Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-08-29
2003-09-30
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S043000
Reexamination Certificate
active
06628350
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an active matrix type liquid crystal display device and a method of producing the same. More particularly, the present invention relates to a surface planarization technique for a drive substrate of such a liquid crystal display device in wiring regions in which conductive lines are formed and regions between the conductive lines.
FIGS. 8A and 8B
schematically show plan and sectional views, respectively, of a principal part of a drive substrate in a conventional active matrix type liquid crystal display device.
FIGS. 9A and 9B
schematically show plan and sectional views, respectively, of the principal part of the drive substrate in another conventional active matrix type liquid crystal display device. In these figures, same reference numbers are given to similar parts.
The structure of the conventional drive substrate shown in
FIGS. 8A and 8B
corresponds to that disclosed in JP-A-4-234820 (published in 1992). In these figures, reference numeral
12
designates a conductive line for wiring, reference numeral
13
designates a pixel electrode, reference numeral
14
designates an insulating film, and reference numeral
16
designates a substrate made up of an insulating film substrate
16
a
and under layers
16
b
formed on the insulating film substrate. This drive substrate is obtained by forming layers and patterns other than the conductive lines
12
and the pixel electrode
13
(i.e. the under layers
16
b
) on the insulating substrate
16
a
, then forming the insulating film
14
, and then forming the pixel electrode
13
on the insulating film
14
as well as forming the lines
12
. When the liquid crystal display device is a transmission type, it is required to use a transparent material for the insulating film
14
as well. Photosensitive transparent polyimide and the like are used, for example.
On the other hand, the structure of the conventional drive substrate shown in
FIGS. 9A and 9B
is formed according to the technique disclosed in JP-A-4-338718 (published in 1992). According to this prior art, in order to flush top surfaces of the lines
12
and the pixel electrode
13
, namely, to make the levels of these parts identical, a transparent insulating film
14
is placed under the pixel electrode
13
to form a convex part.
Alternatively, the lines are etched beforehand to form concave parts. Next, the lines
12
are coated with an insulating material
15
, whereby the level difference between the lines
12
and the transparent pixel electrode
13
is canceled. As the insulating material
15
, for example, polyimide is used.
In the above two prior arts, the insulating film
14
is not associated with the lines
12
(
FIGS. 8A and 8B
) or the lines
12
coated with the insulating material
15
(
FIGS. 9A and 9B
) to form a surface that is continuous at the same level. Therefore, a region in which the pixel electrode
13
is formable is limited to an upper surface of the insulating film
14
. In order to explain a reason why the region in which the pixel electrode
13
is formable is limited to an upper surface of the insulating film
14
,
FIGS. 10 and 11
show cases where the structures shown in
FIGS. 8A and 8B
and
FIGS. 9A and 9B
have been modified such that pixel electrode-forming region is expanded beyond the insulating film
14
onto the lines
12
. In
FIG. 10
, the lines
12
are directly connected to the pixel electrodes
13
, and thus, disadvantageously, the pixels are always electrically connected to the lines
12
. Further, in both of the cases of
FIGS. 10 and 11
, uneven portions (concave portions) arise in the pixel electrodes
13
due to gaps between the lines and the insulating film. Therefore, in a rubbing step conducting an orientation treatment of the liquid crystal, the orientation treatment cannot be performed uniformly due to barriers attributed to the unevenness of the pixel electrodes, resulting in a deterioration of the degree of orientation at the concave portions, namely in the gaps. Because of the reason mentioned above, the pixel electrode
13
cannot be formed on regions other than the insulating film
14
in these prior arts. This leads to a reduction in the numerical aperture, which is inconvenient for the liquid crystal display device.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an active matrix type liquid crystal display device in which a plurality of scanning lines and a plurality of signal lines are arrayed on an insulating substrate in such directions that the scanning lines intersect the signal lines, and in which pixel electrodes are flatly formed even on the scanning lines and/or the signal lines so that the numerical aperture can be improved, and also to provide a method of producing such a device.
In order to achieve the above object, there is provided a liquid crystal display device according to an aspect of the present invention in which a plurality of scanning lines and a plurality of signal lines are arrayed on an insulating substrate in such directions that the scanning lines and the signal lines intersect each other, comprising:
insulating film patterns each formed between the adjacent scanning lines and/or between the adjacent signal lines;
an upper insulating film formed on the insulating film patterns and the lines between which the respective insulating film patterns are formed, and in spaces between the insulating film patterns and the lines, said upper insulating film having a continuous top surface at a same or approximately same level; and
pixel electrodes formed on the upper insulating film.
In this liquid crystal display device, since the upper insulating film, which is formed on the lines and between the lines, has a continuous top surface at the same or approximately same level, it is possible that the whole surface of the pixel electrode also has a same or approximately same level. That is, in all the regions on the lines and between the lines, a structure planarized at an identical level is obtained. Accordingly, it becomes possible to conduct uniform orientation treatment. Also, since the upper insulating film, which is formed on the lines and between the lines, has a continuous top surface at the same or substantially same level, it becomes possible to expand the pixel electrode-forming region towards above the lines without limiting it to between the lines. Therefore, the numerical aperture can be improved.
Further, according to another aspect of the invention, there is provided a method of producing a liquid crystal display device in which a plurality of scanning lines and a plurality of signal lines are arrayed on an insulating substrate in such directions that the scanning lines and the signal lines intersect each other, comprising:
forming an insulating film pattern between the adjacent scanning lines and/or the adjacent signal lines; and
forming an upper insulating film on the insulating film patterns and the lines and in spaces between the insulating film patterns and the lines in such a manner that the upper insulating film has a continuous top surface at a same or approximately same level.
According to this method, the upper insulating film is formed on the lines and between the lines so as to have a continuous top surface at the same or approximately same level. Therefore, it becomes possible to expand the pixel electrode-forming region towards above the lines without limiting it to between the lines, and thus an improvement in the numerical aperture can be attained. Also, if the pixel electrode is formed on the upper insulating film, it is possible that the whole surface of the pixel electrode also has the same or approximately same level. Therefore, a structure planarized at an identical or approximately identical level in all the regions on the lines and between the lines is obtained. Accordingly it becomes possible to conduct uniform orientation treatment.
In order to ensure that the upper insulating film fills spaces between the insulating film patterns and the lines adjacent to the insula
Kim Robert H.
Nguyen H.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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