JP3097647B2 - 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 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 scan line 206 also serving as a gate electrode is formed above the channel region 202, and the scan 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 device has the following problems. FIG. 3 shows a signal waveform of general time-division driving for driving a liquid crystal display device.
Vg is a signal waveform applied to the scanning line 206, which is divided into a selection period T1 and a non-selection period T2. In the selection period T1, about 15 to 20 V is applied to the gate electrode of the thin film transistor to turn on the thin film transistor,
09 is applied to the pixel electrode 208.
To the liquid crystal layer 210 to write electric charges. Next, in the non-selection period T2, the thin film transistor is turned off, and the electric charge written to the liquid crystal layer 210 is held. The display signal Vsig is set to 60 to AC drive the liquid crystal layer 210.
The potential Vcom of the common electrode 211 is determined so that the alternating current has a waveform of about 80 Hz and the alternating current is accurately applied to the liquid crystal layer 210. When a twisted nematic liquid crystal is used as the liquid crystal layer 210, the amplitude of the display signal Vsig needs to be about ± 4 to 6V. On the other hand, the selection period T1 is shorter than the non-selection period T2, and when the number of scanning lines is n, T1 is generally T1 = (T1 + T2) / n. 21
During the period 1, the DC voltage V2 is applied. This V1 is divided by the interlayer insulating film 207 and the liquid crystal layer 210,
When a DC voltage is applied to the liquid crystal layer, the liquid crystal layer 210 is deteriorated, which causes a serious deterioration in display quality such as a decrease in the contrast ratio of the liquid crystal display device. If the amplitude of the display signal Vsig is ± 4 to 6V, V1 is usually larger than
-8 V, and the DC voltage applied to the liquid crystal layer 210 is 3
It becomes about 5V. Further, in the conventional configuration diagram, as shown in FIG. 2, a gate electrode protrudes from a linear scanning line 206 and a channel region 202 is formed via a gate insulating film 205.
Was formed so as to overlap. In such a configuration, the gate electrode protrudes from the pixel defined by the linear scanning line 206 and the linear signal line, so that the aperture ratio contributing to display is reduced.

An object of the present invention is to provide an active matrix type liquid crystal display device having a high aperture ratio, a high display quality and a high reliability.

[0006]

A liquid crystal device according to the present invention comprises a linear scanning line, a linear signal line crossing the scanning line, a thin film transistor connected to the scanning line and the signal line, A liquid crystal device including a pixel electrode connected to the thin film transistor and a storage capacitor, wherein a semiconductor layer serving as a source, drain, and channel region of the thin film transistor sandwiches the scanning line so as to overlap the signal line. The semiconductor layer extends from one side to the other side, and the extended semiconductor layer bends and extends along the wiring direction of the scanning line to become one electrode of the drain region and the storage capacitor. The contact hole connecting the pixel electrode and the storage capacitor are arranged along one side of the pixel electrode, and the other electrode of the storage capacitor overlaps the one electrode. While extending along one side of the serial pixel electrodes, characterized by having a portion notches correspond to the positions of formation of the contact hole. The liquid crystal device according to the present invention is characterized in that the scanning line is covered with a conductive electrode.

Further, the liquid crystal device of the present invention is characterized in that the scanning lines are covered with conductive electrodes.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

Reference Example 1 FIG. 1 shows a reference 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 channel region 102, a drain region 103, and a source region 1 of a thin film transistor are formed on a first insulating substrate 101 such as glass or quartz.
The semiconductor layer forming 04 is thermally decomposed with a monosilane gas in a 600 ° C. atmosphere by a low pressure CVD method to form polycrystalline silicon to a thickness of 25 to 50 nm. The semiconductor layer is not limited to polycrystalline silicon, but a sputtering method,
Non-quality silicon may be used by a plasma CVD method.
Heat treatment for about hours or argon laser,
Irradiation with 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 using the scanning line 106 as a mask, phosphorus ions are implanted into the semiconductor layer through the gate insulating film 105 by an ion implantation method. An N-type source region 104 and a drain region 103 are provided by implantation and self-alignment. 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. The semiconductor layer in the source region 104 and the drain region 103 is activated by irradiating the obtained laser piece to reduce the 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 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 phosphorus ions implanted in the source region 403 and the drain region 404, and when the first insulator 407 is 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.

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 an 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 anodization, and niobium, aluminum, or the like is used. The configuration can be exactly the same.

Reference Example 2 FIG. 6 shows another reference example of the liquid crystal display device according to the present invention.
(A) is a top view, (b) is a cross-sectional view at AA ′,
(C) is a sectional view taken along BB '.

