JP2002196349A - Liquid crystal display - Google Patents

Abstract

(57) Abstract: Provided is a liquid crystal device of high display quality which can prevent malfunction due to light and can increase the capacity of an applied voltage applied to a pixel electrode in an active matrix type liquid crystal device. A scanning line (806), a signal line (809), a transistor connected to the scanning line (806) and the signal line (809), a pixel electrode (808) connected to the transistor, and a storage capacitor unit. (817). The scanning line (806) is covered with a shield electrode (816) via an insulator, and is provided with a storage capacitor (81).
7) a semiconductor layer serving as a source / drain of the transistor and a first insulating film serving as a gate insulating film (805)
And the shield electrode (816) are planarly overlapped.

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 using thin film transistors.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional active matrix type liquid crystal display device using thin film transistors.
(A) is a top view, and (b) is a cross-sectional view along AA '. On a first insulating substrate 201 such as glass or quartz, a source region 203, a drain region 204, and a silicon thin film to which an impurity serving as a donor or an acceptor is added are formed.
Channel region 2 made of silicon thin film containing no impurities
02 is formed.

A gate insulating film 205 is laminated so as to cover them, a scanning line 206 also serving as a gate electrode is formed above the channel region 202, and the scanning line 206 and the signal line 209 are insulated so as to cover them. The interlayer insulating film 207 to be formed is formed. Further, contact holes 213 and 214 are opened, and the signal line 209, the drain region 204, and the pixel electrode 2 are formed.
08 and the source region 203 are connected. First insulating substrate 2
A second insulating substrate 212 provided with a common electrode 211 is provided so as to face the first insulating substrate 201, and a liquid crystal layer 210 is provided between the first insulating substrate 201 and the second insulating substrate 212.

[0004]

However, the conventional liquid crystal display
The indicating device has the following problems. Fig. 3 LCD display
5 shows a signal waveform of a general time-division driving for driving the device.
V_gIs a signal waveform applied to the scanning line 206,
Interval T₁And non-selection period T_TwoDivided into Selection period T ₁In
And about 15-20V to the gate electrode of the thin film transistor
Is applied to turn on the thin film transistor, and the signal line 20 is turned on.
9 is applied to the display signal v_sigTo the pixel electrode 208
And applied to the liquid crystal layer 210 to write electric charges. Then non
Selection period T _TwoThe thin-film transistor in the off state
Then, the charges written to the liquid crystal layer 210 are held. display
Signal V_sigAre from 60 to AC drive the liquid crystal layer 210.
It is an AC waveform of about 80 Hz,
The potential V of the common electrode 211 so that an alternating current is applied._comIs decided
Is determined. Twisted nematic liquid as the liquid crystal layer 210
When the crystal is used, the display signal V_sigAmplitude must be about ± 4-6V
It is important. On the other hand, the selection period T₁Is the non-selection period T_TwoShorter than
Thus, if the number of scanning lines is n, T₁Is generally T₁= (T₁+ T_Two) / N, and the scanning line 206 is connected to the common electrode 21 for most of the time.
DC voltage V_TwoIs applied. This V₁Is a layer break
Divided by the edge film 207 and the liquid crystal layer 210 to the liquid crystal layer 210,
DC voltage is applied, which causes the liquid crystal layer 210 to deteriorate.
Important table, such as a decrease in the contrast ratio of the liquid crystal display
Degraded quality has been caused. Display signal V_sigShake
If the width is ± 4-6V, normal V₁Is larger than 7 ~
8V, and the DC voltage applied to the liquid crystal layer 210 is 3 to
It is about 5V.

An object of the present invention is to solve such a problem, and an object of the present invention is to prevent a direct current voltage from being imprinted on a liquid crystal layer, and to achieve a high display quality and a highly reliable active matrix type liquid crystal display device. Is to provide.

[0006]

The liquid crystal display device of the present invention is characterized in that the scanning lines are covered with a conductive shield electrode via an insulator.

