CA2084551C - Connection of superconducting current paths formed of oxide superconductor material - Google Patents
Connection of superconducting current paths formed of oxide superconductor materialInfo
- Publication number
- CA2084551C CA2084551C CA002084551A CA2084551A CA2084551C CA 2084551 C CA2084551 C CA 2084551C CA 002084551 A CA002084551 A CA 002084551A CA 2084551 A CA2084551 A CA 2084551A CA 2084551 C CA2084551 C CA 2084551C
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- Prior art keywords
- superconducting
- oxide superconductor
- thin film
- substrate
- superconductor thin
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- 239000002887 superconductor Substances 0.000 title claims abstract description 149
- 239000000463 material Substances 0.000 title claims description 19
- 239000010409 thin film Substances 0.000 claims abstract description 74
- 239000000758 substrate Substances 0.000 claims abstract description 43
- 150000001875 compounds Chemical class 0.000 claims description 6
- 229910015901 Bi-Sr-Ca-Cu-O Inorganic materials 0.000 claims description 3
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical class [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 claims description 3
- 229910009203 Y-Ba-Cu-O Inorganic materials 0.000 claims description 3
- 230000005669 field effect Effects 0.000 claims description 3
- 239000004065 semiconductor Substances 0.000 description 12
- 238000004544 sputter deposition Methods 0.000 description 11
- 239000010408 film Substances 0.000 description 7
- 239000013078 crystal Substances 0.000 description 5
- 238000012545 processing Methods 0.000 description 5
- 229910052581 Si3N4 Inorganic materials 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 238000005530 etching Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 230000000149 penetrating effect Effects 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 239000012212 insulator Substances 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 238000000992 sputter etching Methods 0.000 description 2
- 101150090997 DLAT gene Proteins 0.000 description 1
- 230000005668 Josephson effect Effects 0.000 description 1
- 229910002370 SrTiO3 Inorganic materials 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000010884 ion-beam technique Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 238000001020 plasma etching Methods 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
Landscapes
- Superconductor Devices And Manufacturing Methods Thereof (AREA)
- Containers, Films, And Cooling For Superconductive Devices (AREA)
Abstract
A connection between a superconducting current path of an oxide superconductor thin film formed on a substrate through which superconducting current flows at a direction parallel to the substrate and another current path which is inclined at an angle less than 40° to the substrate so that the superconducting current path is smoothly connected to the other current path
Description
2~3~
SPECIFICATION
Title of the Invention CONNECTION OF SUPERCONDUCTING CURl~ENT
S PATHS FORMED OF OXIDE SUPERCONDUCTOR
MATERIAL
Background of the Invention Field of the invention The present inventioll relates to a connection of superconducting current paths formed of an oxide superconductor material. More specifically ~o ~ connection of superconducting current paths formed of an o~ide superconductor material, through which superconducting current flows efficiently.
Description of related art A superconducting current path is one of the electronic applications of a superconductor. If all the curlellt path~ of a conventional electronic - circuit including semiconductor devices is replaced with superconducting current paths, completely, the electronic circllit will operate rapidly with low power consumption. Superconducting signal paths are also expected to reduce the wave form distortion so that the required number of amplifiers and/or repeaters can be reduced. Particularly, by using an oxide superconductor material which has been recently advanced in study, 2~ it is possible to produce a superconducting current path through which superconducting current flows at relatively high temperature.
2 ~ B .Fi4 ~
In order to apply the superconduc~ing current path of an oxide superconductor to a superconducting circuit, the superconducting current path is connected to another one or an device. It should also be taken into consideration a superconducting multilayer interconnection utilizing the S oxide superconductor.
An oxide superconductor has the largest critical current density Jc in direction perpendicular to c-axes of its crystal lattices. Therefore, it is desirable that the superconducting current path through which superconducting current flows horizontally is formed of a c-axis 10 orientated oxide superconductor thin ~ïhn cmd the superconducting path through which superconductillg current flows vertically is folmed of oxide superconductor thin films of which the c-axis is orientated horizontally. ~n this specification, this oxide superconductor thin film of which the c-axis is orientated llorizontally will be called an "a-axis 15 orientated oxide superconductor thin film".
A Josephson junction device is one of superconducting devices - which is constituted of two superconducting electrodes joined by a Josephson junction. The Josephson 3unction can be realized in various structures. Among the various structures, the most preferable structure 20 in practice is a stacked junction realized by a tliin non-superconductor layer sandwiched between a pair of superconductors. However, a point contact type junction and a Dayem bridge type junction which are composed of a pair of superconductor regions which are weakly linked to each other also exhibit Josephson effect. In general, these Josephson 2 5 junctions have fine structures in which the superconductor and/or non-superconductor are composed of thin films.
- 2~8~
In order to realize a stacked type junction by using an oxide superconductor, a first oxide superconductor thin film, a non-superconductor thin film and a second oxide superconductor thin film are stacked on a substrate in the named order.
S In the above men~ioned stacked type junction, an insulator MgO
etc., a semiconductor Si etc., and a metal Au etc. are used for ~he non-superconductor layers so that each superconducting junction has different properties for each application.
The thickness of the non-superconduc~or layer of the stacked type 10 junction is deterrnined by the coherence length of the superconductor. ~n general, the thickness of the non-superconductor layer of the stacked type junction must be within a few times of the coherence length of the superconductor. On the other lland, since oxide superconductor materials have a very short coherence length, therefore, a thickness of a non-1 5 superconductor layer must be about a few nanometers.
However, the superconductor layers and the non-superconductor layer of the staclced type junction must be of high crystallinity for favorable junction properties, which are composed of single crystals or composed of polycrysta~s which are orientated in almost same direction.
2 0 It is difficult to stac3i an extremely thin and high crystalline non-superconductor layer on all oxide superconductor layer.
Additionally, it is very difficu It to st~ck a high crystalline oxide superconductor layer on the non-superconductor layer stacked on the first oxide superconductor layer. Thougll the stacked structure including a 2 5 first oxide superconductor layer, a non-superconductor layer and a second oxide superconductor layer is realized, the illterfaces between the oxide superconductor layers and the non-superconductor layer are not in good 2 ~
condition so that the stacked type jUIICtiOll does not function in good order.
In order to manufacture a point contact type junc~ion and a Dayem bridge type junction by using oxide superconductor, very fine processings S which re~lize a weak link between a pair of superconductor are necessary.
It is very difflcult to conduct a fine processing with good repeatability.
The point contact type jUIlCtiOIl has been formed of two oxide superconductor thin films which are in contact with each other in a -extremely small area which cons~itutes the weak lin~ of the Josephson 1 0 junction.
The Dayem bridge type junction has been iormed of a constant thickness oxide superconductor thill film which is formed on a su~strate and which is patterned in a plan view, so that a superconductor thin film region having a greatly narrow width is formed between a pair of 15 superconductor thin film regions having a sufficient width. In other words, the pair of superconductor thin film regions having a sufficient width are coupled to each other by the superconductor thin film region having the greatly narrow width. Namely, a weak link of the Josephson junction in the superconductor thin film is formed at the greatly narrow 2 0 width region.
In order to resolve the above mentio1led problems, so-called variable thickness bridge type ~osephson device is proposed in a prior art.
The variable thickness bridge type junction has been formed of an oxide superconductor thin film of a sufficient thicklless which is formed on a 2 S substrate having a projection and which is p~rtially thinned in a thickness direction on the projection of the substrate, so ~hat a thinned oxide superconductor thin film portion is formed between a pair of superconductor thin films having the sufficient thickness. In other words, the pair of superconductor thin film portions having the sufficient thickness are coupled to each other by the thinned oxide superconductor thin film portion. Accordingly, a weak link of the Josephson junction is S fo~ned at the reduced thickness portion of tlle oxide superconductor thin film.
