JP2003207805A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a leakage current leaked from an accumulated capacity part and to reduce the whole size of a pixel driving switching element in an active matrix liquid crystal display device. <P>SOLUTION: In a multi-gate type MIS transistor having a plurality of gate electrodes 3 formed on a semiconductor layer and allowed to be used for pixel switching elements, the channel length of the gate electrode 3 close to a drain area 5 and an accumulated capacity part 21 is set longer than that of the other gate electrode 3. <P>COPYRIGHT: (C)2003,JPO

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.

[0002]

2. Description of the Related Art Liquid crystal display devices are used in all fields, not only for OA and AV, because of their thinness and light weight. In particular, a liquid crystal display device using a thin film transistor (hereinafter referred to as TFT) is excellent in gradation display, has a performance close to that of a CRT as a color display, and is required to have higher definition. In particular, since polycrystalline silicon (hereinafter referred to as poly-Si) as a thin film material can be used to form not only the TFTs forming the display section and the sensor section but also the TFTs forming the peripheral driving circuit on the same substrate. It is getting attention.

Regarding a TFT used as a switching element for turning on / off a pixel of an active matrix liquid crystal display device, in the case of normally white which is usually used, in order to suppress a leak current which causes a pixel bright spot defect in particular. Conventionally, various configurations have been proposed and put into practical use.

For example, LDD (Lightly Dope)
A TFT having a d-Drain structure (hereinafter referred to as an LDD TFT) is known. In this LDD TFT, a low-concentration impurity region is provided around the diffusion layer to alleviate the electric field concentration at the ends of the source and drain regions, and it has the same leakage current suppressing effect as the offset gate structure.

As another method of reducing the leak current of the TFT, two or more gate electrodes are provided,
A TFT having a multi-gate structure has been conventionally known. This multi-gate TFT has a plurality of TFTs in terms of an equivalent circuit.
Are connected in series. Since the leak current depends on the TFT having the lowest off current value among the plurality of TFTs, the leak current can be suppressed. Furthermore, a LDD-T having a multi-gate structure combining the above two structures
FT has a synergistic effect by taking advantage of each advantage.

A conventional pixel driving switching element using an LDD-TFT having a multi-gate structure will be briefly described with reference to FIG. A poly-Si film patterned into a predetermined shape is formed on the glass substrate 1a.
A pair of channel regions 3 separated from each other are formed in this poly-Si film, and both are connected to each other by a connection region 6. The source region 4 is formed at the end of one channel region 3 and the other channel region 3 is formed.
A drain region 5 is formed at the end of the. Between the source region 4, the connection region 6, the drain region 5 and each channel region 3, there are a total of 4 low-concentration impurity regions having the same conductivity type as the source region and the drain region, that is, LDD regions 7.
It is formed in some places. A gate electrode 9 is patterned and formed on each channel region 3 through a gate oxide film 8 to form a TFT. Interlayer insulation film 10 on the TFT
Is deposited. Further, a signal electrode 11 is formed thereon by patterning and is electrically connected to the source region 4 and the drain region 5 via a contact hole. Further, a final interlayer insulating film 12 is formed thereon, a contact hole is opened in the signal electrode 11 on the storage capacitor portion 21, a flattening film 13 is formed, and then the signal electrode 12 on the storage capacitor portion 12 is formed.
A contact hole is opened in the pixel electrode (ITO) 14
a is formed and electrically connected.

FIG. 5 is a sectional view showing a pixel driving switching element using a conventional LDD-TFT having a multi-gate structure in which the channel length is shortened and miniaturized. 5, the same parts as those in FIG. 4 are designated by the same reference numerals. The configuration and the manufacturing method are the same as those of the pixel driving switching element using the conventional LDD-TFT having the multi-gate structure described in FIG. 4, but as shown in the figure, the pixel length is reduced by reducing the channel length. It can be seen that the size of the entire drive switching element is also reduced.

FIG. 3 shows an LDD-TF having a multi-gate structure.
1 of active matrix type liquid crystal display device adopting T
It is the equivalent circuit diagram which cut out and showed the pixel part. The switching element is composed of TFT1 to TFTn connected in series, and each gate electrode is commonly connected to the gate wiring. The source region end of the TFT1 is connected to the signal line, while the drain region end of the TFTn drives the liquid crystal through the pixel electrode. The storage capacitor 21 is also connected in parallel with the liquid crystal 24.

