JP2003270654A - Liquid crystal display - Google Patents

Abstract

(57) [Summary] The aperture ratio of the pixel portion is reduced by the black matrix on the counter substrate side. Further, in order to realize a reflective liquid crystal panel, a new reflective film must be formed as compared with a transmissive liquid crystal panel, and the structure is complicated. A plurality of image signal wirings and a plurality of scanning signal wirings are provided so as to intersect with an insulating film interposed therebetween, and a pixel electrode and an image are formed on an intersection of the image signal wirings and the scanning signal wirings. A switching element for supplying a 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 light-reflective strip-shaped metal film that protrudes from the pixel electrode side to the image signal wiring side via an insulating film and is separated for each pixel is provided.

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.

[0002]

2. Description of the Related Art An active matrix type liquid crystal display device has a higher contrast than a simple matrix type liquid crystal display device and is excellent in multi-gradation display characteristics, and is therefore an essential technique for a color liquid crystal display device. In particular, an active matrix type liquid crystal display device using a thin film transistor as a switching element has come to obtain an image quality equivalent to that of a CRT. Further, in recent years, with the spread of color mobile phones and the like, there is an increasing demand for reflective and semi-transmissive liquid crystal display devices that have good visibility outdoors and low power consumption.

A conventional transflective liquid crystal display device will be described below with reference to the drawings. FIG. 13 is an enlarged view of one pixel of a conventional liquid crystal display device, and FIGS. 14 and 15 are sectional views taken along the lines AA ′ and BB ′ of FIG. 13, respectively. 16 is an equivalent circuit diagram of the liquid crystal display device of FIG.

In FIGS. 13, 14, 15, and 16, 5 is an inverted staggered thin film transistor, 1 is a scanning signal wiring made of a metal film, and a gate electrode (G) of the thin film transistor formed at the same time as this scanning signal wiring. Reference numeral 2 is an image signal wiring formed of a laminated film of a metal film and a transparent conductive film and the source electrode (S) of the thin film transistor 5, 3 is a transparent pixel electrode formed of a transparent conductive film, and 14 is a reflection formed of a metal film having a light reflecting function. Pixel electrode, 6 is a semiconductor film of the thin film transistor 5, 8 is a gate insulating film of the thin film transistor 5, 9 is an insulating protective film, 15 is an insulating organic film, 10 is a liquid crystal material,
11 is a counter electrode made of a transparent conductive film, 7 is a black matrix, 7'is an opening of the black matrix, 12, 1
3 is a transparent glass substrate.

Here, the reflective pixel electrode 14 is provided on the transparent pixel electrode 3 via the insulating protective film 9 and the insulating organic film 15, and is transparent in the region where the insulating film is removed in the central portion of the pixel. It has a structure connected to the pixel electrode 3.

Further, in FIG. 12, Clc is a liquid crystal capacitance between the transparent pixel electrode 3 and the reflective pixel electrode 14 and the counter electrode 11, and Cs is an addition between the transparent pixel electrode 3 and the adjacent scanning signal wiring 1 '. Capacity.

According to this active matrix type transflective liquid crystal display device, the inverse stagger type thin film transistor 5 is switched by the scanning signal supplied from the scanning signal wiring 1, and the signal voltage of the image signal wiring 2 is drained (D). ) A voltage is applied to the liquid crystal material 10 held between the transparent pixel electrode 3 and the reflective pixel electrode 14 and the counter electrode 11 by applying to the transparent pixel electrode 3 and the reflective pixel electrode 14 which are extensions of the electrodes, Display the image. Then, the area of the reflective pixel electrode 14 displays a reflective image, and the area of the transmissive pixel electrode 3 at the center of the reflective pixel electrode 14 displays a transmissive image.

Here, the additional capacitance Cs is a charge holding capacitance for holding the voltage applied to the liquid crystal material 10 for a certain period.

Next, an example of another conventional liquid crystal display device will be shown.
17 is an enlarged view of one pixel, and FIGS. 18 and 19 are sectional views taken along the lines AA ′ and BB ′ of FIG. 17, respectively. 16 is an equivalent circuit diagram of the liquid crystal display device of FIG.

