U.S. patent application number 13/442844 was filed with the patent office on 2012-10-11 for metalorganic chemical vapor deposition (mocvd) process and apparatus to produce multi-layer high-temperature superconducting (hts) coated tape.
This patent application is currently assigned to SUPERPOWER, INC.. Invention is credited to Hee-Gyoun Lee, Venkat Selvamanickam.
Application Number | 20120258863 13/442844 |
Document ID | / |
Family ID | 33518099 |
Filed Date | 2012-10-11 |
United States Patent
Application |
20120258863 |
Kind Code |
A1 |
Selvamanickam; Venkat ; et
al. |
October 11, 2012 |
METALORGANIC CHEMICAL VAPOR DEPOSITION (MOCVD) PROCESS AND
APPARATUS TO PRODUCE MULTI-LAYER HIGH-TEMPERATURE SUPERCONDUCTING
(HTS) COATED TAPE
Abstract
An MOCVD apparatus and process for producing multi-layer
HTS-coated tapes with increased current capacity which includes
multiple liquid precursor sources, each having an associated pump
and vaporizer, the outlets of which feed a multiple compartment
showerhead apparatus within an MOCVD reactor. The multiple
compartment showerhead apparatus is located in close proximity to
an associated substrate heater which together define multiple
deposition sectors in a deposition zone.
Inventors: |
Selvamanickam; Venkat;
(Houston, TX) ; Lee; Hee-Gyoun; (Ansan-City,
KR) |
Assignee: |
SUPERPOWER, INC.
Schenectady
NY
|
Family ID: |
33518099 |
Appl. No.: |
13/442844 |
Filed: |
April 9, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10602468 |
Jun 23, 2003 |
8153281 |
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13442844 |
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Current U.S.
Class: |
505/230 ;
174/125.1; 427/62; 505/434; 505/473 |
Current CPC
Class: |
C04B 2235/3224 20130101;
H01L 39/2441 20130101; C23C 16/54 20130101; Y02T 50/60 20130101;
C04B 2235/3215 20130101; Y02T 50/6765 20180501; C23C 16/45523
20130101; C04B 35/6264 20130101; C04B 2235/79 20130101; H01L 39/128
20130101; C04B 2235/6584 20130101; C04B 2235/3225 20130101; C04B
35/4508 20130101; Y02T 50/67 20130101; C23C 16/408 20130101 |
Class at
Publication: |
505/230 ;
505/434; 505/473; 427/62; 174/125.1 |
International
Class: |
H01L 39/24 20060101
H01L039/24; H01B 12/02 20060101 H01B012/02; H01B 13/00 20060101
H01B013/00 |
Claims
1.-10. (canceled)
11. A process for producing multi-layer coated substrates
comprising translating a substrate to be coated through a MOCVD
chamber comprising a vacuum chamber, a heater, a showerhead
delivery apparatus selected from the group consisting of a
multicompartment showerhead and at least two single compartment
showerheads, at least one precursor delivery system, and a
substrate translation system, where the space between the
showerhead and the heater defines an extended length deposition
zone within the vacuum chamber and where the substrate translating
through the extended length deposition zone is heated by the heater
and successively impinged upon by vaporized precursors exiting each
of the individual showerhead compartments to deposit a coating
thereon.
12. The process of claim 11 wherein the vaporized precursors
delivered through each showerhead compartment are the same.
13. The process of claim 11 wherein multi-layered substrates are
produced by delivering different types of vaporized precursors
through one or more showerhead compartments.
14. The process of claim 11 wherein the vaporized precursors are
selected from the group consisting of YBCO, SmBCO, and other rare
earth mixed oxides.
15. The process of claim 11 where the total thickness of the
coating exceeds 1.5 microns and the coated substrate has a critical
current of at least 100 Amperes/cm width.
16. The process of claim 11 where the thickness of each coating
layer is no greater than 1.5 microns.
17. A multi-coated substrate tape prepared by the process of claim
11.
18. The substrate of claim 17 where the multi-coated substrate has
at least two coatings of different composition deposited
thereon.
19. The substrate of claim 17 where the substrate is coated with
successive layers of YBCO, SmBCO, YBCO, SmBCO and YBCO.
20. The substrate of claim 17 where the total thickness of the
coating exceeds 1.5 microns and the coated substrate has a critical
current of at least 100 Amperes/cm width.
21. The substrate of claim 17 where the thickness of each coating
layer is no greater than 1.5 microns.
22. (canceled)
Description
AREA OF THE INVENTION
[0001] The present invention relates to high-throughput
metalorganic chemical vapor deposition (MOCVD) of high-temperature
superconducting (HTS) coated wire having increased current
capability.
BACKGROUND OF THE INVENTION
[0002] 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.
[0003] Wire forms the basic building block of the world's electric
power system, including transformers, transmission and distribution
systems, and motors. The discovery of revolutionary HTS compounds
in 1986 led to the development of a radically new type of wire for
the power industry; this discovery is the most fundamental advance
in wire technology in more than a century.
[0004] HTS wire offers best-in-class performance, carrying over one
hundred times more current than do conventional copper and aluminum
conductors of the same physical dimension. The superior power
density of HTS wire will enable a new generation of power industry
technologies. It offers major size, weight, and efficiency
benefits. HTS technologies will drive down costs and increase the
capacity and reliability of electric power systems in a variety of
ways.
[0005] For example, HTS wire is capable of transmitting two to five
times more power through existing rights of way. This new cable
will offer a powerful tool to improve the performance of power
grids while reducing their environmental footprint.
[0006] However, to date only short samples of the HTS tape used in
the manufacture of next-generation HTS wires have been fabricated
at high performance levels. In order for HTS technology to become
commercially viable for use in the power generation and
distribution industry, it will be necessary to develop techniques
for continuous, high-throughput production of HTS tape.
[0007] MOCVD is a deposition process that shows promise for the
high throughput necessary to cost-effectively produce HTS tapes.
During MOCVD, HTS film, 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 buffered metal substrate via
chemical reactions that occur at the surface of the substrate.
[0008] One way to characterize coated conductors is by their cost
per meter. Alternatively, cost and performance can be characterized
as the cost per kiloamp-meter. More specifically, by increasing the
current for a given cost per meter of coated conductor, the cost
per kiloamp-meter is reduced. This is evidenced in the critical
current (Jc) of the deposited HTS material multiplied by the
cross-sectional area of the film.
[0009] For a given critical current and width of coated conductor,
one way to increase the cross-sectional area is by increasing the
HTS film thickness. However, under conventional process parameters
it has been demonstrated that with critical current as a function
of thickness, the critical current drops off as the thickness of a
single layer of HTS film 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.
[0010] Since, under conventional process parameters simply
increasing the HTS film thickness does not result in a
corresponding increase in critical current, a technical challenge
exists to increase the HTS film thickness above 1.5 microns and at
the same time realize a corresponding increase in current
density.
[0011] In an MOCVD deposition process, factors that contribute to
the morphology of the HTS film include the chamber pressure, the
substrate temperature, the oxygen content and its method of
introduction to the deposition zone, the amount of precursors being
supplied to the deposition zone (determined by both the precursor
molarity and the mass flow rate of the precursor vapors and their
inert carrier gas through the showerhead assembly), the temperature
at which the precursors are maintained prior to their introduction
into the deposition zone, and the exhaust efficiency of the
reaction byproducts away from the deposition zone.
