Transflective liquid crystal display device

Details Transflective liquid crystal display device Transflective liquid crystal display device

2000-12-06

2002-12-10

Dudek, James A. (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S114000, C349S065000

Reexamination Certificate

active

06493051

ABSTRACT:

CROSS REFERENCE
This application claims the benefit of Korean Patent Application No. 1999-55107, filed on Dec. 6, 1999, under 35 U.S.C. §119, the entirety of which is hereby incorporated by reference.
BACKGROUND
1. Field of the invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a transflective LCD device.
2. Description of Related Art
In general, liquid crystal displays are divided into transmissive LCD devices and reflective LCD devices according to whether the display uses an internal or external light source.
A typical transmissive LCD device includes a liquid crystal panel and a back light device. The liquid crystal panel includes upper and lower substrates with a liquid crystal layer interposed. The upper substrate includes a color filter, and the lower substrate includes thin film transistors (TFTs) as switching elements. An upper polarizer is arranged on the liquid crystal panel, and a lower polarizer is arranged between the liquid crystal panel and the backlight device.
FIG. 1
is a partial perspective view of a transflective color LCD device.
A transflective LCD panel
11
comprises upper and lower substrates
15
and
21
opposing each other with liquid crystal
23
interposed. On the opposing surface of the upper substrate
15
, color filters
17
having black matrix
16
and a transparent common electrode
13
are arranged sequentially.
The lower substrate
21
includes switching devices “T” and pixels “P” having pixel electrode
19
divided into transmissive portion
19
a
and reflective portion
19
b.
On the lower substrate
21
, a plurality of gate and data lines
25
and
27
are positioned like an array matrix, and switching devices “T” is introduced into a matrix type.
An area defined by two adjacent gate and data lines
25
and
27
is the pixel “P”. On the pixel “P”, the transmissive portion
19
a
of the pixel electrode
19
can be composed of a transmitting hole or a transparent electrode. For the transmissive portion, the transparent electrode is conventionally employed.
Conductive metallic material having the superior reflectivity is used for the reflective electrode becoming the reflective portion
19
a
of the pixel electrode
19
, and transparent conductive metallic material having the good transmissivity such as ITO (indium tin oxide) is used for the transparent electrode of the transmissive portion
19
a.
FIG. 2
is a cross-sectional view of the LCD device illustrating the operation principle of the transflective LCD device. As shown in
FIG. 2
, the conventional transflective LCD device
57
includes lower and upper substrates
43
and
53
with a liquid crystal layer
56
interposed there between. The upper substrate
43
has a color filter
17
(see FIG.
1
), and the lower substrate
53
includes a switching device “T” (see FIG.
1
), a transparent electrode
51
and a reflective electrode
49
. The reflective electrode
49
is made of a conductive material having a good reflectivity and surrounds a transparent electrode
51
formed therein. The transflective LCD device
57
further includes a backlight device
41
. The light transparent electrode
51
serves to transmit light “A” irradiated from the backlight device
41
and the reflective electrode
49
serves to reflect the ambient light “B”.
The transflective LCD device is operable in both a reflective mode and a transmissive mode. First, in the reflective mode, the ambient light “B” from the upper substrate
43
is reflected in the reflective electrode
49
and directs toward the upper substrate
43
again. At this time, when the electrical signals are applied to the pixel electrode (
49
and
51
) by the switching element “T” (see FIG.
1
), phase of the liquid crystal layer
56
varies and thus the reflected light is colored by the color filter
17
(see
FIG. 1
) and displayed in the form of colored light.
Further, in the transmissive mode, light “A” generated from the backlight device
41
passes through the transparent electrode
51
. At this time, when the electrical signals are applied to the pixel electrode (
49
and
51
) by the switching element “T” (see FIG.
1
), phase of the liquid crystal layer
56
varies. Thus, the light “A” passing through the liquid crystal layer
56
is colored by the color filter
17
(see
FIG. 1
) and displayed in the form of images with other colored lights.
As described above, since the transflective LCD device has both the transmissive mode and the reflective mode, the transflective LCD device can be used without depending on the time of day (e.g., noon or dusk) and has advantages that it can be used for a long time with consuming a low power.
However, the efficiency of the light from the backlight device is lowered in the transmissive mode of the transflective LCD device.
FIG. 3
is a cross-sectional view of the conventional transflective LCD device.
An upper polarizer
45
is formed on the upper substrate
43
, and the lower polarizer
47
and a retardation film
50
are formed sequentially under the lower substrate
53
. Moreover, the upper and lower substrates
43
and
53
opposing each other with liquid crystal
55
interposed. On the opposing surface of the lower substrate
53
, the reflective electrode
49
and the transparent electrode
51
are positioned.
Referring back to
FIG. 1
, an area defined by two adjacent gate and data lines
25
and
27
is the pixel “P”. On the pixel “P”, the pixel electrode
19
is comprised of the transmissive portion or transparent electrode
19
a
and the reflective portion or reflective electrode
19
b.
The LCD panel
57
having the upper substrate
43
and the lower substrate
53
divided into open region “E” and closed region “F” depending on whether the light “C” and “D” generated from the backlight device
41
can be transmitted via the LCD panel
57
. The closed region “F” includes the opaque metallic material such as the reflective electrode
49
of the pixel electrode, the gate line
25
and data line
27
(see FIG.
1
). The open region “E” includes the transparent electrode
51
of the pixel electrode.
In the transmissive mode, the light “D” generated from the backlight device
41
passes through the liquid crystal
55
and transparent electrode
51
. However, the light “C” is absorbed by the lower polarizer
47
after being reflected in the reflective electrode
49
, or a little of the light “C” passes through the liquid crystal
55
.
FIG. 4
shows the state of light while it passes through each of the components described above.
The light generated from the backlight device
41
is first converted into linearly polarized light through the lower polarizer
47
. The light, while passing through the lower polarizer
47
, is absorbed except the parallel light to the transmitting axis of the lower polarizer
47
. Therefore, the quantity of the light is being decreased.
The linearly polarized light is changed into left-circularly polarized light through the retardation film
50
having a phase difference &lgr;/4. Some of the left-circularly polarized light passes through the liquid crystal
55
(see
FIG. 3
) of the open portion “E”, and the other of the left-circularly polarized light is reflected in the reflective electrode
49
. At this time, the left-circularly polarized light is changed into the right-circularly polarized light due to the mirror effect. The right-circularly polarized light enters into the retardation film
50
again, and is converted into the linearly polarized light having a phase difference angle of 45 degrees.
That is, when the linearly polarized light enters into the lower polarizer
47
, it is perpendicular to the transmitting axis of the lower polarizer
47
. Therefore, the lower polarizer
47
absorbs most of the light.
As a result, the conventional transflective LCD device causes the decrease of the brightness since the closed portion “F” having the reflective electrode, gate line and data line absorbs the light.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a transflective liquid cr

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