JPH0618923A - Liquid crystal display - Google Patents

Abstract

PURPOSE:To unnecessitate a hole pierced in an insulating film for connecting the gate electrode of TFT for compensation to a picture element electrode in a liq. crystal display device with the TFT, to prevent producing processes from being made complex and to reduce the cost of production. CONSTITUTION:Since the gate electrode 28 of TFT 26 for compensation formed under a picture element electrode 14 made of ITO extends to a position under the picture element electrode 14, part of the gate electrode 28 overlaps the periphery of the picture element electrode 14 as an electrode 34 for capacity coupling through an insulating film 12 and forms capacity C1 between them. Therefore the compensation controlling electrode 32 of the TFT 26 connects with picture element capacity CLC through capacity CGS-C and the capacity C1.

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 a thin film transistor (TFT).
The present invention relates to an active matrix drive liquid crystal display device using. Active matrix drive liquid crystal display devices using TFTs have already been put to practical use in small televisions and the like, and further demand is expected as displays for large televisions and personal computers. Since this active matrix drive liquid crystal display device has a large area, cost reduction is required by simplifying the process.

[0002]

2. Description of the Related Art In a conventional active matrix drive liquid crystal display device, a TFT is normally turned off after an address for writing a voltage to a pixel is finished, but at this time, a voltage shift due to a parasitic capacitance of the TFT occurs. Occurs. This is called a DC (direct current voltage) level shift.

This DC level shift has a drawback that the afterimage phenomenon becomes large, and especially in the case of a still image, a burn-in phenomenon occurs and the display quality is deteriorated. Therefore, in order to cancel this DC level shift and eliminate the voltage shift, a structure has been devised in which a compensation TFT is provided in addition to a normal address TFT.

An active matrix drive liquid crystal display device provided with a compensation TFT will be described below with reference to FIGS. 4 and 5. 4A is a plan view showing a part of the active matrix drive liquid crystal display device, FIG. 4B is a sectional view taken along the line AA, FIG. 5A is its equivalent circuit diagram, and FIG. FIG. 6 is a diagram for explaining the operation.

An ITO pixel electrode 54 made of an ITO (Indium Tin Oxide) layer is formed on a transparent insulating substrate 50 with an insulating film 52 interposed therebetween. On the upper side of the ITO pixel electrode 54, an address T
An FT 56 is provided. This address TFT 56
Is a gate electrode 58 formed on the transparent insulating substrate 50.
And an a-Si (amorphous silicon) semiconductor layer 60 formed on the gate electrode 58 via the insulating film 52.
And a source electrode 62 connecting the a-Si semiconductor layer 60 and the ITO pixel electrode 54, and a drain electrode 64 provided facing the source electrode 62 and connected to the a-Si semiconductor layer 60. ing. The source electrode 62 and the drain electrode 64 are composed of a Ti / n + layer in which an n + type a-Si layer and a Ti (titanium) layer are laminated.

Below the pixel electrode 54, a compensation T
FT66 is provided. This compensation TFT 66 is
A gate electrode 68 formed on the transparent insulating substrate 50,
It is composed of an a-Si semiconductor layer 70 formed on the gate electrode 68 via an insulating film 52, and a compensation control electrode 72 connected to the a-Si semiconductor layer 70. The gate electrode 68 of the compensation TFT 66 is the wiring layer 7
4 to the ITO pixel electrode 54.
Note that the compensation control electrode 72 and the wiring layer 74 are also n + type aS
It is composed of a Ti / n + layer in which an i layer and a Ti layer are laminated.

The above structure is represented by an equivalent circuit as shown in FIG.
As shown in (a), the gate electrode 58 of the address TFT 56 is connected to the pixel capacitance C _LC of the ITO pixel electrode 54 via the capacitance C _GS-A, and the compensation control electrode 72 of the compensation TFT 66 is also Pixel capacity C _LC via capacity C _GS-C
It is connected to the. And the parasitic capacitance of the TFT has a dependency on the magnitude of the gate voltage, smoothly the polarity of the capacitor C _GS-C of the capacitance C _{GS -A} and compensation TFT66 address for TFT56 conversely The connection between the address TFT and the compensation TFT is reversed so that the cancellation can be performed.

Therefore, the address TFT 56 and the compensation T
The polarity of the pulse added to the FT 66 is reversed and the gate of the address TFT 56 is not selected.
The compensation voltage V _C added to the compensation TFT 66 is not applied to a, and the compensation voltage V _C having the opposite polarity to the gate voltage V _G of the address TFT 56 is applied during the DC level shift compensation operation period Tb. This makes it possible to compensate for the variation in the potential of the ITO pixel electrode 54 that occurs when the gate selection of the address TFT 56 is completed.

