U.S. patent application number 11/698459 was filed with the patent office on 2007-06-28 for nano-wire electrode structure.
Invention is credited to Loucas Tsakalakos.
Application Number | 20070145542 11/698459 |
Document ID | / |
Family ID | 34678340 |
Filed Date | 2007-06-28 |
United States Patent
Application |
20070145542 |
Kind Code |
A1 |
Tsakalakos; Loucas |
June 28, 2007 |
Nano-wire electrode structure
Abstract
An electronic device such as a sensor or a NEMS. The electronic
device comprises at least one substrate; a plurality of electrodes
disposed on the substrate; and at least one nano-wire growing from
an edge of a first electrode to an edge of a second electrode. A
method for making an electrode structure by providing a substrate;
forming a plurality of electrodes on the substrate; growing at
least one nano-wire from the edge of a first electrode; and
connecting the at least one nano-wire to the edge of a second
electrode is also disclosed.
Inventors: |
Tsakalakos; Loucas;
(Niskayuna, NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY (PCPI);C/O FLETCHER YODER
P. O. BOX 692289
HOUSTON
TX
77269-2289
US
|
Family ID: |
34678340 |
Appl. No.: |
11/698459 |
Filed: |
January 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10742036 |
Dec 19, 2003 |
7181836 |
|
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11698459 |
Jan 26, 2007 |
|
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Current U.S.
Class: |
257/659 ;
257/704; 257/712; 257/E29.07; 29/592.1; 438/122 |
Current CPC
Class: |
Y10S 977/895 20130101;
H01L 29/125 20130101; Y10T 29/49174 20150115; H01L 2924/0002
20130101; Y10T 29/49162 20150115; Y10T 29/49002 20150115; G11C
2213/81 20130101; G11C 23/00 20130101; Y10T 29/4916 20150115; Y10S
977/932 20130101; H01L 29/0673 20130101; B81B 7/0006 20130101; H01L
29/0665 20130101; Y10T 29/49155 20150115; Y10T 29/49156 20150115;
B82Y 10/00 20130101; H01L 2924/0002 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
257/659 ;
029/592.1; 257/704; 257/712; 438/122 |
International
Class: |
H01L 21/00 20060101
H01L021/00 |
Claims
1.-27. (canceled)
28. An electrode structure comprising: a) at least one electrode,
said at least one electrode having at least one edge portion; and
b) at least one nano-wire originating from said edge portion.
29. The electrode structure according to claim 28, wherein said at
least one electrode comprises at least one noble metal.
30. The electrode structure according to claim 29, wherein said at
least one noble metal comprises at least one of platinum, gold,
silver, and combinations thereof.
31. The electrode structure according to claim 28, wherein said at
least one electrode comprises at least one of tungsten, niobium,
tantalum, and combinations thereof.
32. The electrode structure according to claim 28, wherein said at
least one electrode comprises a catalyst.
33. The electrode structure according to claim 32, wherein said
catalyst comprises at least one of gold, nickel, iron, chromium,
cobalt, and combinations thereof.
34. The electrode structure according to claim 28, wherein said at
least one nano-wire comprises at least one of a semi-conductor, a
carbide, an oxide, a nitride, a boride, and combinations
thereof.
35. The electrode structure according to claim 34, wherein said
semi-conductor comprises at least one of silicon, germanium, a
III-V compound, a II-VI compound, a IV-VI compound, and
combinations thereof.
36. The electrode structure according to claim 34, wherein said
carbide comprises at least one of silicon carbide, niobium carbide,
molybdenum carbide, tantalum carbide, hafnium carbide, tungsten
carbide, and combinations thereof.
37. The electrode structure according to claim 28, wherein said at
least one nano-wire is oriented perpendicular to said at least one
electrode.
38. The electrode structure according to claim 28, wherein said at
least one nano-wire is oriented by at least one of an electric
field, a magnetic field, and combinations thereof.
39. The electrode structure according to claim 28, wherein said at
least one nano-wire is oriented by a gas flow.
40. The electrode structure according to claim 28, wherein said at
least one nano-wire is coupled to said at least one electrode by a
catalytic particle.
