JPH10239708A - Active matrix type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an active matrix type liquid crystal display device that has high display quality and a sufficient aperture rate, by forming a 1st thin film transistor below a signal line. SOLUTION: On a substrate, 1st and 2nd thin film transistors 50 and 53, which are connected to each other in series are formed at the intersection part of a scanning line 40A and a signal line 52A in one corner of a display area 30. The drain electrode 51 of the 1st transistor 50 is connected to the signal line 52A. The source electrode of the 2nd transistor 53 is connected to a pixel electrode 55. The source area of the 1st transistor 50 and the drain area of the 2nd transistor 53 are connected to a common electrode 56 so that their channel directions are orthogonal to each other. The channel length of the 1st transistor 50 is formed below the signal line 52A along its length direction.

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 in which thin film transistors (also referred to as TFTs) are connected as switching elements between signal lines and display pixel electrodes.

[0002]

2. Description of the Related Art In recent years, a liquid crystal display device capable of obtaining a high-performance and high-definition display while having a high density and a large capacity has been put into practical use. There are various types of liquid crystal display devices. Among them, the directions intersecting each other are selected because the crosstalk between adjacent pixels is small, a high-contrast display is obtained, a transmissive display is possible, and a large area is easily achieved. Many active matrix type liquid crystal display devices include an array substrate in which pixel electrodes are provided in a matrix in a plurality of regions defined by a plurality of scanning lines and a plurality of signal lines provided in a plurality of regions by using thin film transistors as switching elements. Used.

In recent years, attempts have been made to integrate a drive circuit on a substrate using polysilicon having high mobility. In the case of using polysilicon, since the temperature of the array substrate is usually higher than 600 ° C. in the manufacturing process, and the source and drain electrodes of the thin film transistor are formed by self-aligned impurity implantation using the gate electrode,
A top-gate transistor structure is used.

[0004]

When a liquid crystal display device is constructed using such high mobility polysilicon, the mobility of the thin film transistor connected to the display pixel electrode is high. The ON current for charging the connected auxiliary capacitance element increases, and the size of the thin film transistor connected to the pixel electrode can be reduced. However, with a reduction in the size of the thin film transistor connected to the pixel electrode, the off-current also increases, and display defects such as occurrence of crosstalk and uneven display luminance on a screen occur.

In order to solve this problem, it is known to use a configuration in which two or more thin film transistors are connected in series to a pixel electrode, as disclosed in, for example, Japanese Patent Application Publication No. 62-245222. ing. If the number of thin film transistors connected in series increases as described above, the off-state current can be reduced, and the deterioration of display quality as described above can be suppressed.

However, in this known configuration, since a plurality of thin film transistors are formed in a portion surrounded by the scanning lines and the signal lines, the area of the pixel electrode is reduced by that amount, and it is difficult to obtain a sufficient aperture ratio. Become.

The polysilicon film is formed by heating an amorphous silicon film deposited on a glass substrate by a method such as laser scanning and crystallizing the amorphous silicon film. At this time, a portion scanned and crystallized by a laser is used. In addition, a region that is not sufficiently crystallized remains between a portion crystallized by the next laser scan and a portion crystallized by the next laser scan. When a thin film transistor is formed using such a polysilicon film, the characteristics may be varied. Therefore, an object of the present invention is to provide an active matrix liquid crystal display device having a high display quality and a sufficient aperture ratio.

[0008]

An active matrix type liquid crystal display device according to the present invention comprises a plurality of scanning lines formed on an insulating substrate and a plurality of scanning lines formed crossing the plurality of scanning lines. A signal line, a plurality of thin film transistors formed at respective intersections of the scanning lines and the signal lines, and a plurality of pixels formed respectively in regions defined by the scanning lines and the signal lines and connected to the thin film transistors In an active matrix liquid crystal display device including an array substrate provided with electrodes, at each intersection of the scanning line and the signal line, a gate electrode connected to the scanning line and a drain electrode connected to the signal line are provided. A first thin film transistor having a channel length in a longitudinal direction of the signal line;
A gate electrode connected to the scanning line, a drain electrode connected to the source electrode of the first thin film transistor, a source electrode connected to the pixel electrode, a second thin film transistor having a channel length in the longitudinal direction of the scanning line, And the first thin film transistor is formed below the signal line.

