JPH08297301A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To decrease disclinations and to improve the opening rate of a liquid crystal display device. CONSTITUTION: Drain wirings functioning as signal lines are obtd. by forming first drain wirings 3 formed at the same layer as the layer of gate wirings 1 in regions not intersecting the gate wirings 1 functioning as scanning lines and forming second drain wirings 4a formed at the same layer as the layer of drain electrodes 4 in regions intersecting the gate wirings 1. The first drain wirings 3 and the second drain wirings 4a are electrically connected via through- holes 6. Transparent pixel electrodes 8 are formed on the upper layer above the drain wirings 3, thereby, the transverse direction electric fields occurring by the drain wirings 3 are decreased, the reverse tilt regions by the transverse direction electric fields are narrowed, the advance of the disclinations into the pixel electrodes is suppressed and the opening rate is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to an active matrix type liquid crystal display device using thin film transistors as switching elements.

[0002]

2. Description of the Related Art Thin film transistor (hereinafter referred to as TFT)
Driven active matrix liquid crystal display device (hereinafter L
Reverse stagger (or bottom gate type) for CD)
A structured TFT is generally used.

FIG. 5A is a plan view showing an example of a conventional liquid crystal display device, FIG. 5B is a sectional view taken along the line AA 'of FIG. 5A, and FIG. It is a BB 'sectional view taken on the line a).

As shown in FIGS. 5A, 5B and 5C, a gate electrode 2 formed on a transparent insulating substrate 12, a gate wiring 1 connected to the gate electrode 2 and an insulating film 10 are formed.
A semiconductor thin film 5 formed on the gate electrode 2 via
The drain electrode 4 and the source electrode 7 connected to the semiconductor thin film 5, the drain wiring 3 formed integrally with the drain electrode 4 and intersecting the gate wiring 1 through the insulating film 10 and the source electrode 7 are connected. And the transparent pixel electrode 8 formed in this way.

[0005]

In this conventional LCD, since the transparent pixel electrode and the drain wiring are formed in the same layer, a lateral electric field (pixel electrode on the TFT substrate is formed between the transparent pixel electrode and the drain wiring). And the direction in which a voltage is applied to the liquid crystal between the opposite electrodes is defined as the vertical direction). This electric field becomes stronger in a high-definition display in which it is necessary to narrow the gap between the pixel electrode and the drain wiring. Normally, when a voltage is applied, the liquid crystal rises in the pretilt direction induced in the rubbing direction of the alignment film, but when the above-mentioned strong lateral electric field exists in the direction opposite to the pretilt direction, the liquid crystal is aligned in this electric field direction. As a result, in a region where the reverse electric field is strong, the liquid crystal rises in the direction opposite to the normal direction (reverse tilt state). When this reverse tilt is formed, as shown in FIG. 2, an alignment transition region called disclination occurs at the boundary with the normal tilt (normal tilt state) region. This disclination region transmits light during black display on a normally black LCD, resulting in a reduction in display contrast.

In order to shield the disclination region, a black matrix (hereinafter referred to as BM) layer formed of a chromium metal layer or the like formed on a color filter substrate facing the TFT has been conventionally formed. The BM layer on the counter substrate is formed with a considerable overlapping margin with the pixel electrode in order to shield the disclination region from the light due to the restriction of the overlay accuracy of the counter substrate and the TFT. Therefore, there is a problem that the aperture area ratio (aperture ratio) of the BM layer is lowered, and the display brightness is lowered, or the power consumption of the LCD is increased to compensate for it. In addition, since the disclination deeply penetrates into the pixel electrode when the lateral electric field is strong, the BM region must be wide to shield the disclination, which causes a problem that the aperture ratio is further reduced. is there.

An object of the present invention is to provide a liquid crystal display device in which disclination is prevented from entering the pixel electrode and the aperture ratio is improved.

[0008]

According to another aspect of the present invention, there is provided a liquid crystal display device, comprising: a gate wiring connected to a gate electrode arranged on a transparent insulating substrate and formed in the same layer as the gate electrode; and a surface including the gate electrode. An active structure including a thin film transistor having an inverted staggered structure having a semiconductor thin film, a source electrode, and a drain electrode arranged on the gate electrode via the formed insulating film, and a transparent pixel electrode connected to the source electrode. In the matrix type liquid crystal display device, the drain wiring which is connected to the drain electrode and intersects with the gate wiring is the same as the gate wiring in a region close to a peripheral portion of the transparent pixel electrode except a region intersecting with the gate wiring. The first drain wiring arranged in a layer and the drain electrode in the same layer as the drain electrode in a region intersecting with the gate wiring. And and a second drain wiring via a through hole provided in the insulating film connected to the first drain wire.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the drain wiring adjacent to the transparent pixel electrode is formed in the same layer as the gate wiring, and the transparent pixel electrode is arranged above the drain wiring layer. The directional electric field is reduced, and as a result, the reverse tilt region due to the lateral electric field is narrowed, and the disclination is prevented from entering the pixel electrode.