41. The electrode structure according to claim 28, wherein said at
least one nano-wire is coupled to said at least one electrode by a
lithographically patterned electrode film.
42. The electrode structure according to claim 28, wherein said at
least one nano-wire is a nano-ribbon.
43. The electrode structure according to claim 28, wherein said at
least one nano-wire has a diameter in a range from about 5 nm to
about 300 nm.
44. The electrode structure according to claim 43, wherein said at
least one nano-wire has a diameter in a range from about 5 nm to
about 100 nm.
45. The electrode structure according to claim 28, wherein said at
least one nano-wire has a length in a range from about 50 nm to
about 50,000 nm.
46. The electrode structure according to claim 45, wherein said at
least one nano-wire has a length in a range from about 200 nm to
about 20,000 nm.
47. The electrode structure according to claim 28, wherein said
structure comprises at least one of a core-shell structure, a
hetero-epitaxial nano-wire, a GATE dielectric device, a biosensor,
a chemical sensor, an artificial nose, a cross-bar arrays, a
nano-electromechanical system (NEMS) device, a transistor, a
photo-detector, a light emitting diode (LED), a super-conducting
device, a laser device, and combinations thereof.
48. The electrode structure of claim 28, wherein said at least one
nano-wire comprises a plurality of nano-wires.
49. The electrode structure of claim 48, wherein said plurality of
nano-wires comprise an architecture.
50. The electrode structure of claim 49, wherein said architecture
comprises a cross-bar architecture of nano-wires.
51.-112. (canceled)
Description
BACKGROUND OF INVENTION
[0001] This invention relates to an electronic device, such as a
sensor or a nano-electromechanical system (NEMS). More
particularly, the invention relates to a method of integrating
inorganic nano-wires with micron sized electrode structures.
[0002] As device structures become increasingly miniaturized, the
integration of nano-building blocks, such as nano-wires, with a
nano-device is of great interest. As the size of device structures
decrease, such integration becomes increasingly complex. Inorganic
wires, often chosen for applications in devices due to their low
work function, high frequency, or quantum transport properties, are
independently synthesized by techniques such as vapor transport,
laser ablation, or electrochemical filling of porous anodic alumina
templates. The inorganic wires are then assembled onto a final
substrate or device of interest using techniques such as random
dispersion, micro-fluidics, or nano imprint lithography.
[0003] One problem associated with separate assembly in the
integration of nano-wires and devices is the difficulty in scaling
up the involved processes, as many of such assembly steps and
processes are distinct from each other. While hybrid integration
strategies enable scaling up and quickening of some processes, a
method of direct horizontal integration of the nano-wire with the
device architecture of interest is highly desirable in
microelectronics processing and device fabrication.
[0004] The current methods for integrating a nano-wire and a
nano-device do not enable direct integration in minimal turnaround
times nor in high yield. Therefore, what is needed is an electronic
device that is directly integrated with its attendant nano-wires.
What is also needed is a method for direct integration of nano-wire
and nano-device assembly that is applicable to a variety of
nano-wire material compositions and applications. What is also
needed is an assimilation of the direct integration method into
existing micro and nanotechnology and in micro- and
nano-lithography techniques.
BRIEF SUMMARY OF THE INVENTION
[0005] The present invention meets these and other needs by
providing a method for making an electrode structure comprising at
least one substrate, a plurality of electrodes disposed on the
substrate, and at least one nano-wire originating from an edge of a
first electrode and extending to an edge of a second electrode. An
electronic device, such as a nano-electromechanical system (NEMS),
transistor, photo-detector, light emitting diode, super-conducting
device, sensor, and the like that incorporates the electrode
structure described above, is also provided.
[0006] Accordingly, one aspect of the invention is to provide an
electronic device. The electronic device comprises: at least one
substrate; a plurality of electrodes, wherein the plurality of
electrodes are disposed on the substrate; and at least one
nano-wire wherein the nano-wire grows from an edge of a first
electrode to an edge of a second electrode.
[0007] A second aspect of the invention is to provide an electrode
structure. The electrode structure comprises: at least one
electrode, the at least one electrode having at least one edge
portion; and at least one nano-wire originating from the edge
portion.
