CA2195810A1 - Method for manufacturing a superconducting device - Google Patents
Method for manufacturing a superconducting deviceInfo
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- CA2195810A1 CA2195810A1 CA002195810A CA2195810A CA2195810A1 CA 2195810 A1 CA2195810 A1 CA 2195810A1 CA 002195810 A CA002195810 A CA 002195810A CA 2195810 A CA2195810 A CA 2195810A CA 2195810 A1 CA2195810 A1 CA 2195810A1
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- oxide superconductor
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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
.1.' I
SPECIFICATION 2 1 ~ 5 ~ 10 Title of the Invention ~ 5METHOD FOR MANUFACTURING
A SUPERCONDUCTING DEVICE
Background of the Invention Field of the invention The present invention relates to a method for manufacturing a superconducting device.
Description of related art Devices which utilize superconducting phenomena operate rapidly 15 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 possible to produce a superconducting device which operates at relatively high temperature.
Josephson device is one of well-known superconducting devices.
FIowever, since Josephson device is a two-terminal device, a logic gate which utilizes Josephson devices becomes complicated configuration.
I'herefore, three-terminal superconducting devices are more practical.
.~' 2195810 Typical three-terminal superconducting devices include two types of super-FET (field effect transistor). The first type of the super-FET
i~ncludes a semiconductor channel, and a superconductor source electrode and a superconductor drain electrode which are formed closely to each S c~ther on both side of the semiconductor channel. A portion of ~esemiconductor layer bel:ween the superconductor source electrode and ~e superconductor drain electrode has a greatly recessed or undercut rear surface so as to have a reduced thickness. In addition, a gate electrode is forrned through a gate insulating layer on the portion of the recessed or u.ndercut 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 proxinnity effect, the superconductor source electrode and the superconductor drain electrode have to be positioned within a -' 2195810 distance of a few times the coherence length of the superconductor materials of the superconductor source electrode and the superconductor drain electrode. In particular, since an oxide superconductor has a short coherence length, a distance between the superconductor source electrode S and the superconductor drain electrode has to be made less than about a few ten nanometers, if the superconductor source electrode and the superconductor drain electrode are formed of the oxide superconductor material. However, it is very difficult to conduct a fine processing such as a ~me pattern etching, so as to satisfy the very short separation distance 10 n~entioned 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 tl~e 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 superconducting chamnel 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 less than five nanometers and the gate insulating layer should have a 2 O thickness more than ten nanometers which is sufficient to prevent a tunnel c~Lrrent.
In the super-FET, since the extremely thin superconducting channel is connected to the relatively thick superconducting source region and the superconducting drain region at their lower portions, the superconducting 25 current flows substantially horizontally through the superconducting channel and substantially vertically in the superconducting source region and the superconducting drain region. Since the oxide superconductor has ~ ' 21958iO
the largest critical current density Jc in the direction perpendicular to ~-axes of its crystal lattices, the superconducting channel is preferably iformed of a c-axis oriented oxide superconductor thin film and the superconducting source region and the superconducting drain region are S l~referably formed of a axis oriented oxide superconductor thin ~llms.
In a prior art, in order to manufacture the super-FET which has ~e ~uperconducting ch~nnel of c-axis oriented oxide supercondllctQr thin ~
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 oriented oxide superconductor thin film is etched and removed excluding a portion which will be the superconducting channel. Then, an a-axis oriented oxide superconductor thin film is deposited so as to form the superconducting source region and the superconducting drain region.
In another prior art, at first an a-axis oriented oxide superconductor thin film 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 alffected. In addition, the etched surface of the oxide superconductor thin film 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 ~ 2195810 A superconduct;ng device as disclosed herein may comprise 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 5 r,uperconductor thin films on the non-superconducting oxide layer separated from each other and gently inclining to each other, a third r,uperconducting 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 iincline 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 c apability of the superconducting device can be improved.
Preferably the third superconducting region forms a weak link of a Josephson junction, so tlhat the superconducting devicc '- 2195810 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.
~ another preferred embodiment, the third superconducting region S Iol1ns a superconducting channel, so that superconducting current can flow ~etween the ~lrst and second superconducting region through ~e third sllperconducting region. In this case, it is preferable that the superconducting dévice 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 film. 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 20 of a Pr1Ba2Cu3O7 ~ 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 film 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 formed 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 '-'' 219581() diffusion from substrate. Thus, the oxide superconductor thin film deposited on the PrlBa2Cu307 ~ thin f~llm has a high quality.
Ln a preferred embodiment, the oxide superconductor is formed of high-TC (high critical l:emperature) oxide superconductor, particularly, S ~o~ned of a high-TC copper-oxide type compound oxide superconductor for example a Y-Ba-Cu-O compound oxide superconductor material, a ~3,i-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 pireferably 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 forrned on a se:miconductor 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 MgAI04 layer and a BaTiO3 layer if silicon is used as a substrate.
Another form of superconducting device may comprise a substrate, a 2 0 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 25 sicles 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 2 ! 9 58 1 0 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 S superconducting channel is connected to the superconducting source region and the superconducting drain region at the height of their middle po~tions.
According to still ano~er embodiment disclosed herein a superconducting device comprises a substrate having a 10 p)rincipal surface, a non-superconducting oxide layer having a similar crystal structure to that of the oxide superconductor, two superconducting n~gions formed of a c-axis oriented oxide superconductor thin film s~eparated 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 region are formed of one c-axis oriented oxide superconductor thin fillm ~hich 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 provided a superconducting device comprising a substrate having a principal surface, a nom-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 '- 21~5810 extremely thin superconducting channel formed of a c-axis oriented oxide superconductor thin film on the non-superconducting oxide layer, which electrically connects the superconducting source region to the slLlperconducting drain region, so that superconducting current can flow S dlrough the superconducting channel between the superconducting source r~gion and ~e supercon.ducting drain region, and a gate electrode ~rough a gate insulator on the superconducting channel for controlling ~e superconducting curren~ flowing through the superconducting t~h~nnel, in which the superconduc~,ing source region and the superconducting drain 10 region have upper surfaces gently inclined to the superconducting channel.
