JP3207084B2 - 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 device, and more particularly to an active matrix type liquid crystal display device having a switching element in each pixel.

[0002]

2. Description of the Related Art An active matrix type liquid crystal display device has higher contrast and superior multi-tone display characteristics than a simple matrix type liquid crystal display device. In particular, an active matrix type liquid crystal display device using a thin film transistor as a switching element can obtain image quality equivalent to that of a CRT.

Hereinafter, a conventional liquid crystal display device will be described with reference to the drawings. FIG. 9 is an enlarged view of one pixel of a conventional liquid crystal display device, and FIGS.
It is sectional drawing of the A 'line and the BB' line. FIG.
10 is an equivalent circuit diagram of FIG.

In FIG. 9, FIG. 10, FIG. 11, and FIG.
25 is an inverted staggered thin film transistor, 21 is a scanning signal wiring made of a metal film and a gate electrode (G) of the thin film transistor formed simultaneously with this scanning signal wiring, and 22 is an image signal made of a laminated film of a metal film and a transparent conductive film. The wiring and the source electrode (S) of the thin film transistor 25, 23 are pixel electrodes made of a transparent conductive film, and 26 is the thin film transistor 2
5 of the semiconductor film, 28 denotes a gate insulating film of the thin film transistor 25, 29 denotes an insulating protective film, 30 is a liquid crystal material, the counter electrode 31, the black matrix 27, the 32, 33 transparent glass substrate, C _LC1 is the pixel electrode 23 a liquid crystal capacitance between the counter electrode 31, the C _s is the additional capacitance between the scanning signal lines 21 'adjacent to the pixel electrode 23.

In the active matrix type liquid crystal display device, the inverted staggered thin film transistor 25 is switched by the scanning signal supplied from the scanning signal line 21, and the signal voltage of the image signal line 22 is extended by extending the drain (D) electrode. When a voltage is applied to a certain pixel electrode 23, a voltage is applied to the liquid crystal material held between the pixel electrode 23 and the counter electrode 31, and an image is displayed.

Here, the additional capacitance C _s is a charge holding capacitance for holding a voltage applied to the liquid crystal material 30 for a certain period.

[0007]

In this conventional liquid crystal display device, as shown in FIG. 10 and FIG.
The black matrix 27 is formed on the second side with a metal film such as chromium (Cr), and this black matrix 27 reduces the aperture ratio of the pixel portion. That is, in the above-described liquid crystal display device, when the black matrix 27 is formed on the counter substrate 32 side, the opening including the counter substrate 32
There is a problem that the aperture ratio of the pixel portion cannot be improved only in the region indicated by the hatched portion in FIG.

In particular, the pixel electrode 23 and the black matrix 2
7 is formed on the other substrates 32 and 33, and therefore, for example, about 6 to 10 μm from the end of the pixel electrode
3, the aperture ratio of the pixel portion decreases.

The liquid crystal display device according to the present invention has been devised in view of such problems of the prior art, and aims at eliminating a decrease in the aperture ratio due to the black matrix on the counter substrate side. The present invention is to provide a liquid crystal display device as described above.

[0010]

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 to intersect with an insulating film interposed therebetween. At the intersection of the image signal wiring and the scanning signal wiring,
A liquid crystal display device comprising a pixel electrode and a switching element for supplying an image signal to the pixel electrode, wherein a liquid crystal material is held between the pixel electrode and a counter electrode provided to face the pixel electrode. On the back side of the pixel electrode, a band-shaped metal film protruding from the pixel electrode side to the image signal wiring side via the insulating film and separated for each pixel was provided.

As described above, since the strip-shaped metal film is provided on the back side of the pixel electrode with the insulating film interposed between the pixel electrode and the image signal wiring side, light leakage does not occur at this portion. As a result, the black matrix at the portion facing the image signal wiring becomes unnecessary or can be formed to be narrow, and the aperture ratio can be improved.

[0012]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 1 is a plan view of a pixel portion showing an embodiment of a liquid crystal display device according to the present invention, FIG. 2 is a cross-sectional view taken along line AA ′ of FIG. 1, and FIG.
FIG. 4 is a sectional view taken along line B ′, and FIG. 4 is an equivalent circuit diagram of FIG. 1 to 4, 1 is a scanning signal wiring, 2 is an image signal wiring, 3 is a pixel electrode, 4 is a band-shaped metal film, 5 is a switching element composed of a thin film transistor, 7 is a black matrix, 8 is a gate insulating film, 9 is a protective film, 10 is a liquid crystal material, 11 is a counter electrode, and 12 and 13 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.
Is provided.

The switching element 5 includes a gate electrode (G) formed continuously with the scanning signal wiring 2, a gate insulating film 8, a semiconductor film 6 serving as a channel portion, and a source formed continuously with the image signal wiring 2. The drain electrode (D) is formed continuously from the electrode (S) and the pixel electrode 3.

