U.S. patent application number 11/330284 was filed with the patent office on 2006-05-25 for method for patterning carbon nanotube coating and carbon nanotube wiring.
Invention is credited to David J. Arthur, Paul J. Glatkowski.
Application Number | 20060111008 11/330284 |
Document ID | / |
Family ID | 29586556 |
Filed Date | 2006-05-25 |
United States Patent
Application |
20060111008 |
Kind Code |
A1 |
Arthur; David J. ; et
al. |
May 25, 2006 |
Method for patterning carbon nanotube coating and carbon nanotube
wiring
Abstract
A method for making a nanocomposite electrode or circuit pattern
includes forming a continuous carbon nanotube layer impregnated
with a binder and patterning the binder resin using various
printing or photo imaging techniques. An alternative method
includes patterning the carbon nanotube layer using various
printing or imaging techniques and subsequently applying a
continuous coating of binder resin to the patterned carbon nanotube
layer. Articles made from these patterned nanocomposite coatings
include transparent electrodes and circuits for flat panel
displays, photovoltaics, touch screens, electroluminescent lamps,
and EMI shielding.
Inventors: |
Arthur; David J.; (Norwood,
MA) ; Glatkowski; Paul J.; (Littleton, MA) |
Correspondence
Address: |
James Remenick;Intellectual Property Group
Powell Goldstein LLP
901 New York Avenue, N.W. Third Floor
Washington
DC
20001
US
|
Family ID: |
29586556 |
Appl. No.: |
11/330284 |
Filed: |
January 12, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10442176 |
May 21, 2003 |
6988925 |
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11330284 |
Jan 12, 2006 |
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60381809 |
May 21, 2002 |
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60381810 |
May 21, 2002 |
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Current U.S.
Class: |
445/46 |
Current CPC
Class: |
B82Y 10/00 20130101;
Y02E 10/549 20130101; H01J 2201/30469 20130101; H05K 3/046
20130101; Y10S 977/89 20130101; H05K 3/12 20130101; H05K 2203/0522
20130101; H05K 2203/0514 20130101; H01J 1/304 20130101; H01L
51/0018 20130101; H05K 2201/026 20130101; H05K 1/095 20130101; H05K
2201/0323 20130101; H05K 3/02 20130101; H01L 51/0048 20130101; H05K
2203/1147 20130101 |
Class at
Publication: |
445/046 |
International
Class: |
H01J 9/12 20060101
H01J009/12 |
Claims
1. A carbon nanotube wiring comprising: a substrate; and a
patterned wiring line or electrode disposed on the substrate and
comprising carbon nanotubes.
2. The carbon nanotube wiring of claim 1, wherein the wiring line
or the electrode further comprises a binder or a photoresist.
3. The carbon nanotube wiring of claim 1, wherein the carbon
nanotubes have an outer diameter of 3.5 nm or smaller.
4. The carbon nanotube wiring of claim 1, wherein the wiring line
or the electrode further comprises metal fillers.
5. The carbon nanotube wiring of claim 4, wherein the metal fillers
comprises silver, gold, copper or combinations thereof.
6. The carbon nanotube wiring of claim 1, wherein the wiring line
or the electrode has a surface resistance in a range between
10.sup.2 and 10.sup.4 ohms/square.
7. The carbon nanotube wiring of claim 1, wherein the wiring line
or the electrode has a volume resistance in a range between
10.sup.-2 and 10.sup.0 ohms-cm.
8. The carbon nanotube wiring of claim 1, wherein the wiring line
or the electrode has a light transmittance of 80% or higher.
9. The carbon nanotube wiring of claim 1, wherein the wiring line
or the electrode has a carbon nanotube concentration between 5% and
50% by volume.
10. The carbon nanotube wiring of claim 1, further comprising an
insulating layer disposed on the wiring line or the electrode.
11. The carbon nanotube wiring of claim 1, wherein the substrate is
a glass substrate, a polymer substrate, a silicon wafer, a prepreg
or combination thereof.
