JPH10111519A - Active matrix type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active matrix type liquid crystal display device which is capable of shielding light incident on a thin film transistor without forming a black matrix and also is capable of enhancing an opening ratio of pixel and is excellent in a display grade. SOLUTION: In an active matrix type liquid crystal display device displaying characters and graphics or the like by partially orienting liquid crystal L while sealing the liquid crystal L in between the upper glass substrate 10B and the lower glass substrate 10A being confronted with each other, the electrode of the drain 2B of the thin film transistor 2 driving a pixel electrode 1 is formed by providing a prescribed overlapping with the gate 2C of the transistor 2 so as cover the whole of the drain and also to exist along the gate 2C are respectively film. Thus, the channel and the drain 2B of the thin film transistor 2 are respectively shielded from a light by the gate 2C and the electrode of the drain 2B to prevent the generating of a photoelectric current (leakage current).

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 using thin film transistors.

[0002]

2. Description of the Related Art In recent years, with the rapid spread of portable information devices such as notebook type personal computers, the demand for flat displays with excellent space saving and low power consumption is increasing. A liquid crystal display device is known as the surface display. In particular, an active matrix type liquid crystal display device using a thin film transistor has been attracting attention as having extremely high display quality.

In general, in an active matrix type liquid crystal display device, an electric field is applied to liquid crystal sealed between an upper glass substrate and a lower glass substrate to locally align the liquid crystal, thereby irradiating the liquid crystal from the lower glass substrate side. It controls the transmission of backlight light and displays characters and figures. On one side of the lower glass substrate facing the upper glass substrate, a local electric field is applied to the liquid crystal corresponding to the pixels. Of pixel electrodes are formed in a matrix integrally with the thin film transistors. The thin film transistor connected to each pixel electrode is selectively controlled to conduct, and applies a drive voltage for aligning the liquid crystal according to the display content to each pixel electrode.

A conventional active matrix type liquid crystal display device will be described with reference to FIGS.
Here, FIG. 3 is an enlarged view of a unit pixel of a conventional active matrix type liquid crystal display device, and FIG.
It is sectional drawing. As shown in FIG. 3, the unit pixel of the active matrix type liquid crystal display device includes a pixel electrode 1 for aligning liquid crystal, and a thin film transistor 2 including a source 2A, a drain 2B, and a gate 2C. , The drain 2B is electrically connected to the pixel electrode 1 via the drain electrode 2b, and the source 2a of the thin film transistor 2 is connected to the data signal line 3 laid in the vertical direction. The gate 2C is formed by extending a part of the scanning signal line 4 above the channel of the thin film transistor 2, and the scanning signal line 4 and the data signal line 3 are electrically insulated from each other and cross each other. Are arranged in a grid pattern.

As shown in FIG. 4, the source 2A and the drain 2B of the thin film transistor 2 are formed with a channel forming region in a semiconductor thin film layer such as polycrystalline silicon or amorphous silicon deposited on one surface of a lower glass substrate 10A. Formed by selectively doping impurities with P interposed therebetween,
Above the channel forming region P, a gate 2C (scanning signal line 4) for guiding a channel between the source 2A and the drain 2B via an insulating film 5 to control conduction is formed by a first wiring layer of aluminum or the like. Is formed.

On the first wiring layer (gate 2C), a second insulating layer 6 made of aluminum or the like is also interposed with an intermediate insulating film 6 interposed therebetween.
The source electrode 2a and the drain electrode 2b formed by the wiring layer are formed, and the source electrode 2a and the drain electrode 2b are electrically connected to the source 2A and the drain 2B through the contact holes CH, respectively. Then, the pixel electrode 1 includes the drain electrode 2 b and the intermediate insulating film 6.
And is electrically connected to the drain electrode 2b. Note that the second wiring layer forming the source electrode 2a is also used for forming the data signal line 3, and the source electrode 2a
a and the data signal line 3 are integrally formed.