If the drain wiring is formed of a light-shielding metal such as Cr, Ta, or Al by overlapping the end of the pixel electrode and the drain wiring, it also functions as a light-shielding film. It becomes unnecessary in the area, and the aperture ratio can be improved as compared with the conventional completely opposed film light-shielding method.

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1A is a plan view showing a first embodiment of the present invention, FIG. 1B is a sectional view taken along the line CC ′ of FIG. 1A, and FIG. 1A is a cross-sectional view taken along the line DD ′, and FIG. 1D is a cross-sectional view taken along the line EE ′ of FIG.

As shown in FIGS. 1A to 1D, a Cr film is deposited on the transparent insulating substrate 12 by a sputtering method and patterned, and the gate electrode 2 and each of the gate electrodes 2 are connected to the additional capacitance element. A gate wiring 1 having 9 lower electrodes;
The drain wiring 3 is formed respectively. Next, the silicon nitride (Si
N _X) forming a semiconductor thin film 5 on the amorphous silicon (a-Si) film is deposited and patterned insulating film 10 above the gate electrode 2 on the insulating film 10 after depositing an insulating film 10 made of film To do. Next, the insulating film 10 is selectively etched to form the through hole 6 on the drain wiring 3.

Next, the semiconductor thin film 5 and the through hole 6
A Cr film is deposited on the surface including the silicon by a sputtering method and patterned, and the drain electrode 4 connected to the drain wiring 3 in the lower layer through the through hole 6 and the drain wiring 3 connected through the through hole 6 and the gate in the lower layer An upper-layer drain wiring 4a connected to the drain electrode 4 over the wiring 1 and a source electrode 7 are formed. Next, the indium tin oxide (ITO) film deposited by the sputtering method is selectively etched to form the transparent pixel electrode 8 connected to the source electrode 7, and at the same time, the additional capacitance element 9 is formed. Next, a silicon nitride film is deposited on the entire surface to form a protective film 11.

FIG. 2 is a schematic diagram showing the lines of electric force generated between the drain wiring and the transparent pixel electrode of the liquid crystal display device formed according to this embodiment and the alignment of the liquid crystal.

As shown in FIG. 2, the lines of electric force 14 reduce the lateral electric field as compared with the conventional example of FIG. 6, and the liquid crystal alignment is strongly affected by the vertical electric field between the counter electrode and the pixel electrode. Come to do. As a result, the reverse tilt region 17 becomes narrower and the range of the disclination line 16 becomes narrower.

According to the liquid crystal simulation program,
The results of simulating the alignment of the liquid crystals of the liquid crystal device of this example and the conventional liquid crystal device are shown in FIGS. 3 and 7, respectively. At this time, the potentials of the counter electrode, the transparent pixel electrode and the drain wiring are 9V, 14V and 4V, respectively. As compared with the conventional example of FIG. 7, the reverse tilt region of the present example of FIG. 3 is narrower, and the distance of the disclination line entering the transparent pixel electrode from the end of the drain wiring is 5.1 μm in the conventional example.
On the other hand, in the present embodiment, it becomes 3.8 μm.
8 μm shorter. Thus, it can be said that the present invention is more effective in suppressing the invasion of disclination into the pixel electrode.

FIG. 4A is a plan view showing a second embodiment of the present invention, and FIG. 4B is an enlarged sectional view taken along the line FF 'of FIG. 4A.

As shown in FIGS. 4A and 4B, except that a part of the periphery of the transparent pixel electrode 8 is formed on the drain wiring 3 and the drain wiring is made of a light-shielding metal. The structure is similar to that of the first embodiment, and there is an advantage that the BM for shielding the disclination provided in the color filter of the counter substrate in this portion can be omitted. The BM layer on the counter substrate is formed with a large stacking margin due to the constraint of the stacking accuracy of the counter substrate and the TFT substrate. However, by overlapping the end of the transparent pixel electrode and the drain wiring, the drain wiring serves as a light shielding layer. Also, since the BM of the counter substrate is not necessary in that region, the aperture ratio can be improved more than in the past.

[0020]

As described above, according to the present invention, the drain wiring in the region close to the transparent pixel electrode is arranged in the same layer as the gate wiring under the insulating film, and the drain wiring in the region intersecting the gate wiring is drained. It is possible to suppress the disclination from entering the pixel electrode by disposing it in the same layer as the electrode and straddling the gate wiring. Further, by forming the drain wiring and the transparent pixel electrode so as to overlap with each other, the disclination is shielded by the drain wiring, so that the BM in that portion can be omitted, and the area of the transparent pixel electrode becomes large, so that the aperture ratio is increased. It has the effect of increasing the size.

