Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-12-31
2004-10-26
Thomas, Tom (Department: 2815)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000, C349S113000, C349S114000
Reexamination Certificate
active
06809791
ABSTRACT:
CROSS REFERENCE
This application claims the benefit of Korean Patent Applications No. 2001-4937, filed on Feb. 1, 2001 and No. 2001-5044, filed on Feb. 2, 2001, 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 device, and more particularly to a transflective liquid crystal display device.
2. Description of Related Art
Recently, liquid crystal display (LCD) devices with light, thin, and low power consumption characteristics are used in office automation equipment and video units and the like. Such LCDs typically use a liquid crystal (LC) interposed between upper and lower substrates with an optical anisotropy. Since the LC has thin and long LC molecules, the alignment direction of the LC molecules can be controlled by applying an electric field to the LC molecules. When the alignment direction of the LC molecules is properly adjusted, the LC is aligned and light is refracted along the alignment direction of the LC molecules to display images.
In general, LCD devices are divided into transmissive LCD devices and reflective LCD devices according to whether the display device uses an internal or external light source.
A conventional transmissive LCD device includes an LCD panel and a backlight device. The incident light from the backlight is attenuated during the transmission so that the actual transmittance is only about 7%. The transmissive LCD device requires a high, initial brightness, and thus electrical power consumption by the backlight device increases. A relatively heavy battery is needed to supply a sufficient power to the backlight of such a device, and the battery can not be used for a lengthy period of time.
In order to overcome the problems described above, the reflective LCD has been developed. Since the reflective LCD device uses ambient light instead of the backlight by using a reflective opaque material as a pixel electrode, it is light and easy to carry. In addition, the power consumption of the reflective LCD device is reduced so that the reflective LCD device can be used as an electric diary or a PDA (personal digital assistant).
However, the reflective LCD device is affected by its surroundings. For example, the brightness of ambient light in an office differs largely from that of the outdoors. Therefore, the reflective LCD device can not be used where the ambient light is weak or does not exist. In order to overcome the problems described above, a transflective LCD device has been researched and developed. The transflective LCD device can be transferred according to the user's selection from the transmissive mode to the reflective mode, or vise versa.
FIG. 1
is a schematic perspective view of a conventional transflective LCD device
11
.
In
FIG. 1
, the conventional transflective 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
18
. The color filter layer
18
includes a matrix array of sub-color fiters
17
of red (R), green (G), and blue (B) 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
18
and over the black matrix
16
. On a surface facing the upper substrate
15
, the lower substrate
21
includes an array of thin film transistors (TFTs) “T” that act as switching devices. The array of TFTs 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 transmissive portion “A” and a reflective portion “C”. The transmissive portion “A” is usually formed from a transparent conductive material having a good light transmittance, for example, indium-tin-oxide (ITO). Moreover, a conductive metallic material having a superior light reflectivity is used for the reflective portion “C”.
FIG. 2
is a schematic cross-sectional view of a conventional transflective LCD device such as the device
11
of FIG.
1
.
In
FIG. 2
, upper and lower substrates
15
and
21
are facing and spaced apart from each other and a liquid crystal layer
23
is interposed therebetween. A backlight apparatus
45
is disposed over the outer surface of the lower substrate
21
. On the inner side of the upper substrate
15
, a color filter layer
18
for passing only the light of a specific wavelength and a common electrode
14
functioning as one electrode for applying a voltage to the liquid crystal layer
23
are subsequently formed. On the inner surface of the lower substrate
21
, a pixel electrode
32
functioning as the other electrode for applying a voltage to the liquid crystal layer
23
, a passivation layer
34
having a transmissive hole
31
exposing a portion of the pixel electrode
32
, and a reflective plate
36
are subsequently formed. An area corresponding to the reflective plate
36
is a reflective portion “C” and an area corresponding to the portion of the pixel electrode
32
exposed by the transmissive hole
31
is a transmissive portion “A”.
A cell gap “d
1
” at the transmissive portion “A” is about twice of a cell gap “d
2
” at the reflective portion “C” to reduce the light path difference. A retardation “&Dgr;n ·d” of the liquid crystal layer
23
is defined by a multiplication of refractive index anisotropy “&Dgr;n” with a cell gap “d” and the light efficiency of the LCD device is proportional to the retardation. Therefore, to reduce the difference of light efficiencies between the reflective and transmissive modes, the retardations of the liquid crystal layer
23
at two portions should be nearly equal to each other by making the cell gap of the transmissive portion lager than that of the reflective portion.
However, even though the light efficiencies of the liquid crystal layer between the reflective and transmissive modes become equal by making the cell gaps different, the light passing the color filters at different locations is different so that the brightness can be different at the front of the display device. The transmittance of the color filter resin whose absorption coefficient is high for a specific wavelength and low for the other wavelengths has the following relation considering only the absorption, i.e., the transmittance is inversely proportional to the absorption coefficient and the distance that light passes:
T
=exp(−&agr;(&lgr;)
d
)
where T is transmittance, &agr;(&lgr;) is an absorption coefficient depending on the wavelength and d is a distance that light passes.
Since the color filter resin is a viscous material, the thickness of the color filter resin is hard to control and the color filter layer can not be made less than a specific thickness. Therefore, the color filter layers of the reflective and transmissive portions have the same thickness and the different absorption coefficient (i.e., different material) for the uniform transmittance.
However, if the color filter layers of the reflective and transmissive portions are formed of different materials, the process and the cost would be increased and the yield would be decreased.
To solve the above problems, a fabricating method of the color filter layers with the same resin is suggested. In this method, the color filter layers at the reflective and transmissive portions have the same absorption coefficient but a different thickness so that the transmittance has the same value.
FIGS. 3A and 3B
are t
Ha Kyoung-Su
Kwon Oh Nam
Yi Jong-Hoon
LG.Philips LCD Co. , Ltd.
Richards N. Drew
Thomas Tom
LandOfFree
Transflective liquid crystal display device having a color... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transflective liquid crystal display device having a color..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transflective liquid crystal display device having a color... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3270396