Further, a liquid crystal L is sealed between the lower glass substrate 10A on which the thin film transistor 2 and the pixel electrode 1 are formed and the upper glass substrate 10B.
The alignment state is determined by the electric field between the pixel electrode 1 formed on the lower glass substrate 10A side and the transparent electrode (not shown) formed on the upper glass substrate 10B side. Note that, as described later, a black matrix BM is formed on the upper glass substrate 10B to cut off backlight light that is transmitted (leaked) outside the region whose orientation is controlled.

When displaying characters, figures, and the like on the liquid crystal display device configured as described above, the conduction of the thin film transistor 2 connected to the data signal line 3 is controlled in a time division manner, and the display is performed via the thin film transistor 2. A drive voltage according to the content is applied to the pixel electrode 1. The thin film transistor 2 is turned off after a driving voltage is applied to the pixel electrode 1, and the driving voltage applied to the pixel electrode 1 is generated between the pixel electrode 1 and a transparent electrode (not shown) of the upper glass substrate 10B. It is held by the capacitance component. The orientation of the liquid crystal sealed between the lower glass substrate 10A and the upper glass substrate 10B is as follows.
It is determined by the drive voltage held in this dose component.

Here, a characteristic required for the thin film transistor 2 is that it has a large on-current that can supply a sufficient drive voltage to the pixel electrode 1 during a short conduction time of about several μs to several tens μs. In addition, in a holding period (normally, 16.7 msec) after a driving voltage is applied to the pixel electrode 1 to make the pixel electrode 1 non-conductive, a variation in the driving voltage held in the pixel electrode 1 is so small as to be negligible. It is necessary to have a high ratio of on-current to off-current (on-current / off-current).

[0010]

By the way, when light enters the thin film transistor 2 from the outside, carriers are excited inside the thin film transistor 2 to generate a photocurrent, so that the off current of the thin film transistor 2 increases. . As a result, the driving voltage held by the pixel electrode 1 fluctuates, and the alignment state of the liquid crystal is disturbed, and a display failure occurs. In order to prevent this, as shown in FIGS. 3 and 4, there is a method of forming a black matrix BM at a position facing the upper glass substrate 10B so as to cover the upper part of the thin film transistor 2. The black matrix B shown in FIG.
M is a region where the outside (hatched region) of the region surrounded by the broken line is shielded from light.

That is, in FIGS. 3 and 4, one surface of the upper glass substrate 10B facing the lower glass substrate 10A covers an outer edge region of the pixel electrode 1 and a region facing the periphery thereof (including the thin film transistor 2). Thus, the black matrix BM is formed. The black matrix BM not only functions to block external light incident on the thin film transistor 2 from the upper glass substrate 10B side, but also outside the region where the alignment is controlled (the pixel electrode 1 and the scanning signal line 4 / data signal line 4). 3), which cuts light from a backlight (not shown) that passes through (leaks out) and improves display characteristics.

However, according to the conventional active matrix type liquid crystal display device, the black matrix BM
In consideration of the displacement when the upper glass substrate 10B on which the thin film transistor 2 is formed and the lower glass substrate on which the thin film transistor 2 is formed, and the effect of light incident on the thin film transistor 2 from an oblique direction, the black matrix BM It must be formed larger than the size. As a result, while the area of the black matrix BM increases, the ratio of the opening area of the pixel that transmits the backlight (hereinafter, referred to as “opening ratio”) decreases, and the display characteristics deteriorate.

As a method of suppressing the decrease of the aperture ratio,
Forming an insulating film between the data signal line 3 and the pixel electrode 1;
A method has been proposed in which the pixel electrode 1 is overlapped with the scanning signal line 5 or the data signal line 4 via the insulating film so that the scanning signal line or the data signal line plays the role of the black matrix BM. However, even in this method, in order to block light incident on the thin film transistor 2, a black matrix for covering the thin film transistor 2 must be partially formed, and similarly, the aperture ratio of the pixel is reduced.