12-41. (canceled)
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This invention claims priority to U.S. Provisional
Application No. 60/381,809 entitled NT Mixtures, and U.S.
Provisional Application No. 60/381,810 entitled Patterning NT-Based
Coatings, both of which were filed on May 21, 2002.
BACKGROUND
[0002] 1. Filed of the Invention
[0003] This invention is directed to methods for patterning carbon
nanotube coatings and carbon nanotube wiring made by the
methods.
[0004] 2. Description of the Background
[0005] Current electronic devices, including semiconductor-based
devices as well as wiring circuits of larger scale, rely on
conventional wiring technologies that use metal wiring lines or
high impurity regions formed in a semiconductor substrate.
Semiconductor-based devices have metal wiring layers that are
formed on the semiconductor substrate and interconnect device
elements formed on the surface of the semiconductor substrate. The
metal layers themselves are often interconnected by via holes
piercing through insulating layers separating the metal layers. In
addition, portions of the semiconductor substrate that are doped
with impurities function as wiring lines within the elements formed
on the surface of the semiconductor or between these elements.
[0006] Although these wiring lines are made extremely fine using
modern photolithographic technologies and, thus, the
semiconductor-based devices are made compact, the manufacturing
processes of such wiring lines require film forming and
manipulating techniques that are operable only in high vacuum. For
example, metals such as aluminum and copper are formed on the
semiconductor substrate using physical vapor deposition techniques
including sputtering and evaporation. Impurity ions such as boron
and phosphorus are injected into the semiconductor substrate using
ion implantation techniques to form conducting portions in the
substrate. Amorphous silicon layers are formed on the substrate by
chemical vapor deposition techniques and later transformed into
polysilicon by annealing to form a wiring layer. Many of the layers
and films formed as above must be patterned to a predetermined
wiring pattern by etching process such as reactive ion etching. The
level of vacuum may vary depending on the methods, for example
10.sup.-6 torr (sputtering) to a few torr (reactive ion etching).
Whatever the vacuum level is, the installation and maintenance of
such instruments are expensive. Furthermore, all of the wiring
lines formed by above methods do not transmit light well with an
exception of those made of inorganic electrode materials such as
indium tin oxide (ITO). Extremely thin metal films may be
translucent, but stacking of such films results in forming of a
layer that practically blocks light. A transparent ITO film may be
formed relying on the high level vacuum instruments, but is not
flexible due to its inorganic nature. Furthermore, the supply of
indium is limited.
[0007] Wiring circuits of larger scale are fabricated using methods
that do not require expensive installation or maintenance of
manufacturing instruments. Print circuit boards are fabricated by
etching copper clad laminates coupled with print techniques. These
print boards may be rigid when the board is based on epoxy/glass
laminates, and may be flexible when it is based on polyimide
laminates. Similar structures are made by printing conductive pasts
directly on a substrate. The conductive ingredients of the pasts
are typically metal fillers such as silver. The conductive pasts
are printed on the substrate using screen printing technique or the
like. When performance requirements of wiring circuits are very
low, the pastes may be applied by a brush.
[0008] Though these fabrication methods are inexpensive, it is not
possible to make compact device, such as a semiconductor device,
relying on these methods. Furthermore, the wiring lines made by
these methods are not transparent. Light is blocked by copper clad
in the laminate structure and the silver paste applied on a
substrate. Accordingly, the wiring structures made by these methods
are not applicable to devices that require fine patterning of
transparent conductive film, such as electroluminescent display
device and liquid crystal display device.
[0009] Efforts have been made to provide transparent electrodes to
replace ITO film. A typical example is a suspension of ITO
particles in a polymer binder. However, this ITO filled system
cannot match the electrical conductivity of a continuous ITO film.