No fine processing, which is required to manufacture a point contact type Josephson junction device or a Dayem bridge type Josephson junction device, is necessary to manufacture the above mentioned variable 10 thickness bridge type Josephson junctioll device Josephson device is one o~ well-known superconducting devices.
However, since Josephson device is a two-terminal device, a logic gate which utilizes Josephson devices becomes complicated. Therefore, three-teImina1 superconducting devices are more practical.
Typical three-terminal superconducting devices include two types of super-FFT (field effect transistor). The first type of the super-FET
includes a semiconductor channel, and a superconductor source electrode and a superconductor drain electrode which are formed closely to each other on both side of the semiconductor channel. A portion of the 2 0 semiconductor layer ~etween the superconductor source electrode and the superconductor drain electrode has a greatly recessed or undercut rear surface so as to have a reduced thickness. In addition, a gate electrode is ~ormed through a gate insulator layer on the portion of the recessed or undercut rear surface of the semiconductor layer between the 2 5 superconductor source electrode and the superconductor drain electrode.
A superconducting currellt flows through the semiconductor layer (channel) bet~Neen the superconductor source electrode and the ~'.;55~
superconductor drain electrode due to a superconducting proximity effect, and is controlled by an applied gate voltage. This type of the super-FET
operates at a higher speed wit.h a low power consumption.
7'he second type o~ the super-FET includes a channel of a S superconductor formed between a source electrode and a drain electrode, so that a current flowing through the superconducting channel is controlled by a voltage applied to a gate formed above the superconducting channel.
Both of the super-FETs mentioned above are voltage controlled devices which are capable of isola~ing output signal from input one and of h~ving a well defined gain.
However, since the first type of the super-FET utilizes the superconducting proximity effect, the superconductor source electrode and the superconductor drain electrode have to be positioned within a l S distance of a few times the coherence length of the superconductor materials of the superconductor source electrode and the superconductor drain electrode. In particular, since an oxide superconductor has a short coherence length, a distance between the superconductor source electrode and the superconductor drain electrode has to be made less than about a few ten nanometers, if the superconductor source electrode and the superconductor drain electrode are ~ormed of the oxide superconductor material. However, it is very difficult to conduct a fine processing such as a fine pattern etching, so as to satisfy the very short separation distance mentioned above~
On the other hand, the supel-FET having the superconducting channel has a large current capability, and the fine processing which is 2 ~
re~uired to product the first type of the super-FET is not needed to product ~is type of super-FET.
In order to obtain a complete ON/OFF operation, both of the superconducting channel and the gate insulating layer should have an 5 extremely thin thickness. For example, the superconducting channel formed of an oxide superconductor material should have a thickness of less than five nanometers and the gate insulating layer should have a ~ickness more than ten nanometers which is sufficient to prevent a tunnel current.
In a prior art, a superconducting multilayer interconnection which has layered superconducting current paths constituled of c-axis orientated oxide superconductor thin films and a superconducting interconnect current path constituted of an a-axis orientated oxide superconductor ~in film is proposed. However, grain boundaries are genera~ed at the 15 interface between the c-axis orientated oxide superconductor thin ~llm and the a-axis orientated oxide superconductor thin film, which introduce difficulties of supercol-ducting current flow. The grain bo~ndaries sometimes form Josephson junctions whicll pass only tunnel current so - that the current capability is lilnited and the input and output relationships20 become nonlinear. Even if no Josephson junction is formed at the interfaGe, Joule heat may be generated by the electrical resistance formed at the interface, which causes the "quench" phenomenon. Furthermore, the c-axis orientated oxide superconductor thin film and the a-axis orientated oxide superconductol thin film may interfere with each other 2 5 so as ~o degrade them both.
The above variable thickness bridge type Josephson device and superconducting field effect device have portions at which thickness of ~e oxide superconductor thin films decreases sharply. The directions of superconducting current flow suddenly change at these portions so that the superconducting current capability is limited by these portions of the oxide superconductor thin films.
In this case, the superconducting current does not always flow in the direction pel~..dicular to the c-axes of the oxide supercon~ ctQr crystals, so dlat the supercon~ cting cu~lell~ can not flow efficiently.
Summary of the Invention An object of the present invention is to provide a superconducting 10 device such as a Josephson junction device or an FET type device which addresses the above mentioned defects of the prior art.
According to the present invention there is provided a superconducting device comprising a substrate having a principal surface, an insulating region projected on the principal surface of the substrate and an 15 oxide superconductor thin film formed on the principal surface of the substrate, which has a planar surface, two thick portions at the both sides of the insulating region and one thin portion on the insulating region wherein :B
2n8~55~
the insulating region has a trapezoid shape cross section of which both opposite side surfaces are inclined at an angle of less than 40~ to the principal surface of the substrate in which the thick portions of the oxide superconductor thin film and the thin portion of the oxide superconductor 5 thin film are smoothly connected to each other along the inclined side surfaces of the insulating region so as to avoid abrupt change of sectional area of the oxide superconductor thin film so that current can efficiently flow between the thick portions and the thin portion.
In a preferred embodiment, the oxide superconductor is formed of 10 high-TC (high critical temperature) oxide superconductor, particularly, formed of a high-TC copper-oxide type compound oxide superconductor for example a Y-Ba-Cu-O compound oxide superconductor material and a Bi-Sr-Ca-Cu-O
compound oxide superconductor material.
In addition, the substrate can be formed of an insulating substrate, preferably an oxide single crystalline substrate such as MgO, SrTiO3, CdNdAl04, etc. These substrate materials are very effective in forming or growing a crystalline film having a high degree of crystalline orientation.
A superconducting circuit may comprise a substrate, a superconducting current path of an oxide superconductor thin film formed on the substrate 20 through which superconducting current flows at a direction parallel to the substrate and an electronic device connected to the superconducting current path in which the interface between the superconducting current path and the electronic device is inclined at an angle less than 40~ to the substrate so thatthe superconducting current path is smoothly connected to the electronic device.
A superconducting multilayer interconnection may comprise a substrate having a principal surface, a first superconducting current path of a c-axis orientated oxide superconductor thin film formed on the principal surface of the substrate, an insulating layer on the first superconducting current path and a second superconducting current path of a c-axis orientated oxide superconductor thin film formed on the insulating layer so that the first and second superconducting current paths are insulated by the insulating layer, in which the second superconducting current path has a portion which penetrates through the insulating layer and contact with the first superconducting current path and the portion is inclined at an angle less than 40~ to the substrate so that the first and second superconducting current paths are smoothly connected to each other.
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.
~ Q ~1 ~ 5 ~ ~
Brief Description of the Drawings Figure 1 is a diagrammatic enlarged sectional view of a characteristic part of an embodiment of the superconducting circuit;
Figure 2 is a diagrammatic sectional view of a first embodiment of the 5 superconducting multilayer interconnection;
Figure 3 is a diagrammatic sectional view of a second embodiment of the superconducting multilayer interconnection;
Figure 4 is a diagrammatic sectional view of an embodiment of the Josephson junction device in accordance with the present invention; and 10Figure 5 is a diagrammatic sectional view of an embodiment of the super-FET in accordance with the present invention.
Embodiment 1 Referring to Figure 1 an embodiment of a superconducting circuit will 15be described. Figure 1 shows a diagrammatic sectional view of a characteristic part of an embodiment of the superconducting circuit.
