Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-02-28
2004-11-02
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06812978
ABSTRACT:
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 (LCD) device implementing a color filter having various thickness.
2. Discussion of the Related Art
LCD devices are usually classified into transmission type and reflection type according to their difference in a light source.
The transmission type LCD device uses light incident from a back light that is attached to a rear surface of a liquid crystal panel. The light is incident to a liquid crystal layer of the liquid crystal panel, and is absorbed or passes through the liquid crystal layer according to proper alignments of the liquid crystal layer. The alignment of the liquid crystal layer can be controlled by way of controlling an electric field, which is applied to the liquid crystal layer. Therefore, a transmittance ratio of the liquid crystal panel can be controlled by way of applying the electric field to the liquid crystal layer. Conventionally, the back light of the transmission type LCD device is an artificial light source. Therefore, high power consumption due to the back light is a greater disadvantage of the transmission type LCD device.
On the contrary to the above-mentioned transmission type LCD device, the reflection type LCD device uses an ambient light incident from a natural light source or an exterior artificial light source. Because of its low power consumption, the reflection type LCD device is focused on. However, the reflection type LCD device is useless when the whether or exterior light source is dark.
Accordingly, a transflective LCD device is developed to compensate for the reflective type LCD device. The transflective LCD device is useful regardless of the whether or exterior light source.
FIG. 1
is an exploded perspective view illustrating a typical transflective LCD device.
The transflective LCD device
1
includes upper and lower substrates
10
and
20
that are opposed with each other, and an interposed liquid crystal layer
50
therebetween. The upper and lower substrates
10
and
20
are called a color filter substrate and an array substrate, respectively. In the upper substrate
10
, on a surface opposing the lower substrate
20
, black matrix
12
and color filter layer
14
that includes a plurality of red (R), green (G), and blue (B) color filters are formed. That is to say, the black matrix
12
surrounds each color filter, in shape of an array matrix. Further on the upper substrate
10
, a common electrode
16
is formed to cover the color filter layer
14
and the black matrix
12
.
In the lower substrate
20
, on a surface opposing the upper substrate
10
, a TFT “T” as a switching device is formed in shape of an array matrix corresponding to the color filter layer
14
. In addition, a plurality of crossing gate and data lines
26
and
28
are positioned such that each TFT is located near each cross point of the gate and data lines
26
and
28
. Further on the lower substrate
20
, a plurality of reflective electrodes
22
are formed on an area defined by the gate and data lines
26
and
28
. The area there defined is called a pixel region “P.” Each reflective electrode
22
has a transmissive portion
22
a
thereon. The transmissive portion
22
a
beneficially has a shape of a through hole such that it exposes a transparent electrode
24
disposed below the reflective electrode
22
. The reflective electrode
22
is beneficially made of a metal having a high reflectivity, and the transparent electrode
24
is beneficially made of a transparent conductive material, usually indium tin oxide (ITO) or indium zinc oxide (IZO).
FIG. 2
shows a cross-sectional view illustrating the transflective LCD device of FIG.
1
. As shown, between the upper and lower substrates
10
and
20
, a liquid crystal layer
50
is interposed. The upper substrate
10
has the color filter layer
14
and common electrode
16
on the inner surface opposing the lower substrate
20
. On the common electrode
16
, an upper alignment layer
142
is formed. In addition, on the exterior surface of the upper substrate
10
, a retardation film or a half wave plate (HWP)
46
and an upper polarizer
54
are sequentially disposed. The half wave plate (HWP)
46
serves to involve a phase difference of “&lgr;/2” for incident rays such that the incident rays rotate to have a phase difference of “&lgr;/2” after passing through the half wave plate
46
.
In the meanwhile, the lower substrate
20
has the reflective electrode
22
and transparent electrode
24
on its surface opposing the upper substrate
10
. A lower alignment layer
44
is formed on the reflective electrode
22
and exposed portion of the transparent electrode
24
. Between the reflective and transparent electrode
22
and
24
, a passivation layer
48
is interposed to separate them. The reflective electrode
22
has the transmissive portion
22
a
, which exposes the transparent electrode
24
. In addition, on the exterior surface of the lower substrate
20
, a lower polarizer
52
is disposed, and below the lower polarizer
52
, a back light
40
is disposed.
For forming the reflective and transparent electrode
22
and
24
, at first, the transparent conductive material selected from indium tin oxide (ITO) or indium zinc oxide (IZO) is deposited on the lower substrate
20
. The transparent conductive layer is patterned to form the transparent electrode
24
. Then, an insulating material is deposited on the transparent electrode
24
to form the passivation layer
48
. On the passivation layer
48
, aluminum (Al) based metal of a high reflectivity is deposited and patterned such that the reflective electrode
22
is formed. At this point, portions of the reflective electrode
22
and passivation layer
48
are sequentially etched away to form the transmissive portion
22
a.
The liquid crystal layer
50
between the upper and lower substrates
10
and
20
has an optical anisotropy. That is to say, in their first state alignment, long axes of the liquid crystal molecules are aligned parallel to the substrates
10
and
20
. Whereas, with an electric field applied across the liquid crystal layer
50
, the long axes of the molecules are aligned perpendicular to the substrates
10
and
20
. Therefore, the liquid crystal layer
50
serves as a switch for incident rays of light. In the later state alignment, a homeotropic alignment, the rays pass through the liquid crystal layer
50
, without a phase difference.
The liquid crystal layer
50
has a layer thickness or cell gap. Specifically, the liquid crystal layer
50
has a first cell gap “d1” over the reflective electrode
22
and a second cell gap “d2” over the transparent electrode
24
. At this point, the first and second cell gaps “d1” and “d2” beneficially have a definite relationship. That is to say, the second cell gap d2 is beneficially twice as the first cell gap d1 (d2≈2d1). Over the reflective electrode
22
, the liquid crystal layer
50
involves a phase difference of “&lgr;/4.” The above-mentioned different cell gaps “d1” and “d2” improve en efficiency of incident rays passing through the transmissive portion
22
a.
More detailed explanation is followed with reference to relationships (1) and (2):
d
1&Dgr;n=&lgr;/4 (1),
d
2=2
d
1 (2),
such that d2&Dgr;n=&lgr;/2, wherein “d1” is the first cell gap over the reflective electrode
22
, “d2” is the second cell gap over the transmissive portion
22
a
or transparent electrode
24
. The first relationship (1) about the phase difference “&lgr;/4” means that rays get the phase difference of “&lgr;/4” after passing through the liquid crystal layer
50
of the first cell gap “d1” over the reflective electrode
22
. Similarly, the relationship “d2&Dgr;n=&lgr;/2” means that the rays get the phase difference of “&lgr;/2” after passing through the liquid crystal layer
50
of the second cell gap “d2” over the transmissive portion
22
a.
Rays from the back light
Kim Yong-Beom
Lee Jeong-Hwan
Dudek James
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
Rude Timothy
LandOfFree
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