U.S. patent application number 11/191219 was filed with the patent office on 2005-12-01 for active matrix substrate, method of manufacturing active matrix substrate, and intermediate transfer substrate for manufacturing active matrix substrate.
Invention is credited to Akiyama, Masahiko, Hara, Yujiro, Miura, Kentaro, Onozuka, Yutaka.
Application Number | 20050264176 11/191219 |
Document ID | / |
Family ID | 34461012 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050264176 |
Kind Code |
A1 |
Onozuka, Yutaka ; et
al. |
December 1, 2005 |
Active matrix substrate, method of manufacturing active matrix
substrate, and intermediate transfer substrate for manufacturing
active matrix substrate
Abstract
In an active matrix substrate, the substrate includes a pixel
region and a peripheral region surrounding the pixel region. A
plurality of adhesive layers arranged to form a matrix having rows
and columns are arranged in the pixel region, and pluralities of
active elements are formed, respectively, on the plural adhesive
layers. A spacer layer is formed in the peripheral region, and a
uniform pressure is applied between the active element and the
adhesive layer in performing the transfer.
Inventors: |
Onozuka, Yutaka;
(Yokohama-shi, JP) ; Akiyama, Masahiko; (Tokyo,
JP) ; Hara, Yujiro; (Yokohama-shi, JP) ;
Miura, Kentaro; (Kawasaki-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
34461012 |
Appl. No.: |
11/191219 |
Filed: |
July 28, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11191219 |
Jul 28, 2005 |
|
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10947291 |
Sep 23, 2004 |
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Current U.S.
Class: |
313/500 ;
257/E27.13 |
Current CPC
Class: |
H01L 2224/95 20130101;
H01L 27/146 20130101 |
Class at
Publication: |
313/500 |
International
Class: |
H01J 063/04; H01J
001/62; H01L 021/76 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 2003 |
JP |
2003-332815 |
Claims
1-24. (canceled)
25. An intermediate transfer substrate, comprising: a substrate
having an element region and a peripheral region surrounding the
element region; a peeling layer formed on the substrate; a
plurality of active elements formed apart from each other on the
peeling layer on the element region; and a spacer layer formed in
the peripheral region on the substrate.
26. The intermediate transfer substrate according to claim 25,
wherein the spacer layer has a thickness equal to or larger than
the sum of the thickness of the peeling layer and the thickness of
the active element.
27. The intermediate transfer substrate according to claim 25,
wherein the spacer layer and the adhesive layer are formed of the
same material.
28. The intermediate transfer substrate according to claim 27,
wherein each of the spacer layer and the adhesive layer is formed
of an acrylic resin.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2003-332815,
filed Sep. 25, 2003, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an active matrix substrate,
a method manufacturing an active matrix substrate, and an
intermediate transfer substrate for manufacturing an active matrix
substrate.
[0004] 2. Description of the Related Art
[0005] An active matrix type display device having active elements
arranged on matrix-like pixels permits realizing a planar type
display device of a high image quality. Particularly, a liquid
crystal display device (LCD), in which a liquid crystal is used as
an optical shutter and each pixel is driven by an active element
such as a TFT, is widely used in various devices such as a PC
monitor and a television receiver for a video display.
[0006] Also, an organic EL display device that permits displaying a
full color image on a thin panel has been developed. In the organic
EL display device, the organic EL materials that emit light rays of
red, green and blue are formed into pixels by an ink jet method or
a mask vapor deposition method, and each pixel thus formed is
driven by an active element such as a thin film transistor
(TFT).
[0007] In almost all the types of the display device, the active
element is formed on a glass substrate. However, the glass
substrate tends to be cracked and is heavy. Also, the display
device having a glass substrate incorporated therein tends to be
broken and is heavy. Such being the situation, it is desirable to
develop a tough and lightweight display device. It is also
desirable to develop a flexible display device that can be bent or
folded freely.
[0008] Under the circumstances, a display device comprising a
flexible substrate excellent in the impact resistance and light in
weight such as a plastic substrate attracts attentions as a display
device satisfying the requirements given above. In the display
device of the particular type, it is necessary for an active
element such as a thin film transistor (TFT) to be formed on the
plastic substrate. Presently, amorphous silicon or polycrystalline
silicon (polysilicon) is widely used for forming the thin film
transistor. What should be noted is that it is absolutely necessary
to employ a high temperature process of about 350.degree. C. to
600.degree. C. for forming the thin film transistor. On the other
hand, the plastic substrate is resistant to heat of only up to
about 200.degree. C. It follows that it is difficult to form the
thin film transistor directly on the plastic substrate.
[0009] As a method for overcoming the difficulty described above,
proposed is a method of using an element formation substrate and a
final substrate in place of the method of forming an active element
directly on the plastic substrate. To be more specific, the element
formation substrate is formed of a glass substrate having thin film
transistors formed thereon at a high density so as to form a thin
film transistor array. On the other hand, pluralities of plastic
substrates are used as the final substrates. Of course, the thin
film transistor array is transferred from the element formation
substrate onto the plastic substrates used as the final substrates.
The particular method is disclosed in, for example, Japanese Patent
Disclosure (Kokai) No. 6-118441, Japanese Patent Disclosure No.
11-142878 and Japanese Patent Disclosure No. 2001-7340. In this
method, the thin film transistor equivalent in characteristics to
the conventional thin film transistor can be formed on the plastic
substrate because the thin film transistor can be formed at the
temperature substantially equal to that for forming the
conventional thin film transistor. It should also be noted that the
transfer cost can be lowered because the thin film transistor array
can be transferred from a single element formation substrate onto a
plurality of final substrates.
[0010] In the conventional method, however, it is possible for even
the element that should not be transferred to be transferred from
the element formation substrate onto the final substrates so as to
give rise to the problem that the transfer selectivity is
lowered.
BRIEF SUMMARY OF THE INVENTION
[0011] An object of the present invention is to provide a method of
manufacturing an active matrix substrate having high transfer
selectivity, an active matrix substrate manufactured by the
particular manufacturing method, and an intermediate transfer
substrate used in the method of manufacturing the active matrix
substrate.
[0012] According to an aspect of the present invention, there is
provided an active matrix substrate, comprising:
[0013] a substrate having a pixel region and a peripheral region
surrounding the pixel region;
[0014] a plurality of adhesive layers arranged in a matrix having
rows and columns in the pixel region;
[0015] a plurality of active elements formed on the adhesive
layers, respectively; and
[0016] a spacer layer formed in the peripheral region.
[0017] According to another aspect of the present invention, there
is provided a method of manufacturing an active matrix substrate,
comprising:
[0018] forming active elements on an element formation
substrate;
[0019] bonding the active elements formed on the element formation
substrate to an intermediate transfer substrate;
[0020] removing the element formation substrate bonded to the
intermediate transfer substrate with the active elements interposed
therebetween;
[0021] forming adhesive layers in a pixel region of a final
substrate having the pixel region and a peripheral region
surrounding the pixel region;
[0022] forming a spacer layer in the peripheral region of the final
substrate;
[0023] transferring the active elements bonded to the intermediate
transfer substrate to the adhesive layer of the final
substrate;
[0024] forming wirings on the final substrate; and
[0025] connecting the active elements on the final substrate to the
wirings.
