U.S. patent application number 10/820634 was filed with the patent office on 2005-10-13 for chemical vapor deposition (cvd) apparatus usable in the manufacture of superconducting conductors.
Invention is credited to Lee, Hee-Gyoun, Selvamanickam, Venkat.
Application Number | 20050223983 10/820634 |
Document ID | / |
Family ID | 35059262 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050223983 |
Kind Code |
A1 |
Selvamanickam, Venkat ; et
al. |
October 13, 2005 |
Chemical vapor deposition (CVD) apparatus usable in the manufacture
of superconducting conductors
Abstract
A chemical vapor deposition (CVD) apparatus usable in the
manufacture of a superconducting conductor on an elongate substrate
is disclosed. The CVD apparatus includes a reactor, at least one
substrate heater, and at least one precursor injector having a
longitudinal flow distributor. Optionally, the CVD apparatus may
include one of a transverse lateral flow restrictor, a shield for
protecting a low-temperature region of the substrate, and both.
Inventors: |
Selvamanickam, Venkat;
(Wynantskill, NY) ; Lee, Hee-Gyoun; (Kunpo-Si,
KR) |
Correspondence
Address: |
SMITH MOORE LLP
P.O. BOX 21927
GREENSBORO
NC
27420
US
|
Family ID: |
35059262 |
Appl. No.: |
10/820634 |
Filed: |
April 8, 2004 |
Current U.S.
Class: |
118/715 ;
118/720; 427/255.28 |
Current CPC
Class: |
C23C 16/455 20130101;
C23C 16/45565 20130101; C23C 16/45517 20130101; Y10T 29/49014
20150115; H01L 39/2441 20130101; C23C 16/408 20130101; C23C 16/545
20130101; C23C 16/45591 20130101 |
Class at
Publication: |
118/715 ;
427/255.28; 118/720 |
International
Class: |
C23C 016/00 |
Claims
1. A chemical vapor deposition (CVD) apparatus usable in the
manufacture of superconducting conductor on an elongate substrate,
the CVD apparatus comprising: a) a reactor; b) at least one
substrate heater; and c) at least one precursor injector having a
longitudinal flow distributor.
2. The CVD apparatus according to claim 1, wherein the at least one
substrate heater further includes at least one susceptor.
3. The CVD apparatus according to claim 2, wherein the susceptor
has a radius of curvature for accommodating the elongate
substrate.
4. The CVD apparatus according to claim 1, wherein the substrate
heater is a multiple-zone heater.
5. The CVD apparatus according to claim 4, further including a
surface heater.
6. The CVD apparatus according to claim 5, wherein the surface
heater is positioned so as to maintain a temperature at the growth
surface on the substrate at a deposition temperature.
7. The CVD apparatus according to claim 1, wherein the substrate
heater is a single-zone heater.
8. The CVD apparatus according to claim 7, further including a
surface heater.
9. The CVD apparatus according to claim 8, wherein the surface
heater is positioned so as to maintain a temperature at a growth
surface on the substrate at a deposition temperature.
10. The CVD apparatus according to claim 8, wherein the surface
heater is a lamp.
11. The CVD apparatus according to claim 1, wherein the substrate
heater comprises at least one heat source.
12. The CVD apparatus according to claim 11, wherein the heat
source comprises a plurality of lamps.
13. The CVD apparatus according to claim 11, wherein the heat
source is at least one resistance heating element.
14. The CVD apparatus according to claim 1, further including a
shield for protecting a low-temperature region of the
substrate.
15. The CVD apparatus according to claim 14, wherein the substrate
shield is positioned so that the surface temperature over the
deposit coating does not exceed the deposition temperature.
16. The CVD apparatus according to claim 1, further including a
precursor supply system.
17. The CVD apparatus according to claim 16, further including a
precursor source.
18. The CVD apparatus according to claim 17, wherein the precursor
source is a solid.
19. The CVD apparatus according to claim 18, wherein the solid
precursor source is a powder.
20. The CVD apparatus according to claim 17, wherein the precursor
source is a liquid.
21. The CVD apparatus according to claim 20, wherein the liquid is
a solution of THS and thd.
22. The CVD apparatus according to claim 16, further including a
delivery mechanism.
23. The CVD apparatus according to claim 22, wherein the delivery
mechanism comprises a pump when the precursor source comprises a
liquid.
24. The CVD apparatus according to claim 22, wherein the delivery
mechanism comprises one of a mill and a conveyor when the precursor
source comprises a solid.
25. The precursor delivery system according to claim 16, further
including a vaporizer.
26. The CVD apparatus according to claim 25, further including a
carrier fluid supply.
27. The CVD apparatus according to claim 1, further including an
exhaust system.
28. The CVD apparatus according to claim 27, wherein the exhaust
system is for removing reaction products from the elongate
substrate surface.
29. The CVD apparatus according to claim 28, wherein the exhaust
system is a vacuum system.
30. The CVD apparatus according to claim 1, further including a gas
supply.
31. The CVD apparatus according to claim 30, further including a
mass flow control mechanism.
32. The CVD apparatus according to claim 30, further including a
carrier fluid supplied to the precursor supply system.
33. The CVD apparatus according to claim 32, wherein the carrier
fluid is an inert gas.
34. The CVD apparatus according to claim 33, wherein the inner gas
is argon.
35. The CVD apparatus according to claim 30, wherein the gas is a
reactive gas.
36. The CVD apparatus according to claim 35, wherein the reactive
gas is one of oxygen and nitrogen oxide.
37. The CVD apparatus according to claim 1, further including a
tape handler.
38. The CVD apparatus according to claim 37, wherein the tape
handler comprises a tape translation mechanism.
39. The CVD apparatus according to claim 38, wherein the tape
translation mechanism comprises at least one of a conveyor,
reel-to-reel unit, robotic translator, and combinations
thereof.
40. The CVD apparatus according to claim 1, further including at
least one controller in communication with at least the substrate
heater.
41. The CVD apparatus according to claim 40, further including at
least one sensor in communication with the at least one
controller.
42. The CVD apparatus according to claim 41, wherein at least one
sensor includes any one of a flow meter, a species monitor, a
filament state monitor, a deposition sensor, a temperature sensor,
a pressure sensor, a vacuum sensor, a speed monitor, and
combinations thereof.
43. The CVD apparatus according to claim 40, wherein the at least
one controller is for regulating the at least one precursor
injector.
44. The tape-manufacturing system according to claim 40, wherein
the at least one controller is for regulating the at least one
precursor supply system.
45. The tape-manufacturing system according to claim 40, wherein
the at least one controller regulates a translational speed of the
elongate substrate.
46. A precursor injector usable in a reactor of a chemical vapor
deposition (CVD) apparatus in combination with a substrate heater
and usable in the manufacture of superconducting conductor on an
elongate substrate, the precursor injector comprising: a) a
longitudinal flow distributor; and b) a transverse lateral flow
restrictor.
47. The precursor injector according to claim 46, wherein the
longitudinal flow distributor includes an entrance, a receiver
volume, a distributor, a distribution volume, and a plurality of
exits.
48. The precursor injector according to claim 47, wherein the
entrance is a tube.
49. The precursor injector according to claim 47, wherein the
distributor is a perforated member.
50. The precursor injector according to claim 49, wherein the
perforated member has a density of between about 1 to 10 holes per
inch.
51. The precursor injector according to claim 47, wherein the
distribution volume is less than the receiver volume.
52. The precursor injector according to claim 47, wherein the
receiver volume is greater than a total volume of perforations in
the perforated member.
53. The precursor injector according to claim 47, wherein a total
volume of the perforations is greater than the distribution
volume.
54. The precursor injector according to claim 48, wherein there is
an equal volume of perforations on both sides of the tube, and the
tube is substantially in the center of the injector.
55. The precursor injector according to claim 54, wherein the
volume of perforations increases with an increasing direction from
the tube.
56. The precursor injector according to claim 55, wherein the
volume of perforations is increased by increasing the diameter of
the perforations.
57. The precursor injector according to claim 55, wherein the
volume of perforations is increased by increasing the thickness of
the perforated member.
58. The precursor injector according to claim 47, further including
vapor delivery.
59. The precursor injector according to claim 58, wherein a volume
of the vapor delivery is greater than the receiver volume.
60. The precursor injector according to claim 46, further including
a temperature regulation system.
61. The precursor injector according to claim 60, wherein the
temperature regulator further includes a plurality of temperature
sensors.