Furthermore, transparent conductive polymer materials are now being
developed. These polymers typically require dopants to impart
conductive properties, and are applied on a substrate using screen
printing or ink jet application technique. Although they are still
at a development stage and yet to reach the conduction level of a
ITO film, the presence of dopants is expected to have an adverse
effect on controlling the conductive properties, and may not be
compatible with device miniaturization.
[0010] Films made of carbon nanotubes are known to have surface
resistances as low as 10.sup.2 ohms/square. U.S. Pat. No.
5,853,877, entitled "Method for Disentangling Hollow Carbon
Microfibers, Electrically Conductive Transparent Carbon Microfibers
Aggregation Film and Coating for Forming Such Film," describes
formation of such conductive carbon nanotube films, and U.S. Pat.
No. 6,221,330, entitled "Processing for Producing Single Wall
Nanotubes Using Unsupported Metal Catalysts," generally describes
production of such carbon nanotubes used for forming the conductive
films. However, there have been no report in the art on a method
for patterning the film made of carbon nanotubes.
[0011] Coatings comprising carbon nanotubes such as carbon
nanotube-containing films have been previously described (see U.S.
patent application Ser. No. 10/105,623, which is incorporated
herein by reference). For example, such films may have a surface
resistance as low as 10.sup.2 ohms/square and a total light
transmittance as high as 95%. The content of the carbon nanotubes
in the film may be as high as 50%.
[0012] It has been surprisingly discovered that such materials can
be formed by a two step method, which results in carbon nanotube
film that have a low electrical resistance as well as a high light
transmittance. First, a dilute water solution of carbon nanotubes
is sprayed on a substrate, and water is evaporated leaving only the
consolidated carbon nanotubes on the surface. Then, a resin is
applied on the consolidated carbon nanotubes and penetrates into
the network of the consolidated carbon nanotubes.
SUMMARY
[0013] This invention overcomes the problems and disadvantages
associated with current metal-based and silicon-based wiring
technologies and provides new wiring methods that utilize carbon
nanotube film to form a wiring line and an electrode.
[0014] One embodiment of the invention is directed to a carbon
nanotube wiring that includes a substrate and a patterned wiring
line or electrode disposed on the substrate and having carbon
nanotubes.
[0015] Another embodiment of the invention is directed to a method
for patterning a carbon nanotube coating. The method includes
providing a solution of carbon nanotubes, applying the solution to
a substrate to form a film of consolidated carbon nanotubes on the
substrate, impregnating the carbon nanotube film selectively with a
binder, and removing a part of the carbon nanotube film that is not
impregnated with the binder from the substrate.
[0016] Another embodiment of the invention is directed to a method
for patterning a carbon nanotube coating. The method includes
providing a solution of carbon nanotubes, applying the solution to
a substrate to form a film of consolidated carbon nanotubes on the
substrate, impregnating the carbon nanotube film with a
photoresist, projecting a predetermined pattern onto the carbon
nanotube film impregnated with the photoresist to secure a part of
the carbon nanotube film, and removing a part of the carbon
nanotube film that is not secured by the projection from the
substrate.
[0017] Another embodiment of the invention is directed to a method
for patterning a carbon nanotube coating. The method includes
providing a solution of carbon nanotubes, applying the solution to
a substrate to form a film of consolidated carbon nanotubes on the
substrate, exposing the carbon nanotube film to a light source
through a mask, and impregnating the exposed carbon nanotube film
with a binder.
[0018] Another embodiment of the invention is directed to a method
for patterning a carbon nanotube coating. The method includes
providing a coating mixture having carbon nanotubes and a solvent,
applying the coating mixture on a substrate to form a predetermined
pattern, removing the solvent from the coating mixture printed on
the substrate to leave a patterned film of consolidated carbon
nanotubes on the substrate, and impregnating the carbon nanotube
film with a binder.
[0019] Other embodiments and advantages of the invention are set
forth in part in the description, which follows, and in part, may
be obvious from this description, or may be learned from the
practice of the invention.
DESCRIPTION OF THE FIGURES
[0020] FIG. 1 shows process steps of a patterning method of carbon
nanotube film of an embodiment (example 1) of this invention.