[0007]

(Embodiment 1) The present invention will be described in detail below based on embodiments. FIG. 1 shows an example of a liquid crystal display device according to the present invention. (A) is a top view, (b) is a cross-sectional view at AA ', and (c) is a cross-sectional view at BB'. A semiconductor layer forming a channel region 102, a drain region 103, and a source region 104 of a thin film transistor is formed on a first insulating substrate 101 such as glass or quartz by a low pressure CVD method.
The monosilane gas is thermally decomposed in an atmosphere at 0 ° C. to form polycrystalline silicon to a thickness of 25 to 50 nm. The semiconductor layer is not limited to polycrystalline silicon, and non-quality silicon may be used by a sputtering method or a plasma CVD method.
Heat treatment for about 5 to 40 hours or irradiation with an argon laser, an excimer laser, or the like may be used for polycrystallization.

The gate insulating film 105 is formed to a thickness of 100 to 20 by ECR plasma CVD so as to cover the semiconductor layer.
SiO ₂ was laminated to a thickness of 0 nm. ECR Plasma C
The SiO ₂ formed by the VD method can be dense, and high-quality SiO ₂ with few traps can be realized at a low temperature of 100 ° C. or less, and is optimal as a gate insulating film. The gate insulating film 105 may be obtained by thermally oxidizing a semiconductor layer forming the channel region 102, the drain region 103, and the source region 104 in an oxidizing atmosphere containing oxygen.

Further, a scanning line 106 also serving as a gate electrode is formed by stacking tantalum to a thickness of 300 to 500 nm by a sputtering method, and phosphorus ions are ion-implanted through the gate insulating film 105 through the gate insulating film 105 using the scanning line 106 as a mask. Implanted and self-aligned N-type source region 1
04 and the drain region 103 are provided. Further, the surface of the scanning line 106 made of tantalum is oxidized by an anodic oxidation method to provide a first insulator 115 made of tantalum oxide having a thickness of 250 to 450 nm. Irradiation is performed by irradiating the obtained laser piece to form a source region 104 and a drain region 1.
The resistance of the semiconductor layer 03 is reduced.

FIG. 4 shows a more detailed structure of the thin film transistor. After forming the source region 403 and the drain region 404 by ion implantation, the surface of the scanning line 406 made of tantalum is oxidized by anodic oxidation to form a first insulator 407.
Get. At this time, the surface of the scanning line 406 is oxidized and the line width is reduced, and ΔL is applied between the source region 404 and the scanning line 406.
Is generated. At the time of the switching operation of the thin film transistor, ΔL reduces the electric field applied to the source terminal 410, so that the off-state current of the thin film transistor can be significantly reduced. The same is true for the drain end 409.

On the other hand, after the first insulator 407 made of tantalum oxide is formed, a laser beam 408 is irradiated to activate the phosphorus ions implanted into the source region 403 and the drain region 404. And gate insulating film 4
05 is the drain end 4 because the laser beam 408 is transmitted.
09, the source end 410 is also irradiated with a sufficient laser beam, the drain end 409 reduces structural defects at the source end 410, improves junction characteristics, and reduces the parasitic resistance of the thin film transistor.

Next, as shown in FIG.
After the opening 3 is formed, the pixel electrode 108 and the shield electrode 116 are provided with an ITO film having a thickness of 30 to 200 nm. The shield electrode 116 completely covers the scanning line 106,
The scan line 106 is insulated from the first insulator 115. The first insulator 115 is a dense tantalum oxide oxidized by an anodizing method using an aqueous solution of citric acid of 0.01 wt% as a chemical conversion solution.
Almost no short-circuit defects. In order to complete the insulation between the scanning line 106 and the shield electrode 116, the first insulator 115 is replaced with a first insulator 50 as shown in FIG.
7 and a third insulator 508 may be employed. Third
If the insulator 508 is made of the same material as the gate insulating film 505, the contact hole 511 can be opened with the same etchant when the contact hole 511 is opened.
₂ is preferred.

