JP2904173B2 - Active matrix type liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device, and more particularly to an active matrix type liquid crystal display device having a wide viewing angle, high contrast, and high aperture ratio.

[0002]

2. Description of the Related Art An active matrix type liquid crystal display device uses a transparent electrode formed opposite to two transparent insulating substrates as electrodes for driving a liquid crystal layer, and the direction of an electric field applied to the liquid crystal is substantially changed on the transparent insulating substrate. A twisted nematic (TN) display system in which the operation is performed in a vertical direction has been used. However, in this mode, since the liquid crystal molecules rise obliquely, the optical characteristics differ depending on the viewing angle, and there is a problem that the viewing angle is narrow. On the other hand, in a liquid crystal display device used for a large monitor or the like, there is a strong demand for a wide viewing angle, and a lateral electric field method in which a direction of an electric field applied to the liquid crystal is almost parallel to a transparent insulating substrate has been used. In this operation mode, since the liquid crystal molecules are rotated in parallel with the transparent insulating substrate, there is little change in optical characteristics depending on the viewing angle, and a wide viewing angle can be realized. A liquid crystal display device described in JP-A-7-36058 is known as a liquid crystal display device of a horizontal electric field system.

FIG. 8 is a schematic sectional view of a liquid crystal display device of a horizontal electric field type. The active matrix substrate 15 and the counter substrate 15 are integrated at a required gap by the gap material 8,
The liquid crystal 7 is filled in this gap. The active matrix substrate 15 has a common electrode 2 on the inner surface of the transparent insulating substrate 1,
The gate insulating film 3, the liquid crystal drive electrode 4, the video signal electrode 5, and the alignment film 6 are formed, and the polarizer 12 is formed on the outer surface. The opposing substrate 15 has a light-shielding film 14, a colored layer 10, and an alignment film 9 formed on the inner surface of a transparent insulating substrate 11, and a polarizing plate 13 formed on the outer surface.

In such a liquid crystal display device of the in-plane switching mode, since the distance between the common electrode 2 and the liquid crystal driving electrode 4 is important, it is particularly necessary to form the common electrode 2 and the liquid crystal driving electrode 4 at the same time. It is described in JP-A-7-36058. 9 and 10 are a plan view of an active matrix substrate and a cross-sectional view taken along the line CC for explaining the technique. In this technology, the common electrode 2 is configured by a lower common electrode 201 and an upper common electrode 202,
After simultaneously forming the scanning signal electrode 101 also serving as the gate electrode of the thin film transistor and the lower common electrode 201 on the insulating substrate 1, the gate insulating film 3 and the semiconductor film 102 are formed.
The semiconductor film 102 is processed into a desired pattern. Further, an upper common electrode 202 is formed together with the video signal electrode 5 also serving as the drain electrode 501 of the thin film transistor and the liquid crystal drive electrode 4 also serving as the source electrode 401 of the thin film transistor.

In this prior art, the electric field shielding effect can be obtained by forming the common electrode into two layers, thereby shielding the parasitic electric field which disturbs the alignment of the liquid crystal, whereby the liquid crystal alignment is disturbed by the light shielding layer. It is no longer necessary to cover the portion where the light-shielding film is formed, and the area of the light-shielding film can be reduced accordingly, and the aperture ratio can be improved.

[0006]

However, in this prior art, although the area of the light-shielding film can be reduced, a light-shielding liquid crystal drive electrode and a common electric field are provided on the active matrix substrate, and the opposing substrate is also provided. Unless a light shielding film is provided, the minimum required light shielding cannot be performed.
There is naturally a limit in improving the aperture ratio. In addition, the horizontal electric field method has a problem in that crosstalk and smore are easily generated and the contrast is low as compared with a TN liquid crystal display device. The reason is that the resistance of the common electrode is higher than that of the TN method, and it is not possible to sufficiently prevent noise on non-selected pixels due to the video signal electrode and the scanning signal electrode.

An object of the present invention is to solve the above-mentioned problems and to obtain a liquid crystal display device of a horizontal electric field type having a high aperture ratio and a high contrast.