[0009]

The active matrix type liquid crystal display device requires the miniaturization of the TFT for higher performance and higher definition. Conventional multi-gate LDD
-The TFT was able to obtain a great effect of suppressing the leak current to a low level. However, if the channel length is shortened due to the miniaturization of the TFT, the horizontal diffusion of impurities and the expansion of the depletion layer when a voltage is applied are reduced. Therefore, the effective channel length is shortened and the leak current is extremely increased.
There is a problem in that the voltage applied to the liquid crystal layer cannot be held, and a pixel bright spot defect due to current leakage from the storage capacitor portion occurs.

The present invention has been made in view of the above circumstances, and provides a liquid crystal display device capable of preventing an increase in leak current and realizing the miniaturization of the entire switching element.
To that end.

[0011]

In order to achieve the above object, a liquid crystal display device of the present invention is an active matrix array in which pixel electrodes arranged in a matrix and peripheral circuits for driving the pixel electrodes are integrated on the same substrate. A liquid crystal display device comprising a substrate, a counter substrate facing the substrate, a liquid crystal layer held by the both substrates, and a polarizing plate, wherein the polarizing plate is arranged in normally white, and the pixel electrode is provided. And a thin film transistor forming a peripheral circuit are multi-gate MIS transistors having a plurality of gate electrodes, and the transistor has an LDD including a low-concentration impurity region between a source / drain region and a channel region.
In the plurality of gate electrodes, at least one gate electrode has a different size from other gate electrodes.

Since the liquid crystal display device of the present invention has the above-mentioned structure, it is possible to prevent the leak current from increasing, and as a result, it is possible to prevent the occurrence of the pixel bright spot defect and to miniaturize it. Become.

In the liquid crystal display device of the present invention, the thin film transistor is used for a pixel switching element, and a channel length dimension of a gate electrode close to a drain region and a storage capacitance portion is longer than a channel length dimension of another gate electrode. Is preferred. For example, the channel length dimension of the gate electrode near the drain region and the storage capacitor is 0.1 to 1
The channel length dimension of the other gate electrode is in the range of 0.2 to 20 μm, and preferably, the channel length dimension of the gate electrode near the drain region and the storage capacitor portion is 1.0 to 4 The channel length dimension of the other gate electrodes is in the range of 2.0 to 8.0 μm.

The thin film transistor of the present invention has an active matrix array substrate in which pixel electrodes arranged in a matrix and peripheral circuits for driving the pixel electrodes are integrated on the same substrate, a counter substrate facing the active matrix array substrate, and the both substrates. A thin film transistor used in a liquid crystal display device in which the arrangement of the polarizing plate is normally white, the transistor being a multi-gate having a plurality of gate electrodes. Type MIS transistor, which is an LDD having a low concentration impurity region between a source / drain region and a channel region.
In the plurality of gate electrodes, at least one gate electrode has a different size from other gate electrodes.

The thin film transistor is used for a pixel switching element, and it is preferable that the channel length dimension of the gate electrode near the drain region and the storage capacitor portion is longer than the channel length dimension of other gate electrodes.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An example of the liquid crystal display device of the present invention will be described below with reference to the drawings.

FIG. 1 is an enlarged partial cross-sectional view showing the periphery of a TFT, which is particularly important in the active matrix type liquid crystal display device of the present invention. The illustrated TFT is n-
It is a ch type and constitutes a pixel driving switching element of an active matrix type liquid crystal display device. This TFT can be manufactured, for example, as follows.

First, a non-alkali glass substrate (for example, 1737, manufactured by Corning Incorporated) is used as the substrate 1a, and an undercoat 2 (for example, a thickness of 4) made of a silicon oxide thin film is used.
00 nm) is formed. An amorphous silicon thin film is formed on this by a plasma CVD method (for example, a thickness of 50 n
m), and then irradiated with excimer laser light to melt and crystallize to form a polycrystalline silicon thin film. The polycrystalline silicon thin film is processed into a pixel driving switching element part and a storage capacitor part to form a gate insulating film 8 (for example, 90 nm thick) made of a silicon oxide thin film. A photoresist mask is formed on the gate insulating film 9, and a first impurity implantation is performed by an ion implantation method to form a high concentration impurity implantation region (diffusion layer region) of the source region 4, the connection region 6 and the drain region 5. To form. For the first impurity implantation, phosphorus (P) ions are used, for example, with an accelerating voltage of 12 KV and a dose of 2.5 × 10.
Inject under the condition of ¹⁴ / cm ² . After the first impurity implantation, the photoresist mask is removed to form gate electrodes 9a and 9b (for example, an alloy of Mo (molybdenum) with a refractory metal, for example, 35% of W (tungsten) added).
Thickness 300 nm), and the gate electrode 9 on the drain region 5 side
Patterning is performed so that b has a channel length larger than that of the gate electrode 9a on the source region 4 side.

