CA2195809A1 - Superconducting device having an extremely thin superconducting channel formed of oxide superconductor material and method for manufacturing the same - Google Patents
Superconducting device having an extremely thin superconducting channel formed of oxide superconductor material and method for manufacturing the sameInfo
- Publication number
- CA2195809A1 CA2195809A1 CA002195809A CA2195809A CA2195809A1 CA 2195809 A1 CA2195809 A1 CA 2195809A1 CA 002195809 A CA002195809 A CA 002195809A CA 2195809 A CA2195809 A CA 2195809A CA 2195809 A1 CA2195809 A1 CA 2195809A1
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- Prior art keywords
- superconducting
- layer
- oxide superconductor
- thin film
- channel
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Links
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- 238000000034 method Methods 0.000 title claims description 38
- 238000004519 manufacturing process Methods 0.000 title claims description 19
- 239000000463 material Substances 0.000 title description 16
- 239000010409 thin film Substances 0.000 claims abstract description 105
- 239000000758 substrate Substances 0.000 claims abstract description 58
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 16
- 238000005530 etching Methods 0.000 claims description 11
- 239000002184 metal Substances 0.000 claims description 11
- 229910052681 coesite Inorganic materials 0.000 claims description 8
- 229910052906 cristobalite Inorganic materials 0.000 claims description 8
- 239000000377 silicon dioxide Substances 0.000 claims description 8
- 235000012239 silicon dioxide Nutrition 0.000 claims description 8
- 229910052682 stishovite Inorganic materials 0.000 claims description 8
- 229910052905 tridymite Inorganic materials 0.000 claims description 8
- 239000012212 insulator Substances 0.000 claims description 4
- 239000013078 crystal Substances 0.000 abstract description 10
- 238000001451 molecular beam epitaxy Methods 0.000 description 16
- 150000002500 ions Chemical class 0.000 description 15
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 12
- 238000004544 sputter deposition Methods 0.000 description 8
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 6
- 239000004065 semiconductor Substances 0.000 description 6
- 229910001868 water Inorganic materials 0.000 description 6
- 150000001875 compounds Chemical class 0.000 description 5
- 238000012545 processing Methods 0.000 description 5
- 229910002370 SrTiO3 Inorganic materials 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 229910052581 Si3N4 Inorganic materials 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 238000010884 ion-beam technique Methods 0.000 description 3
- 238000007738 vacuum evaporation Methods 0.000 description 3
- 229910015901 Bi-Sr-Ca-Cu-O Inorganic materials 0.000 description 2
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical class [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 description 2
- 229910002480 Cu-O Inorganic materials 0.000 description 2
- 229910009203 Y-Ba-Cu-O Inorganic materials 0.000 description 2
- 229910001422 barium ion Inorganic materials 0.000 description 2
- 229910001417 caesium ion Inorganic materials 0.000 description 2
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 2
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- 238000001312 dry etching Methods 0.000 description 1
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- Superconductor Devices And Manufacturing Methods Thereof (AREA)
Abstract
A superconducting device comprising a substrate having a principal surface, a non-superconducting oxide layer having a similar crystal structure to that of the oxide superconductor, a first and a second superconducting regions formed of c-axis oriented oxide superconductor thin films on the non-superconducting oxide layer separated from each other and gently inclining to each other, a third superconducting region formed of an extremely thin c-axis oriented oxide superconductor thin film between the first and the second superconducting regions, which is continuous to the first and the second superconducting regions.
Description
21 q5~0~
SPECIFICATION
Tille of the Invention SUPE~CONDUCTING DEVICE HAVING AN
S EXTREMELY THIN SUPERCONDUCTING CHANNEL
FORMED OF OXIDE SUPERCONDUCTOR MATERIAL
AND METHOD FOR MANUFACTURING THE SAME
Background of the Invention Field of the invention The present invention relates to a superconducting device and a me thod for manufacturing the same, and more specifically to a superconducting device having an extremely thin superconducting ch~nnel formed of oxide superconductor material, and a method for manufacturing the same.
Description of related art Devices which utilize superconducting phenomena operate rapidly with low power consumption so that they have higher performance than conventional semiconductor devices. Particularly, by using an oxide superconducting material which has been recently advanced in study, it is pos,sible to produce a superconducting device which operates at relatively high temperature.
Josephson device is one of well-known superconducting devices.
However, since Josephson device is a two-terminal device, a logic gate which utilizes Josephson devices becomes complicated configuration.
Therefore, three-terminal superconducting devices are more practical.
21 9580q Typical three-terminal superconducting devices include two types of super-FET (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 S other on both side of the semiconductor channel. A portion of these]~iconductor layer between the superconductor source electrode and dle superconductor drain electrode has a greatly recessed or undercut rear surface so as to have a reduced thickness. In addition, a gate electrode is fo]med through a gate insulating layer on the portion of the recessed or undercut rear surface of the semiconductor layer between the superconductor source electrode and the superconductor drain electrode.
A superconducting current flows through the semiconductor layer (channel) between the superconductor source electrode and the superconductor drain electrode due to the superconducting proximity effect, and is controlled by an applied gate voltage. This type of the super-FET operates at a higher speed with a low power consumption.
The second type of the super-FET includes a channel of a superconductor formed between a source electrode and a drain electrode, so that a current flowing through the superconducting channel is 2 0 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 isolating output signal from input one and of having a well defined gain.
2 5 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 21 9~9 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 leng~, a distance between the superconductor source electrode S and ~e superconductor drain electrode has to be made less than about a fe~w ten nanometers, if the superconductor source electrode and the sujperconductor drain electrode are formed 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 10 mentioned above.
On the other hand, the super-FET having the superconducting channel has a large current capability, and the fine processing which is required to product the first type of the super-FET is not needed to product this type of super-FET.
In order to obtain a complete ON/OFF operation, both of the su]perconducting channel and the gate insulating layer should have an extremely thin thickness. For example, the superconducting channel formed of an oxide superconductor material should have a thickness of les,s than five nanometers and the gate insulating layer should have a 2 0 thickness more than ten nanometers which is sufficient to prevent a tunnel cu rrent.
In the super-FET, since the extremely thin superconducting channel is Iconnected to the relatively thick superconducting source region and the superconducting drain region at their lower portions, the superconducting 25 culrrent flows substantially horizontally through the superconducting ch;mnel and subst~nti~lly vertically in the superconducting source region an~ the superconducting drain region. Since the oxide superconductor has 21 ~80~ 1 the largest critical current density Jc in the direction perpendicular to c-axes of its crystal lattices, the superconducting channel is preferably fol~ned of a c-axis oriented oxide superconductor thin film and the superconducting source region and the superconducting drain region are S pre:ferably fornned of a-a~is oriented oxide superconductor thin films.
~ a prior art, in order to manufacture the super-FET which has the superconducting channel of c-axis oriented oxide superconductor thin film and the superconducting source region and the superconducting drain region of a-axis oriented oxide superconductor thin films, a c-axis oriented oxide superconductor thin film is formed at first and the c-axis ori,ented oxide superconductor thin film is etched and removed excluding a por~tion which will be the superconducting channel. Then, an a-axis oriented oxide superconductor thin film is deposited so as to fornn the superconducting source region and the superconducting drain region.
In another prior art, at first an a-axis oriented oxide superconductor thin fil~n is deposited and etched so as to form the superconducting source region and the superconducting drain region, and then a c-axis oriented oxide superconductor thin film is deposited so as to form the superconducting channel.
However, in the prior art, the oxide superconductor thin film is degraded during the etching so that the superconducting characteristics is affected. In addition, the etched surface of the oxide superconductor thin filnn is roughened, therefore, if another oxide superconductor thin film is formed so as to contact the rough surface, an undesirable Josephson 2 5 junction or a resistance is generated at the interface.
By this, the super-FET manufactured by the above conventional process does not have an enough performance.
219580~ 1 A superconducting device as disclosed herein may comprise a substrate having a principal surface, a non-superconducting oxide layer ha.ving a similar crystal structure to that of the oxide superconductor, a first and a second superconducting regions formed of c-axis oriented oxide 5 su.perconductor thin films on the non-superconducting oxide layer separated from each other and gently inclining to each other, a third superconducting region formed of an extremely thin c-axis oriented oxide superconductor thin film between the first and the second superconducting regions, which is continuous to the first and the second superconducting 10 regions.
Upper surfaces of the first and second superconducting regions gently incline to the third superconducting region of an extremely thin oxide superconductor thin film. Therefore, superconducting current flows into or flows from the third superconducting region efficiently so that the current 15 capability of the superconducting device can be improved.
Preferably the third superconducting region forms a weak link of a Josephson junction, so that the superconducting devicc ~ 2i958Q~ I
constitutes a Josephson device. In this case, the third superconducting region preferably includes a grain boundary which constitutes a weak link of a Josephson junction.
In another preferred embodiment, the third superconducting region 5 fo~ms a superconducting channel, so that superconducting current can flc\w between the first and second superconducting region through ~e third superconducting region. In this case, it is preferable that the superconducting device further includes a gate electrode formed on the third superconducting region, so that the superconducting device 10 constitutes a super-FET, and the superconducting current flowing between the first and second superconducting region through the third superconducting region is controlled by a voltage applied to the gate electrode.
The non-superconducting oxide layer preferably has a similar crystal structure to that of a c-axis oriented oxide superconductor thin filIn. In this case, the superconducting channel of a c-axis oriented oxide superconductor thin film can be easily formed.