62. The precursor injector according to claim 60, wherein the
temperature regulation system includes a heat source.
63. The precursor injector according to claim 60, wherein the
temperature regulation system includes a cooler.
64. The precursor injector according to claim 46, wherein the
lateral flow restrictor is a physical extension of the precursor
injector.
65. The precursor injector according to claim 46, wherein the
lateral flow restrictor is a gas curtain emanating from the
injector.
66. The precursor injector according to claim 46, wherein the
lateral flow restrictor is spaced relative to the substrate heater
in a manner to permit exhausting of reaction products from the
surface of the elongate substrate.
67. A chemical vapor deposition (CVD) apparatus usable in the
manufacture of superconducting conductor on an elongate substrate,
the CVD apparatus comprising: a) a reactor; b) at least one
substrate heater; and c) at least one precursor injector having a
longitudinal flow distributor and a transverse lateral flow
restrictor; and d) a shield for protecting a low-temperature region
of the substrate.
68. The CVD apparatus according to claim 67, wherein the substrate
shield is positioned so that the surface temperature over deposit
coating does not exceed the deposition temperature.
69. A method for manufacturing a high temperature superconducting
conductor, said method comprising the steps of: a) providing an
elongate substrate to a reactor; b) heating at least a portion of
the substrate to a temperature sufficient to facilitate the
formation of one of a predecessor to a superconducting material and
a superconducting material; and c) longitudinally distributing a
flow of at least one precursor so as to communicate the at least
one precursor with the heated at least a portion of the substrate
so as to permit the formation of one of a predecessor to a
superconducting material and a superconducting material.
70. A method for manufacturing a high temperature superconducting
conductor, said method comprising the steps of: a) providing an
elongate substrate to a reactor; b) heating at least a portion of
the substrate to a temperature sufficient to facilitate the
formation of one of a predecessor to a superconducting material and
a superconducting material; and c) longitudinally distributing a
flow of at least one precursor; and d) transversely restricting the
flow of the at least one precursor so as to communicate the at
least one precursor with the heated at least a portion of the
substrate so as to permit the formation of one of a predecessor to
a superconducting material and a superconducting material.
71. A method for manufacturing a high temperature superconducting
conductor, said method comprising the steps of: a) providing an
elongate substrate to a reactor; b) heating at least a portion of
the substrate to a temperature sufficient to facilitate the
formation of one of a predecessor to a superconducting material and
a superconducting material; c) longitudinally distributing a flow
of at least one precursor; d) transversely restricting the flow of
the at least one precursor; e) shielding a low-temperature region
of the substrate so as to communicate the at least one precursor
with the heated at least a portion of the substrate so as to permit
the formation of one of a predecessor to a superconducting material
and a superconducting material.
72. A high temperature superconducting conductor comprising: a) an
elongate substrate; b) at least one oxide superconductor layer
supported by said elongate substrate; and c) an Ic of over about
190 A/cm-width.
Description
[0001] The following related application filed on same day herewith
is hereby incorporated by reference in its entirety for all
purposes: U.S. patent application Ser. No. ______; inventors
Hee-Gyoun Lee and Venkat Selvamanickam; and entitled "A CHEMICAL
VAPOR DEPOSITION (CVD) APPARATUS USABLE IN THE MANUFACTURE OF
SUPERCONDUCTING CONDUCTORS."
[0002] The present invention relates generally to a chemical vapor
deposition (CVD) apparatus and, more particularly, to a CVD
apparatus capable of continuously forming a superconducting
material on the surface of an elongate substrate to manufacture
superconducting conductors. The CVD apparatus is capable of
continuously forming a non-superconducting oxide material on the
surface of an elongate substrate that also may be used to
manufacture superconducting conductors.
BACKGROUND
[0003] In the past three decades, electricity has risen from 25% to
40% of end-use energy consumption in the United States. With this
rising demand for power comes an increasingly critical requirement
for highly reliable, high quality power. As power demands continue
to grow, older urban electric power systems in particular are being
pushed to the limit of performance, requiring new solutions.
[0004] Metal conductors, such as copper and aluminum, form the
foundation of the world's electric power system, including
generators, transmission and distribution systems, transformers,
and motors. The discovery of high-temperature superconducting (HTS)
compounds in 1986 has led to an effort to develop conductors
incorporating HTS compounds for the power industry to replace metal
conductors. HTS conductors are one of the most fundamental advances
in electric power system technology in more than a century.
[0005] HTS conductors can carry over one hundred times more current
than conventional metal conductors of the same physical dimension.
The superior power density of HTS conductors will enable the
development of a new generation of power industry technologies. HTS
conductors offer major size, weight, efficiency, and environmental
benefits. HTS technologies will drive down costs and increase the
capacity and reliability of electric power systems in a variety of
ways. For example, an HTS cable is capable of transmitting two to
five times more power through existing rights-of-way, thus
improving the performance of power grids while reducing their
environmental footprint.
[0006] However, to date, only short samples of the HTS conductors
have been fabricated at high performance levels. For HTS technology
to become commercially viable for use in the power generation and
distribution industry, it will be necessary to develop equipment
for continuous, high-throughput production of HTS conductors.
[0007] One way to characterize HTS conductors is by their cost per
meter. An alternative way to characterize HTS conductors is by cost
per kiloamp-meter. That is, by increasing the current-carrying
capacity for a given cost per meter of an HTS conductor, the cost
per kiloamp-meter is reduced. This is demonstrated in the critical
current density (Jc) of the deposited HTS material multiplied by
the cross-sectional area of the material.
[0008] For a given critical current and width of HTS material, one
way to increase the cross-sectional area is to increase the HTS
material thickness. However, under conventional process parameters,
it has been demonstrated that with critical current density as a
function of thickness, the critical current density drops off as
the thickness of a single layer of HTS material increases beyond
approximately 1.5 microns and may reach saturation. This is because
beyond a film thickness of approximately 1.5 microns, the HTS
material becomes very porous, develops voids, and develops
increased surface roughness, all of which contribute to inhibiting
the flow of current. This results in limiting the critical current
in coated conductors to typically 100 A/cm width.
[0009] Chemical vapor deposition (CVD) is a process that shows
promise for the high throughput necessary to cost-effectively
produce HTS conductors. During CVD, HTS material, such as
yttrium-barium-copper-oxide (YBa.sub.2Cu.sub.3O.sub.7 or "YBCO"),
may be deposited by vapor-phase precursors onto a heated substrate
via chemical reactions that occur at the surface of the substrate.
Also, CVD and, particularly, metalorganic chemical vapor deposition
(MOCVD), is an attractive process for fabrication of HTS coated
conductors at a high throughput. High throughput is partly enabled
by large deposition areas that are possible with MOCVD.
[0010] However, there are several issues that need to be resolved
for the uniform deposition of HTS materials over large areas on
continuously moving substrates including precursor uniformity,
exhaust of precursor waste and substrate temperature uniformity.
Injecting a precursor uniformly over a large deposition area of a
heated substrate, in particular a moving substrate, can be
especially difficult. Further, obtaining sufficiently high
conversion of precursor to HTS material formed on is a challenge in
particular so as to avoid waste of expensive precursors, and
increase deposition rate. Also, depositing HTS material on a moving
substrate within the preferred temperature window is
challenging.
[0011] Thus, there remains a need for a new and improved CVD
apparatus that is capable of continuously and uniformly forming a
superconducting material and non-superconducting material on the
surface of an elongate substrate, especially on continuously moving
substrate, to manufacture superconducting conductors.
SUMMARY
[0012] The present invention is directed to a chemical vapor
deposition (CVD) apparatus usable in the manufacture of a
superconducting conductor on an elongate substrate. The CVD
apparatus includes a reactor, at least one substrate heater, and at
least one precursor injector having a longitudinal flow
distributor. Optionally, the CVD apparatus may include one of a
transverse lateral flow restrictor, a shield for protecting a
low-temperature region of the substrate, and both.
[0013] The substrate heater includes at least one heat source. For
example, the heat source heats the elongate substrate, directly,
indirectly, or directly and indirectly. The heat source may be any
of one of the many that are commercially available. Applicants have
found, for example, that a plurality of lamps and a
resistance-heating element work adequately as the heat source of
the substrate heater.