[0012] While the optimization of some of the aforementioned
parameters is well known, such as the fact that the precursor
vapors and their inert carrier gas are most efficiently delivered
to the deposition zone within a temperature range of 230 to
270.degree. C., the optimization of other parameters is less well
known, requiring technical innovations to be realized. Hubert, et
al., U.S. Pat. No. 5,820,678, entitled "Solid Source MOCVD System,"
describes a system for MOCVD fabrication of superconducting and
non-superconducting oxide films that provides a delivery system for
the feeding of metalorganic precursors for multi-component chemical
vapor deposition. The delivery system can include multiple
cartridges containing tightly packed precursor materials. The
contents of each cartridge can be ground at a desired rate and fed
together with precursor materials from other cartridges to a
vaporization zone and then to a reaction zone within a deposition
chamber for thin film deposition. A drawback of the MOCVD system of
Hubert, et al., is that while it is suitable for depositing
superconducting oxide films, it does not provide a process for
increasing the critical current of thick HTS films.
[0013] Tatekawa, et al., U.S. Pat. No. 6,143,697, entitled "Method
for Producing Superconducting Thick Film," describes a method of
producing a superconducting thick film that involves the steps of
forming a thick layer comprising a superconducting material on a
substrate, firing the thick layer formed on the substrate,
subjecting the fired thick layer to cold isostatic pressing, and
re-firing the thick layer subjected to cold isostatic pressing. A
drawback of Tatekawa, et al., is that while the method is suitable
for forming superconducting oxide thick films, it is not a
cost-effective way of manufacturing high-current HTS-coated
conductors nor does it provide controlled process parameters
sufficient to produce thick HTS films with increased critical
current. Tatekawa, et al., is therefore not suited for the
cost-effective production of high-current HTS coated
conductors.
[0014] It is therefore an object of this invention to produce a
high-current HTS-coated conductor with coatings formed by HTS film
with a thickness in excess of 1.5 microns that have increased
current capacity, over 100 A/cm width.
[0015] It is another object of this invention to provide a low-cost
method of forming high-current HTS-coated conductors using an MOCVD
process for producing multiple layer HTS coated tapes.
[0016] It is an object of this invention to produce YBCO films with
a thickness in excess of 1.5 microns with increased current
capacity for use in the manufacture of high-current HTS-coated
tape.
[0017] It is an object of this invention to provide a
cost-effective method of forming high-current HTS-coated conductors
using an MOCVD process with precisely controlled process parameters
for the deposition of YBCO thick films.
[0018] It is an object of this invention to provide a
cost-effective method of forming high-current multi-layered
HTS-coated conductors where the multi-layers have the same
composition. It is an object of this invention to provide a
cost-effective method of forming high-current multi-layered
FITS-coated conductors where the multi-layers have different
compositions.
SUMMARY OF THE INVENTION
[0019] The present invention is an MOCVD system for producing
multi-layer HTS-coated tapes with increased current capacity. The
MOCVD system of the present invention includes multiple liquid
precursor sources, each having an associated pump and vaporizer,
the outlets of which feed a multiple compartment showerhead
apparatus within an MOCVD reactor. The multiple compartment
showerhead apparatus is located in close proximity to a translating
metal substrate tape and an associated substrate heater.
[0020] The multiple compartment showerhead apparatus is fed by the
multiple vaporized precursor sources, where such sources include
one or more HTS materials, such as a combination of compounds of
yttrium (Y), barium (Ba), and copper (Cu), along with an
appropriate mixture of solvents, or likewise a combination of
compounds of samarium (Sm), or other rare earth, Ba, and Cu, with
an appropriate mixture of solvents. In this way, multiple layers of
HTS material are formed sequentially upon the translating substrate
tape, where each layer is associated with a compartment of the
multiple compartment showerhead apparatus. As a result, a
multi-layer film deposition process is achieved in which each layer
does not exceed a typical thickness of 1.5 microns, and the
resulting structure collectively provides an HTS coated conductor
with increased current capability as compared with a conductor
having a single thick layer of HTS film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 illustrates an MOCVD system in accordance with a
first embodiment of the present invention for producing multiple
layer HTS-coated tapes with increased current capability.
[0022] FIG. 2 illustrates an MOCVD system in accordance with a
second embodiment of the present invention for producing multiple
layer HTS-coated tapes with increased current capability.
[0023] FIG. 3 illustrates the components of the precursor delivery
system of the present invention.
[0024] FIG. 4a illustrates a cross-sectional view of an example
multi-layer coated tape formed via the first embodiment of the
MOCVD system of the present invention.
[0025] FIG. 4b illustrates a cross-sectional view of an example
multi-layer coated tape formed via the second embodiment of the
MOCVD system of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The present invention is an MOCVD system utilizing a set of
controlled process parameters for producing rare earth oxide films,
such as YBCO films, with increased current capacity and with a
thickness in excess of 1.5 microns. Such parameters include but are
not limited to the partial oxygen pressure, the precursor
composition, the precursor delivery rate, and the deposition
temperature.
[0027] The MOCVD system includes an extended length deposition zone
that is further divided into sub-deposition zones arranged
sequentially along its full length, wherein a translating substrate
may experience the vapor deposition process. The conditions within
each sub-deposition zone are dynamically and independently
controlled as the substrate tape translates linearly along the
deposition zone and the HTS film grows thicker and thicker, thereby
providing a method of optimizing the morphology of the film and
thus minimizing defects such as high porosity, voids, and surface
roughness. The HTS film growth achieved via the MOCVD system of the
present invention provides high-quality HTS films with a thickness
in excess of 1.5 microns that have increased material density and
smoothness that results in increased current capacity of over at
least 100 A/cm width. FIG. 1 illustrates an MOCVD system 100 in
accordance with a first embodiment of the invention. The MOCVD
system 100 of the present invention is characterized by precisely
controlled process parameters that allow for the production of YBCO
films with a thickness in excess of 1.5 microns with increased
current capacity.
[0028] The MOCVD system 100 further includes multiple
instantiations of a precursor delivery system 120, for example, a
precursor delivery system 120a, a precursor delivery system 120b, a
precursor delivery system 120c, a precursor delivery system 120d,
and a precursor delivery system 120e. The precursor vapors exit
each instantiation of the precursor delivery system 120 via an
associated precursor vapor line 122 feeding the multi-compartment
showerhead 112 within the reactor 110. More specifically, the
precursor delivery system 120a feeds the compartment 113a of the
multi-compartment showerhead 112 via a precursor vapor line 122a,
the precursor delivery system 120b feeds the compartment 113b of
the multi-compartment showerhead 112 via a precursor vapor line
122b, the precursor delivery system 120c feeds the compartment 113c
of the multi-compartment showerhead 112 via a precursor vapor line
122c, the precursor delivery system 120d feeds the compartment 113d
of the multi-compartment showerhead 112 via a precursor vapor line
122d, and the precursor delivery system 120e feeds the compartment
113e of the multi-compartment showerhead 112 via a precursor vapor
line 122e. Furthermore, each instantiation of the precursor
delivery system 120 is fed by a common gas line 104. It is
preferable to separate the common gas line into 5 individual gas
lines attached to evaporators 120a, 120b, 120c, 120d, and 120d in
order to control the gas flow rate precisely to each precursor
delivery system. The precursor delivery system 120 is further
detailed in reference to FIG. 3. Lastly, the MOCVD system 100
includes a vacuum pump 142 functionally connected to the reactor
110. The vacuum pump 142 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 D408.
Alternatively, the vacuum pressure is maintained by a combination
of a mechanical pump and a mechanical booster, such as Edwards
model EHS00, in order to obtain a proper vacuum pressure with a
large amount of liquid precursor.