According to a fifth aspect of the superconducting device the device comprises a substrate having a principal surface, a non-superconducting oxide layer having a similar 15 clystal structure to that of the oxide superconductor, two superconducting regions formed of c-axis oriented 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 continuous to the two 2 0 superconducting regions and forms a weak link of a Josephson junction, in which the two superconducting regions have upper surfaces gently inclined to the weak link.
According to a sixth aspect of the superconducting device, the device comprises a substrate, a non-superconducting layer formed on a principal 2 5 surface of said substrate, an extremely thin superconducting channel formed of an oxide superconductor thin film on the non-superconducting layer, a ~ 21~5810 s,uperconducting source region and a superconducting drain region of a l~latively thick thickness formed of the oxide superconductor at ~e both s,ides of the superconducting channel separated from each other but ~lectrically connected through the superconducting channel, so ~at a S siuperconducting current can flow through the superconducting channel between the supercondllcting 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 10 superconducting channel is connected to the superconducting source region and the superconducting drain region at the height of their middle F'~rtions.
A method for manufacturing a superconducting device 15 nnay comprise the steps of forming on aprincipal 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 sluperconductor thin film is divided into two superconducting regions by the insulating region, and forming a second extremely thin oxide 2 ~ sluperconductor thin film on the insulating region and the two sllperconducting regions which is continuous to the two superconducting regions.
I O -' ~ 2195810 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 iions, Ba ions and Cs ions.
It is preferable dlat ~e second extremely thin oxide superconductor S lthin film is fonned to have a grain boundary in it so as to foIm a weak k of Josephson junction. It is also preferable that dle second extremely lthin oxide superconductor 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 iFurther includes the steps of forming a gate insulating layer on the second extremely thin oxide superconductor thin film at a portion above the insulating region and forming a gate electrode on the gate insulating ] ayer.
According to another aspect of the method disclosed herein 15 For manufacturing a superconducting device, the method comprises Ithe s~eps 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 i'ilm 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, alld forming a second extremely thin oxide superconductor thin film on the exposed portion of the 25 non-superconducting oxide layer and the two superconducting regions ~vhich is continuous to ~he two superconducting regions.
'~ 21'5810 In one preferred embodiment, the second extremely thin oxide superconductor thin film is formed to includes a grain boundary in it so a.s to constitute a weak link of Josephson junction. It is also preferable that the second extremely thin oxide superconductor thin ~llm is formed S so as to constitute a superconducting ch~nnel of a super~ T. ~ ~is case, ~he method preferably further includes the steps of forming a gate i]nsulating layer on the second extremely thin oxide superconductor thin film at a portion above the the exposed portion of the n.on-superconducting oxide layer and forming a gate electrode on the gate 1 ~ i]:lsulating layer.
According to still another aspect of the method for manufacturing a superconducting device, the method comprises the steps of forming on a principal surface of a substrate a first oxide superconductor thin film having a relatively thick thickness, 15 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 2 0 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 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 ex tremely 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 ins~ tin~ layer and a gate electrode stacked on ~c S gate insulating layer on a portion of the second oxide superconductor thin film above ~e non-superconducting layer, and removing ~e SiO2 layer so that the source electrode and the drain electrode are exposed.
It is preferable ~at the SiO~ layer is removed by using a weak ~i solution.
10' Summary of the ;nvention According to the present invention, t~ere is prc~vided a method for manufacturing a superconducting device, cornprising the steps of forming on a principal surface of a substrate.a 15 lift-off layer, removing the lift-off layer excluding a portion at which a projecting insulating region will be formed, etching dle principal surface 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, forming a first oxide superconductor thin film on the principal surface 2 0 andl the projecting insulating region, removing the rern~inin~ 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 suliFace of the projecting insulating region is exposed, forming a second oxide superconductor thin film on the projecting insulating region which 2 5 constitutes a superconducting channel, and forming a gate insulating layer and gate electrode on the superconducting channel.
In one preferred embodiment, the lift-off layer is preferably forrned of a CaO layer of which surface is covered with a Zr layer. This lift-off layer can be removed by utilizing water and following reaction:
'-' 21~581() CaO + H20 ~ Ca(OH)2 In the above process, no reactive agent is used but water.
~erefore, if the flat-top projection is formed by ~e above process, ~e substrate and the superGonducting ~in film are not degraded.
The above and o~her objects, features and advantages of the present invention will be apparent from ~e following description of preferred e:mbodiments 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 Embodiment 1 Referring to Figures lA to lF, a process for manufacturing the super-FET will be described.
'--' 21958~0 As shown in Figure lA, a MgO (100) single crystalline substrate S
hlaving a subst~nti~lly planar principal surface is prepared.
As shown in Figure lB, an oxide layer 20 having a thickness of 100 nlanometers composed of a c-axis oriented PrlBa2Cu307 e thin film is S deposited on the principal surface of dle substrate S and a c-axis oriented ~ Ba2Cu307.~ oxide superconductor ~in film 1 having a ~ickness of about 300 nanometers is deposited on dle oxide layer 20, by for example a s;puttering, an MBE (molecular beam epitaxy), a vacuum evaporation, a C'VD, etc. A condition of forming the c-axis oriented PrlBa2Cu3O7 ~ thin 10 fiilm and the c-axis oriented YlBa2Cu3O7 ~ oxide superconductor thin film 1 by off-axis sputtering is as follows:
PrlBa2Cu307 ~ thin film Temperature of the substrate 750 ~C
Sputtering Gas Ar: 90%
~2: 10%
Pressure 10 Pa Y'lBa2Cu307 ~ oxide superconductor thin film Temperature of the substrate 700 ~C
Sputtering Gas Ar: 90%
2 O ~2: 10%
Pressure 10 Pa Then, as shown in Figure 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 concave gently. The tilt angle of the concave portion 14 is less than 40~
and its length is about 100 nanometers.
' '' 2195810 Thereafter, Ga ions are implanted into a bottom portion of the concave portion 14 by an energy of 50 to lS0 keV so as to fonn an insulating region 50, as shown in Figure lD. Ln this connection, Al ions, ~1 ions, Si ions, Ba ions and Cs ions can be also used instead of Ga ions.
