JP3386057B2 - Liquid crystal device - Google Patents

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, (b) is sectional drawing in AA '. On a first insulating substrate 201 such as glass or quartz, a source region 203 and a drain region 204, which are made of a silicon thin film to which impurities serving as donors or acceptors are added,
Channel region 2 made of silicon thin film containing no impurities
02 form.

A gate insulating film 205 is laminated so as to cover them, a scanning line 206 also serving as a gate electrode is formed on the channel region 202, and the scanning line 206 and the signal line 209 are insulated so as to cover them. An interlayer insulating film 207 is formed. Further, the 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
The second insulating substrate 212 provided with the common electrode 211 is arranged to face 01, and the 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 display device had the following problems. LCD display in Figure 3
3 shows a signal waveform of a general time division drive for driving the device.
V_gIs a signal waveform applied to the scanning line 206,
Interval T₁And non-selection period T₂It is divided into Selection period T ₁To
About 15 to 20V for the gate electrode of the thin film transistor
The voltage is applied to turn on the thin film transistor, and the signal line 20
Display signal v applied to 9_sigThe pixel electrode 208
Then, a charge is applied to the liquid crystal layer 210 to write an electric charge. Next non
Selection period T ₂And turn off the thin film transistor at
Then, the charge written in the liquid crystal layer 210 is retained. display
Signal V_sigIs 60 to drive the liquid crystal layer 210 with alternating current.
AC waveform of about 80 Hz, which is accurate for the liquid crystal layer 210
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
Display signal V_sigMust have an amplitude of ± 4 to 6V.
It will be important. Meanwhile, the selection period T₁Is the non-selection period T₂Short compared to
Thus, if the number of scanning lines is n, then T₁Is generally T₁= (T₁+ T₂) / N Therefore, most of the time, the scan line 206 is connected to the common electrode 21.
DC voltage V between 1₂Is applied. This V₁There is a break
The liquid crystal layer 210 is divided by the edge film 207 and the liquid crystal layer 210,
A direct current voltage is applied and deteriorates the liquid crystal layer 210.
The LCD display device has a serious
The display quality was deteriorated. Display signal V_sigShaking
If the width is ± 4 to 6V, it is usually V₁Is larger than this
8V, and the DC voltage applied to the liquid crystal layer 210 is 3 to
It will be about 5V.

The present invention is intended to solve such a problem, and an object thereof is to prevent a direct current voltage from being imprinted on a liquid crystal layer, and to provide a liquid crystal display device of an active matrix system having high display quality and high reliability. To provide.

[0006]

According to the present invention, a scanning line, a signal line, a transistor provided corresponding to the scanning line and the signal line, and a pixel electrode provided corresponding to the transistor are provided on a substrate. A liquid crystal device comprising:
Wiring in the drain region of the transistor
One electrode of the storage capacitor extending along the direction and one of the scan line and the storage capacitor provided on the scanning line .
And a second electrode of the storage capacitor overlaps the region of the adjacent pixel electrodes sandwiching the electrodes and the scanning lines, the holding capacity
The overlap of the pixel electrodes adjacent to each other with respect to the other of the two electrodes is one of the storage capacitors formed in the drain region.
One of the pixel electrodes that overlaps with the other electrode is adjacent to this
The other electrode of the storage capacitor is overlapped with the other pixel electrode.
Area of the storage capacitor is widened, and the other electrode of the storage capacitor is
The pixel electrode that overlaps with one electrode of the storage capacitor and the transistor
It has a notch for connecting with the drain region of the transistor .

[0007]

EXAMPLES Example 1 The present invention will be described in detail based on the following examples. FIG. 1 shows an example of a liquid crystal display device according to the present invention. (A) is a top view, (b) is sectional drawing in AA ', (c) is sectional drawing in 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 by a low pressure CVD method.
The monosilane gas is thermally decomposed in an atmosphere of 0 ° C. to form polycrystalline silicon with 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.
It may be heat-treated for about 5 to 40 hours or may be irradiated with an argon laser, an excimer laser or the like to be polycrystallized.