Further, as shown in FIG.
A second insulator 107 of 0 nm SiO ₂ is provided;
After opening the contact hole 114 and the pixel opening window 117, a signal line 109 having a thickness of 500 to 800 nm and made of an alloy of aluminum and silicon is provided.

[0014] Opposite to the first insulating substrate 101, ITO
A second insulating substrate 112 provided with a common electrode 111 made of a film and a metal is arranged, and a liquid crystal layer 110 is provided between the first insulating substrate 101 and the second insulating substrate 112 to constitute a liquid crystal display device. Further, the shield electrode 116 and the common electrode 111 are connected to the outside or the periphery of the liquid crystal display device so that these two electrodes always have the same potential. As a result, the scanning lines 106 are completely electrostatically shielded from the liquid crystal layer 110 by the shield electrode 116. Even when the liquid crystal display device is driven using the driving waveform shown in FIG.
No DC voltage is applied to the liquid crystal 10 and a liquid crystal display device having high reliability over a long period of time and high display quality can be realized.

1 using tantalum as the scanning line 106
Although the example has been described, the scanning line 106 is not limited to tantalum, and any material may be used as long as it can form a dense oxide with good insulating properties on the surface by an anodizing method, and niobium, aluminum, or the like is used. The configuration can be exactly the same.

(Embodiment 2) FIG. 6 shows another embodiment of the liquid crystal display device according to the present invention, wherein (a) is a top view and (b) is A.
FIG. 7C is a cross-sectional view at A ′, and FIG. 7C is a cross-sectional view at BB ′.

A thin film transistor, a first insulating substrate 601 and a second insulating substrate 612 provided with a common electrode 611 constituting the liquid crystal display device shown in FIG. 6 are the same as those in the first embodiment. The difference from the first embodiment is that after the first insulator 615 made of tantalum oxide is provided, it is 100 to 200 nm.
The shield electrode 616 is formed so as to cover the scanning lines 606 with a metal such as chrome, which blocks visible light, and further has a thickness of 200 to 500 nm so as to cover them.
₂ is laminated, and the signal line 609 and the pixel electrode 6 are passed through the contact holes 613 and 614.
08 is a source region 604 and a drain region 603, respectively.
It is configured to be connected to The pixel electrode 608 is configured so as to be insulated by the shield electrode 617 and the shield electrode 616 that shield the preceding scanning line and the second insulator 607 so as to overlap with each other. As a result, light does not pass through the gap between the scanning line 606 and the pixel electrode 608, and only light transmitted through the gap between the signal line 609 and the pixel electrode 608 need be shielded. The accuracy in bonding the second insulating substrate 612 can be reduced, and the aperture ratio of the liquid crystal display device can be increased.

FIG. 7 shows the positional relationship between the light-shielding layer provided on the second insulating substrate 612 and the pixel electrode 608. Only the positional relationship between the light shielding layer and the pixel electrode is shown for simplicity of the drawing,
(A) is a conventional liquid crystal display device, and (b) is a liquid crystal display device according to the present invention.

The conventional liquid crystal display device shown in FIG.
In order to prevent the signal of the scanning line from being written to the pixel electrode due to the capacitive coupling between the scanning line and the pixel electrode, a gap corresponding to the same thickness as the liquid crystal layer is provided between the scanning line and the pixel electrode. In consideration of the wiring width of adjacent pixel electrodes 702 and 70
The interval L1 of _No. 3 was 15 to 20 μm.