[0008] A third aspect of the invention is to provide an electronic
device. The electronic device comprises: at least one substrate,
the at least one substrate comprising at least one of a
semi-conducting material, an insulating material, and combinations
thereof; and an electrode structure disposed on the substrate. The
electrode structure comprises a plurality of electrodes and at
least one nano-wire, wherein the nano-wire originates from an edge
portion of a first electrode and extends to an edge of a second
electrode.
[0009] A fourth aspect of the invention is to provide a method for
making an electrode structure, wherein the electrode structure
comprises at least one substrate, a plurality of electrodes
disposed on the substrate, and at least one nano-wire originating
from an edge of a first electrode and extending to an edge of a
second electrode. The method comprises: providing the substrate;
forming a plurality of electrodes on the substrate; growing the at
least one nano-wire from the edge of the first electrode; and
connecting the at least one nano-wire to the edge of the second
electrode.
[0010] These and other aspects, advantages, and salient features of
the present invention will become apparent from the following
detailed description, the accompanying drawings, and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic view of an electronic device of the
present invention;
[0012] FIG. 2 is a micrograph of a nano-wire growing from a
catalyst particle;
[0013] FIG. 3 is a schematic view of an electronic device of the
present invention in which a nano-wire is coupled to a second
electrode by a lithographically defined contact;
[0014] FIG. 4 is a micrograph showing an array of gold electrodes
deposited on a silicon substrate; and
[0015] FIG. 5 is a micrograph showing a plurality of nano-wires
grown from an electrode; and
[0016] FIG. 6 is a schematic view of a cross-bar architecture of an
array of nano-wires.
DETAILED DESCRIPTION OF THE INVENTION
[0017] In the following description, like reference characters
designate like or corresponding parts throughout the several views
shown in the figures. It is also understood that terms such as
"top," "bottom," "outward," "inward," and the like are words of
convenience and are not to be construed as limiting terms.
[0018] The invention involves synthesis of inorganic nano-wires and
nano-rods at the edge of lithographically defined structures on a
substrate or a device. Within the scope of this invention, the
terms "inorganic nano-wires" and "inorganic nano-tubes" are
understood to include: any oxide, nitride, boride, or carbide of a
metal, boron, or silicon; elemental and compound semiconductors;
and metals.
[0019] Referring to the drawings in general and to FIG. 1 in
particular, it will be understood that the illustrations are for
the purpose of describing a preferred embodiment of the invention
and are not intended to limit the invention thereto. Turning to
FIG. 1, a schematic representation of an electronic device 20 of
the present invention is shown. Among the electronic devices that
fall within the scope of the present invention are core-shell
structures, hetero-epitaxial nano-wires, GATE dielectric devices,
biosensors, chemical sensors, cross-bar arrays,
nano-electromechanical system (NEMS) devices, transistors,
photo-detectors, light emitting diodes (LEDs), super-conducting
devices, laser devices, combinations thereof, and the like.
However, it will be appreciated by those skilled in the art that
other electronic devices will fall within the scope of the
invention.
[0020] One aspect of the present invention is to provide an
electronic device 20. Electronic device 20 comprises at least one
substrate 40; a plurality of electrodes 70 disposed on substrate
40; and at least one nano-wire 140 that grows from an edge 100 of a
first electrode 60 to an edge 120 of a second electrode 80. In one
embodiment, the at least one nano-wire 140 comprises a single
crystal material. In another embodiment, the at least one nano-wire
140 comprises a polycrystalline material. In a third embodiment,
nano-wire 140 comprises an amorphous material.
[0021] Substrate 40 comprises at least one of a semi-conducting
material, an insulating material, and combinations thereof. In one
embodiment, substrate 40 is a semi-conducting material comprising
at least one of silicon, germanium, indium tin oxide, silicon
carbide, and combinations thereof. In another embodiment, substrate
40 is an insulating material comprising at least one of diamond and
a metal oxide. Non-limiting examples of such metal oxides include
magnesium oxide, sapphire, lithium aluminate, and combinations
thereof.
