Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-04-05
2003-05-13
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C427S162000
Reexamination Certificate
active
06563560
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to liquid crystal displays used as a major component of projectors, projection TVs, etc. Particularly, this invention relates to an apparatus and a method of producing alignment layers to be used for liquid crystal displays and a liquid crystal display having alignment layers produced by the alignment-layer producing apparatus and method.
Active-matrix liquid crystal displays having TFTs, liquid crystal displays having a silicon wafer-to-glass plate stuck structure, etc., have been widely used for visual equipment such as projectors, projection TVs and head-mount displays, with increased production.
A known liquid crystal display
10
is shown in
FIGS. 1 and 2
. A glass substrate
2
is covered with a transparent conductive layer
1
. Another glass substrate or a silicon IC substrate
4
has pixel electrodes (a displaying area)
3
thereon. A pair of alignment layers
5
a
and
5
b
are formed on the transparent conductive layer
1
and the glass substrate
4
, respectively.
The glass substrates
2
and
4
are arranged as facing each other with a gap (cell gap). The cell gap is filled with a liquid crystal
6
through a fill-hole
9
. The glass substrates
3
and
4
are then stuck each other via the liquid crystal
6
with a sealant adhesive
7
through the fill-hole
9
which will be sealed later. The sealant adhesive
7
is a mixture of spacers
7
1
and an adhesive (not shown) which define the cell gap. The glass substrate
2
is covered with an anti-reflective layer
8
.
The alignment layers
5
a
and
5
b
are formed, for example, with a parallel alignment procedure in which an organic polymer such as polyimide is subjected to coating, for example, spin coating or offset printing, followed by baking and rubbing.
The parallel alignment procedure, however, has a lot of steps from polyimide printing to cleaning after rubbing. Moreover, rubbing could generate dust. It is further difficult through this procedure to attain high alignment properties (pretilt angle controllability) required for a desired displaying characteristics.
Application of the known liquid crystal display
10
to projectors and projection TVs requires high contrast ratio.
Another method of forming the alignment layers
5
a
and
5
b
for high contrast ratio is, for example, an oblique evaporation procedure with electron-beam deposition to form a metallic oxide layer of oxide silicon (SiO or SiO
2
) on the substrate from an oblique direction. This method requires no rubbing procedures and achieves high alignment properties and also high contrast ratio especially in vertical alignment system.
The oblique perpendicular alignment procedure is explained in detail with reference to FIG.
3
.
Shown in
FIG. 3
is an electron-beam deposition apparatus
20
equipped with an electron-gun unit U having a crucible
11
and an electron gun
19
with a filament
18
. Oxide silicon
12
is contained in the crucible
11
, as an evaporation source. The oxide silicon
12
is irradiated with electron beams
21
from the electron gun
19
, as indicated by an arrow, so that it is heated and evaporated from the crucible
11
. The evaporated particles of the oxide silicon
12
are dispersed upwards and obliquely deposited on the glass substrate
2
at an evaporation angle &thgr; from the direction of normal line on the substrate surface, thus forming an alignment layer of the oxide silicon
12
thereon. The crucible
11
is usually opened in a (vertical) direction
17
of the normal line on a base
16
of the apparatus
20
. This direction of crucible's opening is called the direction of the electron-gun unit U in the following disclosure.
This oblique evaporation utilizes anisotropic properties of the oxide silicon
12
. Deposition (layer deposition) on the glass substrate
2
from an oblique direction provides an oblique thin layer with obliquely aligned long bar-like liquid-crystal molecules.
FIG. 4
illustrates oxide silicon
14
a
to
14
n
obliquely deposited on the glass substrate
2
and liquid-crystal molecules
15
a
to
15
n
aligned over the oxide silicon
14
a
to
14
n.
An angle &agr; is a pretilt angle, and an angle &ggr; is an angle of layer deposition for the oxide-silicon alignment layer as disclosed later.
These methods are disclosed, for example, in Japanese Unexamined Patent Publication Nos. 5-257146, 6-186563 and 7-159788.
The electron-beam deposition for forming an alignment layer with the oxide silicon
12
as explained above has to meet crucial requirements for an oblique evaporation angle &thgr;. It is, however, difficult to meet such crucial requirements and causes problems when several liquid crystal displays
10
shown in
FIGS. 1 and 2
are formed on a large-size glass substrate
2
.
The location of the glass substrate
2
in the electron-beam deposition apparatus
20
shown in
FIG. 3
varies as the size of the substrate
2
varies as illustrated in FIG.
5
. The oblique evaporation angle &thgr; also varies such as &thgr;a and &thgr;b in
FIG. 5
as the location of the glass substrate
2
varies. This causes variation in angle of layer deposition &ggr; for the oxide silicon
14
a
to
14
n
shown in
FIG. 4
, thus alignment of liquid crystals is not uniform. This results in variation in image quality for the liquid crystal display
10
. In illustration of change in deposition angle &thgr; in
FIG. 5
, “d” is the distance from the center of the glass substrate
2
formed by oblique deposition to the substrate edge.
Moreover, twist angles &Dgr;&psgr; are generated as shown in
FIG. 6
when the glass substrate
2
is formed as being large in the direction perpendicular to the direction in which thin layer-structure of the oxide silicon
14
a
to
14
n
grows, or as being large in the direction perpendicular to the planer direction of the substrate
2
for higher productivity as discussed above. The twist angles &Dgr;&psgr; also depend on the location of the glass substrate
2
in the electron-beam deposition apparatus
20
, as shown in FIG.
3
. These angles also cause variation in image quality for the liquid crystal display
10
.
One solution to these problems requires a small glass substrate
2
or a big deposition chamber
13
(
FIG. 3
) in the electron-beam deposition apparatus
20
to have an enough distance (deposition distance) D from the evaporation source
12
to the glass substrate
2
.
However, the smaller the glass substrate
2
, the more it is difficult to install the substrate
2
in the deposition chamber
13
and adopt an automatic substrate-installation mechanism.
Therefore, such solution has to employ a batch system in which small glass substrates
2
are processed. This system, however, causes generation of dust from the substrates while they are being processed, which results in low yielding and also low image quality.
Moreover, such a batch system takes time for sequential procedures of heating the glass substrates
2
, reaching a target vacuum, forming layers on each substrate, cooling the substrates and vacuum bending. The total production process time thus depends on these procedures.
Furthermore, the bigger the deposition chamber
13
, the more expensive the price of the electron-beam deposition apparatus
20
, and also the larger the volume of the chamber, thus causing longer vacuum-reaching time, heating time, etc., for low productivity.
A long deposition distance D in the deposition chamber
13
could be attained with an evaporation-angle direction component of evaporated particles of the oxide silicon
12
to the glass substrate
2
which is obtained by shifting the electron-gun unit U in the direction horizontal to the base
16
of the electron-beam deposition apparatus
20
, which is disclosed in, for example, Japanese Unexamined Patent Publication 6-186563.
This method, however, causes variation in evaporation rate for the oxide silicon
12
in the direction of evaporation, or lower evaporation rate as the electron-beam gun unit is shifted more and more, which thus results in low production.
The electr
Hosoya Takeshi
Katayama Nobuyasu
Moroboshi Takashi
Nakanishi Tatsushi
Ohkouchi Nozomu
Jacobson & Holman PLLC
Ton Toan
Victor Company of Japan Ltd.
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