With the above structure, the first and second thin film transistors are arranged between the signal line and the pixel electrode in a direction crossing each other and connected in series, so that the first and second thin film transistors are formed in the polysilicon film on which the thin film transistors are formed. Even if the distribution of crystal defects to be formed has directionality due to the manufacturing process, variations in the characteristics of the formed thin film transistor do not occur in a specific direction, and the channel length of the first thin film transistor is reduced by the signal line. Since it is formed below the signal line along the longitudinal direction, the channel length of the first thin film transistor can be freely set at the design stage without impairing the aperture ratio.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG.
FIG. 2 is a plan view of the active matrix type liquid crystal display device of the embodiment, and FIG. 2 is a cross-sectional view taken along a dashed line ABCD of FIG.

1 and 2, signal lines 52A and 52B are formed on a glass substrate 59 with respect to scanning lines 40A and 40B.
Are arranged so as to intersect substantially at a right angle, and the pixel electrode 55 is arranged inside thereof so that the display region 30 for one pixel is formed.

First and second thin film transistors 50 and 53 connected in series with each other are formed on the substrate 59 at the intersection of the scanning line 40A and the signal line 52A at one diagonal corner of the display area 30. Is done.

The first and second thin film transistors 50,
53 is used as a switching element.
The drain electrode 51 of the thin film transistor 50 is connected to the connection line 5.
Connected to signal line 52A via 1a. On the other hand, the source electrode 54 of the second thin film transistor 53 is connected to the connection line 54a.
Is connected to the pixel electrode 55 through the. Further, the source region of the first thin film transistor 50 and the drain region of the second thin film transistor 53 are connected by a common electrode 56 so that their respective channel directions are orthogonal to each other.

That is, the channel length direction of the first thin film transistor 50 is formed so as to match the longitudinal direction of the signal line 52A, and the channel length direction of the other second thin film transistor 53 is the scanning line orthogonal to the signal line 52A. 40A
Is formed so as to coincide with the longitudinal direction. And the first,
The second thin film transistors 50 and 53 are connected in series with each other, and are driven by a common gate line 57 and a projecting portion 57a projecting at a right angle from the common gate line 57.

On the substrate 59 at the intersection of the scanning line 40B and the signal line 52B at the other diagonal corner of the display area 30, the auxiliary capacitance element 20B is connected to the pixel electrode 55 through the contact hole 78. It is formed as follows.

The structure of the auxiliary capacitance element 20B is as follows.
It is the same as the other auxiliary capacitance element 20A formed in relation to 0A, and its cross section is shown cut along the line CD in FIG. As shown in FIG. 1, the auxiliary capacitance element 20A is formed between the lower electrode 61 and the upper electrode 64 using a silicon oxide film 62 as a dielectric, and is connected from the electrode 71 to the pixel electrode 55 via the connection line 71a. Adjacent pixel electrode 5
6 is connected.

In the active matrix type liquid crystal display device of this embodiment, the display area having the above-described structure is formed on the glass substrate 59, and the drive circuit for driving this display area is also formed on the same glass substrate 59. Can be formed.

A part of this driving circuit is shown here as a configuration in which an N-channel thin film transistor 67 and a P-channel thin film transistor 70 are connected in series. The gate electrodes 66 of the thin film transistors 67 and 70,
65 are formed at portions corresponding to the channel regions 67a and 70a with the gate oxide film 62 interposed therebetween, and LDD (lightly doped drain) is formed between the source electrode 68 and the drain electrode 69 of the transistor 67 and the channel region 67a.
Regions 74e and 74f are formed.