[0008]

According to the present invention, there is provided a thin film transistor formed on a transparent insulating substrate, a scanning signal electrode connected to a gate electrode of the thin film transistor, a video signal electrode connected to a drain electrode of the thin film transistor, In a liquid crystal display device using an active matrix substrate including a liquid crystal driving electrode connected to a source electrode of the thin film transistor and a common electrode facing the liquid crystal driving electrode and the insulating substrate, the common electrode is formed in two upper and lower layers. A common electrode in the upper layer is formed in the same layer as the liquid crystal drive electrode, and a lower common electrode is formed in the gap between the upper layer common electrode and the video signal electrode and the gap between the drain electrode and the liquid crystal drive electrode. Are formed as light-shielding layers that cover the respective layers. Further, an upper layer common electrode is formed so as to straddle the scanning signal electrode, and adjacent lower layer common electrodes are electrically connected to the scanning signal electrode.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the entire structure of the liquid crystal display device of the present invention. As shown in FIG. 1, the liquid crystal display device is a display device of a horizontal electric field type, and an active matrix substrate 16 and a counter substrate 15 are formed. The gap material 8 opposes and integrates at a required gap, and the gap is filled with liquid crystal. In the active matrix substrate 16, various electrodes, a gate insulating film 3, and an alignment film 6, which will be described in detail later, are formed on the inner surface of the transparent insulating substrate 1, and the polarizing plate 12 is formed on the outer surface. The counter substrate 15 is provided on the inner surface of a transparent insulating substrate 11 with a colored layer 10 as a filter.
And an orientation film 9 are formed, and a polarizing plate 13 is formed on the outer surface.

FIG. 2 is a plan view of the active matrix substrate, and FIG. 3 is a sectional view taken along line AA in FIG. On the inner surface of the insulating substrate 1, a scanning signal electrode 101 also serving as a gate electrode and a lower common electrode 201 of the common electrode 2 are formed in a required pattern with the same conductive layer. On these electrodes, a gate insulating film 3 and a semiconductor layer 102 are formed. In particular, the semiconductor layer 102 is patterned into a required shape. A contact hole 103 is formed in the gate insulating film 3 on the lower common electrode 201, and the upper common electrode 202 and the drain electrode of the common electrode 2 formed in a required pattern on the gate insulating film 3 are formed. The video signal electrode 5 also serving as 501 and the liquid crystal drive electrode 4 also serving as the source electrode 401 are formed of the same conductive layer. Here, as schematically shown in FIG. 4, the lower layer common electrode 201 is arranged so as to fill a gap between the video signal electrode 5 and the upper layer common electrode 202 as a planar layout of the above-described electrodes and their connection. In addition, it is arranged so as to fill the gap between the drain electrode 501 and the liquid crystal driving electrode 4 and is formed so as to fill the gap between the scanning signal electrode 101 and the liquid crystal driving electrode 4. In addition, the upper common electrode 202 extends over the scanning signal electrode 101 and the contact hole 1 is formed on the adjacent lower common electrode 201.
03 are electrically connected.

Next, the operation of the liquid crystal display device configured as described above will be described. When an ON signal is input to the scanning signal electrode 101 and a video signal is input to the video signal electrode 5, electricity flows from the drain electrode 501 through the semiconductor layer 102 to the liquid crystal drive electrode 4 through the source electrode 401. Since a constant DC voltage is applied to the lower and upper common electrodes 201 and 202 for at least one frame, the liquid crystal is turned on by a potential difference between the liquid crystal driving electrode 4 and the upper and lower common electrodes 201 and 202. For example, when one frame is driven at 1/60 second and the number of scanning signal electrodes is 480, the video signal is a high frequency signal of 34.7 microseconds. Here, as described above, the liquid crystal driving electrode 4 is connected to the upper and lower common electrodes 201,
Since the high-frequency signal is disposed inside the upper and lower electrodes 202 and 202, the upper and lower common electrodes 201 and 202 have an adverse effect as noise. The influence of this noise is caused by the upper and lower common electrodes 201 and 202.
It changes depending on the product of the capacitance (C) formed between the pixel electrode 5 and the video signal electrode 5 and the resistance (R) of the common electrode.

