JPH0915621A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To provide a wholly bright liquid crystal display device capable of improving the aperture rate of a pixel part by providing a pixel electrode even between the pixel electrode and scan signal wiring and preventing the reflection owing to the difference of a diffractive index and the lowering in transmissivity owing to that a thickness is increased by constituting the majority of the pixel electrode with a layer of transparent conductive film. CONSTITUTION: This device is the liquid crystal display device constituted so that plural image signal wiring 2 and plural scan signal wiring 1 are provided intersectedly, and the pixel electrodes 3 and switching elements 5 supplying an image signal to the pixel electrodes 3 are provided on crossing parts between the image signal wiring 2 and the scan signal wiring 1 in matrix, and a liquid crystal material is held between the pixel electrodes 3 and counter electrodes provided opposite to the pixel electrodes 3, and belt-like second pixel electrodes 4 projecting to the scan signal wiring side and/or the image signal wiring side from the pixel electrodes 3 are provided on the rear surface side of the pixel electrodes 3.

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 device, and more particularly to an active matrix liquid crystal display device in which a switching element is provided in each pixel electrode.

[0002]

2. Description of the Related Art Liquid crystal display devices of the active matrix type are indispensable for color liquid crystal display devices because they have higher contrast and excellent multi-tone display characteristics than those of the simple matrix type. It has become a technology. Particularly, in an active matrix type liquid crystal display device using a thin film transistor as a switching element, an image quality equivalent to that of a CRT has come to be obtained.

A conventional liquid crystal display device will be described below with reference to the drawings. 10 is an enlarged view of a pixel portion of a conventional liquid crystal display device, and FIGS. 11 and 12 are cross-sectional views taken along the line AA ′ and the line BB ′ of FIG. 10, respectively.

25 in FIGS. 10, 11 and 12.
Is a scanning signal line made of a metal film and a gate electrode (G) of a thin film transistor formed at the same time as the scanning signal line. 26 is an image signal line made of a metal film or a transparent conductive film and a source (S) electrode of a thin film transistor 28.
7 is a pixel electrode formed of a transparent conductive film and a drain (D) electrode of a thin film transistor, 28 is a top-gate thin film transistor, 29 is a semiconductor film of the thin film transistor 28,
Reference numeral 30 is a light-shielding metal film for blocking light incident on the channel portion of the thin film transistor 28, 31 is an insulating film, 32 is a gate insulating film of the thin film transistor 28, 33 is a liquid crystal material, 34 is a counter electrode, and 35 and 36 are transparent. Glass substrate, C
_LC is a liquid crystal capacitance between the pixel electrode 27 and the counter electrode 34, C
_S is an additional capacitance between the pixel electrode 27 and the adjacent scanning signal line 25 '.

In this active matrix type liquid crystal display device, the top gate type thin film transistor 28 is switched by the scanning signal supplied from the scanning signal wiring 25, and the signal voltage of the image signal wiring 26 is extended by the drain (D) electrode. By applying a voltage to a certain pixel electrode 27, a voltage is applied to the liquid crystal material held between the pixel electrode 27 and the counter electrode 34 to display an image. The additional capacitance C _S is a charge holding capacitance for holding the voltage applied to the liquid crystal material 33 for a certain period of time.

In the liquid crystal display device as described above, as shown in FIG. 11, the pixel electrode 27 'adjacent to the pixel electrode 27 is a layer of the same level sandwiched between the insulating film 31 and the gate insulating film 32. However, it is necessary to provide a sufficient space L1 between them so that they are not short-circuited. Therefore, the pixel electrode 27 cannot be made sufficiently large, resulting in a problem that the aperture ratio of the pixel portion decreases. It was Especially, in a small-sized and high-definition liquid crystal display device, the influence was remarkable.

Further, as shown in FIG. 12, the pixel electrode 27
Since the image signal wirings 26 and 26 'are also layers of the same level sandwiched between the insulating film 31 and the gate insulating film 32, it is necessary to provide a sufficient space L2 between them, and for this reason also There is a problem that the aperture ratio is lowered.

That is, in the conventional liquid crystal display device, as shown in FIG.
As shown in FIG. 3, the light-transmittable area in the pixel electrode 27 portion was only the shaded area indicated by P1, and the aperture ratio of the pixel portion was small.