A gate insulating film 105 is formed by the ECR plasma CVD method so as to cover the semiconductor layer by 100 to 20.
SiO ₂ was laminated to a thickness of 0 nm. ECR plasma C
The SiO ₂ formed by the VD method is suitable as a gate insulating film because it can be dense and can form high-quality SiO ₂ with few traps at a low temperature of 100 ° C. or lower. The gate insulating film 105 may be obtained by thermally oxidizing the semiconductor layers 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 in a thickness of 300 to 500 nm by a sputtering method, and phosphorus ions are ion-implanted through the gate insulating film 105 in the semiconductor layer by using the scanning line 106 as a mask. Implanting and self-aligning 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 the anodic oxidation method to provide the first insulator 115 made of tantalum oxide having a thickness of 250 to 450 nm, and then the implanted phosphorus ions are excimer laser. The source region 104 and the drain region 1 are activated by irradiating the obtained laser piece.
The semiconductor layer No. 03 has a low resistance.

FIG. 4 shows a more detailed structure of the thin film transistor. After forming the source region 403 and the drain region 404 by the ion implantation method, the surface of the scanning line 406 made of tantalum is oxidized by the anodic oxidation method, and the first insulator 407 is formed.
To get At this time, the surface of the scan line 406 is oxidized and the line width is narrowed, and ΔL is provided between the source region 404 and the scan line 406.
The interval of occurs. During the switching operation of the thin film transistor, this ΔL can reduce the electric field applied to the source end 410, and the current when the thin film transistor is off can be suppressed to a significantly low level. The same applies to the drain end 409.

On the other hand, after the first insulator 407 made of tantalum oxide is formed, the first insulator 407 is irradiated with laser light 408 to activate phosphorus ions implanted in the source region 403 and the drain region 404. And gate insulating film 4
Since 05 transmits the laser beam 408, the drain end 4
09, the source end 410 is also irradiated with sufficient laser light, structural defects at the drain end 409 and the source end 410 are reduced, junction characteristics are improved, and the parasitic resistance of the thin film transistor can be reduced.

Next, as shown in FIG. 1, the contact hole 11
After making 3 an opening, 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 by the first insulator 115. The first insulator 115 is a dense tantalum oxide that is oxidized by an anodic oxidation method using a 0.01 wt% citric acid aqueous solution as a chemical conversion liquid, and is the scanning line 106 and the shield electrode 116.
Almost no short circuit defects occur. In order to make the insulation between the scanning line 106 and the shield electrode 116 more complete, the first insulator 115 is replaced with the first insulator 50 as shown in FIG.
A two-layer structure of 7 and the third insulator 508 may be used. Third
If the same material as that of the gate insulating film 505 is used for the insulator 508, it is rational because 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. 1, the thickness is 200 to 50.
A second insulator 107 made of 0 nm SiO ₂ is provided,
After opening the contact hole 114 and the pixel opening window 117, a signal line 109 made of an alloy of aluminum and silicon and having a thickness of 500 to 800 nm is provided.

ITO facing the first insulating substrate 101,
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 form a liquid crystal display device. Further, the shield electrode 116 and the common electrode 111 are connected outside or in the peripheral portion of the liquid crystal display device so that these two electrodes are always at the same potential. As a result, the scanning line 106 is completely electrostatically shielded from the liquid crystal layer 110 by the shield electrode 116, and even if the liquid crystal display device is driven using the drive waveform shown in FIG.
No DC voltage is applied to the liquid crystal display device 10, so that a liquid crystal display device having high reliability and long-term 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 can be used as long as it can form a dense oxide having a good insulating property on the surface by the anodic oxidation method, such as niobium or aluminum. However, it can be configured in exactly the same way.

(Embodiment 2) FIG. 6 shows another embodiment of the liquid crystal display device according to the present invention, in which (a) is a top view and (b) is A.
Sectional drawing in A ', (c) is sectional drawing in BB'.

