Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-06-27
2003-06-17
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S113000
Reexamination Certificate
active
06580480
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-38076, filed on Jul. 4, 2000 in Korea, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a transflective liquid crystal display (LCD) device having a color filter substrate and manufacturing method thereof.
2. Discussion of the Related Art
Generally, typical thin film transistor liquid crystal display (TFT-LCD) devices include an upper substrate and a lower substrate with liquid crystal molecules interposed therebetween. The upper substrate and the lower substrate are generally referred to as a color filter substrate and an array substrate, respectively. The upper substrate and the lower substrate respectively include electrodes disposed on opposing surfaces of the upper substrate and the lower substrate. An electric field is generated by applying a voltage to the electrodes, thereby driving the liquid crystal molecules to display images depending on light transmittance.
In accordance with the application of an internal or external light source, LCD devices are commonly classified into two categories: a transmission type and a reflection type. The transmission type LCD has a liquid crystal display panel that does not emit light, and therefore, a backlight is provided to function as a light-illuminating source. The backlight is disposed at a first or rear side of the panel, and light emitted from the backlight passes through the liquid crystal panel to be controlled by the liquid crystal panel, thereby displaying an image. That is, the liquid crystal panel display forms an image according to an arrangement of the liquid crystal molecules which transmit or interupt light emitted from the backlight. However, the backlight of the transmission type LCD consumes 50% or more of the total power consumed by the LCD device. Accordingly, the use of the backlight increases power consumption of the LCD device.
To reduce power consumption, reflection type LCD devices have been developed for portable information apparatuses that are often used outdoors or carried along with users. Such reflection type LCD devices are provided with a reflector formed on one of a pair of substrates, and ambient light is reflected from the surface of the reflector. However, visibility of the display of reflection type LCD devices is extremely poor when the surrounding environment is dark and no ambient light is available.
In order to overcome the above problems, a transflective liquid crystal display device has been proposed that utilizes both a transmissive mode display and a reflective mode display in a single liquid crystal display device. The transflective liquid crystal display (LCD) device alternatively acts as a transmissive LCD device and a reflective LCD device by making use of both internal and external light sources, thereby providing operation with low power consumption in good ambient light conditions.
FIG. 1
is a schematic cross-sectional view showing a layer structure of a typical transflective LCD device. As shown, the transflective LCD device includes an upper substrate
30
and a lower substrates
10
and a horizontally oriented liquid crystal layer
60
interposed therebetween. The lower substrate
10
has a thin film transistor (TFT) (not shown) and a pixel electrode
20
disposed on the surface facing the upper substrate
30
. The pixel electrode
20
includes reflective electrode portion
22
and a transparent electrode portion
21
disposed in an opening therebetween. The transparent electrode
21
is formed of ITO (indium-tin-oxide) or IZO (indium-zinc-oxide), and the reflective electrode
22
is made of aluminum (Al) having low electrical resistance and superior light reflectivity.
In
FIG. 1
, the upper substrate
30
includes a color filter
40
formed on the surface facing the lower substrate
10
corresponding to the pixel electrode
20
, and a common electrode
50
formed on the color filter
40
. Furthermore, a first retardation film
71
and a second retardation film
72
are formed on outer surfaces of the lower substrate
10
and the upper substrate
30
, respectively. The first retardation film
71
and the second retardation film
72
are quarter wave plates (“QWP”s). The first QWP
71
and the second QWP
72
change a polarization state of light transmitted through the liquid crystal layer
60
. Specifically, the first QWP
71
and the second QWP
72
convert linearly polarized light into right- or left-handed circularly polarized light, and conversely convert right- or left-handed circularly polarized light into linearly polarized light. A lower polarizer
81
and an upper polarizer
82
are formed on each outer surface of the first QWP
71
and the second QWP
72
, respectively. Accordingly, a transmissive axis of the upper polarizer
82
makes an angle of 90 degrees with a transmissive axis of the lower polarizer
81
. Furthermore, a backlight device
90
is disposed adjacent to the lower polarizer
81
and functions as a light source in the transmissive mode.
FIG. 2
shows operating principles of the transflective liquid crystal display device shown in FIG.
1
. The transflective LCD device depicted in
FIG. 2
includes a dispersion film
70
formed between the upper substrate
30
and the second QWP
72
to disperse the incident light (light “L” from the backlight device
90
and light “M” from the surroundings) and, thereby widens the viewing angle.
In
FIG. 2
, the light “L” generated from the backlight device
90
passes through the lower polarizer
81
and other elements on the lower substrate
10
, through the liquid crystal layer
60
, and through the upper polarizer
82
. Concurrently, ambient light “M” passes through the upper polarizer
82
and other elements on the upper substrate
30
, and then, through the liquid crystal layer
60
. Then, the ambient light “M” is reflected onto a surface of the reflective electrode
22
and is redirected up toward the upper substrate
30
, and passes back through the upper polarizer
82
. At this time, the liquid crystal layer
60
has an optical retardation (defined by (d·&Dgr;n) hereinafter) &lgr;/4 (at &lgr;=550 nm).
In the above transflective liquid crystal display device, a normally white mode is adopted. Accordingly, the transflective device displays a white color when a signal is not applied. However, only about 50% of the light generated from the backlight device
90
can pass through the upper polarizer
82
in the transmissive mode of the transflective LCD device. Accordingly, a dark gray color is produced due to the transflective LCD device operating in the reflective mode, and also because a first cell gap “d
1
” (in
FIG. 1
) of the reflective portion is substantially equal to a second cell gap “d
2
” (in
FIG. 1
) of the transmitting portion.
In
FIG. 2
, a color purity of the light passing through the color filter
40
is dependent upon a thickness of the color filter
40
. Accordingly, increasing a thickness of the color filter
40
improves the color purity of the light passing through the color filter
40
. In the transflective liquid crystal display device shown in
FIG. 2
, the ambient light “M” passes through the color filter
40
twice due to the reflection on the reflective electrode
22
, while the light “L” from the backlight device
90
passes through the color filter
40
just once. Therefore, there is a difference in color purity produced by the LCD device when operated in the transmissive mode versus operation in the reflective mode.
Furthermore, during operation of the transflective LCD device in the reflective mode, display images can only be seen in a projection direction and not in an incident direction because the ambient light “M” from the outside is reflected from the reflective electrode
22
. To overcome this problem, the light dispersion film
70
is formed on the upper substrate
30
. As a result, the manufacturing cost is raised and deterioration of display image bri
Baek Heum-Il
Ha Kyoung-Su
Kim Dong-Guk
Kim Yong-Beom
Dudek James
LG. Phillips LCD Co., Ltd.
Morgan & Lewis & Bockius, LLP
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