JP2002031816A - Liquid crystal display - Google Patents

Abstract

(57) [Problem] To provide a high-quality liquid crystal display device that suppresses a phenomenon in which light incident from the back surface of an array substrate is reflected by a counter substrate and degrades the off characteristics of a TFT. In a thin film transistor type liquid crystal display device having a plurality of pixel electrodes arranged in a matrix, a source line serving also as a source electrode, a gate line serving also as a gate electrode, and a drain electrode, a drain electrode is provided. Has an extended portion 9b extending in a branch shape along the outer periphery of the thin film transistor. Conventionally, the drain electrode 9 is extended in a branch shape in a region between the gate electrode 2a and the pixel electrode 10 where there is no wiring or electrode pattern.
By reducing the light passing through the array substrate in the vicinity of the FT, the amount of light reflected by the counter electrode of the filter substrate can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device using thin film transistors.

[0002]

2. Description of the Related Art A display device to which liquid crystal is applied has low power and light weight, which are not features of a conventional display. The liquid crystal display device is used for a notebook computer, a car navigation display, and the like because a clear image display with less crosstalk can be obtained. In recent years, the liquid crystal display device has been rapidly used as a large display monitor.

Hereinafter, an example of a conventional active matrix type liquid crystal display device will be described with reference to the drawings. FIG. 3 is a partially enlarged plan view showing a part of an array substrate in a conventional active matrix type liquid crystal display device. In FIG. 3, reference numeral 2 denotes a gate wiring also serving as a gate electrode of the TFT, and 4 denotes a channel, source, and
An amorphous silicon semiconductor layer for forming a drain region, 4 'an amorphous silicon semiconductor layer for protecting the gate wiring 2, 5 a source signal line also serving as a source electrode of the TFT, 9 a drain electrode of the TFT, 10 an IT
It is a pixel electrode made of O or the like. The drain electrode 9 and the pixel electrode 10 are electrically connected via a contact hole 7 opened in the passivation film.

FIG. 4 is a cross-sectional view of the entire liquid crystal display device taken along the line BB 'in FIG. On an upper surface of a glass array substrate 1, a gate wiring 2, a gate insulating film layer 3, a semiconductor layer 4, a passivation film 6, and a pixel electrode 10 are sequentially laminated. Further, a filter substrate 8 is provided facing the array substrate 1 via a liquid crystal layer (not shown), and a counter electrode 11 made of ITO or the like is formed on the lower surface of the filter substrate 8.

The operation of the liquid crystal display device configured as described above will be described. First, when a voltage is applied to the gate wiring 2 and a channel is formed in the amorphous silicon semiconductor layer 4 of the TFT, a video signal from the source signal line 5 flows into the drain electrode 9 through the channel of the TFT and the pixel electrode It is conveyed to 10. Then, an electric field corresponding to the video signal is generated between the pixel electrode 10 and the counter electrode 11, and the pixel electrode 10 and the counter electrode 1 are generated according to the generated electric field.
The alignment of the liquid crystal injected during 1 changes. This allows
The transmittance of the light incident from the back surface of the array substrate 1 changes, and an image corresponding to the video signal is displayed.

[0006]

However, in the above-mentioned conventional liquid crystal display device, when light is irradiated from the back surface of the array substrate 1, a part of the incident light is on the filter substrate 8 as shown in FIG. And may reach the semiconductor layer 4 after being reflected by the opposite electrode 11. The light incident on the semiconductor layer 4 unnecessarily increases the carrier concentration of the semiconductor layer 4 and lowers the electrical resistivity, thereby deteriorating the off-characteristics of the TFT. When the off-characteristics of the TFT deteriorate, image performance such as contrast deteriorates. In recent years, with the demand for a display device having higher luminance, this kind of problem has become more serious.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and reduces the amount of reflected light of light incident from the back surface of an array substrate to reach a semiconductor layer forming a channel. It is an object of the present invention to provide a liquid crystal display device capable of suppressing a decrease in image performance due to deterioration.