[0022] At least one electrode of first electrode 60 and second
electrode 80 comprises at least one noble metal, such as, but not
limited to, platinum, gold, silver, and combinations thereof. In
another embodiment, the at least one electrode comprises at least
one of tungsten, niobium, tantalum, and combinations thereof. In a
third embodiment, at least one of first electrode 60 and second
electrode 80 further includes a catalyst 180, wherein the catalyst
180 comprises at least at least one of gold, nickel, iron,
chromium, cobalt, and combinations thereof.
[0023] The at least one nano-wire 140 comprises at least one of a
semi-conductor, a carbide, an oxide, a nitride, a boride, and
combinations thereof. In one embodiment, the at least one nano-wire
comprises lanthanum hexaboride (LaB.sub.6). In another embodiment,
the at least one nano-wire 140 is a semi-conductor comprising at
least one of silicon, germanium, a III-V compound, a II-VI
compound, a IV-VI compound, and combinations thereof. In another
embodiment, the at least one nano-wire 140 is a carbide comprising
at least one of silicon carbide, niobium carbide, molybdenum
carbide, tantalum carbide, hafnium carbide, tungsten carbide, and
combinations thereof.
[0024] In one embodiment of the present invention, the at least one
nano-wire 140 is oriented perpendicular to first electrode 60. In
another embodiment, the at least one nano-wire 140 is oriented by
at least one of an electric field, a magnetic field, and
combinations thereof. In another embodiment, the at least one
nano-wire 140 is oriented by a gas flow. Orientation of the at
least one nano-wire 140 may take place during growth of the at
least one nano-wire 140.
[0025] The at least one nano-wire 140 is coupled to and is grown
from an edge 100 of first electrode 60. The at least on nano-wire
140 is grown from a portion of catalyst 180 disposed on edge 100 of
first electrode 60. Catalyst 180 may be present as a particle or as
a film deposited on first electrode 60. The at least one nano-wire
grows from catalyst 180 via one of a vapor-solid and a
vapor-liquid-solid (VLS) growth mechanism in which a particle of
catalyst 180 acts as a seed for growing nano-wire 140. FIG. 2 is a
micrograph of a nano-wire 140 growing from a particle of catalyst
180.
[0026] The at least one nano-wire 140 is coupled to second
electrode 80. In one embodiment, the particle of catalyst 180 is
attached to an end of the at least one nano-wire 140 during growth,
and thus precedes the nano-wire 140 in its growth direction towards
second electrode 80, where catalyst 180 serves as a terminal point
for the at least one nano-wire 140 on second electrode 80 (FIG. 1).
Alternatively, the at least one nano-wire 140 makes direct contact
with second electrode 80. In yet another embodiment, shown in FIG.
3, the at least one nano-wire 140 is coupled to second electrode 80
by a lithographically defined contact 200 deposited after growth of
the at least one nano-wire 140. Contact 200 comprises any suitable
contact material, such as, but not limited to, a conductive metal,
and may be deposited by physical vapor deposition means known in
the art.
[0027] In one embodiment, the at least one nano-wire 140 is a
nano-ribbon. In a third embodiment, the at least one nano-wire 140
is a cylindrical wire with a diameter in a range from about 5 nm to
about 300 nm. More preferably, the at least one nano-wire 140 has a
diameter in a range from about 5 nm to about 100 nm. In a fourth
embodiment, the at least one nano-wire 140 has a length in a range
from about 50 nm to about 50,000 nm. More preferably, nano-wire 140
has a length in a range from about 200 nm to about 20,000 nm.
[0028] The plurality of electrodes 70 may be arrayed on substrate
40 and connected by the at least one nano-wire so as to provide an
architecture for electronic device 20. A cross-bar architecture 300
is shown in FIG. 6.
[0029] Another aspect of the present invention is to provide an
electrode structure comprising at least one electrode 70 having at
least one edge portion 100 and at least one nano-wire 140
originating from edge portion 100. The at least one electrode 70,
in one embodiment, comprises at least one noble metal, such as, but
not limited to, platinum, gold, silver, and combinations thereof.
In another embodiment, the at least one electrode comprises at
least one of tungsten, niobium, tantalum, and combinations thereof.