However, in the display device of this embodiment, since the upper common electrode 202 is electrically connected to the adjacent lower common electrode 201 across the scanning signal electrode 101, the adjacent lower common electrode 201 is connected. Are connected in parallel with each other, and the resistance of the upper and lower common electrodes 201 and 202 can be sufficiently reduced to 1/100 or less. Therefore, even if the lower common electrode 201 and the video signal electrode 5 partially overlap, they are hardly affected by the high frequency video signal. Further, a light-shielding layer is formed by arranging between the scanning signal electrode 101 and the liquid crystal drive electrode 401 so as to fill a gap with a lower common electrode 201 via a drain electrode 501 which is a part of the video signal electrode 5, Sufficient light shielding can be performed without forming a light shielding film on the counter substrate 15.
As a result, a liquid crystal display device having a high aperture ratio and a high contrast is less likely to be affected by high-frequency video signals such as crosstalk and smear.

FIG. 5 is a plan view of an active matrix substrate according to a second embodiment of the present invention, and FIG. 6 is a cross-sectional view taken along the line BB. In this embodiment, a lower common electrode 201 is formed on an insulating substrate 1, and an interlayer insulating film 104 is formed thereon. A contact hole is opened in the interlayer insulating film 104, on which a video signal electrode 5 also serving as a drain electrode 501, a liquid crystal drive electrode 4 also serving as a source electrode 401,
And an upper layer common electrode 202 is formed. Further, a semiconductor film 102 is formed in a required region, and a scanning signal electrode 101 including a gate electrode is formed thereon. Also in this configuration, the lower common electrode 201 is connected to the video signal electrode 5.
Is formed so as to fill the gap between the common electrode 202 and the upper layer, and to fill the gap between the drain electrode 501 and the liquid crystal driving electrode 4 so as to fill the gap between the scanning signal electrode 101 and the liquid crystal driving electrode 4. Is done. The upper common electrode 202 straddles the scanning signal electrode 101 on the lower layer side and is electrically connected to the adjacent lower common electrode 201 through the contact hole 103.

Therefore, also in the second embodiment, since the upper common electrode 202 is electrically connected to the adjacent lower common electrode 201 across the scanning signal electrode 101, the upper and lower common electrodes 201, The resistance of the high-frequency video signal is hardly affected even if the lower common electrode 201 and the video signal electrode 5 partially overlap. Further, a light-shielding layer is formed between the scanning signal electrode 101 and the liquid crystal driving electrode 401 so as to fill a gap with a lower common electrode 201 via a drain electrode 501 which is a part of the video signal electrode 5. Thereby, sufficient light shielding can be performed without forming a light shielding film on the opposing substrate 15, and the liquid crystal display device having a high aperture ratio and a high contrast is hardly affected by high-frequency video signals such as crosstalk and smear. can get.

[0015]

Next, the first embodiment of the present invention will be described.
The description will be made according to the embodiment. Referring to FIGS.
The active matrix substrate of this embodiment has a thickness of 0.7 m.
chrome film on a glass substrate 1
A 500 ° pattern was formed, a pattern was formed by a photoresist method, unnecessary portions were removed by etching by a dry etching method, and a scanning signal electrode 101 including a gate electrode and a lower common electrode 201 were simultaneously formed. Next, the gate insulating film 3
The silicon nitride film is continuously formed by 4000Å, the amorphous silicon 3000Å and the n ⁺ amorphous silicon 300Å are continuously formed by the plasma CVD method, and the pattern is formed by the photoresist method. The n ⁺ amorphous silicon and the amorphous silicon are unnecessary by the dry etching method. The portion is removed by etching, so that the semiconductor layer 102 is formed in an island shape.