[0014] When at least one susceptor is included as part of the
substrate heater, the heat source heats the susceptor. In turn, the
susceptor heats the elongate substrate. One advantage of using at
least one susceptor is that the susceptor may be configured to have
a sufficient thermal inertia so as to maintain the elongate
substrate at a temperature that permits the deposition surface of
the substrate at the deposition temperature. Having a sufficient
thermal inertia may be particularly advantageous for a substrate
that is constantly being moved beyond the substrate heater.
Applicants have found that including a radius of curvature in the
design of the susceptor is particularly advantageous. Such a radius
of curvature may accommodate the elongate substrate and, in
particular, the contacting communication of the translating
elongate substrate and the susceptor.
[0015] The substrate heater may be any one of a single-zone heater,
a multiple-zone heater, and combinations thereof. Further, a
surface heater may be included. Whether the substrate heater is a
single-zone heater, a multiple-zone heater, or combinations
thereof, the surface heater is positioned so as to maintain a
temperature at the growth surface on the substrate at a deposition
temperature. Applicants have found that lamp-type heaters, such as
for example, quartz lamps, work satisfactorily as a surface
heater.
[0016] Applicants have found that it may be advantageous to include
one or more shields to protect a low-temperature region of the
substrate. When used, the substrate shield is positioned so that
the surface temperature of the deposition coating does not exceed
the deposition temperature.
[0017] The CVD apparatus may further include at least one precursor
supply system. The precursor supply system includes a precursor
source, delivery mechanism, and a vaporizer. A carrier fluid supply
may be in communication with the vaporizer to provide a carrier for
transporting the vaporizer precursor to the injector.
[0018] The precursor source may be any of the type known in the art
such as, for example, a solid, liquid, and combinations thereof. A
solid precursor source may be provided as mass, a powder, and a
mass that is subsequently powdered. A liquid precursor source may
be provided in a solvent based manner, a solventless based manner,
and combinations thereof.
[0019] Examples of categories of metalorganic compounds usable as
precursors include: metal .beta.-diketonates, such as M(thd)y
(where thd may be a tetramethylheptanedione such as
2,2,6,6-tetramethyl-3,5-heptaned- ionate), M(thd)y(OR)z (where thd
may be a tetramethylheptanedione such as
2,2,6,6-tetramethyl-3,5-heptanedionate and R may be an alkyl
group), and M(acac)y (where acac may be an acetylacetonate such as
2,4-pentanedionate); alkoxides, such as ethoxide (OEth),
isopropoxide (i-OPr), and butoxide (n-OBut); alkylmetal; and
carboxylates, such as benzoate and ethylhexanoate (eha). M may be
any one of Y, Ba, and Cu. When a solution is used any appropriate
solvent that is compatible with the metalorganic compounds may be
used. For example, any one of tetrahydrofuran (THF), isopropanol,
and combinations thereof may be used with M(thd)y.
[0020] The delivery mechanism provides the precursors to the
vaporizer in a predetermined amount. When the precursor source
comprises a liquid, the delivery mechanism may be a pump.
[0021] When the precursor source comprises a solid, the delivery
mechanism may be one of a mill, a conveyor, and combinations
thereof. Further, a liquid solution may be provided and any solvent
evaporated therefrom. Then, the resultant solid may be provided by,
for example, a conveyor.
[0022] Further, the CVD apparatus may include an exhaust system.
The exhaust system is for removing reaction products from the
elongate substrate surface. In this manner, the precursor provided
by the injector may more effectively reach the surface of the
elongate substrate to facilitate the growth of the coating. The
exhaust system may include a vacuum system in communication with
the reactor.
[0023] The CVD apparatus may further include a gas supply that in
turn may include a mass flow control mechanism. The gas supply may
include a carrier fluid supply communicating with the precursor
supply system. The carrier fluid may include an inert gas, such as
argon, a reactive gas, such as one of oxygen and nitrogen oxide,
and combinations of inert gases and reactive gases.
[0024] As applicants contemplate that the CVD apparatus is usable
in the manufacture of superconducting conductors, the CVD apparatus
may further include a tape handler such as a tape translation
mechanism. Examples of usable tape translation mechanisms include
at least one of a conveyor, reel-to-reel unit, robotic translator,
and combinations thereof.
[0025] At least one controller may be part of the CVD apparatus,
for example, to coordinate the operation of its various parts,
components, and peripherals. For example, the controller may be in
communication with the at least the substrate heater. Further, to
facilitate the operation of the CVD apparatus, its various parts,
components, and peripherals, at least one sensor is in
communication with the at least one controller. Examples of the at
least one sensor include any one of a flow meter, a species
monitor, a filament state monitor, a deposition sensor, a
temperature sensor, a pressure sensor, a vacuum sensor, a speed
monitor, and combinations thereof.
[0026] Some specific examples of use of the at least one controller
include regulating: the at least one precursor injector; at least
one precursor supply system; a translational speed of the elongate
substrate, and combinations thereof.
[0027] Turning now to the precursor injector and its parts and
peripherals. For example, the longitudinal flow distributor may
include an entrance, a receiver volume, a distributor, a
distribution volume, and a plurality of exits. The entrance may be
a tube. The distributor may be a perforated member having, for
example, a density of between about 1 to 10 per inch.
[0028] Applicants have found that the precursor injector provides
that precursor in a more desirable manner when the distribution
volume is less than the receiver volume. Also, Applicants have
found that making the receiver volume greater than a total volume
of perforations in the perforated member is beneficial. Further,
Applicants have found that a total volume of the perforations
greater than the distribution volume provides an advantage. A vapor
delivery communicates with the precursor injector. Applicants have
found that it is beneficial for a volume of the vapor delivery to
be greater than the receiver volume.
[0029] Concerning other aspects of the precursor injector, when the
entrance, such as a tubular passage, is substantially in the center
of the injector. Applicants have found that an equal volume of
perforations on both sides of the entrance is beneficial. Further,
Applicants have found that it may be desirable for the volume of
perforations to increase in an increasing direction from the
entrance. For example, the volume of perforations may be increased
by increasing the diameter of the perforations in an increasing
direction from the entrance. Alternatively, the volume of
perforations may be increased by increasing the thickness of the
perforated member in an increasing direction from the entrance.
[0030] Also, it may be advantageous for the precursor injector
according to include a temperature regulation system. At least one
and, optionally, a plurality of temperature sensors may be
communicate with the precursor injector as part of the regulation
system. The temperature regulation system for the injector may
further include one of a heat source, a cooler, and combinations
thereof.
[0031] With respect to the lateral flow restrictor of the precursor
injector, it may be a physical extension of the precursor injector.
Alternatively, the lateral flow restrictor may be a gas curtain
emanating from the precursor injector. In either case, the lateral
flow restrictor is spaced relative to the substrate heater in a
manner so as to permit the exhausting of reaction products from the
surface of the elongate substrate.
[0032] Accordingly, one aspect of the present invention is to
provide a chemical vapor deposition (CVD) apparatus usable in the
manufacture of superconducting conductors on an elongate substrate.
The CVD apparatus includes a reactor, at least one substrate
heater, and at least one precursor injector having a longitudinal
flow distributor.
[0033] Another aspect of the present invention is to provide a
precursor injector usable in a reactor of a chemical vapor
deposition (CVD) apparatus in combination with a substrate heater,
and usable in the manufacture of superconducting conductor on an
elongate substrate. The precursor injector includes a longitudinal
flow distributor and transverse lateral flow restrictor.
[0034] Still another aspect of the present invention is to provide
a chemical vapor deposition (CVD) apparatus usable in the
manufacture of superconducting conductors on an elongate substrate.
The CVD apparatus includes a reactor, at least one substrate
heater, and at least one precursor injector having a longitudinal
flow distributor. The CVD apparatus includes a transverse lateral
flow restrictor and a shield for protecting a low-temperature
region of the substrate.