17, FIG. 18, FIG. 19, and FIG. 16, 5 is an inverted stagger type thin film transistor, 1 is a scanning signal line made of a metal film, and a gate electrode (G) of the thin film transistor formed at the same time as this scanning signal line. Reference numeral 2 is an image signal wiring formed of a laminated film of a metal film and a transparent conductive film and a source electrode (S) of the thin film transistor 5, 3 is a transparent pixel electrode formed of a transparent conductive film, and 4 is a reflection formed of a metal film having a light reflecting function. Pixel electrode, 6 is a semiconductor film of the thin film transistor 5, 8 is a gate insulating film of the thin film transistor 5, 9 is an insulating protective film, 10 is a liquid crystal material, 11 is a counter electrode made of a transparent conductive film, 7 is a black matrix, and 7 ′ is The openings 12 and 13 of the black matrix are transparent glass substrates.

Here, the reflective pixel electrode 4 is the transparent pixel electrode 3
Is provided under the gate electrode via the gate insulating film 8 and has a light reflecting function.

Further, in FIG. 12, Clc is a liquid crystal capacitance between the transparent pixel electrode 3 and the counter electrode 11, and Cs is an additional capacitance between the transparent pixel electrode 3 and the adjacent scanning signal line 1 '.

According to this active matrix type transflective liquid crystal display device, the inverse stagger type thin film transistor 5 is switched by the scanning signal supplied from the scanning signal wiring 1, and the signal voltage of the image signal wiring 2 is drained (D). ) By applying to the transparent pixel electrode 3 which is an extension of the electrode, a voltage is applied to the liquid crystal material 10 held between the transparent pixel electrode 3 and the counter electrode 11 to display an image.
Then, the area of the reflective pixel electrode 4 displays a reflective image, and the area of the transmissive pixel electrode 3 on the outer peripheral portion of the reflective pixel electrode 4 displays a transmissive image.

Here, the additional capacitance Cs is a charge holding capacitance for holding the voltage applied to the liquid crystal material 10 for a certain period.

[0015]

In the conventional transflective liquid crystal display device shown in FIG. 14, an object is to realize a bright liquid crystal display device by enlarging the pixel electrodes as much as possible, as shown in FIGS. 14 and 15. And the thickness of the insulating protective film 9 is 2 to 2
In this structure, an insulating organic film 15 having a thickness of 3 μm is formed, and a reflective pixel electrode 14 is also formed on the thin film transistor 5 and the image signal wiring 2. Therefore, the area of the pixel electrode is large and the aperture ratio is improved, but on the other hand, the number of steps such as film formation and patterning of the insulating organic film 15 and film formation and patterning of the reflective pixel electrode 14 is significantly increased. However, the productivity and the yield are reduced.

Further, in the conventional transflective liquid crystal display device shown in FIG. 17, as shown in FIGS. 18 and 19, generally, chromium is provided on the counter substrate 12 side in order to block the transmitted light around the pixel electrode 3. The black matrix 7 is formed of a metal film such as (Cr), and the black matrix 7 reduces the aperture ratio of the pixel portion which is the size of the opening 7 ′.

That is, in the above-described liquid crystal display device, when the black matrix 7 is formed on the counter substrate 12 side, the opening including the counter substrate 12 is limited to the area 7'shown by the dotted line in FIG. There is a problem that the aperture ratio cannot be improved.

In particular, the pixel electrode 3 and the black matrix 7
Is formed on the other substrates 12 and 13, so that it is necessary to form the substrate from the end of the pixel electrode 3 to the inside of the pixel electrode 3 by about 6 to 10 μm with the amount of deviation of the bonding of the substrates 12 and 13 as a margin. However, there is a problem that the aperture ratio of the pixel portion is significantly reduced.

The present invention has been completed in view of the above problems of the prior art, and an object thereof is to eliminate the decrease in the aperture ratio due to the black matrix on the counter substrate side without increasing the manufacturing process. An object is to provide a liquid crystal display device.

[0020]

In order to achieve the above object, in a liquid crystal display device according to the present invention according to claim 1, a plurality of image signal wirings and a plurality of scanning signal wirings cross each other with an insulating film interposed therebetween. A pixel electrode and a switching element for supplying an image signal to the pixel electrode are provided at an intersection of the image signal wiring and the scanning signal wiring, and the pixel electrode and the pixel electrode are provided so as to face each other. In a reflection-type or semi-transmission-type device in which a liquid crystal material is held between the counter electrode and the pixel electrode, the back side of the pixel electrode is protruded toward the image signal wiring side from the pixel electrode via the insulating film. A light-reflecting strip-shaped metal film is provided for each pixel.

The liquid crystal display device of the present invention according to claim 2 is
Overlap capacitance Cps between the pixel electrode and the strip-shaped metal film
Is the liquid crystal capacitance Clc between the strip metal film and the counter electrode.
It is characterized by being more than twice as many as 1.