S 'l~e YlBa2Cu307~ oxide superconductor thin film 1 is divided into a sluperconducting source region 2 and a superconducting drain region 3 by e insulating region SOO
Then, the substrate S is heated to a temperature of 350 to 400 ~C
under a pressure lower ~han 1 x 10-9 Torr so as to clean the surface of dle 10 YlBa2Cu3O7~ oxide superconductor thin film 1. This heat-treatment is not necessary, if the surface of the YIBa2Cu307 ~ oxide superconductor thin fiLrn 1 is clean enough.
Thereafter, as shown in Figure lE, a c-axis oriented YlBa2Cu307~
oxide superconductor thin film 11 having a thickness on the order of l S albout S nanometers is deposited on the surface of the YlBa2Cu3O7~ oxide superconductor thin film 1 by an MBE (molecular beam epitaxy). A
condition of forming the c-axis oriented YIBa2Cu3O7 ~ 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 O3 atmosphere Pressure 1 x 10-5 Torr Temperature of the substrate 700~C
Since the YlBa2Cu3O7~ oxide superconductor thin film 11 is formed on the gently curved surface of the YIBa2Cu3O7 ~ oxide superconductor thin film 1, it becomes an uniform c-axis oriented oxide '-' 2195810 superconductor thin f~lm. A portion of the YlBa2Cu3O7 8 oxide superconductor thin film 11 on the insulating region 50 becomes a sluperconducting channel.
Finally, as shown in Figure lF, a gate ins~ ting layer 7 is formed S of Si3N4, MgO or SrTiO3 on the superconducting ch~nnel 10 and a gate electrode 4 is formed of Au on ~e gate insulating layer 7. Metal electrodes may be formed on the superconducting source region 2 and the superconducting drain region 3, if necessa~y. With this, the super-FET in accordance with the present invention is completed.
As explained above, the superconducting channel, the slllperconducting source region and the superconducting drain region of the above mentioned super-FET manufactured in accordance with the eimbodiment of thle method of the present invention are formed of c-axis oriented oxide superconductor thin films. Therefore, the super-FET has 15 nf~ undesirable resistance nor undesirable Josephson junction between th~e 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 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 the above method, if the YlBa2Cu3O7 ~ oxide superconductor thin fiLrn 11 is deposited to have a grain boundary so as to form a weak link of 2 5 thle Josephson junction on the insulating region 50, a Josephson junction device is manufactured. In this case, the superconducting source region and the superconducting drain region are two superconducting electrodes.
; ' 219581~) 1 ~lmost all the above mentioned features of the super-FET can apply to the Josephson junction dlevice.
Embo-lim~nt 2 S Referring to Figures 2A to 2C, a second emlbodiment of the process for m~nllfacturing ~e superconducting device will be described.
~ this second embodiment, the same processings as those shown in F'igures lA to lB are performed.
Then, as shown in Figure 2A, the YIBa2Cu3O7 ~ oxide 10 superconductor thin filrn 1 is processed by He ion-beam accelerated by an energy of 3 to S0 keV so that the YlBa2Cu3O7~ oxide superconductor thin fiilm 1 is divided into a superconducting source region 2 and a slLlperconducting drain region 3 which have inclined surfaces gently inclined to each other. The tilt angle of the inclined surfaces is less than 15 40~. The oxide layer 20 of PrlBa2Cu3O7 ~ 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 20 3 and the exposed surface of the oxide layer 20. This heat-treatment is not necessary, if the sul~aces 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 YlBa2Cu307~
25 oxide superconductor thin film 11 having a thickness on the order of albout S nanometers is deposited on the surfaces of the superconducting source region 2 and the superconducting drain region 3 and the exposed "-- 219581~ 1 ~,urface of the oxide layer 20 by an MBE (molecular beam epitaxy). A
condition of forrning the c-axis oriented YlBa2Cu307 ~ oxide superconductor thin rilm 11 by an MBE is the same as that of l_mbodim~nt 1.
S Since the YIBa~Cu307~ oxide superconductor thin f;lm 11 is ionned on ~e gently curved surfaces of the superconducting source ~gion 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 YIBa2Cu307 ~ oxide O 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 SrTi~03 on the superconducting channel 10 and a gate electrode 4 is formed of Au on the gate insulating layer 7. Metal 15 e lectrodes may be forrned on the superconducting source region 2 and the siuperconducting drain region 3, if necessary. With this, the super-FET in ~ccordance with the present invention is completed.
As explained above, the superconducting channel, the superconducting source region and the superconducting drain region of ~0 the above mentioned super-FET manufactured in accordance with the embodiment of the method of the present invention are formed of c-axis oriented 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 25 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 .~'' 21~5810 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 the above method, if the YIBa2Cu307~ oxide superconductor thin S film 11 is deposited to have a grain boundary so as to fo~rn a weak link of ~he Josephson junction on the exposed surface of the oxide layer 20, a Josephson junction device is manufactured. In this case, the superconducting source region and the superconducting drain region are ~wo superconducting electrodes. Almost all the above mentioned features 10 c~f the super-FET can apply to the Josephson junction device.
E mbodiment 3 Referring to Figures 3A to 3J, a third embodiment of the process ~Dr manufacturing 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 YIBa2Cu3O7~ 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 sjputtering is as follows:
Temperature of the substrate 700~C
Sputtering Gas Ar: 90%
~2 10%
Pressure 5 x 10-2 Torr '-'" 2~ 70 Then, as shown in Figure 3C, an Au layer 14 having a ~ickness of 30 to 100 nanometers is formed on the YIBa2Cu3O7.~ oxide superconductor thin film 1. As shown in Figure 3D, a sio2 layer 15 ~laving a thickness of 250 nanometers is fo~ned on the Au layer 14 by a 5 CVD. A center portion of the SiO2 layer 15 is removed by using a ~hotolithography. Using ~e processed SiO2 layer 15 as a mask, center ~ortions of the Au layer 14 and ~e YIBa2Cu307~ oxide superconductor ~in 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 dlat ~e 10 ~u layer 14 is divided into a source electrode 12 and a drain electrode 13, the YlBa2Cu307,~ oxide superconductor thin film 1 is divided into a superconducting source region 2 and a superconducting drain region 3, and a portion 16 of the surface of the substrate 5 is exposed between them, as shown in Figure 3E.
