGA in the future,
Along with the trend toward higher definition, each company is developing a TFT-LCD.

There is also a demand for high-definition images for direct-viewing and for projection as well as for projection, which emphasizes resolution.

In such demands, the brightness of the display is an important point in terms of performance. This brightness is determined by the brightness of the backlight and the transmittance of the panel.
Among these, the factors that determine the transmittance of the panel include, for example, a polarizing plate, a color filter, glass, a liquid crystal, and an aperture ratio of an effective display section. When designing a pixel, how do you get a large aperture ratio?
It is the design know-how of each company. In the design of the TFT array, the size and layout of the bus line, the TFT, and the auxiliary capacitor C _S satisfying the required performance are designed according to the mask pattern design rules.

In particular, as the pixel size becomes smaller,
Since the liquid crystal applied voltage holding ratio cannot be increased only by the liquid crystal capacitance of the pixel portion, an auxiliary capacitance for supplementing the holding capacitance is connected in parallel with the liquid crystal capacitance.

[0006]

By the way, in an active matrix (AM) type LCD, for example, it is necessary to determine the size of the pixel electrode while keeping a balance with the element design for obtaining desired characteristics. This is because, as the definition of the LCD becomes higher, the pitch between the pixels of the LCD becomes finer, the light-shielding portion of the LCD such as the wiring region and the TFT portion becomes large, and the aperture ratio decreases.
As one method of suppressing the decrease of the aperture ratio in this way, there is an additional capacitance method, that is, a C _{S on-} gate structure. In the present structure, each pixel has a second polycrystalline silicon from the top, so-called 2POLY / insulating film / second A dedicated auxiliary capacitance C _S is formed by adopting a structure of 1 polycrystal silicon, so-called 1POLY, for each pixel (see the auxiliary capacitance C _S formation region in FIGS. 7 and 8).

Although the LCD of this system can have a larger aperture ratio than the LCD of the storage capacitance system, for example, as shown in FIG. 7, the auxiliary capacitance region occupies 30% or more of the effective pixel region. . Therefore, even in the LCD of the additional capacitance type, it is inevitable to improve the aperture ratio and decrease the transmittance. Further, in the TFT-LCD device, the capacity of the gate bus line is large with the increase in definition of the TFT, and the additional capacity cannot be ignored, resulting in signal delay.

Further, in order to add a capacitance, a dedicated auxiliary capacitance C _S line runs for each pixel of each line. For this reason, the gate bus line and the source bus line have a structure to overcome the dedicated auxiliary capacitance C _S line. This structure is a cause of signal disconnection. Due to such a cause, the yield of the LCD panel is lowered.

On the other hand, due to the problems of aperture ratio and capacitance, when the auxiliary capacitance C _S is formed just below the bus line,
Coupling occurs between this bus line and the formed auxiliary capacitance C _S. Due to this coupling, in the LCD, the alignment direction of the liquid crystal molecules is disturbed by the influence of the electric field, and light leakage occurs, that is, the domain is caused as a pretilt domain or a reverse tilt domain, and there is a possibility that the contrast is lowered or the bright spot is defective. Come on. Also,
Such a domain phenomenon also occurs when the transparent conductive film forms a step.

Therefore, the present invention has been made in view of the above situation, and a liquid crystal display device capable of improving the aperture ratio of the effective pixel region and adjusting the film thickness according to the auxiliary capacitance. For the purpose of providing.

[0011]

In order to solve the above-mentioned problems, a liquid crystal display device according to the present invention applies a driving voltage according to information through a pixel electrode connected to a liquid crystal cell corresponding to each pixel. In the liquid crystal display device for displaying data using the plurality of liquid crystal cells, it is possible to form an auxiliary capacitance by a structure in which an interlayer film which is an insulating film in the liquid crystal cell region is sandwiched by transparent conductive films such as ITO. It has a feature.

Here, the transparent conductive film may be connected to the gate line of each pixel or the line of the auxiliary capacitor, and the interlayer film in the region in the pixel may be covered with the transparent conductive film. Further, the transparent conductive film connected to the gate line or the auxiliary capacitance line for each pixel may be formed collectively for a plurality of pixels in either the vertical direction or the horizontal direction.

[0013]

In the liquid crystal display device according to the present invention, the auxiliary capacitance is formed in such a structure that the insulating film is sandwiched by the transparent conductive films made of the same material as the pixel electrode, so that the additional capacitance is formed in the entire pixel region. However, the pixel area of the liquid crystal cell is effectively utilized.

