Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-07-13
2003-01-07
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S042000, C349S043000, C349S113000
Reexamination Certificate
active
06504593
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflection type liquid crystal display device of a normally white mode, which employs a thin film transistor (referred to hereinafter as TFT) and a reflective display electrode connected to the TFT.
2. Description of the Related Art
In recent years, effort has been directed towards research and development of a reflection type liquid crystal display device with a reflective display electrode in which an image is displayed by reflecting incident light from the observer side.
A reflection type liquid crystal display device of a normally white mode using a conventional TFT is described below.
In the present application, a “normally” white mode refers to the liquid crystal orientation mode in which light is transmitted when no voltage is applied to the liquid crystal.
A reflection type liquid crystal display device is a display device in which an image is displayed by reflecting incident light from the observer side with a reflective display electrode.
FIG. 1
is a plan view showing an area around a display pixel region in a conventional reflection type liquid crystal display device.
FIG. 2
is a cross-sectional view taken along line B—B in FIG.
1
.
As shown in
FIG. 1
, a gate signal line
51
which includes gate electrodes
11
in portions thereof is provided for supplying a gate signal to a gate. A drain signal line (data signal line)
52
which includes drain electrodes
16
in portions thereof is provided for supplying a drain signal to a drain. A TFT is provided near an intersection of the gate signal line and the drain signal line. In the TFT, the gate
11
is connected to the gate signal line
51
, the drain
13
d
is connected to the drain signal line
52
, and the source
13
s
is connected to a reflective display electrode
20
.
As shown in
FIGS. 1 and 2
, sequentially provided on an insulator substrate
10
made of a material such as quartz glass or non-alkali glass are first gate electrodes
11
composed of a refractory metal such as Cr or Mo, a gate insulating film
12
composed of an SiN film and SiO
2
film, and an active layer
13
formed with poly-silicon film in discrete island patterns.
The active layer
13
includes channels
13
c
provided above the first gate electrodes
11
. The active layer
13
further includes a source
13
s
and a drain
13
d
formed by ion doping on the respective sides of the channels
13
c.
A stopper insulating film
14
made of SiO
2
film is provided over the channels
13
c
to function as the mask covering the channels
13
c
such that ions do not enter into the channels
13
c
during ion doping.
Furthermore, an interlayer insulating film
15
is formed on the entire surface over the gate insulating film
12
, the active layer
13
, and the stopper insulating film
14
, by sequential lamination of a SiO
2
film, a SiN film, and a SiO
2
film.
A contact hole formed in the interlayer insulating film
15
in a position corresponding to the drain
13
d
is filled with metal sing Al only, or by sequentially depositing Mo and Al, to thereby form a drain electrode
16
.
The drain signal line
52
is disposed on the interlayer insulating film
15
. Furthermore, a planarizing insulating film
19
made of a material such as an organic resin is provided on the entire surface.
As shown in
FIG. 2
, a contact hole is formed in the planarizing insulating film
19
in a position corresponding to the source
13
s
. A reflective display electrode
20
that contacts the source
13
s
through this contact hole is formed using a reflective and conductive material such as Al. The reflective display electrode
20
simultaneously serves as a source electrode. An alignment layer
21
for orienting the liquid crystal
36
is provided further on top.
A counter electrode substrate
30
has, on the side facing the insulator substrate
10
and the liquid crystal
36
, color filters
31
for each of red (R), green (G), and blue (B), a counter electrode
32
, and an alignment layer
33
. Provided on the other side of the substrate
30
are a retardation film
34
and a polarizer
35
. The insulator substrate
10
provided with TFTs in the above-described manner and the counter electrode substrate
30
are sealed by surrounding the substrates with a sealing adhesive. The gap created between the two substrates is then filled with liquid crystal
36
to complete the liquid crystal display device.
According to a conventional reflection type liquid crystal display device such as that described above, the reflective display electrodes
20
are arranged such that the gaps between adjacent electrodes
20
lie above the gate signal lines
51
and the drain signal lines
52
, as shown in FIG.
1
. In the example of
FIG. 2
, referring to a drain signal line
52
having drain electrodes as portions thereof, a gap between adjacent reflective display electrodes
20
is arranged above the drain signal line
52
.
In this arrangement, incident light
101
from a light source (the side of an observer
100
) transmits through the polarizer
35
, the retardation film
34
, the counter electrode substrate
30
, the alignment layer
33
, the liquid crystal
36
, the alignment layer
21
, and the planarizing insulating film
19
to reach the drain signal line
52
. The incident light
101
is then reflected by the drain signal line
52
through a reverse path, namely, the path indicated by a dotted line
102
, to radiate out of the polarizer
35
. More specifically, incident light
101
entering through the abovementioned path is reflected by the drain signal line
52
composed of Al having a reflectance of approximately 95% or more, and reflected light
102
is therefore constantly observed by the observer
100
.
In this way, a conventional reflective liquid crystal display device of a normally white mode is disadvantageous in that, even when a black image is displayed, the reflected light
102
generates display defects in the form of white lines along the drain signal lines
52
, thereby decreasing contrast.
A further disadvantage is that the aperture ratio is small because the reflective display electrodes
20
are not formed in areas in which the TFTs are provided.
SUMMARY OF THE INVENTION
The present invention was created in light of the above problems. The purpose of the present invention is to provide a reflection type liquid crystal display device of a normally white mode having a high aperture ratio, in which generation of display defects due to reflection of incident light by signal lines is prevented when a black image is displayed on the device.
The reflection type liquid crystal display device according to the present invention is a reflection type liquid crystal display device of a normally white mode comprising a substrate having a gate signal line and a data signal line arranged to intersect one another, and a plurality of display pixel regions defined by the gate signal line and the data signal line. Each display pixel region includes a thin film transistor connected to the gate signal line and the data signal line, and a reflective display electrode connected to the thin film transistor. The reflective display electrode covers an area in which the thin film transistor is formed, and extends into an adjacent display pixel region located beyond the gate signal line. A gap between the reflective display electrodes in the display pixel regions located adjacent to one another on either side of the gate signal line is positioned in an offset arrangement from the position in which the gate signal line is formed.
In another aspect, the reflection type liquid crystal display device according to the present invention is a reflection type liquid crystal display device of a normally white mode comprising a substrate having a gate signal line and a data signal line arranged to intersect one another, and a plurality of display pixel regions defined by the gate signal line and the data signal line, each display pixel region including a thin film transistor connected to the gate signal l
Noritake Kazuto
Sano Keiichi
Cantor & Colburn LLP
Chowdhury Tarifur R.
Sanyo Electric Co,. Ltd.
Sikes William L.
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