The superconducting circuit includes a resistor 40 of Y1Ba2Cu3O7 ~
oxide semiconductor arranged on a principal surface of an MgO (100) substrate 5 and superconducting current paths 11 and 12 of YlBa2Cu3O7 ~ oxide 20 superconductor, which are connected to the both ends of the resistor 40. Since the superconducting current paths 11 and 12 are connected to the resistor 40 in the same way, only the connection 30 of the superconducting current path 11 and the resistor 40 will be described.
~ ~ 8 ~ 5 5 ~ ' In the superconducting circuit, the superconducting current paths 11 and 12 ~-e formed of c a~ urlenhkd Y _ /
/
2~8~
superconductor thin films, since YlBa2Cu307 ~ oxide superconductor has the largest cIitical current density in the direction perpendicular to c-axes of its crystals. At the connection 30, the interface between the superconducting current path 11 and the resistor 40 is inclined at an angle a of 30~ to the principal surface of the substrate 5. Therefore, the superconducting current path 11 does not deform sharply so that the crystalline structure of the YIBa2Cu3O7 ~ oxide superconductor is not disordered at ~e connection 30.
The superconducting circuit was manufactured by the following 1 0 process.
At first, the resistor 40 was formed of a Y1Ba2Cu3O7 ~ oxide semiconductor thin film on the principal surface of the MgO (100) substrate 5. The Y~Ba2Cu3O7 ~ oxide semiconductor thin film was deposited by a sputtering and pattemed by a lift-off process utilizing CaO.
The condition of forming the YlBa2Cu3O7 ~ oxide semiconductor thin film is as follows:
Temperature of the substrate 800 ~C
Sputtering Gas Ar: 90%
~2: 10%
Total pressure 5 x l0-2 Torr Thickness of the thin film 300 nanometers The both ends of the pattemed YlBa2C~307 ~ oxide semiconductor thin film were processed by an ion beam etching so that the side surfaces of the edges were Inclined at angle of 30~ to the principal surface of the 2 5 substrate 5. Then, the resistor 40 was completed. The resistor 40 had a resistance of severa~ kQ.
~8~5 Thereafter, the superconducting current paths 11 and 12 were formed of c-axis orientated YIBa2Cu3O7~ oxide superconductor thin films on the principal surface of the substrate S. The c-axis orientated YlBa2Cu3O7~ oxide superconductor thin films were formed by a S sputtering. The condition of forming the c-axis orientated YlBa2Cu30 oxide superconductor ~in film by a sputtering is as follows:
Temperature of the substrate 700~C
Sputtering Gas Ar: 90%
~2: 10%
Total pressure S x lo-2 Torr Thickness of the thin film 300 nanometers A conventional superconducting circuit which had the same structure as that of the above superconducting circuit was also formed except a resistor didn't have processed edges. The resistance 1 5 measurements between the superconducting current paths 11 and 12 of the two superconducting circuit were made under liquid nitrogen cooling. In case of the superconducting circuit in accordance with the present invention, the resistance value was the same as that of the resistor 40 itself. On the contrary, in case of the conventional superconducting 20 circuit, the value of the resistance was ten times larger than that of the resistor. Therefore, in the superconducting circuit in accordance with the present invention, the interface between the superconducting current path and the resistor was improved.
2 S Embodiment 2 Referring to Figure 2 an embodiment of the superconducting multilayer interconnection will-' .~3 5 ~
be described. Figure 2 shows a diagrammatic sectional view of a characteristic part of an embodiment of the superconducting multilayer interconnection .
The superconducting multilayer interconnection includes a first 5 superconducting current path 11 formed of a c-axis orientated YlBa2Cu307 ~ oxide superconductor ~in film on a principal surface of an MgO substrate 5, an ins~ tin~ layer 21 formed of MgO or silicon nitride on the superconducting current path 11 and a second superconducting current path 12 formed of a c-axis orientated YlBa2Cu3O7 ~ oxide 10 superconductor thin film on the insulating layer 21. The substrate S may includes a ground plane. The superconducting current path 12 has a portion which constitutes an interconnect current path penetrating the insul~ting layer 21 and contacting to the superconducting current path 11 at a connection 30.
The interconnect current path portion of the superconducting current path 12 descends at an angle oc, penetrates the insulating layer 21, smoothly contacts to the superconducting current path 11 and ascends at an angle a. The angle oc should be less than 40~, otherwise the crystal structure of the c-axis orientated YlBa2Cu307 ~ oxide superconductor thin 20 film which constitutes the superconducting current path 12 becomes disordered at the interconnect current path portion.
Embodiment 3 Figure 3 shows another preferred embodiment of a 25 superconducting multilayer interconnection, which includes four layers of superconducting current paths and two interconnect current path portions.
2~345~1 The superconducting multilayer interconnection includes an MgO
substrate 5, insulating layers 21 to 24 and superconducting current paths 11 to 14 which are stacked alternately on the s~bstrate 5. The insulating layers 21 to 24 are formed of MgO or silicon nitride and the S superconducting c~lrrent paths 11 to 14 are formed of c-axis orientated YlBa2Cu307.~0xide superconductor thin films. The substrate 5 may include a ground plane. The superconducting current path 13 has a portion which constitutes an interconnect current path penetrating the insulating layer 23 ~nd smoothly contacting to the supercondllcting 10 current path 12 at a connection 31 and the superconducting current path 14 has a portion which constitutes an interconnect current path penetrating the insulating layer 24 and smoothly contacting to the superconducting current path 13 at a connection 32. The tilt angles oc of ~e interconnect current path portions of the superconducting multilayer 15 interconnection are less then 40~ as is dle same as Embodiment 2. The relation between distance Is between the connections 31 and 32 and the widths lc is as follows:
ls ~ 2.5 x lc to 3.0 x lc In the above superconducting multilayer interconnection, each of Z 0 the interconnect current paths connects the two neighboring superconducting current paths and does not connects three or more superconducting current paths. Since an interconnect current path which connects three or more superconducting current paths should require a large horizonta] cross-sectional area because of current capability 2 5 requirement, the dens~ty of ~he wiring is decreased. In addition, a large depression is ~ormed at an interconnect current path portion which connects three or more superconducting current paths so that it becomes 2~8~
different to stack another superconducting currellt path on it. Therefore, the ~nterconnect current path preferably connects only the two neighboring superconducting current paths.
In the above superconducting multilayer interconnection, a superconducting current path can be formed on a connection. Even a superconducting current path which cross a interconnection current path above it can be formed. Therefore, the superconducting multilayer interconnection in accordance with the present invention has a high degree of freedom of wiring superconducting current paths with interconnect cu~rent paths so that a complicated wiring and a high density wiring can be easily composed. Even if a complicated wiring is composed of the superconducting multilayer interconnection, the current capability does not decrease.
1 5 Embodiment 4 Referrillg to Figure 4 an embodiment of the Josephson iunction device in accordance with the present invention will be desc~ibed.
Figure 4 shows a diagrammalic sectional view of an embodiment of the Josephson junction device in accordallce with the present invention.
2 0 The Josephson junction device includes an MgO substra~e S having a projecting insulating region 50 of which the cross section is a shape of a trapezoid and superconducting electlodes 101 and 102 coupled to each other by a weak link l0 of a Joseph~on junction on the insulating region 50. Each of the surfaces 51 of the insu~ating region 50 is inclined at angle ocof35~.