[0009]

However, in the active matrix drive liquid crystal display device provided with the compensation TFT 66 shown in FIGS. 4 and 5, the gate electrode 68 and the ITO pixel formed on the transparent insulating substrate 50 are used. When connecting the wiring layer 74 connected to the electrode 54,
As shown in the Q portion of FIG. 4A and its sectional view 4B, the insulating film 52 between the gate electrode 68 and the wiring layer 74 is perforated, and the insulating film perforated portion 76 is used to form a hole. I'm connecting.

The step of drilling the insulating film 52 is carried out by the usual T
It does not exist in the standard process of FT, and is a process required only for connecting the gate electrode 68 of the compensation TFT 66 and the wiring layer 74. Therefore, in the active matrix drive liquid crystal display device provided with the compensating TFT 66, there is a problem in that the process is complicated due to the perforating step and the manufacturing cost is increased accordingly.

Therefore, the present invention does not require an insulating film hole for connecting the gate electrode of the compensation TFT and the pixel electrode in the liquid crystal display device provided with the compensation TFT, thus complicating the manufacturing process. An object of the present invention is to provide a liquid crystal display device capable of preventing the above and reducing the manufacturing cost.

[0012]

Means for Solving the Problems The above-mentioned problems are solved by first and second substrates which are arranged to face each other with a liquid crystal interposed therebetween, a pixel electrode provided on the first substrate, and a predetermined voltage applied to the pixel electrode. An address thin film transistor for writing a voltage, a compensating thin film transistor for compensating for a voltage variation of the pixel electrode that occurs at the end of voltage writing to the pixel electrode by the address thin film transistor, the pixel electrode provided on the second substrate, In a liquid crystal display device having a data bus line facing each other, a gate electrode of the compensation thin film transistor is connected to the pixel electrode via a capacitor,
The liquid crystal display device is characterized in that a compensating pulse is applied to a source electrode or a drain electrode of the compensating thin film transistor.

Further, in the above liquid crystal display device, a part of a gate electrode of the compensation thin film transistor is formed as a capacitive coupling electrode so as to overlap with a peripheral portion of the pixel electrode via an insulating film. And a liquid crystal display device. In the above liquid crystal display device, the gate electrode of the compensation thin film transistor,
A liquid crystal display device, which is made of an opaque material, wherein a part of the gate electrode is formed as a capacitive coupling electrode so as to overlap with the entire peripheral portion of the pixel electrode via an insulating film. .

In the above liquid crystal display device, the gate electrode, which overlaps the entire peripheral portion of the pixel electrode as a capacitive coupling electrode, interposes a liquid crystal and a black matrix provided on the second substrate. It is achieved by a liquid crystal display device characterized by being overlapping.

[0015]

According to the present invention, the gate electrode of the compensation thin film transistor is formed so as to overlap the peripheral portion of the pixel electrode and is connected to the pixel electrode in an alternating current manner through a capacitor.
In addition to effectively exhibiting the function of compensating for the DC level shift when the gate pulse to the pixel electrode of the address TFT is turned off, a hole is formed in the insulating film to connect the gate electrode of the compensation TFT and the pixel electrode. Since the step of opening is not required, the manufacturing process can be prevented from becoming complicated and the manufacturing cost can be reduced.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A concrete description will be given below based on the illustrated embodiments. 1A is a plan view showing a part of an active matrix drive liquid crystal display device according to a first embodiment of the present invention, FIG. 1B is a sectional view taken along the line AA, and FIG. FIG. 2 is a sectional view taken along line BB, and FIG. 2 is an equivalent circuit diagram thereof.

ITO, which is a transparent ITO layer, is formed on a transparent insulating substrate 10 made of glass or the like with an insulating film 12 interposed therebetween.
The pixel electrode 14 is formed. This ITO pixel electrode 1
An address TFT 16 is provided on the upper side of 4. The address TFT 16 is a transparent insulating substrate 10.
The gate electrode 18 formed on the gate electrode 18 and the gate electrode 18
A-Si semiconductor layer 2 formed on top of the insulating film 12
0, the a-Si semiconductor layer 20 and the ITO pixel electrode 14
Source electrode 22 consisting of a Ti / n + layer connecting to
And a-Si provided opposite to the source electrode 22.
The drain electrode 24 is composed of a Ti / n + layer connected to the semiconductor layer 20.

