Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Field effect device in non-single crystal – or...
Reexamination Certificate
2001-07-27
2003-09-16
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Field effect device in non-single crystal, or...
C257S059000, C257S443000, C257S448000, C349S042000, C349S043000, C349S141000
Reexamination Certificate
active
06621102
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention pertains generally to active matrix display devices and, more particularly, relates to wiring design and electrode structure on substrates of the active matrix display devices.
2. Description of the Related Art
The prior art to which the invention is directed includes a conventionally known display device structure, in which a liquid crystal is sandwiched between two substrates, and an electric field is applied to the liquid crystal through a pair of electrodes provided on the substrates to vary optical properties of the liquid crystal for providing a visual display of information.
Operation of a liquid crystal display (LCD) having this conventionally used structure is based on molecular behaviors of the liquid crystal observed when it is subjected to an electric field. When an electric field is applied between the two substrates, molecules of the liquid crystal align with a direction parallel to, or perpendicular to, the surfaces of the substrates, for instance. Such alignment of the molecules in a specific direction causes a change in the optical properties of the liquid crystal, whereby a visual display corresponding to the applied field is obtained.
In a case where the molecules of the liquid crystal align with the field direction, or become perpendicular to the surfaces of the two substrates, the liquid crystal exhibits significant anisotropic properties with respect to the transmission of light. Optical anisotropy of this type of liquid crystal can be recognized through a comparison of images seen on an LCD screen from two different viewing angles, that is, from a direction perpendicular to the screen surface and from a direction inclined at a slight angle relative to the perpendicular direction. This optical anisotropy occurs because the line of sight aligns with crystalline axes when the LCD display is seen from the perpendicular direction, and does not align when the screen is seen from an inclined viewing angle. The anisotropic properties can be easily recognized from the fact that an image displayed on a conventional LCD device becomes unclear or dim when viewed at an oblique angle, for instance.
It is commonly known that the above phenomenon places limitations in the viewing field of the LCD device so that its angle of view is smaller than that of a cathode ray tube (CRT) or an electroluminescent (EL) display device.
To overcome the aforementioned problem, Japanese Examined Patent Application Publication No. 63-21907 discloses a structure of an LCD device, in which long axes of molecules of a liquid crystal are rotated in a plane parallel to a pair of substrates to vary optical properties of the liquid crystal. This structure provides a solution to the problem related to the viewing field as the molecular axes do not become perpendicular to the substrates.
FIG. 21
shows a display element, or pixel, of an LCD device according to a conventional structure for rotating individual molecules of a liquid crystal in a plane parallel to substrates.
The LCD device comprises gate lines
11
and source lines
12
arranged to form a grid pattern as shown in FIG.
21
. Each gate line
11
is a conductor line for transmitting a signal to a gate of a thin-film transistor
13
while each source line
12
is a conductor line for transmitting an image signal to a source of the thin-film transistor
13
. A pixel electrode
14
connected to a drain of the thin-film transistor
13
forms a comb pattern as does another electrode
15
. These electrodes
14
and
15
are arranged in such a way that individual teeth of the former lie in spaces between individual teeth of the latter. As can be seen from
FIG. 21
, the electrode
15
branches out from a conductor line
16
which is maintained at a specified voltage.
The comblike electrodes
14
and
15
thus arranged create an electric field oriented parallel to the surfaces of the substrates, and this makes it possible to cause the individual molecules of the liquid crystal to rotate in the plane parallel to the substrates.
In the structure shown in
FIG. 21
, however, part of the pixel electrode
14
runs side by side with the source line
12
in an area designated by the numeral
17
. Furthermore, part of the pixel electrode
14
runs side by side with the gate line
11
in an area designated by the numeral
18
. This type of close parallel runs in a conductor pattern is apt to induce mutual interference due to coupling between them. More specifically, signals are disturbed between the pixel electrode
14
and source line
12
, and between the pixel electrode
14
and gate line
11
, resulting in degradation in image quality.
In the structure of
FIG. 21
, individual comblike electrodes
15
in each column of the LCD device are connected together by a conductor line
16
.
FIG. 22
shows an alternative conventional structure, in which a plurality of comblike electrodes
25
in each row of an LCD device are connected together by a conductor line
26
which is maintained at a specified voltage. Even when a conductor layout shown in
FIG. 22
is employed, the problem of interference between electrodes remains unsolved though.
In the structure depicted in
FIG. 22
, gate lines
21
and source lines
22
are arranged to form a grid pattern. Each gate line
21
is a conductor line for transmitting a signal to a gate of a thin-film transistor
23
while each source line
22
is a conductor line for transmitting an image signal to a source of the thin-film transistor
23
. A pixel electrode
24
is connected to a drain of the thin-film transistor
23
. Each comblike electrode
25
branches out from the conductor line
26
which is held at the specified voltage. The electrodes
24
and
25
are arranged in such a way that individual teeth of the former lie in spaces between individual teeth of the latter. The comblike electrodes
24
and
25
thus arranged create an electric field oriented parallel to the surfaces of substrates of the LCD device.
The structure of
FIG. 22
is still apt to cause mutual interference between the pixel electrode
24
, which forms a pixel, and the source line
22
in an area designated by the numeral
27
. An area designated by the numeral
28
where the pixel electrode
24
and gate line
21
run parallel to each other is also susceptible to mutual interference.
SUMMARY OF THE INVENTION
The present invention has been made in the light of the aforementioned problems of the prior art. Accordingly, it is an object of the invention to provide a structure which can solve the problem related to limitations in the viewing field of an LCD device. It is another object of the invention to provide a structure which can solve the problem occurring when applying an electric field in a direction parallel to substrates of the LCD device, and thereby present a clear image.
To solve the aforementioned problems, an active matrix display device of the invention comprises gate lines and source lines arranged on a substrate to form together a grid pattern, thin-film transistors located in individual pixels, each of the thin-film transistors having a gate connected to one of the gate lines and a source connected to one of the source lines, first electrodes individually connected to drains of the thin-film transistors, common lines maintained at a specified voltage, and second electrodes branching out from the common lines, wherein the first and second electrodes are arranged into spiral (swirl) form with their arms wound around each other in each pixel.
In another form of the invention, an active matrix display device comprises gate lines and source lines arranged on a substrate to form together a grid pattern, thin-film transistors located in individual pixels, each of the thin-film transistors having a gate connected to one of the gate lines and a source connected to one of the source lines, first electrodes individually connected to drains of the thin-film transistors, common lines maintained at a specified voltage, and second electrodes individually
Hirakata Yoshiharu
Yamazaki Shunpei
Fish & Richardson P.C.
Flynn Nathan J.
Sefer Ahmed N.
Semiconductor Energy Laboratory Co,. Ltd.
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