[0021] FIG. 2 shows process steps of a patterning method of carbon
nanotube film of another embodiment (example 2) of this
invention.
[0022] FIG. 3 shows process steps of a patterning method of carbon
nanotube film of another embodiment (example 3) of this
invention.
[0023] FIG. 4 shows process steps of a patterning method of carbon
nanotube film of another embodiment (example 4) of this
invention.
DESCRIPTION OF THE INVENTION
[0024] As embodied and broadly described herein, this invention is
directed to articles and methods for patterning carbon nanotube
coatings and, in particular, to carbon nanotube wiring made by the
methods.
[0025] In this invention, a unique features of the carbon nanotube
film forming method described above is used. That is, the
consolidated carbon nanotubes dried on the substrate have a
remarkably strong adhesion to the surface of the substrate without
any other ingredient such as a binder. Accordingly, the device
intermediate, i.e., the substrate having the consolidated carbon
nanotubes, is compatible with many existing device processing
techniques. Yet, the adhesion is weak enough to be broken by fairly
moderate disturbance. In addition, the carbon nanotubes
consolidated on the substrate have a network structure that has a
large amount of open porosity. Accordingly, a material that has a
viscosity low enough to penetrate into the open pores may be
applied on the substrate so that the open pores of the consolidated
carbon nanotubes are filled with the material.
[0026] A microscopic observation of the consolidated carbon
nanotubes on the substrate, prior to the application of the resin,
showed that the network structure is based on a formation of ropes
of the carbon nanotubes and the ropes form the frame of the network
structure. This structure provides the low electrical resistance
and the high light transmittance at the same time since the frame
of the ropes can carry the majority of conduction and the
relatively large openings between the ropes allow the penetration
of the resin applied on the carbon nanotubes.
[0027] There are different approaches to forming a patterned carbon
nanotube film relying on these features. For example, a carbon
nanotube film may first be formed on the entire surface of a
substrate. Since the consolidated carbon nanotubes on the substrate
can take in various materials as part of the network structure,
chemical agents for patterning may be introduced to the entire
portion of the consolidated film or a selected portion of the film.
For example, a binder dissolved in a solvent may be applied to the
consolidated carbon nanotube film according to a predetermined
pattern. Application of the binder may be performed by any
conventional methods including preferably screen printing, ink
jetting and gravure roll printing. After drying out the solvent,
the binder remains in the network and reinforces the portion of the
carbon nanotube film impregnated with the binder solution. By
rinsing the substrate having the carbon nanotubes thereon with
water or solvent that does not dissolves the binder, the part of
the carbon nanotubes that are not reinforced by the binder easily
comes off the substrate whiles the reinforced portion of the carbon
nanotube film remains intact. The substrate may be flexible or
rigid, and may be made of a transparent material or a
light-blocking material. For a transparent electrode application,
typically a transparent inorganic glass plate is used as the
substrate, although a transparent flexible polymer film may also be
used. The substrate may also be a silicon substrate when the carbon
nanotube wiring is used as part of integrated circuit. Furthermore,
insulating layer may be formed on the carbon nanotube wiring as a
protection layer. Additional carbon nanotube wiring may be formed
on the insulating layer protecting the first carbon nanotube wiring
to form a multi-layered wiring structure.
[0028] Rather than applying the binder to the selected portion of
the carbon nanotube film, a photoresist may be applied to the
entire carbon nanotube film. Application of the photoresist may be
performed by any conventional methods including preferably spin
coating. Once the photoresist penetrates into the network structure
of the consolidated carbon nanotubes, this device intermediate may
be compatible with any conventional photolithographic processing
step. For example, a predetermined pattern of a reticle is
projected onto the carbon nanotube film impregnated with the
photoresist. Depending on the type of the photoresist used, the
portion of the carbon nanotube film irradiated by light or the
portion of the film not irradiated is removed in the subsequent
process. The wiring pattern of the reticle is transferred onto the
carbon nanotube film. In comparison to the binder patterning
method, this method provides finer patterning of the carbon
nanotube film, and may be more compatible with the existing
silicon-based device manufacturing methods. Any substrate described
herein may be used as the substrate for this manufacturing method.
