Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-04-20
2001-04-17
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S044000, C349S038000
Reexamination Certificate
active
06219118
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the structure of a pixel region of an active matrix display device and, more specifically, to the structure of a black matrix (BM) and auxiliary capacitors that are connected in parallel to respective pixel electrodes.
Further, the invention generally relates to the structure of a pixel region of flat panel displays that require a black matrix.
2. Description of the Related Art
Active matrix liquid crystal display devices are known, in which at least one thin-film transistor is connected to each of a number of pixel electrodes which are arranged in a matrix form, and charging and discharging of each pixel electrode is controlled by the associated thin-film transistor.
Each pixel electrode constitutes a capacitor together with a counter electrode that is opposed to the pixel electrode with a liquid crystal therebetween.
In actual operation, however, since the capacitance of the capacitor constituted by each pixel electrode portion is not sufficiently large, an auxiliary capacitor is desired. However, when an electrode of the auxiliary capacitor is made of a conductive material such as a metal, it acts as a light-shielding portion in each pixel, resulting in a decrease of the aperture ratio.
On the other hand, a light-shielding member called “black matrix” is needed around each pixel electrode.
In general, regions where source lines (wiring lines for supplying currents to the respective source regions of the thin-film transistors) and gate lines (wiring lines for applying signal voltages to the respective gate electrodes of the thin-film transistors) are arranged in a matrix form have an uneven surface. As a result, a rubbing operation on an orientation film can not be performed properly in those regions, so that the orientation of liquid crystal molecules may be disordered there. This may cause a phenomenon that light leaks undesirable or, conversely, a desired quantity of light is not transmitted around the pixels. Further, the liquid crystal may be disabled from performing a desired electro-optical operation in the above regions.
If the above phenomenon occurs, a displayed image is blurred around the pixels, to thereby impair clearness of the image as a whole.
There is known a structure for solving the above problems in which structure a light-shielding film is so formed as to cover the edges of the pixel electrodes. The light-shielding film is called “black matrix” (BM).
U.S. Pat. No. 5,339,181 discloses a structure including a black matrix. In this technique, as shown in FIG. 2C of this patent, a black matrix extending from gate lines is so formed as to overlap with the edges of pixel electrodes. This structure is adapted to form auxiliary capacitors in overlapping portions of the black matrix and the pixel electrodes.
However, the technique of this patent has the following two problems. First, since the black matrix extends from the gate lines, light shielding is not complete. This is because source lines cannot be overlapped with the black matrix to avoid crosstalk. Light leakage should be tolerated in those portions.
Second, since the black matrix occupies the same plane as the gate lines, naturally it cannot perform light shielding for the gate lines themselves. Further, the black matrix cannot perform light shielding for the source lines to avoid crosstalk as described above.
With the recent development of digital equipments, influences of electromagnetic waves from low-frequency waves to microwaves have come to cause problems. In an environment where a liquid crystal electro-optical device is used, there is concern about the influences of electromagnetic waves.
Therefore, liquid crystal display devices need to be so constructed as to be insensitive to external electromagnetic waves.
In view of the above, the above structure as described in U.S. Pat. No. 5,339,181 in which the source lines and gate lines which transmit image signals are exposed to external electromagnetic waves is not preferable, because the source lines and gate lines may serve as an antenna.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a pixel structure of an active matrix liquid crystal display device which structure enables effective light shielding by means of a black matrix.
Another object of the invention is to provide a structure capable of protecting the entire device from being influenced by external electromagnetic waves.
A further object of the invention is to form auxiliary capacitors having a necessary capacitance without reducing the aperture ratio.
According to a first aspect of the invention, there is provided a display device (as shown in
FIGS. 1 and 2
) comprising:
source lines
113
and gate lines
110
arranged in a matrix form;
at least one pixel electrode
118
disposed in each region that is enclosed by the source lines
113
and the gate lines
110
; and
a light shielding electrode
116
so disposed as to cover the source lines
113
and the gate lines
110
,
wherein a periphery of the pixel electrode
118
overlaps with the light shielding electrode
116
, and a coextending region
119
or
120
thereof serves as an auxiliary capacitor.
With this configuration, all the components other than the pixel electrode
118
and a drain electrode
106
of a thin-film transistor
103
can be shielded from incident light. In particular, the source lines
113
and the gate lines
110
can completely be shielded from the exterior. This prevents an event that external electromagnetic waves are received by the source lines
113
and the gate lines
110
to cause an erroneous or faulty operation of the device.
Auxiliary capacitors can be formed without reducing the aperture ratio.
In the above configuration, the pixel electrode
118
is a transparent conductive film made of ITO, for instance. While one pixel electrode is provided in each pixel in the basic configuration, the pixel electrode of each pixel may be divided into a plurality of parts.
The black matrix
116
, which is so disposed as to overlap with the periphery of the pixel electrode
118
, is made of titanium or chromium. The black matrix
116
serves as not only the light-shielding film but also one of the electrodes constituting an auxiliary capacitor.
It is preferable that the metal electrode
116
be so formed as to overlap with the periphery of the pixel electrode
118
over its entire circumference.
FIGS. 3A-3E
are plan views for explaining the locational relationship of each element of FIG.
2
.
According to another aspect of the invention, there is provided, as exemplified in
FIGS. 1 and 2
, a display device comprising:
source lines
113
and gate lines
110
arranged in a matrix form;
at least one pixel electrode
118
disposed in each region that is enclosed by the source lines
113
and the gate lines
110
; and
a light-shielding electrode
116
so disposed as to overlap with a periphery of the pixel electrode
118
,
wherein the pixel electrode
118
and the light-shielding electrode
116
constitute a capacitor through an insulating film
117
, and wherein the light-shielding electrode
116
exists in a different layer than the source lines
113
and the gate lines
110
.
According to a further aspect of the invention, there is provided, as exemplified in
FIGS. 1 and 2
, a display device comprising in an order as written from the side of incident light (i.e., from the top of FIG.
1
):
a pixel electrode
118
;
a light-shielding electrode
116
;
a source line
113
; and
a gate line
110
,
wherein the pixel electrode
118
and the light-shielding electrode
116
constitute a capacitor
119
or
120
in between.
In this configuration, by disposing the pixel electrode
118
closest to the incident light side and disposing the light-shielding electrode (black matrix)
116
next to the pixel electrode
118
, the underlaid source line
113
, gate line
110
, and thin-film transistor (except for a drain region
106
) can completely be shielded from incident light.
This configuration is very useful for not o
Fish & Richardson P.C.
Semiconductor Energy Laboratory Co,. Ltd.
Sikes William L.
Ton Toan
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