JP3145944B2 - Display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an active matrix display device having a high aperture ratio using a display medium such as a liquid crystal.

[0002]

2. Description of the Related Art FIG. 4 is a schematic cross-sectional view of a conventional typical active matrix type twisted nematic (TN) liquid crystal display device, and FIG. 5 is a plan view of an active matrix substrate constituting the display device. . In this display device, as shown in FIG. 5, pixel electrodes 3 are formed in rectangular regions formed by the gate bus lines 5 and the source bus lines 6. As shown in FIG. 4, each pixel electrode 3 is formed on an insulating substrate 1, and a thin film transistor (hereinafter referred to as "T
FT "). A counter electrode 13 is formed on a counter substrate 10 facing the insulating substrate 1,
A voltage is applied to the liquid crystal layer 8 between the picture element electrode 3 and the counter electrode 13.

[0003]

In such an active matrix display device, it is necessary to form the gate bus line 5, the source bus line 6, and the pixel electrode 3 at a certain distance. Therefore, the area of the pixel electrode 3 cannot be increased to a certain degree or more, and the aperture ratio of the display device, that is,
There is a problem that the ratio of the area contributing to the display of the picture element electrode on the display screen cannot be increased. In order to solve such a problem, an active matrix display device shown in a schematic sectional view of FIG. 6 has been proposed. In the display device of FIG. 6, the picture element electrode 3 is provided on the insulating film 4 covering the TFT 2, and the picture element electrode 3 and the TFT 2 are electrically connected via the contact hole provided in the insulating film 4. . In the configuration of FIG. 6, since the area of the pixel electrode 3 is not restricted by the gate bus line 5 and the source bus line 6, the aperture ratio can be increased.

However, in the display device shown in FIG. 6, a certain space must be provided between the pixel electrodes 3 in order to prevent a leak between the adjacent pixel electrodes 3. This space varies depending on the pattern accuracy at the time of producing the pixel electrode 3 and the set value of the target yield, but is set in a range of, for example, 5 μm or more and 30 μm or less. In particular, in the case of a large-sized and high-definition display device, the ratio of the area occupied by the pixel electrodes 3 is relatively small, so that the aperture ratio is very small, 50% or less. If the aperture ratio is small, the display screen becomes dark, which leads to a decrease in display quality. When a black mask is formed on the counter substrate 10, the black mask is formed so as to cover the peripheral edge of the pixel electrode 3 in consideration of the displacement between the insulating substrate 1 and the counter substrate 10. Therefore, there is a problem that the aperture ratio is further reduced.

An object of the present invention is to provide an active matrix display device having a large pixel electrode area and a high aperture ratio.

[0006]

An active matrix display device according to the present invention includes a pair of insulating substrates, a display medium sealed between the substrates, and one of the substrates.
And a picture element electrode for applying a voltage to the display medium, wherein the ends of the picture element electrodes adjacent to each other are arranged in the thickness direction of the display apparatus. And the thickness direction
At least the end of the adjacent pixel electrode when viewed from
Partly overlapped , thereby achieving the above objective.

[0007] Further, the end portions of the adjacent picture element electrodes may be overlapped with each other with an insulating film interposed therebetween.

Further, the picture element electrode may be made of a transparent conductive film.

Further, the picture element electrode may be formed of a metal reflection film.

[0010] In the active matrix display device of the present invention, the ends of the adjacent picture element electrode is formed in the thickness direction of the display device to each other, the deviation greater than the thickness of the end portion of the picture element electrode Therefore, there is no need to provide a space between adjacent picture element electrodes. Therefore, in the active matrix display device of the present invention, it is possible to reduce the area of the portion other than the picture element electrodes which does not contribute to the display, and the aperture ratio is improved.

[0011]

Embodiments of the present invention will be described below.

(Embodiment 1) FIG. 1 is a sectional view of an embodiment of an active matrix display device according to the present invention. FIG. 2 is a plan view of an active matrix substrate included in the display device of FIG. The present embodiment relates to a transmission type TN mode active matrix display device, in which an insulating substrate 1 and a counter substrate 10 made of a pair of glass, and a liquid crystal as a display medium sealed between the insulating substrate 1 and the counter substrate 10 are provided. And a layer 8. A gate bus line 5 and a source bus line 6 intersecting the gate bus line 5 with a gate insulating film 9 interposed therebetween are formed on the insulating substrate 1. A gate electrode 7 branches from the gate bus line 5, and the TFT 2 is formed on the gate electrode 7. Gate bus line 5 and the gate electrode 7 is made of Ta, the gate insulating film 9 is made of SiN _X. The source bus line 6 is made of Ti.

