U.S. patent application number 09/819481 was filed with the patent office on 2001-11-29 for method of manufacturing a display device.
This patent application is currently assigned to SEIKO INSTRUMENTS INC.. Invention is credited to Kumai, Sachiko, Shimada, Kazuo, Suginoya, Mitsuru.
Application Number | 20010046026 09/819481 |
Document ID | / |
Family ID | 12666089 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046026 |
Kind Code |
A1 |
Suginoya, Mitsuru ; et
al. |
November 29, 2001 |
METHOD OF MANUFACTURING A DISPLAY DEVICE
Abstract
In a display device in which a display material is enclosed in a
gap between bonded glass substrates and in a method of
manufacturing the same, in order to use a conventional method of
scratching the surfaces of the glass substrates to divide them into
cells, sodium atoms on the surface of the glass substrate having a
thickness of not larger than 2 mm are replaced with atoms having an
ion radius larger than that of sodium to form a chemically
reinforced layer having a thickness of not larger than 20 .mu.m.
According to this display device and this method of manufacturing
the same, the strength of a flat display device used in a portable
electric equipment can be easily improved.
Inventors: |
Suginoya, Mitsuru;
(Chiba-shi, JP) ; Shimada, Kazuo; (Chiba-shi,
JP) ; Kumai, Sachiko; (Chiba-shi, JP) |
Correspondence
Address: |
Bruce L. Adams
Adams & Wilks
50 Broadway, 31st Floor
New York
NY
10004
US
|
Assignee: |
SEIKO INSTRUMENTS INC.
|
Family ID: |
12666089 |
Appl. No.: |
09/819481 |
Filed: |
March 28, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09819481 |
Mar 28, 2001 |
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08798289 |
Feb 7, 1997 |
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6222604 |
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Current U.S.
Class: |
349/158 |
Current CPC
Class: |
C03C 21/002 20130101;
G02F 1/133345 20130101; G02F 1/133302 20210101; G02F 1/1333
20130101 |
Class at
Publication: |
349/158 |
International
Class: |
G02F 001/1333 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 29, 1996 |
JP |
8-043522 |
Claims
What is claimed is:
1. A display device comprising: a pair of glass substrates, an
electrode being formed on the surface of each of said glass
substrates, and said glass substrates being opposite to each other;
and a display material enclosed in a gap between said glass
substrates; wherein a chemically reinforced layer having a
thickness of not larger than 20 .mu.m is formed on the surface of
at least one of said glass substrates.
2. A method of manufacturing a display device, comprising: a
chemical reinforcing treatment step of immersing a glass substrate
in a solution or a molten solution of salt containing positive ions
having an ion radius larger than that of sodium so that a
chemically reinforced layer having a thickness of not larger than
20 .mu.m is formed on said glass substrate.
3. A method of manufacturing a display device, comprising the steps
of: immersing a glass substrate having a thickness of not larger
than 2 mm in a solution or a molten solution of salt containing
position ions having an ion radius larger than that of sodium;
forming a chemically reinforced layer having a thickness of not
larger than 20 .mu.m on said glass substrate; fabricating a
plurality of cells made of a pair of glass substrates by using said
glass substrate on which said chemically reinforced layer has been
formed; scratching the surface of said glass substrate on which
said chemically reinforced layer has been formed; and cutting said
glass substrate so that said cells are divided into individual
ones.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a display device and a
method of manufacturing the same, and more particularly, to a
display device which has been improved in the strength of
impact-resistant properties or the like and a method of
manufacturing the same.
[0002] A schematic structure of a conventional display device will
be described below. A sodium passivation film made of SiO.sub.2 is
formed on the surface of a glass substrate made of soda-lime glass,
borosilicate glass, or the like, and further a transparent
electrode made of film-like ITO grown by a method such as
evaporation or sputtering is formed thereon while being patterned.
Two glass substrates, on the surface of each of which the sodium
passivation film and the transparent electrode are sequentially
formed as described above, are bonded to each other with a sealing
agent so that they are opposite to each other, and a display
material such as a liquid crystal or an electrochromic material is
enclosed in the gap between the glass substrates to form the
display device.
[0003] Since such a display device is excellent in portability and
consumes little electric power, contrary to a CRT or the like, it
is widely used at present for a digital watch, a display for a
computer, and so on.
[0004] However, since a highly transparent substrate is desired for
such a flat panel display, a glass substrate is used in the
existing circumstances. However, the glass substrate has a defect
that it is liable to break because it is made of glass.
