JP3339190B2 - Liquid crystal display - Google Patents

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. Related to the device.

[0002]

2. Description of the Related Art At present, thin film transistors are used for OA.
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
An aphics Array (VGA) is available on the market. In the future, large screens compatible with XGA (eXtended Graphics Array) specifications and engineer workstation (EWS) specifications, which have upward compatibility with VGA,
Along with the trend toward higher definition, each company is developing a TFT-LCD.

[0003] There is also a demand for higher definition for images for direct-view type and projection, which emphasizes resolution together with projection.

[0004] Under such demands, the brightness of the display is an important point in performance. This brightness is determined by the brightness of the backlight and the transmittance of the panel.
Among them, factors that determine the transmittance of the panel include, for example, a polarizing plate, a color filter, glass, a liquid crystal, an aperture ratio of an effective display section, and the like. In designing a pixel, how to increase the aperture ratio is as follows.
It is the design know-how of each company. Design of TFT array, a bus line to meet the required performance, the size and layout of the TFT and the auxiliary capacitance C _S is performed according to the design rules of the mask pattern.

In particular, as the pixel size decreases,
Since the liquid crystal capacitance of the pixel portion alone cannot increase the liquid crystal applied voltage holding ratio, an auxiliary capacitor for supplementing the holding capacitance is connected in parallel with the liquid crystal capacitor.

[0006]

By the way, for example, in an active matrix (AM) type LCD, it is necessary to determine the size of the pixel electrode while keeping a balance with element design for obtaining desired characteristics. The reason for this is that as the definition of the LCD is increased, the pitch between the pixels in the LCD becomes finer, the light-shielding portion in the LCD such as the wiring area and the TFT portion becomes larger, and the aperture ratio decreases.
Thus additional capacitance method as a method of suppressing a decrease in aperture ratio, i.e. there is C _S on-gate structure, the current structure, each pixel, the second polycrystalline silicon from the top, so-called 2POLY / insulating film / first 1 of the polycrystalline silicon to form a dedicated storage capacitor C _S and the structure of so-called 1POLY to take each pixel (see auxiliary capacitor C _S forming region of FIG. 7 and FIG. 8).

Although the LCD according to this method can increase the aperture ratio as compared with the LCD of the storage capacitance method, for example, as shown in FIG. 7, the area of the auxiliary capacitance occupies 30% or more of the effective pixel area. . For this reason, even in the case of the LCD of the additional capacitance type, it is necessary to improve the aperture ratio or to lower the transmittance. Further, in a TFT-LCD device, the TFT has a large capacity of a gate bus line with high definition, and the additional capacitance cannot be ignored, resulting in a signal delay.

In order to add a capacitance, a dedicated auxiliary capacitance _CS line runs for each pixel of each line. For this reason, the gate bus line and the source bus line, has a structure to overcome a dedicated auxiliary capacitor C _S line. This structure causes disconnection of the signal. Due to such causes, the yield of the LCD panel is reduced.

On the other hand, when the auxiliary capacitance C _S is formed immediately below the bus line due to the problems of aperture ratio and capacitance,
Coupling between the auxiliary capacitance C _S which is formed with the bus line is generated. Due to the coupling, the liquid crystal molecules are disturbed in the alignment direction due to the influence of the electric field, causing light leakage, that is, a domain is caused as a pretilt domain or a reverse tilt domain, which may cause a decrease in contrast and a defective bright spot. Come. Also,
Such a domain phenomenon also occurs when a transparent conductive film forms a step.

Accordingly, the present invention has been made in view of the above-mentioned circumstances, and a liquid crystal display device capable of improving the aperture ratio of an effective pixel region and adjusting the film thickness in accordance with an auxiliary capacitance. The purpose is to provide.

[0011]

In the liquid crystal display device according to the present invention, in order to solve the above-mentioned problems, a driving voltage according to information is applied via a pixel electrode connected to a liquid crystal cell corresponding to each pixel. In a liquid crystal display device that displays data using the plurality of liquid crystal cells, the entire pixel region is formed by sandwiching an insulating film in the liquid crystal cell region with a transparent conductive film on a transparent substrate in the liquid crystal cell region. And forming a storage capacitor, and connecting the transparent conductive film forming the storage capacitor to a storage capacitor line located below the transparent conductive film.

[0012]

In the liquid crystal display device according to the present invention, an auxiliary capacitor is formed over the entire image area by forming a multilayer structure sandwiching the liquid crystal cell on the transparent substrate in the liquid crystal cell area. By connecting the transparent conductive film to a storage capacitor line located below the transparent conductive film, the pixel area of the liquid crystal cell is effectively used. Also,
In this liquid crystal display device, the aperture ratio is improved because the effective pixel area is not cut off. For example, the film thickness is adjusted so as not to affect the transmittance.