In a third embodiment, the at least one electrode includes a
catalyst 180. The catalyst 180 comprises at least at least one of
gold, nickel, iron, chromium, cobalt, and combinations thereof.
[0030] The at least one nano-wire 140 of the electrode structure
comprises at least one of a semi-conductor, a carbide, an oxide, a
nitride, a boride, and combinations thereof. In one particular
embodiment, the at least one nano-wire 140 comprises lanthanum
hexaboride (LaB.sub.6). In another embodiment, nano-wire 140
comprises a semi-conductor. The semi-conductor comprises at least
one of silicon, germanium, a III-V compound, a II-VI compound, a
IV-VI compound, and combinations thereof. In another embodiment,
nano-wire 140 comprises a carbide. The carbide comprises at least
one of silicon carbide, niobium carbide, molybdenum carbide,
tantalum carbide, hafnium carbide, tungsten carbide, and
combinations thereof.
[0031] The at least one nano-wire 140 of the electrode structure
may have a predetermined orientation with respect to the at least
one electrode 70. For example, the at least one nano-wire 140 may
be oriented perpendicular to the at least one electrode 70.
External forces or fields may also be used, either during growth of
nano-wire 140, or after growth of nano-wire 140, to orient the at
least one nano-wire with respect to the electrode. In one
embodiment, the at least one nano-wire is oriented by applying at
least one of a magnetic field, an electric field, and combinations
thereof.
[0032] The electrode structure can be used to build an array of
nano-wires and electrodes, such as the cross-bar array 300 shown in
FIG. 6. One application for such arrays is in memory devices and
sensors.
[0033] Another aspect of the present invention is to provide a
method for making an electrode structure for the electronic device
20 disclosed herein, wherein the electrode structure comprises at
least one substrate 40, a plurality of electrodes 70 disposed on
substrate 40, and at least one nano-wire 140 originating from edge
100 of first electrode 60 and extending to edge 120 of second
electrode 80. The method comprises the steps of: providing
substrate 40; forming a plurality of electrodes 70 on substrate 40;
growing the at least one nano-wire 140 from an edge 100 of first
electrode 60; and connecting the at least one nano-wire 140 to edge
120 of second electrode 80.
[0034] Substrate 40 comprises at least one of a semi-conducting
material, an insulating material, and combinations thereof. The
semi-conducting materials that may comprise the substrate include,
but are not limited to, at least one of silicon, germanium, indium
tin oxide, silicon carbide, combinations thereof, and the like.
Non-limiting examples of insulating material include diamond and
metal oxides, such as, but not limited to, at least one of
magnesium oxide, sapphire, lithium aluminate, and combinations
thereof.
[0035] In one embodiment of the present invention, the step of
providing the substrate 40 further includes cleaning the substrate
40. In one embodiment substrate 40 is cleaned in a chemical bath
(such as sulfuric acid) to obtain a thin native oxide film on the
surface of the substrate. Alternatively, substrate 40 may be
cleaned by other techniques that are known in the art, such as, but
not limited to, plasma etching and the like.
[0036] In one embodiment, each of the plurality of electrodes 70
comprises at least one noble metal, such as, but not limited to,
platinum, gold, silver, and combinations thereof. In another
embodiment, each of the plurality of electrodes 70 comprises at
least one of tungsten, niobium, tantalum, and combinations thereof.
Alternatively, each of the plurality of electrodes 70 further
comprises a catalyst 180, such as at least one of gold, nickel,
iron, chromium, cobalt, combinations thereof, and the like. In one
embodiment, the step of forming a plurality of electrodes 70
comprises spinning a photoresist onto substrate 40, defining
patterns in the photoresist using photolithographic methods that
are known in the art, and then removing portions of the patterned
photoresist, leaving behind exposed portions of substrate 40. An
ashing and/or buffered oxide etch process may be used to clean the
exposed portions of substrate 40. Electrode material is then
deposited on the exposed portions of substrate 40, using vapor
deposition techniques that are known in the art, such as physical
vapor deposition (PVD), and the like. Any remaining photoresist is
then removed using lift-off techniques known in the art. An array
of gold electrodes 70 deposited on a silicon substrate 40 by this
method is shown in FIG. 4.
