JPH10206872A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the aperture ratio of a TFT(thin film transistor) liquid crystal device and to effectively prevent noises caused by a cold-cathode fluorescent tube of a back light unit. SOLUTION: An ITO thin layer 31 is formed on a glass substrate 30 where a TFT 13, etc., of the liquid crystal display device is formed, and a thin insulating film layer 32 is formed thereupon. Then the TFT 13, a display electrode, etc., are formed on the insulating film layer 32. Further, the ITO film layer 31 is connected to the ground GND side of an inverter substrate 35 which drives the back light (cold-cathode fluorescent tube) 28. Consequently, electric charges can be held between an electrode of the TFT 13 and a display electrode, and the ITO film layer 31 and this part operates as an auxiliary capacitor. Therefore, a storage capacitor is removed from the TFT liquid crystal display device to improve the aperture ratio. The ITO layer 31, on the other hand, operates as a shield for noise caused by the back light to a liquid crystal module.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an active matrix type liquid crystal display device requiring an auxiliary capacitor.

[0002]

2. Description of the Related Art Generally, in an active matrix type liquid crystal display device, a liquid crystal 3 is arranged between a common electrode 1 and a display electrode 2 in a pixel portion 1 of each pixel, as schematically shown in FIG. In addition, the display electrode 2 is switched by the active element 4. In an active matrix type liquid crystal display device,
The electric charge is held in the pixel capacitance, and the pixel capacitance is usually the liquid crystal 3 itself. However, the pixel capacitance alone has a small value and the holding operation is insufficient, and is often affected by the parasitic capacitance generated in the active element 4. For example, as shown in FIG. 4, the pixel unit 1 is provided with a storage capacitor 5 as an auxiliary capacitor.

More specifically, each pixel 10 of the liquid crystal display device is surrounded by data lines (source lines) 11 and gate lines (gate electrodes) 12 arranged vertically and horizontally as shown in FIG. For example, an amorphous silicon TFT (thin film tran
A storage electrode (pixel electrode) 15 is connected to a drain electrode 14 of the TFT 13, and a storage capacitor (electrode) 16 having a dedicated wiring 16 a as an auxiliary capacitor is arranged as described above. I have.

The TFT 13 includes an amorphous Si.
Film 18, n + type amorphous Si film 19, source electrode 2
0, the gate electrode 12, the drain electrode 14, and the like. Also, the liquid crystal display device having such a structure basically contributes to display by the TFT 1
3, a portion (opening 21) of the display electrode 15 made of a transparent electrode (ITO (Indium Tin Oxide)) excluding the portions of the wirings 11, 12 and the storage capacitor (storage capacitor 16), and FIG.
1 illustrates an opening 21 to be fastened in one pixel 10.

FIG. 6 shows an equivalent circuit corresponding to one pixel 10 of the above-mentioned liquid crystal display device. As shown in FIG. The storage capacitor 16 holds an electric charge as an auxiliary capacitance. In the liquid crystal display device, the parasitic capacitance (Cg) is present between the gate electrode 12 and the drain electrode 14, between the source electrode 20 and the drain electrode 14, between the display electrode 20 and the data line 11, and the like.
d) 23, a parasitic capacitance (Cds) 24, a parasitic capacitance 25, and the like are generated. Therefore, the above-described storage capacitance 16 is required to avoid the influence of the parasitic capacitances 23, 24, and 25.

In the above liquid crystal display device, a backlight unit for illuminating a display screen from the back side is generally used, and a cold cathode fluorescent tube is often used as a light source of the backlight unit. ing. In the liquid crystal display device, for example, as shown in FIG. 7, a backlight (cold cathode fluorescent tube) 28 is disposed on the back side of the liquid crystal module 26 via a diffusion plate 27.

[0007]

By the way, in the liquid crystal display device having the storage capacitor 16, the portion of the storage capacitor 16 is not included in the opening 21 contributing to the display shown in FIG. Furthermore, since the area of the storage capacitor 16 to be closed in one pixel 10 is relatively large, there is a problem that the aperture ratio, which is the ratio of the area of the opening 21 to the total area of one pixel 10, is reduced.