Preferably, the above non-superconducting oxide layers is formed 2 0 of a PrlBa2Cu3O7 ~ oxide. A c-axis oriented PrlBa2Cu3O7 ~ thin film has almost the same crystal lattice structure as that of a c-axis oriented oxide superconductor thin film. It compensates an oxide superconductor thin filrn for its crystalline incompleteness at the bottom surface. Therefore, a c-axis oriented oxide superconductor thin film of high crystallinity can be 2 5 easily forrned on the c-axis oriented PrlBa2Cu3O7 ~ thin film. In addition, the effect of diffusion of the constituent elements of Pr1Ba2Cu3O7 ~ into the oxide superconductor thin film is negligible and it also prevents the ~ ~19~G9 diffusion from substrate. Thus, the oxide superconductor thin film deposited on the PrlBa2Cu307 ~ thin film has a high quality.
In a preferred embodiment, the oxide superconductor is formed of high-TC (high critical temperature) oxide superconductor, particularly, S folmed of a high-TC copper-oxide type compound oxide superconductor for example a Y-Ba-Cu-O compound oxide superconductor material, a Bi-Sr-Ca-Cu-O compound oxide superconductor material, and a Tl-Ba-Ca-Cu-O compound oxide superconductor material.
In addition, the substrate can be formed of an insulating substrate, 10 preferably an oxide single crystalline substrate such as MgO, SrTiO3, CdNdA104, etc. These substrate materials are very effective in forming or growing a crystalline film having a high degree of crystalline orientation. However, the superconducting device can be formed on a senniconductor substrate if an appropriate buffer layer is deposited 15 thereon. For example, the buffer layer on the semiconductor substrate can be formed of a double-layer coating formed of a MgA104 layer and a BaTiO3 layer if silicon is used as a substrate.
Another form of superconducting device may comprise a substrate, a 2 ~ non-superconducting layer formed on a principal surface of said substrate, an extremely thin superconducting channel formed of an oxide sup~erconductor thin film on the non-superconducting layer, a superconducting source region and a superconducting drain region of a relatively thick thickness formed of the oxide superconductor at the both 25 sides of the superconducting channel separated from each other but electrically connected through the superconducting channel, so that a superconducting current can flow through the superconducting channel ~ ~195~9 between the superconducting source region and the superconducting drain region, and a gate electrode through a gate insulator on the sulperconducting channel for controlling the superconducting current flowing through the superconducting channel, in which the S su~perconducting channel is connected to the superconducting source region and the superconducting drain region at the height of their middle portions.
According to still another embodiment disclosed herein a superconducting device comprises a substrate having a 10 principal surface, a non-superconducting oxide layer having a similar cr~stal structure to that of the oxide superconductor, two superconducting re~rions formed of a c-axis oriented oxide superconductor thin film separated by an insulating region positioned between them, an extremely thin superconducting region formed of a c-axis oriented oxide 15 superconductor thin film on the insulating region, which is continuous to the two superconducting regions and forms a weak link of Josephson junction, in which the two superconducting regions and the insulating re~ion are formed of one c-axis oriented oxide superconductor thin film which has a gently concave upper surface and of which the center portion 2 0 includes much impurity so that the portion does not show superconductivity.
According to a fourth aspect disclosed herein, there is prc,vided a superconducting device comprising a substrate having a principal surface, a non-superconducting oxide layer having a similar 25 crystal structure to that of the oxide superconductor, a superconducting source region and a superconducting drain region formed of a c-axis oriented oxide superconductor thin film separated from each other, an 21 q5~G9 e~tremely thin superconducting channel formed of a c-axis oriented oxide superconductor thin filnn on the non-superconducting oxide layer, which e].ectrically connects the superconducting source region to the s~lperconducting drain region, so that superconducting current can flow S ~lrough the superconducting channel between ~e superconducting source region and the superconducting drain region, and a gate electrode through a gate insulator on the superconducting channel for controlling the sllperconducting current flowing ~rough the superconducting channel, in which the superconducting source region and the superconducting drain 10 region have upper surfaces gently inclined to the superconducting ch~nnel.
According to a fifth aspect of the superconducting device, the device comprises a substrate having a principal surface, a non-15 superconducting oxide layer having a similar crystal structure to that of theoxide superconductor, two superconducting regions formed of c-axis or:iented oxide superconductor thin films separated from each other, an extremely thin superconducting regions formed of a c-axis oriented oxide superconductor thin film on the non-superconducting oxide layer, which 2 o continuous to the two superconducting regions and forms a weak link of a Josephson junction, in which the two superconducting regions have upper su:rfaces gently inclined to the weak link.
Summary of the Invention According to the present invention, there is provided a 25 superconducting device comprising a substrate, a non-superconducting layer formed on a principal surface of said substrate, an extremely thin superconducting channel formed of an oxide superconductor thin film on the non-superconducting layer, a-g ~ ~195~9 superconducting source region and a superconducting drain region of arelatively thick thickness formed of the oxide superconductor at the both sid,es of the superconducting channel separated from each other but electrically connected through the superconducting channel, so that a S superconducting current can flow through the superconducting channel bel;ween the superconducting source region and the supercon~ ctin~ drain re~gion, and a gate electrode through a gate insulator on the superconducting channel for controlling the superconducting current flowing through the superconducting channel, in which the 10 superconducting channel is connected to the superconducting source region and the superconducting drain region at the height of their middle portions.
A method for manufacturing a superconducting device 15 may comprise the steps of forming on a principal surface of a substrate a non-superconducting oxide layer having a similar crystal structure to that of the oxide superconductor, forming a first oxide superconductor thin filrn having a relatively thick thickness on the non-superconducting oxide layer, etching the first oxide superconductor thin film so as to form a 2 0 concave portion which is concave gently on its center portion, implanting ions to the first oxide superconductor thin film at the bottom of the concave portion so as to form an insulating region and the first oxide superconductor thin film is divided into two superconducting regions by the insulating region, and forming a second extremely thin oxide 2 5 superconductor thin film on the insulating region and the two superconducting regions which is continuous to the two superconducting re,~,ions.
21 958~9 In one preferred embodiment, the ions which are implanted so as to folm the insulating region are selected from Ga ions, Al ions, In ions, Si ions, Ba ions and Cs ions.
It is preferable that the second extremely thin oxide superconductor S thin film is formed to have a grain boundary in it so as to form a weak link of Josephson junction. It is also preferable that the second extremely thin oxide superconduc~or thin film is formed so as to constitute a superconducting channel through which superconducting current flows between the two superconducting regions. In this case, the method 10 further includes the steps of forming a gate insulating layer on the second extremely thin oxide superconductor thin film at a portion above the ins,ulating region and forming a gate electrode on the gate insulating layer.
According to another aspect of the method disclosed herein 15 foI manufacturing a superconducting device, the me~od comprises the steps of forming on a principal surface of a substrate a no]n-superconducting oxide layer having a similar crystal structure to that of the oxide superconductor, forming a first oxide superconductor thin film having a relatively thick thickness on the non-superconducting oxide 2 0 layer, etching the first oxide superconductor thin film so as to divide intotwo superconducting regions by the insulating region which have inclined surfaces gently inclined to each other and the non-superconducting oxide layer is exposed between them, and forming a second extremely thin ox ide superconductor thin film on the exposed portion of the 25 non-superconducting oxide layer and the two superconducting regions which is continuous to the two superconducting regions.
~ 2~958~9 In one preferred embodiment, the second extremely thin oxide superconductor thin film is formed to includes a grain boundary in it so as to constitute a weak link of Josephson junction. It is also preferable that the second extremel~ thin oxide superconductor thin film is formed S so as to constitute a superconducting channel of a super-FET. In this case, the method preferably further includes the steps of forming a gate ins~ tin~ layer on the second extremely thin oxide superconductor thin film at a portion above the the exposed portion of the non-superconducting oxide layer and forming a gate electrode on the gate 1 0 insulating layer.
According to another aspect of the present invention, there is provided a method for manufacturing a superconducting device, cornprising the steps of ~orming on a principal surface of a substrate a firsit oxide superconductor thin film having a relatively thick thickness, 15 forming a metal layer on the first superconductor thin film, forming a SiC)2 layer on the metal layer, selectively etching a center portions of the SiC)2 layer, the metal layer and the first oxide superconductor thin film so that the portions of the SiO2 layer, the metal layer and the first oxide suplerconductor thin film is completely removed and a surface of the 2 0 sub~strate is exposed so as to form a superconducting source region and a superconducting drain region separately on the substrate and a source electrode and a drain elec~rode respectively on the superconducting source region and the superconducting drain region, forming a non-superconductor layer having a half thickness of the superconducting 25 source region and the superconducting drain region on the exposed surface of the substrate, forming a second extremely thin oxide superconductor thin film on the non-superconducting layer so that an ~ ~195~
extremely thin superconducting channel which is connected to the sujperconducting source region and the superconducting drain region at ~e height of the middle portions is formed on the non-superconducting er, forming a gate ins~ tin~ layer and a gate electrode stacked on the 5 gate ins~ tin~ layer on a portion of the second oxide superconductor thin fillm above the non-superconducting layer, and removing the sio2 layer so that the source electrode ~nd the drain electrode are exposed.
It is preferable tha~ the SiO2 layer is removed by using a weak HF
solution.
According to another aspect of the method disclosed herein fo] manufacturing a superconducting device, the me~hod comprises ~u~ steps of forming on a principal surface of a subs~rate a lifl:-off layer, removing the lift-off layer excluding a portion at which a projecting insulating region will be formed, etching the principal surface l 5 of a substrate so that a projecting insulating region of which the cross section is a shape of a trapezoid is formed on the principal surface, folming a first oxide superconductor thin film on the principal surface and the projecting insulating region, removing the remaining lift-off layer so that the first oxide superconductor thin film is divided into a superconducting source region and a superconducting drain region and a surface of the projecting insulating region is exposed, forming a second oxiide superconductor thin film on the projecting insulating region which constitutes a superconducting channel, and forming a gate insulating layer and gate electrode on the superconducting channel.