[Brief description of drawings]

1 (a) is a plan view showing a first embodiment of the present invention, FIG. 1 (b) is a sectional view taken along the line CC ′ in FIG. 1 (a), and FIG. 1 (c). 1A is a sectional view taken along the line DD ′ in FIG. 1A, and FIG. 1D is a sectional view taken along the line EE ′ in FIG.

FIG. 2 is a schematic view showing lines of electric force generated between the drain wiring and the transparent pixel electrode and alignment of liquid crystal molecules according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram showing a result of simulating the alignment of liquid crystal molecules in the liquid crystal device according to the first embodiment of the present invention.

4 (a) is a plan view showing a second embodiment of the present invention, and FIG. 4 (b) is an F- line in FIG. 4 (a).
F'line sectional drawing.

5A is a plan view showing a conventional liquid crystal display device, FIG. 5B is a sectional view taken along the line AA ′ in FIG. 5A, and FIG. It is a BB 'sectional view taken on the line in (a).

FIG. 6 is a schematic diagram showing lines of electric force generated between a drain wiring and a transparent pixel electrode and alignment of liquid crystal molecules in a conventional example.

FIG. 7 is a schematic diagram showing a result of simulating the alignment of liquid crystal molecules in a conventional liquid crystal device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 gate wiring 2 gate electrode 3,4a drain wiring 4 drain electrode 5 semiconductor thin film 6 through hole 7 source electrode 8 transparent pixel electrode 9 additional capacitance element 10 insulating film 11 protective film 12 transparent insulating substrate 13 liquid crystal molecule 14 electric force line 15 rubbing Direction 16 Disclination line 17 Reverse tilt area 18 Counter electrode 19 Counter substrate 20 Black matrix layer 21 Color filter

Claims (10)

[Claims] 1. A gate wiring connected to a gate electrode arranged on a transparent insulating substrate and formed in the same layer as the gate electrode, and an insulating film formed on a surface including the gate electrode, on the gate electrode. In an active matrix type liquid crystal display device including an inverted staggered thin film transistor having a semiconductor thin film arranged, a source electrode and a drain electrode, and a transparent pixel electrode connected to the source electrode, in the drain electrode A first drain wiring arranged in the same layer as the gate wiring in a region adjacent to a peripheral portion of the transparent pixel electrode other than a region in which a drain wiring connected to intersect the gate wiring intersects the gate wiring; Via a through hole provided in the insulating film in the same layer as the drain electrode in a region intersecting with the gate wiring. And a second drain wiring connected to the first drain wiring. 2. The liquid crystal display device according to claim 1, wherein the peripheral portion of the transparent pixel electrode is formed on the first drain wiring with an insulating film interposed therebetween. 3. A gate electrode, a drain wiring, and a gate wiring connected to the gate electrode are provided on a transparent substrate, and an insulating film is provided on the gate electrode, the gate wiring, and the drain wiring. A semiconductor thin film disposed on the gate electrode, a source electrode and a drain electrode connected to the semiconductor thin film on the insulating film, and a transparent thin film connected to the source electrode on the insulating film. A liquid crystal display device comprising a pixel electrode, the drain electrode being connected to the drain wiring through a contact hole, and a liquid crystal being sandwiched between a counter substrate having a transparent electrode on a surface thereof and the transparent substrate. 4. The liquid crystal display device according to claim 3, wherein the drain wiring is made of a light-shielding metal. 5. The liquid crystal display device according to claim 4, wherein the drain wiring partly overlaps the transparent pixel electrode via the insulating film. 6. The width of the drain wiring is overlapped on one side with the transparent pixel electrode through the insulating film, and on the other side through the insulating film to an end portion of the other transparent pixel electrode on the drain wiring side. The liquid crystal display device according to claim 4, wherein the liquid crystal display device is set to be present. 7. A switching element, a wiring connected to a first electrode of the switching element, an insulating film, and a transparent pixel electrode connected to a second electrode of the switching element on a first transparent substrate. A liquid crystal display device in which a liquid crystal is sandwiched between a second transparent substrate having a counter electrode and a first transparent substrate, and the transparent pixel electrode is on the insulating film, and the wiring is the transparent pixel. A liquid crystal display device, which is below the insulating film in a region adjacent to an electrode. 8. The liquid crystal display device according to claim 7, wherein the wiring is made of a light-shielding metal. 9. The liquid crystal display device according to claim 8, wherein the wiring partially overlaps the transparent pixel electrode with the insulating film interposed therebetween. 10. The width of the wiring is such that one side overlaps with the transparent pixel electrode via the insulating film, and the other side extends to the end of the other transparent pixel electrode on the drain wiring side via the insulating film. 9. The liquid crystal display device according to claim 8, wherein the liquid crystal display device is set to be present.