Drains of the thin film transistors 67 and 70,
The source electrodes 69 and 73 are connected via a connection line 69a, and the drain electrode 72 of the transistor 70 is connected to the connection line 7a.
Although not shown, the transistor 67 is connected to the scanning line 40A, for example, and the source electrode 68 of the transistor 67 is connected to a power supply terminal (not shown).

With such a structure, the amorphous silicon film deposited on the glass substrate 59 is crystallized to form polysilicon, and the uncrystallized portion generated along the laser scanning direction is generated. , A variation in transistor characteristics can be reduced.

The two thin film transistors 50 and 53
One of the transistors 50 is formed such that an intersection of the signal line 52A and the gate line 40A, that is, a region immediately below the scanning line 40A is a channel region. in this way,
By forming one of the transistors 67 and 70 at the wiring intersection, even if a plurality of thin film transistors are connected in series, the aperture ratio can be increased by that amount, and a high aperture ratio can be obtained.

Further, since a plurality of thin film transistors are connected in series to the pixel electrode, off current can be reduced, and an active matrix type liquid crystal display device with high display quality can be obtained.

Next, a method of manufacturing the active matrix type liquid crystal display device having the structure shown in FIGS. 1 and 2 will be described in detail with reference to FIGS. First, FIG.
3A, an amorphous-silicon (a-S1) film 10 having a thickness of about 50 nm is deposited on a light-transmitting insulating substrate 59 formed of high strain point glass, quartz glass, or the like by a CVD method or the like. After annealing this at 450 ° C. for one hour in a furnace, the amorphous-silicon (a-Sl) film 49 is scanned and irradiated with a linear XeCl excimer laser in a direction perpendicular to this line to form an amorphous-silicon (a-Sl). Is polycrystallized to form a polysilicon film.

Thereafter, the polysilicon film is patterned by a photo-etching method to form first and second thin film transistors 5 in the display area as shown in FIG.
Forming regions 10A of 0 and 53, forming regions 10B of a polysilicon film 61 to be lower electrodes of the auxiliary capacitive element 20A, and driving circuit regions 10C are formed.

Next, an SiOx film 62 serving as a gate insulating film is deposited on the entire surface of the insulating substrate 59 to a thickness of about 100 nm by the CVD method. Subsequently, as shown in FIG.
A single metal such as Ta, Cr, Al, M0, W, and Cu, or a multilayer film or an alloy film thereof, such as
It is deposited to a thickness of about 0 nm and patterned into a predetermined shape by a photo-etching method. The scanning line 40A, the gate electrode 63a of the first thin film transistor 50, the gate electrode 63b of the second thin film transistor 53, and the upper electrode of the auxiliary capacitance element 20A 64, gate electrodes 66 and 65 of the thin film transistors 67 and 70 of the drive circuit, and various wirings in the drive circuit region (not shown) were formed.

Thereafter, these gate electrodes 63a, 63
Impurities are implanted by ion implantation or ion doping using the masks b, 65 and 66 as masks, and the drain electrode 51 of the first thin film transistor 50 and the
Electrode 56 also serving as the source electrode of the second transistor 53 and the drain electrode of the second transistor 53; the source electrode 54 of the second transistor 53;
7, a source electrode 68 and a drain electrode 69 were formed.

At this time, impurities are implanted into the region 10B where the auxiliary capacitance element 20A is to be formed and the electrode forming portion of the P-channel type circuit transistor 70 in the drive circuit region so that the impurities are not implanted. Was. The impurity is implanted, for example, at an acceleration voltage of 80 keV and 5 × 10 ¹⁵
Phosphorus was implanted at a high dose of PH ₃ / H ₂ at a dose of atoms / cm ² .

Next, the first thin film transistor 50 and the second
The thin-film transistor 53 and the N-channel drive circuit transistor 67 in the drive circuit region are covered with a resist so as not to be doped with impurities, and then the upper electrode 64 of the auxiliary capacitance element 20A and the P-channel drive circuit transistor 70 are covered.
The acceleration voltage 8
B ₂ H ₆ at a dose of 5 × 10 ¹⁵ atoms / cm ² at 0 keV
/ H ₂ to implant boron at a high concentration,
The connection electrode 71 of the lower electrode 61 of 0A and the source electrode 72 and the drain electrode 73 of the P-channel type drive circuit transistor 70 were formed.