[0014]

[0015]

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the liquid crystal display device according to the present invention will be described with reference to the drawings. In this liquid crystal display device, a driving voltage according to 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 system in a so-called C _S configuration system. In this embodiment, the amorphous-TF
A liquid crystal display (LCD) using T will be described.

As shown in FIG. 1, for example, a liquid crystal display device according to this system basically has a so-called C _S of a storage capacity system.
Compared to Onkomon structure usually, C _S is no line, or can be increased minimum aperture ratio for C _S line 1 only has the. For example, when there is no C _S line 1, leakage between the C _S line 1 and the gate line 2 is eliminated. In addition, this method has the features that the cross portion between lines is reduced, the capacity of the source line 3 is reduced, and the capacity of the gate line 2 is increased.

In a TFT-LCD, the area occupied by one pixel is reduced with the increase in the size and definition of the TFT. Further, it is known that as the pixel pitch becomes smaller, 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, the required auxiliary capacitance _CS is formed by sandwiching an insulating film using the same material as the pixel electrode with the increase in definition. The liquid crystal display device, a transparent conductive film 4 to form a storage capacitance for each pixel in the C _S transparent conductive film 5 which is connected to the gate line 2 (or dedicated C _S line 1). 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 storage capacitor _CS formation region in the pixel region.

Here, the pixel electrode uses the transparent conductive film 4 as a drive electrode of the pixel. The transparent conductive film 4 has an IT
O (Indium Tin Oxide: hereinafter referred to as ITO) or SnO ₂
Is used. The materials of the transparent conductive film 4 and the _CS 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 planarizing material. Further, signal lines for supplying data include aluminum-based metals, Cu, Ti, Mo,
W or an alloy thereof is used.

As described above, the interlayer film to be described later is
And the CS transparent conductive film 5 to form a storage capacitor C
By forming the S region, it is possible to suppress the area of the region which is conventionally shielded by the CS line 1 from being shaded in the effective pixel region corresponding to the pixel of the liquid crystal while securing the additional capacitance. Thus, the aperture ratio of the pixel can be improved.

Briefly, this manufacturing process will be described with reference to a cross-sectional view of a main part of the liquid crystal display device shown in FIG. Here, the cross section of the main part is a cross section cut along a broken line indicated by a dashed line in FIG. FIG. 1 is also referred to as needed.

First, on the transparent substrate 10, an amorphous-TFT (hereinafter referred to as a-TFT) is formed in the transistor formation region TR. On this transparent substrate 10, a gate layer 2G is formed. When the a-TFT is an Al gate TFT and a channel etch type, after forming a gate pattern, that is, a gate layer 2G forming a gate electrode, Al is a dense and strong film as an interlayer film 6a by, for example, anodic oxidation. ₂ O ₃ is formed. In addition, the occurrence of short-circuit failure is reduced by forming Ta ₂ O ₅ by anodization. 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 having good interface characteristics with a-Si. This SiN film is usually formed by a plasma CVD method similarly to a-Si. a-Si is an i-layer (i
A-Si) and an n-layer (n ⁺ a-Si).

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

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

Thereafter, sputtering or CVD
The pixel electrode is patterned by depositing, for example, ITO, which is a transparent electrode, using a method or the like. Since the additional capacitance method is used, the C _S transparent conductive film 5 made of the ITO electrode overlaps with the gate wiring to make contact. The C _S transparent conductive film 5 is in contact with a 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 the formation of the interlayer film 6b, the TFT
Is performed to form a contact region on the side of the drain (pixel electrode).

Finally, a transparent conductive film 4 serving as a drive electrode is formed and patterned.

[0031] securing the storage capacitance C _S of the mass is in the single-layer structure by this procedure but by sandwiching an interlayer film 6b is an insulating layer C _S transparent conductive film 5, a transparent conductive film 4, which requires while, are finished in a narrow region as compared with the occupied area of the conventional dedicated storage capacitor C _S. By occupying area of the auxiliary capacitance C _S of the dedicated decreases, it can take a wide effective pixel area of one pixel, thereby improving the aperture ratio.

Further, by adjusting the total thickness of the transparent conductive films 4 and 5, a liquid crystal display device with little loss of transmittance as compared with the prior art can be provided.

Next, a specific example of the above-described liquid crystal display device for explaining the present invention will be briefly described with reference to a sectional view of a main part of FIG.

[0034] This example, first, the C _S transparent conductive film 5 is formed over the pixel region on the transparent substrate 10. 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. Thereafter, the processing procedure after the gate metal is formed to form the gate layer 2G and the etching processing is performed is almost the same as the procedure of the above-described embodiment.

[0035] Thus, for example interlayer film 6a, a 6b C _S
Transparent conductive film 5a, a structure such as to sandwich at 5b, and dedicated capacitor portion formed of the auxiliary capacitance C _S in multi-layered (overlap portion of the C _S transparent conductive film 5 in FIG. 1) C
_By connecting to _S line 1, a special 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 thickness of the transparent conductive film can be controlled. As a result, the aperture ratio occupying about 30% of the conventional effective pixels and being reduced is improved.