[0035] These and other aspects of the present invention will become
apparent to those skilled in the art after a reading of the
following description of the preferred embodiment when considered
with the drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0036] FIG. 1 is a schematic illustrating a CVD apparatus
constructed according to the present invention;
[0037] FIG. 2 is a schematic illustrating a precursor supply usable
in the CVD apparatus of FIG. 1;
[0038] FIG. 3A is a cross-sectional schematic illustrating a
longitudinal view of an injector usable in the CVD apparatus of
FIG. 1;
[0039] FIG. 3B is a sectional view illustrating a perforated member
usable in the injector of FIG. 3A;
[0040] FIG. 3C is a sectional view illustrating a bottom view
usable in the injector of FIG. 3A;
[0041] FIG. 4A is a cross-sectional schematic illustrating a
longitudinal view of an alternative injector usable in the CVD
apparatus of FIG. 1;
[0042] FIG. 4B is a sectional view illustrating an alternative
perforated member usable in the injector of FIG. 3A;
[0043] FIG. 5A is a cross-sectional schematic illustrating a
transverse view of an alternative injector including lateral flow
restrictor usable in the CVD apparatus of FIG. 1; and
[0044] FIG. 5B is a cross-sectional schematic illustrating a
transverse view of an alternative injector including an alternative
lateral flow restrictor usable in the CVD apparatus of FIG. 1;
[0045] FIG. 6 is a schematic illustrating a top view of the
arrangement of the substrate shields, the substrate heater, and the
elongate substrate of the CVD apparatus of FIG. 1;
[0046] FIG. 7 is a schematic illustrating an alternative use of an
auxiliary heater in providing for the uniform heating of an
elongate substrate and usable in the CVD apparatus of FIG. 1;
and
[0047] FIG. 8 illustrates a cutaway view of an example HTS
conductor formed via the CVD apparatus 10 of FIG. 1.
DETAILED DESCRIPTION
[0048] 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.
[0049] Referring to the drawings in general and to FIG. I 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. FIG. 1 shows a
chemical vapor deposition (CVD) apparatus 10 according to the
present invention. The CVD apparatus 10 includes a reactor 12, at
least one substrate heater 14, and at least one precursor injector
24 having a longitudinal flow distributor 26. The CVD apparatus 10
shown in FIG. 1 includes transverse lateral flow restrictors 28 and
shields 36 for protecting a low-temperature region of a substrate
18 being coated. The CVD apparatus 10 as depicted in FIG. 1 also
includes a precursor supply system 16, an exhaust system 20, a gas
supply 22, a controller 30, auxiliary heaters 34, a mass flow
regulator 50, and a substrate translation mechanism 74.
[0050] The CVD apparatus 10 is usable in the manufacture of
elongate superconducting conductors by depositing a superconducting
(e.g., LTS material, HTS material, and combinations thereof) or a
non-superconducting material (e.g., buffer materials) on an
elongate substrate 18, such as a tape-like structure. Examples of
an elongate substrate 18 that may be used in a CVD apparatus 10 of
the present invention include, without limitation, a substrate such
as any of those disclosed in U.S. Pat. Nos. 6,610,632; 6,541,121;
6,383,989; and 5,872,080; U.S. Pat. Nos. 6,610,414; 6,610,413;
6,607,839; 6,607,838; 6,602,313; 6,599,346; 6,451,450; 6,447,714;
6,331,199; 6,156,376; 6,106,615; 5,964,966; 5,958,599; 5,898,020;
5,741,377; and 5,739,086; and U.S. Pat. Nos. 6,562,761; 6,475,311;
6,458,223; 6,426,320; 6,027,564; and 6,022,832 (the disclosure of
each being hereby incorporated by reference in their entirety).
Some of these examples of substrates 18 include barrier materials
that, among other things, act as a seed to allow the formation of
an HTS material. Others of these examples of substrates 18 have an
appropriate texture to act as a seed to allow the formation of an
HTS material. Texturized substrates and the attendant methods for
making the same include those disclosed in U.S. Pat. Nos.
6,610,414; 6,610,413; 6,607,839; 6,607,838; 6,602,313; 6,599,346;
6,451,450; 6,447,714; 6,331,199; 6,156,376; 6,106,615; 5,964,966;
5,958,599; 5,898,020; 5,741,377; and 5,739,086 by Goyal et al. and
U.S. Pat. Nos. 6,562,761; 6,475,311; 6,458,223; 6,426,320;
6,027,564; and 6,022,832 by Fritzemeier et al. (the disclosure of
each being hereby incorporated by reference in their entirety).
[0051] Turning now to the precursor injector 24 and its parts and
peripherals, the reader's attention is directed to FIGS. 3A, 3B,
3C, 4A, and 4B. For example, the longitudinal flow distributor 26
of the precursor injector 24 includes an entrance 52, a receiver
volume 54, a distributor 56, a distribution volume 60, and a
plurality of exits 62. The entrance 52 may communicate with a vapor
delivery 48 such as one or more tubes. The distributor 56 may be a
perforated member having, for example, a density of between about 1
to 10 per inch.
[0052] The precursor injector 24 provides that precursor in a more
desirable manner when the distribution volume 60 is less than the
receiver volume 54. Also, Applicants have found that making the
receiver volume 54 greater than a total volume of perforations in
the perforated member 65 is beneficial. Further, Applicants have
found that a total volume of the perforations greater than the
distribution volume 60 provides an advantage. The vapor delivery 48
communicates with the entrance of the precursor injector 24.
Applicant have found that it is beneficial for a volume of the
vapor delivery 48 to be greater than the receiver volume 54.
[0053] Concerning other aspects of the precursor injector 24, when
the entrance 52, such as a tubular passage, is substantially in the
center of the injector 24, Applicants have found that an equal
volume of perforations on both sides of the entrance 52 is
beneficial. Further, Applicants have found that it may be desirable
for the volume of perforations to increase in an increasing
direction from the entrance 52. For example as shown in FIG. 4B,
the volume of perforations may be increased by increasing the
diameter of the perforations in an increasing direction from the
entrance 52. Alternatively as shown in FIG. 4A, the volume of
perforations may be increased by increasing the thickness of the
perforated member 56 in an increasing direction from the entrance
52.
[0054] Turning now to FIG. 3C, it may be advantageous for the
precursor injector 24 to include a temperature regulation system
66. At least one and, optionally, a plurality of temperature
sensors 68 may communicate with the precursor injector 24 as part
of the regulation system 66. The temperature regulation system 66
for the injector 24 may further include one of a heat source 70, a
cooler 72, and combinations thereof.
[0055] As shown in FIGS. 1 and 5A, the lateral flow restrictor 28
of the precursor injector 24 may be a physical extension of the
precursor injector 24. Alternatively, as shown in FIG. 5B, the
lateral flow restrictor 28 may be a gas curtain emanating from the
precursor injector 24. In either case, the lateral flow restrictor
28 is spaced relative to the substrate heater 14 in a manner so as
to permit exhausting of reaction products from the surface of the
elongate substrate 18.
[0056] Returning now to FIG. 1, the substrate heater 14 includes at
least one heat source 14A. As noted, the heat source 14A may heat
the elongate substrate 18, directly, indirectly, or directly and
indirectly. The heat source 14A may be any one of the many that are
commercially available such as, for example, infrared heating,
induction heating, convective heating, microwave heating, radiation
heating, and the like. FIG. 1 schematically depicts a plurality of
lamps in the left portion of the substrate heater 14, such as
commercially available quartz-infrared heating lamps available from
CVD Equipment Corporation, Ronkonkoma, N.Y. and resistance-heating
elements in the central and right portions of the substrate heater
14, such as refractory metal elementals available from Structured
Materials Industries, Inc., Piscataway, N.J. During the deposition
process, the temperature of the elongate substrate 18 is properly
controlled via the substrate heater 14. The substrate heater 14 may
be a single- or multiple-zone substrate heater that provides
heating, typically in the range of between about 700 to 950.degree.
C., to the elongate substrate 18 via a radiant heating element,
such as an infrared lamp. Alternatively, the substrate heater 14 is
a resistance heater via a heating element, such as Kanthal or
MoSi.sub.2.
[0057] In FIG. 1, the substrate heater 14 is depicted having a
susceptor 32 and being heated by the heat source 14A. The susceptor
32 in turn heats the substrate 18. As noted, the susceptor 32 may
be configured to have a sufficient thermal inertia so as to
maintain the elongate substrate 18 at a temperature that permits
the deposition surface of the substrate 18 to be at the deposition
temperature. Having a sufficient thermal inertia may be
particularly advantageous for a substrate that is constantly being
moved beyond the substrate heater 14. Applicants have found that
including a radius of curvature in the design of the susceptor 32
is particularly advantageous. Such a radius of curvature
accommodates the elongate substrate and, in particular, the
contacting communication of the translating elongate substrate 18
and the susceptor 32.
