Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-09-26
2004-02-24
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S122000
Reexamination Certificate
active
06697136
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to the technical field of a liquid crystal device having a structure comprising pixel electrodes arranged in a matrix, and particularly to the technical field of a liquid crystal device having a structure comprising a planarized interlayer insulating film provided below pixel electrodes.
2. Description of Related Art
As shown in
FIG. 11
, a conventional liquid crystal device
400
comprises a liquid crystal layer
50
held between a counter substrate
300
and a TFT array substrate
200
.
FIG. 10
is a plan view showing a TFT array substrate of a liquid crystal device, and
FIG. 11
is a longitudinal sectional view of the liquid crystal device taken along line B-B′ in
FIG. 10
, showing the vicinity of the region between adjacent pixel electrodes arranged along the data line direction.
As shown in
FIGS. 10 and 11
, the TFT array substrate
200
comprises a plurality of scanning lines
3
and a plurality of data lines
6
, which are arranged to cross each other on a substrate
10
made of quartz, glass, or the like, a thin film transistor and a pixel electrode
9
a
electrically connected thereto at each of the intersections of the scanning lines
3
and the data lines
6
, and capacitance lines
3
b
arranged in parallel with the scanning lines. Each of the thin film transistors comprises a semiconductor layer
1
shown by a dotted line, a gate insulating film
2
, and a gate electrode
3
a
which comprises a portion of the scanning lines
3
. Each of the pixel electrodes
9
a
is electrically connected to the semiconductor layer
1
through a contact hole
8
, and a part of each of the data lines
6
functions as a source electrode
6
a
, and is electrically connected to the semiconductor layer
1
through a contact hole
5
.
As shown in
FIG. 11
, in the TFT array substrate
200
, a light shielding film
11
a
patterned in a predetermined shape, a base insulating film
12
, the semiconductor film
1
formed in a predetermined shape, the gate insulating film
2
, the scanning lines
3
and capacitance lines
3
b
, and an interlayer insulating film
4
are successively laminated on the substrate
10
. Furthermore, the data lines
6
(not shown in FIG.
11
), an interlayer insulating film
7
arranged to cover the data lines
6
, and the pixel electrodes
9
a
are successively laminated on the interlayer insulating film
4
.
On the other hand, the counter substrate
300
comprises a counter electrode
21
formed over the entire surface of the lower side.
In the liquid crystal device, the optical properties of liquid crystal molecules of the liquid crystal layer
50
located between the counter electrode
21
and the pixel electrodes
9
a
are changed by a potential difference between the voltage applied to the counter electrode
21
and the voltage applied to each of the pixel electrodes
9
a.
In the conventional liquid crystal device, in order to improve the display properties, the interlayer insulating film
7
provided below the pixel electrodes
9
a
is planarized to planarize the surface of the liquid crystal layer side of the TFT array substrate, preventing orientation defects from occurring in the liquid crystal molecules due to surface steps.
As shown in
FIG. 11
, for example, when voltages of different magnitudes are applied to the adjacent pixel electrodes
9
a
, transverse electric field C occurs in the vicinities of the regions between the adjacent pixel electrodes
9
a
. As a result, in the vicinities of the regions between the adjacent pixel electrode
9
a
, the direction of the liquid crystal molecules
50
a
are affected by the direction of the transverse electric field C. Therefore, the liquid crystal molecules in the vicinities of the regions between the adjacent pixel electrodes are not oriented in the desired direction, thereby causing orientation defects. In the defective liquid crystal orientation regions, the orientation direction of the liquid crystal molecules differs from that of regions where the liquid crystal molecules are normally oriented without being affected by the transverse electric field. As a result, bright lines referred to as “disclination lines” occur, causing the problem of deteriorated display quality of the liquid crystal device. In addition, the pitch of the pixel electrodes has been recently decreased to increase the definition of the liquid crystal device, making the problem more serious.
Furthermore, a light shielding film
23
formed on the counter substrate side in order to conceal such display defects has the problem of significantly decreasing the aperture ratio of the pixel region.
The invention has been designed in consideration of the above-described problems, and one object of the invention is to provide a liquid crystal device causing no display defect and having a high aperture ratio.
SUMMARY OF THE INVENTION
One aspect of the invention relates to a liquid crystal device having a liquid crystal layer held between first and second substrates. A counter electrode is provided on the first substrate. Provided on the second substrate are pixel electrodes arranged in a matrix, switching elements respectively connected to the pixel electrodes, a lower interlayer insulating film having a planarized film and arranged on the switching elements, data lines provided on the lower interlayer insulating film, and a second interlayer insulating film arranged on the data lines below the pixel electrodes. A pattern film is arranged on the lower interlayer insulating film below the pixel electrodes so that the pattern film is located in the regions between the adjacent pixel electrodes arranged along the data lines or scanning lines.
In the above aspect of the invention, the pattern film is provided on the planarized surface of the substrate so that in the vicinities of the regions between adjacent pixel electrodes arranged along the scanning lines or the data lines, the magnitude of a longitudinal electric field produced between the end of each of the pixel electrodes and the counter electrode in the thickness direction of the liquid crystal layer is higher than that of an electric field (referred to as a “transverse electric field” hereinafter) produced between the adjacent pixel electrodes in the transverse direction. Namely, by arranging the pattern film on the planarized substrate surface in the vicinities of the regions between the respective pixel electrodes, the distance between the pixel electrodes and the counter electrode in the vicinities of the regions between the respective pixel electrodes can be controlled easily. In addition, the thickness of the pattern film can be set to any desired value so that the distance between the pixel electrodes and the counter electrode can be set to a desired value to control the magnitude of the longitudinal electric field. This aspect of the invention has the effect of preventing orientation defects from occurring, due to the transverse electric field, and obtains a liquid crystal device having high display quality.
This aspect of the invention is particularly effective for a liquid crystal display which has significant display defects due to the transverse electric field, and which include a planarized second substrate. The pattern film having any desired thickness is arranged at a specified position of the second substrate having the planarized surface, to positively provide steps in the surface and prevent the occurrence of the transverse electric field between the pixel electrodes, thereby obtaining a liquid crystal device causing no display defect due to the transverse electric field.
The pattern film preferably is part of the same film that forms the data lines. This construction permits the simultaneous formation of the data lines and the pattern film, and thus the pattern film can be formed only by changing a pattern mask without increasing the number of the manufacturing steps.
A liquid crystal device according to this aspect of the invention includes a liquid crystal layer held between first and sec
Dudek James
Seiko Epson Corporation
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