Next, a pattern of the contact hole 103 is formed in the gate insulating film 3 by a photoresist method, and the silicon nitride film is removed by a dry etching method. At this time, since the gate insulating film at the terminal portions of the scanning signal electrode 101 and the lower common electrode 201 is also removed, the number of manufacturing steps is not different from the conventional one. Next, a chromium film is formed at 1500 ° by a sputtering method, a pattern is formed by a photoresist method, unnecessary portions are removed by etching by a dry etching method, and a liquid crystal driving electrode also serving as a video signal electrode 5 also serving as a drain electrode 501 and a source electrode 401. 4 and the upper layer common electrode 202 are formed. At this time, the dry etching conditions are switched after the completion of the chromium film etching, and the n ⁺ amorphous silicon is removed. The active matrix substrate 16 formed as described above was subjected to a rubbing treatment for forming a polyimide film 500 as the alignment film 6.

On the other hand, after coloring layers 10 of three primary colors of red, green and blue are sequentially formed on an insulating substrate 11 to form a counter substrate 15, a polyimide film 500 # is formed as an alignment film 9 and rubbing treatment is performed. The active matrix substrate 16 and the opposing substrate 15 are sprayed with a spherical gap member 8 having a diameter of 5 μm and then overlapped, and the periphery is covered with a sealant except for the liquid crystal injection port, and then the liquid crystal is injected to seal the injection port. Further, the polarizers 12 and 13 were attached to the active matrix substrate 16 and the counter substrate 15 to complete the liquid crystal display device shown in FIG.
The number of scanning signal electrodes is 768, and the number of video signal electrodes is 1024.
× 3, a 15-inch XGA liquid crystal display device having a pixel pitch of 300 μm, in which the upper common electrode 202 is electrically connected to the adjacent lower common electrode 201 across the scanning signal electrode, and one lower Although the resistance of the common electrode 201 was about 20 KΩ, the resistance of the entire common electrode was as low as about 50Ω. The connection of the upper-layer common electrode 202 to every other video signal electrode 5 is to facilitate pattern formation, and is not particularly limited to this configuration.

According to the structure of this embodiment, the wiring width of the video signal electrode 5 is 8 μm, and the line width of the upper common electrode 202 is 4 μm.
μm, the distance between the video signal electrode 5 and the upper common electrode 202 is 4 μm, and the lower common electrode 201 overlaps the video signal electrode with an accuracy of 2 μm. The pitch of the video signal electrodes 5 is 100 μm (the pixel pitch is 300 μm because three colors of red, green and blue are used), and the aperture ratio is 63 to 65%.
It became. Since the resistance of the common electrode 2 is about 50Ω as a whole, the capacitance between the video signal electrode 5 and the common electrode is increased by about 50 times as compared with the conventional one, but the resistance can be reduced to about 1/400, so that high frequency such as crosstalk and smear is generated. A high aperture ratio could be realized without display defects caused by the influence of the video signal. FIG. 7 shows the aperture ratio with respect to the pixel pitch of the conventional liquid crystal display device and the liquid crystal display device of the present invention. In a conventional horizontal electric field type liquid crystal display device, an aperture ratio of only about 40% can be obtained with a pixel pitch of 300 μm. I got it.

Next, a second embodiment of the present invention will be described.
Referring to FIGS. 5 and 6, an active matrix substrate according to a second embodiment of the present invention has a chromium film formed on a glass substrate 1 having a thickness of 0.7 mm by sputtering at a thickness of 1500.degree. Is formed, and unnecessary portions are removed by dry etching to form a lower common electrode 201. Further, after forming the silicon oxide film 104 by a sputtering method, a pattern of a contact hole is formed by a photoresist method, and the silicon oxide film 1 on the lower common electrode 201 is formed by a dry etching method.
04 is removed. At this time, the silicon oxide film 104 on the terminal portion of the lower common electrode 201 is also removed.

Next, a chromium film is sputtered to a thickness of 150
0 ° is formed, n ⁺ amorphous silicon is further formed by plasma CVD, then a pattern is formed by a photoresist method, unnecessary portions of chromium and n ⁺ amorphous silicon are removed by etching by dry etching, and an image serving also as a drain electrode 501 is formed. The signal electrode 5, the liquid crystal driving electrode 4 also serving as the source electrode 401, and the upper common electrode 202 are formed. Further, after forming amorphous silicon 1000 .ANG. And silicon nitride film 3 4000 .ANG. By the plasma CVD method, and then forming chromium film 2000 .ANG. By the sputtering method, a pattern is formed by the photoresist method, and the scanning signal electrode 10 including the gate electrode is formed.
1 was formed to form an active matrix substrate. A liquid crystal display device is assembled using the active matrix substrate 16 in the same manner as in the first embodiment.