[0029] Distinct areas within the deposition zone 118 are formed and
associated with each compartment 113 within the multi-compartment
showerhead 112. In the example shown in FIG. 1, vapors distributed
from the compartment 113a are deposited upon the substrate tape 116
within a zone A, vapors distributed from the compartment 113b are
deposited upon the substrate tape 116 within a zone B, vapors
distributed from the compartment 113c are deposited upon the
substrate tape 116 within a zone C, vapors distributed from the
compartment 113d are deposited upon the substrate tape 116 within a
zone D, and vapors distributed from the compartment 113e are
deposited upon the substrate tape 116 within a zone B of the
deposition zone 118. The multi-zone substrate heater 114 is a
well-known multiple zone substrate heater that provides heating,
typically in the range of 700 to 950.degree. C., to the substrate
tape 116 via a radiant heating element, such as an infrared lamp.
Alternatively, the multi-zone substrate heater 114 is a resistance
heater having a heating element, such as Kanthal or MoSi.sub.2
heater. The multi-zone substrate heater 114 includes multiple
independently controlled heating zones (i.e., via multiple
independently controlled heating elements that are not shown) that
associate with zones A, B, C, D, and E of the deposition zone 118.
More specifically, a heating zone A aligns with the substrate tape
116 within zone A of the deposition zone 118, a heating zone B
aligns with the substrate tape 116 within zone B of the deposition
zone 118, a heating zone C aligns with the substrate tape 116
within zone C of the deposition zone 118, a heating zone D aligns
with the substrate tape 116 within zone D of the deposition zone
118, and a heating zone E aligns with the substrate tape 116 within
zone E of the deposition zone 118.
[0030] Furthermore, assuming a direction of travel of the substrate
tape 116 from zone A to zone E, the multi-zone substrate heater 114
may include a pre-heat zone that aligns with the substrate tape 116
just prior to zone A of the deposition zone 118. Lastly, the
multi-zone substrate heater 114 may include a cool-down zone that
aligns with the substrate tape 116 just following zone E of the
deposition zone 118. The pre-heat zone ramps up the temperature of
the substrate tape 116 in preparation for the substrate tape 116
entering the deposition zone 118. Conversely, the cool-down zone
ramps down the temperature of the substrate tape 116 after exiting
the deposition zone 118 in preparation for the substrate tape 116
exiting the reactor 110.
[0031] FIG. 3 shows the elements that are included in each
instantiation of the precursor delivery system 120. More
specifically, each instantiation of the precursor delivery system
120 includes a liquid source 206 that is a reservoir formed of, for
example, stainless steel, that contains a solution containing
organometallic precursors, such as for example tetramethyl
heptanedionate (THD) compounds of yttrium (Y), barium (Ba), and
copper (Cu), along with an appropriate mixture of solvents, such as
tetrahydrofuran and isopropanol. The liquid source 206 feeds a pump
202 that is a liquid precursor delivery pump capable of a low flow
rate between 0.1 and 10 mL/min. The pump 202 is a high-pressure,
low flow rate pump, such as a high-pressure liquid chromatography
(HPLC) pump. The pump 202 feeds a precursor vaporizer 204, which is
a device in which a precursor solution is flash vaporized at, for
example, approximately 240.degree. C. and mixed with an inert
carrier gas, such as argon or nitrogen, for delivery to the
multi-compartment showerhead 112. The inert carrier gas is fed into
the precursor vaporizer 204 via the gas line 104 formed of tubing
or piping. The precursor vapors exit the precursor vaporizer 204
via the precursor vapor line 122, which is a connecting tube or
pipe through which the precursor vapors and their inert carrier gas
pass on their way to the multi-compartment showerhead 112.
[0032] Just prior to the precursor vapor line 122 entering the
reactor 110, an oxygen line 128 opens into the precursor vapor line
122. The oxygen line 128 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 122.
[0033] The pump 202 and the precursor vapor line 122 are sized
appropriately to handle the precursor delivery to a compartment 113
of the multi-compartment showerhead 112, and subsequently to the
deposition zone 118, at the proper delivery rate. The pressure and
flow rate of the precursor is controlled via the combination of the
specifications of the pump 202 and the diameter of the precursor
vapor line 122. Similarly, the oxygen line 128 is sized
appropriately to handle the oxygen delivery to the precursor vapor
line 122 at the proper delivery rate and pressure. Oxygen gas line
is pre-heated to approximately 240.degree. C. in order to prevent
local cold spots by introducing cold oxygen gas into the precursor
delivery line.
[0034] For the purpose of discussing the MOCVD system 100 of the
present invention, it can be said that the precursor delivery
system 120a includes a liquid source 206a, a pump 202a, a precursor
vaporizer 204a, and an oxygen line 128a feeding the precursor vapor
line 122a; the precursor delivery system 120b includes a liquid
source 206b, a pump 202b, a precursor vaporizer 204b, and an oxygen
line 128b feeding the precursor vapor line 122b; the precursor
delivery system 120c includes a liquid source 206c, a pump 202c, a
precursor vaporizer 204c, and an oxygen line 128c feeding the
precursor vapor line 122c; the precursor delivery system 120d
includes a liquid source 206d, a pump 202d, a precursor vaporizer
204d, and an oxygen line 128d feeding the precursor vapor line
122d; and the precursor delivery system 120e includes a liquid
source 206e, a pump 202e, a precursor vaporizer 204e, and an oxygen
line 128e feeding the precursor vapor line 122e. Furthermore, the
precursor vaporizers 204a, 204b, 204c, 204d, and 204e are all fed
by the common gas line 104. It is preferable to separate the common
gas line 104 into 5 individual gas line attached to evaporators
120a, 120b, 120c, 120d, and 120d in order to control the gas flow
rate precisely to each precursor delivery system.
[0035] With continuing reference to FIGS. 1 and 3, the precursor
delivery system 120a, the precursor delivery system 120b, the
precursor delivery system 120c, the precursor delivery system 120d,
the precursor delivery system 120e, the gas line 104, and the
vacuum pump 142 are all located external to the reactor 110.
Additionally, those skilled in the art will appreciate that the
MOCVD system 100 further includes various sensing and control
devices, such as pressure gauges and thermocouples, which are for
simplicity not shown in FIGS. 1 and 3.
[0036] It should be noted that the deposition zone 118 of the MOCVD
system 100 of the present invention is not limited to zones A
through E as shown in FIGS. 1 and 2. The deposition zone 118 may be
expanded to include any number of zones by expanding the
multi-compartment showerhead 112 to include any number of
compartments 113 and by expanding the single or multi-zone
substrate heater 114 to include a corresponding number of
independently controlled heating zones [in a multi-zone heater].
Furthermore, the MOCVD system 100 may be expanded accordingly to
include one instantiation of the precursor delivery system 120 for
each compartment 113 within the multi-compartment showerhead 112.
