Method of manufacturing a liquid crystal cell

Details Method of manufacturing a liquid crystal cell Method of manufacturing a liquid crystal cell

1997-10-30

2001-04-24

Dudek, James A. (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S124000

Reexamination Certificate

active

06222601

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing liquid crystal cell, and more particularly to a simplified method of manufacturing the wide viewing angle liquid crystal cell.
A liquid crystal display device(LCD) which records and processes an optical information basically comprises two substrates, and a liquid crystal between them. In the LCD, it is essential to arrange a liquid crystal director to obtain uniform brightness and high contrast ratio.
Direction of the liquid crystal director is controlled by a variety of process after an alignment layer is formed by depositing polymer on the substrate.
Namely, a coordinate {circle around (n)} of the nematic liquid crystal director in cartesian coordinate of
FIG. 1
is controlled by determining an alignment direction &thgr; and a pretilt angle &phgr; on the alignment layer as follows.
{circle around (n)}=(cos &thgr;cos &phgr;, cos &thgr;cos &phgr;, sin &thgr;)
Recently LCDs used in potable televisions or notebook computers require large size. A twisted nematic liquid crystal display(TN-LCD) has a narrow viewing angle ie., the transmittance in each grey level depends on the viewing angle. This viewing angle dependence, specially, is very strong in the up and down directions. This angular dependence in the up and down directions is caused by the electrically induced liquid crystal(LC) director configuration.
FIG. 2
is drawing showing a structure of the liquid crystal cell having the alignment restricting power, liquid crystal molecules are twisted to right-handed direction by that.
The TN-LC cell is characterized in that the transmittance in each grey level depends on the viewing angle.
FIG. 3
a
is a graph showing a relationship between transmittance and voltage,
FIG. 3
b
is a graph showing a relationship between transmittance and viewing angle in X-X′ direction(right-left direction) of
FIG. 2
, and
FIG. 3
c
is a graph showing a relationship between transmittance and viewing angle in Y-Y′(up-down direction) direction of FIG.
2
.
As shown in
FIGS. 3
a
through
3
c
, while the transmittance in X-X′ direction is symmetrically distributed, the transmittance in Y-Y′ direction is asymmetrically distributed as a result, the wide viewing angle can not be achieved by the gray inversion in Y-Y′ direction.
To solve the above discussed problem, a multi-domain LCD has been introduced as shown in FIG.
4
and FIG.
5
.
FIG. 4
a drawing showing a structure of a two-domain TN LCD(TDTN LCD). Two alignments
26
having a plurality of pretilt angles is formed on each substrate
21
,
22
. When a voltage is applied to the cell, each of the liquid crystal directors is located at opposite directions as a result, the transmittance is compensated and the wide viewing angle is achieved.
Further,
FIG. 5
is a drawing showing a structure of a domain divided TN-LCD(DDTN LCD). A first alignment layer
27
and a second alignment layer
28
are formed on two substrates
21
,
22
, each alignment layer may be organic or inorganic alignment layer. Here, each alignment layer has a different pretilt angle to divide a domain in a single pixel, thereby the wide viewing angle is achieved.
In addition, a four-domain TN LCD using the pixel dividing method provides a improved viewing angle characteristic.
An inverse direction rubbing method as shown in
FIGS. 6
a
through
6
e
have commonly been used to obtain the multi-domain LC cell.
Firstly, a mono-domain is completed as shown in
FIG. 6
b
by rubbing a substrate
21
on which a polyimide
22
is deposited as shown in
FIG. 6
a
. After blocking the domain with a photoresist
23
as shown in
FIG. 6
c
, rubbing is executed in the opposite direction to form the opposite alignment direction as shown in
FIG. 6
d
. Further the photoresist
23
is removed. As a result, as shown in
FIG. 6
e
, the substrate
21
is divided into two domains wherein each domain has a different pretilt angle.
In addition,
FIGS. 7
a
through
7
f
represent a photo-alignment method. Firstly, a first alignment direction is decided by vertically irradiating the linearly polarized light having a first polarization direction on a photo alignment material-coated substrate as shown in
FIG. 7
a
. A first pretilt angle is decided by inclined irradiation of the linearly polarized light as shown in
FIG. 7
b
. After removing a mask to decide a pretilt angle direction of the blocked domain in
FIG. 7
a
, the domain having the first pretilt angle is blocked with a mask. A second alignment direction is decided by vertically irradiating the light having vertical polarization direction against the first polarization direction as shown in
FIG. 7
d
. A second pretilt angle is decided by inclined irradiation of the linearly polarized light to decide a pretilt angle direction in the second alignment direction. When the photoresist is removed, it is possible to provide a two-domain divided substrate as shown in
FIG. 7
f.
In the related art, however, a plurality of complex processes are required. Also in order to provide the four-domain LC cell, double process are required. Namely, in the alignment process of a multi-domain cell such as a two-domain cell, however, since eight exposure processes and four masking processes are needed, the overall process is complicated with an increased cost.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of manufacturing a wide viewing angle liquid crystal cell in which the LC cell is formed by that after forming a pretilt including an alignment direction, a pretilt angle direction, and pretilt angle on a first substrate, then a LC layer is formed between the first substrate and a second substrate without processing a pretilt on the second substrate.
An other object of the present invention is to apply the above-discussed method to a four-domain LC cell.
In order to achieve this object, the manufacturing method of the present invention comprises the steps of forming a first alignment layer and a second alignment layer on a first substrate and a second substrate, forming a pretilt including an alignment direction, a pretilt angle direction, and pretilt angle on an alignment layer of the first substrate, and forming a liquid crystal layer between the first substrate and second substrate. By this method, it is possible to provide the LC cell without processing the pretilt on the second substrate by alignment controlling force of the pretilt on the first substrate.
A multi-domain LC cell applied to the above method comprises the steps of a first alignment layer and a second alignment layer on a first substrate and a second substrate, forming a multi-domain pretilt on an alignment layer of the first substrate, and forming a liquid crystal layer between the first substrate and second substrate. By this method, it is possible to provide the LC cell without processing the pretilt on the second substrate by alignment controlling force of the pretilt on the first substrate.
In accordance with the present invention, it is possible to provide the LC cell without processing the pretilt on the second substrate by alignment controlling force of the pretilt on the first substrate, or by twist force of chiral dopants of the chiral dopants-included LC. As a result, manufacturing process is reduced to ½. Further in multi-domain LC cell according to the present invention, it is possible to provide the multi-domain LC cell without processing the multi pretilt on the second substrate by alignment controlling force of the multi pretilt on the first substrate, or by twist force of chiral dopants of the chiral dopants-included LC. As a result, manufacturing process is reduced to ½.
In the above-discussed method, many alignment processing methods such as the photo alignment method, the rubbing method, and the oblique deposition method may be applied. Also the chiral dopants may be right-handed or left-handed, and its with a weight is preferably about 0.1-0.5% of LC weight.


REFERENCES:
patent: 4323472 (1982-04-01),

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