2 5 In one preferred embodiment, the lift-off layer is preferably formed of a CaO layer of which surface is covered with a Zr layer. This lift-off layer can be removed by ~1ti1i7ing water and following reaction:
~ 21 ~8~ 1 CaO + H20 ~ Ca(OH)2 In the above process, no reactive agent is used but water.
Therefore, if the flat-top projection is formed by the above process, the substrate and the supercomducting thin film are not degraded.
S The above and other objects, features and advantages of ~e present in~ention will be apparent from the following description of preferred e~lbodiments of the invention with reference to the accompanying drawings.
Brief Description of the Drawings Figures lA to lF are diagrammatic sectional views for illustrating a first embodiment of a process for manufacturing the super-FET;
Figures 2A to 2C are diagrammatic sectional views for illustrating featured steps of a second embodiment of the process for manufacturing the 1 5 super-FET;
Figures 3A to 3J are diagrammatic sectional views for illustrating a third embodiment of the process for manufacturing the super-FET; and Figures 4A to 4J are diagrammatic sectional views for illustrating a fourth embodiment of the process for manufacturing the super-FET.
Description of the Preferred embodiments Em~bodiment 1 Referring to Figures lA to lF, a process for manufacturing the super-FET will be described.
~ 2~809 As shown in Figure lA, a MgO (100) single crystalline substrate 5 ha~ving a subst~nti~lly planar principal surface is prepared.
As shown in Figure lB, an oxide layer 20 having a thickness of 100 nanometers composed of a c-axis oriented PrlBa2Cu307.~ thin film is S deposited on the principal surface of the substrate S and a c-axis oriented YlBa2Cu307 ~ oxide superconductor thin film 1 having a thickness of about 300 nanometers is deposited on the oxide layer 20, by for example a sputtering, an MBE (molecular beam epitaxy), a vacuum evaporation, a CVD, etc. A condition of forming the c-axis oriented PrlBa2Cu3O7 ~ thin film and the c-axis oriented YlBa2Cu3O7 ~ oxide superconductor thin film 1 by off-axis sputtering is as follows:
Prl Ba2Cu3O7 ~ thin film Temperature of the substrate 750 ~C
Sputtering Gas Ar: 90%
1 5 ~2: 10%
Pressure 10 Pa YlBa2Cu3O7 ~ oxide superconductor thin film Temperature of the substrate 700 ~C
Sputtering Gas Ar: 90%
~2 10%
Pressure 10 Pa Then, as shown in lFigure lC, a center portion of the YlBa2Cu307 ~
oxide superconductor thin film 1 is processed by He ion-beam accelerated by an energy of 3 to 50 keV so as to form a concave portion 14 which is 2 5 concave gently. The tilt angle of the concave portion 14 is less than 40~ and its length is about 100 nanometers.
~ 21958U9 Thereafter, Ga ions are implanted into a bottom portion of the concave portion 14 by an energy of S0 to lS0 keV so as to form an insulating region S0, as shown in Figure lD. In this connection, Al ions, In ions, Si ions, Ba ions ~nd Cs ions can be also used instead of Ga ions.
S The YlBa2Cu307 ~ oxidle superconductor thin film 1 is divided into a superconducting source region 2 and a superconducting drain region 3 by ~e ins~ ting region S0.
Then, the substrate S is heated to a temperature of 350 to 400 ~C
un~der a pressure lower than 1 x 10-9 Torr so as to clean the surface of the 10 Y1Ba2Cu3O7 ~ oxide superconductor thin film 1. This heat-treatment is not necessary, if the surf~ce of the YlBa2Cu307 ~ oxide superconductor thin film 1 is clean enough.
Thereafter, as shown in Figure lE, a c-axis oriented YlBa2Cu3O7~
oxide superconductor thin film 11 having a thickness on the order of 15 about 5 nanometers is deposited on the surface of the YlBa2Cu3O7,~ oxide superconductor thin film 1 by an MBE (molecular beam epitaxy). A
co]ndition of forming the c-axis oriented YlBa2Cu307~ oxide superconductor thin film 11 by an MBE is as follows:
Molecular beam source Y: 1250~C
2 0 Ba: 600~C
Cu: 1040~C
~2 or 03 atmosphere Pressure 1 x 10-5 Torr Temperature of the substrate 700~C
. 25 Since the YIBa2Cu307~ oxide superconductor thin film 11 is formed on the gently curved surface of the YlBa2Cu307~ oxide superconductor thin film 1, it becomes an uniform c-axis oriented oxide ~1 9~809 superconductor thin film. A portion of the YlBa2Cu3O7~ oxide superconductor thin film 11 on the insulating region 50 becomes a superconducting channel.
Finally, as shown in Figure lF, a gate ins~ tin~ layer 7 is formed 5 of Si3N4, MgO or SrTiO3 on the superconducting channel 10 and a gate electrode 4 is formed of Au on thLe gate insulating layer 7. Metal electrodes may be formedl on the superconducting source region 2 and the superconducting drain region 3, if necessar~r. With this, the super-FET in accordance with the present invention is completed.
As explained above, the superconducting channel, the superconducting source region and the superconducting drain region of the above mentioned super-FET manufactured in accordance with the embodiment of the method of the present invention are formLed of c-axis oriented oxide superconductor thin films. Therefore, the super-FET has 15 no undesirable resistance nor undesirable Josephson junction between the superconducting channel and the superconducting source region and between the superconducting channel and the superconducting drain region. In addition, since the superconducting source region and the superconducting drain region gently inclines to the superconducting 20 chaLnnel, superconducting current efficiently flows into and flows from the superconducting channel. By this, the current capability of the super-FET can be improved.
In the above method, if the YlBa2Cu307 ~ oxide superconductor thin film 11 is deposited to have a grain boundary so as to formL a weak link of 25 the Josephson junction on the insulating region 50, a Josephson junction device is manufactured. In this case, the superconducting source region andl the superconducting drain region are two superconducting electrodes.
. ~ 21~5809 Al]most all the above mentioned features of the super-FET can apply to ~e Josephson junction de~rice.
Embo~liment 2 Referring to Figures 2A to 2C, a second embodiment of the process for manufacturing ~e superconducting device will be described.
In this second embodiment, the same processings as those shown in Fi~ures lA to lB are performed.
Then, as shown in Figure 2A, the YIBa2Cu3O7 ~ oxide superconductor thin film 1 is processed by He ion-beam accelerated by an energy of 3 to 50 keV so l;hat the YlBa2Cu3O7 ~ oxide superconductor thin film 1 is divided into a superconducting source region 2 and a superconducting drain region 3 which have inclined surfaces gently inclined to each other. The tilt angle of the inclined surfaces is less than 40". The oxide layer 20 of PrlBa2Cu3O7 E is exposed between the superconducting source region 2 and the superconducting drain region 3.
Then, the substrate S is heated to a temperature of 350 to 400 ~C
under a pressure lower than 1 x 10-9 Torr so as to clean the surfaces of the superconducting source region 2 and the superconducting drain region 3 and the exposed surface of the oxide layer 20. This heat-treatment is not necessary, if the surfaces of the superconducting source region 2 and the superconducting drain region 3 and the exposed surface of the oxide layer 20 are clean enough.
Thereafter, as shown in Figure 2B, a c-axis oriented YIBa2Cu3O7 ~
oxide superconductor thin film 11 having a thickness on the order of about S nanometers is deposited on the surfaces of the superconducting source region 2 and the superconducting drain region 3 and the exposed 2i 95809 sul~face of the oxide layer 20 by an MBE (molecular beam epitaxy). A
condition of forming the c-axis oriented Y1Ba2Cu3O 7 ~ oxide su]?erconductor thin film 11 by an MBE is the same as that of Embodiment 1.
S Since the YIBa2Cu307~ oxide superconductor thin filrn 11 is fol~ned on the gently curved surfaces of the superconducting source re~sion 2 and the superconducting drain region 3 and the exposed surface of the oxide layer 20, it becomes an uniform c-axis oriented oxide superconductor thin film. A portion of the YlBa2Cu3O7 ~ oxide 1 0 superconductor thin film 11 on the exposed surface of the oxide layer 20 becomes a superconducting channel 10.
Finally, as shown in Figure 2C, a gate insulating layer 7 is formed of Si3N4, MgO or SrTiO3 on the superconducting channel 10 and a gate electrode 4 is formed of Au on the gate insulating layer 7. Metal electrodes may be formed, on the superconducting source region 2 and the superconducting drain region 3, if necessary. With this, the super-FET in accordance with the present invention is completed.
As explained above, the superconducting channel, the superconducting source region and the superconducting drain region of the above mentioned super-FET manufactured in accordance with the embodiment of the method of the present invention are formed of c-axis ori~nted oxide superconductor thin films. Therefore, the super-FET has no undesirable resistance nor undesirable Josephson junction between the superconducting channel and the superconducting source region and between the superconducting channel and the superconducting drain region. In addition, since the superconducting source region and the superconducting drain region gently inclines to the superconducting 2 ~ ~ 5 ~
channel, superconducting current efficiently flows into and flows from the superconducting channel. By this, the current capability of the super-FET can be improved.
In ~e above method, if the YlBa2Cu307 ~ oxide superconductor thin S fi~n 11 is deposited to have a grain boundary so as to form a weak link of ~ Josephson junction on the exposed surface of the oxide layer 20, a Jo sephson junction device is manufactured. In this case, the superconducting source region and the superconducting drain region are tw3 superconducting electrodes. Almost all the above mentioned features 10 of the super-FET can apply to the Josephson junction device.
Embodiment 3 Referring to Figures 3A to 3J, a third embodiment of the process for m~nl~facturing the superconducting device will be described.