[0058] Although the substrate heater 14 in FIG. 1 is depicted as
being a multiple-zone heater, the substrate heater 14 may be a
single-zone heater. Using a multiple-zone heater may be
particularly advantageous for keeping a temperature at a growth
surface of the translating tape at a prescribed reaction
temperature, typically in the range of 700 to 950.degree. C. when
forming an HTS material. It will be appreciated that as material is
deposited on the surface of the substrate 18, the heat transfer
properties of the substrate 18 change. The change may be attributed
to an increase in thickness and a change in material composition.
Thus, if the CVD apparatus 10 is operated to form a coating on a
substrate 18 by a translation of substrate 18 from left to right,
then the temperature of a susceptor 32 at a left end may be the
first temperature to accomplish the desired prescribed reaction
temperature and at a second temperature at a right end to
accomplish the desired prescribed reaction temperature. The
temperature of the susceptor at locations between the left end and
the right end then may be somewhere between the first temperature
and the second temperature to have the temperature at the growth
surface of the translating tape at a prescribed reaction
temperature.
[0059] In addition to, or rather than the substrate heater 14 being
used, one or more surface heaters 36 may be included in a CVD
apparatus 10. Each surface heater 36 is positioned so as to
maintain a temperature at the growth surface on the substrate 18 at
the ends of the deposition zone at a prescribed reaction
temperature. FIG. 1 shows a surface heater 36 at the left end and
another surface heater 36 at the right end of the substrate heater
14. It will be appreciated that the surface heater 36 may be used
in combination with a substrate heater 14 whether it is a
single-zone heater or a multiple-zone heater. Surface heaters 36 of
FIG. 1 are lamp-type heaters, such as for example, quartz-infrared
lamps available from CVD Equipment Corporation, Ronkonkoma,
N.Y.
[0060] Another use of surface heaters 36 as shown in FIG. 1 is to
lengthen an amount of the surface of the translating tape at a
prescribed reaction temperature that supports growth of the desired
product. For example, a substrate heater 14 substantially as
depicted in FIG. 1 having a length of about 32 centimeters (cm)
maintained about 12 cm of a translating substrate made of
HASTELLOY.RTM. C-276 nickel alloy or INCONEL.RTM. nickel alloy
(measuring about between about 50 and about 100 .mu.m thick and
between about 10 and about 13 mm wide) at a prescribe reaction
temperature. By adding auxiliary heaters 36 as schematically shown
in FIG. 1, about 25 cm of the about 32 cm were the prescribed
reaction temperature. At least two benefits realized by having an
increased length at a prescribed reaction temperature include a
faster process for the growth surface at temperature and a more
uniform zone in which growth occurs.
[0061] Yet another use of an auxiliary heater 34 is depicted in
FIG. 7. Here, the substrate heater 14, for whatever reason, does
not heat the substrate 18 uniformly. To remedy the non-uniformity,
an auxiliary heater 34 is directed to the area that is
insufficiently heated to provide additional heating to create a
more uniform heating of the substrate at a prescribed reaction
temperature.
[0062] Referring to FIG. 1 and FIG. 6 relating to shields 36,
Applicants have found that it may be advantageous to include one or
more shields 36 to shield portions of a translating substrate 18 at
a temperature lower than a prescribed reaction temperature. In
using shields 36, Applicants have found that their placement is
such so as to protect the translating substrate 18 from the
precursor composition before the growth surface is at a prescribed
reaction temperature, while at the same time, the placement is such
so that the temperature of the substrate 18 and any coatings
deposited thereon do not exceed the prescribed reaction
temperature.
[0063] The CVD apparatus 10 includes at least one precursor supply
system 16. FIG. 1 show schematically the general arrangement of the
precursor supply system 10, the reactor 12, and the injector 24.
The reactor 12 is a vacuum-sealed deposition chamber in which an
MOCVD process occurs, such as a cold-wall reactor that may be
maintained at a pressure of, for example, about 1.6 Torr. FIG. 2
provides details of the precursor supply system 16, namely, that it
includes a precursor source 40, a delivery mechanism 42, and a
vaporizer 44. A carrier fluid supply 46 is in communication with
the vaporizer 44 to transport vaporized precursor to the substrate
18 via the injector 24. In constructing a precursor supply system
16, a solution of metalorganic compounds in an appropriate solvent
as discussed below is used.
[0064] The delivery mechanism 42 that provided the solution to the
vaporizer 44 is a pump capable of a low flow rate between 0.1 and
10 mL/min. The pump is a high-pressure, low flow rate pump, such as
a high-pressure liquid chromatography (HPLC) pump including an
about 10 mil, i.e., about 254 micrometer (.mu.m), the inner
diameter tube made of a TEFLON.RTM. fluoropolymer.
[0065] The vaporizer 44 is a commercially available unit such as
those available from Cova Technology, Colorado Springs, Colo. The
vaporizer 44 may be constructed and arranged as more fully
described in U.S. Pat. No. 5,204,314 issued Apr. 20, 1993 to Peter
S. Kirlin et al.; U.S. Pat. No. 5,536,323 issued Jul. 16, 1996 to
Peter S. Kirlin et al.; U.S. Pat. No. 5,711,816 issued Jan. 27,
1998 to Peter S. Kirlin, et al. (the disclosure of each being
hereby incorporated by reference in their entirety).
[0066] The carrier fluid supply 46 provided a gas that is capable
of carrying the vaporizer precursor to the substrate 18 through the
injector 24. Gases that are inert with respect to the precursor
composition are appropriate. Such gases include argon and may
include nitrogen. As the vaporized precursor travels to the
injector 24, an oxygen-containing gas, such as any one of oxygen,
water vapor, nitrogen oxides, and combinations thereof may be added
to the vaporized precursor to form an oxide coating on the
substrate 18.
[0067] Although the precursor source 40 of FIG. 2 is a solution,
the precursor supply system 16 may be any of the type known in the
art such as, for example, a solid, liquid, and combinations
thereof. A solid precursor source may be provided as mass, a
powder, and a mass that is subsequently powdered. A liquid
precursor source may be provided in a solvent based manner, a
solventless based manner, and combinations thereof.
[0068] For example, U.S. Pat. No. 5,820,678 (the disclosure being
hereby incorporated by reference in its entirety), issued to
Hubert, et al., entitled "Solid Source MOCVD System," describes a
system for MOCVD fabrication of superconducting and
non-superconducting oxide films that includes multiple cartridges
containing tightly packed precursor materials that are ground and
vaporized for thin film deposition. Also as an other example, C.
Jimenez et al. disclose in "Characterization of a solvant-free
vapour source for MOCVD" published in J. Physique IV France 11
(2001 Pr3-669) a system that permits the separation of a solvent
from the precursors before introducing the precursors vapours into
a deposition chamber. The disclosure of C. Jimenez et al. is hereby
incorporated by reference in its entirety.
[0069] The aforementioned show that when the precursor source 40
comprises a solid, the delivery mechanism may be one of a mill, a
conveyor, and combinations thereof. Further, a liquid may be
provided and any solvent evaporated therefrom. Then, the resultant
solid may be provided by, for example, a conveyor.
[0070] Examples of categories of metalorganic compounds usable as
precursors include: metal .beta.-diketonates, such as M(thd)y
(where thd may be a tetramethylheptanedione such as
2,2,6,6-tetramethyl-3,5-heptaned- ionate), M(thd)y(OR)z (where thd
may be a tetramethylheptanedione such as
2,2,6,6-tetramethyl-3,5-heptanedionate and R may be an alkyl
group), and M(acac)y (where acac may be an acetylacetonate such as
2,4-pentanedionate); alkoxides, such as ethoxide (OEth),
isopropoxide (i-OPr), and butoxide (n-OBut); alkylmetal; and
carboxylates, such as benzoate and ethylhexanoate (eha). M may be
any one of Y, Ba, and Cu. When associated with a
non-superconducting oxide, such as for example, a buffer layer, M
may be any one of Ga, Sr, Ti, Al, La, Mn, Ni, Nb, Mg, Zr, Ce, other
rare-earths (RE), and combinations thereof. When a solution is
used, any appropriate solvent that is compatible with the
metalorganic compounds may be used. For example, any one of
tetrahydrofuran (THF), isopropanol, and combinations thereof may be
used with M(thd)y.
[0071] The delivery mechanism provides the precursors to the
vaporizer in a predetermined amount. When the precursor source
comprises a liquid, the delivery mechanism may be a pump.
[0072] The CVD apparatus 10 of FIG. 1 includes an exhaust system
20. The exhaust system 20 is for removing reaction products from
the elongate substrate surface 18. In this manner, precursor
provided by the injector 24 may more effectively reach the surface
of the elongate substrate 18 to facilitate the growth of a coating.