The TFT 2 is manufactured by a known method. A channel layer 21 made of amorphous silicon (a-Si) is formed on the gate electrode 7 with the gate insulating film 9 interposed therebetween. An etching stopper 22 is formed above the gate electrode 7 on the channel layer 21, and a source electrode 23 and a drain electrode 24 are formed on both sides of the channel layer 21.
Are formed. Source electrode 23 and drain electrode 2
4 are formed at the same time as the source bus lines 6, and therefore are also made of Ti.

On the source electrode 23 and the drain electrode 24, an ITO (Indium Tin Oxide) film 25 is formed in a pattern.
An insulating film 4 made of N _X is formed on the entire surface of the insulating substrate 1. ITO film 25 connected to drain electrode 24
A contact hole 26 is formed in the upper insulating film 4. The picture element electrode 3 made of ITO is formed on the insulating film 4. The picture element electrode 3 is electrically connected to the ITO film 25 via the contact hole 26. Each pixel electrode 3 is also formed on the gate bus line 5 and the source bus line 6, as shown in FIG.

The pixel electrodes 3 are adjacent to the pixel electrodes 3a and 3a.
b. One picture element electrode 3a is an insulating film 4
After the pixel electrode 3a is formed before the pixel electrode 3b is formed thereon, the insulating film 4 is formed around the pixel electrode 3a.
a is patterned. Thereafter, the pixel electrode 3b is patterned. Therefore, adjacent picture element electrodes 3a and 3
The end portions of the pixel electrodes 3b are formed so as to be largely shifted from each other in the thickness direction of the display device by the interposition of the insulating film 4a. As shown in FIG. 2, in the extending direction of the source bus wiring 6, the pixel electrode 3a and the pixel electrode 3
b overlaps with the insulating film 4a interposed therebetween. In this embodiment, the pixel electrodes 3a and 3b are superimposed only in the extending direction of the source bus wiring 6, but they may be superposed in the extending direction of the gate bus wiring 5. it can.

An alignment film 27 is formed on the picture element electrode 3. On the counter substrate 10 facing the insulating substrate 1, a counter electrode 13 made of ITO and an alignment film 27 are formed. A liquid crystal layer 8 is sealed between the insulating substrate 1 and the opposing substrate 10 to form a liquid crystal cell. Further, polarizing plates (not shown) are provided on both outer sides of the insulating substrate 1 and the opposing substrate 10, respectively.

FIG. 3 shows the cell configuration of this display device, that is, the rubbing directions of the two alignment films 27 and the polarization axes of the respective polarizing plates. In FIG. 3, the solid line o indicates the direction of the polarization axis of the upper polarizer, and the arrow m indicates the rubbing direction of the alignment film on the upper substrate. The broken line p indicates the direction of the polarization axis of the lower polarizing plate, and the arrow n indicates the rubbing direction of the alignment film on the lower substrate. As shown in FIG. 3, the twist angle of the liquid crystal molecules in the liquid crystal layer 8 is 90.
The active matrix display device of the present embodiment is in a normally white mode. In this embodiment, the Δn · d value of the liquid crystal cell, that is, the product of the birefringence and the cell thickness is about 0.1.
4 is set. As a chiral agent added to the liquid crystal layer 8, CN (Cholesteryl Nanonat) is used.
Using e), the amount of addition was determined so that the d / p value, that is, the ratio of the cell thickness to the helical pitch length of the liquid crystal was 0.1.

Table 1 shows display characteristics of the active matrix display device of the present embodiment in consideration of the displacement of bonding between the insulating substrate 1 and the counter substrate 10. For comparison, FIG.
The display characteristics of the conventional display device shown in FIG. 6 are shown in Comparative Example 1, and the display characteristics of the conventional display device shown in FIG.

[0019]

[Table 1]

In Table 1, the display luminance is a panel transmittance of light when a display device is driven to obtain a maximum contrast ratio and white display is performed. In the present embodiment, a display screen with higher luminance than that of the conventional display device can be obtained, including a case where a displacement occurs due to bonding. Further, even if a displacement of the bonding of the substrates occurs, the maximum contrast ratio does not change, and a stable contrast ratio and high color reproducibility are obtained. The aperture ratio is 35 to 50% in the comparative example.
On the other hand, in this embodiment, the display quality reaches as high as 80%, and the display quality is greatly improved.

