Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-01-08
2003-09-16
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S117000, C349S114000
Reexamination Certificate
active
06621543
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-00398, filed on Jan. 6, 2000, under 35 U.S.C. §119, the entirety of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
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 the Related Art
In general, a transflective liquid crystal display (LCD) device selectively acts as a transmissive LCD device and as a reflective LCD device. Due to the fact that a transflective LCD device can make use of both internal and external light sources, it can operate in bright ambient light and with low power consumption.
FIG. 1
shows a typical thin film transistor liquid crystal display (TFT-LCD) device
11
. The TFT-LCD device
11
includes upper and lower substrates
15
and
21
with an interposed liquid crystal
23
. The upper and lower substrates
15
and
21
are sometimes respectively referred to as a color filter substrate and an array substrate.
On a surface facing the lower substrate
21
, the upper substrate
15
includes a black matrix
16
and a color filter layer
17
. The color filter layer
17
includes a matrix array of red (R), green (G), and blue (B) color filters that are formed such that each color filter is bordered by the black matrix
16
. The upper substrate
15
also includes a common electrode
13
over the color filter layer
17
and over the black matrix
16
.
On a surface facing the upper substrate
21
, the lower substrate
21
includes an array of thin film transistors (one being designated as TFT “T” in
FIG. 1
) that act as switching devices. The array of thin film transistors is formed to correspond with the matrix of color filters. A plurality of crossing gate and data lines
25
and
27
are positioned such that a TFT is located near each crossing of the gate and data lines
25
and
27
. The lower substrate
21
also includes a plurality of pixel electrodes
19
, each in an area defined between the gate and data lines
25
and
27
. Such areas are often referred to as pixel regions “P.”
Each pixel electrode
19
includes a transparent portion
19
a
and a reflective portion
19
b.
The transparent portion
19
a
is usually formed from a transparent conductive material having good light transmissivity, for example, indium-tin-oxide (ITO). Alternatively, the transparent portion
19
a
can be a hole. However, in
FIG. 1
a transparent conductive material is employed for the transparent portion
19
a.
Moreover, a conductive metallic material having a superior light reflectivity is used for the reflective portion
19
b.
FIG. 2
, a cross-sectional depiction of a transflective LCD device
57
, helps illustrate the operation of such devices. As shown in
FIG. 2
, the transflective LCD device
57
includes lower and upper substrates
53
and
43
and an interposed liquid crystal layer
56
. The upper substrate
43
includes a common electrode
33
. The lower substrate
53
includes transparent and reflective electrodes
51
and
49
that act as a pixel electrode. The transflective LCD device
57
also includes a backlight device
41
.
The reflective electrode
49
, made of a conductive material having a good reflectivity, surrounds the transparent electrode
51
. The transparent electrode
51
transmits light “A” irradiated from the backlight device
41
, while the reflective electrode
49
reflects the ambient light “B.”
The transflective LCD device
57
is operable in both a reflective mode and a transmissive mode. In the reflective mode, the ambient light “B” passes through the upper substrate
43
and reflects from the reflective electrode
49
back toward the upper substrate
43
. With an electrical signal applied between the common electrode
33
and the pixel electrode (reflective electrode
49
and transparent electrode
51
) by the switching element “T” (see FIG.
1
), the phase of the liquid crystal layer
56
changes. Thus, the light “B” passing through the liquid crystal layer
56
is colored by the color filter
17
(see
FIG. 1
) and is displayed as a colored pixel.
In the transmissive mode, light “A” from the backlight device
41
passes through the transparent electrode
51
. With an electrical signal applied between the common electrode
33
and to the pixel electrode (reflective electrode
49
and transparent electrode
51
) by the switching element “T” (see FIG.
1
), the phase of the liquid crystal layer
56
changes. Thus, the light “A” passing through the liquid crystal layer
56
is colored by the color filter
17
(see
FIG. 1
) and is displayed as a colored pixel.
As described above, since the transflective LCD device
57
has both a transmissive mode and a reflective mode, the transflective LCD device can be used anytime, day or night. It also has the advantage of being battery operable for a long time because of its low power drain. However, a significant amount of light from the backlight device is lost in the transmissive mode.
FIG. 3
is a cross-sectional depiction of another conventional transflective LCD device
58
. As shown, an upper retardation film
42
and an upper polarizer
45
are formed on an upper substrate
43
. A lower retardation film
50
and a lower polarizer
47
are formed under a lower substrate
53
. Moreover, a liquid crystal
55
is interposed between the upper substrate
43
and the lower substrate
53
. On the inner surface of the lower substrate
53
are reflective electrodes
49
and transparent electrodes
51
(only one of each is shown in FIG.
3
). The lower substrate
53
also includes gate and data lines
25
and
27
that define pixel regions “P” (reference FIG.
1
). The transparent electrode
51
and the reflective electrode
49
that form the pixel electrode are in a pixel region “P.”
The LCD panel
58
is divided into an open region “E” and a closed region “F,” depending on whether light “C” and “D” from a backlight device
41
passes through the LCD panel
58
. The closed region “F” is associated with an opaque metallic material, including the reflective electrode
49
and the gate lines
25
and data lines
27
(see FIG.
1
). The open region “E” is associated with the transparent electrode
51
.
In the transmissive mode of the LCD panel
58
, the light “D” passes through the transparent electrode
51
into the liquid crystal layer
55
. Most of the light “C” is absorbed by the lower polarizer
47
after being reflected by the reflective electrode
49
. However, a small amount of the light “C” does pass through the liquid crystal
55
.
FIG. 4
shows the states of the light from the backlight device as that light passes through the LCD panel
58
. The light from the lower polarizer
47
is linearly polarized. The lower polarizer
47
absorbs much of its incident light, except that part that is parallel with the transmitting axis of the lower polarizer
47
. Therefore, lower polarizer
47
significantly reduces the light density of its incident light.
The linearly polarized light that passes through the lower polarizer
47
is then changed into left-circularly polarized light by the retardation film
50
, which has a phase difference of &lgr;/4. Some of the left-circularly polarized light passes through the liquid crystal
55
associated with the open portion “E” (see FIG.
3
). The remainder of the left-circularly polarized light is reflected by the reflective electrode
49
(see
FIG. 3
) and is changed into right-circularly polarized light due to a mirror effect. The right-circularly polarized light then enters into the retardation film
50
again, where it is converted into linearly polarized light having a phase difference angle of &lgr;/4.
Moreover, when the linearly polarized light from the retardation film
50
enters the lower polarizer
47
, the phase of the linearly polarized light is perpendicular to the transmitting axis of the lower polarizer
47
. Therefore, the lower polarizer
47
absorbs most of that light.
As a result, the conventional transflective LCD device suffers a se
Kim Robert H.
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
Nguyen Hoan
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