The exhaust system 20 may include a vacuum system in communication
with the reactor 12.
[0073] The vacuum pump may be connected to the reactor 12. The
vacuum pump is a commercially available vacuum pump capable of
maintaining a vacuum of pressure in the order of magnitude of about
10.sup.-3 Torr, such as a Leybold model D65B. Alternatively, the
function of the vacuum pump may be accomplished by a combination of
a mechanical pump and a mechanical booster, such as Edwards model
EH500, in order to obtain the proper vacuum suitable for use with a
large amount of liquid precursor.
[0074] The CVD apparatus 10 may further include a gas supply 22
that in turn communicates with a mass flow control mechanism 50.
The gas supply 22 provides the gas for the carrier fluid supply 46
that communicates with the vaporizer 44 of the precursor supply
system 16. As noted, the carrier fluid may include an inert gas,
such as argon, a reactive gas, such as one of oxygen and nitrogen
oxide, and combinations of inert gases and reactive gases.
[0075] As the CVD apparatus 10 is usable in the manufacture of
superconducting conductors, it includes a substrate translation
mechanism 70 such as a tape handler. Examples of usable substrate
translation mechanisms 70 include at least one of a conveyor, a
reel-to-reel unit, a robotic translator, and combinations
thereof.
[0076] A conventional stepper or AC vector drive motor may be used
to drive the payout spool and take-up spool of the tape handler. In
other applications, AC motors (synchronous or variable frequency)
or DC motors (brushed, brushless serve) and drives may be used. The
motor is selected to be capable of providing the required
translation speed of the elongate substrate 18. Also, the motor may
have the ability to move the elongate substrate 18 in
user-specified increments and to reverse the direction of the
elongate substrate 18. The take-up spool and the payout spool each
may be driven by a conventional torque motor that assists in
providing the proper tension to the elongate substrate 18 as it
translates through the CVD apparatus 10.
[0077] A shown in FIG. 1, at least one controller 30 may be part of
the CVD apparatus 10, for example, to coordinate the operation of
its various parts, components, and peripherals. The controller 30
of FIG. 1 is depicted as being in communication a plurality of
valve, the zone of the substrate heater 14, the precursor supply
16, the exhaust system 20, gas supply 22, the injector 24, the
auxiliary heaters 34, the mass flow regulator 50, and the
translation mechanism 74.
[0078] The controller 30 is a commercially available controller
with a plurality of inputs and outputs that meet the requirements
of the peripherals. The controller 30 may be a micro-controller or
a PC with appropriate hardware and software. Details concerning
controllers that may be used with the CVD apparatus 10 are
discussed in, for example, U.S. Pat. Nos. 5,980,078; 5,726,912;
5,689,415; 5,579,218; 5,351,200; 4,916,600; 4,646,223; 4,344,127;
and 4,396,976, the entire disclosure of each being incorporated by
reference herein.
[0079] Further, to facilitate the operation of the CVD apparatus
10, its various parts, components, and peripherals, at least one
sensor is in communication with the at least one controller 30.
Examples of the at least one sensor include any one of a flow
meter, a species monitor, a deposition sensor, a temperature
sensor, a pressure sensor, a vacuum sensor, a speed monitor, and
combinations thereof Some specific examples of use of the at least
one controller include regulating: the precursor supply system 16,
at least one precursor injector 24, a translational speed of the
elongate substrate 18, and combinations thereof
[0080] Examples of elongate substrates that may be inspected in a
CVD apparatus 10 of the present invention include, without
limitation, a substrate such as any of those disclosed in U.S. Pat.
Nos. 6,610,632; 6,541,121; 6,383,989; and 5,872,080; U.S. Pat. Nos.
6,610,414; 6,610,413; 6,607,839; 6,607,838; 6,602,313; 6,599,346;
6,451,450; 6,447,714; 6,331,199; 6,156,376; 6,106,615; 5,964,966;
5,958,599; 5,898,020; 5,741,377; and 5,739,086; and U.S. Pat. Nos.
6,562,761; 6,475,311; 6,458,223; 6,426,320; 6,027,564; and
6,022,832 (the disclosure of each being hereby incorporated by
reference in their entirety). For the manufacture of an HTS
conductor, the elongate substrate 18 is formed of metals, such as
stainless steel or a nickel alloy such as HASTELLOY.RTM. or
INCONEL.RTM., that are capable of withstanding high temperatures
and vacuum conditions. The elongate substrate 18 is typically
between about 3 to about 60 millimeters (mm) in width and upwards
of several hundred meters in length. Applicant contemplates that
the elongate substrate 18 may be any width between about 1 mm and
100 mm. After processing, an elongate substrate 18 may be sliced
into a plurality if tapes having lesser widths. For example, an
about 60 mm wide, processed elongate substrate 18 may be sliced in
a manner that produces four about 15 mm wide tapes. In a like
manner, an about 12 mm wide processed tape may be sliced in a
manner that produces four about 3 mm wide tapes. Thus, Applicants
contemplate that the elongate substrate 18 may include any width
between 1 and 100 mm, such as for example 4 mm, 5 mm, 10 mm, 11 mm,
12 mm, 98 mm, and 99 mm. The elongate substrate 18 typically has
several meters of "leader" at both ends to aid in handling.
[0081] In operation of CVD apparatus 10, a user first activates the
translation of the elongate substrate 18 by the tape translation
mechanism 74.
[0082] Those skilled in the art will appreciate that the morphology
of the deposited HTS film may change as a function of several
variables, such as but not limited to:
[0083] Deposition temperature: HTS film surface roughness is
affected by the deposition temperature;
[0084] Precursor composition: for example, the molarity
(concentration) of the precursor affects the morphology of the
film, e.g., a barium-deficient film has a morphology that differs
from a barium-rich film as well as a stoichiometric film;
[0085] Precursor delivery rate: for example, the first layer
deposited is continuously exposed to a high temperature as it
translates through the deposition zone 118, which may cause damage
to the morphology of this first layer in the time it takes to
translate through the entire deposition zone 118. Increasing the
precursor delivery rate for subsequent layers will shorten the time
that the first layer experiences this high heat and may thereby
minimize potential damage.
[0086] Oxygen partial pressure: It is necessary to prepare the film
under a different oxygen partial pressure and substrate
temperature. For example, where the precursor delivery rate is
increased twice from 0.25 to 0.5 ml/min, good performance is
obtained when 0.5 Torr higher oxygen partial pressure is used.
[0087] Oxygen partial pressure should be increased in accordance
with the above example when the substrate temperature is increased.
Oxygen partial pressure can be determined empirically depending on
processing parameter changes, such as the distance between the
multi-compartment showerhead 112 and the elongate substrate 18, the
exposure of UV light to source vapor, or the use of atomic oxygen
or ozone as an oxidant.
[0088] Specific analysis of some of the variables affecting the
morphology of the HTS film is provided below.
[0089] It has been demonstrated that, assuming a delivery rate of
about 0.25 mL/min and a deposition temperature of about 800.degree.
C., an increase in the precursor molarity (i.e., the number of
moles of solute per liter of solution) of the precursor results in
an increase in film thickness for a deposition time of about 20
minutes. For example:
[0090] a molarity of about 0.03 mol/L yields a film thickness of
about 1.0 micron;
[0091] a molarity of about 0.045 mol/L yields a film thickness of
about 1.3 microns; and
[0092] a molarity of about 0.06 mol/L yields a film thickness of
about 1.75 microns. It has been demonstrated that, assuming a
precursor molarity of about 0.03 mol/L and a deposition temperature
of about 800.degree. C., an increase in the precursor delivery rate
also results in an increase in film thickness. For example:
[0093] a delivery rate of about 0.25 mL/min yields a film thickness
of about 1.0 micron;
[0094] a delivery rate of about 0.5 mL/min yields a film thickness
of approximately about 2.0 microns; and
[0095] a delivery rate of about 1 mL/min yields a film thickness of
approximately about 4.0 microns.