A thin film transistor, a first insulating substrate 601 and a second insulating substrate 612 provided with a common electrode 611 constituting a liquid crystal display device shown in FIG. 6 are the same as in the first embodiment. The difference from Reference Example 1 is that 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 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, a light shielding layer 701 provided on the second insulating substrate and a pixel electrode 702 provided on the first insulating substrate
Means that L2 is 10 μm because of the accuracy of bonding the two substrates.
Was needed. Similarly, in the wiring direction of the signal line, the distance L3 between the adjacent pixel electrodes 704 and 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%. On the other hand, in the liquid crystal display device according to the present invention, as shown in FIG. 7B, the distance L6 between the pixel electrodes 706 and 707 and the bonding accuracy L7 between the pixel electrode 707 and the light shielding layer 708 are the same as those in the related art. In the light shielding layer in the scanning line wiring direction, a shield electrode made of a metal such as chromium provided on the first insulating substrate also serves as the light shielding layer, and L5 sets the scanning line wiring width to 5 to 10 μm. given that,
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 Reference Example 1, the scanning line is electrostatically shielded by the shield electrode, and no DC voltage is applied to the liquid crystal layer.

(Embodiment) FIG. 8 shows an embodiment of a liquid crystal display device according to the present invention.
(A) is a top view, (b) is a cross-sectional view at AA ′,
(C) is a sectional view taken along 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 that the storage capacitor 817 is replaced with 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 scanning lines 806 and signal lines 80.
9 shows a cross-sectional structure of a crossing portion 9. The basic structure of the thin film transistor is the same as that of the reference examples 1 and 2 except that the drain region 803 and the signal line 809 are capacitively coupled so that the signal of the signal line 809 passes through the drain region 803 and the pixel electrode 8
In order to prevent the data from being written to the drain electrode 08, the drain electrode 803 is electrostatically shielded by the shield electrode 816 to eliminate capacitive coupling. Further, the thin film transistor can be formed below the scanning line 806 and the signal line 809, so that the aperture ratio of the liquid crystal display device is improved. That is, the channel region of the thin film transistor can be formed below the intersection of the scanning line 806 and the signal line 809, and the source region can be formed below the signal line, so that the aperture ratio can be 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 Reference Examples 1 and 2, a role as an electrostatic shield for preventing a DC voltage from being applied to the liquid crystal layer 810. Second, as in Reference Example 2, the scanning line 806 is used.
And a third function of a storage capacitor line for fixing the potential of one electrode of the storage capacitor.

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 compared to 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. Also in Reference Example 2, if tantalum is used, a reduction in defects can be realized.

[0029]

The present invention has the following excellent effects.

Since the thin film transistor can be formed below the scanning line and the signal line and the aperture ratio can be increased, the brightness of the liquid crystal device can be remarkably improved. Thus, a sufficiently large storage capacitor can be realized, and the aperture ratio can be further improved.

[0031]

[0032]

[Brief description of the drawings]

FIG. 1 is a diagram showing a liquid crystal display device according to a first embodiment of 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

FIG. 5 is a cross-sectional view illustrating a structure of a thin film transistor according to Reference Example 1 of the present invention.

FIG. 6 is a diagram showing a liquid crystal display device according to Embodiment 2 of 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 according to a reference example 2 of the present invention.

FIG. 8 is a diagram showing a liquid crystal display according to an embodiment of the present invention.

FIG. 9 is a cross-sectional view illustrating a structure of a thin film transistor according to an example of the present invention.

[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 Second Of 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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/1368

Claims (2)

(57) [Claims] A linear scanning line, a linear signal line intersecting the scanning line, a thin film transistor connected to the scanning line and the signal line, a pixel electrode connected to the thin film transistor, and a holding device. A liquid crystal device comprising a capacitor, wherein a semiconductor layer serving as a source / drain / channel region of the thin film transistor extends from one side to the other side across the scanning line so as to overlap with the signal line; The extended semiconductor layer is bent and extended along the wiring direction of the scanning line to become one electrode of the drain region and the storage capacitor, and a contact hole connecting the drain region and the pixel electrode, and The storage capacitor is disposed along one side of the pixel electrode, and the other electrode of the storage capacitor extends along one side of the pixel electrode so as to overlap the one electrode. Both have a notch corresponding to the position where the contact hole is formed. 2. The liquid crystal device according to claim 1, wherein the scanning line is covered with a conductive electrode.