[0026] According to another aspect of the present invention, there
is provided a method of manufacturing an active matrix substrate,
comprising:
[0027] forming active elements on a element formation
substrate;
[0028] preparing an intermediate transfer substrate having a first
pixel region and a first peripheral region surrounding the first
pixel region;
[0029] bonding the active elements on the element formation
substrate to the first pixel region;
[0030] forming a spacer layer in the first peripheral region;
[0031] removing the element formation substrate bonded to the
intermediate transfer substrate with the active element interposed
therebetween;
[0032] preparing a final substrate having a second pixel region and
a second peripheral region surrounding the second pixel region;
[0033] forming an adhesive layer in the second pixel region;
[0034] transferring the active elements bonded to the intermediate
transfer substrate to the adhesive layer on the final
substrate;
[0035] forming wirings on the final substrate; and
[0036] connecting the active elements on the final substrate to the
wirings.
[0037] Further, according to still another aspect of the present
invention, there is provided an intermediate transfer substrate,
comprising:
[0038] a substrate having an element region and a peripheral region
surrounding the element region;
[0039] a peeling layer formed on the substrate;
[0040] a plurality of active elements formed apart from each other
on the peeling layer on the element region; and
[0041] a spacer layer formed in the peripheral region on the
substrate.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0042] FIG. 1 is a plan view schematically showing the construction
of an active matrix substrate according to a first embodiment of
the present invention;
[0043] FIG. 2 is a cross sectional view for describing the
manufacturing method of the active matrix substrate shown in FIG.
1;
[0044] FIG. 3 is a cross sectional view for describing the
manufacturing method of the active matrix substrate shown in FIG.
1;
[0045] FIG. 4 is a cross sectional view for describing the
manufacturing method of the active matrix substrate shown in FIG.
1;
[0046] FIG. 5 is a cross sectional view for describing the
manufacturing method of the active matrix substrate shown in FIG.
1;
[0047] FIG. 6 is a cross sectional view for describing the
manufacturing method of the active matrix substrate shown in FIG.
1;
[0048] FIG. 7 is a cross sectional view for describing the
manufacturing method of the active matrix substrate shown in FIG.
1;
[0049] FIG. 8 is a plan view for describing the manufacturing
method of the active matrix substrate shown in FIG. 1;
[0050] FIG. 9 is a plan view showing the active elements included
in the active matrix substrate shown in FIG. 1;
[0051] FIG. 10 is a plan view showing the active elements included
in the active matrix substrate shown in FIG. 1;
[0052] FIG. 11 is a cross sectional view for describing the
manufacturing method of the active matrix substrate shown in FIG.
1;
[0053] FIG. 12 is a cross sectional view for describing the
manufacturing method of the active matrix substrate shown in FIG.
1;
[0054] FIG. 13 is a cross sectional view schematically showing the
construction of the active matrix element formed on the active
matrix substrate shown in FIG. 1;
[0055] FIG. 14 is a plan view schematically showing the positional
relationship between a provisional adhesive layer and a spacer
layer in the active matrix substrate according to a modification of
the present invention;
[0056] FIG. 15 is a plan view schematically showing the positional
relationship between a provisional adhesive layer and a spacer
layer in the active matrix substrate according to another
modification of the present invention;
[0057] FIG. 16 is a plan view schematically showing the positional
relationship between a provisional adhesive layer and a spacer
layer in the active matrix substrate according to another
modification of the present invention;
[0058] FIG. 17 is a plan view schematically showing the positional
relationship between a provisional adhesive layer and a spacer
layer in the active matrix substrate according to another
modification of the present invention;
[0059] FIG. 18 is a plan view schematically showing the positional
relationship between a provisional adhesive layer and a spacer
layer in the active matrix substrate according to another
modification of the present invention;
[0060] FIG. 19 is a cross sectional view for describing the
manufacturing method of an active matrix substrate according to
another modification of the present invention; and
[0061] FIG. 20 is a cross sectional view for describing the
manufacturing method of an active matrix substrate according to
still another modification of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0062] An active matrix substrate according to an embodiment of the
present invention and a method of manufacturing the same will now
be described with reference to the accompanying drawings.
[0063] Before describing the active matrix substrate of the present
invention, the situation under which the present inventors have
arrived at the present invention will now be described briefly.
[0064] In the manufacture of an active matrix substrate, an active
element is formed first on a element form ation substrate, followed
by transferring the active element from the element formation
substrate onto an intermediate transfer substrate and subsequently
transferring selectively the active element from the intermediate
transfer substrate onto a final substrate. The present inventors
have looked into the selectivity of the transfer in selectively
transferring the active element in the process of manufacturing the
active matrix substrate.
[0065] It has been clarified that, in the final substrate, the
transfer selectivity is high in the region into which the active
element is to be transferred and in the region in which the pixel
electrode is to be formed, particularly, in the region including
the central portion of the pixel region. On the other hand, it has
been clarified that, in the final substrate, the transfer
selectivity within the pixel region is lowered as the transfer
region approaches the peripheral region onto which the active
element is not transferred from the central portion of the pixel
region, the peripheral region being formed to surround the pixel
region. Particularly, it has been clarified that a first type
defective transfer is generated more frequently than a second type
defective transfer, as the transfer region approaches the
peripheral region in the final substrate, compared with the case
where the transfer region is in the central region of the pixel
region. Incidentally, the first type defective transfer noted above
denotes that the active element that should not be transferred is
transferred. On the other hand, the second type defective transfer
denotes that the active element that should be transferred is not
transferred. It is considered reasonable to understand that the
defective transfer is generated because an adhesive layer for
bonding the active element is not included in the peripheral region
of the final substrate and, thus, the spacer effect produced by the
adhesive layer is lowered. In other words, when the active element
is transferred from the intermediate transfer substrate onto the
final substrate, the pressure for pushing the active element
against the intermediate transfer substrate is applied more
strongly to the active element in the peripheral region than in the
pixel region of the final substrate. It follows that the active
element on the intermediate transfer substrate is brought into
contact more easily with the final substrate, with the result that
the unselected active element in the pixel region or the active
element in the peripheral region of the intermediate transfer
substrate is also transferred onto the final substrate. Such being
the situation, the yield in the manufacture of the active matrix
substrate is lowered so as to increase the manufacturing cost.
[0066] Under the circumstances, in the manufacturing process of the
active matrix substrate according to the present invention, a space
layer is formed in the peripheral region of the intermediate
transfer substrate or in the peripheral region of the final
substrate so as to permit a substantially uniform pressure to be
applied to the active element. In this fashion, it is possible in
the present invention to prevent the defective transfer that the
active element that should not be transferred is transferred.
[0067] The active matrix substrate according to a first embodiment
of the present invention will now be described with reference to
FIG. 1. The active matrix substrate shown in FIG. 1 corresponds to
a final substrate 11. As shown in the drawing, a spacer layer 16 is
formed in a peripheral region 13 of the substrate 11.
[0068] The active matrix substrate, i.e., final substrate) 11 has a
surface that is partitioned into a pixel region 12 including the
central portion of the substrate 11 and expanded to cover the
periphery of the central region, and the peripheral region 13
formed to surround the pixel region 12. A plurality of adhesive
layers 14 are arranged to form a matrix in the pixel region 12 on
the active matrix substrate 11, and an active element 15 is formed
on each of the adhesive layers 14. Also, the spacer layers 16 are
formed in the peripheral region 13 on the active matrix substrate
11 such that the adhesive layers 14 and the spacer layers 16 are
arranged to form a matrix including a plurality of rows and a
plurality of columns on the active matrix substrate 11. The
adhesive layers 14 are sized substantially equal to or slightly
larger than the active elements 15, and the spacers 16 are sized
substantially equal to the adhesive layers 14.
[0069] As described above, the spacer layers 16 are formed in the
present invention in the peripheral region 13 on the active matrix
substrate 11 so as to prevent the defective transfer that the
active element 15 is transferred onto a non-transfer section. To be
more specific, in the process of allowing an intermediate transfer
substrate (not shown), which is described herein later, to be
pushed against the active matrix substrate 11 for transferring the
active element 15 onto the active matrix substrate 11, the spacer
layers 16 permit the pressure substantially equal to the pressure
applied to the central portion of the pixel region 2 to be applied
between the active matrix substrate 11 and the intermediate
transfer substrate even in the edge portion of the pixel region
12.
