Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-11-12
2001-10-02
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06297867
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a liquid crystal display device, and more specifically, to a wide view angle liquid crystal display device operable in an IPS (In-Plane Switching) mode.
2. Description of the Related Art
In general, there are two different modes of liquid crystal display devices (LCD). That is, in an TN (Twisted Nematic) mode LCD, a direction of a molecular axis (will be referred to as a “director” hereinafter) of oriented liquid crystal molecules is rotated along a vertical direction with respect to a substrate so as to perform an LCD display. In an IPS (In-Plane switching) mode LCD, a director of oriented liquid crystal molecules is rotated within a horizontal plane with respect to a substrate so as to execute an LCD display.
As to the IPS mode of the LCD device, even when a visual point is moved, only the short axial direction of the liquid crystal molecules is basically observed. As a result, the wide view angle can be achieved without view angle dependency of “rising ways” of the liquid crystal molecules, as compared with a TN mode of a liquid crystal display. As a consequence, such an IPS mode of a liquid crystal display device will be called a “wide view angle liquid crystal display device”.
Conventionally, in this sort of wide view angle liquid crystal display device, as described in, for instance, Japanese Patent Laid-open Application No. Hei6-148595 published in 1994, the pixel electrodes and the common electrodes, which are used to apply the electric field to the liquid crystal are provided in such a manner that these electrodes are arrayed in a predetermined interval within the same plane. The electric field is applied between both the pixel electrode and the common electrode in a parallel manner with respect to the surface of the substrate, and the director of the liquid crystal molecule is rotated within the horizontal plane so as to perform the LCD display.
FIG. 7
is a plan view for indicating the structure of one pixel employed in the liquid crystal display device as described in the above-mentioned official publication document.
FIG. 8
is a sectional view for showing this liquid crystal display device, taken along a line E to E of FIG.
7
.
FIG. 9
is a sectional view for indicating this liquid crystal display device, taken along a line F to F of FIG.
7
.
Referring to
FIG. 7
to
FIG. 9
, the structure of the conventional liquid crystal display device will be described.
In the conventional liquid crystal display device, a plurality of scanning lines
3
and a plurality of signal lines
4
are arranged in the matrix form on the transparent insulating substrate
1
. Furthermore, the common electrode line
11
is formed in parallel to the scanning lines
3
. The thin-film transistor (TFT)
6
is formed, and the pixel electrode
10
electrically connected to the source electrode of the thin-film transistor
6
is formed at the intersection portion of the scanning line
3
and the signal line
4
.
As indicated in
FIG. 7
, the stripe-shaped drawing electrodes are branched from the pixel electrode
10
and the common electrode line
11
and are extended along the direction of the signal line
4
. The drawing electrodes connected to the respective electrodes
10
and
11
are staggered in a parallel manner. When the voltage is applied to these drawing electrodes, such an electric field
100
is produced which mainly has the electric field component in parallel to the scanning line
3
, and also in parallel to the substrate surface.
Next, the above-described thin-film transistor
6
will be described more in detail with reference to FIG.
9
. This thin-film transistor
6
has such a structure, generally called as a “reverse stagger structure” that the channel layer
5
, the source electrode
10
, and the drain electrode
4
are located above the gate electrode
3
.
As indicated in
FIG. 9
, the gate electrode
3
electrically connected to the scanning line
3
is formed on the transparent insulating substrate
1
. The gate insulating film
16
is formed on the entire surface of this gate electrode
3
so as to cover this gate electrode
3
.
Then, the amorphous silicon layer
5
is formed on the gate insulating film
16
above the gate electrode
3
, and this amorphous silicon layer
5
constitutes the channel layer. The drain electrode
4
is connected to one side of the amorphous silicon layer
5
. The drain electrode
4
is electrically connected to the signal line
4
. The source electrode
4
is connected to another side of this amorphous silicon layer
5
, and the source electrode
10
is further connected to the pixel electrode
10
.
It should be noted that the n
+
type amorphous silicon layer
15
to which the n type impurity is doped in high concentration is provided among the drain electrode
4
, the source electrode
10
, and the amorphous silicon layer
5
. The reason why this n
+
type amorphous silicon layer
15
is provided is to establish to ohmic contact among the amorphous silicon layer
5
, the drain electrode, and the source electrode. Furthermore, the passivation layer
13
is provided in such a manner that this passivation layer
13
entirely covers all of these components. The TFT-sided liquid crystal orientation layer
17
used to orientate the liquid crystal molecules along the direction suitable for the liquid crystal operation mode is provided on the passivation film
13
.
The active element substrate
19
is constituted by the structural elements defined from the above-explained transparent insulating substrate
1
up to the TFT-sided liquid crystal orientation layer
17
.
In addition, the counter substrate
20
equal to the color filter (CF) is provided via the liquid crystal layer
14
opposite to this active element substrate
19
. As this counter substrate
20
, the black matrix layer
7
, the color layer
8
, and the CF-sided liquid crystal orientation layer
12
are successively stacked on the transparent insulating substrate
2
. This black matrix layer
7
is provided so as to hide the thin-film transistor
6
, the scanning line
3
, the signal line
4
, and the like with respect to the external field of this thin-film transistor
6
. The counter substrate
20
on the side of the CF-sided liquid crystal orientation layer
12
is faced to the liquid crystal layer.
The above-explained active element substrate
19
, liquid crystal layer
14
, and counter substrate
20
constitute the active matrix liquid crystal display device.
In this counter substrate
20
, when the thickness of the black matrix layer
7
becomes thick, a difference between the thicknesses of the portions within the counter substrate
20
, in which the black matrix layer
7
is present and is not present, is increased. The dimensions of the concaves/convexes formed on the substrate of the counter substrate
20
are increased. As a result, since the thickness of the liquid crystal layer
14
sandwiched between the active element substrate
19
and the counter substrate
20
is fluctuated within the panel surface, this thickness fluctuation may cause display fluctuations. To avoid such a difficulty, this black matrix layer
7
is made of a thinner metal in order that the thickness of the black matrix layer
7
can be made thinner.
Referring to
FIG. 8
, a description will be made of a structure of such a portion that the scanning line
3
is located in parallel to the common electrode line
11
. As indicated in this drawing, on the side of the active element substrate
19
, both the scanning line
3
and the common electrode line
11
are located in a parallel manner on the transparent insulating substrate
11
, on which the gate insulating film
16
, the passivation film
13
, and the TFT-sided liquid crystal orientation layer
17
are stacked. Also, on the side of the counter substrate
20
, there is provided the same structure as that shown in FIG.
9
.
On the other hand, different from the conventional TN mode of liquid crystal display device, in the conventional IPS m
Kikkawa Hironori
Miyahara Tae
Sakamoto Michiaki
NEC Corporation
Parker Kenneth
Sughrue Mion Zinn Macpeak & Seas, PLLC
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