Next, using the gate electrodes 9a and 9b as a mask, a second impurity implantation is performed to form a low concentration impurity implantation region () between the source region 4, the connection region 6, the drain region 5 and each channel region 3. LDD regions) 7 are formed at four locations in total. The number of LDD regions is not limited to four, and may be appropriately determined according to various conditions. The second impurity implantation is phosphorus.
(P) ions are implanted, for example, under the conditions of an acceleration voltage of 70 KV and a dose amount of 2.5 × 10 ¹⁴ / cm ² . After that, the implanted impurities are activated. Then, an interlayer insulating film 10 made of silicon oxide is formed (for example, a thickness of 400 n
Then, contact holes are opened on the source and drain regions to form the signal electrode 11 and electrically connect. Then, a final insulating film 12 made of silicon oxide is formed (for example, a thickness of 400 nm), and the drain region 5 on the storage capacitor is formed.
A contact hole is opened on the signal electrode 11 on the side, and a transparent positive type photosensitive alkali resin (for example, trade name: FV
R, manufactured by Fuji Pharmaceutical Co., Ltd.), and then formed with a flattening film 13, and then irradiated with ultraviolet rays using a predetermined photomask,
A contact hole is opened on the drain electrode, a pixel electrode (ITO) 14a is formed, and the pixel electrode (ITO) 14a is electrically connected to the signal electrode 11 on the drain region side 5. In this way, an active matrix array substrate can be manufactured.

Next, referring to FIG. 2, the multi-gate structure L
A configuration example of the active matrix type liquid crystal display device configured by using the DD-TFT will be described.

A pigment dispersion type red, green and blue stripe array and a black matrix layer 17 are formed on the substrate 1b as a color filter layer 16 by photolithography, and indium tin oxide is used as a transparent electrode thereon. The counter substrate can be manufactured by forming the pixel electrode 14b.

Next, for example, a solution in which 5% by mass of polyimide is dissolved in γ-butyrolactone is printed on the pixel electrodes 14a and 14b and heated (for example, 250 ° C.) to be cured, and then rayon cloth or the like is used. The alignment layers 18a and 18b are formed by performing the alignment treatment by the rotating rubbing method.

Then, the pixel electrode (IT
O) 14b is printed with a thermosetting seal resin (for example, trade name: Struct Bond, manufactured by Mitsui Toatsu Chemicals, Inc.) containing 1.0% by weight of glass fiber on the periphery of the active matrix. The resin beads 15 are scattered on the side substrate 1a at a rate of 100 to 200 pieces / mm ² , and the opposite side substrate 1b and the active matrix side substrate 1 are dispersed.
After a is bonded to each other and heated (for example, 150 ° C.) to cure the seal resin, for example, a fluoroester nematic liquid crystal 19 is vacuum-injected, sealed with an ultraviolet curable resin, and then cured with ultraviolet light.

Polarizing films 20a and 20b are attached to the outside of the opposing substrate 1b and the outside of the active matrix side substrate 1a thus formed (arrangement is normally white) to complete the active matrix type liquid crystal display device. . In addition, in FIG. 2, 22 shows a circuit configuration part.

The graph of FIG. 6 shows the characteristics of the channel length (μm) of the dual gate electrode and the drain current. In this figure, the horizontal axis is the channel length of the gate electrode,
For example, in the case of two gate electrodes of 4 μm and 3 μm,
It is displayed as 4 + 3. The vertical axis represents the drain current when Vg = 0V. As shown in this graph, when the channel length of the gate electrode is less than 4 μm, the drain current (leakage current) conventionally increases, but in the present invention, the leak current hardly increases.