An insulating layer may be formed over the patterned carbon
nanotube film, and a multi-layered carbon nanotube wiring may also
be formed.
[0029] Furthermore, the carbon nanotube film formed on the
substrate may not have to be physically patterned at all. That is,
the electronic nature of the carbon nanotube film may be
manipulated without removing the film physically form the
substrate. Single-walled carbon nanotubes (SWNTs) undergoe large
structural reconstruction when irradiated by a strong light source.
Although SWNTs may burn out in air under strong light irradiation,
they transform into materials with much higher resistance under a
proper irradiation condition. Such features of carbon nanotubes are
described, in "Nanotubes in a Flash--Ignition and Reconstruction,"
P. M. Ajayan et. al, Science 296, 70 (2002). For the light
irradiation, conventional photolithographic instruments may be used
to project a predetermined pattern onto the carbon nanotube film.
When the wiring pattern to be formed is relatively large, the light
irradiation may be performed by simply placing a mask on the
substrate. When the substrate is transparent, preferably the mask
may be placed on the back side of the substrate. The mask may also
be directly placed on the carbon nanotube film. The change in the
conductivity is not expected to have significant influence on the
light transmittance of the carbon nanotube film as well as the
network structure of the nanotube ropes. A binder is then applied
to the entire carbon nanotube film and penetrates into the network
structure to reinforce the structure. An insulating layer may be
formed over the carbon nanotube film, and a multi-layered carbon
nanotube wiring may also be formed.
[0030] A patterned carbon nanotube film may be formed directly on a
substrate using application methods of the invention including
preferably screen printing, ink jetting and gravure roll printing.
However, the carbon nanotube water solution used above to form the
carbon nanotube film may not be appropriate for this method since
the viscosity of the solution is not high enough to be compatible
with these application method. Accordingly, chemical agents may
need to be added to the solution to increase viscosity.
Alternatively, a mixture of the carbon nanotubes and a binder, such
as those described in U.S. Ser. No. 10/105,623, may be used as an
ink for these application methods. After a predetermined pattern of
the carbon nanotube is formed on the substrate, the chemical agents
used for increasing the viscosity may be removed to gain a proper
conductivity and light transmittance by drying the substrate or
burning the chemical agents in a proper atmosphere. This processing
step transforms the carbon nanotubes printed on the substrate into
a network structure similar to that created by the application of
the carbon nanotube water solution to the substrate. To secure the
patterned carbon nanotube film thus formed, a binder may be applied
on the entire surface of the substrate. The binder penetrates into
the network structure at the portions of the substrate on which the
carbon nanotube film is formed, and directly covers the substrate
between the carbon nanotube wiring lines. Any substrate may be used
as the substrate for this manufacturing method. An insulating layer
may be formed over the binder layer, and a multi-layered carbon
nanotube wiring may also be formed. This method is effective in
reducing the amount of carbon nanotubes used, and provides a planar
device intermediate, which may otherwise include the formation of
planarization layer for subsequent processing steps.
[0031] A continuous carbon nanotube film coated onto a substrate
may be patterned by placing a patterned "sticky" surface (roll or
plate) in direct contact with the carbon nanotube film. If the
sticky substance is patterned in the reverse image of the
predetermined wiring pattern, then the portion of the film not used
in the wiring will transfer from the film onto the transfer roll or
plate. A patterned carbon nanotube film is formed when the carbon
nanotube coated substrate is released from the transfer roll or
plate.