Further, as a method of blocking light incident on the thin film transistor, a method of covering the channel region with a non-transparent source electrode has been proposed (Japanese Patent Publication No. 5-3483).
No. 6). However, even with this method, it is necessary to similarly provide a black matrix in order to effectively block light incident from oblique directions. In addition, according to this method, since the source electrode greatly overlaps the gate electrode, the parasitic capacitance between the gate and the source increases, and crosstalk occurs between the gate and the source of the thin film transistor via the parasitic capacitance. As a result, the signal distortion increases. As a result, the driving voltage applied to the pixel electrode fluctuates, and the display quality deteriorates.

The present invention has been made in view of such a problem, and it is possible to effectively block incident light to a thin film transistor without forming a black matrix and to improve the aperture ratio of a pixel. It is an object of the present invention to provide an active matrix liquid crystal display device which is capable of providing excellent display quality.

[0016]

Means for Solving the Problems The present invention has the following arrangement to achieve the above object. That is, claim 1
The active matrix type liquid crystal display device according to the invention described in (1), an active matrix liquid crystal is sealed between the upper glass substrate and the lower glass substrate facing each other, and the liquid crystal is locally oriented to display characters, graphics, and the like. A liquid crystal display device, wherein a scanning signal line and a data signal line laid in a grid pattern so as to intersect with each other on one surface side of the lower glass substrate, and at an intersection of the scanning signal line and the data signal line. Pixel electrodes, which are formed in a matrix on one surface side, are electrically connected to the data signal lines and the pixel electrodes, respectively, and the gates are electrically connected to the scanning signal lines. And a non-light-transmitting drain electrode connected to the drain. A structure of an active matrix type liquid crystal display device, wherein said active matrix type liquid crystal display device is formed so as to cover said entire drain and to extend above said gate via an insulating layer with a predetermined overlap between said gate and said gate. Having.

In the active matrix type liquid crystal display device according to the second aspect of the present invention, the gate is made of a non-light-transmitting conductive member. It has a configuration of a liquid crystal display device.

Further, in the active matrix type liquid crystal display device according to the third aspect of the present invention, the thin film transistor has a non-transparent source electrode electrically connected to the source, and the source electrode is the entire source. 3. The active matrix type liquid crystal display device according to claim 2, wherein a predetermined overlap is formed between the gate and the gate so as to extend over the gate via the insulating layer. Having a configuration.

Further, in the active matrix type liquid crystal display device according to the present invention, the scanning signal lines and the data signal lines are formed of a non-transmissive conductive member,
4. The active matrix type liquid crystal display device according to claim 1, wherein the active matrix type liquid crystal display device is formed by providing a predetermined overlap between the pixel electrode and the pixel electrode via an insulating layer.

Further, in the active matrix type liquid crystal display device according to the present invention, the source electrode and the drain electrode are formed using the same wiring layer as the data signal line. Item 5 has a configuration of the active matrix type liquid crystal display device according to any one of Items 1 to 4.

The active matrix type liquid crystal display device according to any one of the first to fifth aspects operates as follows. That is, according to the active matrix type liquid crystal display device of the first aspect, the drain electrode of the thin film transistor covers the entire drain including the boundary between the drain and the channel. Accordingly, the entire drain of the thin film transistor and a part of the channel near the drain are shielded, and the generation of current leaking from the drain (pixel electrode) due to the photocurrent is prevented, and the voltage of the pixel electrode is stabilized.

According to a second aspect of the present invention, in the active matrix type liquid crystal display device according to the first aspect, the channel is shielded by a gate made of a non-translucent member. In addition, generation of current leaking from the channel due to photocurrent is prevented.