[0070] It should also be noted that, in the active matrix substrate
11 shown in FIG. 1, the pitches in the X- and Y-directions of the
adhesive layers 14, the pitches in the X- and Y-directions of the
spacer layers 16, and the distance between the adhesive layer 14
and the spacer layer 16 are defined to be 1x(0)=1x(1)=1x(2) and
1y(0)=1y(1)=1y(2), where 1x(0) and 1y(0) denote the pitches of the
adhesive layers 14 in the pixel region 12 in the X-direction (row
direction) and the Y-direction (column direction), respectively,
1x(2) and 1y(2) denote the pitches of the spacer layers 16 in the
peripheral region 13 in the X- and Y-directions, respectively, and
the 1x(1) and 1y(1) denote the distances between the adhesive layer
14 and the spacer layer 16 in the X- and Y-directions,
respectively. In other words, the adhesive layers 14 and the spacer
layers 16 are arranged in the same period in the pixel region 12
and the peripheral region 13. Where the adhesive layers 14 and the
spacer layers 16 are arranged at the same pitch as pointed out
above, it is possible to allow the pressures applied to the pixel
region 12 and the peripheral region 13 to be substantially equal to
each other. Also, in the particular arrangement, the spacer layers
16 can be formed simultaneously with formation of, for example, the
adhesive layers 14.
[0071] Concerning the spacer pitch, it suffices for the conditions
of 1x(2).ltoreq.1x(0) and 1y(2).ltoreq.1y(0) to be satisfied even
if the adhesive layers 14 and the spacer layers 16 are not arranged
at the same pitch. If the conditions given above are satisfied, it
is possible for the active elements 15 to be transferred
successively in any order.
[0072] As shown in FIG. 1, a provisional adhesive layer for
allowing the active matrix substrate 11 to be provisionally bonded
to an intermediate transfer substrate (not shown) is formed in the
intermediate transfer substrate in the range denoted by a reference
numeral 17. It is desirable for the distance 1y(3) between the
inner peripheral edge of the range 17 of the provisional adhesive
layer and the edge of the spacer layer 16 to be set larger than the
pitch 1y(0) of the adhesive layers 14 in the Y-direction. If the
distance 1y(3) is set larger than the pitch 1y(0), the spacer layer
16 is brought into contact with the provisional adhesive layer 17
when the active elements 15 are repeatedly transferred
successively. As a result, the effect produced by the spacer layers
16 for allowing the distribution of the applied pressure to be
uniform without fail is increased so as to prevent the defective
transfer of the active elements 15.
[0073] The manufacturing method of a liquid crystal display device
comprising the active matrix substrate shown in FIG. 1 will now be
described with reference to FIGS. 2 to 11.
[0074] In the first step, prepared is an element formation
substrate 201 formed of a glass substrate having a high resistance
to heat. An undercoat layer 202 made of, for example, a SiO.sub.x
film or a SiN.sub.x film is formed on the element formation
substrate 201 in a thickness of about 200 nm to 1 .mu.m. Then, the
undercoat layer 202 is selectively removed so as to form a
plurality of undercoat layers 202 in the form of islands on the
element formation substrate 201 as shown in FIG. 2. A thin film
transistor 15 is formed on the surface of each of the island-like
undercoat layers 202. Further, a protective layer 203 made of, for
example, a photosensitive polyimide resin is formed to cover the
thin film transistor 15 and the undercoat layer 202. Similarly, the
protective layer 203 is selectively removed such that the thin film
transistor 15 is covered with the undercoat layer 202 and the
protective film 203. In this fashion, the thin film transistor 15
is left on the undercoat layer 202.
[0075] Incidentally, the thin film transistor 15 will be described
later in detail. In the following description, the combination of
the thin film transistor 15, the undercoat layer 202 and the
protective film 203 is called an active element 100.
[0076] In the next step, prepared is an intermediate transfer
substrate 204 onto which all the active elements 100 formed on the
element formation substrate 201 are temporarily transferred, as
shown in FIG. 3. A peeling layer 205 is formed on the intermediate
transfer substrate 204. The peeling layer 205 is formed of a UV
peeling resin that is peeled upon irradiation with an ultraviolet
light, "Liva-alpha" (trade name of a resin manufactured by Nitto
Denko K.K., which is foamed upon heating so as to lower the
adhesivity), or "Intellimer" (trade name of a resin manufactured by
K.K. Nitta, the adhesion of which is changed by utilizing the phase
transfer phenomenon in the non-crystalline state). By the adhesion
of the peeling layer 205, the protective layer 203 wrapping the
active element 100 on the element formation substrate 201 is bonded
to the intermediate transfer substrate 204.
[0077] In the next step, the element formation substrate 201 is
removed as denoted by a dotted line in FIG. 4. For removing the
element formation substrate 201, it is possible to employ a wet
etching method that uses a chemical material such as hydrofluoric
acid. It is also possible to employ a chemical mechanical polishing
method in which the element formation substrate 201 is mechanically
polished while dipping the substrate 201 in a chemical solution.
Also, in place of removing the element formation substrate 201
itself, it is possible to form, for example, a hydrogenated
amorphous silicon layer between the undercoat layer 202 and the
element formation substrate 201. In this case, the amorphous
silicon layer is abraded by means of a laser beam irradiation so as
to peel the element formation substrate 201 while leaving the
active element 100 etc. unremoved on the side of the intermediate
transfer substrate 204. By this process, the active elements 100
are independently bonded provisionally to the intermediate transfer
substrate 204.
[0078] Further, as shown in FIG. 5, prepared is a final substrate
11 onto which the active elements 100 are selectively transferred
from the intermediate transfer substrate 204 to which the active
elements 100 are bonded provisionally. It is possible for the final
substrate 11 to be formed of a plastic substrate made of, for
example, polyether ether ketone (PEEK), polyethylene naphthalate
(PEN), polyether sulfone (PES) or polyimide (PI). It is also
possible to use a flexible substrate as the final substrate 11. In
the case of using a flexible substrate, it is possible to achieve a
display device that can be bent or folded like a paper sheet.
Further, it is apparently possible to use a substrate that is not
flexible such as a glass substrate or a silicon substrate as the
final substrate 11.
[0079] The spacer layers 16 are formed by using an acrylic resin in
a thickness of 0.5 .mu.m to 10 .mu.m in the peripheral region on
the final substrate 11. Also, the adhesive layers 14 are formed by
using an acrylic resin in a thickness of about 1 .mu.m to 5 .mu.m
in that region on the final substrate 11 into which the active
elements are to be transferred. Incidentally, in this embodiment,
the adhesive layers 14 and the spacer layers 16 are arranged in the
planar pattern shown in FIG. 1.
[0080] It is possible for the spacer layer 16 to be formed of an
organic resin such as an acrylic resin or a polyimide series resin
or an inorganic material such as SiO.sub.x. The acrylic resin is
excellent in adhesivity, transparent, excellent in flexibility, and
is unlikely to be cracked. Therefore, it is particularly desirable
to use the acrylic resin for forming the spacer layer 16. In the
case of using a photosensitive organic resin for forming the spacer
layer 16, the spacer layer 16 can be patterned easily so as to make
it possible to lower the manufacturing cost, compared with the use
of a resin that is not photosensitive. Of course, the spacer layer
16 can be patterned by means of etching or printing even if the
spacer layer 16 is formed of a resin that is not
photosensitive.