The superconducting electrodes 101 and 102 and the weak link 10 are formed of a c-axis orientated YlBa2Cu307 ~ oxide superconductor thin 2~8~551 film, namely sufficiently thick portions of the c-axis orientated YlBa2Cu~O7 ~ oxide superconductor thin film constitute the superconducting electrodes 101 and 102 and a thin portion of the c-axis orientated YlB~2Cu307 ~ oxide superconductor thin film between the two thick portions constitutes the weak link 10. The c-axis orientated YlBa2Cu307 ~ oxide superconductor thin film is constituted of uniform crystalline YIBa2Cu307 ~oxide supercond~lctor even near the inclined surfaces 51 of the insulating region 50. The uniformity of the c-axis orient~ted YlBa2Cu3O7 ~ oxide superconductor thin film is achieved by the inclined angles o~ of 35~ of the sur~aces 51 of the insu}ating region 50.
Since the Josephsoll junction device is forrned of an uniform c-axis orientated YlBa2Cu3O7~0xide superconductor thin film and the the superconducting electrodes 101 and 102 are smoothly connected to the weak link portion 10, current flowing through the superconducting electrodes 101 and 102 efficiently flows into or from the weak link portion 10. Therefore, the ~osephson 3unction device has a high performance.
The Josephson junction device was manuf~ctured by the following process.
At first, an insulating region 50 having a height of 0.3 llm was formed by an ion-milling using Ar gas on a principal surface of an MgO (100) substrate 5 having a size of 15 mm x 8mm and a thickness of 0.5 mm. In order to incline the sur~aces 51 at angles a of 35~, the Ar ions were ~rradiated diagonally. The inclined surfaces 51 can also be 2 5 formed by a side-etching using a seeking effect of-e~chunt.
Then, the substrate S was heated to a temperature of 350 to 400 ~C
under a pressure lower than l x l0-'~ Torr in order to clean the etched surfaces. Thereafter, a c-axis orientated YIBa2Cu3O7 ~ oxide superconductor thin film was formed on the principal surface of the substrate S by a sputtering. The condition of forming the c-axis oricnt~te~ YlBa2Cu307 ~ oxide superconductor thin ~llm by a sputtering is S as follows:
Temperature of the substrate 700~C
Sputtering Gas Ar: 90%
~2: 10%
Total pressure 5 x 10-2 Torr Thickness of the thin film 3~0 nanometers Finally, the c-axis orientated Y~Ba2C~3O7 ~ oxide superconductor thin film was etched back so th~t a planar surface was fo~ned. Then, the Josephson junction device in accordance with the present invention was completed.
Embodiment 5 Referring to F~gure 5 an embodiment of the super-FET in accordance with the present invention will be described. Figure 5 shows a diagr~mm~tic sectional view of an embodiment of the super-FET in 2 0 accordance with the present invention.
The super-Fl~T includes an MgO subs~rate S having a projecting insulating region 50 of which the cross section is a shape of a trapezoid and a superconducting source region 2 and a superconducting drain region 3 electrically connected by a superconducting channe~ 1 on the 25 insulating region 50. ~ach of the surfaces 51 of the insulating region 50 is inclined at angle a o~ 35~.
2~551 The superconducting source region 2 ~nd the superconducting drain region 3 and the superconducting channel 1 are formed of a c-axis orientated YlBa2Cu3O7 ~oxide superconductor thin film, namely sufficiently thick portions of the c-axis orientated YIBa2Cu307 ~oxide - 5 superconductor thin film constitute the superconducting source region 2 and the superconducting drain region 3 and a thin portion of the c-axis orient~te~ YlBa2Cu307.~ oxide superconductor thin film between the thick portions constitutes the superconducting channel 1. The superconducting source region 2 and the superconductin~ drain region 3 have a thickness of on the order of 200 nanometers and the superconducting channel has a thickness of on the order of S nanometels. The gate insulating layer 7 is forrned of silicon nitride or MgO having a thickness of on the order of 15 nanometers. The gate electrode 4 is formed of Au.
The c-axis orientated YIBa2Cu307 ~ oxide superconductor thin film 1 5 is constituted of unif~rm crystalline ~IBa2Cu3O7 ~ oxide supe~conductor even near the inclined surfaces 51 of the insulating region 50. The uniformity of the c-axis orientated YlBa2Cu3O7.~oxide superconductor thin fi~m is achieved by the inclined angles oc of 35~ of the surfaces 51 of the insulating region 50.
2 0 Since the superconducting portion of the super-FET is formed of an uniforrn c-axis orientated YIBa2Cu3O7.~0xide superconductor thin film and the superconducting channel ~ is smoothly connected to the superconducting source region 2 and the superconducting drain region 3, ~ere is no undesired jUI7CtiOIl nor resistallce ~t this portion and current 2 5 flowing through the superconducting source region 2 and the superconducting drain region 3 efficiently flows into or from the 2 Q~
superconducting channel 1. Therefore, the super-FET has a high performance.
The super-FET was manufactured by the following process.
At first, an insulating region 50 having a trapezoid shape cross section was fo~ned by a reactive ion etching or an ion-milling using Ar gas on a principal surface of an MgO (100) substrate S. In order to incline the surfaces 51 at angles a of 35~, ions were irradiated diagonally.
Then, the substrate 5 was heated to a temperature of 350 to 400 ~C
under a pressure lower than 1 x 10-9 Torr in order to clean the etched surfaces. Thereafter, a c-axis orientated ~lBa2Cu3O7.~ oxide superconductor thin ~ilm was formed on the principal surface of the substrate 5 by a sputtering. The condition of forming the c-axis orientated YlBa2Cu3O7 ~ oxide superconductor thin film by a sputtering is as follows:
1 5 Temperature of the substra~e 700~C
Sputtering Gas Ar: 90%
~2 10%
Total pressure 5 x 10-2 Torr Thickness of the thin film 200 nanometers 2 0 Then, the c-axis orientated YlBa2Cu3O7.~ oxide superconductor thin film was etched back so that a planar surface was formed. Thick portions of the c-a~is orientated YIBa2Cu307 ~ oxide superconductor thin film at the both sides of the insulating region 50 would be a superconducting source region 2 and a superconducting drain region 3. A thin portion of 2 5 the c-axis orientated YIBa2Cu307 ~ oxide superconductor thin film on the insulating region 50 would be a superconducting channel 1. A gate ins~ ting layer 7 was formed of MgO or silicon nitride on a poltion of - 2l -2~8~
the c-axis orientated YlBa2Cu307 ~ oxide superconductor thin film above the insul~ing region 50 and a gate electrode 4 was formed of Au on the gate insulating layer 7. Metal electrodes might be formed on the superconducting source region 2 and superconducting drain region 3, if S necessary. Then, the super-FET in accordance with the present invention was completed.
In the above mentioned embodiments, the oxide superconductor thin fi~m can be formed of not only the Y-Ba-Cu-O compound oxlde superconductor material, but also a high-Tc (high critical temperature) 10 oxide superconductor material, particularly a high Tc copper-oxide type compound oxide superconductor material, for example a Bi-Sr-Ca-Cu-O
compound oxide superconductor material.
The invention has thus been shown and described with reference to the spec;fic embodiments. However, it should be noted that the present 15 invention is in no way limited to the details of the illustrated structures but converts and modifications may be made within the scope of the appended claims.
SPECIFICATION
Title of the Invention CONNECTION OF SUPERCONDUCTING CURl~ENT
S PATHS FORMED OF OXIDE SUPERCONDUCTOR
MATERIAL
Background of the Invention Field of the invention The present inventioll relates to a connection of superconducting current paths formed of an oxide superconductor material. More specifically ~o ~ connection of superconducting current paths formed of an o~ide superconductor material, through which superconducting current flows efficiently.
