Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-11-03
2004-07-27
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06768528
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field Of Invention
The present invention relates to a liquid crystal display (hereinafter abbreviated LCD) which realizes a high brightness and improves viewing angles.
2. Discussion Of Related Art
Lately, LCDs have been widely used as planarized plate displays. As techniques for fabricating thin film transistors using amorphous silicon are developed, the image quality of these LCDs is greatly improved. Thus, LCDs are widely used in notebook computers, personal computer monitors, and the like.
FIG. 1
shows a cross-sectional view of an LCD according to a related art. Referring to
FIG. 1
, the LCD includes a back light unit a
1
for generating and uniformly supplying light, and a lower polarizing plate
110
for transforming a polarization characteristic of the supplied light from the back light unit al to a given direction. The LCD also includes a lower substrate
120
on which thin film transistors (not shown) are formed to control the transmissive rate of the light polarized by the lower polarizing plate
110
. A liquid crystal layer
130
changes a polarization direction of the light whose transmissive rate has been controlled by the lower substrate
120
. An upper substrate
140
, on which a color filter layer
142
is disposed, causes the polarized light to have a specific color wavelength matching a corresponding color filter. An upper polarizing plate
150
changes the polarization characteristic of the light having passed through the upper substrate
140
.
The back light unit al is constructed with a light source
102
for generating light, and a light-guiding plate
104
for guiding the light generated from the light source
102
to a liquid crystal panel uniformly. A reflection plate
100
under the light-guiding panel
104
reflects incident light from the bottom or side of the light-guiding plate
104
toward the liquid crystal panel.
In the above-constructed related art LCD, the light generated from the light source
102
passes through the light-guiding plate
104
, and is uniformly polarized after passing through the lower polarizing plate
110
.
A polarizing direction of the light having been polarized through the lower polarizing plate
110
is changed at the thin film transistor (not shown) on the lower substrate
120
and the liquid crystal layer
130
. Namely, the polarization direction of the polarized light is selectively revolved according to a state of the transistor when passing through the liquid crystal layer
130
. Then, the changed light passes through the color filter layer
142
of the upper substrate
140
, which only transmits wavelengths of the specific colors corresponding to the respective color filters.
An image is realized when the light having a specific color transmitted by the color filter layer
142
proceeds to the upper polarizing plate
150
. The upper polarizing plate
150
only transmits the light whose polarized direction has been revolved by the liquid crystal. In this case, the polarizing characteristic of the upper polarizing plate
150
is perpendicular to that of the lower polarizing plate
110
.
Thus, the basic principle of the LCD is that the polarized direction of the light is revolved after the polarized light from the lower polarizing plate
110
passes through the liquid crystal layer
130
. The length that the light travels in the liquid crystal is important. When the liquid crystal is placed between the upper and lower polarizing plates
150
and
110
, the thickness of the liquid crystal changes the polarized direction of the light according to the following formula.
(&Dgr;
n
)
Z=&lgr;/
4 (I)
wherein &Dgr;n is a difference of a refractive index between a perpendicular direction and a parallel direction of the proceeding direction of the light in double refraction, Z is a thickness of the liquid crystal, and &lgr; is a wavelength of the light.
In this case, once the proceeding direction of the light is perpendicular to the liquid crystal layer, the proceeding length of the light becomes z to show the same result of the formula (I). Thus, the cut-off of the light by the vertical polarizing plate becomes very effective.
However, when the light proceeds at a slant (i.e., an acute angle to perpendicular), the proceeding (or path) length of the light becomes longer. Thus, the upper polarizing plate is unable to cut off the light precisely due to the change of the polarized direction of the light. Hence, the optimal way to achieve cut-off of polarized light is to improve the straightness (with respect to perpendicular) of the light passing though the liquid crystal.
Unfortunately, the LCD according to the related art limits the viewing angles of the LCD once the straightness of the light is elevated.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a liquid crystal display that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, in one aspect the present invention includes a back light unit to produce and supply light; a collimating sheet to collimate the light supplied by the back light unit; a cholesteric liquid crystal (CLC) polarizer to transmit one of left-circularly polarized light and right-circularly polarized light from the collimating sheet, and to reflect other light not transmitted; a lower substrate on which a CLC color filter layer is formed wherein the CLC color filter layer transmits the circularly polarized light from the CLC polarizer having specific red, green, and blue wavelengths and reflects other light not transmitted; a liquid crystal layer to selectively revolve a polarized direction of the circularly polarized light from the CLC color filter layer; an upper substrate over the liquid crystal layer having a hologram diffuser and a planarization layer disposed thereon and wherein the hologram diffuser diffuses the changed circularly polarized light from the liquid crystal layer; and a linear polarizing transformer to transform the diffused circularly polarized light from the hologram diffuser into linearly polarized light.
In another aspect, the present invention includes a back light unit to produce and supply light; a collimating sheet to collimate the light supplied by the back light unit; a cholesteric liquid crystal (CLC) polarizer to transmit one of left-circularly polarized light and right-circularly polarized light from the collimating sheet, and to reflect other light not transmitted; a lower substrate on which a CLC color filter layer is formed wherein the CLC color filter layer transmits the circularly polarized light from the CLC polarizer having specific red, green, and blue wavelengths and reflects other light not transmitted; a &lgr;/4 film to transform the circularly polarized light from the CLC color filter layer into linearly-polarized light; a first linear polarizer above the &lgr;/4 film; a liquid crystal layer to selectively transmit the linearly-polarized light; and an upper substrate over the liquid crystal layer having a hologram diffuser and a planarization layer disposed thereon and wherein the hologram diffuser diffuses the linearly-polarized light from the liquid crystal layer.
In still another aspect, the present invention includes a back light unit to produce and supply light; a collimating sheet to collimate the light supplied by the back light unit; a cholesteric liquid crystal (CLC) polarizer to transmit one of left-circularly polarized light and right-circularly polarized light from the collimating sheet, a
Kwon Young-Wan
Moon Jong-Weon
Chowdhury Tarifur R.
Duong Thoi V.
LG.Philips LCD Co. , Ltd.
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