[0032] Furthermore, any two or more of the patterning methods of
the carbon nanotubes may be combined to form wiring structures of a
device. For example, gate lines and associated gate electrodes of
switching transistors of an electroluminescent display device may
be formed by the photolithographic process of the photoresist
impregnated with the carbon nanotubes. On the other hand, anode
electrodes of electroluminescent elements of the display device may
be formed by screen printing the high viscosity carbon nanotube
solution on a device intermediate that has the gate lines and gate
electrode formed therein.
[0033] It is preferable that the average outer diameter of the
carbon nanotubes of the carbon nanotube film is 3.5 nm or smaller.
Carbon nanotubes used in the film forming methods above include
straight and bent multi-walled nanotubes (MWNTs), straight and bent
double-walled nanotubes (DWNTs), straight and bent single-walled
nanotubes (SWNTs) and carbon nanotubes that have been chemically
modified to include other compounds and functional groups. SWNTs
are preferable because they naturally aggregate to form the ropes
of the carbon nanotubes. The concentration of the carbon nanotube
by volume in the carbon nanotube film, i.e., how much space is
filled by the carbon nanotube, is preferably 5-50%, 5-10%, 10-15%,
15-20%, 20-25%, 25-30%, 30-35%, 35-40%, 40-45%, 45-50%, 10-20%,
5-25%, 5-20%, 10-30%, or 5-30%, but may fall outside this range
depending on the application of the carbon nanotube wiring. The
aspect ratio of the carbon nanotubes may be between 10 and
2000.
[0034] The surface resistance and the volume resistance of the
carbon nanotube film may vary depending on the type and the
concentration of the carbon nanotube used. The surface resistance
of the film may be between 10.sup.2 and 10.sup.10 ohms/square, and
is preferably between 10.sup.2 and 10.sup.4 ohms/square, between
10.sup.4 and 10.sup.6 ohms/square, between 10.sup.6 and 10.sup.8
ohms/square, or between 10.sup.8 and 10.sup.10 ohms/square. The
volume resistance of the film may be between 10.sup.-2 and
10.sup.10 ohms-cm, and is preferably between 10.sup.-2 and 10.sup.0
ohms-cm, between 10.sup.0 and 10.sup.2 ohms-cm, between 10.sup.2
and 10.sup.4 ohms-cm, between 10.sup.4 and 10.sup.6 ohms-cm,
between 10.sup.6 and 10.sup.8 ohms-cm, or between 10.sup.8 and
10.sup.10 ohms-cm. Preferably, the light transmittance of the
carbon nanotube is 80% or higher (e.g., 85, 90, 95, 97, 99), and
the haze value of the carbon nanotube film is 0.5% (e.g. 0.4, 0.3,
0.2, 0.1, 0.01) or lower. Nonetheless, carbon nanotube films with
much low light transmittance or much higher haze value may be used
to form the carbon nanotube wiring. The thickness of the carbon
nanotube film may be between 0.5 nm and 1 .mu.m (e.g., 0.8, 1, 2,
3, 5, 10, 25, 50, 100, 150, 500, 750 nm), and is preferably between
1 and 100 nm.
[0035] The binder to secure the network structure of the carbon
nanotube film and the insulating overcoat may be made of polymeric
materials, which may be selected from a wide range of natural or
synthetic polymeric resins. The particular polymer may be chosen in
accordance with the strength, structure, or design needs of a
desired application, such as thermoplastics, thermosetting
polymers, elastomers and combinations thereof. Specifically, they
may be polyethylene, polypropylene, polyvinyl chloride, styrenic,
polyurethane, polyimide, polycarbonate, polyethylene terephthalate,
cellulose, gelatin, chitin, polypeptides, polysaccharides,
polynucleotides and mixtures thereof. Furthermore, ceramic hybrid
polymers, phosphine oxides and chalcogenides may be used.
[0036] Conducting fillers may be added into the carbon nanotubes.
The fillers may be conductive organic materials, inorganic
materials or combinations or mixtures of such materials. The
conductive organic materials may be buckeyballs, carbon black,
fullerenes and combinations and mixtures thereof. Conductive
inorganic materials may be aluminum, antimony, beryllium, cadmium,
chromium, cobalt, copper, doped metal oxides, iron, gold, lead,
manganese, magnesium, mercury, metal oxides, nickel, platinum,
silver, steel, titanium, zinc, or combinations or mixtures thereof.