[0008] The auxiliary capacitance of the liquid crystal display device is as follows.
In addition to the storage capacitance type in which the storage capacitance 16 having the dedicated wiring 16a is provided, there is an additional capacitance type in which the display electrode 15 and the preceding gate line 12 are overlapped. The additional capacitance type is larger than the storage capacitance type. An aperture ratio can be obtained. But,
The additional capacitance type has problems such as an increase in capacitance connected to the gate line 12 and an increase in wiring delay, and the storage capacitance type is more suitable when the size and definition of the liquid crystal display device are considered. It is excellent, and it is not possible to select the additional capacitance type simply due to the problem of the aperture ratio.

Further, in the liquid crystal display device using the backlight unit having the cold cathode fluorescent tube as described above, there is a problem that noise is generated by the cold cathode fluorescent tube, and as shown in FIG. Grounded to prevent noise from the cold cathode fluorescent tubes
The TO sheet 29 is connected to the liquid crystal module 26 and the backlight 2
However, there is a possibility that the ITO sheet 29 may be a bad factor when the thin mounting is performed, or may be a cause of display unevenness. I didn't get it.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the aperture ratio in an active matrix type liquid crystal display device requiring an auxiliary capacitor and to prevent noise from a cold cathode fluorescent tube.

[0011]

According to a first aspect of the present invention, there is provided a liquid crystal display device of an active matrix type having an active element for each pixel and a display electrode connected to the active element on a substrate. A transparent electrode layer is provided on the substrate between the active element and the display electrode via a transparent insulating layer, and the transparent electrode layer is grounded.

According to the above configuration, a state in which the active element and the display electrode are insulated on the substrate (for example, between the substrate and at least one of the active element and the display electrode). Since the transparent electrode layer is provided, at least one of the electrode of the active element and the display electrode and the transparent electrode layer are arranged to face each other, and charges can be held in this portion. The portion can be used as an auxiliary capacitor instead of the conventional storage capacitor.

In a case where charge is held between at least one of the electrode of the active element and the display electrode and the transparent electrode layer, a state in which the pixel and the transparent auxiliary capacitance are vertically overlapped. Thus, the aperture ratio of the liquid crystal display device can be improved by making the portion where the storage capacitor has conventionally been used as the opening without the transparent electrode layer narrowing the opening of the pixel.

According to a second aspect of the present invention, the transparent electrode layer is provided over substantially the entire surface of the substrate, and the transparent electrode layer is connected to the ground of an inverter circuit for a fluorescent tube of a backlight unit to be grounded. It is characterized by having been done. According to the above configuration, when the transparent electrode layer provided on the substrate is provided between the substrate and the active element or the display electrode, the active element
A display electrode, a substantial liquid crystal display unit comprising liquid crystal,
Since the transparent electrode layer is disposed between the backlight unit and the ground, and the transparent electrode layer is connected to the ground of the inverter circuit, the transparent electrode layer efficiently functions as a shield against the fluorescence noise of the backlight unit. . Therefore, in the liquid crystal display device, the influence of the noise of the fluorescent tube can be prevented, and since the transparent electrode layer serving as the shield is directly formed on the glass substrate, the shield hinders the thin mounting of the liquid crystal display device. And display unevenness due to the transparent electrode layer serving as a shield does not occur.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a liquid crystal display according to an embodiment of the present invention will be described with reference to the drawings. FIG.
FIG. 2 is a cross-sectional view of an active element portion of one pixel 10 of a liquid crystal display device of this example. In this example, components similar to those of a conventional liquid crystal display device are denoted by the same reference numerals and description thereof is omitted.

As shown in FIG. 1, in this example of the liquid crystal display device, an ITO film layer 31 serving as a transparent electrode layer is formed on a glass substrate 30 and a thin insulating film layer 32 is formed thereon. The TFT 13 and the display electrode 15 (shown in FIG. 3) are formed. That is, while the TFT 13 and the display electrode 15 are conventionally formed on the glass substrate 30, in this example, the TFT 13 and the display electrode 1 are formed.
5 and the glass substrate 30, the insulating film layer 32
IT insulated from T13 and display electrode 15
It is in a state where the O film layer 31 is provided.