Further, according to a third aspect of the present invention, there is provided an active matrix type liquid crystal display device according to the second aspect, wherein the source electrode includes a boundary between the source and the channel. Cover the whole. Therefore, the entire source and drain and the entire channel of the thin film transistor are shielded from light, and the generation of current leaking from the source and drain (pixel electrode) and the channel due to the photocurrent is prevented.

According to a fourth aspect of the present invention, there is provided an active matrix type liquid crystal display device according to any one of the first to third aspects, wherein a scanning signal line and a pixel electrode are connected to each other. Since an overlap is provided between the data signal lines and the pixel electrode via an insulating layer, the space between these is covered with any one of the scanning signal line, the data signal line and the pixel electrode, Leaks are prevented.

According to a fifth aspect of the present invention, there is provided an active matrix type liquid crystal display device according to any one of the first to fourth aspects, wherein a source electrode and a drain constituting a thin film transistor are provided. The electrodes are formed of the same wiring layer as the data signal lines, and the gates are formed of the same wiring layer as the scanning signal lines. That is, the source electrode, the drain electrode, and the gate constitute a data signal line and a scanning signal line, respectively.
It is formed using only different types of wiring layers.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An active matrix type liquid crystal display device according to an embodiment of the present invention will be described with reference to FIGS. Here, FIG. 1 is an enlarged view of a unit pixel of the liquid crystal display device according to the embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AA. In each of the drawings, the same or corresponding elements have the same reference characters allotted.

The apparatus of the present embodiment shown in FIG.
The main difference from the conventional device shown in FIG. 5 is that the source electrode 2a (a part of the data signal line 3A) and the drain electrode 2b of the thin film transistor 2 included in the device of the present embodiment are connected via an intermediate insulating layer 6 described later. There are two points: a point formed by providing a predetermined overlap so as to extend over the gate, and a point formed by providing the data signal line 3A and the scanning signal line 4A so as to overlap the pixel electrode 1. Accordingly, it is possible to prevent light from entering the thin film transistor without requiring a black matrix and to prevent transmission (leakage) of backlight from around the pixel electrode.

That is, as shown in FIG. 2 in detail, the source electrode 2a and the drain electrode 2b connected to the source 2A and the drain 2B of the thin film transistor 2 provided in the device of the present embodiment through the contact holes CH, respectively, are shown in FIG. , And an overlap d is provided on the gate 2C with the intermediate insulating layer 6 interposed therebetween. Also, the data signal line 3A
The (source electrode 2a) is formed so as to overlap with the pixel electrode 1 with the second intermediate insulating film 6B interposed therebetween and to be provided with D1.
A (gate 2C) is formed so as to overlap D2 with the pixel electrode 1 with the intermediate insulating layer 6 and the second intermediate insulating layer 6B interposed therebetween.

Hereinafter, the manufacturing process of the apparatus according to the present embodiment will be described with reference to an example in which a two-layer metal process is used.
This will be described with reference to FIG. First, the lower glass substrate 1
After a semiconductor thin film S such as polycrystalline silicon or amorphous silicon is formed on 0A, an impurity as a donor or an acceptor is selectively doped to form a source 2A and a drain 3A with a channel forming region P interposed therebetween. Next, an insulating film 5 is formed, and the scanning signal line 4A shown in FIG. 1 is formed using a first wiring layer such as aluminum. At this time, a part of the scanning signal line 4A is extended above the channel formation region P with the insulating film 5 interposed therebetween as the gate electrode 2C.

Next, an intermediate insulating layer 6 is formed on the first wiring layer (gate 2C, scanning signal line 4A),
After a contact hole CH is formed so as to penetrate the insulating film 5 and the intermediate insulating layer 6 above the A and the drain 2B, the source electrode 2a (the data signal line 3A) and the drain electrode 2b are connected to the second wiring layer. It is formed by using. The source electrode 2a and the drain electrode 2b are electrically connected to a source region and a drain region through a contact hole CH, respectively. Here, the first wiring layer forming the gate 2C and the scanning signal line 4A, and the second wiring layer forming the drain electrode 2b, the source electrode 2a and the data signal line 3A are made of a non-translucent conductive member. Become.