In the embodiment described above, a transparent conductive film connected to a gate line or a storage capacitor line for each pixel is formed for a plurality of pixels in either the vertical direction or the horizontal direction. Is also good. That is, to form a C _S transparent conductive film 5 without at all providing the C _S line 1 dedicated collectively across a plurality of pixels of each full pixel or several pixels used in alternative storage capacitor C _S. Actually, the transparent conductive film 4 shown in FIG. 4 is formed so as to cover only a liquid crystal cell, that is, a range corresponding to a pixel region. In this case, cross-section taken along the broken line of one-dot chain line B-B 'it is structured such as to sandwich an interlayer film 6b C _S transparent conductive film 5, a transparent conductive film 4 as shown in FIG. Incidentally, C _S transparent conductive film 5 in FIG. 4 may be formed in the vertical direction by the total pixel or several pixels.

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

Next, a specific example for explaining the present invention will be described with reference to FIGS.

[0039] In this example, C _S transparent conductive film 5 is formed together by all the pixels or a few pixels in a horizontal row so as to overlap with the gate line 3 which runs in the transverse direction which is the next stage gate line . C _S transparent conductive film 5 is also in this case
By forms a storage capacitance C _S in the transparent conductive film 4, as in the second modification, finished without completely not form a C _S line 1. Since the _CS transparent conductive film 5 is transparent, the effective pixel area is effectively used and the amount of transmitted light is optimized by adjusting the film thickness without lowering the aperture ratio of the pixel area where the liquid crystal is arranged. Can be. Storage capacitance C _S region of each pixel to form each layer of the interlayer film 6, as shown in FIG. 6 in this embodiment the structure sandwiched between the transparent conductive film 4 and C _S transparent conductive film 5, i.e., to form a capacitor region You can see that

[0040] It should be noted that, in this example, C _S transparent conductive film 5
And shows the case where is overlapped with the gate lines of the second-stage, C _S transparent conductive film 5 may be made to the gate line and overlapping 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
For C _S Onkomon structure employed in FT, if so be the source line overlaps running in the longitudinal direction, it is possible to improve the aperture ratio as compared to the conventional aperture ratio.

[0042] By the above configuration, supplement auxiliary capacitance C _S which is required along with the miniaturization of pixels using a C _S transparent conductive film, the C _S line dedicated was provided prior minimal Thus, the aperture ratio of the effective pixel region can be improved. By adjusting the thickness of the transparent conductive film, the amount of transmitted light can be maintained within a predetermined range.

In addition to being connected to a gate line or a storage capacitor line of each pixel, an interlayer film in a region inside the pixel is covered with the transparent conductive film, or a gate line or storage capacitor of each pixel is connected. 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 when the definition is increased. It is possible to provide an LCD that does not allow the LCD to be operated.

[0044]

According to the present invention, an auxiliary capacitance is formed in the entire pixel region by sandwiching an insulating film in the liquid crystal cell region with a transparent conductive film on a transparent substrate in the liquid crystal cell region. The transparent conductive film is connected to a storage capacitor line located below the transparent conductive film. As a result, a liquid crystal display device with higher definition can provide a liquid crystal display device with high luminance, that is, bright, and high resolution. In addition to being connected to a gate line or a storage capacitor line of each pixel, an interlayer film in a region in the pixel is covered with the transparent conductive film, or a gate line or a storage capacitor line of each pixel is formed. The aperture ratio can be improved even if the connected transparent conductive film is formed collectively for a plurality of pixels in either the vertical direction or the horizontal direction, and the aperture ratio can be reduced even when the definition is increased. No LCD can be provided.

The aperture ratio can also be improved by forming a transparent conductive film connected to a gate line or a storage capacitor line for each pixel for a plurality of pixels in either the vertical direction or the horizontal direction. Thus, it is possible to provide an LCD that does not lower the aperture ratio even when the definition is increased.

[Brief description of the drawings]

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

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

FIG. 3 is a cross-sectional view of a principal part explaining a first modification of the liquid crystal display device.

FIG. 4 is a cross-sectional view of a principal part explaining a second modification of the liquid crystal display device.

5 is a plan view illustrating the positional relationship between the C _S transparent conductive film and the gate lines in the liquid crystal display device.

FIG. 6 is a cross-sectional view of main 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 sectional view of a main part of a conventional liquid crystal display device.

[Explanation of symbols]

1 auxiliary capacitor C _S Line 2 gate lines 3 signal lines (source lines) 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 forming region

Claims (1)

(57) [Claims] 1. A liquid crystal display device in which a drive voltage according to 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. On the transparent substrate in the region, an auxiliary capacitor is formed in the entire pixel region by sandwiching the insulating film in the liquid crystal cell region with the transparent conductive film, and the transparent conductive film forming the auxiliary capacitor is formed of the transparent conductive film. A liquid crystal display device connected to a storage capacitor line located in a lower layer.