Preferred conductive materials include tin-indium mixed oxide,
antimony-tin mixed oxide, fluorine-doped tin oxide, aluminum-doped
zinc oxide and combinations and mixtures thereof.
[0037] Vacuum annealing of the carbon nanotube film prior to the
binder impregnation may further reduce the resistance of the carbon
nanotube film. This is promoted by a fusion of the carbon nanotubes
at the junction of the carbon nanotube ropes. Since the rope itself
has an almost metal-like conductivity and the total conductivity of
the film is likely determined by the morphologies of the rope
junctions, any treatment to thicken the junctions increases the
conductivity of the carbon nanotube film. When nanometer-size
particles of metals are mixed into the carbon nanotube film, those
nano particles may migrate into the junctions upon annealing. This
will also result in reducing the resistance.
[0038] Larger metal particles may be introduced into the carbon
nanotube film in a large amount. Such a composite film may also be
considered as adding the carbon nanotubes into the dispersion of
large conductive metal particles. When metals such as silver, gold,
copper, blends, aluminum, magnesium and their alloys are used, this
combination achieves improvement in conductivity over the pure
carbon nanotube film by about six orders of magnitude or larger.
Yet, the amount of the metal fillers of this composite film is much
less than the amount required to achieve the percolation threshold
relying on only the metal fillers. Accordingly, the composite
carbon nanotube film may maintain light transmittance suitable for
transparent electrode applications. As an alternative, carbon black
particles may replace the metal particles in the composite film.
This combination may not achieve high conductivity, but
manufacturing cost of the carbon nanotube film may be reduced
because of the reduced amount of the carbon nanotubes used in the
film.
[0039] Wiring made from these patterned nanocomposite coatings may
be used as for example transparent electrodes and circuits for flat
panel displays, photovoltaics, touch screens, electroluminescent
lamps, and EMI shielding.
[0040] The following examples illustrate embodiments of the
invention, but should not be viewed as limiting the scope of the
invention.
EXAMPLES
[0041] Four examples of formation of carbon nanotube wiring are
described below with reference to FIGS. 1-4, respectively. The
following examples are only for illustrative purposes and do not
limit the general descriptions on the patterned carbon nanotube
film formation described above.
Example 1
[0042] First, as purchased SWNTs are purified by process steps
including acid reflex, water rinsing, centrifuge and
microfiltration. Then, the purified SWNTs are mixed into a solution
of isopropyl alcohol (IPA) and water to form a carbon nanotube
coating solution. The SWNT solids content is in the range of 10 to
100 ppm by weight. The weight ratio of IPA to water is in the range
of 1:3 to 3:1, depending on the drying rate desired for the
coating. Once a reasonably stable dispersion has been achieved, the
viscosity of the SWNT dispersion is increased by adding a
sufficient amount of a polyacrylic acid, a viscosity modifying
agent (Acrysol ASE 75, available from Rohm & Haas), to provide
a coating composition having a viscosity suitable for gravure
coating, (e.g., approximately 1000 cP). The carbon nanotube coating
solution is printed onto a clear plastic film (e.g.,
polyethersulfone) using a patterned gravure roll. The IPA/water and
viscosity modifier are then removed by heating, leaving behind a
film of consolidated carbon nanotubes that is patterned. A
dielectric binder coating (e.g., acrylic resin dissolved in ethyl
acetate) is then applied using an atomized spraying technique. The
binder coating permeates the carbon nanotube film, enhancing
adhesion and mechanical properties. The resulting patterned
electrode or circuit exhibits good transparency and low electrical
resistance. This method is schematically shown in FIG. 1.
