Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1998-08-17
2004-06-29
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S113000
Reexamination Certificate
active
06757032
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electronic devices such as an active matrix panel having a pixel unit comprising a plurality of pixel electrodes, cellular phone having a pixel unit, personal computers, etc., and to a method for fabricating the same.
2. Prior Art
In the field of information systems, flat panel displays such as liquid crystal panels, which converts an electric signal (image signal) into an optical signal to display images, are attracting much attention. In order to implement full color displays and animated image displays, matrix drive system is employed as the display method for the flat panel displays.
FIG. 9
shows a cross section view of a pixel unit of a conventional reflection type active matrix liquid crystal display. Shown in
FIG. 9
is a cross section diagram corresponding to a substrate known as a so-called TFT substrate. Referring to
FIG. 9
, a thin film transistor (TFT)
2
is formed per each of the pixels provided on the insulating surface of a substrate
1
. The TFT
2
comprises an active layer
3
, a gate insulating film
4
, a gate electrode
5
, and a source electrode
6
and a drain electrode
7
connected to source/drain regions of the active layer
3
.
The gate electrode
5
, the source electrode
6
, and the drain electrode
7
are each insulated and isolated from each other by a first interlayer insulating film
8
. A second interlayer insulating film
11
is provided in such a manner to cover the source electrode
6
and the drain electrode
7
. A black matrix
12
is formed on the second interlayer insulating film
11
, and a third interlayer insulating film
13
is formed in such a manner that it covers the black matrix
12
. A pixel electrode (reflecting electrode)
14
is connected to the drain electrode
7
of the TFT
2
via contact holes formed in the second and the third interlayer insulating films
11
and
13
.
After the process steps such as the formation of an orientation film and rubbing treatment, a substrate having an opposing electrode formed thereon is adhered to the element substrate shown in FIG.
9
. Thus, a cell assembly for a reflection type liquid crystal display device is completed by incorporating a liquid crystal material sealed between the substrates.
Although it appears in
FIG. 9
that the black matrix
12
is cut and separated, actually, it is formed monolithically on the interlayer insulating film
11
in a lattice-like structure, such that it clogs the interstice (space)
20
between the neighboring pixel electrodes. Thus, the black matrix
12
functions as a shield against a light incident from the interstice
20
of the pixel electrodes.
Recently, further increase in the number of pixels and higher density are required in the market of display devices such as a HDTV (high definition TV), a SXGA display, a photograph negative reader, and the like. Accordingly, much progress is being made to achieve pixels provided at finer pitches. However, as the pitches between the pixels become finer, the ratio of the interstices of pixel electrodes becomes relatively wider. Thus, the problems attributed to the interstices of the pixel electrodes are found to become no longer negligible.
A first problem which occurs due to the interstice of the pixel electrodes is described below. Referring to the reflection system panel of a conventional type shown in
FIG. 9
, the black matrix
12
is generally formed by a metallic material. Thus, when an incident light
30
is incident from the interstice
20
of the pixel electrodes, irregular reflection may undesirably occur due to the presence of black matrix
12
, or furthermore, due to the pixel electrode
14
. If such an irregularly reflected light
31
(indicated by an arrowhead) is irradiated to TFT
2
, TFT
2
may undergo degradation or generate cross talk. Moreover, as is illustrated by the case of an irregularly reflected light
32
(indicated by an arrowhead), if the light should be mixed with the reflected light from the pixel electrode
14
, there occurs problems such as a drop in contrast, and particularly, a degradation of black level.
Then, a second problem is described. In case of a liquid crystal display device, the alignment of a liquid crystal molecule is interrupted by the stepped portion at the interstice
20
between the pixel electrodes. Since the cell gap in a transmission type panel is relatively thick as to yield a value in a range of from approximately 7 to 10 &mgr;m, the step difference (the thickness of the pixel electrode) accounts for a relatively low ratio in the cell gap. Thus, the irregularity in the alignment does not greatly influence the display.
However, in case of a reflection type liquid crystal panel, the cell gap is as small as in a range of from about 2 to 4 &mgr;m. Moreover, to disintegrate the coiling of liquid crystal molecules in case of ferroelectric or antiferroelectric liquid crystal panels, the cell gap therefor is set to be 2 &mgr;m or less. It can be understood that the cell gap is extremely narrow as compared with the case of transmission type liquid crystal panels. Thus, in these liquid crystal panels, because the step difference accounting for in the cell gap becomes larger, the effect of irregularity in liquid crystal molecules greatly influences the device as to impair the contrast.
Accordingly, an object of the present invention is to provide a long-life highly reliable electronic device equipped with a pixel unit capable of high image quality display by overcoming the aforementioned problems, and further, to provide a method for fabricating the same.
Thus, the aforementioned problem can be solved by an etectronic device of a constitution comprising a plurality of active elements, an insulator layer which covers the plurality of active elements, and a pixel region having placed thereon a plurality of pixel electrodes and being formed on the insulator layer, wherein:
said insulator layer comprises a groove portion having an opening which is superposed on the interstice between the neighboring pixel electrodes; and
said groove portion, or said groove portion and said interstice between said neighboring pixel electrodes, comprise(s) an insulating light absorber buried therein.
Furthermore, the problem above can be solved by a method for fabricating an electronic device comprising a plurality of active elements, an insulator layer which covers the plurality of active elements, and a pixel region having placed thereon a plurality of pixel electrodes and being formed on the insulator layer, which comprises:
a first step of forming said plurality of pixel electrodes on said insulator layer;
a second step of forming a groove portion by removing said insulator layer that is provided to the interstice between said neighboring pixel electrodes; and
a third step of forming an insulating light absorber being buried in said groove portion.
Another constitution according to the method for fabricating an electronic device of the present invention comprises:
a first step of forming said plurality of pixel electrodes on said insulator layer;
a second step of forming a groove portion by removing said insulator layer that is provided to the interstice between said neighboring pixel electrodes;
a third step of forming an insulating light absorber which is buried in said groove portion and in the interstice between said pixel electrodes and which covers the surface of said plurality of pixel electrodes; and
a fourth step of exposing the surface of said pixel electrodes by removing at least said light absorber covering the surface of said plurality of pixel electrodes.
A still other constitution according to the method for fabricating an electronic device of the present invention comprises:
a first step of forming said plurality of pixel electrodes by forming an electrically conductive firm on said insulator layer, followed by forming a resist mask on said electrically conductive film and patterning said electrically conductive film;
a second step of forming a groove portion while leaving s
Sakakura Masayuki
Zhang Hongyong
LandOfFree
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