In order to solve such a problem, the present applicant discloses in Japanese Patent Application No. 5-330785 that a pixel electrode is an upper layer pixel electrode 43, as shown in FIGS. 14, 15, 16 and 17. And the lower layer pixel electrode 44. The lower layer pixel electrode 44 is formed so as to project to the scanning signal wiring 41 side and the image signal wirings 42, 42 ′ side with respect to the upper layer pixel electrode 43, and the scanning signal wiring 41 made of a metal film is formed. A liquid crystal display device provided with an additional capacitance electrode 47 formed of a transparent conductive film was proposed. An insulating film 48 made of a silicon nitride film, a tantalum oxide film, or the like is interposed between the upper layer pixel electrode 43 and the lower layer pixel electrode 44. The upper layer pixel electrode 43 and the lower layer pixel electrode 44 are formed of a transparent conductive film such as ITO (indium tin oxide) or tin oxide (SnO). In this case, since the upper layer pixel electrode 43 and the lower layer pixel electrode 44 overlap each other with a large area via the gate insulating film 48, the upper and lower pixel electrodes are compared with the liquid crystal capacitance C _LC2 between the lower layer pixel electrode 44 and the counter electrode 51. The overlap capacitance Ca between 43 and 44 is significantly increased, and as a result, the lower layer pixel electrode 44 also has the same function as the upper layer pixel electrode 43.

FIG. 15 is a sectional view taken along the line AA 'in FIG. 14, FIG. 16 is a sectional view taken along the line BB' in FIG. 14, and FIG.
4 is a sectional view taken along line CC ′ of FIG.

As described above, the pixel electrode is replaced by the upper layer pixel electrode 43.
And the lower layer pixel electrode 44, and the lower layer pixel electrode 4
When 4 is formed so as to project to the scanning signal wiring 41 and the image signal wirings 42 and 42 ', the pixel electrode can be expanded not only to the region of P1 but also to the regions of P2, P3 and P4 as shown in FIG. The aperture ratio of the pixel portion can be improved.

However, in this conventional liquid crystal display device, although the upper layer pixel electrode 43 and the lower layer pixel electrode 44 are formed of a transparent conductive film, the upper layer pixel electrode 43 and the lower layer pixel electrode 4 are formed.
Since 4 is overlapped in most areas, the substantial film thickness of the pixel electrode is increased in this overlap area. Further, when the upper layer pixel electrode 43 and the lower layer pixel electrode 44 are provided,
Light is transmitted through a plurality of layers having different refractive indexes, and light is reflected at the interface. As a result, this conventional liquid crystal display device has a problem that the light transmittance is reduced by 5 to 10% and the entire display device becomes dark.

[0013]

SUMMARY OF THE INVENTION The liquid crystal display device according to the present invention has been invented in view of the above problems of the conventional device, and has a large aperture ratio in the pixel portion and a reduced light transmittance. It is an object to provide a bright liquid crystal display device.

[0014]

In order to achieve the above object, in a liquid crystal display device according to the present invention, a plurality of image signal wirings and a plurality of scanning signal wirings are provided so as to intersect with each other, and the image signal wirings and scanning are performed. Pixel electrodes and switching elements for supplying image signals to the pixel electrodes are provided in a matrix at intersections with the signal lines, and a liquid crystal is provided between the pixel electrodes and a counter electrode provided so as to face the pixel electrodes. In a liquid crystal display device in which a material is held, a strip-shaped second pixel electrode protruding from the pixel electrode to the scanning signal wiring side and / or the image signal wiring side is provided on the back surface side of the pixel electrode. .

[0015]

As described above, when the second pixel electrode protruding from the pixel electrode is provided on the back surface side of the pixel electrode, the aperture ratio of the pixel portion is improved and most of the pixel portion is further transparent. Since it is made of a conductive film, the light transmittance is improved, and the liquid crystal display device is bright as a whole.

[0016]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 1 is a diagram showing an embodiment of a liquid crystal display device according to the present invention, FIG. 2 is a sectional view taken along the line AA ′ of FIG. 1, and FIG. 3 is a sectional view taken along the line BB ′ of FIG. . 1 to 3, 1 is a scanning signal wiring, 2 is an image signal wiring,
3 is a pixel electrode, 4 is a second pixel electrode, 5 is a switching element composed of a thin film transistor, 6 is a protective film, 7 is a liquid crystal material, 8 is a counter electrode, and 9 and 10 are transparent glass substrates.

