Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2001-04-05
2004-08-17
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S108000
Reexamination Certificate
active
06778234
ABSTRACT:
This application claims priority under 35 U.S.C. §§ 119 and/or 365 to 00-22467 filed in Republic of Korea on Apr. 27, 2000; the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to liquid crystal display (LCD) devices, and more particularly, to a liquid crystal display device adopting a field emission device as a backlight.
2. Description of the Related Art
As shown in
FIG. 1
, a conventional LCD device has a structure in which a backlight
2
adopting a cold cathode lamp
2
a
and a light plate
2
b
is installed to the rear of a liquid crystal panel
1
. The backlight
2
provides white light. In the liquid crystal panel
1
, three unit pixels of red, green and blue for which three color filters
1
R,
1
G and
1
B are installed, respectively, constitute a color pixel. The color filters
1
R
1
G and
1
B are installed at predetermined intervals on the inner surface of a front plate
11
, and a common electrode
12
is formed on the resultant structure of the front plate
11
. Pixel electrodes
2
R,
2
G and
2
B for the color filters
1
R,
1
G and
1
B, respectively, and thin film transistors (TFTs)
3
R,
3
G and
3
B for driving the pixel electrodes
2
R,
2
G and
2
B, respectively, are installed on the inner surface of a rear plate
13
spaced a predetermined interval apart from the front plate
11
. A liquid crystal LC is interposed between the front plate
11
and the rear plate
13
.
In the above-described conventional TFT LCD, the unit pixels switch incident white light to determine whether the white light passes through the unit pixels, and only color light within a given wavelength band is transmitted by a predetermined color filter installed on each of the unit pixels.
According to this structural characteristics, power consumption in the LCD mostly occurs in the backlight. In particular, in the backlight, light emitted from the lamp is considerably absorbed into the light plate by a reflection plate and a scattering structure installed on the light plate, and then proceeds toward the panel. Hence, the amount of light actually used for image display is smaller than power consumed, thus degrading the efficiency of power consumption.
In the conventional LCD, only one color light among three color components of white light is selected by the color filters installed on the liquid crystal panel, so that the light efficiency is very low. Also, the manufacturing costs of color filters which are installed on an LCD occupy a large portion of the total manufacturing cost for a liquid crystal display device.
Furthermore, since a color pixel is actually constituted by the combination of three color pixels, a single color pixel requires three TFTs and three pixel electrodes. In particular, since a TFT occupies an area by one side of a pixel electrode, the aperture efficiency is greatly degraded by the TFT, and accordingly the luminance is deteriorated.
The conventional LCD having such an inefficient structure can be improved by U.S. Pat. No. 5,760,858 which discloses an LCD in which a triode field emission device is coupled to a liquid crystal panel. This LCD uses a field emission device as a backlight, so that it can be driven with low power, and can provide uniform highly-luminant light over the entire surface without reflection plates. Also, separated color light rather than single white light is radiated to a liquid crystal by red, green and blue fluorescent materials, so that no color filters are needed, increasing the light efficiency and reducing the manufacturing costs of LCD. However, since a general triode field emission device must be manufactured to manufacture an LCD having such a structure, the LCD has no great advantages except that the circuit configuration is simple, compared to an LCD which forms a video image using an existing field emission device. This is because the costs of an LCD rather than the costs for establishing the circuit of a field emission device are expected to occupy the majority of the total costs for an image driving apparatus. Also, since R, G and B pixels are formed on a backlight to correspond to the R, G and B pixels on a liquid crystal panel, if a panel has high definition, each of the components of the backlight also must have high definition. Thus, the manufacture of a backlight is complicated, and the yield is low.
These problems are solved by applying a planar field emission device having a diode structure with a cathode electrode and an anode electrode such that separated red, green and blue light can be simply provided. Referring to
FIG. 2
, a backlight
4
having a diode field emission device is installed to the rear of a liquid crystal panel
3
. Black matrixes
31
a
are formed at intervals of a unit pixel on the inner surface of a front plate
31
in the liquid crystal panel
3
, and a common electrode
32
is formed on the resultant structure of the front plate
31
. Pixel electrodes
33
R,
33
G and
33
B, each facing the area between adjacent black matrixes
31
a
, and TFTs
34
R,
34
G and
34
B for driving the pixel electrodes
33
R,
33
G and
33
B, respectively, are installed on the inner surface of a rear plate
33
. Liquid crystal (LC) sandwiches between the front plate
31
and the rear plate
33
.
The backlight
4
includes a front plate
41
, on the inner surface of which anode electrodes
42
R,
42
G and
42
B for unit pixels and R, G and B fluorescent layers
43
R,
43
G and
43
B on the anode electrodes
42
R,
42
G and
42
B are installed, and a rear plate
42
, on the inner surface of which R, G and B cathode electrodes
44
R,
44
G and
446
corresponding to the anode electrodes
42
R,
42
G and
42
B are installed. R, G and B electron emitting sources
45
R,
45
G and
45
B are formed of graphite, diamond, carbon nanotube, or the like, on the cathode electrodes
44
R,
44
G and
44
B, respectively, by a simple thin film process such as a printing method or an electrophoretic method.
In the backlight
4
having this diode field emission device, the rear plate
42
(that is, a cathode plate), on which electron emitting sources are formed on cathode electrodes by a thin film process, is coupled to the front plate
41
(that is, an anode plate) on which the R, G and B fluorescent layers
43
R,
43
G and
43
B and the anode electrodes
42
R,
42
G and
42
B are formed. Thus, the backlight
4
is easily manufactured, and, particularly, a large backlight can be manufactured at low costs. Also, since the backlight radiates red, blue and green light separated per unit pixel to a liquid crystal panel, a liquid crystal panel requires no existing color filters, so that it has a simple structure and performs a simple circuit operation. The backlight having such a diode field emission device provides R, G and B light separated per pixel, is cheap, large, highly efficient and highly luminant, and operates with low power, so that it is an epoch-making technique in which no color filters are required, and the light efficiency is high, in contrast with existing LCDs.
However, as shown in
FIG. 3
, when separated red, blue and green light is radiated from the backlight
4
to a liquid crystal panel, light radiated from a fluorescent material on each unit pixel disperses while passing through a glass substrate layer at the upper side. For example, as shown in
FIG. 3
, when a red pixel
3
R and a green pixel
3
G in a liquid crystal panel
3
are maintained in an on state, some of light from a red area
4
R and a green area
4
G in the backlight
4
at the lower side enter in wrong areas in the liquid crystal panel
3
due to scattering. Scattering occurs because the front plate
41
of the backlight
4
must be 1000 &mgr;m or thicker to maintain the internal vacuum of the backlight
4
. The generation of the cross talk prevents formation of a clear image.
This cross talk serves as a disadvantage, in contrast with an existing LCD in which color filters are located at the end in the direction of traveling of light. The LCD adopt
Jang Jae-eun
Park Kwan-sun
Akkapeddi P. R.
Burns Doane Swecker & Mathis L.L.P.
Chowdhury Tarifur R.
Samsung SDI & Co., Ltd.
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