As shown in FIGS. 1 and 2, each of the source electrode 2a and the drain electrode 2b covers the entire source region 2A and the drain region 2B, and is connected to the gate 2C via the intermediate insulating layer 6. Are formed with an overlap d between them. The overlap d forms a parasitic capacitance between the gate electrode 2C and the source electrode 2a / drain electrode 2b, and promotes crosstalk between these electrodes. For this reason, the amount of the overlap d needs to be minimized, and is set to be as small as possible as long as the alignment accuracy of the process allows.

Note that, as shown in FIG.
When forming the A (second wiring layer) and the scanning signal line 4A (first wiring layer), the data signal line 3A is formed so as to overlap the pixel electrode 1 with the second intermediate insulating layer 6B interposed therebetween, and to provide D1. By forming the scanning signal line 4A so as to overlap with the pixel electrode 1 with the intermediate insulating layer 6 and the second intermediate insulating layer 6B interposed therebetween and to form the scanning signal line 4A, the peripheral region and the periphery of the pixel electrode 1 are non-transparent first and Cover with the second wiring layer. Accordingly, light transmitted (leaked) outside the region of the pixel electrode 1 is blocked without providing a black matrix.

Next, a second intermediate insulating layer 6B is formed on the second wiring layer.
And a second electrode is formed so as to be located on the drain electrode 2b.
A contact hole CH2 is formed, a pixel electrode 1 is formed on the second intermediate insulating layer 6B, and the pixel electrode 1 is electrically connected to the drain electrode through the second contact hole. As described above, the outer edge and the periphery (including the thin film transistor 2) of the pixel electrode 1 are covered with the first and second wiring layers,
A lower glass substrate 10A having the scanning signal line 4A, the data signal line 3A, the pixel electrode 1, and the thin film transistor 2 formed on one surface thereof is obtained.

The lower glass substrate 1 thus obtained
0A and an upper glass substrate 10B on which a transparent electrode (not shown) is formed in advance, and a liquid crystal L is sealed and bonded to complete the active matrix liquid crystal display device of the present embodiment. Note that no black matrix is formed on the upper glass substrate 10B in the present embodiment.

The device according to the present embodiment described above is configured so that the periphery of the pixel electrode including the thin film transistor 2 is covered with the first and second wiring layers, but only the thin film transistor 2 is connected to the first and second wiring layers. The backlight which is covered with a layer and equalized from the periphery of the pixel electrode 1 may be cut by a black matrix as in the related art. What is necessary is just to combine and configure as needed.

As shown in FIG. 2, the device according to the present embodiment is formed by forming a second intermediate insulating layer 6B between the pixel electrode 1 and the drain electrode 2b (second wiring layer). However, the process can be easily realized by the conventional process configuration shown in FIG. 4 and does not cause any complexity in the manufacturing process. Rather, the process can be simplified because a black matrix is not required. .

[0037]

As is apparent from the above description, according to the present invention, the following effects can be obtained. That is, according to the first aspect of the present invention, since the drain electrode is formed so as to cover the entire drain and a part of the channel of the thin film transistor to which the pixel electrode is connected, it is caused by light incident on the drain of the thin film transistor. The occurrence of a leak current can be prevented. For this reason, without being affected by light, it is possible to effectively prevent a change in the voltage held by the pixel electrode, and to stably maintain an extremely excellent display quality.

According to the second aspect of the present invention, in the first aspect of the present invention, since the gate of the thin film transistor is formed by using a non-transmissive conductive member, light incident on the channel can be reduced. It is also possible to prevent the occurrence of leakage current due to the above. For this reason, in addition to the effect obtained by the first aspect of the present invention, the fluctuation of the voltage held by the pixel electrode can be more effectively prevented, and excellent display quality can be maintained more stably. .