Description of related art A superconducting current path is one of the electronic applications of a superconductor. If all the curlellt path~ of a conventional electronic - circuit including semiconductor devices is replaced with superconducting current paths, completely, the electronic circllit will operate rapidly with low power consumption. Superconducting signal paths are also expected to reduce the wave form distortion so that the required number of amplifiers and/or repeaters can be reduced. Particularly, by using an oxide superconductor material which has been recently advanced in study, 2~ it is possible to produce a superconducting current path through which superconducting current flows at relatively high temperature.
2 ~ B .Fi4 ~
In order to apply the superconduc~ing current path of an oxide superconductor to a superconducting circuit, the superconducting current path is connected to another one or an device. It should also be taken into consideration a superconducting multilayer interconnection utilizing the S oxide superconductor.
An oxide superconductor has the largest critical current density Jc in direction perpendicular to c-axes of its crystal lattices. Therefore, it is desirable that the superconducting current path through which superconducting current flows horizontally is formed of a c-axis 10 orientated oxide superconductor thin ~ïhn cmd the superconducting path through which superconductillg current flows vertically is folmed of oxide superconductor thin films of which the c-axis is orientated horizontally. ~n this specification, this oxide superconductor thin film of which the c-axis is orientated llorizontally will be called an "a-axis 15 orientated oxide superconductor thin film".
A Josephson junction device is one of superconducting devices - which is constituted of two superconducting electrodes joined by a Josephson junction. The Josephson 3unction can be realized in various structures. Among the various structures, the most preferable structure 20 in practice is a stacked junction realized by a tliin non-superconductor layer sandwiched between a pair of superconductors. However, a point contact type junction and a Dayem bridge type junction which are composed of a pair of superconductor regions which are weakly linked to each other also exhibit Josephson effect. In general, these Josephson 2 5 junctions have fine structures in which the superconductor and/or non-superconductor are composed of thin films.
- 2~8~
In order to realize a stacked type junction by using an oxide superconductor, a first oxide superconductor thin film, a non-superconductor thin film and a second oxide superconductor thin film are stacked on a substrate in the named order.
S In the above men~ioned stacked type junction, an insulator MgO
etc., a semiconductor Si etc., and a metal Au etc. are used for ~he non-superconductor layers so that each superconducting junction has different properties for each application.
The thickness of the non-superconduc~or layer of the stacked type 10 junction is deterrnined by the coherence length of the superconductor. ~n general, the thickness of the non-superconductor layer of the stacked type junction must be within a few times of the coherence length of the superconductor. On the other lland, since oxide superconductor materials have a very short coherence length, therefore, a thickness of a non-1 5 superconductor layer must be about a few nanometers.
However, the superconductor layers and the non-superconductor layer of the staclced type junction must be of high crystallinity for favorable junction properties, which are composed of single crystals or composed of polycrysta~s which are orientated in almost same direction.
2 0 It is difficult to stac3i an extremely thin and high crystalline non-superconductor layer on all oxide superconductor layer.
Additionally, it is very difficu It to st~ck a high crystalline oxide superconductor layer on the non-superconductor layer stacked on the first oxide superconductor layer. Thougll the stacked structure including a 2 5 first oxide superconductor layer, a non-superconductor layer and a second oxide superconductor layer is realized, the illterfaces between the oxide superconductor layers and the non-superconductor layer are not in good 2 ~
condition so that the stacked type jUIICtiOll does not function in good order.
In order to manufacture a point contact type junc~ion and a Dayem bridge type junction by using oxide superconductor, very fine processings S which re~lize a weak link between a pair of superconductor are necessary.
It is very difflcult to conduct a fine processing with good repeatability.
The point contact type jUIlCtiOIl has been formed of two oxide superconductor thin films which are in contact with each other in a -extremely small area which cons~itutes the weak lin~ of the Josephson 1 0 junction.
The Dayem bridge type junction has been iormed of a constant thickness oxide superconductor thill film which is formed on a su~strate and which is patterned in a plan view, so that a superconductor thin film region having a greatly narrow width is formed between a pair of 15 superconductor thin film regions having a sufficient width. In other words, the pair of superconductor thin film regions having a sufficient width are coupled to each other by the superconductor thin film region having the greatly narrow width. Namely, a weak link of the Josephson junction in the superconductor thin film is formed at the greatly narrow 2 0 width region.
In order to resolve the above mentio1led problems, so-called variable thickness bridge type ~osephson device is proposed in a prior art.
The variable thickness bridge type junction has been formed of an oxide superconductor thin film of a sufficient thicklless which is formed on a 2 S substrate having a projection and which is p~rtially thinned in a thickness direction on the projection of the substrate, so ~hat a thinned oxide superconductor thin film portion is formed between a pair of superconductor thin films having the sufficient thickness. In other words, the pair of superconductor thin film portions having the sufficient thickness are coupled to each other by the thinned oxide superconductor thin film portion. Accordingly, a weak link of the Josephson junction is S fo~ned at the reduced thickness portion of tlle oxide superconductor thin film.
No fine processing, which is required to manufacture a point contact type Josephson junction device or a Dayem bridge type Josephson junction device, is necessary to manufacture the above mentioned variable 10 thickness bridge type Josephson junctioll device Josephson device is one o~ well-known superconducting devices.
However, since Josephson device is a two-terminal device, a logic gate which utilizes Josephson devices becomes complicated. Therefore, three-teImina1 superconducting devices are more practical.
Typical three-terminal superconducting devices include two types of super-FFT (field effect transistor). The first type of the super-FET
includes a semiconductor channel, and a superconductor source electrode and a superconductor drain electrode which are formed closely to each other on both side of the semiconductor channel. A portion of the 2 0 semiconductor layer ~etween the superconductor source electrode and the superconductor drain electrode has a greatly recessed or undercut rear surface so as to have a reduced thickness. In addition, a gate electrode is ~ormed through a gate insulator layer on the portion of the recessed or undercut rear surface of the semiconductor layer between the 2 5 superconductor source electrode and the superconductor drain electrode.
A superconducting currellt flows through the semiconductor layer (channel) bet~Neen the superconductor source electrode and the ~'.;55~
superconductor drain electrode due to a superconducting proximity effect, and is controlled by an applied gate voltage. This type of the super-FET
operates at a higher speed wit.h a low power consumption.
7'he second type o~ the super-FET includes a channel of a S superconductor formed between a source electrode and a drain electrode, so that a current flowing through the superconducting channel is controlled by a voltage applied to a gate formed above the superconducting channel.
Both of the super-FETs mentioned above are voltage controlled devices which are capable of isola~ing output signal from input one and of h~ving a well defined gain.
However, since the first type of the super-FET utilizes the superconducting proximity effect, the superconductor source electrode and the superconductor drain electrode have to be positioned within a l S distance of a few times the coherence length of the superconductor materials of the superconductor source electrode and the superconductor drain electrode. In particular, since an oxide superconductor has a short coherence length, a distance between the superconductor source electrode and the superconductor drain electrode has to be made less than about a few ten nanometers, if the superconductor source electrode and the superconductor drain electrode are ~ormed of the oxide superconductor material. However, it is very difficult to conduct a fine processing such as a fine pattern etching, so as to satisfy the very short separation distance mentioned above~
On the other hand, the supel-FET having the superconducting channel has a large current capability, and the fine processing which is 2 ~
re~uired to product the first type of the super-FET is not needed to product ~is type of super-FET.