[0081] Suppose N.times.M active elements 100 are arranged at a high
density on the element formation substrate 201, all of these active
elements 100 are transferred in the same pattern onto the
intermediate transfer substrate 204, and the active elements 100 on
the intermediate transfer substrate 204 are transferred onto a
single final substrate 11 such that all the active elements 100 are
distributed on four final substrates 11. Since the active elements
on the element formation substrate 201 and the intermediate
transfer substrate 204 are distributed onto the four final
substrate 11, N/2.times.M/2 active elements 100 are selectively
transferred from the intermediate transfer substrate 204 onto each
of the four final substrates 11.
[0082] The adhesive layer 14 performs the function of selectively
transferring the active elements 100 from the intermediate transfer
substrate 204 onto the final substrate 11. To be more specific,
since the adhesive layers 14 are arranged at a prescribed arranging
pattern on the final substrate 11, the active elements 100
provisionally bonded to the intermediate transfer substrate 204 are
classified into a selected group of the active elements 100 that
are in contact with the adhesive layers 14 and a non-selected group
of the active elements 100 that are not in contact with the
adhesive layers 14. The active elements in the selected group are
peeled off from the intermediate transfer substrate 204 so as to be
provisionally bonded to the final substrate 11, and the active
elements in the non-selected group are left to be held by the
intermediate transfer substrate 204. The final substrate 11 is
constructed to permit the adhesive layers 14 to be formed in the
final substrate 11 in an arrangement corresponding to the
arrangement of the active elements 100 in the selected group and to
permit the adhesive layers 14 not to be formed in that region on
the final substrate 11 which corresponds to the arranging positions
of the active elements in the non-selected group.
[0083] It is possible to use, for example, an acrylic resin or a
polyimide series resin for forming the adhesive layer 14. In the
case of using the resin exemplified above, the adhesive layer 14 is
not denatured even under a high temperature state of about
200.degree. C. to 300.degree. C. in the process of forming a wiring
or the process of forming a passivation film, which are described
herein later. Particularly, it is desirable to use an acrylic resin
for forming the adhesive layer 14 because the acrylic resin is
excellent in adhesivity, transparent, excellent in flexibility, and
is unlikely to be cracked. Also, in the case of manufacturing a
transmission type liquid crystal display device, use of the acrylic
resin for forming the adhesive layer 14 is advantageous in terms of
the light efficiency because the acrylic resin exhibits a high
transmittance of a visible light. It is possible to disperse fine
particles of a metal such as Cr in the adhesive layer 14 or to use
a black resist for forming the adhesive layer 14. If the adhesive
layer 14 is blackened or rendered opaque, it is possible to
suppress the light leakage into the active element transferred onto
the adhesive layer 14 so as to improve the switching ratio of the
transistor. As a result, the image quality of the display device
that is finally formed is improved. If a photosensitive organic
resin is used for forming the adhesive layer 14, the organic resin
layer can be patterned easily into the adhesive layer 14. Also, in
the case of using an organic resin, the manufacturing cost can be
lowered, compared with the case of using a resin that is not
photosensitive. Of course, in the case of using an organic resin
that is not photosensitive, the resin layer can be patterned by
means of, for example, etching or printing.
[0084] It is possible to form the spacer layers 16 and the adhesive
layers 14 in the same process by using the same material, though
the spacer layers 16 are formed to have a height larger than that
of the adhesive layers 14. As shown in FIG. 5, the spacer layer 16
is formed in a height equal to the sum of the thickness of the
adhesive layer 14 and the height of the active element 100 that is
to be transferred onto the adhesive layer 14. If the spacer layers
16 and the adhesive layers 14 can be formed simultaneously, the
number of process steps is decreased so as to lower the
manufacturing cost of the active matrix substrate.
[0085] Incidentally, if a fluorination treatment such as a CF.sub.4
plasma processing is applied selectively to the surfaces of the
spacers 16 after formation of the spacer layers 16 with the region
other than the peripheral region 13 masked with, for example, a
resist pattern, it is possible to obtain the effect of suppressing
the transfer of the active elements 100 onto the spacer layers 16
even if the active elements 100 are brought into contact with the
spacer layers 16. Likewise, if a fluorination treatment such as a
CF.sub.4 plasma processing is applied to the surface of the pixel
region 12 after formation of the adhesive layers 14 with the
adhesive layers 14 masked with, for example, a resist, the peeling
capability is promoted in the region other than the adhesive layers
14 so as to obtain the effect that the active elements 100 are
unlikely to be transferred into the non-selected section.
[0086] In the next step, the intermediate transfer substrate 204 is
aligned with the final substrate 11 such that the active elements
100 that are to be transferred are brought into contact with the
adhesive layers 14, followed by bonding the active elements 100 to
the adhesive layers 14, as shown in FIG. 6. For performing the
bonding, it is possible to use a bonding device including two flat
plates that are arranged in parallel or in substantially parallel.
In this case, the objects to be bonded are held between the two
flat plates so as to permit the objects, which are to be bonded, to
be pushed against the two flat plates. It is also possible to use a
bonding device including a flat plate and a single roller arranged
on the flat plate. In this case, the objects to be bonded are
rolled by the roller on the flat plate so as to achieve the desired
bonding. Further, it is also possible to achieve the desired
bonding by using a contact bonding device formed of two rollers. In
the bonding device exemplified above, the objects to be bonded are
heated under a pressurized state and, then, cooled to room
temperature. In this embodiment of the present invention, the
active elements 100 bonded to the adhesive layers 14 are arranged
in the pixel region 12, and the spacer layers 16 are formed in the
peripheral region 13. As a result, a substantially uniform pressure
is applied to the pixel region 12 and the peripheral region 13.
[0087] In the next step, the intermediate transfer substrate 204
and the final substrate 11, which are kept bonded, are removed from
the bonding device, followed by applying a treatment for promoting
the peeling to the peeling layer 205, as shown in FIG. 7. In this
embodiment, used is the adhesive peeling layer 205 that can be
peeled off by the heating and, thus, a heat treatment is applied to
the peeling layer 205 so as to peel off the active element 100 from
the peeling layer 205. For example, in the case of using the
peeling layer 205 that is peeled off upon irradiation with an
ultraviolet light, it suffices to irradiate the peeling layer 205
with an ultraviolet light so as to permit the active element 100 to
be peeled off from the peeling layer 205. Particularly, selectivity
of the transfer can be improved by applying a heat treatment or an
ultraviolet light irradiation to only that region which corresponds
to the active element 100 that is to be transferred. By applying
the particular peeling treatment, the adhesive force of the peeling
layer 205 formed on the intermediate transfer substrate 204 is
lowered, and the active element 100 in contact with the adhesive
layer 14 is thermally bonded by the contact bonding to the adhesive
layer 14, with the result that the active element 100 can be
selectively transferred onto the adhesive layer 14. Incidentally,
the active matrix substrate 11 shown in FIG. 7 corresponds to the
cross section along the line VII-VII shown in FIG. 1.
[0088] It is possible to form a plurality of active matrix
substrates 11 from a single intermediate transfer substrate 204
having the active elements 100 formed thereon at a high density by
repeating the selective transfer process described above a
plurality of times. As a result, it is possible to lower the
manufacturing cost of the active matrix substrate. It is also
possible to form the active matrix substrate 11 sized larger than
the intermediate transfer substrate 204 by performing the transfer
operation from the intermediate transfer substrate 204 a plurality
of times. In other words, it is possible to form an active matrix
substrate for a large display device from a small substrate so as
to make it possible to miniaturize the manufacturing apparatus of
the active elements.
