Method for manufacturing liquid crystal cell using light

A twisted nematic liquid crystal display which have a pixel divided into at least one is fabricated by using a UV light irradiated photo-polymer layer provided on a substrate, which includes a polysiloxane based material or polyvinylfluorocinnamate. The alignment direction and pretilt angle direction are adjusted by anchoring energy and flowing effect of liquid crystal material between substrates.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for manufacturing a liquid 
crystal cell, and more particularly to a method for manufacturing a 
twisted nematic(referred as TN) liquid crystal cell using an ultraviolet 
light irradiated an alignment layer to make two domains in each pixel, 
that is, each domain has a different alignment direction. Thereby, the 
viewing angle compensates each other so as to provide a wider viewing 
angle without grayscale-reversal problem. 
It is well known that the TN LCD, which is now most commonly employed, has 
a narrow and non-uniform viewing angle causing changing a transmittance in 
the gray level FIG. 1a is showing the relation between the transmittance 
of LC cell and a voltage, FIG. 1b is showing the relation between the 
viewing angle in the horizontal direction and the transmittance, and FIG. 
1c is showing the relation between the viewing angle in the vertical 
direction and transmittance. Particularly, referring to FIG. 1, while it 
is a symmetric transmittance between right and left viewing angle, it is 
asymmetric transmittance between upper and lower viewing angle. The 
viewing angle gets narrower because an image inversion occurs between an 
upper and lower viewing angle. To overcome this problem of the narrow 
viewing angle, two major approaches have been proposed i.e., a 
multi-domain TN LCD such as a two-domain TN LCD, a domain-divided TN LCD 
and a four-domain TN LCD, and an optical compensation using two 
retardation films compensated birefringence mode LCD. Referring to a 
structure of LC cell in FIG. 2, each pixel has two-director configuration, 
wherein the two directors are in the opposite direction. Applying a gray 
level voltage to this cell, the LC directors are tilted in opposite 
directions, thereby, two domains is obtained. The two-domain TN LC cell is 
made by the following steps: rubbing the entire alignment layer 2 coated 
on a substrate 1 in the first rubbing direction; making mask to block one 
domain by a photoresist; rubbing the other domain at the reverse direction 
to the first rubbing direction; and removing said photoresist. Thereby, it 
obtains two liquid crystal directors which are in opposite directions in 
each pixel. 
Referring to domain-divided LC cell in FIG. 3, the alignment layers 12,13 
consist of two materials having different pretilt angles. The first 
alignment layer 12 is organic and the second alignment layer 13 is 
inorganic. 
According to the reverse rubbing process in FIG. 4, the polyimide 22 coated 
substrate 21 is rubbed in the first rubbing direction, then photoresist 23 
as a mask is formed on some area of the substrate 21. Then other area of 
the substrate 21 is rubbed in the opposite direction to the first rubbing 
direction and finally, the photoresist 23 is removed. 
For the double SiOx oblique evaporation in FIG. 5, SiOx is evaporating the 
substrate with some angle, the photoresist is formed to divide a pixel. 
Then SiOx is evaporating in the opposite direction to the previous 
evaporating direction on the substrate 21 and the photoresist 23 used as a 
mask is removed. Thereby, two domains having the different pretilt angle 
each other are provided. 
However, the two-domain TN and the domain-divided TN are fabricated through 
the rubbing process and photolithography process so the process becomes 
very complicated, also a particle and an electrostatic discharge are 
generated during the rubbing process. Therefore, the yield is decreased, 
or liquid crystal gets damaged. 
SUMMARY OF THE INVENTION 
An object of the present invention is to improve on the narrow viewing 
angle of TN cells and in particular to provide a method of manufacturing 
multi-domain TN cells using UV light. 
It is other object of the present invention to provide a method for 
manufacturing TN liquid crystal displays to prevent the damage of LC cell, 
and to reduce the number of processes by means of the photo alignment on 
the alignment layer. 