[0005] Especially, since the flat panel display is often used for a
portable electric equipment, it is required to be strong against
impact of drop. On the other hand, since the portable electric
equipment is desired to be light, thin, short, and small, the
thickness of the glass substrate is required to be thin, which
results in deterioration in the strength. That is, the display
device has such a contradictory problem.
SUMMARY OF THE INVENTION
[0006] It is therefore an object of the present invention to
realize a display device which has sufficient strength even if the
thickness of a glass substrate is made thin.
[0007] In order to solve the problem, according to the present
invention, in a display device in which a pair of glass substrates,
on the surface of each of which an electrode is formed, are
opposite to each other, and a display material is enclosed in the
gap between the substrates, a chemically reinforced layer having a
thickness of not larger than 20 .mu.m is formed on the surface of
at least one of the glass substrates. Further, a method of
manufacturing the display device comprises a chemical reinforcing
treatment step of immersing a glass substrate in a solution or a
molten solution of salt containing positive ions having an ion
radius larger than that of sodium to form a chemically reinforced
layer having a thickness of not larger than 20 .mu.m on the glass
substrate.
[0008] Still further, a method of manufacturing the display device
comprises the steps of immersing a glass substrate in a solution or
a molten solution of salt containing positive ions having an ion
radius larger than that of sodium, forming a chemically reinforced
layer having a thickness of not larger than 20 .mu.m on the glass
substrate, forming a plurality of cells composed of a pair of glass
substrates using the glass substrate on which the chemically
reinforced layer is formed, scratching the surface of the glass
substrate on which the chemically reinforced layer is formed, and
cutting the glass substrate to divide the cells into individual
ones.
[0009] In the display device according to the present invention,
sodium atoms on the surface of the glass substrate are replaced
with atoms having an ion radius larger than that of sodium, so that
the substrate is chemically reinforced and improved in the
mechanical strength.
[0010] Further, the strength of the glass of the display device can
be improved by merely adding a step of immersing the glass
substrate in the solution or molten solution containing the
positive ions having an ion radius larger than that of sodium,
which is very simple. Further, according to this method, the
thickness of the chemically reinforced layer can be easily
controlled by adjusting an immersion time or the like, and the
device can be formed under such a condition that working of glass
cutting or the like can be carried out even after reinforcement of
the substrate.
[0011] Still further, in the case where glass having a thickness of
not larger than 2 mm, if the thickness of the chemically reinforced
layer is not larger than 20 .mu.m, the display device having
sufficient mechanical strength can be easily obtained without
extremely complicating a conventional step of glass cutting or the
like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a sectional view showing a display device
according to the present invention; and
[0013] FIGS. 2(A) to 2(F) are views depicting manufacturing steps
of the display device according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] Glass has originally considerable strength in theory.
However, in practice, it is easily broken because of its
brittleness. The reason is that since tensile stress exists on the
surface of glass, if some kind of defects are distributed on the
surface, the stress is concentrated to the defects and they become
break starting points so that the glass is broken at a level
considerably lower than theoretical strength. In view of such
breaking mechanism of glass, there are proposed reinforced glass
such as wind-cooled tempered glass, low expansion glass, high
elasticity glass, crystallized glass, and chemically reinforced
glass.
[0015] The wind-cooled tempered glass has strength against
breakage, which is improved by converting tensile stress existing
on the surface of glass to compressive stress. Concretely, jets of
air are blown to the surface of a glass plate heated up to about
700.degree. C., and the glass plate is cooled while keeping the
temperature difference between the interior and the surface. As a
result, in the solidified state, distortion remains as compressive
stress on the surface and as tensile stress in the interior
according to the temperature difference, so that the strength of
the glass is improved. At this time, the compressive stress on the
surface reaches 900-1500 kg/cm.sup.2, and the tensile stress in the
interior becomes 300- 500 kg/cm.sup.2. It is said that the
thickness of a practical reinforced layer is one sixth of the
thickness of the glass or not less than 100 .mu.m.
[0016] The low expansion glass is devised to prevent glass from
breaking due to thermal stress generated when the glass is heated
or cooled.
[0017] The high elasticity glass is made by introducing nitrogen,
which has strong bonding force, into conventional oxide glass to
reinforce the mesh of the glass. The elasticity thereof is much
improved to the degree of 30 to 50 percent, and therefore the
strength is improved.
[0018] The crystallized glass is a kind of composite material in
which crystal grains are dispersed into the matrix by reheating
glass, and the progress of crack from breakage is blocked by the
crystal grains.