A compensation TFT 26 is provided below the ITO pixel electrode 14. This compensation TFT 2
6 is a gate electrode 2 formed on the transparent insulating substrate 10.
8, an a-Si semiconductor layer 30 formed on the gate electrode 28 via the insulating film 12, and a compensation control electrode 32 composed of a Ti / n + layer connected to the a-Si semiconductor layer 30. It consists of

Here, the gate electrode 2 of the compensation TFT 26
8 extends below the ITO pixel electrode 14,
As shown in part (a) of FIG. 1 and part (c) of FIG. 1, a part of the gate electrode 28 serves as the electrode 34 for capacitive coupling.
This embodiment is characterized in that it overlaps with the peripheral portion of the O pixel electrode 14 via the insulating film 12 and forms the capacitance C1 between them. That is, a part of the gate electrode 28 is shared with one capacitive coupling electrode 34 of the capacitance C1.

Therefore, as shown in the equivalent circuit of FIG. 2, the gate electrode 18 of the address TFT 16 is connected to the pixel capacitance C _LC of the ITO pixel electrode 14 via the capacitance C _GS-A , and the compensation TFT 26 is The compensation control electrode 32 is also connected to the pixel capacitance C _LC via the capacitance C _GS-C and the capacitance C 1. Thus, according to this embodiment, the compensation T
A part of the gate electrode 28 of the FT 26 is a capacitive coupling electrode 34.
Since the capacitance C1 is formed by overlapping with the peripheral portion of the ITO pixel electrode 14, the compensation control electrode 32 is also connected to the pixel capacitance C _LC via the capacitance C _GS-C and the capacitance C1. In addition, the function of compensating for the DC level shift can be retained.

Further, the gate electrode 28 of the compensation TFT 26
Since the ITO pixel electrode 14 and the ITO pixel electrode 14 are AC-connected by capacitive coupling through the capacitor C1, the step of opening a hole in the insulating film 12 is not required, and therefore the manufacturing process is prevented from being complicated and the manufacturing process is prevented. The cost can be reduced.
Next, an active matrix drive liquid crystal display device according to a second embodiment of the present invention will be described with reference to FIG.

FIG. 3A is a plan view showing an active matrix drive liquid crystal display device according to the second embodiment.
(B) is the AA sectional view taken on the line. The same components as those of the active matrix drive liquid crystal display device shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. The present embodiment has substantially the same configuration as that of the first embodiment shown in FIG. 1, except that the gate electrode 28 of the compensation TFT 26 provided below the ITO pixel electrode 14 is below the ITO pixel electrode 14. To the IT as the capacitive coupling electrode 36.
It is characterized in that it overlaps with the entire peripheral portion of the O pixel electrode 14 via the insulating film 12 and forms a capacitance C2 between them.

That is, unlike the first embodiment, the capacitive coupling electrode 36 is arranged so as to surround the entire periphery of the ITO pixel electrode 14. The inside of the capacitive coupling electrode 36 extends inward of the ITO pixel electrode 14 by a distance a, and the capacitance C2 is formed by the overlap of both electrodes at this portion. In addition, the transparent insulating substrate 1
On the insulating film 12 and the ITO pixel electrode 14 formed on the transparent substrate 0, a transparent insulating counter substrate 40 made of glass or the like is arranged with a liquid crystal 38 interposed. A black matrix 42 for shielding light is formed on the liquid crystal 38 side of the counter substrate 40. The present embodiment is also characterized in that the end of the black matrix 42 provided on the counter substrate 40 is designed to be located near the center of the width 2b of the capacitive coupling electrode 36. Here, b is the positioning accuracy when the counter substrate 40 is bonded.

In this manner, the capacitive coupling electrode 36 overlapping the entire peripheral portion of the ITO pixel electrode 14 overlaps the black matrix 42 provided on the counter substrate 40, thereby forming a two-layer black matrix. And as shown by the arrow in the figure,
Light will pass only in a region where neither the black matrix 42 of the counter substrate 40 nor the capacitive coupling electrode 36 of the transparent insulating substrate 10 exists.

Normally, since the black matrix is present only on the counter substrate side, the alignment with the pixel electrode is a pattern alignment between different substrates. Therefore, the alignment accuracy is poor, and the light transmitting area is sufficient. There was a problem that I could not get it big. That is, in the case of the black matrix only on the counter substrate side, the above positioning accuracy b has to be taken as a positioning margin for the pixel electrode, which causes a problem that the aperture ratio is lowered.

In this embodiment, the alignment margin a is determined by the alignment accuracy of the capacitive coupling electrode 36 and the ITO pixel electrode 14, and both electrodes are formed on the same transparent insulating substrate 10. Therefore, the accuracy is significantly improved as compared with the conventional case where the different substrates are aligned with each other. Therefore, the distance a can be smaller than the alignment margin b when the black matrix is used only on the counter substrate side, and a large aperture ratio can be obtained.