In order to achieve the object, a method for fabricating liquid crystal 
displays according to the present invention comprises the steps of forming 
the pretilt angle by irradiating ultraviolet light on alignment layers, 
and injecting the LC materials between said alignment layers.

DETAILED DESCRIPTION OF THE INVENTION 
According to the conventional photo alignment method using an ultraviolet 
light suggested by Kobayashi, et. al.(SID95 DIGEST 877), the substrate 
coated by PVCN (polyvinylcinnamate) based materials, obtains a pretilt 
angle by adopting a photo-irradiation method of double exposure. That is, 
the alignment direction is oriented by the first UV irradiation, the 
second oblique irradiation with angles of 30 degree, 45 degree, and 60 
degree forms a pretilt angle. However, the pretilt angle formed by this 
method is not desired because it is only 0.1-0.3 degree. 
To obtain a larger pretilt angle in this invention, the alignment layer 
includes a polysiloxane based material or PVCN-F 
(polyvinylfluorocinnamate) which shifts the pretilt angle depending on the 
UV irradiation energy, so that it is possible to obtain the pretilt angle 
more than 45 degree. 
FIG. 6 is showing the TN LC configuration formed by the UV irradiation, the 
linearly polarized UV light irradiates photo-polymer coating the substrate 
to form the alignment direction, then the LC is injected to select desired 
pretilt angle by the flowing effect of the liquid crystal. In the figure, 
the solid arrow indicates the alignment direction or orientation of the 
upper layer, the dotted arrow indicates to the alignment direction or 
orientation of the lower layer. The alignment direction angle of the upper 
layer corresponding to a reference direction refers to .theta.1, and the 
alignment angle of lower layer corresponding to a reference direction 
refers to .theta.2. The difference between .theta.1 and .theta.2 is about 
90 degree. In FIG. 6a, the alignment angle of upper layer .theta.1 is 
90.ltoreq..theta.,.ltoreq.180, and the alignment angle of lower layer 
.theta.2 is 0.ltoreq..theta.2.ltoreq.90, and in FIG. 6b, 
0.ltoreq..theta.1.ltoreq.90, -90.ltoreq..theta.2.ltoreq.0, respectively. 
The above values for .theta..sub.1 and .theta..sub.2, and the values for 
.theta..sub.1-.theta..sub.4 in the remainder of the specification, all 
have units of degrees. 
The liquid crystal molecules blended left-handed chiral dopant, such as 
S-811, is oriented to the alignment angle, and LC is injected between the 
upper layer and the lower layer, thereby the alignment direction and the 
alignment angle is selected. Although most pretilt angle is uniform by 
flowing effect of LC, some is not uniform. Accordingly, the uniform LC 
cell structure is formed by applying an electric field or thermal setting. 
In the case of the pretilt angle settled only by the flowing effect of the 
LC as in FIG. 6b, the pretilt direction of the lower layer is not uniform 
by itself. Even though, the pretilt angle direction of the lower layer can 
be determined by the anchoring energy of the upper layer which is larger 
than lower layer's, and the twisting power of chiral dopant mixed to the 
LC. The magnitude of the pretilt angle is dependent upon the incident 
polarized UV light intensity. 
FIG. 7a is a view showing the first embodiment of a method of manufacturing 
the two-domain TN cell using light, it is set up 
0.ltoreq..theta.1.ltoreq.90, 270.ltoreq..theta.2.ltoreq.360, 
180.ltoreq..theta.3.ltoreq.270, 90.ltoreq..theta.4.ltoreq.180. The 
anchoring energy of the first domain upper layer and the second domain 
lower layer is made larger than the anchoring energy of the first domain 
lower layer and the second domain upper layer, then the LC cell is 
injected in the direction of FIG. 7a. 