Further, the light shielding layer 701 provided on the second insulating substrate and the pixel electrode 702 provided on the first insulating substrate
Is that L ₂ is 10 μm from the bonding accuracy of both substrates.
Was needed. Distance L ₃ between the pixel electrode 704 adjacent to the same for the wiring direction of the signal line 705 is 15 to 2
0 μm, and the bonding accuracy L ₄ between the light shielding layer 701 and the pixel electrode 704 was required to be 10 μm. When the pixel ratio is determined by setting the pixel pitch to 100 μm each for X and Y, the aperture ratio is 42 to 36%. In contrast, the liquid crystal display device according to the invention as shown in FIG. 7 (b), distance L ₆ of the pixel electrode 706 and 707, bonding accuracy L ₇ of the pixel electrode 707 and the light shielding layer 708 is the same as the conventional the case, the light shielding layer of the wiring direction of the scanning lines, the shield electrode made of a metal such as chromium, which is provided on the first insulating substrate serves also as a light shielding layer, L ₅ is a wiring width of the scan line If it is 5 to 10 μm,
10 to 15 μm is sufficient.

Similarly to the conventional example, when the X and Y pixel pitches are each set to 100 μm and the aperture ratio is calculated, 58 to 51
% And the aperture ratio is improved by 38 to 42% or more as compared with the related art,
The brightness of the liquid crystal display device can be significantly improved. On the other hand, the bonding accuracy of the first insulating substrate and the second insulating substrate is not different from the conventional one in the X direction, but is alignment-free in the Y direction, so that the bonding can be rationalized and the yield can be improved. By setting the shield electrode and the common electrode to the same potential as in the first embodiment, the scanning line is electrostatically shielded by the shield electrode and no DC voltage is applied to the liquid crystal layer.

(Embodiment 3) FIG. 8 shows another embodiment of the liquid crystal display device according to the present invention, wherein (a) is a top view and (b) is A.
FIG. 7C is a cross-sectional view at A ′, and FIG.

The second embodiment differs from the second embodiment shown in FIG. 6 in that a thin film transistor is provided at the intersection of a scanning line 806 and a signal line 809, and that a storage capacitor 817 is provided in the drain region 803.
The point is that the gate insulating film 805, the shield electrode 816, the second insulator 807, and the pixel electrode 808 are provided by stacking.

FIG. 8B shows a scanning line 806 and a signal line 809.
2 shows a cross-sectional structure of the crossing part of FIG. The basic structure of the thin film transistor is the same as that of the first and second embodiments, except that the drain region 803 and the signal line 809 are connected to each other by capacitive coupling.
09 is applied to the pixel electrode 80 through the drain region 803.
The drain electrode 803 is electrostatically shielded by a shield electrode 816 to prevent the data from being written into the memory cell 8, thereby eliminating the capacitive coupling. As a result, the thin film transistor can be formed below the scanning line 806 and the signal line 809, and the aperture ratio of the liquid crystal display device is improved.

FIG. 8C shows a sectional structure of the storage capacitor portion. The storage capacitor portion 817 includes a drain region 803 made of doped silicon, a gate insulating film 805, a shield electrode 816, a second insulator 807, and a pixel electrode 808.
And the drain electrode 803 and the pixel electrode 808 have the same potential via the contact hole 813. As a result, the storage capacitor has a configuration in which a capacitor having the gate insulating film 805 sandwiched between the drain regions 803 with the shield electrode 816 as one electrode and a capacitor sandwiching the second insulator 807 between the pixel electrodes 808 are arranged in parallel. In addition, a sufficiently large storage capacity can be realized with a small occupied area, and the aperture ratio is improved. The shield electrode 816 thus configured has three functions. First, as in the first and second embodiments, a role as an electrostatic shield for preventing a DC voltage from being applied to the liquid crystal layer 810. Second, as in the second embodiment, the scanning line 806 and the pixel electrodes 808, 818 are used. Third, there is a role of a storage capacitor line for fixing the potential of one electrode of the storage capacitor, as a light shielding layer for light leaking from the gap.