[0026]

As described above, the liquid crystal display device of the present invention enhances the ability to hold the voltage applied to the liquid crystal layer, and in particular, pixel bright spot defects caused by current leakage from the storage capacitor portion. It is possible to suppress the occurrence of. Further, the size of the entire pixel driving switching element can be reduced as compared with the conventional one, and as a result, high performance and high definition of the active matrix type liquid crystal display device can be realized.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing an example of the structure of a liquid crystal display device of the present invention.

FIG. 2 is a cross-sectional view showing an example of the structure of the liquid crystal display device of the present invention.

FIG. 3 is an equivalent circuit diagram of one pixel in an active matrix type liquid crystal display device including a pixel driving switching element using a conventional multi-gate structure LDD-TFT.

FIG. 4 is a sectional view showing a pixel driving switching element using a conventional multi-gate structure LDD-TFT.

FIG. 5 is a cross-sectional view showing a pixel driving switching element using a conventional multi-gate structure LDD-TFT with a shortened channel length and miniaturization.

FIG. 6 is a graph showing characteristics of a channel length of a gate electrode and a drain current.

[Explanation of symbols]

1a, 1b: glass substrate 2: Undercoat 3: Channel area 4: Source area 5: Drain region 6: Connection area 7: LDD area 8: Gate oxide film 9: Gate electrode 10: Interlayer insulating film 11: Wiring electrode 12: Final insulating film 13: Flattening film 14a, 14b: Pixel electrodes (ITO) 15: Resin beads 16: Color filter layer 17: Black matrix layer 18a, 18b: Hardened film 19: Liquid crystal 20a, 20b: Polarizing film

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H092 JA24 JA31 JA37 KA04 MA27                       NA13 PA06                 5F110 AA06 BB02 CC02 DD02 DD13                       EE06 EE28 FF02 GG02 GG13                       GG25 GG45 HJ01 HJ04 HJ13                       HJ23 HL07 HL11 HM15 NN02                       NN03 NN04 NN23 NN27 NN73                       PP03 QQ11

Claims (6)

[Claims] 1. An active matrix array substrate in which pixel electrodes arranged in a matrix and peripheral circuits for driving the pixel electrodes are integrated on the same substrate, a counter substrate facing the active matrix array substrate, and a liquid crystal layer held by the both substrates. And a polarizing plate, wherein the polarizing plate is arranged in normally white, and the thin film transistor forming the pixel electrode and the peripheral circuit is a multi-gate MIS transistor having a plurality of gate electrodes. The transistor has an LDD structure including a low-concentration impurity region between a source / drain region and a channel region, and in the plurality of gate electrodes, at least one gate electrode has a size different from that of other gate electrodes. Liquid crystal display device characterized by different. 2. The thin film transistor is used for a pixel switching element, and a channel length dimension of a gate electrode near a drain region and a storage capacitor portion is longer than a channel length dimension of another gate electrode. 1. The liquid crystal display device according to 1. 3. The channel length dimension of the gate electrode near the drain region and the storage capacitor portion is in the range of 0.1 to 10 μm, and the channel length dimension of the other gate electrode is 0.2 to.
The liquid crystal display device according to claim 2, wherein the liquid crystal display device has a range of 20 μm. 4. An active matrix array substrate in which pixel electrodes arranged in a matrix and peripheral circuits for driving the pixel electrodes are integrated on the same substrate, a counter substrate facing the active matrix array substrate, and a liquid crystal layer held by the both substrates. A thin film transistor used in a liquid crystal display device in which the arrangement of the polarizing plate is normally white, the transistor being a multi-gate type MIS transistor having a plurality of gate electrodes, This has an LDD structure having a low-concentration impurity region between a source / drain region and a channel region, and in the plurality of gate electrodes, at least one gate electrode is different in size from other gate electrodes. And a thin film transistor. 5. The thin film transistor is used for a pixel switching element, and a channel length dimension of a gate electrode near a drain region and a storage capacitor portion is longer than a channel length dimension of another gate electrode. 4. The thin film transistor according to 4. 6. The channel length dimension of the gate electrode near the drain region and the storage capacitor portion is in the range of 0.1 to 10 μm, and the channel length dimension of the other gate electrode is 0.2 to.
The thin film transistor according to claim 5, having a thickness in the range of 20 μm.