In this example, the TFT 13 serving as an active element is a well-known amorphous Si TFT 1.
3, a gate electrode 12, a gate insulating film 33, an amorphous Si film 18, a channel protective film 34, and a glass substrate 30 having the insulating film layer 32 and the ITO film layer 31.
An n + type amorphous Si film 19, a source electrode 20, and a drain electrode 14 are formed. Further, the active element is not limited to the amorphous Si TFT 13, but may be any active element used in a known active matrix system.

The ITO film layer 31 is basically the same as the well-known common electrode (not shown) of the liquid crystal display device and the display electrode 15, and is formed similarly to the common electrode and the display electrode. It is. Also, the portion of the ITO film layer 31 is
A transparent conductor may be used, and a transparent electrode made of a metal oxide other than ITO or another material may be used. The ITO film layer 31 is provided with a backlight (cold cathode fluorescent tube) 28 of a backlight unit as described later.
GND of the inverter board 35 for driving the
Side and grounded.

The insulating film layer 32 only needs to be transparent and highly insulating when formed into a film. For example, the same insulating film layer as the above-described gate insulating film 33 is used. It can be formed similarly. Also,
FIG. 1 shows only the lower substrate side of the liquid crystal module. In an actual liquid crystal display device, a liquid crystal 22 (shown in FIG. 2) is arranged on the lower substrate, and for example, a common electrode ( An upper substrate on which (not shown) and the like are formed is disposed.

On the back side of the glass substrate 30, a diffusion plate 27 and a backlight 28 are disposed as a backlight unit as in the conventional case. The backlight 28 is provided with an inverter board 35 as a power supply for driving the cold cathode fluorescent tubes, and the ITO film layer 3 is connected to the ground (GND) of the inverter board 35.
1 is connected and grounded. Therefore, the ITO film layer 3
1 and an electrode of the TFT 13, for example, the gate electrode 12 are opposed to each other in a state of being close to each other, and the ITO film layer 3
1 and the display electrode 15 connected to the drain electrode 14 are arranged close to and opposed to each other.
When a voltage is applied to the gate electrode 12 and the display electrode 15, charges can be held between the gate electrode 12 and the display electrode 15 and the ITO film layer 31, which are insulated from each other by an insulating film, This portion operates as an auxiliary capacitor 36 (shown in FIG. 2).

That is, as shown in an equivalent circuit corresponding to one pixel of the liquid crystal display device of this example in FIG.
5 and a common electrode (Vcom) serve as a pixel capacitor and are insulated from each other.
TO film layer 31 and display electrode 15 (and electrode of TFT 13)
Function as the auxiliary capacitance 36. Further, as shown in FIG. 1, the ITO film layer 31
13, the display electrode 15, the liquid crystal (shown in FIG. 2) 22 and the backlight 28, and the ITO film layer 31 is placed on the ground GND side of the inverter substrate 35 of the backlight 28 as described above. Since the ITO film layer 31 is connected and grounded, the ITO film layer 31 effectively functions as a shield for the noise of the backlight 28 with respect to the liquid crystal module, thereby preventing the noise of the backlight 28 from affecting the liquid crystal display device. ing. Further, as shown in FIG. 3, in one pixel 10 surrounded by the data line 11 and the gate line 12, the display electrode 15 is formed so as to occupy almost the entire portion except for the TFT 13, the data line 11 and the gate line 12. Are arranged, and this portion becomes an opening.

Next, the operation of this example of the liquid crystal display device having the above configuration will be described. In the above liquid crystal display device, as described above, the ITO film layer 3 is formed on the glass substrate 30.
1 and a thin insulating film layer 32 are formed, and the TFT 13 and the display electrode 15 are formed on the insulating film layer 32. Therefore, it is possible to hold charges between the electrode (gate electrode 12) of the TFT 13 and the display electrode 15 and the ITO film layer 31, and this portion can be used as the auxiliary capacitor. Therefore, there is no need to provide a storage capacitor as in the related art.