[0089] FIGS. 8 and 9 collectively exemplify the case where the
active element 100 is transferred from a small intermediate
transfer substrate 204 onto a large final substrate 11 by repeating
the transfer of the active element 100. As shown in FIG. 8, the
active elements 100 are arranged to form a matrix having rows N and
columns M in the central region of the intermediate transfer
substrate 204. Also, the adhesive layers 16 are arranged at a
prescribed pitch in a manner to form rows and columns in the pixel
region 12 of the final substrate 11. The pitch of the adhesive
layers 16 is set integer number times as large as the pitch of the
active elements 100 on the intermediate transfer substrate 204. It
follows that, after the active elements 100 are transferred from
the intermediate transfer substrate 204 onto the final substrate
11, a prescribed active element 100 can be aligned with the
adhesive layer 16 on the final substrate 11 by shifting the
intermediate transfer substrate 204 in an amount corresponding to
the pitch of the active elements 100 on the intermediate transfer
substrate 204.
[0090] Also, the intermediate transfer substrate 204 is aligned
with the final substrate 11 such that the prescribed active element
100 is allowed to face the adhesive layer 16 in the transfer
region, as shown in FIG. 8. In this case, the peripheral portion of
the intermediate transfer substrate 204 is allowed to face the
spacer 16 of the final substrate 11. If the intermediate transfer
substrate 204 is pushed against the final substrate 11 under the
particular state, a prescribed active element 100 is pushed against
the adhesive layer 16 under the state that the spacer 16 abuts
against the peripheral portion of the intermediate transfer
substrate 204, with the result that the prescribed active element
100 is transferred onto the final substrate 11. It follows that, in
the example shown in FIG. 8, the prescribed active element 100 is
transferred onto 3.times.4 adhesive layers 16.
[0091] In the next step, the intermediate transfer substrate 204 is
separated from the final substrate 11 and moved by a prescribed
distance so as to permit the intermediate transfer substrate 204 to
be aligned with the final substrate 11 such that a prescribed
active element 100, which is newly selected, is allowed to face a
new adhesive layer 16 in the transfer region. In this stage, the
peripheral portion of the intermediate transfer substrate 204 is
allowed to face the spacer 16 of the final substrate 11 and the
active element 100 that has been already transferred. If the
intermediate transfer substrate 204 is pushed against the final
substrate 11 under this state, a prescribed active element 100,
which is newly selected, is pushed against the adhesive layer 16
under the state that the spacer 16 and the prescribed active
element 100, which is newly selected, are pushed against the
adhesive layer 16. As a result, the prescribed active element 100
is transferred onto the final substrate 11. It follows that the
prescribed active element 100 is transferred onto 3.times.4
adhesive layers 16. The transfer process described above is
repeated so as to permit the active element 100 to be transferred
onto all of the final substrates 11.
[0092] In the example shown in FIGS. 8 and 9, six active elements
are arranged to form a row in the intermediate transfer substrate
204. It follows that it is possible to transfer the active element
100 from a single intermediate transfer substrate 204 into the
pixel region 12 having an area 6 times as large as the area of the
intermediate transfer substrate 204. In the transfer in the edge
portion of the screen, it is possible to prevent the defective
transfer in the edge portion of the screen by the arrangement that
the edge portion of the intermediate transfer substrate 204
overlaps with the spacer layer 16.
[0093] In the example shown in FIGS. 8 and 9, the intermediate
transfer substrate 204 is sufficiently smaller than the final
substrate 11, and all the active elements 100 can be transferred
onto the final substrate 11 by a plurality of transfer operations.
However, it is possible for the active element 100 to be
transferred from the intermediate transfer substrate 204 onto all
the adhesive layers of the final substrate 11 by a single transfer
operation, as shown in FIG. 10. To be more specific, the pixel
region 12 of the final substrate 11 is substantially equal to the
area of the active element-forming region on the intermediate
transfer substrate 204 as shown in FIG. 10, and the active element
100 is transferred from the single intermediate transfer substrate
204 onto a single final substrate 11 having a screen region of
substantially the same area. Since the active element that is six
times as large as the adhesive layer 16 formed in the final
substrate 11 is arranged in the intermediate transfer substrate
204, it is possible to transfer the active element from the single
intermediate transfer substrate onto the six final substrates each
having a screen region substantially equal to the area of the
element region.
[0094] As shown in FIG. 11, an organic film layer made of a
photosensitive polyimide is formed as a first flattening layer 206
in a thickness of about 5 to 10 .mu.m on the active matrix
substrate 11 having the active element 100 transferred thereonto.
Then, the photosensitive polyimide layer is irradiated with an
ultraviolet light so as to expose the photosensitive polyimide
layer to the ultraviolet light in a prescribed pattern for the
etching purpose. By this etching treatment, through-holes are
formed on the gate electrode, the source electrode and the drain
electrode of the active element 100. After formation of the
through-holes, a gate wiring (not shown) is formed by using a metal
film such as a Mo film or an Al film, with the result that the gate
electrode (not shown) of the thin film transistor is connected to
an electrode wiring (not shown) via a gate line extending through
the through-hole. Further, a second flattening film 207 made of a
photosensitive polyimide is formed in a thickness of about 1 to 2
.mu.m. The second flattening film 207 is irradiated with an
ultraviolet light so as to cause the second flattening film 207 to
be exposed to the ultraviolet light in a prescribed pattern for the
etching purpose. By this etching treatment, through-holes are
formed similarly on a source electrode (not shown) and a drain
electrode (not shown). Then, a metal film such as an Al film is
formed so as to form a signal line (not shown) and a pixel
electrode 208. The signal line is connected to the source electrode
of the thin film transistor via the through-hole, and the pixel
electrode 208 is connected to the drain electrode of the thin film
transistor via the through-hole. It follows that, in the structure
shown in FIG. 13, the wiring is formed on the flattening film and,
thus, the wiring is not broken even if the wiring extends though a
region above the spacer layer 16. It should be noted in this
connection that, even where the thickness of the flattening film is
decreased, it is possible to prevent the breakage of the wiring by
allowing at least a part of the wiring to extend through a region
in which the spacer layer 16 is not formed.
[0095] Finally, prepared is a transparent counter substrate
including a counter electrode layer made of a transparent
conductive film such as an ITO film (not shown), a black matrix
layer (not shown) and a color filter layer (not shown). The counter
substrate is bonded to the final substrate with a gap of several
microns provided therebetween by using a spacer. The periphery of
the bonded structure is sealed with a sealant and, then, a liquid
crystal is injected into the clearance between the bonded
substrates. It is desirable for the liquid crystal injected into
the clearance between the bonded substrates to be a twisted nematic
type liquid crystal. However, it is also possible to use another
liquid crystal such as a host-gust type liquid crystal, a
cholesteric liquid crystal, or a ferroelectric liquid crystal. A
liquid crystal display cell having an active element is formed
through the processes described above. The gate line, the signal
line and the counter electrode are connected to a driving circuit
so as to finish the manufacture of a liquid crystal display
device.
[0096] As described above, the intermediate transfer substrate 204
and the final substrate 11 are held apart from each other by the
spacers 16 and, thus, the active element 100 is unlikely to be
erroneously transferred into the non-selected portion in the
transfer stage of the active element 100 from the intermediate
transfer substrate 204 onto the final substrate 11. The particular
effect can be obtained because the spacer layers 16 serve to
prevent the active element 100 in the non-transfer portion from
being brought into contact with the final substrate 11. Also, even
if the active element 100 in the non-transfer portion should be in
contact with the final substrate 11, the spacer layers 16 permit
lowering the contact pressure so as to lower the probability for
the active element 100 to be erroneously transferred onto the
non-transfer portion.