The transparent conductive film is connected to the gate line or the auxiliary capacitance line for each pixel, and the interlayer film in the region inside the pixel is covered with the transparent conductive film to form an effective pixel region. Since it is not ground, the aperture ratio is improved and, for example, the film thickness is adjusted so as not to affect the transmittance.

Even if the transparent conductive film connected to the gate line or the auxiliary capacitance line for each pixel is formed collectively for a plurality of pixels in either the vertical direction or the horizontal direction, the aperture ratio of the liquid crystal cell and the The amount of transmitted light can be increased.

[0016]

Embodiments of the liquid crystal display device according to the present invention will be described below with reference to the drawings. In this liquid crystal display device, a drive voltage according to the supplied information is applied via a pixel electrode connected to a liquid crystal cell corresponding to each pixel, and data is displayed using the plurality of liquid crystal cells. This liquid crystal display device employs a C _{S on-} gate structure using an auxiliary capacitance, that is, an additional capacitance method in a so-called C _S configuration method. In this example, amorphous-TF
A liquid crystal display (LCD) using T will be described.

A liquid crystal display device according to this system is basically a so-called C _S of the storage capacity system as shown in FIG.
As compared with the on-common structure, the aperture ratio can be increased because there is usually no C _S line or only the minimum C _S line 1. For example, when there is no C _S line 1, there is no leakage between the C _S line 1 and the gate line 2. In addition, this system is characterized in that the cross portion between lines is reduced, the capacitance of the source line 3 is reduced, and the capacitance of the gate line 2 is increased.

In the TFT-LCD, the area occupied by one pixel becomes smaller as the size of the TFT-LCD becomes higher. Further, it is known that as the pixel pitch becomes finer, the storage capacity becomes smaller only by the liquid crystal capacity of the pixel portion.

In the liquid crystal display device of the present invention, with the increase in definition, the necessary auxiliary capacitance C _S is formed by sandwiching an insulating film using the same material as the pixel electrode. In the liquid crystal display device, the transparent conductive film 4 and the C _S transparent conductive film 5 connected to the gate line 2 (or the dedicated C _S line 1) form an auxiliary capacitance for each pixel. In schematic fragmentary plan view of a liquid crystal display device of FIG. 1, the transparent conductive film 4 and C _S transparent conductive film 5 and are overlapped portion is indicated by hatching. The hatched portion corresponds to the liquid crystal cell, that is, the auxiliary capacitance C _S forming region in the pixel region.

Here, the pixel electrode uses the transparent conductive film 4 as a driving electrode of the pixel. This transparent conductive film 4 has IT
O (Indium Tin Oxide: ITO) and SnO ₂
Material such as is used. The material of the transparent conductive film 4 and C _S transparent conductive film 5 may be the same.

The insulating film corresponds to an interlayer film described later, and the material of the interlayer film is, for example, PSG (Ph
ospho Silicate Glass), NSG, SiO ₂ , SiN, and a flattening material. Further, the signal line for supplying data includes aluminum-based metal, Cu, Ti, Mo,
W or their alloys are used.

As described above, the transparent conductive film 4 is formed as the interlayer film described later.
And the C _S transparent conductive film 5 are sandwiched by the auxiliary capacitance C
By forming the region of _S , it is possible to suppress the area of the region shielded by the conventional C _S line 1 in the effective pixel region corresponding to the pixel of the liquid crystal while securing the additional capacitance. . This can improve the aperture ratio of the pixel.

This manufacturing process will be briefly described with reference to the sectional view of the main part of the liquid crystal display device shown in FIG. Here, the cross section of the main part is a cross section taken along the broken line indicated by the alternate long and short dash line in FIG. Further, FIG. 1 is also referred to when necessary.

First, an amorphous-TFT (hereinafter referred to as a-TFT) is formed in the transistor formation region TR on the transparent substrate 10. The gate layer 2G is formed on the transparent substrate 10. When the a-TFT is an Al gate TFT or a channel etch type, Al is a dense and strong film as the interlayer film 6a by, for example, the anodic oxidation method after forming the gate layer 2G forming the gate pattern, that is, the gate electrode. ₂ O ₃ is formed. Further, the Ta ₂ O ₅ film is formed by the anodic oxidation method to reduce the occurrence of short circuit defects. Both Al ₂ O ₃ and Ta ₂ O ₅ have been put to practical use as gate insulating films.

Next, in order to form a so-called a-Si island, a two-layer structure is formed using SiN, which has good interface characteristics with a-Si. This SiN film is usually formed by the plasma CVD method as in the case of a-Si. a-Si is an i layer (i
-A-Si) and an n layer (n ⁺ -a-Si) are formed.