In the second embodiment, the same operation and effect as in the first embodiment can be obtained. In each of the above embodiments, chromium was used as the electrode material, but it goes without saying that the same effect can be expected using any metal material having a lower specific resistance than chromium.

[0022]

As described above, according to the present invention, the common electrode is composed of two layers, and in particular, the lower common electrode is formed by the gap between the upper common electrode and the video signal electrode, and the gap between the drain electrode and the liquid crystal drive electrode. Since the light-shielding layers are formed to cover the gaps, an effect that an aperture ratio equal to or higher than that of the TN liquid crystal display can be obtained even in the in-plane switching mode liquid crystal display device can be obtained.
Further, the upper common electrode is formed so as to straddle the scanning signal electrode, and the adjacent lower common electrode is electrically connected to the scanning signal electrode, so that the resistance of the common electrode is reduced to the conventional value. There is an effect that noise caused by a high-frequency video signal is shielded by a common electrode and crosstalk and smear do not occur, and substantial contrast can be made substantially equal to the maximum value of the TN mode liquid crystal display.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an overall configuration of a liquid crystal display device to which the present invention is applied.

FIG. 2 is a plan view of the active matrix substrate according to the first embodiment of the present invention.

FIG. 3 is a sectional view taken along the line AA in FIG. 2;

FIG. 4 is a diagram schematically illustrating a planar layout of each electrode and a connection state thereof in the first embodiment.

FIG. 5 is a plan view of an active matrix substrate according to a second embodiment of the present invention.

FIG. 6 is a sectional view taken along the line BB of FIG. 5;

FIG. 7 is a diagram for explaining the effect of the present invention.

FIG. 8 is a cross-sectional view of an example of a conventional in-plane switching mode liquid crystal display device.

FIG. 9 is a plan view of an example of an active matrix substrate of a conventional liquid crystal display device with an improved aperture ratio.

FIG. 10 is a sectional view taken along the line CC in FIG. 9;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Common electrode 3 Gate insulating film 4 Liquid crystal drive electrode 5 Video signal electrode 6 Alignment film 7 Liquid crystal 8 Gap material 9 Alignment film 10 Coloring layer 11 Insulating substrate 12, 13 Polarizer 15 Counter substrate 16 Active matrix substrate 101 Scan signal Electrode (gate electrode) 102 Semiconductor film 103 Contact hole 201 Lower common electrode 202 Upper common electrode 401 Source electrode 501 Drain electrode

Claims (4)

(57) [Claims] 1. A thin film transistor formed on a transparent insulating substrate, a scanning signal electrode connected to a gate electrode of the thin film transistor, a video signal electrode connected to a drain electrode of the thin film transistor, and connected to a source electrode of the thin film transistor. In an active matrix type liquid crystal display device using an active matrix substrate including a liquid crystal drive electrode and a common electrode opposed to the liquid crystal drive electrode on the insulating substrate, the common electrode is formed in two upper and lower layers, Is formed in the same layer as the liquid crystal driving electrode, and the lower common electrode covers the gap between the upper common electrode and the video signal electrode and the gap between the drain electrode and the liquid crystal driving electrode, respectively. An active matrix type liquid crystal display device characterized by comprising as a light shielding layer. 2. The method according to claim 1, wherein the upper layer common electrode is formed across the scanning signal electrode, and the adjacent lower layer common electrode is electrically connected to the scanning signal electrode. The active matrix liquid crystal display device according to claim 1. 3. The active matrix type liquid crystal display device according to claim 2, wherein the lower common electrode is formed in the same layer as the scanning signal electrode. 4. The active matrix type liquid crystal display device according to claim 2, wherein an upper layer common electrode is formed below the scanning signal electrode.