FIG. 9 shows that the shield electrode 916 has tantalum,
A cross section of a thin film transistor including a tantalum oxide in which the surface of a shield electrode 916 is oxidized by an anodic oxidation method as a second insulator 907 is shown. The tantalum oxide formed by the anodic oxidation method can provide a dense insulating film having few defects such as pinholes at room temperature, and has excellent controllability and reproducibility of the film thickness. As a result, a short circuit defect between the signal line 909 and the shield electrode 916 can be eliminated. Tantalum oxide dielectric constant as large as 25 to 28, 1/6 when there 6-7 times SiO _2, the area occupied by the storage capacitor using SiO ₂
The aperture ratio can be reduced to 1/7, and the aperture ratio can be further increased as compared with the above example. On the other hand, since the short-circuit defect of the storage capacitor can be eliminated, the pixel defect of the liquid crystal display device can be greatly reduced. In the second embodiment as well, the use of tantalum can reduce the number of defects.

[0027]

The present invention has the following excellent effects.

First, the scanning line is electrostatically shielded by a shield electrode to prevent a DC voltage from being applied to the liquid crystal layer, and to provide a liquid crystal display having high reliability and good display quality for a long period of time. The device can be realized.

Second, the bonding accuracy between the first insulating substrate and the second insulating substrate may be low, and the bonding may be simplified.
The yield can be improved.

Third, the aperture ratio can be increased, and the brightness of the liquid crystal display device can be significantly improved.

Fourth, a sufficiently large storage capacitor can be configured with a small occupied area, and the aperture ratio can be increased, and at the same time, the definition of the liquid crystal display device can be increased and the display quality can be improved.

Fifth, a short-circuit defect between the scanning line and the shield electrode can be eliminated by using tantalum as the scanning line and tantalum oxide obtained by the anodic oxidation method as the first insulator. realizable. Similarly, by forming the shield electrode from tantalum, short-circuit defects between the shield electrode and the signal line can be eliminated.

As described above, the liquid crystal display device of the present invention has many excellent effects, and can be applied from a direct-view large liquid crystal display device to a small high-definition liquid crystal display device for projection.

[Brief description of the drawings]

FIG. 1 is a diagram showing a liquid crystal display device according to the present invention.

FIG. 2 is a diagram showing a conventional liquid crystal display device.

FIG. 3 is a diagram showing signal waveforms of general time division driving for driving a liquid crystal display device.

FIG. 4 is a cross-sectional view illustrating a structure of a thin film transistor.

FIG. 5 is a cross-sectional view illustrating a structure of a thin film transistor.

FIG. 6 is a diagram showing a liquid crystal display device according to the present invention.

FIG. 7 is a diagram illustrating a positional relationship between a light-shielding layer provided on a second insulating substrate and a pixel electrode.

FIG. 8 is a diagram showing a liquid crystal display device according to the present invention.

FIG. 9 is a cross-sectional view illustrating a structure of a thin film transistor.

[Explanation of symbols]

101, 201, 401, 501, 601, 801, 9
01 first insulating substrate 102, 202, 402, 502, 602, 802, 9
02 channel area 103, 204, 403, 503, 603, 803, 9
03 Drain regions 104, 203, 404, 504, 604, 804, 9
04 Source area 105, 205, 405, 505, 605, 805, 9
05 Gate insulating film 106, 206, 406, 506, 606, 806, 9
06 Scan line 107, 607, 807, 907 Second insulator 108, 208, 510, 608, 808, 702, 7
03, 704, 705, 706, 707, 818 Pixel electrode 109, 209, 609, 809, 909 Signal line 110, 210, 610, 810 Liquid crystal layer 111, 211, 611, 811 Common electrode 112, 212, 612, 812 2 insulating substrates 113, 114, 213, 214, 511, 613, 6
14, 813, 814 Contact hole 115, 407, 507, 615, 815, 915 First insulator 116, 509, 616, 617, 816, 916 Shield electrode 117 Pixel opening window 207 Interlayer insulating film 408 Laser light 409 Drain end 410 Source end 508 Third insulator 701, 708 Light shielding layer 817 Storage capacitance portion

