Liquid crystal cells – elements and systems – With specified nonchemical characteristic of liquid crystal... – Within smectic phase
Reexamination Certificate
2001-06-29
2003-04-08
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
With specified nonchemical characteristic of liquid crystal...
Within smectic phase
C349S188000
Reexamination Certificate
active
06545738
ABSTRACT:
This application claims the benefit of Korean Patent Application Nos. P2000-44443 and P2001-37132 filed Jul. 31, 2000 and Jun. 27, 2001, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a liquid crystal display having reduced flicker and wide a viewing angle. The present invention also relates to a method of fabricating the above-mentioned liquid crystal display having reduced flicker.
2. Description of the Related Art
A ferroelectic liquid crystal (hereinafter, “FLC”) has a response time faster than other liquid crystal modes, as about several ten micro seconds to several mile seconds. This results from that the FLC has a spontaneous polarization characteristic without an electric field. The FLC also is able to realize a wide viewing angle without a special electrode structure and/or a compensating film, as such an In-plane Switching (IPS) mode. Accordingly, the FLC is spot-lighted because of being applied to a motion picture display representing a liquid crystal television.
The liquid crystal mode using such a FLC includes a deformed helix FLC (DHFLC), a surface stabillized FLC (SSFLC), an anti-FLC (AFLC), a V-shape FLC, a half V-shape FLC and so on. Since liquid crystal molecules in FLC mode among the above liquid crystal modes have only a bi-stable state, the SSFLC mode can be driven in a On/Off and has a disadvantage that it's impossible to realize a gray scale. Meanwhile, the V-shape and half V-shape FLC modes allow the gray scale to be realized, because the liquid crystal molecules each has a mono stable state. In view of this point, the V-shape and half V-shape FLC have been actively studied. Furthermore, the half V-shape FLC has a primary alignment state better than that of the V-shape FLC. Therefore, the half V-shape FLC enhances a contrast ratio and enables the liquid crystal to be easily driven.
The half V-shape FLC uses a chiral smetic C (hereinafter, Sm C*) phase maintained at a normal temperature in a temperature induced phase transition process. Conventionally, in accordance with a temperature which becomes lower, the half V-shape FLC has a phase-transition in a sequence of a isotropic (hereinafter, “I”) phase→a chiral nematic (hereinafter, “N*”) phase→Sm C* phase→a crytal, as shown in FIG.
1
. Referring to
FIG. 1
, if the temperature is low from a temperature maintaining the isotropic phase which does not have a director and a directional order, the liquid crystal molecules are aligned in the N* phase having the director. In sequence, when the temperature is lower than that of the N* phase, the liquid crystal molecules are aligned in the Sm C* phase having a constant director and a directional order, that is, a layer structure and a special tilt. When the phase of the liquid crystal is changed from the N* to the Sm C* through a smetic A phase, that is, at a second phase transition, a chevron or a bookself is formed to identify a layer normal direction with a rubbing direction, thereby allowing the liquid crystal molecules to be in the bi-stable state. In the bi-stable state, the liquid crystal molecules are stably positioned at both ends of a virtual cone. Meanwhile, in the liquid crystal having a phase transition sequence of the I phase→N* phase→Sm C* phase, a transition from the N* phase to the Sm C* phase as a first transition forces the liquid crystal layers to be inclined in two directions being symmetrized with a center at the rubbing direction, as shown in FIG.
2
. At the phase transition from the N* phase to the Sm C* phase, if a direct current voltage is applied to the liquid crystal, only one of two layer directions is selected. Accordingly, the liquid crystal molecule in the Sm C* phase has the mono stable state forming an uniform alignment which a spontaneous polarization direction of the liquid crystal molecule identifies to a direction of electric field. The liquid crystal molecules of the mono stable state responds to an external electric field having a polarity contrary to that at the alignment and circles to draw an outer line of the virtual cone with a center in a normal line of a smetic layer, thereby controlling an amount of lights to be transmitted. As a result, the liquid crystal molecules in the mono stable state can realize the gray scale. A method of manufacturing the half V-shape FLC using such a phase transition process of the liquid crystal molecules will be described.
As shown in
FIG. 3
, a half V-shape liquid crystal cell includes liquid crystals injected between an upper substrate
1
and a lower substrate
11
. The upper substrate is provided with a common electrode
3
and an upper alignment film
5
thereon, and the lower substrate
11
includes a thin film transistor array
9
and a lower alignment film
7
. The thin film transistor array
9
and the lower alignment film
7
are disposed on the lower substrate
11
. The liquid crystals are injected between the upper and lower substrates
1
and
11
at a temperature maintaining the N* phase or the isotropic phase, to be easy an injection of the liquid crystal. In sequence, if its temperature is low into a temperature allowing the liquid crystal to have the N* phase, the liquid crystal
15
are aligned in parallel with a rubbing direction of the alignment films
5
and
7
, in a perpendicular direction. Then, an electric field is applied to the liquid crystal and the temperature is slowly low at the same time. To this end, the liquid crystal
15
changes into the Sm C* phase and become stable in the mono stable state having an uniform alignment which spontaneous polarization directions of the liquid crystal
15
are equal to a direction of the electric field, as shown in FIG.
3
. Such a liquid crystal
15
being stable in the mono stable state responds to only an electric field having a polarity contrary to the electric field used at the alignment process. For example, if a negative polarity of electric field −E is applied to the liquid crystal
15
at the phase transition, the spontaneous polarization directions of the liquid crystal
15
are aligned to identify with a direction of the electric field −E. The liquid crystal
15
having such an alignment state are driven although the negative polarity of the electric field is applied to it. Accordingly, the liquid crystal
15
has a characteristic same as that of the primary alignment. Meanwhile, when a positive polarity of electric field +E is applied to the liquid crystals
15
, the liquid crystal
15
is driven, that is, circles along with an outside of virtual cone structure by its spontaneous polarization. In other words, the alignment state of the liquid crystal
15
changes. Accordingly, it is possible to realize a continuous gray scale. As a result, the half V-shape mode of the liquid crystal
15
using a crossed polarizer have a characteristic of half V-shape voltage-transmission V-T as shown in FIG.
5
.
Referring to
FIG. 5
, since the liquid crystal
15
of half V-shape mode, which a primary uniform alignment is formed by the negative polarity of electric field, are not driven, it is not almost the lights transmitted the liquid crystals
15
. On and under the liquid crystal cell, there are disposed a first and a second polarizers having transmission axes orthogonal to each other. The first polarizer disposed under the liquid crystal cell has a transmission axis same as the primary alignment direction of the liquid crystal
15
, and the second on the liquid crystal cell has another transmission axis orthogonal to the primary alignment direction of the liquid crystal
15
. A linerly-polarization light passed the first polarizer is shielded by the second polarizer after transmitting the liquid crystal
15
, thereby allowing a black state to be displayed.
On other hand, if the positive polarity of voltage is applied to the liquid crystal cell, the liquid crystal
15
of the half V-shape mode are driven to increase an amount of light tran
Choi Su Seok
Park Jong Jin
Son Hyeon Ho
Kim Robert H.
LG.Philips LCD Co. , Ltd.
Morgan & Lewis & Bockius, LLP
Rude Timothy
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