FIG. 7b is a view showing the second embodiment of the two-domain TN cell, 
in the first domain, upper layer alignment angle .theta.1 is set up 
0.ltoreq..theta.1.ltoreq.90, 270.ltoreq..theta.2.ltoreq.360, for lower 
layer's alignment angle .theta.2, and in the second domain, upper layer 
alignment angle .theta.3 is set up 90.ltoreq..theta.3.ltoreq.180, 
0.ltoreq..theta.4.ltoreq.90 for lower layer's alignment angle .theta.4. 
The anchoring energy of upper alignment layer is formed higher than the 
anchoring energy of lower alignment layer in both first domain and second 
domain. Then liquid crystal material is injected therebelow. 
Both the upper and lower layers, the alignment direction of first domain is 
oriented parallel to that of the second domain, but anchoring energies of 
the first domain upper layer and the second domain lower layer are set up 
larger than anchoring energies of the first domain lower layer and the 
second domain upper layer. When liquid crystal molecules are injected 
between layers, the pretilt angle directions are determined by the flowing 
effect of liquid crystal molecules. The pretilt directions of the first 
domain upper layer and the second lower layer having larger anchoring 
energy are controlling the opposing pretilt direction in same domain. 
Thereby, the main viewing angle is set in the opposite direction between 
first and second domains. 
In the second embodiment, the alignment directions of upper 
layer(.theta.1,.theta.3) and lower layer(.theta.2,.theta.4) is opposite to 
each other, in addition, the anchoring energies of upper layers are same 
each other as well as the anchoring energies of lower layers being same 
each other, but, the anchoring energies of upper layers are larger than 
the anchoring energies of lower layers. Then the liquid crystal material 
is injected therebelow, thereby the liquid crystal molecules are aligned 
in opposite direction. 
FIG. 8 is the figure showing the configuration of domain-divided TN LC cell 
according to the present invention. That is, the linearly polarized 
ultraviolet light is irradiated into the entire alignment layer to give a 
alignment direction, then, the first domain of the alignment layer is 
blocked with a mask, then the linearly polarized ultraviolet light is 
irradiated into the second domain to give the same alignment direction as 
previous alignment direction, then the mask is removed. At this time, by 
controlling irradiation intensity of the linearly polarized ultraviolet 
light, the sizes of pretilt angles formed on the alignment layer can be 
controlled. Thereby, the domain-divided layer which has a different 
pretilt in each domain, can be obtained. 
The angle between the alignment direction of first domain upper layer and a 
reference direction or horizontal line of substrate, is .theta.1 and angle 
between the alignment direction of the first domain lower layer and the 
horizontal line of substrate is .theta.2, the angle between the alignment 
direction of second domain upper layer and the horizontal line of 
substrate, is .theta.3 and angle between the alignment direction of the 
second domain lower layer and the horizontal line of substrate is 
.theta.4. The angles constituted by alignment directions are respectively 
made 90.ltoreq..theta.1, .theta.3.ltoreq.180 and the alignment direction 
of lower layer in the fist and 0.ltoreq..theta.2, .theta.4.ltoreq.90, 
then, liquid crystal material is injected below the cell. 
In this cell, although the alignment direction angles are same in upper 
layer(.theta.1,.theta.3), and in lower layer(.theta.2,.theta.4), the 
different pretilt angles are set up between domains. Then, when the LC 
material is injected into the LC cell, the pretilt direction is selected 
by flowing effect of LC material. Therefore, it is made opposite the 
direction of main viewing angle between first and second domains, thereby, 
the viewing angle will be compensated. The point above the arrow indicates 
the direction of main viewing angle. 
The present invention provides TN LCDs in which the viewing angle is wider 
by composing of a plurality of domains having a different alignment 
direction each other when it is irradiated by the UV light, in addition, 
the number of processes will be reduced, so the manufacturing cost will be 
decreased, and damage to the LC cell caused for the rubbing process will 
be prevented. 
While the invention has been described in its preferred embodiments, this 
should not be constructed as limitation on the scope of the present 
invention. Accordingly, the scope of the present invention should be 
determined not by the embodiments illustrated, but by the appended claims 
and their legal equivalents.