[0096] It has been demonstrated that, assuming a deposition
temperature of about 800.degree. C., varying the combination of the
precursor delivery rate, the precursor molarity, and the oxygen
partial pressure affects the critical current (Jc) value of the
resulting film. For example:
[0097] Example 1: a delivery rate of 0.25 mL/min, combined with a
molarity of about 0.03 mol/L, combined with an oxygen partial
pressure of about 0.56 Torr yields a critical current of about 2.7
MA/cm.sup.2 for an about 0.6 micron thick film (Example 1);
[0098] Example 2: a delivery rate of about 0.50 mL/min, combined
with a molarity of about 0.03 mol/L, combined with an oxygen
partial pressure of about 0.56 Torr yields a critical current of
about 0 A/cm.sup.2 for an about 0.6 micron thick film (the same
thickness of film was obtained even though the deposition time was
reduced to half that of Example 1);
[0099] Example 3: a delivery rate of about 0.5 mL/min, combined
with a molarity of about 0.03 mol/L, combined with an oxygen
partial pressure of about 1.08 Torr yields a critical current of
about 2.5 MA/cm.sup.2 for an about 0.6 micron thick film (the same
thickness of film was obtained even though the deposition time was
reduced to half that of Example 1); and
[0100] Example 4: a delivery rate of about 0.5 mL/min, combined
with a molarity of about 0.06 mol/L, combined with an oxygen
partial pressure of about 1.08 Torr yields a critical current of
about 2.2 MA/cm.sup.2 for an about 0.6 micron thick film (the same
thickness of film was obtained even though the deposition time was
reduced to half that of Example 3).
[0101] Furthermore, precursor vapors and their inert carrier gas
are efficiently delivered to the deposition zone within a
temperature range of between about 230 and 300.degree. C.
[0102] Lastly, the temperature of the elongate substrate 18 during
the deposition process may affect the end properties. For example,
high critical current (Jc) of about 35 A was obtained for the film
with a thickness of about 0.35 microns that was prepared at about
800.degree. C. (Jc=1 MA/cm.sup.2). However, for a film having the
same thickness but prepared at about 810.degree. C. the Jc dropped
to about 10 A.
[0103] Using the example of FIG. 1, parameters, including those
outlined above, that may affecting the film deposition process
within CVD apparatus 10 are given in Table 1 below.
1TABLE 1 Parameters regarding CVD apparatus 10 Acceptable examples
or Narrower acceptable examples acceptable range or acceptable
range Liquid organometallic precursor THD compounds of Y, Ba, and
THD compounds of Y, Ba, and solution within the precursor supply Cu
with a molar ratio of Cu with a molar ratio of system 16 Y: about 1
Y: about 1 Ba: between about 1.8 & 2.6 Ba: between about 1.9
& 2.5 Cu: between about 2.5 & 3.5, Cu: between about 2.8
& 3.2, with solvents, such as with solvents, such as
tetrahydrofuran and tetrahydrofuran and isopropanol. isopropanol.
Alternately, THD compounds of Alternately, THD compounds of Sm(or
Nd, Eu), Ba, and Cu Sm(or Nd, Eu), Ba, and Cu with a molar ratio of
with a molar ratio of Sm(or Nd, Eu): about 1 Sm(or Nd, Eu): about 1
Ba: between about 1.8 & 2.6 Ba: between about 1.9 & 2.5 Cu:
between about 2.5 & 3.5. Cu: between about 2.8 & 3.2.
Alternately, part of Y is Alternately, part of Y is substituted
with Sm (or Nd, substituted with Sm (or Nd, Eu) up to 50%. Eu) up
to 50%. Molarity of the precursor solution Between about Between
about within precursor supply system 16 0.015 & 0.070 mol/L
0.050 & 0.070 mol/L Temperature of the liquid precursor Between
about Between about solution within precursor supply 200 &
300.degree. C. 250 & 270.degree. C. system 16 Liquid flow rate
via precursor supply Between about Between about system 16 0.1 and
10 mL/min 0.5 & 5 mL/min Flash vaporization temperature within
Between about Between about vaporizer 44 200 & 300.degree. C.
250 & 270.degree. C. Inert gas pressure Between about Between
about 16 & 30 psi 16 & 20 psi Partial oxygen Between about
Between about 0.4 & 5 Torr 0.5 & 3 Torr Vapor precursor
temperature via the Between about Between about precursor vapor
line 48 200 & 300.degree. C. 250 & 270.degree. C. Length of
precursor injector 24 Between about Between about 10 & 30 cm 15
& 20 cm The substrate tape 18 temperature via Between about
Between about heating with substrate heater 14 700 &
950.degree. C. 750 & 820.degree. C. The substrate tape 18
translation rate Between about Between about 0.25 & 40 cm/min 1
& 40 cm/min Resulting HTS film thickness Between about Between
about 0.5 & 10 microns 3 & 10 microns
[0104] The detailed operation of the CVD apparatus 10 is described
using an example HTS-coated tape as shown in FIG. 8.
[0105] FIG. 8 illustrates a cutaway view of an example HTS
conductor 80 formed via the CVD apparatus 10 of FIG. 1. The HTS
conductor 80 includes an elongate substrate 18, such as a metallic
material. Suitable metallic materials include, but are not limited
to, steel, nickel, nickel alloys, and alloys of copper, iron, and
molybdenum. The elongate substrate 18 may be lattice-matched to the
oxide superconductor, such as by the deformation texturing of the
elongate substrate 18. Alternatively, the elongate substrate 18 is
coated with a buffer layer 82 that contains some degree of
crystallographic alignment and which is reasonably lattice-matched
with the oxide superconductor. The buffer layer 82 has an epitaxial
oxide superconductor layer 84 deposited thereon. Suitable
compositions for the buffer layer 82 include but are not limited
to, zirconia, YSZ, LaAlO.sub.3, SrTiO.sub.3, CeO.sub.2, and MgO,
preferably ion-beam assisted deposition (IBAD) YSZ, LaAlO.sub.3,
SrTiO.sub.3, CeO.sub.2, and MgO. For example, the elongate
substrate 18 may be a flexible length of substrate formed from a
variety of metals, such as stainless steel or a nickel alloy such
as HASTELLOY.RTM. or INCONEL.RTM., upon which buffer layers, such
as yttria-stabilized zirconia (YSZ) and/or cerium oxide (CeO.sub.2)
have been previously deposited with a bi-axial texture, for
instance, a (100)<001> cube texture. The oxide superconductor
layer 84 desirably has a thickness in the range of greater than or
equal to about 0.5 microns (.mu.m), preferably greater than or
equal to about 0.8 microns (.mu.m) and most preferably greater than
or equal to about 1.0 microns (.mu.m). When the elongate substrate
18 is lattice-matched to the oxide superconductor, the
superconductor layer 84 is deposited as one or more layers to the
desired thickness on the elongate substrate 18 to form an HTS film,
such as YBCO, via the CVD apparatus 10 of FIG. 1. Alternatively,
when the elongate substrate 18 is coated with a buffer layer 82
that contains some degree of crystallographic alignment that is
reasonably lattice-matched with the oxide superconductor, the
superconductor layer 84 is deposited as one or more layers to the
desired thickness on the buffer layer 82 to form an HTS film.
Finally, the superconductor layer may be covered by a noble metal
layer 86.
[0106] With reference to FIGS. 1, 2, 3 A, 3B, 3C, 4A, the operation
of the CVD apparatus 10 of the present invention is as follows.
[0107] Sufficient vacuum is developed within the reactor 12 by
activating the exhaust system 20. The linear translation of the
elongate substrate 18 through the deposition zone begins in a
direction progressing from left to right. (The mechanisms for
translating the elongate substrate 18 are tape translation
mechanism 74.) All heating elements within the substrate heater 14
are activated to provide the desired temperature to the elongate
substrate 18 according to Table 1.
[0108] The liquid source 40 contains a liquid organometallic
precursor solution according to Table 1. The pump 42 is activated
to feed the liquid precursor from the liquid source 40 into
vaporizer 44. There, the solution is flash vaporized and then mixed
with a carrier fluid, such as argon or nitrogen, feeding into the
vaporizer 44 from the carrier fluid supply 46 to form a
superconductor (e.g., yttrium-barium-copper-oxide
(YBa.sub.2Cu.sub.3O.sub.7 or "Y123") or
samarium-barium-copper-oxide (SmBa.sub.2Cu.sub.3O.sub.7 or
"Sm123")) precursor vapor. The superconductor precursor vapor from
vaporizer 44 is then carried to the reactor 12 through a line via a
delivery column 48 to the precursor injector 24. The line, delivery
column 48, and precursor injector 24 are maintained at an
appropriate temperature, according to Table 1, via heating coils
(not shown). Additionally, oxygen is introduced to the line just
prior to the superconductor precursor vapor entering the reactor 12
via an oxygen line coming from mass flow regulator 50.