The liquid crystal display device of the present invention according to claim 3 is
The strip-shaped metal film partially overlaps the image signal wiring in the vertical direction.

A liquid crystal display device according to a fourth aspect of the present invention is
The overlapping capacitance between the pixel electrode and the strip-shaped metal film is C
ps, the overlapping capacitance between the strip metal film and the image signal wiring is Csd, the capacitance between the gate electrode and the drain electrode of the switching element is Cgd, and the capacitance between the pixel electrode and the scanning signal wiring of the adjacent pixel is Where Cs is the overlapping capacitance of Cs and Clc is the liquid crystal capacitance between the pixel electrode and the counter electrode,
(Cps · Csd / (Cps + Csd)) becomes (Clc + Cs +
Cgd) is 1/5 or less.

The liquid crystal display device of the present invention according to claim 5 is
The strip-shaped metal film is formed of the same material as the scanning signal wiring and is separated from the scanning signal wiring.

A liquid crystal display device according to a sixth aspect of the present invention is
The switching element is an inverted staggered thin film transistor.

According to the liquid crystal display device of the present invention, as in the above structure, a light-reflective strip-shaped metal film is provided on the back surface side of the pixel electrode so as to extend toward the image signal wiring side from the pixel electrode via the insulating film. Therefore, light leakage does not occur at this portion, and the strip-shaped metal film functions as a reflective electrode. As a result, the black matrix at the portion facing the image signal wiring becomes unnecessary or can be formed in a narrow width, and as a result, a reflective or semi-transmissive liquid crystal panel with an improved aperture ratio can be realized. .

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below 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 sectional view taken along the 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 the liquid crystal display device of FIG. 1.

1 to 4, 1 is a scanning signal wiring, 2 is an image signal wiring, 3 is a pixel electrode, 4 is a strip-shaped metal film (reflection pixel electrode) having a light reflecting function, and 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,
Reference numeral 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 the pixel electrode 3 and the 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 has a gate electrode (G) formed continuously on the scanning signal line 2, a gate insulating film 8, a semiconductor film 6 to be a channel portion, and a source continuously formed on the image signal line 2. The drain electrode (D) is formed continuously with the electrode (S) and the pixel electrode 3.

The scanning signal line 1 and the gate electrode (G) are
It is formed of a metal film having a light reflecting function, such as aluminum alloy (AlX) or tantalum (Ta).

The gate insulating film 8 is made of silicon nitride (SiN
x), silicon oxide (SiO2), tantalum oxide (Ta
Ox) and 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 a laminated film of a metal film 2a such as titanium (Ti), molybdenum (Mo) and aluminum alloy (AlX) and a transparent conductive film 2b such as ITO. It is formed. 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 only the metal film 2b. But it's okay.

In the liquid crystal display device of the present invention, the pixel electrode 3 is projected on the image signal wiring 2 side from the pixel electrode 3 through the insulating film 8 to provide a light reflection function separated for each pixel. The band-shaped metal films 4 and 4 ′ are formed. Since the metal films 4 and 4 ′ have a light shielding property, the pixel electrode 3
The gap where light leakage occurs between the image signal wiring 2 and the image signal wiring 2 becomes small. Therefore, as shown in FIGS. 1, 2 and 3,
Black matrix 7 in a portion facing the image signal wiring 2
Can be made narrower and the area 7'of the opening is enlarged,
The aperture ratio of the pixel portion can be improved.

Further, since the strip-shaped metal film has a light reflecting function, it functions as a reflective pixel electrode of a reflective / semi-transmissive liquid crystal display device.

When the strip-shaped metal film 4 is separated for each pixel in this way, even if a short circuit occurs between the metal film 4 and another wiring, it becomes only a point defect of one pixel and affects other pixels. It does not affect.

Here, an additional capacitance Cs for holding the voltage applied to the liquid crystal material 10 for a certain period is provided between the pixel electrode 3 and the counter electrode 11 between the pixel electrode 3 and the adjacent scanning signal line 1 '. The liquid crystal capacitance Clc is between the strip metal films 4, 4'and the counter electrode 11, and the liquid crystal capacitance Clc1, Clc2 is between the pixel electrode 3 and the strip metal films 4, 4'Cps1, Cp.
Each of ps2 is formed to form an equivalent circuit as shown in FIG.