However, for the purpose of illustration, the example of five
zones, A through E, within the deposition zone 118 of the MOCVD
system 100 and their associated hardware and control parameters is
disclosed. Alternatively, a single precursor delivery system may
feed more than one compartment of the showerhead.
[0037] 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: [0038] Deposition
temperature: HTS film surface roughness is affected by the
deposition temperature; [0039] 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; [0040] 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. [0041] 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. 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
substrate tape 116, the exposure of UV light to source vapor, or
the use of atomic oxygen or ozone as an oxidant.
[0042] Specific analysis of some of the variables affecting the
morphology of the HTS film is provided below.
[0043] It has been demonstrated that, assuming a delivery rate of
0.25 mL/min and a deposition temperature of 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 example: [0044] a molarity of 0.030
mol/L yields a film thickness of approximately 1.0 micron; [0045] a
molarity of 0.045 mol/L yields a film thickness of approximately
1.25 microns; and [0046] a molarity of 0.060 mol/L yields a film
thickness of approximately 1.75 microns. It has been demonstrated
that, assuming a precursor molarity of 0.030 mol/L and a deposition
temperature of 800.degree. C., an increase in the precursor
delivery rate also results in an increase in film thickness. For
example: [0047] a delivery rate of 0.25 mL/min yields a film
thickness of approximately 1.0 micron; [0048] a delivery rate of
0.50 mL/min yields a film thickness of approximately 2.0 microns;
and [0049] a delivery rate of 1.00 mL/min yields a film thickness
of approximately 4.0 microns.
[0050] It has been demonstrated that, assuming a deposition
temperature of 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:
Example 1
[0051] a delivery rate of 0.25 mL/min, combined with a molarity of
0.03 mol/L, combined with a oxygen partial pressure of 0.56 Torr
yields a critical current of approximately 2.7 MA/cm.sup.2 for a
0.6 micron thick film (Example 1);
Example 2
[0052] a delivery rate of 0.50 mL/min, combined with a molarity of
0.03 mol/L, combined with a oxygen partial pressure of 0.56 Torr
yields a critical current of approximately 0.0 A/cm.sup.2 for a 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);
Example 3
[0053] a delivery rate of 0.50 mL/min, combined with a molarity of
0.03 mol/L, combined with a oxygen partial pressure of 1.08 Torr
yields a critical current of approximately 2.5 MA/cm.sup.2 for a
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
Example 4
[0054] a delivery rate of 0.50 mL/min, combined with a molarity of
0.06 mol/L, combined with a oxygen partial pressure of 1.08 Torr
yields a critical current of approximately 2.2 MA/cm.sup.2 for a
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).
[0055] Furthermore, it is well known that the precursor vapors and
their inert carrier gas are most efficiently delivered to the
deposition zone within a temperature range of 230 to 300.degree.
C.
[0056] Lastly, the temperature of the substrate tape 116 during the
deposition process may affect the end properties. For example, high
critical current (Jc) of 35 A was obtained for the film with a
thickness of 0.35 microns that was prepared at 800.degree. C. (Jc=1
MA/cm.sup.2). However, for a film having the same thickness but
prepared at 810.degree. C. the Jc dropped to 10 A.
[0057] Using the example of FIG. 1, the specific parameters,
including those outlined above, affecting the film deposition
process within zones A, B, C, D, and E of the deposition zone 118
of the MOCVD system 100 are defined in Tables 1 through 5
below.
TABLE-US-00001 TABLE 1 Control parameters regarding zone A of the
deposition zone 118 Control parameters regarding zone A of the
deposition zone 118 Acceptable examples or Preferred example or
acceptable range preferred range Liquid organometallic precursor
THD compounds of Y, Ba, THD compounds with a solution within the
liquid source 206a and Cu with a molar ratio of molar ratio of
Y:Ba:Cu = Y:Ba:Cu = 1:1.8-2.6:2.5-3.5, 1:1.9-2.5:2.8-3.2, with
solvents, such with solvents. as tetrahydrofuran and isopropanol.
Molarity of the precursor solution 0.015 to 0.070 mol/L 0.050 to
0.070 mol/L within the liquid source 206a Temperature of the liquid
precursor 200 to 300.degree. C. 250 to 270.degree. C. solution
within the liquid source 206a Liquid flow rate via the pump 202a
0.1 and 10 mL/min 0.5 to 5 mL/min Flash vaporization temperature
within 200 to 300.degree. C. 250 to 270.degree. C. the precursor
vaporizer 204a Inert gas pressure via the gas line 104 16 to 30 psi
16 to 20 psi Partial oxygen pressure via the oxygen 0.4 to 5 Torr
0.5 to 3 Torr line 128a Vapor precursor temperature via the 200 to
300.degree. C. 250 to 270.degree. C. precursor vapor line 122a
Length of the compartment 113a of the 10 to 30 cm 15 to 20 cm
multi-compartment showerhead 112 The substrate tape 116 temperature
via 700 to 950.degree. C. 750 to 820.degree. C. heating zone A of
the multi-zone substrate heater 114 The substrate tape 116
translation rate 0.25 to 40 cm/min 1 to 40 cm/min Resulting HTS
film thickness 1.5 to 10 microns 3 to 10 microns
TABLE-US-00002 TABLE 2 Control parameters regarding zone B of the
deposition zone 118 Control parameters regarding zone B of the
deposition zone 118 Acceptable examples or Preferred example or
acceptable range preferred range Liquid organometallic precursor
THD compounds of Y, Ba, THD with a molar ratio solution within the
liquid source 206b and Cu with a molar ratio of of Y:Ba:Cu =
1:1.9-2.5:2.8-3.2, Y:Ba:Cu = 1:1.8-2.6:2.5-3.5, with solvents. with
solvents, such Alternately, THD as tetrahydrofuran and compounds of
Sm(or isopropanol. Alternately, Nd, Eu), Ba, and Cu THD compounds
of Sm(or with a molar ratio of Nd, Eu), Ba, and Cu with a Y:Ba:Cu =
1:1.9-2.5:2.8-3.2. molar ratio of Y:Ba:Cu = Alternately, part of Y
is 1:1.8-2.6:2.5-3.5. substituted into Sm (or Alternately, part of
Y is Nd, Eu) up to 50%. substituted into Sm (or Nd, Eu) up to 50%.
Molarity of the precursor solution 0.015 to 0.070 mol/L 0.050 to
0.070 mol/L within the liquid source 206b Temperature of the liquid
precursor 200 to 300.degree. C. 250 to 270.degree. C. solution
within the liquid source 206b Liquid flow rate via the pump 202b
0.1 and 10 mL/min 0.5 to 5 mL/min Flash vaporization temperature
within 200 to 300.degree. C. 250 to 270.degree. C. the precursor
vaporizer 204b Inert gas pressure via the gas line 104 16 to 30 psi
16 to 20 psi Partial oxygen pressure via the oxygen 0.4 to 5 Torr
0.5 to 3 Torr line 128b Vapor precursor temperature via the 200 to
300.degree. C. 250 to 270.degree. C. precursor vapor line 122b
Length of the compartment 113b of the 10 to 30 cm 15 to 20 cm
multi-compartment showerhead 112 The substrate tape 116 temperature
via 700 to 950.degree. C. 750 to 820.degree. C. heating zone B of
the multi-zone substrate heater 114 The substrate tape 116
translation rate 0.25 to 40 cm/min 1 to 40 cm/min Resulting HTS
film thickness 1.5 to 10 microns 3 to 10 microns
TABLE-US-00003 TABLE 3 Control parameters regarding zone C of the
deposition zone 118 Control parameters regarding zone C of the
deposition zone 118 Acceptable examples or Preferred example or
acceptable range preferred range Liquid organometallic precursor
THD compounds of Y, Ba, THD with a molar ratio solution within the
liquid source 206c and Cu with a molar ratio of of Y:Ba:Cu =
1:1.9-2.5:2.8-3.2, Y:Ba:Cu = 1:1.8-2.6:2.5-3.5, with with solvents,
such solvents. Alternately, as tetrahydrofuran and THD compounds of
Sm isopropanol. Alternately, (or Nd, Eu), Ba, and Cu THD compounds
of Sm(or with a molar ratio of Nd, Eu), Ba, and Cu with a Y:Ba:Cu =
1:1.9-2.5:2.8-3.2. molar ratio of Y:Ba:Cu = Alternately,
1:1.8-2.6:2.5-3.5. part of Y is substituted Alternately, part of Y
is into Sm (or Nd, Eu) up substituted into Sm (or Nd, to 50%. Eu)
up to 50%. Molarity of the precursor solution 0.015 to 0.070 mol/L
0.050 to 0.070 mol/L within the liquid source 206c Temperature of
the liquid precursor 200 to 300.degree. C. 250 to 270.degree. C.
solution within the liquid source 206c Liquid flow rate per the
pump 202c 0.1 and 10 mL/min 0.5 to 5 mL/min Flash vaporization
temperature within 200 to 300.degree. C. 250 to 270.degree. C. the
precursor vaporizer 204c Inert gas pressure via the gas line 104 16
to 30 psi 16 to 20 psi Partial oxygen pressure via the oxygen 0.4
to 5 Torr 0.5 to 3 Torr line 128c Vapor precursor temperature via
the 200 to 300.degree. C. 250 to 270.degree. C. precursor vapor
line 122c Length of the compartment 113c of the 10 to 30 cm 15 to
20 cm multi-compartment showerhead 112 The substrate tape 116
temperature via 700 to 950.degree. C. 750 to 820.degree. C. heating
zone C of the multi-zone substrate heater 114 The substrate tape
116 translation rate 0.25 to 40 cm/min 1 to 40 cm/min Resulting HTS
film thickness 1.5 to 10 microns 3 to 10 microns
TABLE-US-00004 TABLE 4 Control parameters regarding zone D of the
deposition zone 118 Control parameters regarding zone D of the
deposition zone 118 Acceptable examples or Preferred example or
acceptable range preferred range Liquid organometallic precursor
THD compounds of Y, Ba, THD with a molar ratio solution within the
liquid source 206d and Cu with a molar ratio of of Y:Ba:Cu =
1:1.9-2.5:2.8-3.2, Y:Ba:Cu = 1:1.8-2.6:2.5-3.5, with solvents. with
solvents, such Alternately, THD as tetrahydrofuran and compounds of
Sm (or isopropanol. Alternately, Nd, Eu), Ba, and Cu THD compounds
of Sm (or with a molar ratio of Nd, Eu), Ba, and Cu with Y:Ba:Cu =
1:1.9-2.5:2.8-3.2. a molar ratio of Y:Ba:Cu = Alternately, part of
Y is 1:1.8-2.6:2.5-3.5. substituted into Sm (or Alternately, part
of Y is Nd, Eu) up to 50%. substituted into Sm (or Nd, Eu) up to
50%. Molarity of the precursor solution 0.015 to 0.070 mol/L 0.050
to 0.070 mol/L within the liquid source 206d Temperature of the
liquid precursor 200 to 300.degree. C. 250 to 270.degree. C.
solution within the liquid source 206d Liquid flow rate per the
pump 202d 0.1 and 10 mL/min 0.5 to 5 mL/min Flash vaporization
temperature within 200 to 300.degree. C. 250 to 270.degree. C. the
precursor vaporizer 204d Inert gas pressure via the gas line 104 16
to 30 psi 16 to 20 psi Partial oxygen pressure via the 0.4 to 5
Torr 0.5 to 3 Torr oxygen line 128d Vapor precursor temperature via
the 200 to 300.degree. C. 250 to 270.degree. C. precursor vapor
line 122a Length of the compartment 113d of 10 to 30 cm 15 to 20 cm
the multi-compartment showerhead 112 The substrate tape 116
temperature 700 to 950.degree. C. 750 to 820.degree. C. via heating
zone D of the multi-zone substrate heater 114 The substrate tape
116 translation rate 0.25 to 40 cm/min 1 to 40 cm/min Resulting HTS
film thickness 1.5 to 10 microns 3 to 10 microns
TABLE-US-00005 TABLE 5 Control parameters regarding zone E of the
deposition zone 118 Control parameters regarding zone E of the
deposition zone 118 Acceptable examples or Preferred example or
acceptable range preferred range Liquid organometallic precursor
THD compounds of Y, Ba, THD with a molar ratio solution within the
liquid source 206e and Cu with a molar ratio of Y:Ba:Cu
=1:1.9-2.5:2.8-3.2, of Y:Ba:Cu =1:1.8-2.6:2.5-3.5, with solvents.
with solvents, such Alternately, THD as tetrahydrofuran and
compounds of Sm (or isopropanol. Alternately, Nd, Eu), Ba, and Cu
THD compounds of Sm (or with a molar ratio of Nd, Eu) Ba, and Cu
with Y:Ba:Cu =1:1.9-2.5:2.8-3.2. a molar ratio of Y:Ba:Cu =
Alternately, part of Y is 1:1.8-2.6:2.5-3.5. substituted into Sm
(or Alternately, part of Y is Nd, Eu) up to 50%. substituted into
Sm (or Nd, Eu) up to 50%. Molarity of the precursor solution 0.015
to 0.070 mol/L 0.050 to 0.070 mol/L within the liquid source 206e
Temperature of the liquid precursor 200 to 300.degree. C. 250 to
270.degree. C. solution within the liquid source 206e Liquid flow
rate via the pump 202e 0.1 and 10 mL/min 0.5 to 5 mL/min Flash
vaporization temperature within 200 to 300.degree. C. 250 to
270.degree. C. the precursor vaporizer 204e Inert gas pressure via
the gas line 104 16 to 30 psi 16 to 20 psi Partial oxygen pressure
via the 0.4 to 5 Torr 0.5 to 3 Torr oxygen line 128e Vapor
precursor temperature via the 200 to 300.degree. C. 250 to
270.degree. C. precursor vapor line 122e Length of the compartment
113e of 10 to 30 cm 15 to 20 cm the multi-compartment showerhead
112 The substrate tape 116 temperature 700 to 950.degree. C. 750 to
820.degree. C. via heating zone E of the multi-zone substrate
heater 114 The substrate tape 116 translation rate 0.25 to 40
cm/min 1 to 40 cm/min Resulting HTS film thickness 1.5 to 10
microns 3 to 10 microns
[0058] The detailed operation of the MOCVD system 100 is described
using an example HTS-coated tape as shown in FIG. 4a.
[0059] FIG. 4a illustrates a cross-sectional view of an example
HTS-coated tape 150 formed via the MOCVD system 100 of FIG. 1. The
HTS-coated tape 150 includes the substrate tape 116, upon which is
first deposited a layer 160, followed by a layer 158, followed by a
layer 156, followed by a layer 154, and followed lastly by a layer
152. The layer 160, the layer 158, the layer 156, the layer 154,
and the layer 152 are each formed of an HTS film, such as YBCO, via
the MOCVD system 100 of FIG. 1.
[0060] With reference to FIGS. 1, 3, and 4a, the operation of the
MOCVD system 100 of the present invention is as follows.
[0061] Sufficient vacuum is developed within the reactor 110 by
activating the vacuum pump 142. The linear translation of the
substrate tape 116 through the deposition zone 118 begins in a
direction progressing from zone A to zone E. (The mechanisms for
translating the substrate tape 116 are not shown.) All heating
elements within the multi-zone substrate heater 114 are activated
to provide the desired temperature to the substrate tape 116
according to Tables 1 through 5.
[0062] The liquid sources 206a, 206b, 206c, 206d, and 206e contain
a liquid organometallic precursor solution according to Tables 1
through 5. The pumps 202a, 202b, 202c, 202d, and 202e are activated
to feed the liquid precursor from the liquid sources 206a, 206b,
206c, 206d, and 206e, respectively, into the precursor vaporizers
204a, 204b, 204c, 204d, and 204e, respectively. There, the
solutions are flash vaporized instantly and then mixed with the
inert carrier gas, such as argon or nitrogen, feeding into the
precursor vaporizers 204a, 204b, 204c, 204d, and 204e from the gas
line 104 to form a yttrium-barium-copper vapor precursor. The
yttrium-barium-copper vapor precursors from the precursor
vaporizers 204a, 204b, 204c, 204d, and 204e are then carried to the
reactor 110 via the carrier gas through the precursor vapor lines
122a, 122b, 122c, 122d, and 122e, respectively. The precursor vapor
lines 122a, 122b, 122c, 122d, and 122e are maintained at an
appropriate temperature, according to Tables 1 through 5, via
heating coils (not shown). Additionally, oxygen is introduced to
the precursor vapor lines 122a, 122b, 122c, 122d, and 122e just
prior to the vapor precursor entering the reactor 110 via the
oxygen lines 128a, 128b, 128c, 128d, and 128e, respectively.
[0063] Having activated the deposition process within the reactor
110 of the MOCVD system 100 and set all control parameters
according to Tables 1 through 5, the HTS-coated tape 150 is formed
as follows.
[0064] Firstly, the precursor vapor line 122a delivers the
yttrium-barium-copper containing precursor vapor to the compartment
113a of the multi-compartment showerhead 112, which uniformly
directs this vapor precursor toward the substrate tape 116 within
zone A of the deposition zone 118. The result of the oxygen
reacting with the yttrium-barium-copper containing precursor vapor
and then this reacting combination coming into contact with the hot
substrate tape 116 within zone A of the deposition zone 118 causes
the yttrium-barium-copper containing precursor to decompose and
form the layer 160 of YBCO atop the substrate tape 116 as it
translates through zone A of the deposition zone 118. The defects
within the layer 160 are minimized via the control parameters
according to Table 1. Thus, the layer 160 provides a high quality
template for growing additional YBCO material.
[0065] Subsequently, the precursor vapor line 122b delivers the
yttrium-barium-copper containing precursor vapor or an alternative
precursor containing vapor such as that shown in Table 2 to the
compartment 113b of the multi-compartment showerhead 112, which
uniformly directs this vapor precursor toward the substrate tape
116 within zone B of the deposition zone 118. The result of the
oxygen reacting with the yttrium-barium-copper containing precursor
vapor or the alternative precursor vapor shown in Table 2 and then
this reacting combination coming into contact with the hot
substrate tape 116 within zone B of the deposition zone 118 causes
the yttrium-barium-copper containing precursor vapor or the
alternative precursor vapor shown in Table 2 to decompose and form
the layer 158 of YBCO or HTS corresponding to alternate precursor
used atop the substrate tape 116 as it translates through zone B of
the deposition zone 118. The defects within the layer 158 are
minimized via the control parameters according to Table 2. Thus,
the layer 158 provides a high quality template for growing
additional YBCO material or HTS layers corresponding to alternate
precursor used.
[0066] Subsequently, the precursor vapor line 122c delivers the
yttrium-barium-copper containing precursor vapor or the alternative
precursor shown in Table 3 to the compartment 113c of the
multi-compartment showerhead 112, which uniformly directs this
vapor precursor toward the substrate tape 116 within zone C of the
deposition zone 118. The result of the oxygen reacting with the
yttrium-barium-copper containing precursor vapor or the alternative
precursor vapor shown in Table 3 and then this reacting combination
coming into contact with the hot substrate tape 116 within zone C
of the deposition zone 118 causes the yttrium-barium-copper
containing precursor vapor or the alternative precursor vapor shown
in Table 3 to decompose and form the layer 156 of YBCO or HTS
corresponding to alternate precursor used atop the substrate tape
116 as it translates through zone C of the deposition zone 118. The
defects within the layer 156 are minimized via the control
parameters according to Table 3. Thus, the layer 156 provides a
high quality template for growing additional YBCO material or HTS
layers corresponding to alternate precursor used.
[0067] Subsequently, the precursor vapor line 122d delivers the
yttrium-barium-copper containing precursor vapor or the alternative
precursor vapor shown in Table 4 to the compartment 113d of the
multi-compartment showerhead 112, which uniformly directs this
vapor precursor toward the substrate tape 116 within zone D of the
deposition zone 118. The result of the oxygen reacting with the
yttrium-barium-copper containing precursor vapor or the alternative
precursor vapor shown in Table 4 and then this reacting combination
coming into contact with the hot substrate tape 116 within zone D
of the deposition zone 118 causes the yttrium-barium-copper
containing precursor vapor or the alternative precursor vapor shown
in Table 4 to decompose and form the layer 154 of YBCO or HTS
corresponding to alternate precursor used atop the substrate tape
116 as it translates through zone D of the deposition zone 118. The
defects within the layer 154 are minimized via the control
parameters according to Table 4. Thus, the layer 154 provides a
high quality template for growing additional YBCO material or HTS
layers corresponding to alternate precursor used.
[0068] Lastly, the precursor vapor line 122e delivers the
yttrium-barium-copper containing precursor vapor or the alternative
precursor vapor shown in Table 5 to the compartment 113e of the
multicompartment showerhead 112, which uniformly directs this vapor
precursor toward the substrate tape 116 within zone E of the
deposition zone 118. The result of the oxygen reacting with the
yttrium-barium-copper containing precursor vapor or the alternative
precursor vapor shown in Table 5 and then this reacting combination
coming into contact with the hot substrate tape 116 within zone E
of the deposition zone 118 causes the yttrium-barium-copper
containing precursor vapor or the alternative precursor vapor shown
in Table 5 to decompose and form the layer 152 of YBCO or HTS
corresponding to alternate precursor used atop the substrate tape
116 as it translates through zone E of the deposition zone 118.
[0069] The defects within the layer 152 are minimized via the
control parameters according to Table 5. Thus, the layer 152
provides a high quality template for growing additional HTS
material or material such as silver or copper, which can be
deposited by any film deposition method. As a result, collectively
the YBCO layers or HTS layers corresponding to any alternate
precursor used that form the HTS-coated tape 150 have a thickness
of greater than 2 microns with a critical current density of
approximately greater than 0.6 MA/cm.sup.2.
[0070] In summary, by optimizing the deposition control parameters,
a thick layer of YBCO or HTS corresponding to alternate precursor
used is formed by applying one high-quality YBCO coating or HTS
corresponding to alternate precursor used atop another via multiple
independently controlled deposition regions (i.e., zones A, B, C,
D, and B) within the deposition zone 118. In this way, the
morphology of each YBCO coating or HTS corresponding to alternate
precursor used that is applied one atop another is carefully
controlled to minimize film defects, such as high porosity, voids,
and surface roughness, thereby forming a high-quality growth
template. As a result, the MOCVD system 100 of the present
invention is capable of producing a YBCO film or HTS corresponding
to alternate precursor used with a thickness in excess of 1.5
microns that has increased material density and smoothness that
results in increased current capacity of over at least 100 A/cm
width.
[0071] In an alternative embodiment, multiple precursors may be
delivered to the deposition zone 118 of the MOCVD system 100 by
separately installed showerheads to supply the separate precursors
to the substrate tape 116 instead of using a multi-compartment
showerhead designed as a single unit. Each separately installed
showerhead would have an associated separate heater for supplying
heat to the substrate tape 116.
[0072] FIG. 2 illustrates an MOCVD system 101 in accordance with an
embodiment of the invention for producing multiple layer HTS-coated
tapes with increased current capability. The MOCVD system 101
includes a conventional MOCVD reactor 110, which 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, 1.6 Torr. The MOCVD reactor 110 houses a multi-compartment
showerhead 112 located in close proximity to a substrate heater
114. A substrate tape 116 is positioned and translates (during
operation) between the multi-compartment showerhead 112 and the
substrate heater 115 within a deposition zone 118 along the length
of the multi-compartment showerhead 112, i.e., the area in which
the substrate tape 116 is exposed to the precursor vapors. The
substrate tape 116 is a flexible length of substrate formed from a
variety of metals, such as stainless steel or a nickel alloy such
as Inconel, 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 substrate tape 116 is capable of withstanding
temperatures over 900.degree. C. and has dimensions that may vary
to meet the desired finished product and system limitations. For
example, the substrate tape 116 may have a thickness of 25 microns,
a width of 1 cm, and a length of 100 meters.
[0073] The multi-compartment showerhead 112 is a device for
uniformly distributing vapors onto the substrate tape 116 via fine
holes within multiple compartments 113, for example, a compartment
113a, a compartment 113b, a compartment 113c, a compartment 113d,
and a compartment 113e, as shown in FIGS. 1 and 2. Each compartment
113 within the multi-compartment showerhead 112 includes multiple
fine holes evenly distributed throughout its area that are fed by a
common inlet (not shown). Furthermore, each compartment 113 within
the multi-compartment showerhead 112 is physically isolated from
one another such that vapor precursors being distributed by one
compartment 113 are not mixed with vapor precursors of an adjacent
compartment 113. The overall length of the multi-compartment
showerhead 112, the number of compartments 113 within the
multi-compartment showerhead 112, the length of each compartment
113, and the specific composition of the vapor precursor feeding
each compartment 113 may be user defined depending on the
application.
[0074] During the deposition process, the temperature of the
substrate tape 116 is properly controlled via the substrate heater
114. The substrate heater 114 is a well-known single or multiple
zone substrate heater that provides heating, typically in the range
of 700 to 950.degree. C., to the substrate tape 116 via a radiant
heating element, such as an infrared lamp. Alternatively, the
substrate heater 114 is a resistance heater via a heating element,
such as Kanthal or MoSi.sub.2.
[0075] The MOCVD system 101 further includes a first and second
precursor delivery system. As shown in FIG. 3 each delivery system
comprises a liquid source 206 that is a reservoir formed of, for
example, stainless steel, that contains a solution containing
organometallic precursors, such as yttrium, barium, and copper,
along with an appropriate mixture of solvents. The liquid source
206 feeds a liquid precursor delivery pump 202 capable of a low
flow rate between 0.1 and 10 mL/min. The pump 202 is a
high-pressure, low flow rate pump, such as a high-pressure liquid
chromatography (HPLC) pump. The pump 202 feeds a precursor
vaporizer 204 which are elements in which a precursor solution is
flash vaporized and mixed with an inert carrier gas, such as argon
or nitrogen, for delivery to the multi-compartment showerhead 112.
The vaporized precursors exit the vaporizer via line 122. Just
prior to each vapor line 122 entering the reactor 110 an oxygen
line 128 opens into the vapor line 142. The oxygen line 128 and 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 122. Each instantiation of the precursor vapor
line, designated 122 by a lower case letter after the number,
enters the reactor 110 ready for delivery through the showerhead
112 onto a substrate 116. Lastly, the MOCVD system 101 includes a
vacuum pump 142 connected to the reactor 110. The vacuum pump 142
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 D408. Alternatively, the function of the
vacuum pump 142 may be accomplished by a combination of a
mechanical pump and a mechanical booster, such as Edwards model
EHS00, in order to obtain the proper vacuum suitable for use with a
large amount of liquid precursor.
[0076] The precursor delivery system 120 and the vacuum pump 142
are all located external to the reactor 110. Additionally, those
skilled in the art will appreciate that the MOCVD system 101
further includes various sensing and control devices, such as
pressure gauges and thermocouples, which are for simplicity not
shown in FIG. 2 or 3. Distinct areas within the deposition zone 118
are formed and associated with each compartment 113 within the
multi-compartment showerhead 112. In the example shown in FIG. 2,
vapors distributed from the compartment 113a are deposited upon the
substrate tape 116 within a zone A, vapors distributed from the
compartment 113b are deposited upon the substrate tape 116 within a
zone B, vapors distributed from the compartment 113c are deposited
upon the substrate tape 116 within a zone C, vapors distributed
from the compartment 113d are deposited upon the substrate tape 116
within a zone D, and vapors distributed from the compartment 113e
are deposited upon the substrate tape 116 within a zone E.
Furthermore, the example illustrated in FIG. 2 shows the vapor
precursor developed from the liquid source 120x feeding the
compartments 113a, 113c, and 113e via the vapor line 122x.
Likewise, the vapor precursor developed from the liquid source 120y
feeds the compartments 113b and 113d via the vapor line 122y.
[0077] The detailed operation of the MOCVD system 100 is described
using an example multi-layer coated tape as shown in FIG. 4b.
[0078] FIG. 4b illustrates a cross-sectional view of an example
multi-layer coated tape 200 formed via the MOCVD system 101 of FIG.
2. The multi-layer coated tape 200 includes the substrate tape 116,
upon which is first deposited a layer 210, followed by a layer 212,
followed by a layer 214, followed by a layer 216, and followed
lastly by a layer 218. The layer 210, the layer 212, the layer 214,
the layer 216, and the layer 218 are each formed of an HTS film via
the MOCVD system 101 of FIG. 2. As an example, the layer 210, the
layer 214, and the layer 218 are formed of YBCO with each layer
having a typical thickness of up to 1.5 microns, and the layer 212
and the layer 216 are formed of samarium-barium-copper-oxide
(SmBa.sub.2Cu.sub.3O.sub.7 or "Sm123") with each layer having a
typical thickness of up to 0.2 microns.
[0079] The formation of the multi-layer coated tape 200 with the
layers formed of the specific HTS materials as mentioned above by
the MOCVD system 101 is as follows.
[0080] Sufficient vacuum is developed within the reactor 110 by
activating the vacuum pump 142. The linear translation of the
substrate tape 116 through the deposition zone 118 begins in a
direction progressing from zone A to zone E. (The mechanical
mechanisms for translating the substrate tape 116 are not shown.)
The substrate heater 114 is activated and the substrate tape 116 is
ramped up to a temperature typically in the range of 700 to
950.degree. C.
[0081] The liquid source 206 contains a room temperature solution
of tetramethyl heptanedionate (THD) compounds of yttrium, barium,
and copper, along with an appropriate mixture of solvents such as
tetrahydrofuran and isopropanol, to form a first liquid
organometallic precursor.
[0082] The pump 202 is activated to feed the yttrium-barium-copper
liquid precursor from the liquid source 206 into the precursor
vaporizer 204 where the solution is flash vaporized instantly at
approximately 240.degree. C. and then mixes with the inert carrier
gas such as argon or nitrogen, entering the precursor vaporizer 204
from the gas line 104 to form a yttrium-barium-copper vapor
precursor. The yttrium-barium-copper vapor precursor is then
carried to the reactor 110 using a carrier gas such as argon
through the precursor vapor line 122x, which is maintained at an
appropriate temperature, typically in the range of 200 to
300.degree. C., via a heating coil (not shown). Additionally,
oxygen is introduced to the vapor precursor via the oxygen line 128
just prior to the vapor precursor entering the reactor 110. The
vapor line 122x delivers the yttrium-barium-copper containing
precursor vapor to the compartments 113a, 113c, and 113e of the
multi-compartment showerhead 112, which uniformly directs this
precursor vapor toward the substrate tape 116 within zone A, zone
C, and zone E of the deposition zone 118. All the while, the
temperature of the substrate tape 116 is properly controlled via
the substrate heater 114. The result of the oxygen reacting with
the yttrium-barium-copper containing precursor vapor and precursor
vapor then coming into contact with the hot substrate tape 116
causes the yttrium-barium-copper containing precursor vapor to
decompose and form a film of YBCO atop the substrate tape 116
within zone A, zone C, and zone E of the deposition zone 118.
[0083] Concurrently with the pump 202 being activated to feed the
yttrium-barium-copper containing liquid precursor, an identical
pump is activated to feed the samarium-barium-copper containing
liquid precursor from the samarium-barium-copper containing liquid
source into the samarium-barium-copper containing precursor
vaporizer where the solution is flash vaporized instantly at
approximately 240.degree. C. and then mixes with the inert carrier
gas such as argon or nitrogen, entering the precursor vaporizer 204
from the gas line 140 to form a samarium-barium-copper containing
precursor vapor. The samarium-barium-copper containing precursor
vapor is then carried to the reactor 110 by using a carrier gas
such as argon through the vapor line 122y, which is maintained at
an appropriate temperature, typically in the range of 200 to
300.degree. C., via a heating coil (not shown). Additionally,
oxygen is introduced to the vapor precursor via the oxygen line 128
just prior to the vapor precursor entering the reactor 110. The
vapor line 122y delivers the samarium-barium-copper containing
precursor vapor to the compartments 113b and 113d of the
multi-compartment showerhead 112, which uniformly directs this
vapor precursor toward the substrate tape 116 within zone B and
zone D of the deposition zone 118. All the while, the temperature
of the substrate tape 116 is properly controlled via the substrate
heater 114. The result of the oxygen reacting with the
samarium-barium-copper containing precursor vapor and this vapor
precursor then coming into contact with the hot substrate tape 116
causes the samarium-barium-copper containing precursor vapor to
decompose and form a film of Sm123 atop the substrate tape 116
within zone B and zone D of the deposition zone 118.
[0084] Having activated the deposition process within the reactor
110 of the MOCVD system 101 and with continuing reference to FIGS.
2 and 4b, the multi-layer coated tape 200 is formed as follows. The
translating substrate tape 116 experiences the deposition of a
first layer of YBCO within zone A of the deposition zone 118 to
form the layer 210. Subsequently, atop the first layer of YBCO the
substrate tape 116 experiences the deposition of a first layer of
Sm123 within zone B of the deposition zone 118 to form the layer
212. Subsequently, atop the first layer of Sm123 the substrate tape
116 experiences the deposition of a second layer of YBCO within
zone C of the deposition zone 118 to form the layer 214.
Subsequently, atop the second layer of YBCO, the substrate tape 116
experiences the deposition of a second layer of Sm123 within zone D
of the deposition zone 118 to form the layer 216. Lastly, atop the
second layer of Sm123 substrate tape 116 experiences the deposition
of a third layer of YBCO within zone E of the deposition zone 118
to form the layer 218.
[0085] Samarium and yttrium belong to the same group within the
periodic table of elements, which means that the
samarium-barium-copper precursor behaves in 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 122n of between 250 and 300.degree.
C., the substrate tape 116 temperature of between 700 to
950.degree. C., the deposition pressure of 1 to 10 Torr, the oxygen
partial pressure of 0.5 to 5 Torr, and the liquid precursor
delivery rate of 0.25-10 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 MOCVD system 101 need no special design to accommodate
the different materials.
[0086] In general, the thickness of each layer being deposited is
determined by the combination of three factors: (1) the physical
length of its associated compartment, (2) its associated vapor
precursor 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
more concentrated the associated precursor solution, the thicker
the film.
[0087] As one example of these controls, the thickness of the layer
212 is determined by the combination of the physical length of the
compartment 113b within the multi-compartment showerhead 112, the
delivery rate of the samarium-barium-copper containing precursor,
and the concentration of the samarium-barium-copper containing
liquid precursor.
[0088] In the case of the YBCO single layer, research indicates
that the critical current reaches a maximum and levels off at
around 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.
[0089] 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.
[0090] The formation of a multi-layer HTS-coated tape such as the
multi-layer coated tape 200 using the MOCVD system 100 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), Gadolinium
(Gd)), may be used. Additionally, a multi-layer HTS-coated tape
formed using the MOCVD system 100 is not limited to any specific
number of layers. The multi-compartment showerhead 112 may be
expanded to any number of compartments 113 as long as all precursor
delivery lines and pumps are sized to handle delivery to multiple
zones at the proper delivery rate. Furthermore, the substrate
heater 114 may be expanded to any length accordingly.
Alternatively, there may be separate heater zones within the
substrate heater 114 that directly correlate to the compartments
113 and resulting deposition zones for further temperature control
if needed.
[0091] In an alternative embodiment, multiple precursors may be
delivered to the deposition zone 118 of the MOCVD system 100 or 101
by separately installed showerheads to supply the separate
precursors to the substrate tape 116 instead of using a
multi-compartment showerhead designed as a single unit. Each
separately installed showerhead would have an associated separate
heater for supplying heat to the substrate tape 116. While multiple
layer deposition is possible using other well-known deposition
processes, such as a pulsed laser deposition (PLD) process, the
equipment costs associated with a PLD process are prohibitive
because there is a laser associated with each layer. Thus, multiple
layers require multiple lasers, which are the most expensive
component of a PLD system. Therefore, the MOCVD systems 100 and 101
of the present invention are desirable, cost-effective,
high-throughput way of producing multi-layer HTS-coated tapes with
increased current capability.
* * * * *