[0109] Having activated the deposition process within the reactor
12 of the CVD apparatus 10, and having set all control parameters
according to Table 1, the HTS conductor 80 is formed as
follows.
[0110] A line delivers the superconductor precursor vapor to the
delivery column 48 of the precursor injector 24 that uniformly
directs this vapor precursor toward the elongate substrate 18
within the deposition zone. The result of the oxygen reacting with
the superconductor precursor vapor, and then this reacting
combination coming into contact with the hot elongate substrate 18
within the deposition zone, causes the superconductor precursor to
decompose and form a layer of superconductor atop the elongate
substrate 18 as it translates through the deposition zone. The
defects within the layer are minimized via the control parameters
according to Table 1.
[0111] Thus, the layer provides a high quality template for growing
additional superconductor material or material such as silver or
copper, which can be deposited by any film deposition method. As a
result, the superconductor layer or, collectively, the
superconductor layers or HTS layers corresponding to any alternate
precursor used that form the HTS conductor 80 have a thickness of
greater than about 2 microns with a critical current density of
approximately greater than about 1 MA/cm.sup.2.
[0112] As a result, the CVD apparatus 10 of the present invention
is capable of producing a YBCO film or HTS corresponding to
alternate precursor used with a thickness in excess of about 1.5
microns that has increased material density and smoothness that
results in increased current capacity of over at least about 150
A/cm width.
[0113] In an alternative embodiment, precursor may be delivered to
multiple deposition 0 zones of a CVD apparatus 10 by a
multi-compartment precursor injector 24 to supply the precursor to
the elongate substrate 18 as a single unit. Alternatively,
precursor may instead be delivered to multiple deposition zones of
a CVD apparatus 10 by a multiple precursor injectors 24. Each
compartment of a multi-compartment precursor injector 24 or
separately installed precursor injectors 24 could have an
associated separate heater for supplying heat to the elongate
substrate 18.
[0114] In another alternative embodiment, multiple precursors may
be delivered to the deposition zone of the CVD apparatus 10 by
separately installed precursor injectors 24 to supply the separate
precursors to the elongate substrate 18 instead of using a
multi-compartment precursor injectors 24 designed as a single unit.
Each separately installed precursor injector 24 would have an
associated separate heater for supplying heat to the elongate
substrate 18.
[0115] The CVD apparatus 10 includes a precursor supply system 16.
As shown in FIG. 2, the precursor supply system 16 comprises a
liquid source 40 that is a reservoir formed of, for example, a
metal or plastic vessel that contains a solution containing
organometallic precursors, such as yttrium, barium, and copper,
along with an appropriate mixture of solvents. The liquid source 40
feeds a delivery mechanism 42 such as, for example, a pump, capable
of a low flow rate between 0.1 and 10 mL/min. An example of a
delivery mechanism 42 is a high-pressure, low flow rate pump, such
as a high-pressure liquid chromatography (HPLC) pump. The delivery
mechanism 42 feeds a vaporizer 44 that includes elements with which
a precursor solution may be flash vaporized and mixed with an inert
carrier gas, such as argon or nitrogen, for delivery to the
precursor injector 24. The vaporized precursors exit the vaporizer.
Just prior to the line entering the reactor 12, an oxygen line
opens into the vapor line. The oxygen line is a tube or pipe
through which oxygen passes for introduction to the precursor
vapors and their inert carrier gas flowing within the precursor
vapor line. Each instantiation of the precursor vapor line enters
the reactor 12 ready for delivery through the precursor injector 24
onto a substrate 18. The CVD apparatus 10 includes an exhaust
system 20 connected to the reactor 12. The exhaust system 20 is a
commercially available vacuum pump capable of maintaining a vacuum
of pressure in the order of magnitude of 10.sup.-3 Torr, such as a
Leybold model D65B. Alternatively, the function of the exhaust
system 20 may be accomplished by a combination of a mechanical pump
and a mechanical booster, such as Edwards model EH500, in order to
obtain the proper vacuum suitable for use with a large amount of
liquid precursor.
[0116] The precursor supply system 16 and the exhaust system 20 are
shown as being located external to the reactor 12. Additionally,
those skilled in the art will appreciate that the CVD apparatus 10
further includes various sensing and control devices, such as
pressure gauges and thermocouples, which are, for simplicity, not
shown in FIGS. 1 and 2.
[0117] Samarium and yttrium belong to the same group within the
periodic table of elements, which means that the
samarium-barium-copper precursor behaves in a very similar manner
to the yttrium-barium-copper containing precursor. As a result, the
samarium-barium-copper superconducting compound may be deposited
with similar deposition conditions as the yttrium-barium-copper
superconducting compound. Such processing conditions include the
temperature of the vapor lines between about 250 and 300.degree.
C., the elongate substrate 18 temperature of between about 700 and
950.degree. C., the deposition pressure of between about 1 and 10
Torr, the oxygen partial pressure of between about 0.5 to 5 Torr,
and the liquid precursor delivery rate of between about 0.25 and 10
mL/min. Since the yttrium-barium-copper precursor and the
samarium-barium-copper precursor have similar properties, the
heating or cooling requirements of the elements within the CVD
apparatus 10 need no special design to accommodate the different
materials.
[0118] In general, the thickness of each layer being deposited is
determined by the combination of three factors: (1) the physical
length, (2) precursor vapor delivery rate, and (3) its associated
precursor molarity (i.e., concentration of the precursor solution).
Additionally, the thickness of each film is directly proportional
to each of these three factors. For example, the longer the
physical length of its associated compartment, the thicker the
film; the higher the associated vapor precursor delivery rate, the
thicker the film; and the more concentrated the associated
precursor solution, the thicker the film.
[0119] As one example of these controls, the thickness of the layer
84 may be determined by the combination of the physical length of
the heater 14 within the precursor injector 24, the delivery rate
of the samarium-barium-copper containing precursor, and the
concentration of the samarium-barium-copper containing liquid
precursor.
[0120] In the case of the YBCO single layer, research indicates
that the critical current reaches a maximum and levels off at
around about 1.5 microns because, as the film thickens, the surface
roughness progressively increases, making a progressively poorer
and poorer template for crystal growth and causing misaligned
crystals, thereby inhibiting any increase in current flow.
Additionally, the film becomes more porous as the film thickens,
thereby inhibiting any increase in current flow.
[0121] By contrast, the Sm123 is a smoother film than YBCO. Thus,
growing Sm123 atop a layer of YBCO reduces the surface roughness
and makes a better template for growing any additional YBCO layer.
The YBCO-Sm123 sequence may be repeated without limiting or
inhibiting the flow of current; by contrast, a single thick layer
of YBCO shows no more increase of current flow beyond a thickness
of about 1.5 micron. Sm123 and YBCO are both superconducting
materials with similar properties, so diffusion between layers
should not pose a significant problem. See e.g., U.S. patent
application Publication Nos. US 2001/0056041, "Architecture for
high critical current superconducting tapes," Dec. 27, 2001; and US
2003/0036483, "High temperature superconducting thick films," Feb.
20, 2003 as well as U.S. Pat. No. 6,541,136, "Superconducting
structure," Apr. 1, 2003 (the disclosure of each being hereby
incorporated by reference in their entirety).
[0122] The formation of a multi-layer HTS-coated tape using the CVD
apparatus 10 is not limited to YBCO with Sm123; other
superconducting materials may be used. For example, other oxides
that are chemically compatible to YBCO, such as RE123 (where
RE=rare earth metals such as neodymium (Nd), europium (Eu),
lanthanum (La), holmium (Ho), and Gadolinium (Gd)) may be used.
Additionally, an HTS-coated tape formed using the CVD apparatus 10
is not limited to any specific number of layers. The precursor
injector 24 may be expanded to any number of compartments, as long
as precursor delivery lines and pumps are sized to handle delivery
to multiple zones at the proper delivery rate. Furthermore, the
substrate heater 14 may be expanded to any length accordingly.
Alternatively, there may be separate heater zones within the
substrate heater 14 that directly correspond to the compartments
and resulting deposition zones for further temperature control if
needed.
[0123] 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. It should be understood
that all such modifications and improvements have been deleted
herein for the sake of conciseness and readability but are properly
within the scope of the following claims.
* * * * *