The scanning signal wiring 1 and the gate electrode (G)
It is formed of a metal film such as aluminum (Al) or tantalum (Ta). The gate insulating film 8 is made of silicon nitride (Si)
N _x ), silicon oxide (SiO ₂ ), tantalum oxide (T
aO _x ) or the like. The semiconductor film 6 is formed of an amorphous silicon film or the like. The pixel electrode 3 is formed of a transparent conductive film such as ITO. The image signal wiring 2, the source electrode (S) and the drain electrode (D) are made of titanium (Ti).
And a laminated film of a metal film 2a such as molybdenum (Mo) and a transparent conductive film 2b such as ITO. The image signal wiring 2, the source electrode (S), and the drain electrode (D) are not limited to the two-layer structure of the metal film 2a and the transparent conductive film 2b, but have a single-layer structure of the metal film 2b. It may be something.

In the liquid crystal display device according to the present invention, a strip-shaped metal film which protrudes from the pixel electrode 3 to the image signal wiring 2 side via the insulating film 8 on the back side of the pixel electrode 3 and is separated for each pixel. 4, 4 'are formed. This metal film 4, 4 '
Has a light-shielding property, so that a gap where light leakage occurs between the pixel electrode 3 and the image signal wiring 2 is reduced. Therefore, as shown in FIG. 5, the width of the black matrix 7 at the portion facing the image signal wiring 2 can be reduced, and the aperture ratio of the pixel portion can be improved.

As described above, if the strip-shaped metal film 4 is separated for each pixel, even if a short circuit occurs between the metal film 4 and another wiring, it will only cause a point defect of one pixel, Does not affect

In this case, assuming that the voltage applied to the pixel electrode 3 is V _p , the band-shaped metal film 4 has C _Ps1 / (C _Ps1 +
A voltage of C _LC3 ) × V _P is applied, and a voltage of C _Ps2 / (C _Ps2 + C _LC4 ) × V _P is applied to the belt-shaped metal film 4 ′, but C _Ps1 > 2C _LC3 and C _Ps2 > for _{2C LC4, '2/3 · V p} ~V p (voltage close to the pixel electrode 3) is applied to the pixel electrode 3 and the strip-shaped metal 4,4' band of the metal film 4, 4 and Since the potential difference substantially disappears, good display characteristics without disclination at this portion can be obtained. That is, the overlap capacitance C _Ps (C _Ps1 + C _Ps2 ) between the pixel electrode 3 and the band-shaped metal films 4 and 4 ′ is increased by the liquid crystal capacitance C _LC between the band-shaped metal films 4 and 4 ′ and the counter electrode 11.
It may be formed so as to be at least twice as large as (C _LC3 + C _LC4 ).

[0019] In between the scanning signal lines 1 'and the adjacent pixel electrode 3, the liquid crystal additional capacitance C _s for holding constant a voltage applied to the liquid crystal material 10 period between the pixel electrode 3 and the counter electrode 11 'liquid crystal capacitor between the counter electrode 11 C _LC3, C _LC4 is, the pixel electrode 3 and the belt-like metal film 4, 4' capacitance C _LC1 is band-shaped metal film 4,4 capacitance C _Ps1 overlap between, C
Each of _Ps2 is formed, resulting in an equivalent circuit as shown in FIG.

6 and 7 show another embodiment. FIG. 6 is a plan view, and FIG. 7 is a sectional view taken along the line BB 'of FIG. 6 and 7, 1 is a scanning signal wiring, 2 is an image signal wiring, 3 is a pixel electrode, 4 is a band-shaped metal film, 5 is a switching element composed of a thin film transistor, 7 is a black matrix, 8 is a gate insulating film, 9 is a protective film, 10
Is a liquid crystal material, 11 is a counter electrode, and 12 and 13 are transparent glass substrates.

This embodiment is almost the same as the embodiment shown in FIGS. 1 to 5, but in this embodiment, a belt-like shape projecting to the image signal wiring 2 side through the insulating film 8 on the back surface side of the pixel electrode 3. Metal film 4 is provided so as to partially overlap the image signal wiring 2 in the vertical direction.

The metal film 4 is made of aluminum (Al), tantalum (Ta), or the like, and has a light shielding property. The image signal wiring 2 is also made of titanium (Ti) or molybdenum (M
o) and a transparent conductive film 2b such as ITO, and has a light shielding property.

Therefore, no light leaks from between the pixel electrode 3 and the image signal wiring 2, and it is not necessary to provide the black matrix 7 in a portion of the counter substrate 11 facing the image signal wiring 2. .