(Embodiment 2) The active matrix display device of this embodiment has the same configuration as that of the above-described Embodiment 1, except that the picture element electrode 3 is made of a Ti metal layer. Therefore, this embodiment is a reflection type active matrix display device having the configuration shown in FIGS.
As in the first embodiment, Table 2 shows the display characteristics in consideration of the displacement of the bonding between the insulating substrate 1 and the counter substrate 10 in the present embodiment. For comparison, the display characteristics of the conventional reflective display device having the configuration shown in FIG. 4 are shown in Comparative Example 3, and the display characteristics of the conventional reflective display device having the configuration shown in FIG. 6 are shown in Comparative Example 4.

[0022]

[Table 2]

Here, the display luminance refers to the luminance of light emitted in a direction of 45 degrees with respect to the luminance of light incident from a direction of 45 degrees with respect to the normal of the screen of the display device. Or reflectance).

In this embodiment as well, a display screen having a higher luminance than that of a conventional display device can be obtained, including a case where a displacement occurs due to bonding. Further, even if a displacement of the bonding of the substrates occurs, the maximum contrast ratio does not change, and a stable contrast ratio and high color reproducibility are obtained. Also, the aperture ratio is
Compared with the comparative example, it is 50 to 70%, but in the present embodiment, it can be 100%, and the display quality is greatly improved.

In this embodiment, similar to the first embodiment,
The rubbing direction of the alignment film 27 and the polarization axis of each polarizing plate were set as shown in FIG. 3, but the display luminance was considerably smaller than that of the first embodiment. Therefore, although it is necessary to use another display mode in the reflection type display device, it has been confirmed that the effects of the present invention appear similarly to Table 2 even when the display mode is changed.

In the first and second embodiments, each parameter is set as described above, but the Δn · d value of the cell is set to 0.24.
When the d / p value is set in the range of 0.56 or less and various chiral agents are used and the d / p value is 0.01 or more and 0.5 or less, similar results can be obtained. Has been confirmed. As the gate bus wiring 5 and the source bus wiring 6, Cr, Mo, Ni, other than Ta and Ti,
A simple substance or alloy such as Cu, Au, and Al can also be used.

In the first embodiment, the picture element electrode 3
Although O was used, another transparent conductive film may be used.
Further, in the second embodiment, Ti is used as the pixel electrode 3, but Al, Mo, or an alloy thereof can be used. In the first and second embodiments, the insulating film 4 is made of SiN.
_{Although X} is used, similar effects can be obtained by using other insulating films such as SiO ₂ , SiO, and Ta ₂ O ₅ .

[0028]

The active matrix display device according to the present invention has a configuration in which the ends of adjacent picture element electrodes are shifted from each other in the thickness direction of the display apparatus by more than the thickness of the end of the picture element electrode. I have. With this configuration, it is not necessary to provide a space that does not contribute to display between the pixel electrodes, and the aperture ratio is improved. Therefore, according to the present invention, a display screen with high contrast and high brightness can be obtained, which can contribute to improvement in image quality.

[Brief description of the drawings]

FIG. 1 is a sectional view of one embodiment of an active matrix display device of the present invention.

FIG. 2 is a plan view of an active matrix substrate included in the display device of FIG.

FIG. 3 is a diagram showing a cell configuration of the active matrix display device shown in FIG.

FIG. 4 is a sectional view of a conventional active matrix display device.

FIG. 5 is a plan view of an active matrix substrate included in the display device of FIG.

6 is a cross-sectional view of a conventional active matrix display device in which the display device of FIG. 4 is improved.

[Explanation of symbols]

 Reference Signs List 1 insulating substrate 2 TFT 3, 3a, 3b picture element electrode 4, 4a insulating film 5 gate bus wiring 6 source bus wiring 7 gate electrode 8 liquid crystal layer 9 gate insulating film 10 counter substrate 13 counter electrode 21 channel layer 22 etching stopper 23 Source electrode 24 Drain electrode 25 ITO film 26 Contact hole 27 Alignment film

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-245742 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/136 G02F 1/1343

Claims (1)

(57) [Claims] 1. A pair of insulating substrates, a display medium sealed between the substrates, and a picture element electrode arranged on one of the substrates for applying a voltage to the display medium. An active matrix display device comprising: an end portion of an adjacent pixel electrode that is greatly displaced from each other in a thickness direction of the display device by a thickness larger than an end portion of the pixel electrode ; and
The edge of the adjacent pixel electrode when viewed from the thickness direction.
An active matrix display device characterized in that at least a part thereof is overlapped .