[0019] The chemically reinforced glass is, like the wind-cooled
tempered glass, improved in the strength against breakage by
converting the tensile stress existing on the glass surface to the
compressive stress. Concretely, glass containing alkaline ions (Li,
Na, etc.) having a small ion radius is immersed in alkaline molten
salt having a large ion radius at a temperature (for example,
400.degree. C.) within a range not higher than the glass transition
point, so that ion exchange between both is carried out on the
surface of the glass. As a result, the volume is increased in the
layer of glass surface, where the compressive stress exists after
cooling. The compressive stress of about 100 Kg/mm.sup.2 can be
obtained.
[0020] Among these reinforced glasses, the wind-cooled tempered
glass, low expansion glass, high elasticity glass, and crystallized
glass are difficult to be applied to a display device since they
have such restriction that their glass compositions themselves are
changed or the reinforcing treatment is carried out during the
production of glass so that it can not be carried out at a post
working step. On the other hand, the chemically reinforced glass
can be included in manufacturing steps of a display device since
the chemical reinforcing treatment can be carried out at a
relatively low temperature. That is, even after a step (polishing
step, etc.) peculiar to a display device is carried out, the
chemical reinforcing treatment can be carried out, so that the use
of the chemically reinforced glass does not largely change and
complicate conventional manufacturing steps of a display
device.
[0021] When a flat panel display for a liquid crystal display
device or the like is fabricated, there are adopted steps in which
a large number of display device cells are formed on two large
glass substrates, the two large glass substrates are bonded to each
other, and then the substrates are cut to divide the display device
cells into individual ones. This cutting is generally carried out
by scratching the surface of the glass by a hard blade of diamond
or the like and then applying a pressure to the glass to break it.
In the case where the glass is chemically reinforced, if the
chemically reinforced layer is too thick, the scratch is hard to be
transmitted into the interior of the glass, so that the cutting and
dividing can not be carried out well and end faces of the divided
cells do not become linear.
[0022] Accordingly, in the present invention, the chemical
reinforcement is selected as a method of reinforcing glass, and the
chemical reinforcing step is made to be carried out in
manufacturing steps of a display device so that the cutting and
dividing step can be carried out like a conventional method.
[0023] That is, a glass substrate having a thickness of not larger
than 2 mm is immersed in a solution or a molten solution of salt
containing positive ions having an ion radius larger than that of
sodium, so that a chemically reinforced layer having a thickness of
not larger than 20 .mu.m is formed on the surface of the glass
substrate.
[0024] According to this method, since sodium atoms on the surface
of the glass substrate are replaced with atoms having an ion radius
larger than that of sodium so that the glass substrate is
chemically reinforced, even if the thickness of the glass substrate
is made thin, sufficient strength can be kept. Further, this method
does not complicate conventional steps such as glass cutting.
[0025] Here, it is sufficient that the glass substrate contains
alkaline ions even if the quantity thereof is extremely small. Lead
glass, borosilicate glass and the like can be used, not to mention
soda glass.
[0026] Hereinafter, examples of the present invention will be
concretely described with reference to FIGS. 1 and 2.
Embodiment 1
[0027] FIG. 1 is a schematic sectional view showing an example of a
display device according to the present invention. Although the
basic structure thereof is similar to that of a conventional
display device, the surfaces of glass substrates 1 and 4 made of
soda glass are chemically reinforced. Sodium passivation films 2
and 5 made of SiO.sub.2 are formed on the chemically reinforced
glass substrates, and further transparent electrodes 3 and 6 made
of film-like ITO grown by a method such as evaporation or
sputtering are formed on the upper surfaces of the passivation
films while being patterned. The thus formed glass substrates 1 and
4 are made opposite to each other and bonded with a sealing agent
7, and a display material 8 made of an STN liquid crystal is
enclosed in the gap between the substrates to form the display
device.
[0028] FIGS. 2(A) to 2(F) depict a method of manufacturing a
display device, including a chemical reinforcing step of the
present invention. In FIG. 2(A), a soda glass 31 having a thickness
of 0.55 mm is prepared. In FIG. 2(B), the soda glass is polished
until the flatness of the surface sufficient for a display device
can be obtained. In FIG. 2(C), the soda glass is immersed in a
reinforcing solution 32 made of a mixed molten salt of 50%
KNO.sub.3 and 50% KNO.sub.2 with a temperature of 430.degree. C.,
so that a chemically reinforced glass substrate 33 is obtained.