The band-shaped metal film 4 and a part of the image signal wiring 2 are
When vertically overlapped, the pixel electrode 3 and the image signal wiring 2
Is the capacitance between the pixel electrode 3 and the strip-shaped metal film 4.
Quantity C _ps(C_Ps1+ C_Ps2), The band-shaped metal film 4 and the image signal
Capacitance C between signal wiring 2_sd(C_sd1+ C_sd2) In series with
Quantity, ie (C_ps× C_sd/ (C_ps+ C_sd)) Proportional to
However, the liquid crystal capacitance between the pixel electrode 3 and the counter electrode 11 is C
_LC1Between the pixel electrode 3 and the adjacent scanning signal line 1 ′
Additional capacity C_s, Gate electrode of switching element 5
The capacitance between (G) and the drain electrode (D) is C_gdAnd when
In addition, (C_ps× C_sd/ (C_ps+ C_sd)) To (C_LC1
+ C_s+ C_gd) Is less than 1/5
A good display device in which talk hardly occurs is provided.

It is preferable that the band-shaped metal film 4 is formed of the same material as the scanning signal, since the band-shaped metal film can be formed without complicating the manufacturing process.

Further, when the liquid crystal alignment direction is set so that the amount of light leakage differs in the left-right direction of the pixel electrode 3, the band-shaped metal film 4 may be provided only on one side of the pixel electrode 3.

[0027]

As described above, in the liquid crystal display device according to the present invention, on the back surface side of the pixel electrode, via the insulating film, the pixel electrode extends beyond the pixel electrode to the image signal wiring side, and is separated for each pixel. Since the strip-shaped metal film is provided, light leakage between the image signal wiring and the pixel electrode can be reduced, and the black matrix in this portion can be reduced. Accordingly, the aperture ratio of the pixel portion is improved.

Further, since the strip-shaped metal film is independent of the peripheral wiring without being connected thereto, the load capacity of the pixel electrode and the load capacitance of the peripheral wiring due to the strip-shaped metal film hardly increase. It is possible to realize a low-power-consumption panel that can operate at high speed without increasing the capacity of the liquid crystal panel when the screen is enlarged.

[Brief description of the drawings]

FIG. 1 is an enlarged view of one pixel 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 an equivalent circuit diagram of the liquid crystal display device shown in FIG.

5 is an explanatory diagram of an opening in a pixel portion of the liquid crystal display device shown in FIG.

FIG. 6 is a view showing another embodiment of the liquid crystal display device according to the present invention.

FIG. 7 is a sectional view taken along line B-B 'of FIG.

8 is an equivalent circuit diagram of the liquid crystal display device shown in FIG.

FIG. 9 is an enlarged view of one pixel of a conventional liquid crystal display device.

FIG. 10 is a sectional view taken along line A-A ′ of FIG. 9;

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

12 is an equivalent circuit diagram of the liquid crystal display device shown in FIG.

13 is an explanatory diagram of an opening in a pixel portion of the liquid crystal display device shown in FIG.

[Explanation of symbols]

1 ... scanning signal wiring, 2 ... image signal wiring, 3 ...
・ Pixel electrode, 4 ・ ・ ・ Band-shaped metal film, 5 ・ ・ ・ Switching element, 7 ・ ・ ・ Black matrix, 8 ・ ・ ・ Gate insulating film, 9 ・ ・ ・ Protective film, 10 ・ ・ ・ Liquid crystal material, 11
... Counter electrode, 12, 13 ... Transparent glass substrate

Claims (6)

(57) [Claims] A plurality of image signal lines and a plurality of scanning signal lines are provided to intersect with an insulating film interposed therebetween, and a pixel electrode and a pixel electrode are provided at an intersection between the image signal lines and the scanning signal lines. A switching element for supplying an image signal, and a liquid crystal display device in which a liquid crystal material is held between the pixel electrode and a counter electrode provided to face the pixel electrode; A liquid crystal display device, wherein a strip-shaped metal film is provided for each pixel so as to protrude from the pixel electrode to the image signal wiring side via the insulating film. 2. An overlap capacitance C _ps between the pixel electrode and the band-shaped metal film is at least twice as large as a liquid crystal capacitance C _LC2 between the band-shaped metal film and the counter electrode. The liquid crystal display device according to claim 1. 3. The liquid crystal display device according to claim 1, wherein the band-shaped metal film partially overlaps the image signal wiring in a vertical direction. 4. An overlapping capacitance between the pixel electrode and the band-shaped metal film is C _ps , an overlapping capacitance between the band-shaped metal film and the image signal wiring is C _sd , a gate electrode of the switching element. The capacitance between the pixel electrode and the drain electrode is C _gd , the overlap capacitance between the pixel electrode and the scanning signal wiring of the adjacent pixel is C _s , and the liquid crystal capacitance between the pixel electrode and the counter electrode is C _LC1 . Then, ( _Cps · _Csd / ( _Cps + _Csd ))
Is less than or equal to 1/5 of (C _LC1 + C _s + C _gd ). 5. The liquid crystal display device according to claim 1, wherein the strip-shaped metal film is formed of the same material as the scanning signal wiring, and is separated from the scanning signal wiring. . 6. The liquid crystal display device according to claim 1, wherein the switching element is an inverted staggered thin film transistor.