Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-02-03
2001-01-09
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S039000, C349S145000
Reexamination Certificate
active
06172728
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active matrix reflective liquid crystal display device with switching elements such as thin film transistors (hereinafter simply referred to as “TFTs”). More specifically, the present invention relates to a reflective liquid crystal display device characterized by the shapes of its scanning lines, signal lines and pixel electrodes, and a method for producing the liquid crystal display device.
2. Description of the Related Art
Reflective liquid crystal display devices perform a display function by reflecting externally incident light. Since the reflective liquid crystal display devices require low consumption power and are able to provide thin displays for lightweight products, they are recently receiving much attention, for example, for use in displays of portable information terminals such as PDAs (Personal Digital Assistants).
Reflective plates of the reflective liquid crystal display device, which also serve as pixel electrodes, are flat. The flat mirror surfaces of the reflective plates may undesirably reflect objects close to the display, may cause the display to be easily affected by external scattered light, or may cause nonuniform wavelength characteristics of the reflected light due to diffraction or interference which results in coloring of the reflected light, thereby deteriorating the display quality of the device. In order to enhance the display quality of the device under the sunlight or under any kind of indoor light, Japanese Laid-Open Publication No. 7-159776 discloses a technique for providing reflective plates with uneven surfaces.
FIG. 12
is a partial plan view showing an active matrix substrate used in the reflective liquid crystal display device disclosed in the above-mentioned publication.
Referring to
FIG. 12
, the active matrix substrate includes a plurality of pixel electrodes
54
made of a metal material with a high reflectance provided in a matrix on a base substrate
60
(FIG.
13
). Gate lines
52
and source lines
53
run in an intersecting manner so as to surround each of the pixel electrodes
54
. At each intersection of the gate lines
52
and the source lines
53
, a TFT
51
is provided as a switching element connected to the pixel electrode
54
. Each gate electrode
62
(
FIG. 13
) of each TFT
51
is connected to the corresponding gate lines
52
so that the TFTs
51
are driven and controlled by signals input to the gate electrodes
62
(FIG.
13
). Each source electrode
63
(
FIG. 13
) of each TFT
51
is connected to the corresponding source line
53
so that data signals input to the source electrodes
63
(
FIG. 13
) are applied to the pixel electrodes
54
via the TFTs
51
. Lattice-like storage capacitor lines
55
(hereinafter, simply referred to as Cs lines
55
) are disposed beneath the pixel electrodes
54
via a gate insulating film
57
(FIG.
13
), thereby forming storage capacitors. The Cs lines
55
are provided with holes
55
a
, whereby the surfaces of the pixel electrodes
54
are made uneven.
FIG. 13
is a cross-sectional view showing one pixel portion of the reflective liquid crystal display device using the active matrix substrate shown in
FIG. 12
, taken along line E-E′.
With reference to
FIG. 13
, the gate electrode
62
protruding from the gate line
52
(
FIG. 12
) is provided on the base substrate
60
. The gate insulating film
57
is formed so as to cover the gate electrode
62
. A semiconductor layer
65
and n
+
Si layers
67
and
68
are formed on the gate insulating film
57
. On the thus-obtained layers, the source electrode
63
protruding from the above-described source line
53
and a drain electrode
64
which is integrated with the pixel electrode
54
are formed.
Still referring to
FIG. 13
, a counter electrode
71
is formed on a counter substrate
70
so as to face the pixel electrode
54
. A shielding film
73
is provided so as to face the TFT
51
. The base substrate
60
and the counter substrate
70
with alignment films (not shown) are disposed in an opposing manner with a liquid crystal layer
80
interposed therebetween, thereby forming a liquid crystal display device. If necessary, a color filter may be provided where the counter electrode
71
is provided. As can be seen from
FIGS. 12 and 13
, since holes
55
a
are provided through the Cs electrode
55
, the surface of the pixel electrode
54
which is formed thereon via the gate insulating film
57
reflects the holes
55
a
and becomes uneven.
In order to enhance the use of light efficiency of the liquid crystal display device shown in
FIG. 13
, the pixel electrode
54
needs to be placed as close to the gate line
52
and the source line
53
as possible, and be made as large as possible. However, at a portion where the pixel electrode
54
is close to the gate line
52
and the source line
53
, a transverse electric field may cause reverse tilted domains within the liquid crystal material which leads to poor display quality, or may cause a frequent leakage failure.
The pixel electrode
54
and the source line
53
are formed so as to overlap the gate line
52
via the insulating film
57
in order to minimize the effects caused by the above-described problems. In this case, parasitic capacitance may occur at the overlapping portion of the gate line
52
with the source line
53
and the pixel electrode
54
, thereby inducing display defects caused by, for example, cross-talk. Moreover, since the periphery of the pixel electrode
54
is straight, the display quality may be deteriorated (e.g., coloring of the reflected light) due to nonuniform wavelength characteristics of the device caused by light interference.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a reflective liquid crystal display device includes: a plurality of scanning lines; a plurality of signal lines disposed so as to intersect with the plurality of scanning lines; a plurality of pixel electrodes which also serve as reflective plates and which overlap at least one of the scanning lines and the signal lines via an interlayer insulating film; and a plurality of switching elements for driving the pixel electrodes, each provided in a vicinity of the intersection of the scanning lines and the signal lines. At least one of the scanning lines or the signal lines have at least one of bends, notches, protrusions and holes.
Accordingly, the parasitic capacitance between the lines and the pixels is reduced, thereby preventing deterioration of the display quality caused by, for example, cross-talk. By randomly patterning the signal lines, the parasitic capacitance caused between the signal lines and the pixel electrodes may be slightly different for each pixel. Thus, display unevenness caused by the offset of blocks for stepper exposures is prevented. Moreover, the nonuniform wavelength characteristics at the periphery of the pixel electrodes are minimized, thereby eliminating the influence of the light interference.
In accordance with one embodiment of the present invention, the notches of at least one of the scanning lines or the signal lines are provided in an asymmetric manner with respect to a center line along a length of each of the scanning lines or the signal lines.
Accordingly, the widths of the scanning lines and the widths of the signal lines are maintained sufficiently wide for preventing discontinuities in the scanning lines and the signal lines.
In accordance with another embodiment of the present invention, a parasitic capacitance between each of the scanning lines and each of the pixel electrodes is substantially constant.
Accordingly, a direct-current component applied to the liquid crystal material is minimized, thereby enhancing the display quality and the reliability of the liquid crystal display device.
In accordance with still another embodiment of the present invention, island-shaped portions made of at least one of the materials used for the scanning lines or the signal lines are provided in areas where the scanni
Chowdhury Tarifur R.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Sikes William L.
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