[0037] In another embodiment, a film of catalyst 180 is deposited
on at least one of the plurality of electrodes 70. Catalyst 180
comprises at least one of gold, nickel, iron, chromium, cobalt, and
combinations thereof. In one embodiment, catalyst 180 comprises at
least one noble metal. The film of catalyst 180 has a thickness in
a range from about 10 Angstroms to about 120 Angstroms. More
preferably, the film of catalyst 180 has a thickness in a range
from about 30 Angstroms to about 100 Angstroms. The film of
catalyst 180 is deposited using at least one of electron-beam
evaporation, laser ablation, radio frequency (rf) sputtering,
plasma sputtering, molecular beam epitaxy, chemical vapor
deposition, physical vapor deposition, metal organic chemical vapor
deposition, and combinations thereof. Alternatively, catalyst may
be deposited by spin-coating a slurry of nanoparticles of catalyst
180 onto a surface of the plurality of electrodes 70.
[0038] At least one nano-wire 140 is then grown from an edge of a
first electrode 60. The at least one nano-wire 140 comprises at
least one of a semi-conductor, a carbide, an oxide, a nitride, a
boride, and combinations thereof. In one embodiment, the at least
one nano-wire comprises a semi-conductor, wherein the
semi-conductor comprises at least one of silicon, germanium, a
III-V compound, a II-VI compound, a IV-VI compound, and
combinations thereof. In another embodiment, the at least one
nano-wire comprises 140 a carbide, wherein the carbide comprises at
least one of silicon carbide, niobium carbide, molybdenum carbide,
tantalum carbide, hafnium carbide, tungsten carbide, and
combinations thereof. FIG. 5 is a micrograph showing a plurality of
nano-wires 140 grown from first electrode 60 and extending toward
second electrode 80
[0039] In one embodiment of the present invention, the step of
growing at least one nano-wire 140 from an edge of first electrode
60 comprises heating the electrode structure, which comprises
substrate 40, plurality of electrodes 70 formed thereon, and
catalyst 180 to a predetermined temperature in the presence of a
metal containing vapor. The at least one nano-wire 140 grows from
catalyst 180 via one of a vapor-solid and a vapor-liquid-solid
(VLS) growth mechanism in which catalyst 180 acts as a seed-for
growing nano-wire 140. In one embodiment, the electrode structure
is heated to a predetermined temperature in the presence of at
least one additional reactive gas. The composition of the at least
one additional reactive gas depends upon the desired composition of
the plurality of nano-wires. In order to obtain nano-wires
comprising a nitride, for example, the electrode structure is
heated in the presence of ammonia and a metal-containing vapor.
Similarly, the electrode structure is heated in the presence of
ammonia and a metal-containing vapor oxygen to obtain oxide
nano-wires. To obtain carbide nano-wires, the electrode structure
is heated in the presence of a metal-containing vapor and at least
one hydrocarbon, such as methane or the like, to obtain carbide
nano-wires.
[0040] In one embodiment, the step of heating the electrode
structure to a predetermined temperature comprises at least one
heating period, a dwell time at the predetermined temperature, and
a cooling period during which the metal vapor condenses on the
electrode structure and the electrode structure is returned to room
temperature. Heating and cooling of the electrode structure may be
carried out at a controlled, predetermined rate. Multiple heating
periods at different predetermined temperatures may also be used to
grow the at least one nano-wire 140. The nano-wires may be grown by
heating the electrode structure in a furnace such as a vacuum tube
furnace, a muffle furnace, an annealing furnace, a controlled
environment furnace, combinations thereof, and the like. The
predetermined temperature that is used to grow the at least one
nano-wire 140 depends on the desired composition of the at least
one nano-wire. Generally, the at least one nano-wire 140 is grown
at a temperature in a range from about 500.degree. C. to about
1400.degree. C. In another embodiment, the at least one nano-wire
140 is grown at a temperature in a range from 750.degree. C. to
about 1100.degree. C. In one particular embodiment, the at least
one nano-wire 140 is grown by heating the electrode assembly to a
temperature of about 1200.degree. C. The metal-containing vapor
source comprises at least one of a semi-conductor, a carbide, an
oxide, a nitride, a boride, a metal iodide, a metal bromide, a
metal-organic liquid or vapor, a metal hydride, a metal chloride, a
metal in elemental form, and combinations thereof.