According to the third aspect of the present invention,
According to the second aspect of the present invention, since the source electrode is formed so as to cover the entire source of the thin film transistor, it is possible to prevent generation of a leak current due to light incident on the source. For this reason, in addition to the effect obtained by the second aspect of the invention, voltage fluctuation on the source side of the thin film transistor can be effectively prevented, and stable operation can be maintained.

Further, according to the invention described in claim 4,
In the invention according to any one of claims 1 to 3, the non-light-transmitting scanning signal line and the data signal line are formed so as to overlap with the pixel electrode. In addition to the effects obtained by the present invention, it is possible to block light that is going to be transmitted (leaked) in the outer edge region and the periphery of the pixel electrode without providing a black matrix, thereby simplifying a manufacturing process (process). .

According to a fifth aspect of the present invention, in the first aspect, the source electrode and the drain electrode are formed using the same wiring layer as the data signal line. Therefore, in addition to the effects obtained by the invention according to any one of claims 1 to 4, a source electrode and a drain electrode for blocking light incident on the thin film transistor are formed without increasing the number of wiring layers. be able to.

Therefore, according to the present invention, it is possible to effectively block incident light to a thin film transistor without forming a black matrix, to improve the aperture ratio of a pixel, and to increase the number of steps without increasing the number of steps. An active matrix liquid crystal display device having excellent display quality can be realized.

[Brief description of the drawings]

FIG. 1 is an enlarged view of a unit pixel of an active matrix liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA of the unit pixel of the active matrix type liquid crystal display device according to the embodiment of the present invention.

FIG. 3 is an enlarged view of a unit pixel of a conventional active matrix type liquid crystal display device.

FIG. 4 is a sectional view of a conventional active matrix type liquid crystal display device, taken along line BB.

[Explanation of symbols]

 Reference Signs List 1 pixel electrode 2 thin film transistor 2A source 2B drain 2C gate 2a source electrode 2b drain electrode 3,3A data signal line 4,4A scanning signal line 5 insulating film 6 intermediate insulating layer 6B second intermediate insulating layer 10A lower glass substrate 10B upper glass substrate BM Black matrix CH Contact hole CH2 Second contact hole L Liquid crystal P Channel formation region S Semiconductor thin film D1, D2, d Overlap

Claims (5)

[Claims] 1. An active matrix type liquid crystal display device in which liquid crystal is sealed between an upper glass substrate and a lower glass substrate facing each other, and the liquid crystal is locally oriented to display characters, graphics, and the like. A scanning signal line and a data signal line laid in a lattice pattern so as to intersect with each other on one surface side of the lower glass substrate; and a matrix shape on the one surface side in correspondence with an intersection of the scanning signal line and the data signal line. A pixel electrode, and a thin film transistor, the source and the drain of which are electrically connected to the data signal line and the pixel electrode, respectively, and the gate of which is electrically connected to the scanning signal line. The thin film transistor has a non-light-transmitting drain electrode connected to the drain, and the drain electrode covers the entire drain and has an insulating layer interposed therebetween. Active matrix liquid crystal display device characterized by being formed with a predetermined overlap between the gate so as to extend over the gate Te. 2. The active matrix type liquid crystal display device according to claim 1, wherein the gate is formed of a non-light-transmitting conductive member. 3. The thin film transistor has a non-light-transmitting source electrode electrically connected to the source, the source electrode covering the entire source and extending over the gate via an insulating layer. 3. The active matrix liquid crystal display device according to claim 2, wherein a predetermined overlap is provided between the gate and the gate. 4. The scanning signal line and the data signal line are made of a non-transmissive conductive member, and are formed with a predetermined overlap between the scanning signal line and the pixel electrode via an insulating layer. Item 4. An active matrix liquid crystal display device according to any one of Items 1 to 3. 5. The active matrix type liquid crystal display device according to claim 1, wherein the source electrode and the drain electrode are formed using the same wiring layer as the data signal line.