[0008]

In order to achieve the above object, a liquid crystal display device according to the present invention comprises a plurality of pixel electrodes arranged in a matrix on an insulative transparent substrate; A gate line formed between rows of the pixel electrodes, a part of the source line serving as a source electrode adjacent to an intersection of the source line and the gate line, A thin film transistor, wherein a part of the thin film transistor is used as a gate electrode and a metal electrode formed by connecting to the pixel electrode is used as a drain electrode, and the drain electrode is formed along the outer periphery of the thin film transistor. It is characterized in that it has an extended portion extending in a branch shape.

As described above, in the conventional liquid crystal display device, a region where there is no wiring or electrode pattern serving as a light-shielding member in the vicinity of the TFT exists widely especially between the gate electrode and the pixel electrode. The reflected light is reflected by the counter electrode on the filter substrate, reaches the semiconductor layer forming the channel, and degrades the off characteristics of the TFT. In the liquid crystal display device according to the present invention, the drain electrode has a pattern shape in which the drain electrode is extended in a branch shape in a region between the gate electrode and the pixel electrode, which has no conventional light-shielding pattern.
Reduce the light passing through the array substrate near T,
The amount of light reflected on the counter electrode of the filter substrate and incident on the TFT can be reduced. With this, TFT
Can be suppressed from deteriorating the image performance caused by the characteristic deterioration.

An extension of a metal electrode serving as a drain electrode extends along two sides on the outer periphery of the thin film transistor. The metal electrode, the source wiring, and the gate wiring make the thin film transistor four sides. Preferably, it is substantially enclosed.

Since the drain electrode, the source wiring, and the gate wiring are all light-shielding members formed of metal, they surround four sides of the TFT, thereby reducing the amount of light passing near the TFT, thereby reducing the amount of light passing through the TFT. Return of reflected light to the light source can be further suppressed.

Further, it is preferable that an extension of the metal electrode is formed so as to overlap with the pixel electrode. The alignment state of liquid crystal molecules is controlled by receiving a vertical electric field between the pixel electrode and the counter electrode.However, the electric field is disturbed near the outer edge of the pixel electrode. Easy to do. Since the drain electrode is always at the same potential as the pixel electrode, the extended portion of the drain electrode overlaps with the pixel electrode, so that the light-shielded portion that has been disturbed by the electric field near the outer edge of the pixel electrode is shielded, and the pixel electrode is Can be suppressed from being displayed abnormally at the outer edge of the display.

The present invention is also an image display application device having the liquid crystal display device according to the present invention. The liquid crystal display device according to the present invention has a T
Since there is little deterioration in the off characteristic of the FT and high image quality can be maintained, high-luminance and high-quality image display application equipment can be configured by combining with a high-luminance backlight light source.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, members denoted by the same reference numerals as those in FIGS. 3 and 4 represent the same or corresponding members. FIG. 1 is a partially enlarged plan view showing a part of an array substrate in an active matrix type liquid crystal display device according to an embodiment of the present invention. In the array substrate shown in FIG. 1, the TFT is formed adjacent to the intersection of the gate wiring 4 and the source signal line 5,
A gate electrode portion 2a protruding from the source wiring 5 as a gate electrode;
Is the source electrode, and the metal electrode 9 connected to the pixel electrode 10
As a drain electrode. In the region where the TFT is formed, the pixel electrode 10 has a shape in which a corner is cut off.

The drain electrode 9 has a pattern portion 9a which linearly connects the amorphous silicon semiconductor layer 4 and the pixel electrode 10 as in the conventional case, and further has a gate electrode portion orthogonal to the pattern portion 9a. It has a pattern portion 9b protruding in a branch shape along 2a. The pattern portion 9b protruding in a branch shape extends along the outer periphery of the TFT, and reduces the amount of light incident from the back surface of the array substrate and passing through the vicinity of the TFT toward the opposite substrate. Play a role.