In this case, assuming that the voltage applied to the pixel electrode 3 is Vp, the strip metal film 4 has Cps1 / (Cps1 +
A voltage of Clc1) × Vp is applied, and a voltage of Cps2 / (Cps2 + Clc2) × Vp is applied to the strip-shaped metal film 4 ′, but in the case of Cps1> 2Clc1 and Cps2> 2Clc2, the strip-shaped metal films 4, 4 ′. Is applied with a voltage of 2/3 · Vp to Vp (a voltage close to that of the pixel electrode 3), the potential difference between the pixel electrode 3 and the strip-shaped metal films 4 and 4 ′ is almost eliminated, and thus the strip-shaped metal film 4, 4'also has the same function as the pixel electrode, and good display characteristics can be obtained without the occurrence of disclination in this portion. That is, the overlapping capacitances Cps1 and Cps2 between the pixel electrode 3 and the strip-shaped metal films 4 and 4'are
2 of liquid crystal capacitors Clc1 and Clc2 between 4'and the counter electrode 11
It may be formed so as to be double or more.

Next, another embodiment will be described. 5, FIG. 6, FIG. 7, and FIG. 8 are views showing another embodiment, FIG. 5 is a plan view of one pixel, FIG. 6 is a sectional view taken along the line AA ′ of FIG.
7 is a sectional view taken along the line BB 'of FIG. 6, and FIG. 8 is an equivalent circuit diagram of the liquid crystal display device of FIG.

In FIGS. 5, 6, 7, and 8, 1 is a scanning signal wiring, 2 is an image signal wiring, 3 is a pixel electrode, 4 is a strip-shaped metal film, 5 is a switching element composed of a thin film transistor, and 7 is black. Matrix, 8 is a gate insulating film, 9
Is a protective film, 10 is a liquid crystal material, 11 is a counter electrode, 12, 1
3 is a transparent glass substrate.

This example is also almost the same as the embodiment shown in FIGS. 1 to 4, but in this example, a strip-like shape is projected to the image signal wiring 2 side through the insulating film 8 on the back surface side of the pixel electrode 3. The metal film 4 having the light reflecting function is provided so as to partially overlap the image signal wiring 2 in the vertical direction.

This metal film 4 is made of aluminum alloy (Al
It is made of X) or tantalum (Ta) and has a light reflection function and a transmitted light shielding property. The image signal wiring 2 is also formed of a metal film 2a of titanium (Ti), molybdenum (Mo), aluminum alloy (AlX) or the like and a transparent conductive film 2b of ITO or the like, and has a light shielding property.

Therefore, as shown in FIGS. 5, 6 and 7, the width of the black matrix 7 in the portion facing the image signal wiring 2 can be made narrower and the area 7'of the opening can be further expanded. The aperture ratio of the pixel portion can be significantly improved.

When the strip-shaped metal film 4 and a part of the image signal wiring 2 are vertically overlapped, the crosstalk between the pixel electrode 3 and the image signal wiring 2 is caused by the capacitance C between the pixel electrode 3 and the strip-shaped metal film 4.
In proportion to ps (Cps1, Cps2) and the capacitance Csd (Csd1, Csd2) between the strip-shaped metal film 4 and the image signal wiring 2 in series, that is, (Cps × Csd / (Cps + Csd)),
The liquid crystal capacitance between the pixel electrode 3 and the counter electrode 11 is CLC1,
When the additional capacitance between the pixel electrode 3 and the adjacent scanning signal line 1'is Cs and the capacitance between the gate electrode (G) and the drain electrode (D) of the switching element 5 is Cgd, the above (Cps × Csd / (Cps + Csd)) becomes (Clc + Cs + Cg
By setting it to 1/5 or less of d), a good display device in which crosstalk hardly occurs can be obtained.

Further, it is preferable to form the strip-shaped metal film 4 from the same material as that of the scanning signal, because the strip-shaped metal film can be formed without complicating the manufacturing process at all.

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

FIG. 9, FIG. 10, FIG. 11 and FIG. 12 show still another embodiment. FIG. 9 is a plan view of one pixel, and FIG.
0 is a sectional view taken along the line AA ′ of FIG. 9, and FIG. 11 is a sectional view taken along the line BB ′ of FIG. 9.
12 is an equivalent circuit diagram of the liquid crystal display device of FIG.

In this example as well, although it is almost the same as the example shown in FIGS. 1 to 4, in this example, two pieces are projected to the image signal wiring 2 side through the insulating film 8 on the back surface side of the pixel electrode 3. The strip-shaped metal films 4 and 4'having a light reflection function are connected to one another.

