Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-11-14
2004-10-26
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S113000
Reexamination Certificate
active
06809786
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2001-71519, filed on Nov. 16, 2001, which is hereby incorporated by reference as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a reflective LCD device having a cholesteric liquid crystal (CLC) color filter.
2. Discussion of the Related Art
Presently, LCD devices are developed as next generation display devices because of their light weight, thin profile, and low power consumption characteristics. In general, an LCD device is a non-emissive display device that displays images using a refractive index difference utilizing optical anisotropy properties of liquid crystal material that is interposed between an array (TFT) substrate and a color filter (C/F) substrate. Among the various type of LCD devices commonly used, active matrix LCD (AM-LCD) devices have been developed because of their high resolution and superiority in displaying moving images. The AM-LCD device includes a thin film transistor (TFT) per each pixel region as a switching device, a first electrode for ON/OFF, and a second electrode used for a common electrode.
FIG. 1
is a perspective view of an LCD device according to the related art.
In
FIG. 1
, first and second substrates
10
and
30
are arranged to face each other with a liquid crystal material layer
50
interposed therebetween. On an inner surface of the first substrate
10
, a color filter (C/F) layer
12
and a common electrode
16
, which functions as one electrode for applying an electric field to the liquid crystal layer
50
, are subsequently formed. The C/F layer
12
includes a color filter for transmitting only light of a specific wavelength, and a black matrix (not shown) that is disposed at a boundary of the color filter and shields light of a region in which alignment of the liquid crystal material is uncontrollable. On an inner surface of the second substrate
30
, a plurality of gate lines
32
and a plurality of data lines
34
are formed in a matrix array. A TFT “T”, which functions as a switching device, is disposed at a region where each gate line
32
and data line
34
crosses, and a pixel electrode
46
that is connected to the TFT “T” is disposed at a pixel region “P” defined by the region where the gate and data lines
32
and
34
cross. First and second polarizing plates
52
and
54
, which transmit only light parallel to a polarizing axis, are disposed on an outer surface of the first and second substrates
10
and
30
, respectively. An additional light source such as a backlight, for example, is disposed below the second polarizing plate
54
.
The LCD device of
FIG. 1
is a transmissive LCD device that displays images by transmitting only desired light through the first substrate using an optic/dielectric anisotropy of the liquid crystal layer after light from the backlight passes through the second substrate.
FIG. 2
is a schematic plan view of an LCD device according to the related art.
FIG. 2
shows gate and data pads for connection with an external circuit.
In
FIG. 2
, a liquid crystal panel
60
for an LCD device includes a first substrate
10
, a second substrate
30
larger than the first substrate
10
, and a liquid crystal layer
50
interposed between the first and second substrates
10
and
30
. The liquid crystal panel
60
can be divided into a display region “D,” and first and second non-display regions “N1” and “N2” in plan view. The first non-display region “N1” is defined by the first and second substrates
10
and
30
, and the second non-display region “N2” is defined by a larger portion of the second substrate
30
. Elements such as a TFT, gate and data lines, a pixel electrode, a color filter layer and a common electrode illustrated in
FIG. 1
are formed in the display region “D.” Gate and data pads
62
and
64
connected to an external circuit (not shown) are formed in the second non-display region “N2” to apply a display signal to the display region “D.” Since a black matrix
66
formed in the first non-display region “N1” of the first substrate
10
absorbs incident light, a boundary of the display region “D” maintains a black state.
FIG. 3
is a schematic cross-sectional view of an LCD device according to the related art. A boundary of a display region is mainly shown in FIG.
3
.
In
FIG. 3
, a boundary of first and second substrates
10
and
30
with a liquid crystal layer
50
therebetween is sealed with a seal pattern
68
. A color filter layer
40
on an inner surface of the first substrate
10
is extended to a first non-display region “N1” so that a deterioration at a boundary of a display region “D” by a step difference between the display region “D” and the first non-display region “N1” can be prevented during a rubbing process for aligning the liquid crystal layer
50
. Array elements
42
such as a TFT and a pixel electrode (of
FIG. 1
) are formed on an inner surface of the second substrate
30
. When light is emitted into the first non-display region “N1,” a black matrix
66
of the first non-display region “N1” absorbs the light. Accordingly, a black state is maintained in the boundary of the display region “D.”
Reflective LCD devices without a backlight are being researched and developed. Transflective LCD devices use a backlight to provide light. However, only about 7% of the light that is emitted by the backlight passes through each cell of the LCD device. Since the backlight should emit light of a relatively high brightness, corresponding power consumption increases. Accordingly, a large capacity heavy battery is commonly used to supply sufficient power for the backlight. Moreover, use of the large capacity battery limits operating time. On the other hand, because power consumption of the reflective LCD devices greatly decreases due to use of ambient light as a light source, operating time increases. Such reflective LCD devices are used for portable information apparatuses such as electronic diaries and personal digital assistants (PDAs). In the reflective LCD devices, a pixel area, which is covered with a transparent electrode in conventional transmissive LCD devices, is covered with a reflective plate or reflective electrode having opaque reflection characteristics.
However, brightness of reflective LCD devices is very poor because the devices use only ambient light as a light source. The poor brightness results from operational characteristics of the reflective LCD devices in which ambient light which passes through a color filter substrate, is reflected on a reflective electrode on a second substrate, is passed through the color filter substrate again and then displays an image. Accordingly, brightness is decreased as a result of reduction of the transmittance when the ambient light passes through a color filter layer twice. Since overall thickness of the color filter layer is inversely proportional to transmittance and is directly proportional to color purity of the light, the problem of inadequate brightness of the reflective LCD devices can be remedied by forming a thin color filter layer with high transmittance and low color purity. However, there is a limit in fabricating the color filter layer below a threshold thickness due to characteristics of the resin used to form the color filter layer.
Accordingly, one possible solution to this problem is fabricating LCD devices using cholesteric liquid crystal (CLC) that has selective reflection and transparency characteristics. In reflective LCD devices using a CLC color filter (CCF) layer, the fabrication processes are simplified due to omission of the reflective layer, and high color purity and high contrast ratio are achieved. Moreover, since CLC has a spiral structure and spiral pitch determines a selective reflection bandwidth of the CLC, the reflection bandwidth can be controlled by a distribution of the spiral pitch at one pixel. To illustrate this in more detail, a wavelength range of visible light is from about 400 n
Chowdhury Tarifur R.
Di Grazio Jeanne Andrea
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
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