The light-shielding effect of the pattern portion 9b of the drain electrode will be described with reference to a sectional view. FIG.
FIG. 2 is a sectional view of the entire liquid crystal display at the position of line AA ′ in FIG. 1. On the upper surface of an array substrate 1 made of glass, a gate wiring 2, a gate insulating film layer 3, an amorphous silicon semiconductor layer 4 for forming a channel region of a TFT, a passivation film 6, and a pixel electrode 10 are sequentially laminated. The passivation film 6 is, for example, an insulating film made of SiNx, SiO ₂ , acrylic resin, polyimide, polyamide, polycarbonate, or a laminated film of these. Further, a filter substrate 8 is provided facing the array substrate 1 via a liquid crystal layer (not shown), and a counter electrode 11 made of ITO or the like is formed on the lower surface of the filter substrate 8.

As described above, in the conventional liquid crystal display device, the gate wiring serving as a light shielding member near the TFT,
There is a portion without a source wiring or a drain electrode, and light incident therefrom is reflected by a counter electrode on the filter substrate 8,
The semiconductor has reached the semiconductor layer 4 forming the channel, and the off-characteristics of the TFT have been deteriorated. Light that passes through the vicinity of the TFT can reach the semiconductor layer 4 even if the light has a small incident angle, so that the off characteristic is likely to be deteriorated. In particular, T
In the region between the gate electrode portion 2a and the pixel electrode 10 constituting the FT, a large amount of light passes through the array substrate 1 in the vicinity of the TFT, which has been a major factor for deteriorating the OFF characteristics of the TFT.

On the other hand, in the liquid crystal display device according to the present invention, as shown in FIG. 2, in the region between the gate electrode portion 2a and the pixel electrode 10, the drain electrode 9 is
It has a pattern portion 9b protruding in a branch shape along the outer periphery of a. For this reason, in a region between the gate electrode portion 2a and the pixel electrode 10, light incident from the back surface of the array substrate 1 is blocked by the extended portion 9b of the drain electrode, and reflected by the counter electrode 11 of the filter substrate. The amount can be reduced. Thereby, the amount of light reaching the semiconductor layer 4 where the channel of the TFT is formed can be reduced, and the deterioration of the image performance caused by the deterioration of the TFT characteristics can be suppressed. For example, such a TFT
When a TFT liquid crystal display device using the above configuration was created,
Even when the incident light luminance was as high as 7000 cd / m ² , good image display performance with a contrast of 300 or more was obtained.

The extension pattern portion 9b of the drain electrode is
As shown in FIG. 1, it is preferable to extend the TFT in an L-shape along two outer peripheral sides. Thereby, the TF is formed by the drain electrode 9, the source wiring 5, and the gate wiring 2.
It can almost surround four sides of T. The drain electrode 9, the source wiring 5, and the gate wiring 2 are all light-shielding members formed of a metal. Therefore, by surrounding them with four sides, the amount of light passing near the TFT is reduced, thereby reducing the amount of light passing near the TFT. Return of reflected light to the light source can be further suppressed.

The extension 9b of the drain electrode is preferably formed so as to overlap the pixel electrode 10, as shown in FIG. The liquid crystal molecules are the pixel electrodes 1
The arrangement state is controlled by receiving a vertical electric field between the pixel electrode 10 and the counter electrode 11. However, the electric field is easily disturbed near the outer edge of the pixel electrode 10, so that the liquid crystal arrangement is disturbed and display abnormalities such as light leakage occur. easy. Since the drain electrode 9 is always at the same potential as the pixel electrode 10, the extension 9b of the drain electrode is
, The disturbance of the electric field near the outer edge of the pixel electrode 10 can be reduced. Therefore, abnormal display at the outer edge of the pixel electrode 10 can be suppressed, and the effective pixel area (= pixel aperture ratio) of the liquid crystal display device can be increased.