[0041] The at least one nano-wire 140 grows from an edge of the
first electrode 60, with catalyst 180 facilitating growth at the
predetermined temperature in the presence of a metal containing
vapor. The at least one nano-wire 140 may, in one embodiment, grow
to and contact second electrode 80. Alternatively, a contact
between the at least one nano-wire 140 and second electrode 80 is
established by catalyst 180, which remains attached to the end of
the at least one nano-wire 140, as shown in FIG. 1. Contact between
the at least one nano-wire 140 and second electrode 80 can also be
established by lithographically depositing a conductive element to
establish contact between the at least one nano-wire 140 and second
electrode 80, as shown in FIG. 1.
[0042] The following example is included to illustrate the various
features and advantages of the present invention, and is not
intended to limit the invention in any way.
EXAMPLE 1
[0043] In illustration, a silicon substrate (Si<111>)
substrate is cleaned in a standard "piranha" or keros bath
(sulfuric acid) to obtain a thin native oxide layer on the
substrate. Photoresist is spun onto the substrate, patterns are
defined thereon using photolithography, and the patterns are
cleaned with an ashing and buffered oxide etch process to remove
the native oxide in the patterns. Metallic gold (Au) having a
thickness of 30-100 .ANG. is deposited by electron-beam
evaporation. The substrate is placed in a vacuum tube furnace with
a metal vapor source for growing nano-rods. For growing zinc oxide
nano-rods, ZnO is ground and mixed with carbon powder in a
stoichiometric molar ratio of 1:1. While simple vapor transport by
carbothermal reduction processes are used as the source for growing
nano-rods, other techniques, such as laser ablation, evaporation,
chemical vapor deposition (CVD), metal organic chemical vapor
deposition (MOCVD), and combinations thereof are equally
acceptable. In the case of ZnO, the furnace is heated to a
temperature in range from about 890.degree. C. to about
1000.degree. C. for a time period ranging from about 1 minute to
about 30 minutes and then allowed to cool. The actual dwell time
period at the predetermined temperature is long enough to permit
the at least one nano-wire 140 to grow to a length that is
sufficient to connect first electrode 60 to second electrode 80, or
to substantially cover the distance separating first electrode 60
from second electrode 80.
[0044] On cooling, the patterned feature breaks into "islands" with
ZnO nano-rods found at the edge of these islands. The mechanism for
the formation of the islands is believed to be selective diffusion
of the Au catalyst into the underlying Si substrate except for the
edge, that causes an etch step. The effect of a surface energy
interaction with the native oxide at the edge of the patterns may
also play a role in the process. Various strategies and approaches
to engineer catalyst interaction for growing nano-wires and
obtaining selective growth of nano-wires in precise locations is
provided by the present invention. Various external fields,
including well-defined gas flow, electric field, and magnetic
fields applied in situ during synthesis are used to align the
nano-wires across electrodes in configurations such as but not
limited to core-shell structures, hetero-epitaxial nano-wires, GATE
dielectric devices, biosensors, chemical sensors, artificial nose,
cross-bar arrays and NEMS devices, and combinations thereof.
[0045] The method also provides for placement of nano-rods and
nano-wires within a device architecture without having to
independently synthesize the nano-rods and nano-wires. The
invention is applicable to any suitable combination of substrate,
catalyst, and nano-wire as may be known to one skilled in the art.
Embodiments of the invention teach the growth of nano-wires at the
edge of micron scale features for integration with larger scale
structures; the devices and the fabrication processes for making
the nano-wire; a cross-bar architecture 300 fabricated per the
disclosed method as shown in FIG. 6, and the use of a bilayer
nano-wire that is the selectively etched to make a NEMS device.
[0046] While typical embodiments have been set forth for the
purpose of illustration, the foregoing description should not be
deemed to be a limitation on the scope of the invention.
Accordingly, various modifications, adaptations, and alternatives
may occur to one skilled in the art without departing from the
spirit and scope of the present invention.
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