In this example, the pixel electrode 3 and the metal films 4 and 4'having a band-shaped light reflecting function are insulated via the gate insulating film 8, but the gate insulating film 8 is partially removed, There is no problem even if the pixel electrode 3 and the metal films 4, 4'having a band-shaped light reflecting function are connected.

[0050]

As described above, according to the liquid crystal display device of the present invention, the pixel electrodes are separated from each other by projecting to the image signal wiring side from the pixel electrodes through the insulating film on the back surface side. By providing the light-reflective strip-shaped metal film, it is possible to reduce light leakage between the image signal wiring and the pixel electrode and reduce the black matrix in this portion, and as a result, the aperture ratio of the pixel portion is improved.

Further, according to the present invention, since the strip-shaped metal film has a light reflecting function, the strip-shaped metal film functions as a reflective pixel electrode, and a reflective / semi-transmissive liquid crystal panel having an improved aperture ratio is realized. We were able to.

Furthermore, according to the present invention, since the strip-shaped metal film is not connected to the peripheral wiring and is independent, the load capacitance of the pixel electrode and the load capacitance of the peripheral wiring are increased by the strip-shaped metal film. There was almost no increase, and there was no increase in the capacity of the liquid crystal panel when the screen was enlarged, and a liquid crystal panel of low power consumption capable of high-speed operation was realized.

[Brief description of drawings]

FIG. 1 is an enlarged view of one pixel of a liquid crystal display device of the present invention.

FIG. 2 is a sectional view taken along the line A-A ′ in FIG.

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

FIG. 4 is an equivalent circuit diagram of the liquid crystal display device shown in FIG.

FIG. 5 is an enlarged view showing another liquid crystal display device of the present invention.

6 is a cross-sectional view taken along the line A-A ′ of 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 still another liquid crystal display device of the present invention.

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

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.

FIG. 13 is an enlarged view of one pixel of a conventional liquid crystal display device.

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

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

16 is an equivalent circuit diagram of the liquid crystal display device shown in FIGS. 13 and 17. FIG.

FIG. 17 is an enlarged view of one pixel of another conventional liquid crystal display device.

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

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

[Explanation of symbols]

1 ... Scan signal wiring, 2 ... Image signal wiring, 3 ...
.Pixel electrodes, 4 ... Metal film having band-shaped light reflection function,
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, 14 ... Metal film, 15 ... Insulating organic film

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H042 DA02 DA12 DA22                 2H091 FA14Y FA35Y FB08 FD04                       FD06 GA02 LA12 LA13 LA16                       LA17 LA18                 2H092 GA17 GA24 GA25 JA24 JB07                       JB24 JB26 JB31 JB33 JB35                       JB51 JB52 JB54 JB61 JB64                       JB68 JB69 NA01 NA07 NA29

Claims (6)

[Claims] 1. A plurality of image signal wirings and a plurality of scanning signal wirings are provided so as to intersect each other with an insulating film interposed, and a pixel electrode and this pixel electrode are provided at the intersection of the image signal wirings and the scanning signal wirings. In a liquid crystal display device in which a switching element for supplying an image signal is provided, and 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 is provided on the back surface side of the pixel electrode. A reflective or semi-transmissive liquid crystal characterized by being provided with a light-reflective strip-shaped metal film, which extends over the image signal wiring side from the pixel electrode through the insulating film and is separated for each pixel. Display device. 2. The overlapping capacitance Cps between the pixel electrode and the strip metal film is at least twice the liquid crystal capacitance Clc1 between the strip metal film and the counter electrode. The reflective or semi-transmissive liquid crystal display device according to item 1. 3. The reflective or semi-transmissive liquid crystal display device according to claim 1, wherein the strip-shaped metal film partially overlaps the image signal wiring in the vertical direction. 4. The overlapping capacitance between the pixel electrode and the strip metal film is Cps, the overlapping capacitance between the strip metal film and the image signal wiring is Csd, and the gate electrode and the drain electrode of the switching element are formed. Is Cgd, and the overlapping capacitance between the pixel electrode and the scanning signal wiring of the adjacent pixel is Cs.
, The liquid crystal capacitance between the pixel electrode and the counter electrode is Cl
Assuming c, (Cps · Csd / (Cps + Csd))
The reflective or semi-transmissive liquid crystal display device according to claim 3, wherein the liquid crystal display device has a ratio of 1/5 or less of (Clc + Cs + Cgd). 5. The reflection type or semi-reflector 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. Transmissive liquid crystal display device. 6. The reflective or semi-transmissive liquid crystal display device according to claim 1, wherein the switching element is an inverted staggered thin film transistor.