This immersion time was adjusted so that the thickness of a
chemically reinforced layer was 8 .mu.m from the surface. In FIG.
2(D), a sodium passivation film 34 made of SiO.sub.2, and
transparent electrodes 35 made of film-like ITO grown by a method
such as evaporation or sputtering, the number of which is equal to
that of a plurality of display devices to be formed and the
patterns of which are equal to each other, are formed on the glass
substrate. In FIG. 2(E), a sodium passivation film 37 and a
plurality of transparent electrodes 38 are formed on a glass
substrate 36, the surface of which is chemically reinforced like
the glass substrate 33. The glass substrate 36 is made opposite to
the glass substrate 33 and both are bonded with sealing agents 39,
so that a plurality of cells are formed from the same glass
substrates. In FIG. 2(F), linear scratches 40 are made on the glass
substrates by a diamond blade at positions where the substrates are
expected to be divided. Thereafter, the vicinities of the scratches
40 are pressurized to cut and divide the glass. A display material
made of an STN liquid crystal is enclosed in the gap of
individually divided cells to form the display device.
[0029] In such an STN liquid crystal device, to realize the uniform
thickness of a liquid crystal layer, the precision of 0.05 .mu.m is
required for the flatness of the surface of the substrate. Thus,
polishing of the glass surface is an indispensable step. However,
if the reinforced glass is used as a raw material from the first,
polishing of the surface is hard to be performed and causes an
extreme difficulty. However, as in this example, if the chemical
reinforcing treatment is carried out at a relatively low
temperature after polishing, the flatness of the glass surface can
be easily obtained, and the warp and undulation of the glass can be
avoided even in the subsequent reinforcing treatment, so that the
display device improved in the strength can be realized without
degrading the display performance.
[0030] Further, in spite of the reinforced glass, cutting and
dividing was able to be carried out almost without changing a
conventional step, so that the display device was able to be
fabricated very simply. Nevertheless, when the display device
according to this example was fallen from the height of 2 m, no
damage was observed, which showed that the device was superior in
the
Comparative Example
[0031] A display device was fabricated under the same conditions as
example 1 except that a time of chemical reinforcement treatment in
example 1 was prolonged so that the thickness of the chemically
reinforced layer was 25 .mu.m from the surface thereof. In the
cutting and dividing step, the broken surface of glass become
sawlike and a large number of cracks were observed. Further, when
the display device was fallen from the height of 2 m, it was broken
from the cracks.
Example 2
[0032] A glass substrate was a soda glass having a thickness of 0.7
mm, which was immersed in a reinforcement solution 42 made of
KNO.sub.3 molten salt heated up to 400.degree. C. so that it was
chemically reinforced. A display device was fabricated under the
same conditions as example 1 except that an immersion time at the
chemical reinforcement was adjusted so that the thickness of a
chemically reinforced layer was 15 .mu.m from the surface thereof.
Also in this example, the same effects as example 1 were
obtained.
Example 3
[0033] A glass substrate was a soda glass having a thickness of 1.1
mm, and an immersion time for chemical reinforcement was adjusted
so that the thickness of a chemically reinforced layer was 20 .mu.m
from the surface thereof. A display device was fabricated under the
same conditions as example 1 except the above. Also in this
example, the same effects as example 1 were obtained.
Example 4
[0034] A glass substrate was a lead glass and a display device was
fabricated under the same conditions as example 1 except the above.
Also in this example, the same effects as example 1 were
obtained.
Example 5
[0035] A glass substrate was a borosilicate glass, and a display
device was fabricated under the same conditions as Example 1 except
the above. Also in this example, the same effects as Example 1 were
obtained.
[0036] According to these methods, sodium atoms on the surface of
the glass are replaced with atoms having an ion radius larger than
that of sodium so that the chemical reinforcement was carried out.
Accordingly, even if the thickness of the glass substrate is made
thin, sufficient strength can be kept. Further, since the chemical
reinforcing treatment can be carried out after polishing of the
surface of the glass substrate, the reinforced glass having high
precision of surface roughness can be easily obtained.
[0037] Further, in the case where the glass substrate having a
thickness of not larger than 2 mm, if the thickness of the
chemically reinforced layer is made not larger than 20 .mu.m,
sufficient mechanical strength can be obtained, and further a
conventional step such as glass cutting is not complicated. That
is, a portable display device improved in strength against impact
of drop can be easily obtained.
[0038] A glass substrate especially effective in the present
invention is a soda glass substrate containing a large amount of
sodium.
* * * * *