[0097] It should also be noted that, even in the bonding step of
the active element 100 to the adhesive layer 14, the contact
bonding pressure is concentrated on the adhesive layer 14 through
the active element 100 in the pixel region 12 positioned close to
the peripheral region 13, with the result that the adhesive layer
14 is collapsed. Also, the problem that the active element 100
itself is collapsed is generated in some cases, and an additional
problem is generated that the nonuniformity in the height of the
active element 100 from the surface of the final substrate 11 is
increased after the transfer operation. In the case of forming the
spacer layers 16, however, the distance between the intermediate
transfer substrate 204 and the final substrate 11 is maintained
constant within a plane during the contact bonding process so as to
decrease the nonuniformity in the height of the active element 100
after the transfer operation. It follows that the damage done to
the active element 100 can be lowered.
[0098] It is desirable for the thickness of the spacer layer 16 to
be substantially equal to or larger than the sum of the thickness
of the adhesive layer 14 and the thickness of the active element
100. In this case, the defective transfer can be further
suppressed.
[0099] In the embodiment described above, the spacer layers 16 are
arranged to face the peeling layer 205 acting as a provisional
adhesive layer. However, it is also possible for the spacer layer
16 to be arranged to face the substrate 204, not the peeling layer
205 acting as a provisional adhesive layer, such that the spacer
layer 16 is in direct contact with the substrate 204, as shown in
FIG. 12. Where the spacer layer 16 is arranged in that region of
the substrate 11 which is not positioned to face the peeling layer
205 as shown in FIG. 12, it is desirable for the thickness of the
spacer layer 16 to be equal to or larger than the sum of the
thickness of the active element 100, the thickness of the adhesive
layer 14 and the thickness of the provisional adhesive layer
205.
[0100] The construction of the active element 100 according to this
embodiment of the present invention will now be described with
reference to FIG. 13.
[0101] As shown in FIG. 13, the active element 100 comprises the
undercoat layer 202 separated for each of the thin film transistors
formed on the element formation substrate 201, a thin film
transistor formed on the undercoat layer 202, and the protective
layer 203 covering the thin film transistor together with the
undercoat layer 202. The thin film transistor comprises a gate
electrode 301 patterned on the undercoat layer 202, a gate
insulating film 302 covering the gate electrode 301, and a channel
layer 303 formed on the gate insulating film 302. Also, a patterned
channel protective film 304 is formed on the channel layer 303, and
two separated n-type semiconductor layers 305 are formed on the
channel protective film 304. Further, a source electrode 306 and a
drain electrode 307 are formed to cover, respectively, the two
n-type semiconductor layers 305.
[0102] The method of manufacturing the active element 100 shown in
FIG. 13 will now be described.
[0103] In the first step, the undercoat layer 202 is formed in a
thickness of about 200 nm to 1 .mu.m on the element formation
substrate 201 formed of a glass substrate having a high resistance
to heat. It is desirable for the undercoat layer 202 to be formed
of, for example, a SiO.sub.x film or a SiN.sub.x film in view of
the blocking effect for preventing the ionic impurities from
migrating into the thin film transistor. Also, the blocking effect
can be further increased in the case of using a laminate structure
of, for example, a SiO.sub.x film and a SiN.sub.x film as the
undercoat layer 202.
[0104] In the next step, a metal such as MoTa or MoW is deposited
in a thickness of about 300 nm by, for example, a sputtering method
so as to form a metal thin film. The metal thin film thus formed is
patterned so as to form the gate electrode 301. Then, the gate
insulating film made of, for example, SiO.sub.x or SiN.sub.x, the
channel layer 303 formed of a semiconductor material such as
amorphous silicon, and an insulating film such as a SiN.sub.x film
are deposited successively by, for example, a plasma CVD method.
The film having a large dielectric constant thus deposited is
patterned so as to form the channel protective layer 304. It is
desirable to form the gate insulating film 302, the channel layer
303 and the channel protective layer 304 in a thickness of about
100 nm to 400 nm, about 50 nm to 300 nm and about 50 nm to 200 nm,
respectively. Incidentally, it is possible for the SiN.sub.x film
used as the gate insulating film 302 to be replaced by a film of a
material having a large dielectric constant such as a TaO.sub.x
film or a PZT film or by a ferroelectric film. The film having a
large dielectric constant or the ferroelectric film has a large
dielectric constant so as to make it possible to further decrease
the thickness of the gate insulating film 302. It follows that it
is possible to obtain the effect of lowering the cost for forming
the gate insulating film 302. Further, in the case of using a
ferroelectric film, the memory-like driving can be achieved so as
to lower the driving power.
[0105] In the next step, the n-type semiconductor layer 305 doped
with phosphorus is formed in a thickness of about 30 nm to 100 nm
by, for example, a plasma CVD method in a manner to cover the
channel layer 303 and the channel protective layer 304. Then, the
laminate structure including the gate insulating film 302 and the
n-type semiconductor layer 305 is patterned so as to form an
island-shaped pattern. Further, a single layer of, for example, Mo
or Al or a laminate structure formed of a Mo layer and an Al layer
is formed on the island-shaped pattern by, for example, a
sputtering method in a thickness of about 200 nm to 400 nm. Then,
the electrode layer and the n-type semiconductor layer 305 are
etched by a wet etching method or a dry etching method, with the
result that the electrode layer is formed into the source electrode
306 and the drain electrode 306. In this stage, the channel
protective layer 304 acts as an etching stopper and, thus, the
channel layer 303 does not incur an etching damage.
[0106] In the next step, the undercoat layer 202 and the thin film
transistor structure describe above are coated with a
photosensitive polyimide resin and, then, the polyimide resin layer
is selectively exposed to an ultraviolet light in a mask pattern so
as to form the protective layer 203 in a thickness of about 2 .mu.m
to 10 .mu.m. Further, the undercoat layer 202 is etched with the
patterned protective film 203 used as a mask. As a result, formed
is the active element 100 in which the protective layer 203 covers
the individual thin film transistor structures, and the thin film
transistor structures are separated from each other.
[0107] In the process described above, a thin film transistor is
formed on a glass substrate having a high resistance to heat as in
the liquid crystal display device widely used nowadays. Such being
the situation, it is possible to form the thin film transistor by
the high temperature process as in the prior art. It follows that
the thin film transistor prepared by the process described above is
allowed to exhibit the electric characteristics substantially equal
to those of the conventional thin film transistor. Further, since
many final substrates are formed on the basis of the element
formation substrate having the active elements formed thereon at a
high density, the thin film transistors are arranged on the element
formation substrate and the intermediate transfer substrate at a
pitch finer than that in the final substrate.
[0108] Incidentally, in the embodiment described above, a reverse
stagger type amorphous silicon TFT is used as the active element.
However, it is also possible to use a thin film transistor of
another type such as a polysilicon TFT. Also, it is possible to use
any element such as a thin film diode or a thin film capacitor as
the active element. In the case of manufacturing, for example, an
organic EL display device, it is possible to combine a plurality of
thin film transistors so as to form the active element.
[0109] Incidentally, in this embodiment of the present invention,
the pitches 1x(0) and 1y(0) of the adhesive layers 14 in the pixel
region 12, the pitches 1x(2) and 1y(2) of the spacer layers 16 in
the peripheral region 13, and the distances 1x(1) and 1y(1) between
the adhesive layer 14 and the spacer layer 16 are made equal to
each other, as shown in FIG. 1. Also, the adhesive layers 14 and
the spacer layers 16 are arranged at the same period
(1x(0)=1x(1)=1x(2) and 1y(0)=1y(1)=1y(2)). The spacer layers 16
provided by the formed dummy adhesive layers are arranged to form a
matrix having two rows in the X-direction and two columns in the
Y-direction. For example, even where the spacer layers 16 are
formed to have a single row and a single column at the period equal
to that of the adhesive layers 14, the spacer layers 16 are
effective for suppressing the defective transfer. With increase in
the number of spacer layers 16, a ratio of the area of the pixel
region to the entire area is lowered. However, the defective
transfer within the pixel region 12 tends to be lowered. In order
to suppress the defective transfer and to improve the area ratio of
the pixel region, it is desirable for the spacer layers 16 to be
arranged to form a matrix having about 3 to 4 rows and about 9 to
12 columns in the case of a TFT array in the screen having a
diagonal length of 3.2 inches because it is possible in this case
to prevent substantially the defective transfer within the screen.