In order to obtain a complete ON/OFF operation, both of the superconducting channel and the gate insulating layer should have an 5 extremely thin thickness. For example, the superconducting channel formed of an oxide superconductor material should have a thickness of less than five nanometers and the gate insulating layer should have a ~ickness more than ten nanometers which is sufficient to prevent a tunnel current.
In a prior art, a superconducting multilayer interconnection which has layered superconducting current paths constituled of c-axis orientated oxide superconductor thin films and a superconducting interconnect current path constituted of an a-axis orientated oxide superconductor ~in film is proposed. However, grain boundaries are genera~ed at the 15 interface between the c-axis orientated oxide superconductor thin ~llm and the a-axis orientated oxide superconductor thin film, which introduce difficulties of supercol-ducting current flow. The grain bo~ndaries sometimes form Josephson junctions whicll pass only tunnel current so - that the current capability is lilnited and the input and output relationships20 become nonlinear. Even if no Josephson junction is formed at the interfaGe, Joule heat may be generated by the electrical resistance formed at the interface, which causes the "quench" phenomenon. Furthermore, the c-axis orientated oxide superconductor thin film and the a-axis orientated oxide superconductol thin film may interfere with each other 2 5 so as ~o degrade them both.
The above variable thickness bridge type Josephson device and superconducting field effect device have portions at which thickness of ~e oxide superconductor thin films decreases sharply. The directions of superconducting current flow suddenly change at these portions so that the superconducting current capability is limited by these portions of the oxide superconductor thin films.
In this case, the superconducting current does not always flow in the direction pel~..dicular to the c-axes of the oxide supercon~ ctQr crystals, so dlat the supercon~ cting cu~lell~ can not flow efficiently.
Summary of the Invention An object of the present invention is to provide a superconducting 10 device such as a Josephson junction device or an FET type device which addresses the above mentioned defects of the prior art.
According to the present invention there is provided a superconducting device comprising a substrate having a principal surface, an insulating region projected on the principal surface of the substrate and an 15 oxide superconductor thin film formed on the principal surface of the substrate, which has a planar surface, two thick portions at the both sides of the insulating region and one thin portion on the insulating region wherein :B
2n8~55~
the insulating region has a trapezoid shape cross section of which both opposite side surfaces are inclined at an angle of less than 40~ to the principal surface of the substrate in which the thick portions of the oxide superconductor thin film and the thin portion of the oxide superconductor 5 thin film are smoothly connected to each other along the inclined side surfaces of the insulating region so as to avoid abrupt change of sectional area of the oxide superconductor thin film so that current can efficiently flow between the thick portions and the thin portion.
In a preferred embodiment, the oxide superconductor is formed of 10 high-TC (high critical temperature) oxide superconductor, particularly, formed of a high-TC copper-oxide type compound oxide superconductor for example a Y-Ba-Cu-O compound oxide superconductor material and a Bi-Sr-Ca-Cu-O
compound oxide superconductor material.
In addition, the substrate can be formed of an insulating substrate, preferably an oxide single crystalline substrate such as MgO, SrTiO3, CdNdAl04, etc. These substrate materials are very effective in forming or growing a crystalline film having a high degree of crystalline orientation.
A superconducting circuit may comprise a substrate, a superconducting current path of an oxide superconductor thin film formed on the substrate 20 through which superconducting current flows at a direction parallel to the substrate and an electronic device connected to the superconducting current path in which the interface between the superconducting current path and the electronic device is inclined at an angle less than 40~ to the substrate so thatthe superconducting current path is smoothly connected to the electronic device.
A superconducting multilayer interconnection may comprise a substrate having a principal surface, a first superconducting current path of a c-axis orientated oxide superconductor thin film formed on the principal surface of the substrate, an insulating layer on the first superconducting current path and a second superconducting current path of a c-axis orientated oxide superconductor thin film formed on the insulating layer so that the first and second superconducting current paths are insulated by the insulating layer, in which the second superconducting current path has a portion which penetrates through the insulating layer and contact with the first superconducting current path and the portion is inclined at an angle less than 40~ to the substrate so that the first and second superconducting current paths are smoothly connected to each other.
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.
~ Q ~1 ~ 5 ~ ~
Brief Description of the Drawings Figure 1 is a diagrammatic enlarged sectional view of a characteristic part of an embodiment of the superconducting circuit;
Figure 2 is a diagrammatic sectional view of a first embodiment of the 5 superconducting multilayer interconnection;
Figure 3 is a diagrammatic sectional view of a second embodiment of the superconducting multilayer interconnection;
Figure 4 is a diagrammatic sectional view of an embodiment of the Josephson junction device in accordance with the present invention; and 10Figure 5 is a diagrammatic sectional view of an embodiment of the super-FET in accordance with the present invention.
Embodiment 1 Referring to Figure 1 an embodiment of a superconducting circuit will 15be described. Figure 1 shows a diagrammatic sectional view of a characteristic part of an embodiment of the superconducting circuit.
The superconducting circuit includes a resistor 40 of Y1Ba2Cu3O7 ~
oxide semiconductor arranged on a principal surface of an MgO (100) substrate 5 and superconducting current paths 11 and 12 of YlBa2Cu3O7 ~ oxide 20 superconductor, which are connected to the both ends of the resistor 40. Since the superconducting current paths 11 and 12 are connected to the resistor 40 in the same way, only the connection 30 of the superconducting current path 11 and the resistor 40 will be described.
~ ~ 8 ~ 5 5 ~ ' In the superconducting circuit, the superconducting current paths 11 and 12 ~-e formed of c a~ urlenhkd Y _ /
/
2~8~
superconductor thin films, since YlBa2Cu307 ~ oxide superconductor has the largest cIitical current density in the direction perpendicular to c-axes of its crystals. At the connection 30, the interface between the superconducting current path 11 and the resistor 40 is inclined at an angle a of 30~ to the principal surface of the substrate 5. Therefore, the superconducting current path 11 does not deform sharply so that the crystalline structure of the YIBa2Cu3O7 ~ oxide superconductor is not disordered at ~e connection 30.
The superconducting circuit was manufactured by the following 1 0 process.
At first, the resistor 40 was formed of a Y1Ba2Cu3O7 ~ oxide semiconductor thin film on the principal surface of the MgO (100) substrate 5. The Y~Ba2Cu3O7 ~ oxide semiconductor thin film was deposited by a sputtering and pattemed by a lift-off process utilizing CaO.
The condition of forming the YlBa2Cu3O7 ~ oxide semiconductor thin film is as follows:
Temperature of the substrate 800 ~C
Sputtering Gas Ar: 90%
~2: 10%
Total pressure 5 x l0-2 Torr Thickness of the thin film 300 nanometers The both ends of the pattemed YlBa2C~307 ~ oxide semiconductor thin film were processed by an ion beam etching so that the side surfaces of the edges were Inclined at angle of 30~ to the principal surface of the 2 5 substrate 5. Then, the resistor 40 was completed. The resistor 40 had a resistance of severa~ kQ.
~8~5 Thereafter, the superconducting current paths 11 and 12 were formed of c-axis orientated YIBa2Cu3O7~ oxide superconductor thin films on the principal surface of the substrate S. The c-axis orientated YlBa2Cu3O7~ oxide superconductor thin films were formed by a S sputtering. The condition of forming the c-axis orientated YlBa2Cu30 oxide superconductor ~in film by a sputtering is as follows:
Temperature of the substrate 700~C
Sputtering Gas Ar: 90%
~2: 10%
Total pressure S x lo-2 Torr Thickness of the thin film 300 nanometers A conventional superconducting circuit which had the same structure as that of the above superconducting circuit was also formed except a resistor didn't have processed edges. The resistance 1 5 measurements between the superconducting current paths 11 and 12 of the two superconducting circuit were made under liquid nitrogen cooling. In case of the superconducting circuit in accordance with the present invention, the resistance value was the same as that of the resistor 40 itself. On the contrary, in case of the conventional superconducting 20 circuit, the value of the resistance was ten times larger than that of the resistor. Therefore, in the superconducting circuit in accordance with the present invention, the interface between the superconducting current path and the resistor was improved.
