Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2001-10-30
2004-04-06
Flynn, Nathan J. (Department: 2826)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S113000, C349S114000, C349S138000, C349S139000, C257S059000, C257S072000
Reexamination Certificate
active
06717632
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-0063915, filed on Oct. 30, 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 that transmit or interrupt 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 transmissive and reflective mode displays 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 upper and lower substrates
30
and
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 portions
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) having high light transmittance, and the reflective electrode
21
is made of aluminum (Al) having low electrical resistance and superior light reflectance.
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, first and second retardation films
71
and
72
are formed on outer surfaces of the lower and upper substrates
10
and
30
, respectively. The first and second retardation films
71
and
72
are quarter wave plates (QWPs). The first and second QWPs
71
and
72
change a polarization state of light transmitted through the liquid crystal layer
60
, specifically, 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. Lower and upper polarizers
81
and
82
are formed on each outer surface of the first and the second QWPs
71
and
72
, respectively. Here, a polarization axis of the upper polarizer
82
makes an angle of 90 degrees with a polarization 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.
However, since the transflective LCD device is designed on the basis of the reflective mode, the transmittance of the transmissive mode is only about 50% of that of the reflective mode without the applying voltage the liquid crystal layer. Therefore, the transmittances of the reflective and transmissive modes can be the same by making the liquid crystal layer of the transmissive area thicker than that of the reflective area.
FIG. 2
is a schematic cross-sectional view showing the array substrate of the transflective LCD device as described above.
The region of the array substrate is divided into transmissive and reflective areas. As shown, the gate electrode
121
is patterned on the insulating substrate
110
and the gate insulator
130
is formed thereon. The active layer
140
of amorphous silicon is patterned on the gate insulator
130
and the source and drain electrodes
151
and
152
are patterned thereon. The ohmic contact layer (not shown) is interposed between the active layer
140
and the source and drain electrodes
151
and
152
. The source and drain electrodes
151
and
152
are covered with the first passivation layer
160
of the organic insulator, which includes the first contact hole
161
that exposes the drain electrode
152
and the first transmissive hole
162
at the position corresponding to the transmissive area. Since the liquid crystal layer of the transmissive area is thicker than that of the reflective area due to the first transmissive hole
162
, the brightness of the transmissive and reflective modes can be made uniform. It is desirable to make the thickness of the transmissive area twice as that of the reflective area. The transmissive electrode
170
of the transparent conducting material is patterned on the first passivation layer
160
and connected with the drain electrode
152
through the first contact hole
161
. The second passivation layer
180
of a material such as silicon nitride (SiNx) is formed on the transmissive electrode
170
and includes a second contact hole
181
that exposes the transmissive electrode
170
on the first contact hole
161
. The reflective electrode
190
is patterned on the second passivation layer
180
and connected with the transmissive electrode
170
through the second contact hole
181
. Furthermore, the reflective electrode
190
includes the second transmissive hole
191
that exposes the transmissive electrode
170
on the first transmissive hole
162
and can be made of the aluminous metal of low resistance and high reflectance.
Consequently, in the transflective LCD devices, the transmittance of the transmissive mode can be made nearly the same as that of the reflective mode by forming the hole at the transmissive area of the organic insulator and making the thickness of the liquid crystal layer at the transmissive area twice that at the reflective area.
However, since the thickness of the liquid crystal layer increases by the depth of the first and second contact holes
161
and
181
, the light efficiency of the area on the co
Ha Kyoung-Su
Kim Woong-Kwon
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge
Sefer Ahmed N.
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