The width of the spacer region is about 1.0 mm to 1.5 mm in each of
the row direction and the column direction. It is desirable for the
ratio of the spacer region to the diagonal length of the screen to
be about 1 to 2% because, in this case, it is possible to prevent
substantially the defective transfer.
[0110] Incidentally, it is possible for the pitches 1x(0) and 1y(0)
of the adhesive layers 14 in the pixel region 12, the pitches 1x(2)
and 1y(2) of the spacer layers 16 in the peripheral region 13 and
the distances 1x(1) and 1y(1) between the adhesive layer 14 and the
spacer layer 16 not to be equal to each other. It should be noted,
however, that, when the active element 100 is transferred from the
single intermediate transfer substrate 204 onto a plurality of
final substrates 11, it is necessary to satisfy the conditions of
1x(1).gtoreq.1x(0) and 1y(1).gtoreq.1y(0) in order to prevent the
defective transfer that the active element 100 is brought into
contact with the spacer layer 16 so as to be transferred onto the
spacer layer 16.
[0111] Where the adhesive layers 14 and the spacer layers are not
arranged at the same period as described above, it is possible for
the spacer layer to be formed like a stripe or to be formed
rectangular, as shown in FIG. 14. In FIG. 14, arranged are three
kinds of spacer layers including a first spacer layer 401 shaped
like a stripe, a second spacer layer 402 shaped like a stripe, and
a third spacer layer 403 that is shaped rectangular. If the
conditions of 1x(0).gtoreq.1x(1) and 1y(0).gtoreq.1y(1) are
satisfied in the arrangement shown in FIG. 14, it is possible to
prevent the active element 100 from being brought into contact with
the spacer layers 401, 402 and 403 even if the active element 100
formed on a single intermediate transfer substrate 204 is
transferred onto a plurality of final substrates 11. Where the
spacer layers 401, 402 and 403 are shaped like a stripe or formed
rectangular, the area occupied by the spacer layers 401, 402 and
403 per unit area is larger than that in the case where the spacer
layers are formed in the form of islands as shown in FIG. 1. It
follows that the effect of moderating the pressure can be enhanced.
Also, since it is possible to allow the wiring to extend through
the clearances among the rod-like spacer layers 401, 402, 403, the
breakage of the wiring can be prevented. It follows that it is
possible to decrease the width of the spacer layer, i.e., the width
in a direction perpendicular to the Y-direction in the case of the
first spacer 401, or the width in the Y-direction in the case of
the second spacer 402. To be more specific, it is possible to
prevent the defective transfer of the TFT by setting the width of
the spacer layer at about 0.2 mm to 0.7 mm in the TFT array of 3.2
inches. The arrangement shown in FIG. 14 is excellent in its effect
of moderating the pressure concentration in the vicinity of the
peripheral region and, thus, permits diminishing the regions for
forming the spacer layers 401, 402, 403 that are required for
bringing about the pressure moderating effect. In the case of
arranging stripe-shaped spacer layers, a desired effect can be
obtained by only the first spacer layer 401 and the second spacer
layer 402. However, the defective transfer can be further
suppressed in, particularly, the corner portions each having a high
contact pressure by arranging the rectangular or stripe-shaped
third spacer layers 403 at the four corners of the screen.
[0112] It is desirable for the distance 1y(3) between the
provisional adhesive layer 17 and the edge of the spacer layer on
the intermediate transfer substrate to be set larger than 1y(0) as
shown in FIG. 14. In this case, the active elements are
successively transferred while allowing the intermediate transfer
substrate to deviate from the final substrate, and where the
transfer is repeated, the spacer layer 16 is brought into contact
with the provisional adhesive layer 17. It follows that the
defective transfer can be prevented without fail by the spacer
layer 16.
[0113] Also, FIG. 15 is a plan view showing a final substrate in
which a frame-like spacer layer 501 surrounding the entire screen
is formed on the substrate 11 in place of the island-shaped spacer
layers shown in FIG. 1. In this transfer substrate, the density of
the spacer layer 501 is substantially increased so as to make it
possible to moderate the pressure applied to the substrate, with
the result that it is possible to suppress the defective transfer
with a smaller spacer layer area ratio. In the arrangement shown in
FIG. 15, it is desirable to arrange the spacer layer 501 in the
peripheral region 13 that is positioned as close to the pixel
region 12 as possible in view of the various conditions.
[0114] FIG. 16 is a plan view schematically showing the
relationship between the region in which the adhesive layer 14 is
arranged and the region in which the spacer layer 16 is arranged on
the surface of the active matrix substrate 11. FIG. 16 shows that,
in general, the adhesive layers 14 are arranged at the constant
pitches 1x(0) and 1y(0) on the active matrix substrate 11 as
denoted by the broken lines. Where the active elements 100 arranged
at a high density on the single intermediate transfer substrate 204
are transferred onto a plurality of final substrates 11, a region
601 in which the spacer layers 16 can be arranged is determined by
the position of the edges of the adhesive layers 14 arranged on the
periphery no matter how the spacer layer 16 may be shaped. To be
more specific, the spacer layers 16 are arranged such that the
inner edges of the spacer layers 16 are positioned away from the
inner edges of the adhesive layers 14 that are arranged at the
outermost circumferential region by the distances of 1x(1) and
1y(1), and the region 601 in which the spacer layers 16 are
arranged is determined to be at the distances 1x(1) and 1y(1) as
denoted by the broken lines. In this case, it is necessary for the
relationship of 1x(1).gtoreq.1x(0) and 1y(1).gtoreq.1y(0) to be
established.
[0115] The arrangement of the adhesive layers and the spacer layers
according to a first modification of the first embodiment of the
present invention will now be described with reference to FIG. 17.
In the arrangement shown in FIG. 17, the adhesive layers 14 are
arranged in symmetry with respect to each of the horizontal and
vertical center lines denoted by the broken lines on the surface of
the active matrix substrate 11. The size of the intermediate
transfer substrate 204 is defined to be 1/4 of the size of the
pixel region 12 on the active matrix substrate 11 to which the
active element 100 is to be transferred. The active elements 100
are arranged on the intermediate transfer substrate 204 at a
density not lower than 4 times as high as the density of the active
elements 100 arranged on the final substrate 11. An n-number of
active elements 100 are arranged on the intermediate transfer
substrate 204, and n-1/4-number of active elements selected from
the n-number of active elements are transferred from the
intermediate transfer substrate 204 onto the final substrate 11 by
a single transfer operation. Therefore, all of the n-number of
active elements 100 is transferred from the intermediate transfer
substrate 204 onto the final substrate 11 by performing the
transfer operation 4 times. Since the distances 1x(1) and 1y(1)
between a region 602 in which the spacer layers 16 can be arranged
and the adhesive layers 14 are defined to be in symmetry in each of
the X-direction and the Y-direction with respect to each of the
horizontal and vertical center lines, the pressure balance is
further improved in the process of bonding the intermediate
transfer substrate to the final substrate so as to suppress the
nonuniform transfer.