The thin film transistor, the first insulating substrate 601, and the second insulating substrate 612 liquid crystal layer 610 provided with the common electrode 611 which compose 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 100 to 200 nm after the first insulator 615 made of tantalum oxide is provided.
The shield electrode 616 is formed so as to cover the scanning line 606 with a metal such as chrome which blocks visible light, and further has a film thickness of 200 to 500 nm so as to cover these.
_{A second} insulator 607 made of 2 is stacked, and the signal line 609 and the pixel electrode 6 are formed 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 with. The pixel electrode 608 is configured such that the shield electrode 617 and the shield electrode 616 that shield the scanning line in the previous stage and the second insulator 607 are kept insulated and overlap 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 that passes through the gap between the signal line 609 and the pixel electrode 608 needs to be blocked. The accuracy in bonding the second insulating substrate 612 can be lowered, 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. To simplify the drawing, only the positional relationship between the light shielding layer and the pixel electrode is shown.
(A) is a conventional liquid crystal display device, (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 in the pixel electrode due to capacitive coupling between the scanning line and the pixel electrode, a gap corresponding to the thickness of the liquid crystal layer is provided between the scanning line and the pixel electrode. Of the adjacent pixel electrodes 702 and 70
The interval L ₁ of 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.
, From both of the bonded accuracy of the substrate, L ₂ is 10μm
Was needed. Similarly in the wiring direction of the signal line, the interval L ₃ between the adjacent pixel electrodes 704 and 705 is 15 to 2
The bonding precision L ₄ of the light shielding layer 701 and the pixel electrode 704 was 0 μm, and 10 μm was required. The aperture ratio is 42 to 36% when the pixel pitch is set to 100 μm for each of X and Y. On the other hand, in the liquid crystal display device according to the present invention, as shown in FIG. 7B, the distance L ₆ between the pixel electrodes 706 and 707 and the bonding precision L ₇ between the pixel electrode 707 and the light shielding layer 708 are the same as those in the conventional case. However, in the light shielding layer in the scanning line wiring direction, the shield electrode made of metal such as chromium provided on the first insulating substrate also serves as the light shielding layer, and L ₅ is the wiring width of the scanning line. If it is 5 to 10 μm,
10 to 15 μm is sufficient.

Similar to the conventional example, when the pixel pitches of X and Y are set to 100 μm and the aperture ratio is calculated, it is 58 to 51.
%, The aperture ratio is improved by 38 to 42% or more compared with the conventional one,
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 the same as the conventional one in the X direction, but it 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 have 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, (a) is a top view and (b) is A.
Sectional drawing in A ', (c) is sectional drawing in BB'.

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

A scanning line 806 and a signal line 809 are shown in FIG.
The cross-sectional structure of the crossing part of is shown. The basic structure of the thin film transistor is the same as that of the first and second embodiments, but the drain region 803 and the signal line 809 are capacitively coupled to each other to form the signal line 8.
09 signal passes through the drain region 803 and the pixel electrode 80.
The drain electrode 803 is electrostatically shielded by the shield electrode 816 in order to prevent the data from being written in 8 to eliminate 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.
The drain electrode 803 and the pixel electrode 808 have the same potential through the contact hole 813. As a result, the storage capacitor includes a capacitor having the gate insulating film 805 sandwiched between the drain regions 803 and a capacitor having the second insulator 807 sandwiched between the pixel electrodes 808 in parallel with the shield electrode 816 as one electrode. , A sufficiently large storage capacitor can be realized with a small occupied area, and the aperture ratio is improved. The shield electrode 816 thus configured has three roles. First, as in the first and second embodiments, it functions as an electrostatic shield that prevents a DC voltage from being applied to the liquid crystal layer 810. Secondly, as in the second embodiment, the scanning lines 806 and the pixel electrodes 808 and 818 are formed. It serves as a light shielding layer for light leaking from the gap, and thirdly, it serves as a storage capacitor line that fixes the potential of one electrode of the storage capacitor.

