Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-12-14
2004-03-30
Niebling, John (Department: 2812)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C428S001250, C349S061000
Reexamination Certificate
active
06714272
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-79354, filed on Dec. 20, 2000, 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 device, and more particularly to a color liquid crystal display device without a color filter.
2. Description of the Related Art
As our information-oriented society rapidly develops, display devices are increasingly developed. The display device processes and displays a great deal of information. A cathode ray tube (CRT) has served as a mainstream of the display device field. However, a flat panel display devices having small size, lightweight, and low power consumption are actively being researched in order to meet the needs of the times. Accordingly, a thin film transistor-liquid crystal display (TFT-LCD) device that has high color quality and small size is developed.
The LCD device uses the optical anisotropy and polarization properties of liquid crystal molecules to produce an image. Liquid crystal molecules have a definite orientational alignment as a result of their long, thin shapes. The orientational alignment can be controlled by an applied electric field. In other words, as an applied electric field changes, so does the alignment of the liquid crystal molecules. Due to the optical anisotropy, the refraction of incident light depends on the orientational alignment of the liquid crystal molecules. Thus, by properly controlling the applied electric field a desired image can be produced.
FIG. 1
is a schematic perspective view of a conventional TFT-LCD device.
The TFT-LCD device includes upper and lower substrates
5
and
22
, and a liquid crystal layer
14
interposed therebetween. The upper and lower substrates
5
and
22
are sometimes referred to as a color filter substrate and an array substrate, respectively. On a surface facing the lower substrate
22
, the upper substrate
5
includes a black matrix
6
and a color filter layer
7
. The color filter layer
7
includes a matrix array of red (R), green (G), and blue (B) sub-color filters that are formed such that each sub-color filter is bordered by the black matrix
6
. The upper substrate
5
also includes a transparent common electrode
18
over the color filter layer
7
and the black matrix
6
. On a surface facing the upper substrate
5
, the lower substrate
22
includes an array of thin film transistors (TFTs) shown as a “T” that act as switching devices. The array of thin film transistors is formed to correspond with the matrix of sub-color filters. A plurality of crossing gate and data lines
13
and
15
are positioned such that a TFT is located near each crossing of the gate and data lines
13
and
15
. The lower substrate
22
also includes a plurality of pixel electrodes
17
, which are made of a transparent material such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO). Each pixel electrode is disposed in a corresponding area defined between the gate and data lines
13
and
15
and often referred to as pixel regions P.
In LCD devices an electro optic effect of the liquid crystal material is a phenomenon where an electro optic modulation occurs by the change of the optical property of the liquid crystal material, that is, an alignment state of the liquid crystal material turns to another alignment state by an applied electric field.
The LCD devices utilize the electro-optic effect of the liquid crystal mateiial and can be divided into
4
display types. The following is description of the LC operating modes using various electro-optical effects, including a twisted nematic (TN) mode, a guest host (GH) mode, electrically controlled birefringence (ECB) effect and ferroelectric liquid crystal (FLC) mode. The display type can be selected and used according to a design characteristic of the liquid crystal panel.
Recently, various methods to express colors without the color filter by using wavelength property of light due to the birefringence of the liquid crystal material have been suggested. Among them are a method using the ECB effect and will be explained with the color TFT-LCD device using the ECB mode. In the ECB mode LCD device, the pretilt angle is nearly 90° and the liquid crystal molecules are aligned parallel to the substrate by the applied voltage such that a transmittance of light can be controlled.
FIGS. 2A and 2B
are cross-sectional views of a conventional ECB mode reflective LCD device and shows the operation of liquid crystal molecules when an applied voltage is off or on, respectively.
As shown in
FIG. 2A
, upper and lower substrates
31
and
33
are spaced apart from each other with a specific gap (d) and liquid crystal molecules
35
are interposed therebetween. An upper polarization plate
39
is formed on an outer surface of the upper substrate
31
and as a result of the upper polarization plate only light parallel to the transmittance axis of the polarization plate can be emitted to the exterior of the display. The liquid crystal molecules
35
are aligned with an arbitrary pretilt angle &thgr;
p
between about 0° and 90°, preferably an angle between 60° and 85° considering a property of viewing angle and gray scale inversion. To acquire the desired pretilt angle, orientation films
37
and
38
are formed on each facing surface of the upper and lower substrates
31
and
33
and a rubbing process of the orientation films
37
and
38
is performed.
As shown in
FIG. 2B
, when a voltage is applied to the upper and lower substrates
31
and
33
, the liquid crystal molecules
35
are aligned with another angle &thgr;
m
. The light is polarized as it passes through the polarization plate
39
, the upper substrate
31
, the liquid crystal molecules
35
and a reflection plate
41
. The transmittance of the light changes according to the angle between the light axis of the liquid crystal molecules
35
and the transmittance axis of the polarization plate
39
when the voltage is applied to the LCD device.
The transmittance of the ECB mode LCD device is dependent on the wavelength in contrast with the transmittance of the TN mode LCD device.
An equation for the transmittance (T) of the ECB mode reflective LCD devices is as follows. The angle between the light axis of the liquid crystal molecules and the transmission axis of the polarization plate is assumed to be 45° and the LCD device includes the polarization plate, the liquid crystal layer and the reflection plate from the top.
T=
cos
2
(2&pgr;
d·&Dgr;n
(&lgr;)/&lgr;)/2 (Equation 1)
where d is a cell gap between the upper and lower substrates
31
and
33
, &Dgr;n is a refractive index anisotropy, &lgr; is a wavelength and d·&Dgr;n is a retardation. As shown from the equation 1 the transmittance is a function of retardation (d·&Dgr;n) for a specific wavelength (&lgr;) of the incident light.
FIG. 3
shows the transmittances of red (R), green (G) and blue (B) light
43
,
45
and
47
, respectively, for the conventional ECB mode reflective LCD device as a function of the effective retardation (d·&Dgr;n
eff
), which can be calculated by using the equation (1). The colors of transmitted light continuously change in a series of white, black, blue, green and pink according to the effective retardation (d·&Dgr;n
eff
) by the applied voltage.
However, in the conventional ECB mode LCD device, since the viewing angle is too narrow, the color is different according to the viewing direction. Moreover, since the transmittance curves of the colors have the peaks of the same height, the number of the expressible colors is limited.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a color liquid crystal display device and manufacturing method thereof that substantially obviates one or more of problems due to limitations and disadvantages of the related art.
An advantage of the present invention is to provide a color liquid crystal display device and a manufacturing method thereof that can realize multiple colors o
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
Niebling John
Stevenson Andre′
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