In the next process, a-Si is etched. In the island-shaped pattern a-Si, the i layer and the n layer are left so as not to come out of the gate pattern, and contacts are formed in the gate region (1Con and 2Con in FIGS. 1 and 2).
See). Also, the source / drain electrodes of the TFT are formed.

Then, a metal film 3S to be the signal line (that is, the gate line 3) is formed. This signal line 3 is
It is formed by etching using the wiring pattern as a mask.

After this, a sputtering method or CVD
A transparent electrode, for example, ITO is deposited by a method or the like to pattern the pixel electrode. Because of the use of additional capacitance method, C _S transparent conductive film 5 of ITO electrodes, so that contact by the gate wiring overlaps. The C _S transparent conductive film 5 is in contact with the dedicated auxiliary capacitance C _S line as a transparent conductive film forming a part of the auxiliary capacitance C _S (see FIGS. 1 and 2).

Next, the region corresponding to the patterning is again covered with the interlayer film 6b. After forming the film of the interlayer film 6b, the TFT
Etching is performed to form a contact region on the drain (pixel electrode) side of.

Finally, the transparent conductive film 4 which will be the drive electrode is formed and patterned.

By such a procedure, the interlayer film 6b, which is a single-layer structure but is an insulating layer, is sandwiched between the C _S transparent conductive film 5 and the transparent conductive film 4 to secure a necessary large capacity auxiliary capacitance C _S. However, the area is smaller than the area occupied by the conventional dedicated auxiliary capacitance C _S. By reducing the area occupied by the dedicated auxiliary capacitance C _S , the effective pixel area of one pixel can be increased, and the aperture ratio can be improved.

Further, by adjusting the total film thickness of the transparent conductive films 4 and 5, it is possible to provide a liquid crystal display device having almost no loss of transmittance as compared with the conventional one.

Next, a first modified example of the above-mentioned liquid crystal display device will be briefly described with reference to the sectional view of the main part of FIG.

In this embodiment, first, the C _S transparent conductive film 5 is formed on the transparent substrate 10 over the pixel region. This formation region is formed so as to occupy substantially the same region as the region of the transparent conductive film 4 as shown in FIG. After that, the gate metal film is formed to form the gate layer 2G, and the processing procedure after the etching processing is almost the same as the procedure of the above-described embodiment.

In this way, for example, the interlayer films 6a and 6b are formed with C _S
The structure is such that it is sandwiched between the transparent conductive films 5a and 5b, and the capacitor portion (overlap portion with the C _S transparent conductive film 5 in FIG. 1) in which the auxiliary capacitance C _S is formed by multi-layering and the dedicated C are formed.
_By connecting to _S line 1, a dedicated C
The area of the _S line can be minimized, the effective pixel area can be secured, the aperture ratio can be improved, and the film thickness of the transparent conductive film can be controlled. As a result, the aperture ratio, which has been reduced by occupying about 30% of the conventional effective pixel, is improved.

As a second modification of the above-described embodiment, the transparent conductive film connected to the gate line or the auxiliary capacitance line for each pixel is combined into a plurality of pixels in either the vertical direction or the horizontal direction. You may form it. That is, without providing the dedicated C _S line 1 at all, C _S
The transparent conductive film 5 is collectively formed over all pixels or a plurality of pixels of several pixels and used as a substitute for the auxiliary capacitance C _S. Actually, the transparent conductive film 4 shown in FIG.
That is, it is formed so as to cover only the range corresponding to the pixel region. At this time, the cross-section taken along the broken line of the one-dot chain line BB ′ shows the interlayer film 6b as the C _S transparent conductive film 5 as shown in FIG.
The structure is such that it is sandwiched between the transparent conductive films 4. The C _S transparent conductive film 5 of FIG. 4 may be formed in the vertical direction for all pixels or for several pixels.

Thus, the area where the transparent conductive film 4 and the C _S transparent conductive film 5 overlap each other functions as a capacitor for each pixel, so that the aperture ratio of the pixel can be further improved. .

Next, a third modification of the liquid crystal display device will be described with reference to FIGS. 5 and 6.