Thereafter, as shown in FIG. 3C, impurities are implanted using the resist 45 as a mask,
The implanted impurities are activated by annealing the whole to form N-channel LDD (Lightly Doped Drain) regions 74a, 74b, 74c, 74d, 74e, 74f at the channel ends of the transistors 50, 53, 67, respectively. .

Next, a resist 45 was entirely removed in this state, the interlayer insulating film Si0 ₂ 75 on the entire surface of the insulating substrate for example by using a PECVD method as shown in FIG. 4 (a) 50
Deposit about 0 nm.

Next, ITO was sputtered for 100 n
About m of the film were formed and patterned into a predetermined shape by a photo-etching method to form pixel electrodes 55 and 56. Subsequently, the contact hole 7 reaching the drain electrode 51 of the first thin film transistor 50 is formed by photoetching.
6, a contact hole 77 reaching the source electrode 54 of the second thin film transistor 53, a contact hole 78 reaching the connection electrode 71 of the lower electrode 61 of the auxiliary capacitance element 20A, and source electrodes 68, 72 of the driving circuit transistors 67, 70.
Hole 68 reaching the drain electrodes 69 and 73
b, 72b, 69b, and 73b.

Next, Ta, Cr, Al, Mo, W, Cu
Such as a single metal or a laminated film or an alloy film thereof
and a signal line 52A, a connection line 5 between the drain electrode 51 of the first thin film transistor 50 and the signal line 52A.
1a, a connection line 54a between the source electrode 54 of the second thin film transistor 53 and the pixel electrode 55, and a connection line 7 between the connection electrode 71 of the lower electrode 61 of the auxiliary capacitive element 20A and the pixel electrode 56.
1a, various wirings 68a, 69a, 72a, etc. of the circuit transistors 67, 70 in the drive circuit area were formed. This state is shown in FIG.

Finally, as shown in FIG.
An array substrate 80 of an active matrix type liquid crystal display device is obtained by forming a protective insulating film 79 made of SiNx on the entire surface of the insulating substrate 59 by the CVD method and patterning it into a predetermined shape by a photoetching method.
On the side of the array substrate 80 facing the liquid crystal, an orientation film 86 made of a low-temperature curing type polyimide is further applied by printing.
Rubbing is performed so that the orientation axis is in a predetermined direction.

The array substrate 80 manufactured as described above
Is assembled with a counter substrate 85 as shown in FIG. 1, and assembled as a liquid crystal display device with a liquid crystal 88 interposed therebetween. The opposing substrate 85 has a light-shielding film 82 formed by, for example, coating a Cr film on a glass substrate 81 as a transparent insulating substrate by a sputtering method and then performing photoetching in a predetermined shape.

Next, by forming a colored layer 83 in which, for example, a pigment or the like is dispersed, and forming a counter electrode 84 which is a transparent electrode made of, for example, ITO by a sputtering method, a counter substrate 85 is manufactured.

Subsequently, the pixel electrodes 55, 5
An orientation film 87 made of a low-temperature cure type polyimide is applied by printing on the entire surface of the counter electrode 84 facing the substrate 6.
After the rubbing process is performed so that the alignment axis is 90 ° with respect to the alignment film 86 at the time of facing the alignment film 5, the substrates 80 and 85 are assembled facing each other to form a cell, and a nematic liquid crystal 88 is injected into the gap therebetween and sealed. Stop. Then, by attaching a polarizing plate (not shown) to the insulating substrates 59 and 81 of the substrates 80 and 85, an active matrix liquid crystal display device is obtained.