A plurality of scanning signal wirings 1 and a plurality of image signal wirings 2 are provided, and a pixel electrode 3 and a switching element 5 are provided at each intersection of the scanning signal wirings 1 and the image signal wirings 2.

The switching element 5 includes a gate electrode (G) and a gate insulating film 1 formed continuously on the scanning signal line 1.
1, a semiconductor film 12 serving as a channel portion, a source electrode (S) continuously formed on the image signal wiring 2, and a drain electrode (D) continuously formed on the pixel electrode 3. The switching element 5 is formed in an inverted stagger structure in which the gate electrode (G) is located below and the source electrode (S) and the drain electrode (D) are located above. When the switching element 5 is formed in the inverted staggered structure in this manner, the light shielding metal film of the channel portion of the transistor which is conventionally required is not necessary, and the additional capacitance electrode described later can be simultaneously formed by the transparent conductive film. Become.

Scan signal wiring 1 and gate electrode (G)
Is formed of a metal thin film such as aluminum (Al) or tantalum (Ta). The gate insulating film 11 is formed of silicon nitride (SiN _x ), silicon oxide (SiO ₂ ), tantalum oxide (TaO _x ), or the like. The semiconductor film 12 is formed of an amorphous silicon film or the like.

The image signal wiring 2, the source electrode (S) and the drain electrode (D) are metal films such as aluminum (Al), titanium (Ti), and mobribden (Mo), or these metal films and a transparent conductive film such as ITO. And a laminated film of. The pixel electrode 3 and the second pixel electrode 4 are formed of a transparent conductive film such as ITO.

Between the pixel electrode 3 and the adjacent scanning signal line 1 ′, an additional capacitance C _S for holding the voltage applied to the liquid crystal material 7 for a certain period is provided between the pixel electrode 3 and the counter electrode 8. The liquid crystal capacitance C _LC1 is formed between the second pixel electrode 4 and the counter electrode 8 and the liquid crystal capacitance C _LC2 is overlapped between the pixel electrode 3 and the second pixel electrode 4 to form a capacitance Ca.

In this liquid crystal display device, switching is performed by the thin film transistor 5 of the inverted stagger type, and the signal voltage of the image signal wiring 2 is applied to the pixel electrode 3 which is an extension of the drain electrode (D). A voltage is applied to the liquid crystal material 7 held between the second pixel electrode 4 and the counter electrode 11 to display an image.

Further, the insulating film 11 is formed on the back surface side of the pixel electrode 3.
A band-shaped second pixel electrode 4 is formed so as to project toward the scanning signal line 1 and the image signal line 2 via the. In this case, in the pixel electrode 3 and the second pixel electrode 4, the overlapping capacitance Ca between the pixel electrode 3 and the second pixel electrode 4 is equal to the liquid crystal capacitance C _LC2 between the second pixel electrode and the counter electrode. It is desirable to form it so that it is double or more. In this way, the overlap capacitance Ca between the second pixel electrode 4 and the second pixel electrode 4 is twice or more the liquid crystal capacitance C _LC2 between the second pixel electrode 4 and the counter electrode. When it is formed as described above, the voltage of ⅔ or more of the pixel electrode 3 is applied to the second pixel electrode 4, and the second pixel electrode 4 also has the same function as the pixel electrode 3. .

Even if the strip-shaped second pixel electrode 4 is provided only on the scanning signal wiring side, the aperture ratio of the pixel portion can be improved as long as it is provided.

4 to 6 are views showing another embodiment. In this embodiment, one end of the pixel electrode 3 is formed so as to extend midway on the adjacent scanning signal line 1 ′, and the other end of the pixel electrode 3 is provided close to the scanning signal line 1. . The pixel electrode 3 and the scanning signal line 1 are formed of an insulating film 11
The other end of the pixel electrode 3 can be provided in the vicinity of the scanning signal line 1 since the layers are of different levels.

Further, in this embodiment, the strip-shaped second pixel electrode 4 is formed on the back surface side of the pixel electrode 3 so as to project to the image signal wiring 2 side from the pixel electrode 3.