2 S Embodiment 2 Referring to Figure 2 an embodiment of the superconducting multilayer interconnection will-' .~3 5 ~
be described. Figure 2 shows a diagrammatic sectional view of a characteristic part of an embodiment of the superconducting multilayer interconnection .
The superconducting multilayer interconnection includes a first 5 superconducting current path 11 formed of a c-axis orientated YlBa2Cu307 ~ oxide superconductor ~in film on a principal surface of an MgO substrate 5, an ins~ tin~ layer 21 formed of MgO or silicon nitride on the superconducting current path 11 and a second superconducting current path 12 formed of a c-axis orientated YlBa2Cu3O7 ~ oxide 10 superconductor thin film on the insulating layer 21. The substrate S may includes a ground plane. The superconducting current path 12 has a portion which constitutes an interconnect current path penetrating the insul~ting layer 21 and contacting to the superconducting current path 11 at a connection 30.
The interconnect current path portion of the superconducting current path 12 descends at an angle oc, penetrates the insulating layer 21, smoothly contacts to the superconducting current path 11 and ascends at an angle a. The angle oc should be less than 40~, otherwise the crystal structure of the c-axis orientated YlBa2Cu307 ~ oxide superconductor thin 20 film which constitutes the superconducting current path 12 becomes disordered at the interconnect current path portion.
Embodiment 3 Figure 3 shows another preferred embodiment of a 25 superconducting multilayer interconnection, which includes four layers of superconducting current paths and two interconnect current path portions.
2~345~1 The superconducting multilayer interconnection includes an MgO
substrate 5, insulating layers 21 to 24 and superconducting current paths 11 to 14 which are stacked alternately on the s~bstrate 5. The insulating layers 21 to 24 are formed of MgO or silicon nitride and the S superconducting c~lrrent paths 11 to 14 are formed of c-axis orientated YlBa2Cu307.~0xide superconductor thin films. The substrate 5 may include a ground plane. The superconducting current path 13 has a portion which constitutes an interconnect current path penetrating the insulating layer 23 ~nd smoothly contacting to the supercondllcting 10 current path 12 at a connection 31 and the superconducting current path 14 has a portion which constitutes an interconnect current path penetrating the insulating layer 24 and smoothly contacting to the superconducting current path 13 at a connection 32. The tilt angles oc of ~e interconnect current path portions of the superconducting multilayer 15 interconnection are less then 40~ as is dle same as Embodiment 2. The relation between distance Is between the connections 31 and 32 and the widths lc is as follows:
ls ~ 2.5 x lc to 3.0 x lc In the above superconducting multilayer interconnection, each of Z 0 the interconnect current paths connects the two neighboring superconducting current paths and does not connects three or more superconducting current paths. Since an interconnect current path which connects three or more superconducting current paths should require a large horizonta] cross-sectional area because of current capability 2 5 requirement, the dens~ty of ~he wiring is decreased. In addition, a large depression is ~ormed at an interconnect current path portion which connects three or more superconducting current paths so that it becomes 2~8~
different to stack another superconducting currellt path on it. Therefore, the ~nterconnect current path preferably connects only the two neighboring superconducting current paths.
In the above superconducting multilayer interconnection, a superconducting current path can be formed on a connection. Even a superconducting current path which cross a interconnection current path above it can be formed. Therefore, the superconducting multilayer interconnection in accordance with the present invention has a high degree of freedom of wiring superconducting current paths with interconnect cu~rent paths so that a complicated wiring and a high density wiring can be easily composed. Even if a complicated wiring is composed of the superconducting multilayer interconnection, the current capability does not decrease.
1 5 Embodiment 4 Referrillg to Figure 4 an embodiment of the Josephson iunction device in accordance with the present invention will be desc~ibed.
Figure 4 shows a diagrammalic sectional view of an embodiment of the Josephson junction device in accordallce with the present invention.
2 0 The Josephson junction device includes an MgO substra~e S having a projecting insulating region 50 of which the cross section is a shape of a trapezoid and superconducting electlodes 101 and 102 coupled to each other by a weak link l0 of a Joseph~on junction on the insulating region 50. Each of the surfaces 51 of the insu~ating region 50 is inclined at angle ocof35~.
The superconducting electrodes 101 and 102 and the weak link 10 are formed of a c-axis orientated YlBa2Cu307 ~ oxide superconductor thin 2~8~551 film, namely sufficiently thick portions of the c-axis orientated YlBa2Cu~O7 ~ oxide superconductor thin film constitute the superconducting electrodes 101 and 102 and a thin portion of the c-axis orientated YlB~2Cu307 ~ oxide superconductor thin film between the two thick portions constitutes the weak link 10. The c-axis orientated YlBa2Cu307 ~ oxide superconductor thin film is constituted of uniform crystalline YIBa2Cu307 ~oxide supercond~lctor even near the inclined surfaces 51 of the insulating region 50. The uniformity of the c-axis orient~ted YlBa2Cu3O7 ~ oxide superconductor thin film is achieved by the inclined angles o~ of 35~ of the sur~aces 51 of the insu}ating region 50.
Since the Josephsoll junction device is forrned of an uniform c-axis orientated YlBa2Cu3O7~0xide superconductor thin film and the the superconducting electrodes 101 and 102 are smoothly connected to the weak link portion 10, current flowing through the superconducting electrodes 101 and 102 efficiently flows into or from the weak link portion 10. Therefore, the ~osephson 3unction device has a high performance.
The Josephson junction device was manuf~ctured by the following process.
At first, an insulating region 50 having a height of 0.3 llm was formed by an ion-milling using Ar gas on a principal surface of an MgO (100) substrate 5 having a size of 15 mm x 8mm and a thickness of 0.5 mm. In order to incline the sur~aces 51 at angles a of 35~, the Ar ions were ~rradiated diagonally. The inclined surfaces 51 can also be 2 5 formed by a side-etching using a seeking effect of-e~chunt.
Then, the substrate S was heated to a temperature of 350 to 400 ~C
under a pressure lower than l x l0-'~ Torr in order to clean the etched surfaces. Thereafter, a c-axis orientated YIBa2Cu3O7 ~ oxide superconductor thin film was formed on the principal surface of the substrate S by a sputtering. The condition of forming the c-axis oricnt~te~ YlBa2Cu307 ~ oxide superconductor thin ~llm by a sputtering is S as follows:
Temperature of the substrate 700~C
Sputtering Gas Ar: 90%
~2: 10%
Total pressure 5 x 10-2 Torr Thickness of the thin film 3~0 nanometers Finally, the c-axis orientated Y~Ba2C~3O7 ~ oxide superconductor thin film was etched back so th~t a planar surface was fo~ned. Then, the Josephson junction device in accordance with the present invention was completed.
Embodiment 5 Referring to F~gure 5 an embodiment of the super-FET in accordance with the present invention will be described. Figure 5 shows a diagr~mm~tic sectional view of an embodiment of the super-FET in 2 0 accordance with the present invention.