The array substrate 8 thus completed
The drain electrode 51 of one of the two thin film transistors 50 and 53 connected to the pixel electrode 55 is connected to the signal line 52A, and its source region is connected to the drain region of the second transistor 53 and the common electrode. 65
And the source electrode 54 of the second transistor 53 is connected to the pixel electrode 55. That is, the two transistors 50 and 53 are connected to the signal line 52A.
And the pixel electrode 55 are connected in series.

The two transistors 5 having such a configuration
When the off-state current of the series circuit consisting of 0 and 53 was measured,
The off-state current is at least one digit smaller than the off-state current when one conventional transistor is used.

The pixel electrode 55 of the array substrate 80 of this embodiment
The two thin film transistors 50 and 53 connected to each other are disposed so that their respective channel length directions are orthogonal to each other. Therefore, crystal defects generated when the amorphous silicon film is laser-annealed to form the polysilicon film are reduced. The resulting uneven ELA irradiation was eliminated, and good display without uneven display was obtained.

The first transistor 50 of the array substrate 80 of the present embodiment has a channel length at the intersection of the scanning line 40A and the signal line 52A so as to coincide with the longitudinal direction of the signal line 52A, and the signal line 52A. Is formed directly below.
With such a configuration, the thin film transistor 50 can be disposed in place of the conventional wiring portion. Therefore, even when a configuration in which a plurality of thin film transistors are connected to the pixel electrode as switching elements is used, the conventional configuration is reduced accordingly. Since the aperture ratio is expected to be improved as compared with the above, a brighter display can be obtained.

[0041]

As described in detail above, according to the present invention,
By connecting two or more thin film transistors connected as switching elements to the pixel electrode in series and arranging at least two of the transistors such that the channel length directions are orthogonal to each other, the laser of amorphous silicon during laser annealing can be used. Variations in display characteristics due to crystal defects occurring in the scanning direction can be suppressed.

Further, the aperture ratio can be improved by forming one of the thin film transistors in the pixel portion at the intersection with the scanning line so that the channel length direction coincides with the longitudinal direction of the signal line.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view of the array substrate cut along a line ABCD in FIG. 1 and including a corresponding opposing substrate portion along with a drive circuit portion.

FIG. 3 is a process chart for explaining an example of a method for manufacturing the array substrate of the embodiment shown in FIGS. 1 and 2;

FIG. 4 is a process chart for explaining an example of a method of manufacturing the array substrate of the embodiment shown in FIGS. 1 and 2.

[Explanation of symbols]

 40A, 40B scanning line 50, 53, 67, 70 thin film transistor 52A, 52B signal line 55, 56 pixel electrode 60a, 60b channel region 63a, 63b gate electrode

Claims (4)

[Claims] A plurality of scanning lines formed on an insulating substrate, a plurality of signal lines formed to intersect the plurality of scanning lines, and an intersection of the scanning lines and the signal lines. Active matrix type liquid crystal including an array substrate provided with a plurality of formed thin film transistors and a plurality of pixel electrodes formed in regions defined by the scanning lines and the signal lines and connected to the thin film transistors, respectively. In the display device, a gate electrode connected to a scanning line, a drain electrode connected to a signal line, and a first thin film transistor having a channel length in a longitudinal direction of the signal line are provided at each of intersections of the scanning line and the signal line. A gate electrode connected to the scanning line, a drain electrode connected to the source electrode of the first thin film transistor, and a source electrode connected to the pixel electrode Wherein a second thin film transistor having a channel length in the longitudinal direction of the scanning lines, the at least comprising said first thin film transistor active matrix liquid crystal display device characterized by being formed below the signal line. 2. The method according to claim 1, wherein a channel region of the second thin film transistor connected to the pixel electrode is formed together with the pixel electrode in a region defined by the scanning line and the signal line. Item 7. An active matrix liquid crystal display device according to item 1. 3. The active matrix type liquid crystal display device according to claim 1, wherein the first and second thin film transistors are formed such that channel length directions thereof are orthogonal to each other. 4. The active matrix according to claim 1, wherein a drive circuit for driving the plurality of scanning lines and signal lines is formed on the insulating substrate. Liquid crystal display device.