Then, the substrate 5 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 sl~urce region 2 and tlhe superconducting drain region 3. While the PrlBa2Cu3O7 ~ thin filrn 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 PrlBa2Cu307 ~ oxide thin filrn 20 by MBE is as follows:
Molecularbeam source Pr: 1225~C
'~' 21~5810 Ba: 600~C
Cu: 1040~C
Pressure 1 x 10-5 Torr Temperature of ~e substrate 750~C
S Then, the Pr molecular beam source is exchanged to a Y molecular beam source and dle temperature of ~e substrate is lowered to 700 ~C so at a superconducting ch~nnel 10 of a c-axis oriented YlBa2Cu307~ oxide superconductor thin film having a thickness of about S nanometer is continuously formed on the oxide layer 20 of PrlBa2Cu307 ,~ dlin film, as 10 sihown 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 r~gion 2, the superconducting channel 10 and the superconducting drain region 3. The gate insulating layer 7 has a thickness of 10 to 20 15 nanometers and covers side surfaces of the superconducting source region 2 and 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 gate insulating layer 7 by a vacuum evaporation.
Finally, as shown in Figure 3J, the SiO2 layer 15 is removed by 20 using a 10% HF solution. Metal layers are formed on the source e]lectrode 12 and the drain electrode 13 respectively, so as to planarize the u;pper surface of the device, if necessary. With this, the super-FET in aecordance with the present invention is completed.
The above mentioned super-FET manufactured in accordance with 2 5 the third embodiment o:f the method has a superconducting channel which is formed on the PrlBa2Cu307 ~ non-superconducting oxide layer of which tl~e crystal structure is similar ~ 3 '9~81'D
to that of ~e YlBa2Cu3O7 ~ oxide superconductor. Therefore, the bottom portion of the superconducting channel is not degraded so that the s,ubst~nti~l cross-sectional area of the superconducting channel of the ~,uper-FET is larger than ~at of a conventional super-FET.
S Additionally, sinc~ the superconducting channel is connected to ~e s,uperconducting source region and the superconducting drain region at the height of their middle portions, superconducting current ef~lciently flows into and flows from 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 insulating layer and the ~ate electrode are self-aligned. In the above method, since the oxide superconductor thin films are covered during the etching process, the superconducting 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 nnanufactured super-FET has a excellent performance.
E mbodiment 4 Referring to Figures 4A to 4J, a forth embodiment of the process f~r manufacturing the superconducting device will be described.
As shown Figure 4A, an MgO (100) substrate 5 similar to that of Embodiment 1 is prepared. As shown in Figure 4B, a lift-off layer 16 of a CaO layer having a tllickness of 1 ~lm covered with Zr layer having a thickness of 50 nanome~ers is deposited on the substrate S.
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 the substrate 5 is etched by areactive ion etching"I,on millinE using Ar ions etc. In ~is etc-hin process, the rem~ining lift-off layer 16 is used as a mask so that a projecting 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 film 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 YlBa2Cu307 ~ 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 follows:
Molecularbeam source Y: 1250 ~C
Ba: 600~C
Cu: 1040~C
~2 or O3 atmosphere Pressure 1 x 10-5 Torr Temperature of the substrate 680~C
Then, the lift-off layer 16 is removed so that the YlBa2Cu3O7 ~
oxide superconductor thin film 1 is divided into a superconducting source "~' 21958tO
region 2 and a superconducting drain region 3 and the insulating region '50 is exposed, as shown in figure 4F. This lift-off process l~tili7~s water and a following reaction:
CaO + H2O ~ Ca(OH)~
S Since the lift-off process does not use an agent of high reactivity but use only water, ~e Y1Ba2Cu3O7~ oxide superconductor ~in film 1 and lhe substrate S are not degraded.
Thereafter, the substrate S is again heated to a temperature of 350 to 400 ~C under a pressure lower than 1 x 1o-9 Torr so as to clean the 10 e xposed insulating region 50, the superconducting source region 2 and the superconducting drain region 3.
Then, a c-axis oriented YlBa2Cu307~ oxide superconductor thin film 11 having a thickness of 5 nanometers is deposited on the insul~tin~
region 50 by an MBE, as shown in Figure 4G. A condition of forming 1 5 the YIBa2Cu3O7 ~ oxide superconductor thin film 11 by an MBE is as follows:
~olecular 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 YlBa2Cu3O7 ~ oxide superconductor thin film 11 on the insulating region 50 becomes a superconducting channel 10.
Then, a insulating layer 17 is fonned of Si3N4, MgO or SrTiO3 on the YlBa~Cu307 ~ oxide superconductor thin film 11, as sho-vn in ~ 2195810 Figure 4H, and an Au layer 14 on the insulating layer 17, as shown in ~igure 4I.
Finally, the Au layer 14 is processed into a gate electrode 4, the ins~ tin~ layer 17 is processed into a gate insulating layer 7, and ~e S s~ource electrode 12 and the drain electrode 13 are folmed of Au on the superconducting source region 2 and superconducting drain rcgion 3.
With this, he super-FET i~ accordance with ~e present invention is completed.
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 r~laxed, and the manufactured super-FET has a excellent performance.
In the above mentioned embodiment, the oxide superconductor thin film 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 lmaterial, particularly a high-TC copper-oxide type compound oxide superconductor material, for example a Bi-Sr-Ca-Cu-O
compound 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 invention is in no way limited to the details of the illustrated structures 9~
but converts and modifications may be made within the scope of the appended claims.
SPECIFICATION 2 1 ~ 5 ~ 10 Title of the Invention ~ 5METHOD FOR MANUFACTURING
A SUPERCONDUCTING DEVICE
Background of the Invention Field of the invention The present invention relates to a method for manufacturing a superconducting device.
Description of related art Devices which utilize superconducting phenomena operate rapidly 15 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 possible to produce a superconducting device which operates at relatively high temperature.
Josephson device is one of well-known superconducting devices.
FIowever, since Josephson device is a two-terminal device, a logic gate which utilizes Josephson devices becomes complicated configuration.
I'herefore, three-terminal superconducting devices are more practical.
.~' 2195810 Typical three-terminal superconducting devices include two types of super-FET (field effect transistor). The first type of the super-FET
i~ncludes a semiconductor channel, and a superconductor source electrode and a superconductor drain electrode which are formed closely to each S c~ther on both side of the semiconductor channel. A portion of ~esemiconductor layer bel:ween the superconductor source electrode and ~e superconductor drain electrode has a greatly recessed or undercut rear surface so as to have a reduced thickness. In addition, a gate electrode is forrned through a gate insulating layer on the portion of the recessed or u.ndercut 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 proxinnity effect, the superconductor source electrode and the superconductor drain electrode have to be positioned within a -' 2195810 distance of a few times the coherence length of the superconductor materials of the superconductor source electrode and the superconductor drain electrode. In particular, since an oxide superconductor has a short coherence length, a distance between the superconductor source electrode S and the superconductor drain electrode has to be made less than about a few ten nanometers, if the superconductor source electrode and the superconductor drain electrode are formed of the oxide superconductor material. However, it is very difficult to conduct a fine processing such as a ~me pattern etching, so as to satisfy the very short separation distance 10 n~entioned 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 tl~e 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 superconducting chamnel 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 less than five nanometers and the gate insulating layer should have a 2 O thickness more than ten nanometers which is sufficient to prevent a tunnel c~Lrrent.
In the super-FET, since the extremely thin superconducting channel is connected to the relatively thick superconducting source region and the superconducting drain region at their lower portions, the superconducting 25 current flows substantially horizontally through the superconducting channel and substantially vertically in the superconducting source region and the superconducting drain region. Since the oxide superconductor has ~ ' 21958iO
the largest critical current density Jc in the direction perpendicular to ~-axes of its crystal lattices, the superconducting channel is preferably iformed of a c-axis oriented oxide superconductor thin film and the superconducting source region and the superconducting drain region are S l~referably formed of a axis oriented oxide superconductor thin ~llms.
In a prior art, in order to manufacture the super-FET which has ~e ~uperconducting ch~nnel of c-axis oriented oxide supercondllctQr thin ~
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 oriented oxide superconductor thin film is etched and removed excluding a portion which will be the superconducting channel. Then, an a-axis oriented oxide superconductor thin film is deposited so as to form the superconducting source region and the superconducting drain region.
In another prior art, at first an a-axis oriented oxide superconductor thin film 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 alffected. In addition, the etched surface of the oxide superconductor thin film 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 ~ 2195810 A superconduct;ng device as disclosed herein may comprise 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 5 r,uperconductor thin films on the non-superconducting oxide layer separated from each other and gently inclining to each other, a third r,uperconducting 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 iincline 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 c apability of the superconducting device can be improved.
Preferably the third superconducting region forms a weak link of a Josephson junction, so tlhat the superconducting devicc '- 2195810 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.
~ another preferred embodiment, the third superconducting region S Iol1ns a superconducting channel, so that superconducting current can flow ~etween the ~lrst and second superconducting region through ~e third sllperconducting region. In this case, it is preferable that the superconducting dévice 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 film. 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 20 of a Pr1Ba2Cu3O7 ~ 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 film 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 formed 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 '-'' 219581() diffusion from substrate. Thus, the oxide superconductor thin film deposited on the PrlBa2Cu307 ~ thin f~llm has a high quality.
Ln a preferred embodiment, the oxide superconductor is formed of high-TC (high critical l:emperature) oxide superconductor, particularly, S ~o~ned of a high-TC copper-oxide type compound oxide superconductor for example a Y-Ba-Cu-O compound oxide superconductor material, a ~3,i-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 pireferably 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 forrned on a se:miconductor 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 MgAI04 layer and a BaTiO3 layer if silicon is used as a substrate.
Another form of superconducting device may comprise a substrate, a 2 0 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 25 sicles 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 2 ! 9 58 1 0 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 S superconducting channel is connected to the superconducting source region and the superconducting drain region at the height of their middle po~tions.
According to still ano~er embodiment disclosed herein a superconducting device comprises a substrate having a 10 p)rincipal surface, a non-superconducting oxide layer having a similar crystal structure to that of the oxide superconductor, two superconducting n~gions formed of a c-axis oriented oxide superconductor thin film s~eparated 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 region are formed of one c-axis oriented oxide superconductor thin fillm ~hich 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 provided a superconducting device comprising a substrate having a principal surface, a nom-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 '- 21~5810 extremely thin superconducting channel formed of a c-axis oriented oxide superconductor thin film on the non-superconducting oxide layer, which electrically connects the superconducting source region to the slLlperconducting drain region, so that superconducting current can flow S dlrough the superconducting channel between the superconducting source r~gion and ~e supercon.ducting drain region, and a gate electrode ~rough a gate insulator on the superconducting channel for controlling ~e superconducting curren~ flowing through the superconducting t~h~nnel, in which the superconduc~,ing source region and the superconducting drain 10 region have upper surfaces gently inclined to the superconducting channel.
According to a fifth aspect of the superconducting device the device comprises a substrate having a principal surface, a non-superconducting oxide layer having a similar 15 clystal structure to that of the oxide superconductor, two superconducting regions formed of c-axis oriented 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 continuous to the two 2 0 superconducting regions and forms a weak link of a Josephson junction, in which the two superconducting regions have upper surfaces gently inclined to the weak link.
According to a sixth aspect of the superconducting device, the device comprises a substrate, a non-superconducting layer formed on a principal 2 5 surface of said substrate, an extremely thin superconducting channel formed of an oxide superconductor thin film on the non-superconducting layer, a ~ 21~5810 s,uperconducting source region and a superconducting drain region of a l~latively thick thickness formed of the oxide superconductor at ~e both s,ides of the superconducting channel separated from each other but ~lectrically connected through the superconducting channel, so ~at a S siuperconducting current can flow through the superconducting channel between the supercondllcting 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 10 superconducting channel is connected to the superconducting source region and the superconducting drain region at the height of their middle F'~rtions.
A method for manufacturing a superconducting device 15 nnay comprise the steps of forming on aprincipal 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 sluperconductor thin film is divided into two superconducting regions by the insulating region, and forming a second extremely thin oxide 2 ~ sluperconductor thin film on the insulating region and the two sllperconducting regions which is continuous to the two superconducting regions.
I O -' ~ 2195810 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 iions, Ba ions and Cs ions.
It is preferable dlat ~e second extremely thin oxide superconductor S lthin film is fonned to have a grain boundary in it so as to foIm a weak k of Josephson junction. It is also preferable that dle second extremely lthin oxide superconductor 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 iFurther includes the steps of forming a gate insulating layer on the second extremely thin oxide superconductor thin film at a portion above the insulating region and forming a gate electrode on the gate insulating ] ayer.
According to another aspect of the method disclosed herein 15 For manufacturing a superconducting device, the method comprises Ithe s~eps 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 i'ilm 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, alld forming a second extremely thin oxide superconductor thin film on the exposed portion of the 25 non-superconducting oxide layer and the two superconducting regions ~vhich is continuous to ~he two superconducting regions.
'~ 21'5810 In one preferred embodiment, the second extremely thin oxide superconductor thin film is formed to includes a grain boundary in it so a.s to constitute a weak link of Josephson junction. It is also preferable that the second extremely thin oxide superconductor thin ~llm is formed S so as to constitute a superconducting ch~nnel of a super~ T. ~ ~is case, ~he method preferably further includes the steps of forming a gate i]nsulating layer on the second extremely thin oxide superconductor thin film at a portion above the the exposed portion of the n.on-superconducting oxide layer and forming a gate electrode on the gate 1 ~ i]:lsulating layer.
According to still another aspect of the method for manufacturing a superconducting device, the method comprises the steps of forming on a principal surface of a substrate a first oxide superconductor thin film having a relatively thick thickness, 15 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 2 0 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 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 ex tremely 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 ins~ tin~ layer and a gate electrode stacked on ~c S gate insulating layer on a portion of the second oxide superconductor thin film above ~e non-superconducting layer, and removing ~e SiO2 layer so that the source electrode and the drain electrode are exposed.
It is preferable ~at the SiO~ layer is removed by using a weak ~i solution.
10' Summary of the ;nvention According to the present invention, t~ere is prc~vided a method for manufacturing a superconducting device, cornprising the steps of forming on a principal surface of a substrate.a 15 lift-off layer, removing the lift-off layer excluding a portion at which a projecting insulating region will be formed, etching dle principal surface 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, forming a first oxide superconductor thin film on the principal surface 2 0 andl the projecting insulating region, removing the rern~inin~ 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 suliFace of the projecting insulating region is exposed, forming a second oxide superconductor thin film on the projecting insulating region which 2 5 constitutes a superconducting channel, and forming a gate insulating layer and gate electrode on the superconducting channel.
In one preferred embodiment, the lift-off layer is preferably forrned of a CaO layer of which surface is covered with a Zr layer. This lift-off layer can be removed by utilizing water and following reaction:
'-' 21~581() CaO + H20 ~ Ca(OH)2 In the above process, no reactive agent is used but water.
~erefore, if the flat-top projection is formed by ~e above process, ~e substrate and the superGonducting ~in film are not degraded.
The above and o~her objects, features and advantages of the present invention will be apparent from ~e following description of preferred e:mbodiments 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 Embodiment 1 Referring to Figures lA to lF, a process for manufacturing the super-FET will be described.
'--' 21958~0 As shown in Figure lA, a MgO (100) single crystalline substrate S
hlaving a subst~nti~lly planar principal surface is prepared.
As shown in Figure lB, an oxide layer 20 having a thickness of 100 nlanometers composed of a c-axis oriented PrlBa2Cu307 e thin film is S deposited on the principal surface of dle substrate S and a c-axis oriented ~ Ba2Cu307.~ oxide superconductor ~in film 1 having a ~ickness of about 300 nanometers is deposited on dle oxide layer 20, by for example a s;puttering, an MBE (molecular beam epitaxy), a vacuum evaporation, a C'VD, etc. A condition of forming the c-axis oriented PrlBa2Cu3O7 ~ thin 10 fiilm and the c-axis oriented YlBa2Cu3O7 ~ oxide superconductor thin film 1 by off-axis sputtering is as follows:
PrlBa2Cu307 ~ thin film Temperature of the substrate 750 ~C
Sputtering Gas Ar: 90%
~2: 10%
Pressure 10 Pa Y'lBa2Cu307 ~ oxide superconductor thin film Temperature of the substrate 700 ~C
Sputtering Gas Ar: 90%
2 O ~2: 10%
Pressure 10 Pa Then, as shown in Figure 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 concave gently. The tilt angle of the concave portion 14 is less than 40~
and its length is about 100 nanometers.
' '' 2195810 Thereafter, Ga ions are implanted into a bottom portion of the concave portion 14 by an energy of 50 to lS0 keV so as to fonn an insulating region 50, as shown in Figure lD. Ln this connection, Al ions, ~1 ions, Si ions, Ba ions and Cs ions can be also used instead of Ga ions.
S 'l~e YlBa2Cu307~ oxide superconductor thin film 1 is divided into a sluperconducting source region 2 and a superconducting drain region 3 by e insulating region SOO
Then, the substrate S is heated to a temperature of 350 to 400 ~C
under a pressure lower ~han 1 x 10-9 Torr so as to clean the surface of dle 10 YlBa2Cu3O7~ oxide superconductor thin film 1. This heat-treatment is not necessary, if the surface of the YIBa2Cu307 ~ oxide superconductor thin fiLrn 1 is clean enough.
Thereafter, as shown in Figure lE, a c-axis oriented YlBa2Cu307~
oxide superconductor thin film 11 having a thickness on the order of l S albout S nanometers is deposited on the surface of the YlBa2Cu3O7~ oxide superconductor thin film 1 by an MBE (molecular beam epitaxy). A
condition of forming the c-axis oriented YIBa2Cu3O7 ~ 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 O3 atmosphere Pressure 1 x 10-5 Torr Temperature of the substrate 700~C
Since the YlBa2Cu3O7~ oxide superconductor thin film 11 is formed on the gently curved surface of the YIBa2Cu3O7 ~ oxide superconductor thin film 1, it becomes an uniform c-axis oriented oxide '-' 2195810 superconductor thin f~lm. A portion of the YlBa2Cu3O7 8 oxide superconductor thin film 11 on the insulating region 50 becomes a sluperconducting channel.
Finally, as shown in Figure lF, a gate ins~ ting layer 7 is formed S of Si3N4, MgO or SrTiO3 on the superconducting ch~nnel 10 and a gate electrode 4 is formed of Au on ~e gate insulating layer 7. Metal electrodes may be formed on the superconducting source region 2 and the superconducting drain region 3, if necessa~y. With this, the super-FET in accordance with the present invention is completed.
As explained above, the superconducting channel, the slllperconducting source region and the superconducting drain region of the above mentioned super-FET manufactured in accordance with the eimbodiment of thle method of the present invention are formed of c-axis oriented oxide superconductor thin films. Therefore, the super-FET has 15 nf~ undesirable resistance nor undesirable Josephson junction between th~e 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 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 the above method, if the YlBa2Cu3O7 ~ oxide superconductor thin fiLrn 11 is deposited to have a grain boundary so as to form a weak link of 2 5 thle Josephson junction on the insulating region 50, a Josephson junction device is manufactured. In this case, the superconducting source region and the superconducting drain region are two superconducting electrodes.
; ' 219581~) 1 ~lmost all the above mentioned features of the super-FET can apply to the Josephson junction dlevice.
Embo-lim~nt 2 S Referring to Figures 2A to 2C, a second emlbodiment of the process for m~nllfacturing ~e superconducting device will be described.
~ this second embodiment, the same processings as those shown in F'igures lA to lB are performed.
Then, as shown in Figure 2A, the YIBa2Cu3O7 ~ oxide 10 superconductor thin filrn 1 is processed by He ion-beam accelerated by an energy of 3 to S0 keV so that the YlBa2Cu3O7~ oxide superconductor thin fiilm 1 is divided into a superconducting source region 2 and a slLlperconducting drain region 3 which have inclined surfaces gently inclined to each other. The tilt angle of the inclined surfaces is less than 15 40~. The oxide layer 20 of PrlBa2Cu3O7 ~ 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 20 3 and the exposed surface of the oxide layer 20. This heat-treatment is not necessary, if the sul~aces 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 YlBa2Cu307~
25 oxide superconductor thin film 11 having a thickness on the order of albout S nanometers is deposited on the surfaces of the superconducting source region 2 and the superconducting drain region 3 and the exposed "-- 219581~ 1 ~,urface of the oxide layer 20 by an MBE (molecular beam epitaxy). A
condition of forrning the c-axis oriented YlBa2Cu307 ~ oxide superconductor thin rilm 11 by an MBE is the same as that of l_mbodim~nt 1.
S Since the YIBa~Cu307~ oxide superconductor thin f;lm 11 is ionned on ~e gently curved surfaces of the superconducting source ~gion 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 YIBa2Cu307 ~ oxide O 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 SrTi~03 on the superconducting channel 10 and a gate electrode 4 is formed of Au on the gate insulating layer 7. Metal 15 e lectrodes may be forrned on the superconducting source region 2 and the siuperconducting drain region 3, if necessary. With this, the super-FET in ~ccordance with the present invention is completed.
As explained above, the superconducting channel, the superconducting source region and the superconducting drain region of ~0 the above mentioned super-FET manufactured in accordance with the embodiment of the method of the present invention are formed of c-axis oriented 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 25 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 .~'' 21~5810 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 the above method, if the YIBa2Cu307~ oxide superconductor thin S film 11 is deposited to have a grain boundary so as to fo~rn a weak link of ~he Josephson junction on the exposed surface of the oxide layer 20, a Josephson junction device is manufactured. In this case, the superconducting source region and the superconducting drain region are ~wo superconducting electrodes. Almost all the above mentioned features 10 c~f the super-FET can apply to the Josephson junction device.
E mbodiment 3 Referring to Figures 3A to 3J, a third embodiment of the process ~Dr manufacturing 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 YIBa2Cu3O7~ 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 sjputtering is as follows:
Temperature of the substrate 700~C
Sputtering Gas Ar: 90%
~2 10%
Pressure 5 x 10-2 Torr '-'" 2~ 70 Then, as shown in Figure 3C, an Au layer 14 having a ~ickness of 30 to 100 nanometers is formed on the YIBa2Cu3O7.~ oxide superconductor thin film 1. As shown in Figure 3D, a sio2 layer 15 ~laving a thickness of 250 nanometers is fo~ned on the Au layer 14 by a 5 CVD. A center portion of the SiO2 layer 15 is removed by using a ~hotolithography. Using ~e processed SiO2 layer 15 as a mask, center ~ortions of the Au layer 14 and ~e YIBa2Cu307~ oxide superconductor ~in 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 dlat ~e 10 ~u layer 14 is divided into a source electrode 12 and a drain electrode 13, the YlBa2Cu307,~ oxide superconductor thin film 1 is divided into a superconducting source region 2 and a superconducting drain region 3, and a portion 16 of the surface of the substrate 5 is exposed between them, as shown in Figure 3E.
Then, the substrate 5 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 sl~urce region 2 and tlhe superconducting drain region 3. While the PrlBa2Cu3O7 ~ thin filrn 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 PrlBa2Cu307 ~ oxide thin filrn 20 by MBE is as follows:
Molecularbeam source Pr: 1225~C
'~' 21~5810 Ba: 600~C
Cu: 1040~C
Pressure 1 x 10-5 Torr Temperature of ~e substrate 750~C
S Then, the Pr molecular beam source is exchanged to a Y molecular beam source and dle temperature of ~e substrate is lowered to 700 ~C so at a superconducting ch~nnel 10 of a c-axis oriented YlBa2Cu307~ oxide superconductor thin film having a thickness of about S nanometer is continuously formed on the oxide layer 20 of PrlBa2Cu307 ,~ dlin film, as 10 sihown 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 r~gion 2, the superconducting channel 10 and the superconducting drain region 3. The gate insulating layer 7 has a thickness of 10 to 20 15 nanometers and covers side surfaces of the superconducting source region 2 and 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 gate insulating layer 7 by a vacuum evaporation.
Finally, as shown in Figure 3J, the SiO2 layer 15 is removed by 20 using a 10% HF solution. Metal layers are formed on the source e]lectrode 12 and the drain electrode 13 respectively, so as to planarize the u;pper surface of the device, if necessary. With this, the super-FET in aecordance with the present invention is completed.
The above mentioned super-FET manufactured in accordance with 2 5 the third embodiment o:f the method has a superconducting channel which is formed on the PrlBa2Cu307 ~ non-superconducting oxide layer of which tl~e crystal structure is similar ~ 3 '9~81'D
to that of ~e YlBa2Cu3O7 ~ oxide superconductor. Therefore, the bottom portion of the superconducting channel is not degraded so that the s,ubst~nti~l cross-sectional area of the superconducting channel of the ~,uper-FET is larger than ~at of a conventional super-FET.
S Additionally, sinc~ the superconducting channel is connected to ~e s,uperconducting source region and the superconducting drain region at the height of their middle portions, superconducting current ef~lciently flows into and flows from 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 insulating layer and the ~ate electrode are self-aligned. In the above method, since the oxide superconductor thin films are covered during the etching process, the superconducting 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 nnanufactured super-FET has a excellent performance.
E mbodiment 4 Referring to Figures 4A to 4J, a forth embodiment of the process f~r manufacturing the superconducting device will be described.
As shown Figure 4A, an MgO (100) substrate 5 similar to that of Embodiment 1 is prepared. As shown in Figure 4B, a lift-off layer 16 of a CaO layer having a tllickness of 1 ~lm covered with Zr layer having a thickness of 50 nanome~ers is deposited on the substrate S.
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 the substrate 5 is etched by areactive ion etching"I,on millinE using Ar ions etc. In ~is etc-hin process, the rem~ining lift-off layer 16 is used as a mask so that a projecting 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 film 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 YlBa2Cu307 ~ 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 follows:
Molecularbeam source Y: 1250 ~C
Ba: 600~C
Cu: 1040~C
~2 or O3 atmosphere Pressure 1 x 10-5 Torr Temperature of the substrate 680~C
Then, the lift-off layer 16 is removed so that the YlBa2Cu3O7 ~
oxide superconductor thin film 1 is divided into a superconducting source "~' 21958tO
region 2 and a superconducting drain region 3 and the insulating region '50 is exposed, as shown in figure 4F. This lift-off process l~tili7~s water and a following reaction:
CaO + H2O ~ Ca(OH)~
S Since the lift-off process does not use an agent of high reactivity but use only water, ~e Y1Ba2Cu3O7~ oxide superconductor ~in film 1 and lhe substrate S are not degraded.
Thereafter, the substrate S is again heated to a temperature of 350 to 400 ~C under a pressure lower than 1 x 1o-9 Torr so as to clean the 10 e xposed insulating region 50, the superconducting source region 2 and the superconducting drain region 3.
Then, a c-axis oriented YlBa2Cu307~ oxide superconductor thin film 11 having a thickness of 5 nanometers is deposited on the insul~tin~
region 50 by an MBE, as shown in Figure 4G. A condition of forming 1 5 the YIBa2Cu3O7 ~ oxide superconductor thin film 11 by an MBE is as follows:
~olecular 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 YlBa2Cu3O7 ~ oxide superconductor thin film 11 on the insulating region 50 becomes a superconducting channel 10.
Then, a insulating layer 17 is fonned of Si3N4, MgO or SrTiO3 on the YlBa~Cu307 ~ oxide superconductor thin film 11, as sho-vn in ~ 2195810 Figure 4H, and an Au layer 14 on the insulating layer 17, as shown in ~igure 4I.
Finally, the Au layer 14 is processed into a gate electrode 4, the ins~ tin~ layer 17 is processed into a gate insulating layer 7, and ~e S s~ource electrode 12 and the drain electrode 13 are folmed of Au on the superconducting source region 2 and superconducting drain rcgion 3.
With this, he super-FET i~ accordance with ~e present invention is completed.
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 r~laxed, and the manufactured super-FET has a excellent performance.
In the above mentioned embodiment, the oxide superconductor thin film 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 lmaterial, particularly a high-TC copper-oxide type compound oxide superconductor material, for example a Bi-Sr-Ca-Cu-O
compound 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 invention is in no way limited to the details of the illustrated structures 9~
but converts and modifications may be made within the scope of the appended claims.
Claims (3)
1. A method for manufacturing a superconducting device, comprising the steps of forming on a principal surface of a substrate, a lift-off layer, removing the lift-off layer excluding a portion at which a projecting insulating region will be formed, etching the principal surface 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, forming 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 oxide 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. A method claimed in Claim 1 wherein the lift-off layer is formed of a CaO layer covered with a Zr layer.
3. A method claimed in Claim 2 wherein the lift-off layer is removed by utilizing water and following reaction:
CaO + H2O ~ Ca(OH)2
CaO + H2O ~ Ca(OH)2
Applications Claiming Priority (11)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP35219791 | 1991-12-13 | ||
| JP35219391 | 1991-12-13 | ||
| JP352197/1991 | 1991-12-13 | ||
| JP352193/1991 | 1991-12-13 | ||
| JP352194/1991 | 1991-12-13 | ||
| JP35219491 | 1991-12-13 | ||
| JP35518791 | 1991-12-20 | ||
| JP355187/1991 | 1991-12-20 | ||
| JP4352659A JPH05251776A (en) | 1991-12-13 | 1992-12-10 | Superconducting element and manufacture thereof |
| JP352659/1992 | 1992-12-10 | ||
| 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 |
|---|---|
| CA2195810A1 true CA2195810A1 (en) | 1993-06-14 |
Family
ID=27543454
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| 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 |
| CA002195810A Abandoned CA2195810A1 (en) | 1991-12-13 | 1992-12-14 | Method for manufacturing a superconducting device |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| 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 |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA2195809A1 (en) |
-
1992
- 1992-12-14 CA CA002195809A patent/CA2195809A1/en not_active Abandoned
- 1992-12-14 CA CA002195810A patent/CA2195810A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| CA2195809A1 (en) | 1993-06-14 |
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