In this embodiment, the C _S transparent conductive film 5 is formed in one row in a row so that all the pixels or several pixels are grouped together so as to overlap with the gate line 3 running in the horizontal direction which is the gate wiring of the next stage. . Also in this case, the C _S transparent conductive film 5
By forming the auxiliary capacitance C _S with the transparent conductive film 4, the C _S line 1 need not be formed at all, as in the second modification. Since the C _S transparent conductive film 5 is transparent, it is possible to effectively use the effective pixel region and optimize the amount of transmitted light by adjusting the film thickness without lowering the aperture ratio of the pixel region where the liquid crystal is arranged. You can Also in this embodiment, as shown in FIG. 6, each layer is formed in a structure in which the interlayer film 6 is sandwiched between the transparent conductive film 4 and the C _S transparent conductive film 5 to form an auxiliary capacitance C _S region for each pixel, that is, a capacitor region. You can see that

In this embodiment, the C _S transparent conductive film 5 is used.
Although the case where the gate line on the rear side and the gate line on the rear side are overlapped with each other is shown, the C _S transparent conductive film 5 may be overlapped with the gate line on the front side.

Further, the above-mentioned embodiment, all is described a-TFT of C _S-gate structure is not limited to the embodiments described above, a-T of the storage capacitance method
In the case of the C _{S on-} common structure adopted in the FT, the aperture ratio can be improved as compared with the conventional aperture ratio by overlapping the source line running in the vertical direction.

With the above-mentioned structure, the auxiliary capacitance C _S required with the miniaturization of the pixel is supplemented by using the C _S transparent conductive film, and the dedicated C _S line conventionally provided is minimized. Thus, the aperture ratio of the effective pixel area can be improved. By adjusting the film thickness of the transparent conductive film, the amount of transmitted light can be kept within a predetermined range.

Further, it is connected to the gate line or the auxiliary capacitance line of each pixel, and the interlayer film in the region in the pixel is covered with the transparent conductive film, or the gate line or the auxiliary capacitance of each pixel is formed. The aperture ratio can be improved even if the transparent conductive film connected to the line is formed collectively for a plurality of pixels in either the vertical direction or the horizontal direction, and the aperture ratio is reduced even if the definition is increased. It is possible to provide an LCD that does not cause it.

[0044]

In the liquid crystal display device according to the present invention, by sandwiching the insulating film with the transparent conductive film which plays the role of the auxiliary capacitance, the aperture ratio of the pixel can be improved while satisfying the required auxiliary capacitance. . As a result, the liquid crystal display device having a higher definition can provide a liquid crystal display device having high brightness, that is, bright and high resolution.

Further, it is connected to the gate line or the auxiliary capacitance line for each pixel, and the interlayer film in the region in the pixel is covered with the transparent conductive film, or the gate line or the auxiliary capacitance for each pixel is formed. The aperture ratio can be improved even if the transparent conductive film connected to the line is formed collectively for a plurality of pixels in either the vertical direction or the horizontal direction, and the aperture ratio is reduced even if the definition is increased. It is possible to provide an LCD that does not cause it.

[Brief description of drawings]

FIG. 1 is a schematic plan view of a main part of a liquid crystal display device according to the present invention.

FIG. 2 is a cross-sectional view of essential parts when the liquid crystal display device is cut along a break line AA ′.

FIG. 3 is a main-portion cross-sectional view illustrating a first modification example of the liquid crystal display device.

FIG. 4 is a main-portion cross-sectional view illustrating a second modification example of the liquid crystal display device.

FIG. 5 is a plan view of relevant parts for explaining the positional relationship between the C _S transparent conductive film and the gate line in the liquid crystal display device.

FIG. 6 is a cross-sectional view of essential parts when the liquid crystal display device is cut along a break line BB ′.

FIG. 7 is a schematic plan view of a main part of a conventional liquid crystal display device.

FIG. 8 is a cross-sectional view of a main part of a conventional liquid crystal display device.

[Explanation of symbols]

1 auxiliary capacitance C _S line 2 gate line 3 signal line (source line) 4 transparent conductive film 5, 5a, 5b C _S transparent conductive film 6, 6a, 6b interlayer film 2G gate layer 3S signal line TR transistor formation region

Claims (3)

[Claims] 1. A liquid crystal display device in which a driving voltage according to information is applied through a pixel electrode connected to a liquid crystal cell corresponding to each pixel, and data is displayed by using the plurality of liquid crystal cells. A liquid crystal display device, wherein an auxiliary capacitance is formed by a structure in which an insulating film in a region is sandwiched by transparent conductive films. 2. The transparent conductive film is connected to a gate line or an auxiliary capacitance line for each pixel, and an interlayer film in a region within the pixel is covered with the transparent conductive film. The liquid crystal display device according to claim 1. 3. The transparent conductive film connected to the gate line or the auxiliary capacitance line for each pixel is formed collectively for a plurality of pixels in either the vertical direction or the horizontal direction. The described liquid crystal display device.