As shown Figure 3A, an MgO (100) substrate 5 similar to that of Embodiment 1 is prepared. As shown in Figure 3B, a c-axis oriented YlBa2Cu3O7 ~ oxide superconductor thin film 1 having a thickness of about 250 nanometers is deposited on a principal surface of a MgO
substrate 5, by for example a sputtering, an MBE (molecular beam 20 epitaxy~, a vacuum evaporation, a CVD, etc. A condition of forming the c-axis oriented YlBa2Cu3O7 ~ oxide superconductor thin film 1 by off-axis sputtering is as follows:
Temperature of the substrate 700~C
Sputtering Gas Ar: 90%
~2 10%
Pressure 5 x 10-2 Torr '~ ~IqS809 Then, as shown in Figure 3C, an Au layer 14 having a thickness of 30 to 100 nanometers is formed on the YIBa2Cu3O7 ~ oxide superconductor thin film 1. As shown in Figure 3D, a sio2 layer 15 ha~ving a thickness of 250 nanometers is formed on the Au layer 14 by a 5 C~D. A center portion of the sio2 layer 15 is removed by using a photoli~ography. Using the processed sio2 layer 15 as a mask, center portions of the Au layer 14 and the YlBa2Cu307 ~ oxide superconductor thin film 1 are selectively etched by a reactive ion etching using a chloric gas" an ion milling using Ar-ions or a focused ion beam etching so that the 10 Au layer 14 is divided into a source electrode 12 and a drain electrode 13, the YlBa2Cu3O7 ~ oxide superconductor thin film 1 is divided into a superconducting source region 2 and a superconducting drain region 3, an~1 a portion 16 of the surface of the substrate 5 is exposed between them, as shown in Figure 3E.
Then, the substrate S is heated to a temperature of 350 to 400 ~C
under a pressure lower than 1 x 10-9 Torr so as to clean the exposed surface 16 of the substrate 5. This heat-treatment is not necessary, if the exposed surface 16 of the substrate 5 is clean enough. As shown in Figure 3F, an oxide layer 20 composed of c-axis oriented PrlBa2Cu3O7 ~ is 20 deposited on the exposed surface 16 of the substrate 5, by an MBE. The oxide layer 20 preferably has a half thickness of the superconducting source region 2 and the superconducting drain region 3. While the Pr]Ba2Cu307 ,~ thin film 20 is growing, the surface morphology of the PrlBa2Cu3O7 ~ thin film 20 is monitored by RHEED. A condition of 2 5 forming the c-axis oriented PrlBa2Cu3O7 ~ oxide thin film 20 by MBE is as irollows:
Molecular beam source Pr: 1225~C
~ 2195809 Ba: 600~C
Cu: 1040~C
Pressure 1 x 10-5 Torr Temperature of the substrate 750~C
S Then, the Pr molecular beam source is exchanged to a Y molecular be~am source and the temperature of the substrate is lowered to 700 ~C so tha~t a superconducting channel 10 of a c-axis oriented YlBa2Cu307~ oxide superconductor thin film having a thickness of about S nanometer is co]:ltinuously formed on the oxide layer 20 of PrlBa2Cu307 ~ thin film, as shown in Figure 3G.
Thereafter, as shown in Figure 3H, a gate insulating layer 7 of MgO
is formed by a sputtering successively on the superconducting source regrion 2, the superconducting channel 10 and the superconducting drain re~rion 3. The gate insulating layer 7 has a thickness of 10 to 20 nanometers and covers side surfaces of the superconducting source region 2 a~nd the superconducting drain region 3 for their insulation.
Then, as shown in Figure 3I, a gate electrode 4 of Au is formed on a center portion of the ga~e insulating layer 7 by a vacuum evaporation.
Finally, as shown in Figure 3J, the SiO2 layer 15 is removed by 2 0 using a 10% HF solution. Metal layers are formed on the source electrode 12 and the drain electrode 13 respectively, so as to planarize the upper surface of the device, if necessary. With this, the super-FET in accordance with the present invention is completed.
The above mentioned super-FET manufactured in accordance with 2 5 the third embodiment of the method has a superconducting channel whichis formed on the PrlBa2Cu307 ~ non-superconducting oxide layer of which the crystal structure is similar ~ I
''- 2195~09 to that of the YlBa2Cu3O7 ~ oxide superconductor. Therefore, the bottom pa~rtion of the superconducting channel is not degraded so that the subst~nti~l cross-sectional area of the superconducting channel of the super-FET is larger than that of a conventional super-FET.
S Additionally, since the superconducting channel is connected to the superconducting source region and the superconducting drain region at ~e height of their middlle portions, superconducting current ef~lciently f~c~ws into and flows frorn the superconducting channel. By all of these, the current capability of the super-FET can be improved.
In addition, since the substantially planarized upper surface is obtained, it become easy to form conductor wirings in a later process.
Furthermore, according to the method the oxide layer, the superconducting channel, the gate ins~ ting layer and the gate electrode are self-aligned. In the above method, since the oxide sujperconductor thin films are covered during the etching process, the su]perconducting characteristics of the oxide superconductor thin films are not affected. Therefore, the limitation in the fine processing technique required for manufacturing the super-FET is relaxed, and the m~mufactured super-FET has a excellent performance.
En~bodiment 4 Referring to Figures 4A to 4J, a forth embodiment of the process for manufacturing the superconducting device will be described.
As shown Figure 4A, an MgO (100) substrate S similar to that of ~mbodiment 1 is prepared. As shown in Figure 4B, a lift-off layer 16 of a CaO layer having a thickness of 1 ,um covered with Zr layer having a thickness of 50 nanometers is deposited on the substrate 5.
21 9~D~ I
Then as shown in Figure 4C, the lift-off layer 16 is removed excluding a portion at which a insulating region will be positioned. The lift-off layer 16 can be processed by a dry etching using a photoresist or a lift-off.
S Thereafter, the principal surface of ~e substrate S is etched by a reactive ion etching, ion millin~ using Ar ions etc. In this etching prc~cess, the rem~ining lift-off layer 16 is used as a mask so that a prcljecting insulating region 50 of which the cross section is a shape of a trapezoid is formed on the substrate.
Then, the substrate S is heated to a temperature of 350 to 400 ~C
under a pressure lower than 1 x 10-9 Torr so as to clean the etched surface of the substrate 5.
Thereafter, as shown in Figure 4E, a YlBa2Cu3O7 ~ oxide superconductor thin filrn 1 having a thickness on the order of 200 to 300 nanometers is deposited on the etched surface of the substrate 5 and the lift-off layer 16. The YIBa2Cu307~ oxide superconductor thin film 1 is preferably formed by an MBE (molecular beam epitaxy). A condition of forming the YlBa2Cu3O7 ~ oxide superconductor thin film 1 by an MBE is as i~ollows:
Molecular beam source Y: 1250 ~C
Ba: 600~C
Cu: 1040~C
~2 or 03 atmosphere Pressure 1 x 10-5 Torr Temperature of the substrate 680~C
Then, the lift-off layer 16 is removed so that the YlBa2Cu307 ~
oxide superconductor thin film 1 is divided into a superconducting source ' ~ 2iq~8U9 re,gion 2 and a superconducting drain region 3 and the insulating region SCI is exposed, as shown in figure 4F. This lift-off process lltili7.es water and a following reaction:
CaO + H2O ~ Ca(OH)2 S Since the lift-off process does not use an agent of high reactivity but use only water, the YlBa2Cu307~ oxide superconductor dlin film 1 and the substrate 5 are not degraded.
Thereafter, the substrate 5 is again heated to a temperature of 350 to 400 ~C under a pressure lower than 1 x 10-9 Torr so as to clean the exposed ins~ tin~ region 50, the superconducting source region 2 and the superconducting drain region 3.
Then, a c-axis oriented YIBa2Cu307~ oxide superconductor thin film 11 having a thickness of 5 nanometers is deposited on the insulating repion 50 by an MBE, as shown in Figure 4G. A condition of forming 1 5 the YlBa2Cu3O7 ~ oxide superconductor thin film 11 by an MBE is as fo].lows:
Molecular beam source Y: 1250~C
Ba: 600~C
Cu: 1040~C
Pressure 1 x 10-5 Torr Temperature of the substrate 700~C
A portion of the deposited YIBa2Cu307 ~ oxide superconductor thin film 11 on the insulating region 50 becomes a superconducting channel 10.
2~ Then, a insulating layer 17 is formed of Si3N4, MgO or SrTiO3 on the YlBa2Cu307,~ oxide superconductor thin film 11, as shown in - 25 - .
58Q~ I
Fipure 4H, and an Au layer 14 on the insulating layer 17, as shown in Figure 4I.
Finally, the Au layer 14 is processed into a gate electrode 4, the in~ tin~s layer 17 is processed into a gate insulating layer 7, and the sol!lrce electrode 12 and the drain electrode 13 are formed of Au on the su]perconducting source region 2 and superconducting drain region 3.
With this, he super-FET in accordance with the present invention is co]~pleted.
The above mentioned super-FET manufactured in accordance with the fourth embodiment of the method has the substantially planarized upper surface, it become easy to form conductor wirings in a later process.
Furthermore, according to the method the superconducting channel is formed without using etching. Thus, the superconducting channel is not affected. Therefore, the limitation in the fine processing technique required for manufacturing the super-FET is relaxed, and the manufactured super-FET has a excellent performance.
In the above mentioned embodiment, the oxide superconductor thin fil]~ can be formed of not only the Y-Ba-Cu-O compound oxide superconductor material, but also a high-TC (high critical temperature) oxide superconductor material, particularly a high-TC copper-oxide type compound oxide superconductor material, for example a Bi-Sr-Ca-Cu-O
co]~pound oxide superconductor material, and a Tl-Ba-Ca-Cu-O
compound oxide superconductor material.
2 5 The invention has thus been shown and described with reference to the specific embodiments. However, it should be noted that the present in~ention is in no way limited to the details of the illustrated structures ~ ~. 2 ~ 958~q but converts and modifications may be made within the scope of the appended claims.
- ~7 -
SPECIFICATION
Tille of the Invention SUPE~CONDUCTING DEVICE HAVING AN
S EXTREMELY THIN SUPERCONDUCTING CHANNEL
FORMED OF OXIDE SUPERCONDUCTOR MATERIAL
AND METHOD FOR MANUFACTURING THE SAME
Background of the Invention Field of the invention The present invention relates to a superconducting device and a me thod for manufacturing the same, and more specifically to a superconducting device having an extremely thin superconducting ch~nnel formed of oxide superconductor material, and a method for manufacturing the same.
Description of related art Devices which utilize superconducting phenomena operate rapidly with low power consumption so that they have higher performance than conventional semiconductor devices. Particularly, by using an oxide superconducting material which has been recently advanced in study, it is pos,sible to produce a superconducting device which operates at relatively high temperature.
Josephson device is one of well-known superconducting devices.
However, since Josephson device is a two-terminal device, a logic gate which utilizes Josephson devices becomes complicated configuration.
Therefore, three-terminal superconducting devices are more practical.
21 9580q Typical three-terminal superconducting devices include two types of super-FET (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 S other on both side of the semiconductor channel. A portion of these]~iconductor layer between the superconductor source electrode and dle superconductor drain electrode has a greatly recessed or undercut rear surface so as to have a reduced thickness. In addition, a gate electrode is fo]med through a gate insulating layer on the portion of the recessed or undercut rear surface of the semiconductor layer between the superconductor source electrode and the superconductor drain electrode.
A superconducting current flows through the semiconductor layer (channel) between the superconductor source electrode and the superconductor drain electrode due to the superconducting proximity effect, and is controlled by an applied gate voltage. This type of the super-FET operates at a higher speed with a low power consumption.
The second type of the super-FET includes a channel of a superconductor formed between a source electrode and a drain electrode, so that a current flowing through the superconducting channel is 2 0 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 isolating output signal from input one and of having a well defined gain.
2 5 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 21 9~9 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 leng~, a distance between the superconductor source electrode S and ~e superconductor drain electrode has to be made less than about a fe~w ten nanometers, if the superconductor source electrode and the sujperconductor drain electrode are formed 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 10 mentioned above.
On the other hand, the super-FET having the superconducting channel has a large current capability, and the fine processing which is required to product the first type of the super-FET is not needed to product this type of super-FET.
In order to obtain a complete ON/OFF operation, both of the su]perconducting channel and the gate insulating layer should have an extremely thin thickness. For example, the superconducting channel formed of an oxide superconductor material should have a thickness of les,s than five nanometers and the gate insulating layer should have a 2 0 thickness more than ten nanometers which is sufficient to prevent a tunnel cu rrent.
In the super-FET, since the extremely thin superconducting channel is Iconnected to the relatively thick superconducting source region and the superconducting drain region at their lower portions, the superconducting 25 culrrent flows substantially horizontally through the superconducting ch;mnel and subst~nti~lly vertically in the superconducting source region an~ the superconducting drain region. Since the oxide superconductor has 21 ~80~ 1 the largest critical current density Jc in the direction perpendicular to c-axes of its crystal lattices, the superconducting channel is preferably fol~ned of a c-axis oriented oxide superconductor thin film and the superconducting source region and the superconducting drain region are S pre:ferably fornned of a-a~is oriented oxide superconductor thin films.
~ a prior art, in order to manufacture the super-FET which has the superconducting channel of c-axis oriented oxide superconductor thin film and the superconducting source region and the superconducting drain region of a-axis oriented oxide superconductor thin films, a c-axis oriented oxide superconductor thin film is formed at first and the c-axis ori,ented oxide superconductor thin film is etched and removed excluding a por~tion which will be the superconducting channel. Then, an a-axis oriented oxide superconductor thin film is deposited so as to fornn the superconducting source region and the superconducting drain region.
In another prior art, at first an a-axis oriented oxide superconductor thin fil~n is deposited and etched so as to form the superconducting source region and the superconducting drain region, and then a c-axis oriented oxide superconductor thin film is deposited so as to form the superconducting channel.
However, in the prior art, the oxide superconductor thin film is degraded during the etching so that the superconducting characteristics is affected. In addition, the etched surface of the oxide superconductor thin filnn is roughened, therefore, if another oxide superconductor thin film is formed so as to contact the rough surface, an undesirable Josephson 2 5 junction or a resistance is generated at the interface.
By this, the super-FET manufactured by the above conventional process does not have an enough performance.
219580~ 1 A superconducting device as disclosed herein may comprise a substrate having a principal surface, a non-superconducting oxide layer ha.ving a similar crystal structure to that of the oxide superconductor, a first and a second superconducting regions formed of c-axis oriented oxide 5 su.perconductor thin films on the non-superconducting oxide layer separated from each other and gently inclining to each other, a third superconducting region formed of an extremely thin c-axis oriented oxide superconductor thin film between the first and the second superconducting regions, which is continuous to the first and the second superconducting 10 regions.
Upper surfaces of the first and second superconducting regions gently incline to the third superconducting region of an extremely thin oxide superconductor thin film. Therefore, superconducting current flows into or flows from the third superconducting region efficiently so that the current 15 capability of the superconducting device can be improved.
Preferably the third superconducting region forms a weak link of a Josephson junction, so that the superconducting devicc ~ 2i958Q~ I
constitutes a Josephson device. In this case, the third superconducting region preferably includes a grain boundary which constitutes a weak link of a Josephson junction.
In another preferred embodiment, the third superconducting region 5 fo~ms a superconducting channel, so that superconducting current can flc\w between the first and second superconducting region through ~e third superconducting region. In this case, it is preferable that the superconducting device further includes a gate electrode formed on the third superconducting region, so that the superconducting device 10 constitutes a super-FET, and the superconducting current flowing between the first and second superconducting region through the third superconducting region is controlled by a voltage applied to the gate electrode.
The non-superconducting oxide layer preferably has a similar crystal structure to that of a c-axis oriented oxide superconductor thin filIn. In this case, the superconducting channel of a c-axis oriented oxide superconductor thin film can be easily formed.
Preferably, the above non-superconducting oxide layers is formed 2 0 of a PrlBa2Cu3O7 ~ oxide. A c-axis oriented PrlBa2Cu3O7 ~ thin film has almost the same crystal lattice structure as that of a c-axis oriented oxide superconductor thin film. It compensates an oxide superconductor thin filrn for its crystalline incompleteness at the bottom surface. Therefore, a c-axis oriented oxide superconductor thin film of high crystallinity can be 2 5 easily forrned on the c-axis oriented PrlBa2Cu3O7 ~ thin film. In addition, the effect of diffusion of the constituent elements of Pr1Ba2Cu3O7 ~ into the oxide superconductor thin film is negligible and it also prevents the ~ ~19~G9 diffusion from substrate. Thus, the oxide superconductor thin film deposited on the PrlBa2Cu307 ~ thin film has a high quality.
In a preferred embodiment, the oxide superconductor is formed of high-TC (high critical temperature) oxide superconductor, particularly, S folmed of a high-TC copper-oxide type compound oxide superconductor for example a Y-Ba-Cu-O compound oxide superconductor material, a Bi-Sr-Ca-Cu-O compound oxide superconductor material, and a Tl-Ba-Ca-Cu-O compound oxide superconductor material.
In addition, the substrate can be formed of an insulating substrate, 10 preferably an oxide single crystalline substrate such as MgO, SrTiO3, CdNdA104, etc. These substrate materials are very effective in forming or growing a crystalline film having a high degree of crystalline orientation. However, the superconducting device can be formed on a senniconductor substrate if an appropriate buffer layer is deposited 15 thereon. For example, the buffer layer on the semiconductor substrate can be formed of a double-layer coating formed of a MgA104 layer and a BaTiO3 layer if silicon is used as a substrate.
Another form of superconducting device may comprise a substrate, a 2 ~ non-superconducting layer formed on a principal surface of said substrate, an extremely thin superconducting channel formed of an oxide sup~erconductor thin film on the non-superconducting layer, a superconducting source region and a superconducting drain region of a relatively thick thickness formed of the oxide superconductor at the both 25 sides of the superconducting channel separated from each other but electrically connected through the superconducting channel, so that a superconducting current can flow through the superconducting channel ~ ~195~9 between the superconducting source region and the superconducting drain region, and a gate electrode through a gate insulator on the sulperconducting channel for controlling the superconducting current flowing through the superconducting channel, in which the S su~perconducting channel is connected to the superconducting source region and the superconducting drain region at the height of their middle portions.
According to still another embodiment disclosed herein a superconducting device comprises a substrate having a 10 principal surface, a non-superconducting oxide layer having a similar cr~stal structure to that of the oxide superconductor, two superconducting re~rions formed of a c-axis oriented oxide superconductor thin film separated by an insulating region positioned between them, an extremely thin superconducting region formed of a c-axis oriented oxide 15 superconductor thin film on the insulating region, which is continuous to the two superconducting regions and forms a weak link of Josephson junction, in which the two superconducting regions and the insulating re~ion are formed of one c-axis oriented oxide superconductor thin film which has a gently concave upper surface and of which the center portion 2 0 includes much impurity so that the portion does not show superconductivity.
According to a fourth aspect disclosed herein, there is prc,vided a superconducting device comprising a substrate having a principal surface, a non-superconducting oxide layer having a similar 25 crystal structure to that of the oxide superconductor, a superconducting source region and a superconducting drain region formed of a c-axis oriented oxide superconductor thin film separated from each other, an 21 q5~G9 e~tremely thin superconducting channel formed of a c-axis oriented oxide superconductor thin filnn on the non-superconducting oxide layer, which e].ectrically connects the superconducting source region to the s~lperconducting drain region, so that superconducting current can flow S ~lrough the superconducting channel between ~e superconducting source region and the superconducting drain region, and a gate electrode through a gate insulator on the superconducting channel for controlling the sllperconducting current flowing ~rough the superconducting channel, in which the superconducting source region and the superconducting drain 10 region have upper surfaces gently inclined to the superconducting ch~nnel.
According to a fifth aspect of the superconducting device, the device comprises a substrate having a principal surface, a non-15 superconducting oxide layer having a similar crystal structure to that of theoxide superconductor, two superconducting regions formed of c-axis or:iented oxide superconductor thin films separated from each other, an extremely thin superconducting regions formed of a c-axis oriented oxide superconductor thin film on the non-superconducting oxide layer, which 2 o continuous to the two superconducting regions and forms a weak link of a Josephson junction, in which the two superconducting regions have upper su:rfaces gently inclined to the weak link.
Summary of the Invention According to the present invention, there is provided a 25 superconducting device comprising a substrate, a non-superconducting layer formed on a principal surface of said substrate, an extremely thin superconducting channel formed of an oxide superconductor thin film on the non-superconducting layer, a-g ~ ~195~9 superconducting source region and a superconducting drain region of arelatively thick thickness formed of the oxide superconductor at the both sid,es of the superconducting channel separated from each other but electrically connected through the superconducting channel, so that a S superconducting current can flow through the superconducting channel bel;ween the superconducting source region and the supercon~ ctin~ drain re~gion, and a gate electrode through a gate insulator on the superconducting channel for controlling the superconducting current flowing through the superconducting channel, in which the 10 superconducting channel is connected to the superconducting source region and the superconducting drain region at the height of their middle portions.
A method for manufacturing a superconducting device 15 may comprise the steps of forming on a principal surface of a substrate a non-superconducting oxide layer having a similar crystal structure to that of the oxide superconductor, forming a first oxide superconductor thin filrn having a relatively thick thickness on the non-superconducting oxide layer, etching the first oxide superconductor thin film so as to form a 2 0 concave portion which is concave gently on its center portion, implanting ions to the first oxide superconductor thin film at the bottom of the concave portion so as to form an insulating region and the first oxide superconductor thin film is divided into two superconducting regions by the insulating region, and forming a second extremely thin oxide 2 5 superconductor thin film on the insulating region and the two superconducting regions which is continuous to the two superconducting re,~,ions.
21 958~9 In one preferred embodiment, the ions which are implanted so as to folm the insulating region are selected from Ga ions, Al ions, In ions, Si ions, Ba ions and Cs ions.
It is preferable that the second extremely thin oxide superconductor S thin film is formed to have a grain boundary in it so as to form a weak link of Josephson junction. It is also preferable that the second extremely thin oxide superconduc~or thin film is formed so as to constitute a superconducting channel through which superconducting current flows between the two superconducting regions. In this case, the method 10 further includes the steps of forming a gate insulating layer on the second extremely thin oxide superconductor thin film at a portion above the ins,ulating region and forming a gate electrode on the gate insulating layer.
According to another aspect of the method disclosed herein 15 foI manufacturing a superconducting device, the me~od comprises the steps of forming on a principal surface of a substrate a no]n-superconducting oxide layer having a similar crystal structure to that of the oxide superconductor, forming a first oxide superconductor thin film having a relatively thick thickness on the non-superconducting oxide 2 0 layer, etching the first oxide superconductor thin film so as to divide intotwo superconducting regions by the insulating region which have inclined surfaces gently inclined to each other and the non-superconducting oxide layer is exposed between them, and forming a second extremely thin ox ide superconductor thin film on the exposed portion of the 25 non-superconducting oxide layer and the two superconducting regions which is continuous to the two superconducting regions.
~ 2~958~9 In one preferred embodiment, the second extremely thin oxide superconductor thin film is formed to includes a grain boundary in it so as to constitute a weak link of Josephson junction. It is also preferable that the second extremel~ thin oxide superconductor thin film is formed S so as to constitute a superconducting channel of a super-FET. In this case, the method preferably further includes the steps of forming a gate ins~ tin~ layer on the second extremely thin oxide superconductor thin film at a portion above the the exposed portion of the non-superconducting oxide layer and forming a gate electrode on the gate 1 0 insulating layer.
According to another aspect of the present invention, there is provided a method for manufacturing a superconducting device, cornprising the steps of ~orming on a principal surface of a substrate a firsit oxide superconductor thin film having a relatively thick thickness, 15 forming a metal layer on the first superconductor thin film, forming a SiC)2 layer on the metal layer, selectively etching a center portions of the SiC)2 layer, the metal layer and the first oxide superconductor thin film so that the portions of the SiO2 layer, the metal layer and the first oxide suplerconductor thin film is completely removed and a surface of the 2 0 sub~strate is exposed so as to form a superconducting source region and a superconducting drain region separately on the substrate and a source electrode and a drain elec~rode respectively on the superconducting source region and the superconducting drain region, forming a non-superconductor layer having a half thickness of the superconducting 25 source region and the superconducting drain region on the exposed surface of the substrate, forming a second extremely thin oxide superconductor thin film on the non-superconducting layer so that an ~ ~195~
extremely thin superconducting channel which is connected to the sujperconducting source region and the superconducting drain region at ~e height of the middle portions is formed on the non-superconducting er, forming a gate ins~ tin~ layer and a gate electrode stacked on the 5 gate ins~ tin~ layer on a portion of the second oxide superconductor thin fillm above the non-superconducting layer, and removing the sio2 layer so that the source electrode ~nd the drain electrode are exposed.
It is preferable tha~ the SiO2 layer is removed by using a weak HF
solution.
According to another aspect of the method disclosed herein fo] manufacturing a superconducting device, the me~hod comprises ~u~ steps of forming on a principal surface of a subs~rate a lifl:-off layer, removing the lift-off layer excluding a portion at which a projecting insulating region will be formed, etching the principal surface l 5 of a substrate so that a projecting insulating region of which the cross section is a shape of a trapezoid is formed on the principal surface, folming a first oxide superconductor thin film on the principal surface and the projecting insulating region, removing the remaining lift-off layer so that the first oxide superconductor thin film is divided into a superconducting source region and a superconducting drain region and a surface of the projecting insulating region is exposed, forming a second oxiide superconductor thin film on the projecting insulating region which constitutes a superconducting channel, and forming a gate insulating layer and gate electrode on the superconducting channel.
2 5 In one preferred embodiment, the lift-off layer is preferably formed of a CaO layer of which surface is covered with a Zr layer. This lift-off layer can be removed by ~1ti1i7ing water and following reaction:
~ 21 ~8~ 1 CaO + H20 ~ Ca(OH)2 In the above process, no reactive agent is used but water.
Therefore, if the flat-top projection is formed by the above process, the substrate and the supercomducting thin film are not degraded.
S The above and other objects, features and advantages of ~e present in~ention will be apparent from the following description of preferred e~lbodiments of the invention with reference to the accompanying drawings.
Brief Description of the Drawings Figures lA to lF are diagrammatic sectional views for illustrating a first embodiment of a process for manufacturing the super-FET;
Figures 2A to 2C are diagrammatic sectional views for illustrating featured steps of a second embodiment of the process for manufacturing the 1 5 super-FET;
Figures 3A to 3J are diagrammatic sectional views for illustrating a third embodiment of the process for manufacturing the super-FET; and Figures 4A to 4J are diagrammatic sectional views for illustrating a fourth embodiment of the process for manufacturing the super-FET.
Description of the Preferred embodiments Em~bodiment 1 Referring to Figures lA to lF, a process for manufacturing the super-FET will be described.
~ 2~809 As shown in Figure lA, a MgO (100) single crystalline substrate 5 ha~ving a subst~nti~lly planar principal surface is prepared.
As shown in Figure lB, an oxide layer 20 having a thickness of 100 nanometers composed of a c-axis oriented PrlBa2Cu307.~ thin film is S deposited on the principal surface of the substrate S and a c-axis oriented YlBa2Cu307 ~ oxide superconductor thin film 1 having a thickness of about 300 nanometers is deposited on the oxide layer 20, by for example a sputtering, an MBE (molecular beam epitaxy), a vacuum evaporation, a CVD, etc. A condition of forming the c-axis oriented PrlBa2Cu3O7 ~ thin film and the c-axis oriented YlBa2Cu3O7 ~ oxide superconductor thin film 1 by off-axis sputtering is as follows:
Prl Ba2Cu3O7 ~ thin film Temperature of the substrate 750 ~C
Sputtering Gas Ar: 90%
1 5 ~2: 10%
Pressure 10 Pa YlBa2Cu3O7 ~ oxide superconductor thin film Temperature of the substrate 700 ~C
Sputtering Gas Ar: 90%
~2 10%
Pressure 10 Pa Then, as shown in lFigure lC, a center portion of the YlBa2Cu307 ~
oxide superconductor thin film 1 is processed by He ion-beam accelerated by an energy of 3 to 50 keV so as to form a concave portion 14 which is 2 5 concave gently. The tilt angle of the concave portion 14 is less than 40~ and its length is about 100 nanometers.
~ 21958U9 Thereafter, Ga ions are implanted into a bottom portion of the concave portion 14 by an energy of S0 to lS0 keV so as to form an insulating region S0, as shown in Figure lD. In this connection, Al ions, In ions, Si ions, Ba ions ~nd Cs ions can be also used instead of Ga ions.
S The YlBa2Cu307 ~ oxidle superconductor thin film 1 is divided into a superconducting source region 2 and a superconducting drain region 3 by ~e ins~ ting region S0.
Then, the substrate S is heated to a temperature of 350 to 400 ~C
un~der a pressure lower than 1 x 10-9 Torr so as to clean the surface of the 10 Y1Ba2Cu3O7 ~ oxide superconductor thin film 1. This heat-treatment is not necessary, if the surf~ce of the YlBa2Cu307 ~ oxide superconductor thin film 1 is clean enough.
Thereafter, as shown in Figure lE, a c-axis oriented YlBa2Cu3O7~
oxide superconductor thin film 11 having a thickness on the order of 15 about 5 nanometers is deposited on the surface of the YlBa2Cu3O7,~ oxide superconductor thin film 1 by an MBE (molecular beam epitaxy). A
co]ndition of forming the c-axis oriented YlBa2Cu307~ oxide superconductor thin film 11 by an MBE is as follows:
Molecular beam source Y: 1250~C
2 0 Ba: 600~C
Cu: 1040~C
~2 or 03 atmosphere Pressure 1 x 10-5 Torr Temperature of the substrate 700~C
. 25 Since the YIBa2Cu307~ oxide superconductor thin film 11 is formed on the gently curved surface of the YlBa2Cu307~ oxide superconductor thin film 1, it becomes an uniform c-axis oriented oxide ~1 9~809 superconductor thin film. A portion of the YlBa2Cu3O7~ oxide superconductor thin film 11 on the insulating region 50 becomes a superconducting channel.
Finally, as shown in Figure lF, a gate ins~ tin~ layer 7 is formed 5 of Si3N4, MgO or SrTiO3 on the superconducting channel 10 and a gate electrode 4 is formed of Au on thLe gate insulating layer 7. Metal electrodes may be formedl on the superconducting source region 2 and the superconducting drain region 3, if necessar~r. With this, the super-FET in accordance with the present invention is completed.
As explained above, the superconducting channel, the superconducting source region and the superconducting drain region of the above mentioned super-FET manufactured in accordance with the embodiment of the method of the present invention are formLed of c-axis oriented oxide superconductor thin films. Therefore, the super-FET has 15 no undesirable resistance nor undesirable Josephson junction between the superconducting channel and the superconducting source region and between the superconducting channel and the superconducting drain region. In addition, since the superconducting source region and the superconducting drain region gently inclines to the superconducting 20 chaLnnel, superconducting current efficiently flows into and flows from the superconducting channel. By this, the current capability of the super-FET can be improved.
In the above method, if the YlBa2Cu307 ~ oxide superconductor thin film 11 is deposited to have a grain boundary so as to formL a weak link of 25 the Josephson junction on the insulating region 50, a Josephson junction device is manufactured. In this case, the superconducting source region andl the superconducting drain region are two superconducting electrodes.
. ~ 21~5809 Al]most all the above mentioned features of the super-FET can apply to ~e Josephson junction de~rice.
Embo~liment 2 Referring to Figures 2A to 2C, a second embodiment of the process for manufacturing ~e superconducting device will be described.
In this second embodiment, the same processings as those shown in Fi~ures lA to lB are performed.
Then, as shown in Figure 2A, the YIBa2Cu3O7 ~ oxide superconductor thin film 1 is processed by He ion-beam accelerated by an energy of 3 to 50 keV so l;hat the YlBa2Cu3O7 ~ oxide superconductor thin film 1 is divided into a superconducting source region 2 and a superconducting drain region 3 which have inclined surfaces gently inclined to each other. The tilt angle of the inclined surfaces is less than 40". The oxide layer 20 of PrlBa2Cu3O7 E is exposed between the superconducting source region 2 and the superconducting drain region 3.
Then, the substrate S is heated to a temperature of 350 to 400 ~C
under a pressure lower than 1 x 10-9 Torr so as to clean the surfaces of the superconducting source region 2 and the superconducting drain region 3 and the exposed surface of the oxide layer 20. This heat-treatment is not necessary, if the surfaces of the superconducting source region 2 and the superconducting drain region 3 and the exposed surface of the oxide layer 20 are clean enough.
Thereafter, as shown in Figure 2B, a c-axis oriented YIBa2Cu3O7 ~
oxide superconductor thin film 11 having a thickness on the order of about S nanometers is deposited on the surfaces of the superconducting source region 2 and the superconducting drain region 3 and the exposed 2i 95809 sul~face of the oxide layer 20 by an MBE (molecular beam epitaxy). A
condition of forming the c-axis oriented Y1Ba2Cu3O 7 ~ oxide su]?erconductor thin film 11 by an MBE is the same as that of Embodiment 1.
S Since the YIBa2Cu307~ oxide superconductor thin filrn 11 is fol~ned on the gently curved surfaces of the superconducting source re~sion 2 and the superconducting drain region 3 and the exposed surface of the oxide layer 20, it becomes an uniform c-axis oriented oxide superconductor thin film. A portion of the YlBa2Cu3O7 ~ oxide 1 0 superconductor thin film 11 on the exposed surface of the oxide layer 20 becomes a superconducting channel 10.
Finally, as shown in Figure 2C, a gate insulating layer 7 is formed of Si3N4, MgO or SrTiO3 on the superconducting channel 10 and a gate electrode 4 is formed of Au on the gate insulating layer 7. Metal electrodes may be formed, on the superconducting source region 2 and the superconducting drain region 3, if necessary. With this, the super-FET in accordance with the present invention is completed.
As explained above, the superconducting channel, the superconducting source region and the superconducting drain region of the above mentioned super-FET manufactured in accordance with the embodiment of the method of the present invention are formed of c-axis ori~nted oxide superconductor thin films. Therefore, the super-FET has no undesirable resistance nor undesirable Josephson junction between the superconducting channel and the superconducting source region and between the superconducting channel and the superconducting drain region. In addition, since the superconducting source region and the superconducting drain region gently inclines to the superconducting 2 ~ ~ 5 ~
channel, superconducting current efficiently flows into and flows from the superconducting channel. By this, the current capability of the super-FET can be improved.
In ~e above method, if the YlBa2Cu307 ~ oxide superconductor thin S fi~n 11 is deposited to have a grain boundary so as to form a weak link of ~ Josephson junction on the exposed surface of the oxide layer 20, a Jo sephson junction device is manufactured. In this case, the superconducting source region and the superconducting drain region are tw3 superconducting electrodes. Almost all the above mentioned features 10 of the super-FET can apply to the Josephson junction device.
Embodiment 3 Referring to Figures 3A to 3J, a third embodiment of the process for m~nl~facturing the superconducting device will be described.
As shown Figure 3A, an MgO (100) substrate 5 similar to that of Embodiment 1 is prepared. As shown in Figure 3B, a c-axis oriented YlBa2Cu3O7 ~ oxide superconductor thin film 1 having a thickness of about 250 nanometers is deposited on a principal surface of a MgO
substrate 5, by for example a sputtering, an MBE (molecular beam 20 epitaxy~, a vacuum evaporation, a CVD, etc. A condition of forming the c-axis oriented YlBa2Cu3O7 ~ oxide superconductor thin film 1 by off-axis sputtering is as follows:
Temperature of the substrate 700~C
Sputtering Gas Ar: 90%
~2 10%
Pressure 5 x 10-2 Torr '~ ~IqS809 Then, as shown in Figure 3C, an Au layer 14 having a thickness of 30 to 100 nanometers is formed on the YIBa2Cu3O7 ~ oxide superconductor thin film 1. As shown in Figure 3D, a sio2 layer 15 ha~ving a thickness of 250 nanometers is formed on the Au layer 14 by a 5 C~D. A center portion of the sio2 layer 15 is removed by using a photoli~ography. Using the processed sio2 layer 15 as a mask, center portions of the Au layer 14 and the YlBa2Cu307 ~ oxide superconductor thin film 1 are selectively etched by a reactive ion etching using a chloric gas" an ion milling using Ar-ions or a focused ion beam etching so that the 10 Au layer 14 is divided into a source electrode 12 and a drain electrode 13, the YlBa2Cu3O7 ~ oxide superconductor thin film 1 is divided into a superconducting source region 2 and a superconducting drain region 3, an~1 a portion 16 of the surface of the substrate 5 is exposed between them, as shown in Figure 3E.
Then, the substrate S is heated to a temperature of 350 to 400 ~C
under a pressure lower than 1 x 10-9 Torr so as to clean the exposed surface 16 of the substrate 5. This heat-treatment is not necessary, if the exposed surface 16 of the substrate 5 is clean enough. As shown in Figure 3F, an oxide layer 20 composed of c-axis oriented PrlBa2Cu3O7 ~ is 20 deposited on the exposed surface 16 of the substrate 5, by an MBE. The oxide layer 20 preferably has a half thickness of the superconducting source region 2 and the superconducting drain region 3. While the Pr]Ba2Cu307 ,~ thin film 20 is growing, the surface morphology of the PrlBa2Cu3O7 ~ thin film 20 is monitored by RHEED. A condition of 2 5 forming the c-axis oriented PrlBa2Cu3O7 ~ oxide thin film 20 by MBE is as irollows:
Molecular beam source Pr: 1225~C
~ 2195809 Ba: 600~C
Cu: 1040~C
Pressure 1 x 10-5 Torr Temperature of the substrate 750~C
S Then, the Pr molecular beam source is exchanged to a Y molecular be~am source and the temperature of the substrate is lowered to 700 ~C so tha~t a superconducting channel 10 of a c-axis oriented YlBa2Cu307~ oxide superconductor thin film having a thickness of about S nanometer is co]:ltinuously formed on the oxide layer 20 of PrlBa2Cu307 ~ thin film, as shown in Figure 3G.
Thereafter, as shown in Figure 3H, a gate insulating layer 7 of MgO
is formed by a sputtering successively on the superconducting source regrion 2, the superconducting channel 10 and the superconducting drain re~rion 3. The gate insulating layer 7 has a thickness of 10 to 20 nanometers and covers side surfaces of the superconducting source region 2 a~nd the superconducting drain region 3 for their insulation.
Then, as shown in Figure 3I, a gate electrode 4 of Au is formed on a center portion of the ga~e insulating layer 7 by a vacuum evaporation.
Finally, as shown in Figure 3J, the SiO2 layer 15 is removed by 2 0 using a 10% HF solution. Metal layers are formed on the source electrode 12 and the drain electrode 13 respectively, so as to planarize the upper surface of the device, if necessary. With this, the super-FET in accordance with the present invention is completed.
The above mentioned super-FET manufactured in accordance with 2 5 the third embodiment of the method has a superconducting channel whichis formed on the PrlBa2Cu307 ~ non-superconducting oxide layer of which the crystal structure is similar ~ I
''- 2195~09 to that of the YlBa2Cu3O7 ~ oxide superconductor. Therefore, the bottom pa~rtion of the superconducting channel is not degraded so that the subst~nti~l cross-sectional area of the superconducting channel of the super-FET is larger than that of a conventional super-FET.
S Additionally, since the superconducting channel is connected to the superconducting source region and the superconducting drain region at ~e height of their middlle portions, superconducting current ef~lciently f~c~ws into and flows frorn the superconducting channel. By all of these, the current capability of the super-FET can be improved.
In addition, since the substantially planarized upper surface is obtained, it become easy to form conductor wirings in a later process.
Furthermore, according to the method the oxide layer, the superconducting channel, the gate ins~ ting layer and the gate electrode are self-aligned. In the above method, since the oxide sujperconductor thin films are covered during the etching process, the su]perconducting characteristics of the oxide superconductor thin films are not affected. Therefore, the limitation in the fine processing technique required for manufacturing the super-FET is relaxed, and the m~mufactured super-FET has a excellent performance.
En~bodiment 4 Referring to Figures 4A to 4J, a forth embodiment of the process for manufacturing the superconducting device will be described.
As shown Figure 4A, an MgO (100) substrate S similar to that of ~mbodiment 1 is prepared. As shown in Figure 4B, a lift-off layer 16 of a CaO layer having a thickness of 1 ,um covered with Zr layer having a thickness of 50 nanometers is deposited on the substrate 5.
21 9~D~ I
Then as shown in Figure 4C, the lift-off layer 16 is removed excluding a portion at which a insulating region will be positioned. The lift-off layer 16 can be processed by a dry etching using a photoresist or a lift-off.
S Thereafter, the principal surface of ~e substrate S is etched by a reactive ion etching, ion millin~ using Ar ions etc. In this etching prc~cess, the rem~ining lift-off layer 16 is used as a mask so that a prcljecting insulating region 50 of which the cross section is a shape of a trapezoid is formed on the substrate.
Then, the substrate S is heated to a temperature of 350 to 400 ~C
under a pressure lower than 1 x 10-9 Torr so as to clean the etched surface of the substrate 5.
Thereafter, as shown in Figure 4E, a YlBa2Cu3O7 ~ oxide superconductor thin filrn 1 having a thickness on the order of 200 to 300 nanometers is deposited on the etched surface of the substrate 5 and the lift-off layer 16. The YIBa2Cu307~ oxide superconductor thin film 1 is preferably formed by an MBE (molecular beam epitaxy). A condition of forming the YlBa2Cu3O7 ~ oxide superconductor thin film 1 by an MBE is as i~ollows:
Molecular beam source Y: 1250 ~C
Ba: 600~C
Cu: 1040~C
~2 or 03 atmosphere Pressure 1 x 10-5 Torr Temperature of the substrate 680~C
Then, the lift-off layer 16 is removed so that the YlBa2Cu307 ~
oxide superconductor thin film 1 is divided into a superconducting source ' ~ 2iq~8U9 re,gion 2 and a superconducting drain region 3 and the insulating region SCI is exposed, as shown in figure 4F. This lift-off process lltili7.es water and a following reaction:
CaO + H2O ~ Ca(OH)2 S Since the lift-off process does not use an agent of high reactivity but use only water, the YlBa2Cu307~ oxide superconductor dlin film 1 and the substrate 5 are not degraded.
Thereafter, the substrate 5 is again heated to a temperature of 350 to 400 ~C under a pressure lower than 1 x 10-9 Torr so as to clean the exposed ins~ tin~ region 50, the superconducting source region 2 and the superconducting drain region 3.
Then, a c-axis oriented YIBa2Cu307~ oxide superconductor thin film 11 having a thickness of 5 nanometers is deposited on the insulating repion 50 by an MBE, as shown in Figure 4G. A condition of forming 1 5 the YlBa2Cu3O7 ~ oxide superconductor thin film 11 by an MBE is as fo].lows:
Molecular beam source Y: 1250~C
Ba: 600~C
Cu: 1040~C
Pressure 1 x 10-5 Torr Temperature of the substrate 700~C
A portion of the deposited YIBa2Cu307 ~ oxide superconductor thin film 11 on the insulating region 50 becomes a superconducting channel 10.
2~ Then, a insulating layer 17 is formed of Si3N4, MgO or SrTiO3 on the YlBa2Cu307,~ oxide superconductor thin film 11, as shown in - 25 - .
58Q~ I
Fipure 4H, and an Au layer 14 on the insulating layer 17, as shown in Figure 4I.
Finally, the Au layer 14 is processed into a gate electrode 4, the in~ tin~s layer 17 is processed into a gate insulating layer 7, and the sol!lrce electrode 12 and the drain electrode 13 are formed of Au on the su]perconducting source region 2 and superconducting drain region 3.
With this, he super-FET in accordance with the present invention is co]~pleted.
The above mentioned super-FET manufactured in accordance with the fourth embodiment of the method has the substantially planarized upper surface, it become easy to form conductor wirings in a later process.
Furthermore, according to the method the superconducting channel is formed without using etching. Thus, the superconducting channel is not affected. Therefore, the limitation in the fine processing technique required for manufacturing the super-FET is relaxed, and the manufactured super-FET has a excellent performance.
In the above mentioned embodiment, the oxide superconductor thin fil]~ can be formed of not only the Y-Ba-Cu-O compound oxide superconductor material, but also a high-TC (high critical temperature) oxide superconductor material, particularly a high-TC copper-oxide type compound oxide superconductor material, for example a Bi-Sr-Ca-Cu-O
co]~pound oxide superconductor material, and a Tl-Ba-Ca-Cu-O
compound oxide superconductor material.
2 5 The invention has thus been shown and described with reference to the specific embodiments. However, it should be noted that the present in~ention is in no way limited to the details of the illustrated structures ~ ~. 2 ~ 958~q but converts and modifications may be made within the scope of the appended claims.
- ~7 -
Claims (3)
1. A superconducting device comprising a substrate, a non-superconducting layer formed on a principal surface of said substrate, an extremely thin superconducting channel formed of an oxide superconductor thin film on the non-superconducting layer, a superconducting source region and a superconducting drain region of a relatively thick thickness formed of the oxide superconductor at the both sides of the superconducting channel separated from each other but electrically connected through the superconducting channel, so that a superconducting current can flow through the superconducting channel between the superconducting source region and the superconducting drain region, and a gate electrode through a gate insulator on the superconducting channel for controlling the superconducting current flowing through the superconducting channel, in which the superconducting channel is connected to the superconducting source region and the superconducting drain region at the height of their middle portions.
2. A method for manufacturing a superconducting device, comprising the steps of forming on a principal surface of a substrate a first oxide superconductor thin film having a relatively thick thickness, forming a metal layer on the first superconductor thin film, forming a SiO2 layer on the metal layer, selectively etching a center portions of the SiO2 layer, the metal layer and the first oxide superconductor thin film so that the portions of the SiO2 layer, the metal layer and the first oxide superconductor thin film is completely removed and a surface of the substrate is exposed so as to form a superconducting source region and a superconducting drain region separately on the substrate and a source electrode and a drain electrode respectively on the superconducting source region and the superconducting drain region, forming a non-superconductor layer having a half thickness of the superconducting source region and the superconducting drain region on the exposed surface of the substrate, forming a second extremely thin oxide superconductor thin film on the non-superconducting layer so that an extremely thin superconducting channel which is connected to the superconducting source region and the superconducting drain region at the height of the middle portions is formed on the non-superconducting layer, forming a gate insulating layer and a gate electrode stacked on the gate insulating layer on a portion of the second oxide superconductor thin film above the non-superconducting layer, and removing the SiO2 layer so that the source electrode and the drain electrode are exposed.
3. A method claimed in Claim 2 wherein the SiO2 layer is removed by using a weak HF solution.
Applications Claiming Priority (11)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP35219391 | 1991-12-13 | ||
| JP35219491 | 1991-12-13 | ||
| JP35219791 | 1991-12-13 | ||
| JP352193/1991 | 1991-12-13 | ||
| JP352197/1991 | 1991-12-13 | ||
| JP352194/1991 | 1991-12-13 | ||
| JP35518791 | 1991-12-20 | ||
| JP355187/1991 | 1991-12-20 | ||
| JP352659/1992 | 1992-12-10 | ||
| JP4352659A JPH05251776A (en) | 1991-12-13 | 1992-12-10 | Superconducting element and manufacture thereof |
| CA002085290A CA2085290C (en) | 1991-12-13 | 1992-12-14 | Superconducting device having an extremely thin superconducting channel formed of oxide superconductor material and method for manufacturing the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2195809A1 true CA2195809A1 (en) | 1993-06-14 |
Family
ID=27543454
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002195810A Abandoned CA2195810A1 (en) | 1991-12-13 | 1992-12-14 | Method for manufacturing a superconducting device |
| CA002195809A Abandoned CA2195809A1 (en) | 1991-12-13 | 1992-12-14 | Superconducting device having an extremely thin superconducting channel formed of oxide superconductor material and method for manufacturing the same |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002195810A Abandoned CA2195810A1 (en) | 1991-12-13 | 1992-12-14 | Method for manufacturing a superconducting device |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA2195810A1 (en) |
-
1992
- 1992-12-14 CA CA002195810A patent/CA2195810A1/en not_active Abandoned
- 1992-12-14 CA CA002195809A patent/CA2195809A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| CA2195810A1 (en) | 1993-06-14 |
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