Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-03-09
2004-06-08
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000
Reexamination Certificate
active
06747717
ABSTRACT:
CROSS REFERENCE
This application claims the benefit of Korean Patent Application No. 2000-11884, filed on Mar. 9, 2000, 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, it relates to the LCD device having a cholesteric liquid crystal polarizer and cholesteric liquid crystal color filters.
2. Description of Related Art
In general, a liquid crystal display device uses the optical anisotropy and polarization properties of liquid crystal molecules. Because of their peculiar characteristics, the liquid crystal molecules have a definite orientational order in arrangement. The arrangement direction of the liquid crystal molecules can be controlled by an applied electric field. In other words, when electric fields are applied to liquid crystal molecules, the arrangement of the liquid crystal molecules changes. Since incident light is refracted according to the arrangement of the liquid crystal molecules, due to the optical anisotropy of liquid crystal molecules, image data can be displayed.
Of the different types of LCDs, an active matrix LCD (AM-LCD) (having thin film transistors and pixel electrodes are arranged in the form of a matrix) is the majority subject of research and development activity due to its high resolution and superiority in displaying moving images.
FIG. 1
is a cross-sectional view illustrating a related art liquid crystal display (LCD) panel. As shown in
FIG. 1
, the LCD panel
20
has lower and upper substrates
2
and
4
and an interposed liquid crystal layer
10
. The lower substrate
2
, which is referred to as an array substrate, has a TFT “S” as a switching element that changes the orientation of the liquid crystal molecules. A pixel electrode
14
applies a voltage to the liquid crystal layer
10
according to the state of the TFT “S”. The upper substrate
4
has a color filter
8
for implementing a color and a common electrode
12
on the color filter
8
. The common electrode
12
serves as an electrode for applying a voltage to the liquid crystal layer
10
. The pixel electrode
14
is arranged over a pixel portion “P”, of a display area. Further, to prevent leakage of the liquid crystal layer
10
, the two substrates
2
and
4
are sealed using a sealant
6
.
In the above-mentioned AM-LCD device, the data signal is applied to the pixel electrode
14
in accordance with the scanning signal of the gate electrode of the TFT “S”, i.e., the TFT “S” is turned ON. On the contrary, the data signal is not applied to the pixel electrode
14
when the TFT “S” is turned OFF.
The LCD device is a sort of light modulator and uses light from the backlight device (not shown). However, the LCD device is not efficient because the light generated from the backlight device has to pass through the several layers to display the color images. These several layers are a pair of linear polarizers, color filters, etc.
Especially, since the linear polarizer only transmits a linear component of the light, i.e., the linearly polarized light of the light from the backlight, the density of the light decreases. Namely, less than half of the light passes through the LCD panel such that the LCD device is not efficient at using the light from the backlight device. Therefore, the brightness is degraded. Moreover, the color filters that are used in the LCD device usually absorb the light except for the light having the intrinsic wavelength, and thus the optical density and the brightness is lowered.
For the purpose of solving the aforementioned problems, the light transmissivity of the color filters should be increased. And, for the purpose of raising the light transmissivity, the color purity should be lowered. However, there is a limitation upon decreasing the color purity.
Accordingly, a cholesteric liquid crystal color filter (referred to as CLC color filter hereinafter) and a cholesteric liquid crystal polarizer (referred to as CLC polarizer hereinafter) are researched and applied to the LCD device to improve the brightness. The CLC color filter has characteristics of both the liquid crystal and the color filter. Namely, the CLC color filter selectively reflects or transmits incident light, and selectively displays a certain color. Moreover, it is widely known that using the CLC color filter and CLC polarizer in the LCD device increases the efficiency of the light emitted from the backlight device.
FIG. 2
is a schematic sectional view of a related art LCD device having the CLC color filter and the CLC polarizer. As shown, the LCD device
25
has upper and lower substrates
40
and
30
corresponding to upper and lower substrates
4
and
2
of
FIG. 1
, and an interposed liquid crystal layer
38
. CLC color filters
34
having red (R), green (G) and blue (B) colors are on the lower substrate
30
. A black matrix
36
is positioned between the CLC color filters
34
and the lower substrate
30
, in the boundary between the CLC color filters
34
.
The CLC color filters
34
are color filters made of a cholesteric liquid crystal (CLC). They selectively reflect or transmit incident light. For example, if the molecular structure of the CLC is twisted in the right direction, the CLC reflect only right-handed circularly polarized light. Additionally, objects have an intrinsic wavelength. The color that an observer sees when looking at an object is the wavelength of the light reflected from or transmitted through the object. The wavelength range of visible light is from about 400 nm to 700 nm. Visible light can be broadly divided into red, green, and blue regions. The wavelength of the red light region is centered at about 660 nm, that of green is centered at about 530 nm, and that of blue is centered at about 470 nm. The pitch of the cholesteric liquid crystal is controllable and, therefore it is possible that a CLC color filter can selectively transmit light having the intrinsic wavelength of the color corresponding to a pixel. This enables a pixel to display red (R), green (G) or blue (B) with a high purity. To implement a precise color, a plurality of the CLC color filters can be selectively arranged. Therefore, a CLC color filter can display a selected color better than a conventional absorptive color filter.
Referring to
FIG. 2
, a backlight device
50
is located under the lower substrate
30
. A CLC polarizer
32
is located under the lower substrate
30
and between the backlight device
50
and the lower substrate
30
. The backlight device
50
generates artificial light that displays color images in accordance with the color filters
34
. The CLC polarizer
32
is a polarizer made of a cholesteric liquid crystal. It reflects or transmits a left- or right-handed circularly polarized light. Therefore, the CLC polarizer
32
passes a much larger amount of light than the linear polarizer. The CLC polarizer
32
is used substantially for changing the phase of the light, i.e., converting the light into the left- or right circularly polarized light. A black matrix
36
that is made of an organic substance or a metallic material is formed on the lower substrate
30
. The black matrix
36
is also arranged in the boundary between the CLC color filters
34
such that it divides the color filters
34
into the displaying areas.
Still referring to
FIG. 2
, a retardation film
42
and a linear polarizer
46
are formed in series on the upper substrate
40
. The retardation film
42
, which has a phase difference of &lgr;/4, respectively converts the circularly polarized light into the linearly polarized light, or the linearly polarized light into the circularly polarized light. The liquid crystal layer
38
is interposed between the upper substrate
40
and the lower substrate
30
and functions as an optical shutter for changing a direction or a phase of the light that is colored by the CLC color filters
34
.
As mentioned above, since the CLC polarizer is adopted in the LCD device, the efficiency of the light from backlight device is raised; t
Birch & Stewart Kolasch & Birch, LLP
LG. Philips LCD Co. Ltd.
Ton Toan
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