Example 2
[0043] First, as purchased SWNTs are purified by process steps
including acid reflex, water rinsing, centrifuge and
microfiltration. Then, the purified SWNTs are mixed into a solution
of isopropyl alcohol (IPA) and water to form a carbon nanotube
coating solution. The SWNT solids content is in the range of 10 to
100 ppm by weight. The weight ratio of IPA to water is in the range
of 1:3 to 3:1, depending on the drying rate desired for the
coating. The SWNT coating is applied to a clear plastic film (e.g.,
polyester film such as PET or PEN film from Dupont Teijin Films)
using an atomized spraying technique. The substrate is heated to
60.degree. C. to increase drying rate of the IPA/water. A
sufficient thickness of the consolidated carbon nanotubes is
applied to achieve the desired electrical resistance (e.g., 500
ohms/square). Then, a binder coating such as acrylic resin
dissolved in ethyl acetate is printed using a screen printing
technique. The binder coating permeates selected regions of the
carbon nanotube film, enhancing adhesion and mechanical properties.
The solvent is removed by heating. Then, the unprotected carbon
nanotube regions are removed by a spray washing technique using a
mixture of water and Triton X-100 surfactant. The resulting
patterned electrode or circuit exhibits good transparency and low
electrical resistance. This method is schematically shown in FIG.
2.
Example 3
[0044] First, as purchased SWNTs are purified by process steps
including acid reflex, water rinsing, centrifuge and
microfiltration Then, the purified SWNTs are mixed into a solution
of isopropyl alcohol (IPA) and water to form a carbon nanotube
coating solution. The SWNT solids content is in the range of 10 to
100 ppm by weight. The weight ratio of IPA to water is in the range
of 1:3 to 3:1, depending on the drying rate desired for the
coating. The SWNT coating is applied to a glass substrate using an
atomized spraying technique. The substrate is heated to 60.degree.
C. to increase drying rate of the IPA/water. A sufficient thickness
of consolidated carbon nanotubes is applied to achieve the desired
electrical resistance (e.g., 500 ohms/square). Then, a photo
definable polyimide binder such as HD-4000 Series from HD
Microsystems is applied to the consolidated carbon nanotube film
using a Meyer rod coating technique. The photoresist permeates the
carbon nanotube film. A predetermined wiring pattern is projected
onto the photoresist impregnated with carbon nanotubes using
standard photolithographic techniques. Selected regions of the
carbon nanotube film are removed when the uncured polyimide regions
are rinsed away by the developer. The resulting patterned electrode
or circuit exhibits good transparency and low electrical
resistance. This method is schematically shown in FIG. 3.
Example 4
[0045] The coating solution is prepared as in Example 3. is applied
to a glass substrate using an atomized spraying technique. The
substrate is heated to 60.degree. C. to increase drying rate of the
IPA/water. A sufficient thickness of the consolidated carbon
nanotubes is applied to achieve the desired electrical resistance
(e.g., 500 ohms/square). A high intensity mercury light source is
projected through a mask onto the carbon nanotube coated glass.
This exposure results in higher electrical resistance for selected
regions of the carbon nanotube film, without significantly reducing
the optical transparency. A dielectric binder coating (e.g.,
acrylic resin dissolved in ethyl acetate) is then applied using an
atomized spraying technique. The binder coating permeates the
carbon nanotubes, enhancing adhesion and mechanical properties. The
resulting patterned electrode or circuit exhibits good transparency
and low electrical resistance. This method is schematically shown
in FIG. 3.
[0046] In Examples 2 and 3, the carbon nanotube films do not have
to be completely removed. As long as neighboring wiring elements
are not electrically connected, a certain amount of the nanotubes
may remain on the substrate.
[0047] Other embodiments and uses of the invention will be apparent
to those skilled in the art from consideration of the specification
and practice of the invention disclosed herein. All references
cited herein, including all publication, U.S. patents and patent
applications including the priority documents, are specifically and
entirely incorporated by reference. It is intended that the
specification and examples be considered exemplary only with the
true scope and spirit of the invention indicated by the following
claims.
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