The drain electrode 9 overlaps the pixel electrode 10 to cause a large capacitive coupling between the two. However, since both are at the same potential, this capacitive coupling is equal to T.
There is no adverse effect on the driving of the FT.

Since the liquid crystal display device according to the present invention has the same configuration as the conventional liquid crystal display device except for the pattern of the drain electrode, a conventional method for manufacturing a general active matrix type liquid crystal display device is used. Can be manufactured. The drain electrode 9 is, like the amorphous silicon semiconductor film 4, the source signal line 5, the pixel electrode 10, and the like,
Patterning can be performed by a general method.
For example, a drain electrode 9 can be formed by depositing a thin metal film for forming the drain electrode 9 by a sputtering film forming method and patterning the thin metal film by a photolithography process and an etching process.

In this embodiment, a case of a bottom gate type thin film transistor using amorphous silicon for a semiconductor layer has been described as an example, but the present invention is not limited to this. For example, in the case of using another semiconductor layer such as polycrystalline silicon or in the case of a top-gate thin film transistor, the same operation and effect can be obtained by forming the drain electrode in the same manner as described in this embodiment mode. Can play.

[0024]

As described above, according to the liquid crystal display device of the present invention, since the drain electrode has a pattern extending along the outer periphery of the TFT, incident light from the back surface of the array substrate is partially blocked. In addition, the amount of light reflected by the counter electrode on the filter substrate can be reduced. Therefore, the amount of light reaching the semiconductor layer forming the channel of the TFT can be reduced, and the deterioration of the image performance caused by the deterioration of the off characteristics of the TFT can be suppressed.

[Brief description of the drawings]

FIG. 1 is a partially enlarged plan view showing an array substrate of a liquid crystal display device according to the present invention.

FIG. 2 is a partially enlarged cross-sectional view showing the liquid crystal display device taken along the line AA ′ in FIG. 1;

FIG. 3 is a partially enlarged plan view showing an array substrate of a conventional liquid crystal display device.

FIG. 4 is a partially enlarged cross-sectional view showing the liquid crystal display device taken along the line BB ′ in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Array substrate 2 Gate wiring 2a Gate electrode part 3 Gate insulating film 4 Amorphous silicon semiconductor layer 5 Source signal line 5a Source electrode part 6 Passivation film 7 Contact hole 8 Filter substrate 9 Drain electrode 9b Drain electrode extension part 10 Pixel electrode 11 Counter electrode

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Taku Hamaoka 1006 Kazuma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F-term (reference) 2H092 JA25 JA26 JA42 JB54 KA18 MA05 MA13 MA17 NA22 5C094 AA02 AA11 BA03 BA43 CA19 DA13 EA01 EA04 EA07 5F110 AA06 AA30 BB01 CC01 CC05 CC07 DD02 GG02 GG13 GG15 HK33 HM04 HM19 NN03 NN23 NN24 NN27 NN44

Claims (4)

[Claims] A plurality of pixel electrodes arranged in a matrix on an insulating transparent substrate; a source line formed between columns of the pixel electrodes; and a gate line formed between rows of the pixel electrodes. A part of the source wiring formed adjacent to an intersection of the source wiring and the gate wiring is formed as a source electrode, a part of the gate wiring is formed as a gate electrode, and connected to the pixel electrode. A thin film transistor having a metal electrode as a drain electrode, wherein the drain electrode has an extended portion extending in a branch shape along the outer periphery of the thin film transistor. Liquid crystal display device. 2. An extended portion of the drain electrode extends along two sides of an outer periphery of the thin film transistor, and the metal electrode, the source wiring, and the gate wiring make four sides of the thin film transistor thin. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is substantially enclosed. 3. The liquid crystal display device according to claim 1, wherein an extension of the drain electrode is formed to overlap with the pixel electrode. 4. An image display application device having the liquid crystal display device according to claim 1.