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] October 22, 2001 (2001.10.
22)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

[0006]

According to the present invention, there is provided a liquid crystal device comprising a substrate having a scanning line, a signal line, a transistor connected to the scanning line and the signal line, and a pixel electrode connected to the transistor. Wherein a channel region of the transistor is arranged to face an intersection of the scanning line and the signal line, and the scanning line, the signal line and a light-shielding conductive layer are formed on the channel region. And are arranged,
The width of the light-blocking conductive electrode and the width of the signal line are wider than the width of the channel region at the intersection.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

[0027]

According to the present invention, by satisfying the above constitutional requirements, the following remarkable effects can be obtained. (1) a scanning line immediately above a channel region of a transistor;
Since the signal line and the light-blocking conductive layer are formed, light can be prevented from entering the channel region. (2) Since the width of the signal line and the light-blocking conductive layer is wider than the width of the channel region, light can be prevented from entering the channel region from the lateral side, and malfunction of the transistor can be prevented.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 29/78 619B F term (Reference) 2H092 GA24 GA25 JB22 JB24 JB54 JB79 NA14 NA16 NA23 NA30 5C094 AA05 AA10 AA31 AA42 AA43 AA48 BA03 BA43 CA19 DA13 DB01 DB04 EA04 EA07 EA10 FA01 FA02 FB02 FB12 FB15 5F110 AA21 BB01 CC02 DD02 DD03 EE03 EE04 EE34 EE37 EE44 FF02 FF23 NN31 NN02 GG13 NN72 NN73 PP03 PP10 QQ11

Claims (7)

[Claims] A first insulating substrate has a plurality of scanning lines and signal lines, thin film transistors are provided in a matrix at intersections of the scanning lines and the signal lines, and pixel electrodes are connected to outputs of the thin film transistors. A liquid crystal display device in which a second insulating substrate provided with a common electrode is disposed facing the first insulating substrate, and a liquid crystal layer is provided between the first insulating substrate and the second insulating substrate. 3. The liquid crystal display device according to claim 1, wherein the scanning line is covered with a conductive shield electrode via a first insulator. 2. The liquid crystal display device according to claim 1, wherein said shield electrode is arranged simultaneously with said pixel electrode. 3. A plurality of scanning lines and signal lines are provided on a first insulating substrate, thin film transistors are provided in a matrix at intersections of the scanning lines and the signal lines, and pixel electrodes are connected to outputs of the thin film transistors. A liquid crystal display device having a second insulating substrate provided with a common electrode opposed to the first insulating substrate, and a liquid crystal layer provided between the first insulating substrate and the second insulating substrate; , The scanning line is covered with a conductive shield electrode via a first insulator, the shield electrode is covered with a second insulator, and a part of the pixel electrode is provided via the second insulator. A liquid crystal display device having a structure overlapping part of the shield electrode. 4. A first insulating substrate having a plurality of scanning lines and signal lines, thin film transistors provided in a matrix at intersections of the scanning lines and the signal lines, and a pixel electrode connected to an output of the thin film transistors. A liquid crystal display device having a second insulating substrate provided with a common electrode opposed to the first insulating substrate, and a liquid crystal layer provided between the first insulating substrate and the second insulating substrate; Has a structure in which a drain electrode, a gate insulating film, a conductive shield electrode, a second insulator, and a pixel electrode are sequentially laminated at least partially of a silicon film to which an impurity serving as a donor or an acceptor is added. A liquid crystal display device characterized in that: 5. The liquid crystal display device according to claim 1, wherein the potential of the shield electrode is set to be the same as that of the common electrode. 6. The scanning line according to claim 1, 3 or 4, wherein the scanning line is tantalum, and the first insulator is tantalum oxide. Liquid crystal display device. 7. The liquid crystal device according to claim 3, wherein the shield electrode of the third and fourth aspects is tantalum and the second insulator is a tantalum oxide.