Further, the insulating film layer 32 and the ITO film layer 31 are both transparent, so that the aperture ratio of the liquid crystal display device is not reduced, and the portion where the storage capacitor has been conventionally can be used as the aperture. Thus, the aperture ratio of the liquid crystal display device can be greatly improved. In addition, the ITO film layer 31
Inverter board 35 for driving backlight 28
Connected to the ground GND side of the
Since the ITO film layer 31 is disposed between the backlight 28 and a substantial liquid crystal module including the TFT 13 and the liquid crystal 22 layer on the glass substrate 30, the ITO film layer 31 functions as a shield of the liquid crystal module against noise of the backlight 28.

Since the ITO film layer 31 is formed on the glass substrate 30 as described above, the ITO film layer 3
If the ITO film layer 1 does not interfere with the thin mounting of the liquid crystal display device and the ITO film layer 31 is formed to have a uniform thickness on the entire surface of the glass substrate 30, display unevenness can be obtained. And the like can be prevented.

In the above example, basically, the IT
Although the O film layer 31 is formed on the entire surface of the glass substrate 30, for example, the O film layer 31 may be formed for each pixel 10 or may be provided for each portion corresponding to the display electrode 15 of each pixel. . In this case, since a large number of ITO film layers 31 are formed, it is necessary to connect each ITO film layer 31 to the ground GND by a wiring formed on the glass substrate 30.

[0026]

According to the liquid crystal display device of the first aspect of the present invention, at least one of the electrode of the active element and the display electrode and the transparent electrode layer are arranged to face each other. The charge can be retained, and this portion can be used as an auxiliary capacitor instead of the conventional storage capacitor. Since this portion is transparent, the area of the portion through which light can be transmitted on the substrate is not reduced, and the aperture ratio can be improved by the amount of the conventional storage capacitor.

According to the liquid crystal display device of the second aspect of the present invention, the transparent electrode layer provided on the glass substrate is
An active element, a display electrode, a substantial liquid crystal display unit composed of liquid crystal, and the backlight unit are arranged over the entire surface, and the transparent electrode layer is connected to the ground of the inverter circuit and grounded.
The transparent electrode layer can effectively act as a shield against the fluorescence noise of the backlight unit. In addition, since the shield is formed on the substrate, the shield made of the transparent electrode layer does not hinder thin mounting of the liquid crystal display device. In addition, by forming a transparent electrode layer with a uniform thickness on a glass substrate,
It is possible to prevent display unevenness or the like from occurring.

[Brief description of the drawings]

FIG. 1 shows T of one pixel of a lower substrate of a liquid crystal display device of the present invention.
It is sectional drawing which shows FT part and a backlight.

FIG. 2 is a circuit diagram showing an equivalent circuit corresponding to one pixel of the liquid crystal display device of the present invention.

FIG. 3 is a plan view showing one pixel of a lower substrate of the liquid crystal display device of the present invention.

FIG. 4 is a block diagram illustrating a schematic configuration of one pixel of a conventional liquid crystal display device.

FIG. 5 is a plan view showing a lower substrate of a conventional liquid crystal display device.

FIG. 6 is a circuit diagram showing an equivalent circuit corresponding to one pixel of a conventional liquid crystal display device.

FIG. 7 is a schematic sectional view showing a relationship between a liquid crystal module and a backlight of a conventional liquid crystal display device.

[Explanation of symbols]

 Reference Signs List 10 pixel 13 TFT (active element) 15 display electrode 28 backlight (fluorescent tube) 30 glass substrate (substrate) 31 ITO film layer (transparent electrode layer) 32 insulating film layer 35 inverter substrate (inverter circuit)

Claims (2)

[Claims] 1. An active matrix type liquid crystal display device having an active element for each pixel and a display electrode connected to the active element on a substrate, wherein the active element and the display electrode are provided on the substrate. A liquid crystal display device, wherein a transparent electrode layer is provided via a transparent insulating layer therebetween, and the transparent electrode layer is grounded. 2. The method according to claim 1, wherein the transparent electrode layer is provided over substantially the entire surface of the substrate, and the transparent electrode layer is grounded by being connected to a ground of an inverter circuit for driving a fluorescent tube of a backlight unit. The liquid crystal display device according to claim 1, wherein: