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AU773535B2 - Superconducting device - Google Patents

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AU773535B2
AU773535B2 AU58423/99A AU5842399A AU773535B2 AU 773535 B2 AU773535 B2 AU 773535B2 AU 58423/99 A AU58423/99 A AU 58423/99A AU 5842399 A AU5842399 A AU 5842399A AU 773535 B2 AU773535 B2 AU 773535B2
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Australia
Prior art keywords
inhibitor
niobium
superconducting
regions
superconducting material
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AU5842399A (en
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Simon Lam
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Commonwealth Scientific and Industrial Research Organization CSIRO
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Commonwealth Scientific and Industrial Research Organization CSIRO
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Priority claimed from AUPP5907A external-priority patent/AUPP590798A0/en
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  • Superconductor Devices And Manufacturing Methods Thereof (AREA)

Description

1
AUSTRALIA
Patents Act 1990 0e 0 0 a a 9 0@ a.
4000 03*~ a-, a a pg 0e 0. 6 000 9.
COMPLETE SPECIFICATION STANDARD PATENT Invention Title: 0 9O~ 600 0 0a0 a 0S00 0 Method of selective epitaxial growth The following statement is a full description of this invention including the best method of performing it known to us:- "Method of selective epitaxial growth" Technical Field The present invention relates to the manufacture of high critical temperature superconducting (HTSC) devices, and in particular provides a method of manufacture that allows improved passivation and increased device lifetime.
Background Art Superconducting materials are currently finding applications in a number of areas. For example, superconducting quantum interference devices (SQUIDs) have applications in geophysical mineral prospecting.
Due to the nature of superconducting materials and any accompanying S"substrate, it is necessary to passivate a superconducting device during or Safter manufacture, in order to prevent reaction between the device itself and :15 other elements with which it may come into contact. For example, 0000 superconducting devices preferably exclude air in order to prevent water and nitrogen coming into contact with the superconducting material and the substrate. Known methods of fabrication of HTSC devices typically require a number of steps after deposition of the superconducting material, and therefore there exists a period of time after deposition in which the superconducting material has not been passivated, raising the possibility of performance degradation.
0.00 Consequently there exists a need for improved methods of manufacture of high temperature superconductors.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base **OO or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application.
Disclosure of Invention Throughout the following, the terms 'superconducting material', 'superconducting device' and the like are used to refer to a material or device which, in a certain state and at a certain temperature, is capable of exhibiting superconductivity. The use of such terms does not imply that the material or device exhibits superconductivity in all states or at all temperatures.
According to a first aspect the present invention provides an operative high critical temperature superconducting (HTSC) device including a niobium inhibitor deposited over selected regions of a substrate surface, and a superconducting material deposited over substantially the entire substrate surface, wherein the superconducting material possesses a high resistivity in *0 S S se 00 *0* 5 WO 00/16413 PCT/AU99/00773 2 the selected regions and exhibits superconducting characteristics only in regions in which the niobium inhibitor has not been deposited.
The superconducting material may be deposited over some or all of the niobium inhibitor. The superconducting material is preferably deposited over the niobium inhibitor at least in regions immediately adjacent to the regions in which the niobium inhibitor has not been deposited.
In typical embodiments of the device of the present invention, the superconducting material will be in amorphous form in the selected regions and in the form of an epitaxial film in regions in which the niobium inhibitor has not been deposited.
The resistivity of the superconducting material in the selected regions is preferably significantly greater than the normal resistivity of the superconducting material in the regions in which the niobium inhibitor has not been deposited. Preferably, the resistivity of the superconducting material in the selected regions is 4 orders of magnitude or more greater than the normal resistivity of the superconducting material in the regions in which the niobium inhibitor has not been deposited.
In preferred embodiments of the invention there is a sharp boundary between the selected regions and the regions in which the niobium inhibitor has not been deposited. In particular, the formation of material having low critical current density at the boundary is particularly undesirable in features such as microbridges as it may have deleterious effects on the critical current density and critical temperature of the device.
The use of niobium as an inhibitor in the device of the first aspect of the present invention is advantageous as niobium has a number of desirable properties. For example, niobium has a high melting point, so that production of devices of the present invention may include processing steps at high temperature. Niobium is also chemically stable, which can reduce diffusion of niobium near the boundaries of the selected regions, enabling a sharp boundary to be formed. Furthermore, should any oxidation of the inhibitor occur, niobium oxide is also chemically stable.
The superconducting material is preferably YBa 2 Cu 3 0, (YBCO), where x has a value of 6 to 7, which is preferably in the form of an amorphous layer in the selected regions and in the form of an epitaxial film in the regions in which the niobium inhibitor has not been deposited.
WO 00/16413 PCT/AU99/00773 3 The device may further include a passivation layer. The passivation layer may be amorphous YBCO.
The device may include a Josephson Junction formed over a step edge in the substrate, or a microbridge or submicron bridge. The device of the present invention may be used to good effect in a superconducting quantum interference device (SQUID) for example in the field of geophysical prospecting.
The substrate of the device of the present invention may be of any suitable material, however it has been found that a single crystal MgO (100) substrate may be used to good effect.
In some embodiments of the invention, formation of the device may include exposing the niobium inhibitor to an atmosphere of argon and oxygen while subjecting the device to RF plasma sputtering at a temperature greater than substantially 500 degrees centigrade, and at a pressure between 20Pa and 1OOPa. The temperature in such embodiments is preferably substantially 770 degrees centigrade and the pressure is preferably substantially From a second aspect the present invention provides a method of forming a high temperature superconducting (HTSC) device including the steps of: depositing a niobium inhibitor over selected regions of a substrate surface; providing an atmosphere of argon and oxygen and subjecting the device to RF plasma sputtering at a temperature greater than substantially 500 degrees centigrade, and at a pressure between 20Pa and 100Pa; and depositing a superconducting material over substantially the entire substrate surface, wherein the niobium inhibitor alters the characteristics of the superconducting material such that it possesses a high resistivity and does not exhibit superconductivity, thereby providing material exhibiting superconducting characteristics only in those regions in which the niobium inhibitor has not been deposited.
In the present invention, providing a niobium inhibitor prior to deposition of the superconducting material enables selective epitaxial growth (SEG) to occur. That is, in those regions where no inhibitor was deposited, the superconducting material undergoes epitaxial growth, whereas in those
I
WO 00/16413 PCT/AU99/00773 4 areas where an inhibitor was deposited the superconducting material grows as an amorphous layer having a high resistivity.
The method of the second aspect of the present invention preferably includes the subsequent step of depositing or forming a protective layer in order to passivate the device. The protective layer may be amorphous YBCO.
Any substrate may be used in accordance with the second aspect of the present invention. Preferably a single crystal MgO (100) substrate is used.
In accordance with the second aspect of the invention, the ratio of argon to oxygen is preferably between 10:1 and 20:1, and more preferably lies between 13:1 and 17:1. The ratio of argon to oxygen is most preferably 15:1.
The method of the second aspect of the present invention may be used to form a number of superconducting circuits, for example a thin film YBCO step edge junction on a MgO substrate, or a submicron bridge.
The method of the second aspect of the present invention may be applied in the production of SQUIDs for the purpose of geophysical prospecting.
By using SEG the present invention enables passivation to be provided in-situ. This enables the elimination of post-deposition steps such as etching or lithography, thereby providing less time in which the device can degrade, and increasing device performance, stability and lifetime.
The use of a Niobium inhibitor is advantageous due to the high melting point and chemical stability of niobium. By having a high melting point, the niobium is less likely to melt or react during high temperature processing. Chemical stability in an inhibitor is advantageous because less migration or diffusion of the inhibitor will occur, providing a sharper definition between the inhibited region and the superconducting region, and reducing distortion between the deposited niobium pattern and the resulting pattern of inhibition. Providing a sharp boundary can also be advantageous in that an ill-defined boundary in which superconducting material of low critical current density is formed can have a deleterious effect on superconductivity of the device or circuit as a whole.
Embodiments of the present invention in accordance with the second aspect of the invention might include the steps of: placing the device in substantially a vacuum; introducing oxygen to provide a partial pressure of substantially 0.2Pa; introducing argon to provide an argon to oxygen ratio of substantially to 1; and reducing a pumping rate of a vacuum pump such that at equilibrium the device is subjected to a pressure of substantially In accordance with the second aspect of the invention, the device is preferably subjected to RF plasma sputtering at a temperature between 700 and 850 degrees centigrade, and most preferably at a temperature of substantially 770 degrees centigrade.
In accordance with the second aspect of the invention, the device is preferably subjected to RF plasma sputtering at a pressure between 40Pa and and most preferably at a pressure of substantially Brief Description of Drawings Embodiments of the invention will now be described by way of .15 example with reference to the accompanying drawings in which: Figure 1 illustrates a simple circuit in accordance with the present invention; and Figures 2 and 3 illustrate various steps in the production of a HTSC in accordance with the method of the present invention.
Modes for Carrying Out the Invention •Figure 1 illustrates a simple circuit in accordance with the first aspect of the present invention. The operative high critical temperature superconducting (HTSC) device 2'0 includes a niobium inhibitor deposited 25 over selected regions 23 of a surface of a substrate 21, which is a single crystal MgO (100) substrate. A superconducting material, being YBa 2 Cu 3 Ox (YBCO), where x has a value of 6 to 7, is deposited over substantially the entire surface of the substrate 21. The YBCO possesses a high resistivity in the selected regions 23 and exhibits superconducting characteristics only in regions 22 in which the niobium inhibitor has not been deposited.
In the present embodiment of the invention, the superconducting material is in amorphous form in the selected regions 23 and in the form of an epitaxial film in regions 22 in which the niobium inhibitor has not been deposited. At 100K, the resistivity of the superconducting material in the selected regions 23 is around 12.cm which is about 10 4 greater than the WO 00/16413 PCT/AU99/00773 6 resistivity of the superconducting material in the regions 22 in which the niobium inhibitor has not been deposited.
Due to the use of a niobium inhibitor, a sharp boundary exists between the selected regions 23 and the regions 22 in which the niobium inhibitor has not been deposited.
Figures 2 and 3 illustrate a high temperature superconductor 20 being formed in accordance with the second aspect of the present invention. A niobium inhibitor 24 has been deposited over selected regions 23 of a substrate 21. The device has been subjected to RF plasma sputtering in an atmosphere of argon and oxygen at a temperature of 770 degrees centigrade and at a pressure of 60Pa. As shown in Figure 3, the next step in the method of the present invention is the deposition of a superconducting material over substantially the entire substrate 21, wherein the inhibitor 24 alters the superconducting material 25 such that it possesses a high resistivity and does not exhibit superconductivity in regions 23, thereby providing material exhibiting superconducting characteristics only in those regions 22 in which the inhibitor 24 has not been placed.
The second aspect of the present invention provides a method of forming a high temperature superconducting (HTSC) device 20 wherein Selective Epitaxy Growth (SEG) patterning using an inhibitor 24 permits processing steps of the HTSC film 25 such as etching or lithography to be eliminated, and allows in situ passivation to protect it from environmental attack. The inhibitor 24, which is pre-patterned on the substrate 21 by lithography, alters the HTSC material 25 such that it possesses a high resistivity and does not exhibit superconductivity. SEG patterning with Niobium as an inhibitor provides a simple technique to obtain stable and high quality YBCO submicron structures. This method may be used to fabricate YBCO thin film microbridges, step edge grain boundary Josephson junction and RF SQUIDs incorporating a step edge junction. The method increases device durability and reduces excessive low frequency noise for RF circuits, such as SQUIDs, fabricated by this technique.
The method of the second aspect of the invention is now further described by way of example. Step edges were fabricated using a photoresist mask with a specified ion beam etching orientation on 1 cm x 1 cm MgO substrate. The step angle and height are 400 and 500 nm respectively. Prior to YBCO deposition, a 10 nm thick Nb inhibitor was pre-patterned on the WO 00/16413 PCT/AU99/00773 7 substrate by standard photolithography and lift off. After the YBCO film was deposited by DC sputtering, some of the samples were deposited in situ with nm amorphous YBCO at room temperature as a protective layer. Some microbridges were also fabricated by using ion beam etching to pattern the YBCO film.
The superconducting material (barrier) in region 23 on top of the inhibitor 24 preferably has a significantly higher resistance than the superconducting material in region 22, and forms a sharp boundary with the superconducting material in region 22. The present invention enables the region 23 to have a resistivity about 4 orders of magnitude higher than the epitaxy YBCO film in region 22. YBCO microbridges with different dimensions were fabricated which show a critical temperature T, of 85-87K and critical current density Jc of 1.5-2.8 mA/cm 2 at 77K. Step edge junctions of 2-3 [Lm wide show a RSJ behaviour with normal resistance Rn 2.7-3.0 n.
The IRn product of 50-150 uV is comparable to the junction fabricated by ion beam etching.
Amorphous YBCO passivation has been found to provide effective passivation and preservation of circuit characteristics, such as low frequency noise level.
The present invention provides a simple technique to fabricate microstructures based on selective epitaxy growth of HTSC thin films, allowing in situ passivation which performs well under severe environmental tests.
By providing an inhibitor prior to deposition of the superconducting material, selective epitaxial growth occurs. That is, in those regions where no inhibitor was deposited, the superconducting material undergoes epitaxial growth, whereas in those areas where an inhibitor was deposited the superconducting material grows as an amorphous layer having a high resistivity.
Any substrate may be used in accordance with the second aspect of the present invention. Preferably a single crystal MgO (100) substrate is used.
The use of a Niobium inhibitor is advantageous due to the high melting point and chemical stability of niobium. By having a high melting point, the niobium is less likely to melt or react during high temperature processing. Chemical stability in an inhibitor is advantageous because less migration of the inhibitor will occur, providing a sharper definition between the inhibited region and the superconducting region, and reducing distortion WO 00/16413 PCT/AU99/00773 8 between the deposited niobium pattern and the resulting pattern of inhibition.
It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims (31)

1. An operative high critical temperature superconducting (HTSC) device including a niobium inhibitor deposited over selected regions of a substrate surface, and a superconducting material deposited over substantially the entire substrate surface, wherein the superconducting material possesses a high resistivity in the selected regions and exhibits superconducting characteristics only in regions in which the niobium inhibitor has not been deposited.
2. The device according to claim 1, wherein the superconducting material is deposited over the niobium inhibitor in regions immediately adjacent to the regions in which the niobium inhibitor has not been deposited.
3. The device according to claim 1, wherein the superconducting material :0 is deposited over all of the niobium inhibitor.
4. The device according to any preceding claim, wherein the 15 superconducting material is in amorphous form in the selected regions and in the form of an epitaxial film in regions in which the niobium inhibitor has not been deposited.
5. The device according to any preceding claim, wherein the resistivity of the superconducting material in the selected regions is significantly greater than the normal resistivity of the superconducting material in the regions in which the niobium inhibitor has not been deposited.
6. The device according to claim 5 wherein the resistivity of the 0000 •superconducting material in the selected regions is 4 orders of magnitude or more greater than the normal resistivity of the superconducting material in S 25 the regions in which the niobium inhibitor has not been deposited.
7. The device according to any preceding claim wherein a sharp ••boundary exists between the selected regions and the regions in which the ••niobium inhibitor has not been deposited.
8. The device according to any preceding claim wherein production of the device includes processing steps at high temperature.
9. The device according to any preceding claim wherein some or all of the niobium inhibitor is oxidised. The device according to any preceding claim wherein the superconducting material is YBa 2 Cu 3 where x has a value of 6 to 7. WO 00/16413 PCT/AU99/00773
11. The device according to any preceding claim wherein the superconducting material is in the form of an amorphous layer in the selected regions.
12. The device according to any preceding claim wherein the superconducting material is in the form of an epitaxial film in the regions in which the niobium inhibitor has not been deposited.
13. The device according to any preceding claim further including a passivation layer.
14. The device according to claim 13 wherein the passivation layer is amorphous YBCO. The device according to any preceding claim wherein the device includes a Josephson Junction formed over a step edge in the substrate.
16. The device according to any preceding claim wherein the device includes a microbridge or submicron bridge.
17. The device according to any preceding claim wherein the device is a superconducting quantum interference device (SQUID).
18. The device according to any preceding claim wherein the substrate is a single crystal MgO (100).
19. The device according to any preceding claim wherein formation of the device includes exposing the niobium inhibitor to an atmosphere of argon and oxygen and subjecting the device to RF plasma sputtering at a temperature greater than substantially 500 degrees centigrade, and at a pressure between 20Pa and A method of forming a high temperature superconducting (HTSC) device including the steps of: depositing a niobium inhibitor over selected regions of a substrate surface; providing an atmosphere of argon and oxygen and subjecting the device to RF plasma sputtering at a temperature greater than substantially 500 degrees centigrade, and at a pressure between 20Pa and 10OPa; and depositing a superconducting material over substantially the entire substrate surface, wherein the niobium inhibitor alters the characteristics of the superconducting material such that it possesses a high resistivity and does not exhibit superconductivity, thereby providing material exhibiting superconducting characteristics only in those regions in which the niobium inhibitor has not been deposited. WO 00/16413 PCT/AU99/00773 11
21. The method according to claim 20 wherein the device is subjected to RF plasma sputtering at a temperature between 700 and 850 degrees centigrade.
22. The method according to claim 21 wherein the device is subjected to RF plasma sputtering at a temperature of substantially 770 degrees centigrade.
23. The method according to any one of claims 20 to 22 wherein the device is subjected to RF plasma sputtering at a pressure between 40Pa and
24. The method according to claim 23 wherein the device is subjected to RF plasma sputtering at a pressure of substantially The method according to any one of claims 20 to 24 wherein the method includes the subsequent step of depositing a protective layer in order to passivate the device.
26. The method according to Claim 25 wherein the protective layer is amorphous YBCO.
27. The method according to any one of Claims 20 to 26 wherein a single crystal MgO (100) substrate is used.
28. The method according to any one of Claims 20 to 27 wherein the ratio of argon to oxygen is between 10:1 and 20:1.
29. The method according to Claim 28 wherein the ratio of argon to oxygen is between 13:1 and 17:1. The method according to Claim 29 wherein the ratio of argon to oxygen is 15:1.
31. The method according to any one of Claims 20 to 30 wherein the method is used to form a superconducting circuit.
32. The method according to Claim 31 wherein the method is used to form a thin film YBCO step edge junction on a MgO substrate.
33. The method according to Claim 31 wherein the method is used to form a submicron bridge.
34. The method according to any one of claims 20 to 33 further including the steps of: placing the device in substantially a vacuum; introducing oxygen to provide an oxygen partial pressure of substantially 0.2Pa; introducing argon to provide an argon to oxygen ratio of substantially to 1; and reducing a pumping rate of a vacuum pump such that at equilibrium a pressure of substantially 60Pa is provided.
35. An operative high critical temperature superconducting (HTSC) device substantially as herein described and with reference to the accompanying drawings.
36. A method of forming a high temperature superconducting (HTSC) device substantially as herein described and with reference to the accompanying drawings. Dated this tenth day of April 2001 SO 0 Commonwealth Scientific and Industrial S Research Organisation Patent Attorneys for the Applicant F B RICE CO Pooe* a '000 *0 e^ ae
AU58423/99A 1998-09-14 1999-09-14 Superconducting device Expired AU773535B2 (en)

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Application Number Priority Date Filing Date Title
AU58423/99A AU773535B2 (en) 1998-09-14 1999-09-14 Superconducting device

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
AUPP5907 1998-09-14
AUPP5907A AUPP590798A0 (en) 1998-09-14 1998-09-14 Method of manufacture of high temperature superconductors
PCT/AU1999/000773 WO2000016413A1 (en) 1998-09-14 1999-09-14 Superconducting device
AU58423/99A AU773535B2 (en) 1998-09-14 1999-09-14 Superconducting device

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AU773535B2 true AU773535B2 (en) 2004-05-27

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4790903A (en) * 1986-04-28 1988-12-13 University Of Tokyo Intermittent etching process
JPH07142776A (en) * 1993-11-16 1995-06-02 Hitachi Ltd Pattern formation method
JPH0883935A (en) * 1994-09-12 1996-03-26 Hitachi Ltd Superconducting circuit

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4790903A (en) * 1986-04-28 1988-12-13 University Of Tokyo Intermittent etching process
JPH07142776A (en) * 1993-11-16 1995-06-02 Hitachi Ltd Pattern formation method
JPH0883935A (en) * 1994-09-12 1996-03-26 Hitachi Ltd Superconducting circuit

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