The super-Fl~T includes an MgO subs~rate S having a projecting insulating region 50 of which the cross section is a shape of a trapezoid and a superconducting source region 2 and a superconducting drain region 3 electrically connected by a superconducting channe~ 1 on the 25 insulating region 50. ~ach of the surfaces 51 of the insulating region 50 is inclined at angle a o~ 35~.
2~551 The superconducting source region 2 ~nd the superconducting drain region 3 and the superconducting channel 1 are formed of a c-axis orientated YlBa2Cu3O7 ~oxide superconductor thin film, namely sufficiently thick portions of the c-axis orientated YIBa2Cu307 ~oxide - 5 superconductor thin film constitute the superconducting source region 2 and the superconducting drain region 3 and a thin portion of the c-axis orient~te~ YlBa2Cu307.~ oxide superconductor thin film between the thick portions constitutes the superconducting channel 1. The superconducting source region 2 and the superconductin~ drain region 3 have a thickness of on the order of 200 nanometers and the superconducting channel has a thickness of on the order of S nanometels. The gate insulating layer 7 is forrned of silicon nitride or MgO having a thickness of on the order of 15 nanometers. The gate electrode 4 is formed of Au.
The c-axis orientated YIBa2Cu307 ~ oxide superconductor thin film 1 5 is constituted of unif~rm crystalline ~IBa2Cu3O7 ~ oxide supe~conductor even near the inclined surfaces 51 of the insulating region 50. The uniformity of the c-axis orientated YlBa2Cu3O7.~oxide superconductor thin fi~m is achieved by the inclined angles oc of 35~ of the surfaces 51 of the insulating region 50.
2 0 Since the superconducting portion of the super-FET is formed of an uniforrn c-axis orientated YIBa2Cu3O7.~0xide superconductor thin film and the superconducting channel ~ is smoothly connected to the superconducting source region 2 and the superconducting drain region 3, ~ere is no undesired jUI7CtiOIl nor resistallce ~t this portion and current 2 5 flowing through the superconducting source region 2 and the superconducting drain region 3 efficiently flows into or from the 2 Q~
superconducting channel 1. Therefore, the super-FET has a high performance.
The super-FET was manufactured by the following process.
At first, an insulating region 50 having a trapezoid shape cross section was fo~ned by a reactive ion etching or an ion-milling using Ar gas on a principal surface of an MgO (100) substrate S. In order to incline the surfaces 51 at angles a of 35~, ions were irradiated diagonally.
Then, the substrate 5 was heated to a temperature of 350 to 400 ~C
under a pressure lower than 1 x 10-9 Torr in order to clean the etched surfaces. Thereafter, a c-axis orientated ~lBa2Cu3O7.~ oxide superconductor thin ~ilm was formed on the principal surface of the substrate 5 by a sputtering. The condition of forming the c-axis orientated YlBa2Cu3O7 ~ oxide superconductor thin film by a sputtering is as follows:
1 5 Temperature of the substra~e 700~C
Sputtering Gas Ar: 90%
~2 10%
Total pressure 5 x 10-2 Torr Thickness of the thin film 200 nanometers 2 0 Then, the c-axis orientated YlBa2Cu3O7.~ oxide superconductor thin film was etched back so that a planar surface was formed. Thick portions of the c-a~is orientated YIBa2Cu307 ~ oxide superconductor thin film at the both sides of the insulating region 50 would be a superconducting source region 2 and a superconducting drain region 3. A thin portion of 2 5 the c-axis orientated YIBa2Cu307 ~ oxide superconductor thin film on the insulating region 50 would be a superconducting channel 1. A gate ins~ ting layer 7 was formed of MgO or silicon nitride on a poltion of - 2l -2~8~
the c-axis orientated YlBa2Cu307 ~ oxide superconductor thin film above the insul~ing region 50 and a gate electrode 4 was formed of Au on the gate insulating layer 7. Metal electrodes might be formed on the superconducting source region 2 and superconducting drain region 3, if S necessary. Then, the super-FET in accordance with the present invention was completed.
In the above mentioned embodiments, the oxide superconductor thin fi~m can be formed of not only the Y-Ba-Cu-O compound oxlde superconductor material, but also a high-Tc (high critical temperature) 10 oxide superconductor material, particularly a high Tc copper-oxide type compound oxide superconductor material, for example a Bi-Sr-Ca-Cu-O
compound oxide superconductor material.
The invention has thus been shown and described with reference to the spec;fic embodiments. However, it should be noted that the present 15 invention is in no way limited to the details of the illustrated structures but converts and modifications may be made within the scope of the appended claims.
Claims (5)
1. A superconducting device comprising a substrate having a principal surface, an insulating region projected on the principal surface of the substrate and an oxide superconductor thin film formed on the principal surface of the substrate, which has a planar surface, two thick portions at the both sides of the insulating region and one thin portion on the insulating region wherein the insulating region has a trapezoid shape cross section of which both opposite side surfaces are inclined at an angle of less than 40° to the principal surface of the substrate in which the thick portions of the oxide superconductor thin film and the thin portion of the oxide superconductor thin film are smoothly connected each other along the inclined side surfaces of the insulating region so as to avoid abrupt change of sectional area of the oxide superconductor thin film so that current can efficiently flows between the thick portions and the thin portion .
2. A superconducting device as claimed in Claim 1 wherein the oxide superconductor thin film is formed of high-Tc (high critical temperature) oxide superconductor, particularly, formed of a high-Tc copper-oxide type compound oxide superconductor.
3 A superconducting device as claimed in Claim 2 wherein the oxide superconductor thin film is formed of oxide superconductor material selected from the group consisting of a Y-Ba-Cu-O compound oxide superconductor material and a Bi-Sr-Ca-Cu-O compound oxide superconductor material.
4. A superconducting device as claimed in Claim 1 wherein the thick portions of the oxide superconductor thin film constitute superconducting electrodes and the thin portion of the oxide superconductor thin film constitutes a weak link of a Josephson junction so as to form a Josephson junction device.
5. A superconducting device as claimed in Claim 1 wherein the device further comprises a gate electrode on the thin portion of the oxide superconductor thin film though a gate insulating layer in which the thick portions of the oxide superconductor thin film constitute a superconducting source region and a superconducting drain region, and the thin portion of the oxide superconductor thin film constitutes a superconducting channel and current flowing between the superconducting source region and the superconducting drain region through the superconducting channel is controlled by a signal voltage applied to the gate electrode so as to form a superconducting field effect device.
Applications Claiming Priority (8)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP34875791 | 1991-12-05 | ||
| JP348757/1991 | 1991-12-05 | ||
| JP34896591 | 1991-12-06 | ||
| JP348965/1991 | 1991-12-06 | ||
| JP35030291 | 1991-12-09 | ||
| JP350302/1991 | 1991-12-09 | ||
| JP352195/1991 | 1991-12-13 | ||
| JP35219591 | 1991-12-13 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2084551A1 CA2084551A1 (en) | 1993-06-06 |
| CA2084551C true CA2084551C (en) | 1998-04-21 |
Family
ID=27480693
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002084551A Expired - Fee Related CA2084551C (en) | 1991-12-05 | 1992-12-04 | Connection of superconducting current paths formed of oxide superconductor material |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH05251769A (en) |
| CA (1) | CA2084551C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2740460B2 (en) * | 1994-12-07 | 1998-04-15 | 株式会社日立製作所 | Superconducting circuit |
-
1992
- 1992-12-03 JP JP4350407A patent/JPH05251769A/en not_active Withdrawn
- 1992-12-04 CA CA002084551A patent/CA2084551C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
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| JPH05251769A (en) | 1993-09-28 |
| CA2084551A1 (en) | 1993-06-06 |
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