In FIG. 9, the shield electrode 916 has tantalum,
As a second insulator 907, a cross section of a thin film transistor in which the surface of the shield electrode 916 is made of tantalum oxide that is oxidized by anodization is shown. The tantalum oxide formed by the anodic oxidation method has an insulating film that is dense and has few defects such as pinholes at room temperature, and has excellent film thickness controllability and reproducibility. As a result, the short circuit defect between the signal line 909 and the shield electrode 916 can be eliminated. Tantalum oxide has a large relative permittivity of 25 to 28, is 6 to 7 times that of SiO ₂ , and has a storage capacitor occupying area ⅙ to that in the case of using SiO ₂ .
It can be reduced to 1/7, and the aperture ratio can be further increased as compared with the above example. On the other hand, the short circuit defect of the storage capacitor can be eliminated, so that the pixel defect of the liquid crystal display device can be greatly reduced. In the second embodiment as well, if tantalum is used, it is possible to reduce the number of defects.

[0027]

EFFECTS OF THE INVENTION By virtue of having the above-mentioned constitutional requirements, the present invention can exert remarkable effects as described below. (1) The storage capacitor existing between the scanning line and the pixel electrode is charged.
The poles can electrostatically shield the scanning lines and prevent a direct current from being applied to the liquid crystal layer. In addition, capacitive coupling between the scanning line and the pixel electrode can be reduced. (2) Further, by using the storage capacitor electrode as a light shielding film,
It is possible to prevent malfunction of the transistor due to entry of light as much as possible.

First, the scanning line is electrostatically shielded by a shield electrode, prevents application of a DC voltage to the liquid crystal layer, is highly reliable for a long period of time, and has a good display quality. The device can be realized.

Secondly, the bonding accuracy of the first insulating substrate and the second insulating substrate is low, and the rationalization of bonding is achieved.
Yield can be improved.

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

Fourthly, it is possible to construct a storage capacitor of a sufficient size with a small occupied area, to increase the aperture ratio, and at the same time, to improve the definition of the liquid crystal display device and improve the display quality.

Fifth, by forming tantalum as the scanning line and tantalum oxide obtained by the anodic oxidation method as the first insulator, the short-circuit defect between the scanning line and the shield electrode can be eliminated, and a liquid crystal display device having no defect can be obtained. realizable. Similarly, if the shield electrode is made of 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 to a large-sized direct-view liquid crystal display device to a small high-definition liquid crystal display device for projection.

[Brief description of 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 a signal waveform of a general time division drive for driving a liquid crystal display device.

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

FIG. 5 is a cross-sectional view showing the 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 showing 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 showing 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 regions 103, 204, 403, 503, 603, 803, 9
03 drain regions 104, 203, 404, 504, 604, 804, 9
04 source regions 105, 205, 405, 505, 605, 805, 9
05 gate insulating film 106, 206, 406, 506, 606, 806, 9
06 scan lines 107, 607, 807, 907 second insulators 108, 208, 510, 608, 808, 702, 7
03, 704, 705, 706, 707, 818 Pixel electrodes 109, 209, 609, 809, 909 Signal lines 110, 210, 610, 810 Liquid crystal layers 111, 211, 611, 811 Common electrode 112, 212, 612, 812 Two 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 capacitor portion

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02F 1/1343 G02F 1/1368

Claims (3)

(57) [Claims] 1. A liquid crystal device comprising: a substrate; scan lines; signal lines; transistors provided corresponding to the scan lines and signal lines; and pixel electrodes provided corresponding to the transistors. Formed in the drain region of the transistor,
One electrode of the storage capacitor extending along the wiring direction of the line
And provided on the scanning line , the scanning line and the storage capacitor
One electrode and the other electrode of the storage capacitor that overlaps the region of the pixel electrode that is adjacent to the scan line, and the overlap of the pixel electrodes that are adjacent to the other electrode of the storage capacitor is in the drain region. Formed said protection
This is the one pixel electrode that overlaps with the one electrode of the holding capacity.
Of the other of the storage capacitors than the other of the pixel electrodes adjacent to
The area overlapping the electrode is widened, and the other electrode of the storage capacitor is connected to one electrode of the storage capacitor.
A liquid crystal device having a notch for connecting a pixel electrode overlapping a pole and a drain region of the transistor . 2. The liquid crystal device according to claim 1, wherein the pixel electrode has a side length in the signal line direction longer than a side length in the scanning line direction. 3. The other electrode of the storage capacitor is a light-shielding film.
The liquid crystal device according to claim 1 or 2, wherein
Place