Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-01-31
2003-05-13
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S084000, C349S112000, C349S138000, C349S139000
Reexamination Certificate
active
06563559
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a reflective liquid crystal display (LCD) having a light diffuser.
2. Background of the Invention
Reflective LCDs, in which incident light from the viewer's direction is reflected for display, have been proposed.
FIG. 1
is a cross sectional view of such a reflective LCD.
The reflective LCD shown in
FIG. 1
comprises thin film transistors (hereinafter referred to as “TFTs”), which function as switching elements, on an insulating substrate
10
composed of a quartz glass, non-alkali glass or the like.
More specifically, on the insulating substrate (TFT substrate)
10
, gate electrodes
11
comprising a refractory metal such as chromium (Cr) or molybdenum (Mo), a gate insulating film
12
, and an active layer
13
comprising a polycrystalline silicon film are sequentially formed in that order.
In the active layer
13
, channels
13
c
are formed at positions directly above the respective gate electrodes
11
, and a source
13
s
and a drain
13
d
are formed at outer sides of the channels
13
c
by ion doping using stopper insulating films
14
above the respective channels
13
c
as a mask.
An interlayer insulating film
15
, formed by accumulating an SiO
2
film, an SiN film and an SiO
2
in that order, is disposed over the entire surface covering the gate insulating film
12
, the active layer
13
and the stopper insulating films
14
. Then, a metal such as aluminum is used to fill a contact hole located corresponding to the drain
13
d
, thereby forming a drain electrode
16
. A planarization insulating film
17
composed of an organic resin or the like is further disposed so as to cover the entire films located below for surface planarization. Another contact hole is formed in the planarization insulating film
17
at a position corresponding to the source
13
s
, and a reflective display electrode
19
composed of Al is formed on the planarization insulating film
17
. The reflective display electrode
19
contacts with the source
13
s
via this contact hole and also serves as a source electrode
18
. Then, an alignment film
20
composed of an organic resin such as polyimide for performing alignment of liquid crystal
21
is disposed on the reflective display electrode
19
.
On an opposing electrode substrate
30
composed of an insulating substrate which faces the TFT substrate
10
, at the side of the TFT substrate
10
, a color filter
31
comprising red (R), green (G), and blue (B) filters and black matrixes
32
having light shielding function, a protecting film
33
composed of a resin, an opposing electrode
34
, and an alignment film
35
are sequentially formed in that order. Further, on the other side of the opposing electrode substrate
30
, a retardation film
44
and a polarization film
45
are disposed. The opposing electrode substrate
30
and the TFT substrate
10
are adhered to each other at the periphery using a sealing adhesive (not shown) to sandwich twisted nematic (TN) liquid crystal
21
in the gap formed therebetween.
The path light travels when the above-described reflective LCD is viewed will next be described.
Referring to
FIG. 1
, as indicated by the dotted line with an arrow, natural light
100
enters the device from the polarization film
45
provided at the side of an viewer
101
, transmits sequentially through the retardation film
44
, the opposing electrode substrate
30
, the color filter
31
, the protecting film
33
, the opposing electrode
34
, the alignment film
35
, the TN liquid crystal
21
, and the alignment film
20
on the TFT substrate
10
, and is then reflected by the reflective display electrode
19
. The reflected light then passes through these layers in the reverse order and direction, and is emitted out of the device from the polarization film
45
disposed on the opposing electrode substrate
30
to reach the eyes of the viewer
101
.
Referring now to
FIGS. 2A and 2B
, the luminance measurements of reflective light in a reflective LCD will be described.
FIG. 2A
depicts a method for measuring luminance of a surface of a reflective LCD and
FIG. 2B
shows the measurement results.
As shown in
FIG. 2A
, a reflective LCD panel comprising a TFT substrate
10
and an opposing electrode substrate
30
is disposed with the display surface located above. Light entering the display panel is made to do so at a predetermined angle of inclination &thgr;in with respect to the normal direction of the display surface. This incident light
105
is reflected by a reflective display electrode. A light intensity detector
106
measures the reflected light emitted from the display panel at predetermined emission angles. More specifically, the light intensity detector
106
is moved to a position having an angle of &thgr;out with respect to the normal line (indicated by dotted line) of the LCD panel of
FIG. 2A
to detect the reflected light at the angle &thgr;out for intensity measurements.
The measurement results are shown in
FIG. 2B
by dotted lines. In
FIG. 2B
, the horizontal axis indicates a detection angle of reflected light and the vertical axis indicates the intensity of reflected light at respective detection angles.
However, as indicated by the dotted lines in
FIG. 2B
, a reflective LCD of the type described above is disadvantageous in that high intensity light is only reflected at certain detection angles, such that over a wide range of the display panel, bright display cannot be achieved.
In order to overcome this disadvantage, providing a light diffuser between the protecting film
33
and the opposing electrode
34
on the opposing electrode substrate
30
has been considered.
The relationship between the emission angle and the intensity of reflected light when the light diffuser is provided is also shown in
FIG. 2B
by a solid line. As shown, compared with the results shown by the dotted line, light with intensity can be obtained over a wider variety of angles, in other words, over a wider range, and bright display can be achieved when the light diffuser is provided.
However, at an angular range of &thgr;1 in
FIG. 2B
, the intensity of reflected light becomes low, and brightness of the display changes abruptly. This causes non-uniformity of brightness when the viewer changes the viewing angle from the normal direction to the horizontal direction. Thus, these proposed reflective LCDs still can not overcome the disadvantage that brightness of display is not uniform and depends on the viewing angle.
SUMMARY OF THE INVENTION
The present invention was made in view of the foregoing disadvantages of the related art, and aims to provide a reflective liquid crystal display (LCD) capable of achieving uniformly bright display with increased luminance for each display pixel.
In accordance with one aspect of the present invention, there is provided a reflective liquid crystal display device, comprising liquid crystal provided in a gap between first and second substrates disposed facing each other, and electrodes for driving the liquid crystal each provided on the first and second substrates at the side opposing the liquid crystal, wherein, of said electrodes, an electrode formed on one of said first and second substrates is a reflective display electrode composed of a conductive reflective material, said reflective display electrode includes, at least on a surface opposing the liquid crystal, a concave portion depressed toward said first substrate in each pixel region, and said concave portion includes a base portion and a slope portion inclined toward said base portion.
In accordance with another aspect of the present invention, in the above reflective liquid crystal display device, said reflective display electrode is formed on an insulating film having a portion concave toward said first substrate.
In accordance with still another aspect of the present invention, in the above reflective liquid crystal display device, said reflective display electrode is formed on an insulating film having a portion concave toward said first substrat
Cantor & Colburn LLP
Chowdhury Tarifur R.
Sanyo Electric Co,. Ltd.
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