As described above, according to this embodiment, the compensation TF is used.
Since a part of the gate electrode 28 of T26 overlaps the entire peripheral portion of the ITO pixel electrode 14 as the capacitive coupling electrode 36 to form the capacitance C2, the same effect as that of the first embodiment can be obtained. At the same time, since the capacitive coupling electrode 36 overlaps the black matrix 42 provided on the counter substrate 40 to form a two-layer black matrix, it is possible to reduce the alignment margin, thus reducing the aperture ratio. Can be prevented.

In the above first and second embodiments, the case of the TFT having the inverted stagger structure has been described, but the present invention can be applied to other structures such as the TFT having the stagger structure or the planar structure. You can

[0029]

As described above, according to the present invention, in a liquid crystal display device provided with a compensating TFT for compensating a DC level shift that adversely affects image display, a part of the gate electrode of the compensating thin film transistor is provided. Is formed as a capacitive coupling electrode so as to overlap with the peripheral portion of the pixel electrode, the gate electrode and the pixel electrode are AC-connected by capacitive coupling. It is unnecessary, and thus the manufacturing process can be prevented from being complicated and the manufacturing cost can be reduced.

Further, since the capacitive coupling electrode which overlaps with the entire peripheral portion of the pixel electrode to form the capacitance simultaneously overlaps with the black matrix provided on the counter substrate, a two-layer black matrix structure is formed. For,
It is possible to reduce the alignment margin and thus prevent the aperture ratio from decreasing.

[Brief description of drawings]

FIG. 1 is a plan view and a sectional view showing an active matrix drive liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the active matrix drive liquid crystal display device shown in FIG.

FIG. 3 is a plan view and a sectional view showing an active matrix drive liquid crystal display device according to a second embodiment of the present invention.

FIG. 4 is a plan view and a cross-sectional view showing a conventional active matrix drive liquid crystal display device.

5 is an equivalent circuit diagram of the active matrix drive liquid crystal display device shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Transparent insulating substrate 12 ... Insulating film 14 ... ITO pixel electrode 16 ... Address TFT 18 ... Gate electrode 20 ... a-Si semiconductor layer 22 ... Source electrode 24 ... Drain electrode 26 ... Compensation TFT 28 ... Gate electrode 30 ... a-Si semiconductor layer 32 ... Compensation control electrode 34 ... Capacitive coupling electrode 36 ... Capacitive coupling electrode 38 ... Liquid crystal 40 ... Counter substrate 42 ... Black matrix 50 ... Transparent insulating substrate 52 ... Insulating film 54 ... ITO pixel electrode 56 ... Address TFT 58 ... Gate electrode 60 ... a-Si semiconductor layer 62 ... Source electrode 64 ... Drain electrode 66 ... Compensation TFT 68 ... Gate electrode 70 ... a-Si semiconductor layer 72 ... Compensation control electrode 74 ... Wiring layer 76 ... Insulation Membrane drilling part

Claims (4)

[Claims] 1. A first substrate and a second substrate which are opposed to each other with a liquid crystal interposed therebetween, and a pixel electrode provided on the first substrate,
An address thin film transistor for writing a predetermined voltage to the pixel electrode, a compensating thin film transistor for compensating for a voltage variation of the pixel electrode that occurs when the address thin film transistor finishes writing a voltage to the pixel electrode, and the second substrate In the liquid crystal display device having a data bus line facing the pixel electrode, the gate electrode of the compensation thin film transistor is connected to the pixel electrode through a capacitor, and the source electrode or the drain electrode of the compensation thin film transistor is connected to the pixel electrode. A liquid crystal display device, wherein a compensation pulse is applied. 2. The liquid crystal display device according to claim 1, wherein a part of a gate electrode of the compensation thin film transistor is formed as a capacitive coupling electrode so as to overlap with a peripheral portion of the pixel electrode via an insulating film. A liquid crystal display device characterized by the above. 3. The liquid crystal display device according to claim 2, wherein a gate electrode of the compensation thin film transistor is made of an opaque material, and a part of the gate electrode serves as a capacitive coupling electrode in the entire peripheral portion of the pixel electrode. And a liquid crystal display device, which are formed to overlap with each other with an insulating film interposed therebetween. 4. The liquid crystal display device according to claim 3, wherein the gate electrode that overlaps with the entire peripheral portion of the pixel electrode as a capacitive coupling electrode includes a black matrix and a liquid crystal provided on the second substrate. A liquid crystal display device characterized in that they are overlapped with each other.