In this case as well, the overlapping capacitance Ca between the pixel electrode 3 and the second pixel electrode 4 is set to the second pixel electrode 4 so that the second pixel electrode 4 functions the same as the pixel electrode 3. The liquid crystal capacitance C _LC2 between the counter electrode 11 and the counter electrode 11 is twice or more.

In this way, the pixel electrode 3 is connected to the scanning signal wiring 1
If the strip-shaped second pixel electrode 4 is provided on the back surface side of the pixel electrode 3 so as to project toward the image signal wirings 2 and 2 ′, the aperture ratio of the pixel portion can be increased. The light transmittance of the pixel portion can be increased.

7 to 9 are diagrams showing other embodiments. In this embodiment, the strip-shaped second electrode is formed on the back surface side of the pixel electrode 3.
The pixel electrode 4 is provided in a square shape. Thus, the second
If the pixel electrode 4 is provided in a square shape, the pixel electrode and the second pixel electrode 4 overlap each other over a relatively wide area on the back surface side of the pixel electrode 4, so that part of the second pixel electrode 4 is disconnected. However, the other parts can function effectively.

[0030]

As described above, according to the liquid crystal display device of the present invention, the strip-shaped first portion is formed on the back surface side of the pixel electrode and extends over the scanning signal wiring side and / or the image signal wiring side with respect to the pixel electrode. Since the second pixel electrode is provided, the pixel electrode also exists between the pixel electrode and the scanning signal wiring, the area of the pixel electrode is substantially increased, and the aperture ratio of the pixel portion is improved. Since most of them are composed of a single layer of transparent conductive film, it is possible to prevent reflection when a plurality of layers having different refractive indexes are laminated and decrease in light transmittance due to increase in thickness, and thus a bright liquid crystal as a whole. It becomes a display device.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is a sectional view taken along line A-A 'of FIG.

FIG. 3 is a sectional view taken along line B-B 'of FIG.

FIG. 4 is a diagram showing another embodiment of the liquid crystal display device according to the present invention.

FIG. 5 is a sectional view taken along line A-A ′ of FIG. 4;

6 is a cross-sectional view taken along the line B-B ′ of FIG.

FIG. 7 is a diagram showing another embodiment of the liquid crystal display device according to the present invention.

8 is a cross-sectional view taken along the line A-A ′ of FIG.

9 is a cross-sectional view taken along the line B-B ′ of FIG. 7.

FIG. 10 is an enlarged view of a pixel portion of a conventional liquid crystal display device.

11 is a sectional view taken along line A-A 'of FIG.

12 is a sectional view taken along line B-B ′ of FIG.

FIG. 13 is a diagram showing an opening of a pixel portion in a conventional liquid crystal display device.

FIG. 14 is a diagram showing a pixel portion of another conventional liquid crystal display device.

15 is a cross-sectional view taken along the line A-A ′ of FIG.

16 is a cross-sectional view taken along the line B-B ′ of FIG.

17 is a cross-sectional view taken along the line C-C ′ of FIG.

FIG. 18 is a diagram showing an aperture ratio of a pixel portion in another conventional liquid crystal display device.

[Explanation of symbols]

1 ... Scan signal wiring, 2 ... Image signal wiring, 3 ...
・ Pixel electrode, 4 ... Second pixel electrode, 5 ... Switching element, 6 ... Protective film, 7 ... Liquid crystal material, 8.
..Counter electrodes

Claims (3)

[Claims] 1. A plurality of image signal wirings and a plurality of scanning signal wirings are provided so as to intersect with each other, and a pixel electrode and an image signal are supplied to the pixel electrode at the intersection of the image signal wirings and the scanning signal wirings. Provided with switching elements in a matrix,
In a liquid crystal display device in which a liquid crystal material is held between the pixel electrode and a counter electrode provided so as to face the pixel electrode, on the back surface side of the pixel electrode, on the scanning signal wiring side with respect to the pixel electrode. And / or a liquid crystal display device having a strip-shaped second pixel electrode projecting to the image signal wiring side. 2. The overlap capacitance Ca between the pixel electrode and the second pixel electrode is at least twice the liquid crystal capacitance C _LC2 between the second pixel electrode and the counter electrode. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a liquid crystal display device. 3. The liquid crystal display device according to claim 1, wherein the switching element is an inverted staggered thin film transistor.