[0116] FIG. 18 shows the arrangement of the adhesive layers 14 and
the spacer layers 16 according to a second modification of the
first embodiment of the present invention. In the arrangement shown
in FIG. 18, the adhesive layers 14 in the adjacent columns are
arranged deviant from each other by a half pitch (1y(0)/2).
Similarly, the spacer layers 16 in the adjacent columns are
arranged deviant from each other by a half pitch (1y(2)/2). It
should be noted that the adhesive layers 14 in the even-numbered
columns have a period equal to that of the spacer layers 16 in the
even-numbered columns. Likewise, the adhesive layers 14 in the
odd-numbered columns have a period equal to that of the spacer
layers 16 in the odd-numbered columns.
[0117] In the transfer according to the prior art, the defective
transfer tends to be generated when the distance between the
adjacent adhesive layers is short, and the defective transfer tends
to be generated such that the active elements positioned between
the adjacent adhesive layers are also transferred. It is considered
reasonable to understand that the deformation of the peeling layer
in the periphery of the region corresponding to the adhesive layer
14 promotes the peeling of the active element arranged between the
adjacent adhesive layers. Such being the situation, where the pixel
pitch is narrow, the distance between the adjacent adhesive layers
14 can be set long by arranging the adhesive layers 14 deviant from
the row and the column, compared with the case where all the
adhesive layers 14 are arranged on the row and the column. It is
desirable for the spacer layers 16 to be also arranged deviant in
accordance with the deviant arrangement of the adhesive layers 14.
By this arrangement, it is possible to suppress the defective
transfer that tends to be generated around the adhesive layers
14.
[0118] In the arrangement shown in FIG. 18, all of the pitches
1x(0), 1y(0) of the adhesive layers 14 in the pixel region 12, the
pitches 1x(2), 1y(2) of the spacer layers 16 in the peripheral
region 13, and the distances 1x(1), 1y(1) between the adhesive
layer 14 and the spacer layer 16 are set equal to each other.
However, it is possible for these pitches and the distances not to
be equal to each other. It should be noted, however, that, where
the active element 100 formed on the single intermediate transfer
substrate 204 is transferred onto a plurality of final substrates
11, it is necessary for the conditions of 1x(1).gtoreq.1x(0) and
1y(1).gtoreq.1y(0) to be satisfied in order to prevent the
defective transfer that the active element 100 is brought into
contact with the spacer layer 16 so as to be transferred onto the
spacer layer 16. It should also be noted that, in the arrangement
shown in FIG. 18, the positions of the adhesive layers and the
spacer layers are allowed to deviate by a half period for every row
and column. However, the positional deviation noted above is not
limited to the particular case noted above. It is possible for the
number "m" in the case of the positional deviation by "m-periods"
to denote an optional value. Also, it is possible for the value "m"
in the row to differ from that in the column. In the sense that the
maximum distance is provided between the adjacent adhesive layers,
it is desirable to provide the deviation by a half period as shown
in FIG. 18. Incidentally, in the arrangement shown in FIG. 18, the
columns are allowed to deviate from each other. However, in place
of deviation of the column, it is possible to allow the adhesive
layers 14 in the adjacent rows to deviate from each other by a half
pitch (1x(0)/2). Similarly, it is also possible to allow the spacer
layers 16 in the adjacent rows to deviate from each other by a half
pitch (1x(2)/2, 1y(2)/2).
[0119] If the distance 1y(3) between the edge of the provisional
adhesive layer 17 and the edge of the spacer layer in the
intermediate transfer substrate is set larger than 1y(0), the
spacer layer is brought into contact with the provisional adhesive
layer 17 without fail when the transfer is successively repeated
with the intermediate transfer substrate allowed to deviate from
the final substrate. As a result, the effect produced by the
arrangement of the spacer layer 16 is increased so as to prevent
the defective transfer.
[0120] A second embodiment of the present invention will now be
described. In the second embodiment, the spacer layers are formed
in the periphery of the region of the intermediate transfer
substrate to which the active element 100 is bonded. In the
following description, those portions alone of the second
embodiment which differ from the first embodiment will be
described, and the same reference numerals are put to the
corresponding portions so as to avoid the overlapping
description.
[0121] The second embodiment differs from the first embodiment
described above in that the spacer layer is not formed in the final
substrate and the spacer layer is formed in the intermediate
transfer substrate. The manufacturing method of the intermediate
transfer substrate and the active matrix substrate for the second
embodiment will now be described with reference to FIGS. 19 and
20.
[0122] As shown in FIG. 19, a spacer layer 701 is formed on the
intermediate transfer substrate 204. The spacer layer 701 can be
formed by, for example, forming first the peeling layer 205 on the
intermediate transfer substrate 204, followed by patterning the
periphery of the region to which the active element 100 is to be
bonded so as to remove the peeling layer 205 and subsequently
forming the spacer layer 701 in the portion from which the peeling
layer 205 has been removed. In this case, the thickness of the
spacer layer 701 is set substantially equal to or larger than the
sum of the thickness of the peeling layer 205, the thickness of the
active element 100, and the thickness of the adhesive layer. The
material and the forming method of the spacer layer 701 are equal
to those in the first embodiment. The peeling layer 205 can be
patterned by, for example, forming a photo resist on the peeling
layer 205 and by applying a sputter etching with, for example, Ar
ions to the peeling layer 205 with the photo resist layer used as a
mask. The transfer can be achieved by bonding the intermediate
transfer substrate 204 having the active elements 100 transferred
thereonto to the final substrate having the adhesive layers 14
formed thereon, followed by peeling the intermediate transfer
substrate 204, in the second embodiment, too. In this case, the
spacer layers are not formed on the final substrate. However, the
transfer process itself for the second embodiment is equal to that
for the first embodiment described previously. It is possible to
obtain the effects similar to those obtained in the first
embodiment in the second embodiment, too.
[0123] In order to improve, particularly, the nonuniform transfer,
it is desirable for the thickness of the spacer layer 701 to be
substantially equal to or larger than the sum of the thickness of
the peeling layer 205, the thickness of the active element 100, and
the thickness of the adhesive layer. Also, it is possible to form
the spacer layer 702 on the peeling layer 205, as shown in FIG. 20.
In this case, the produced effect can be increased by making the
thickness of the spacer layer 702 substantially equal to the
thickness of the active element 100 and, thus, a desired effect can
be obtained by using the spacer layer 702 having a smaller
thickness. It should be noted, however, that, in the case of using
the peeling layer 205 that can be peeled by, for example, the
heating because the spacer layer 702 on the peeling layer 205 is
not transferred simultaneously with the active element 100 in the
transfer stage, it is desirable for the heat treatment not to be
applied to the region in which the spacer layer 702 is formed.
Also, in the case of using the peeling layer 205 that can be peeled
upon irradiation with an ultraviolet light, the region in which the
spacer layer 702 is formed should not be irradiated with the
ultraviolet light. Incidentally, it is possible to use in the
second embodiment, too, the planar patterns of the spacer layers
701 and 702 similar to those for the spacer layers formed on the
final substrate 11 in the first embodiment of the present invention
described previously. Where the spacer layers 701 and 702 are
formed on the intermediate transfer substrate 204 as in the second
embodiment, the spacer layers are not left on the final substrate
that is used finally as the active matrix substrate so as to lower
the possibility that the wiring formed in the subsequent step is
not broken by the stepped portion of the spacer layer. It follows
that it is possible to obtain the effect of enhancing the degree of
freedom in the pattern of the spacer layer.
[0124] As described above, the present invention provides a
manufacturing method of an active matrix substrate having a high
transfer selectivity, an active matrix substrate that is
manufactured by the particular method, and an intermediate transfer
substrate used in the manufacturing method of the active matrix
substrate.
[0125] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *