JPH0376173A - Superconducting element and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a metal superconducting material laminated layer structure having high superconducting critical temperature by forming a laminated layer structure of a thin film of a material superconducted by alloying different metal to metal antiferromagnetic material and a thin film of different material from the antiferromagnetic material. CONSTITUTION:In the case of a laminated layer structure made of a metal superconducting material, sapphire board 1 is cleaned with hot phosphoric acid by a vacuum depositing method, surface-treated, CrRe alloy 2, Si 3 are alternately formed to form a laminated layer thin film. The arriving vacuum degree of a depositing chamber is about 10<-11>Torr, an electron beam depositing method is used, Cr, Re are simultaneously deposited, and Re concentration is set to 30%. The thickness of the film is set by a period of CrRe alloy/Si = 50/100Angstrom to 1500Angstrom of total film thickness. As a result, a structure similar to an oxide superconductor having high superconducting critical temperature Tc is obtained, thereby realizing a high superconducting critical temperature Tc.

Description

[Detailed description of the invention] [Industrial application field]

The present invention describes phase diagrams of superconducting materials and compound superconducting materials with high critical temperatures.
38 (1988) pp. 2477-2485 (
Phy, Rev, B 38 (1988) pp, 24
77-2485). In addition, regarding the phase diagram of alloys of metals Cr and Re, which are antiferromagnetic materials, please refer to the Journal of the Physiology Society.
of Japan 52 (1983) pp. 2301-2303 (J, Phys, Soc, Jpn
52 (1983) pp. 2301-2303). Regarding superconducting three-terminal devices using magnetoelectric effects, see IEE Electron Device Letters EDL-10 (198
9) pages 183 to 185 (I EEE Ele
ctron Device Lett. EDL-10 (1989) pp. 183-185).

[Problem to be solved by the invention]

The superconducting properties of the above oxide superconducting materials are strongly affected by the amount of oxygen, and since they are quaternary and have many constituent elements, they tend to form mixed phases, and when an element is fabricated using them, compared to metal superconducting materials, There were many problems such as difficulty in microfabrication. Furthermore, the superconducting three-terminal device that utilizes the above-mentioned magnetoelectric effect is called a Josephson junction, as shown in Figure 2. It consists of a magnetoelectric material Cr2O formed on the opposite side of one superconducting electrode and a gate electrode. The operation is performed by applying a gate voltage to the magnetoelectric material Cr2O to generate a magnetic moment, and applying the resulting magnetic field to the Josephson junction to control the Josephson current. However, in the configuration shown in FIG. 2, since the magnetic field is applied to the Josephson junction via the superconducting electrode, the magnetic field is excluded by the Meissner effect of the superconducting material, and there is a problem that the effect of the gate voltage cannot be sufficiently obtained. Furthermore, conventionally, Josephson devices using Nb-based superconducting materials are two-terminal devices, so conventional silicon devices such as MO
There was a problem in that it was difficult to apply the logic used in the S transistor. Further, it has been difficult to realize a superconducting three-terminal device using an oxide superconducting material due to problems inherent to the above-mentioned oxide superconducting material. A first object of the present invention is to provide a metal superconducting material laminated structure having a high superconducting critical temperature Tc and a superconducting element using the same. A second object of the present invention is to provide a structure suitable for a superconducting three-terminal element with a high rate of increase, which utilizes the above magnetoelectric effect. A third object of the present invention is to provide a structure suitable for using the above-mentioned metal superconducting material in a superconducting three-terminal element utilizing the above-mentioned magnetoelectric effect, and a method for manufacturing the same. A fourth object of the present invention is to provide a structure suitable for using the conventional Nb-based superconducting material in a superconducting three-terminal element utilizing the above-mentioned magnetoelectric effect, and a manufacturing method thereof. A fifth object of the present invention is to provide a superconducting element using an oxide superconducting material and utilizing the magnetoelectric effect.

[Means to solve the problem]

In order to achieve the above first object, the superconducting material laminated structure of the present invention comprises a thin film of a material made superconducting by alloying a metal antiferromagnetic material with an underlying metal, and a material different from the thin film. It consists of a laminated structure with a thin film. Further, this laminated structure is used to form a superconducting element. In order to achieve the above second object, the superconducting element of the present invention includes a pair of superconducting electrodes, a Josephson tunnel barrier film made of a magnetoelectric material existing between the superconducting electrodes, and an electric field generated in the magnetoelectric material. and a gate electrode that connects the gate electrode. In order to achieve the third object, the superconducting element of the present invention uses an alloy containing at least Cr as a superconducting electrode and an oxide thereof as a magnetoelectric material. Further, the alloy containing at least Cr is, for example, a CrRe alloy. In order to achieve the fourth object, the superconducting element of the present invention includes a pair of superconducting electrodes made of gold and @Nb. Josephson tunnel barrier film made of magnetoelectric material;
a gate electrode capable of generating an electric field in the magnetoelectric material, preferably an oxide containing at least Al, such as TbA Q OX, or G
This uses dA Q Ox or DyAlOx. In order to achieve the fifth object, the superconducting element of the present invention includes a superconducting electrode made of an oxide superconducting material, a magnetoelectric material in contact with the superconducting electrode, and a gate electrode that can be used to generate an electric field in the magnetoelectric material. Preferably, the magnetoelectric material is one having a perovskite crystal structure similar to that of the oxide superconducting material, such as Tb.
Al○×, or GdA Q Ox, or DyAlO
This uses x.

[Effect]

Oxide superconducting materials, for example, have a superconducting critical temperature Tc of about 90
In Y-Ba-Cu-0, as shown in the phase diagram shown in Figure 3, when the amount of oxygen increases and the concentration of holes increases, the antiferromagnetic order disappears, and immediately after that, superconductivity appears. do. This antiferromagnetic order is realized in the two-dimensional plane of CuO. The fact that antiferromagnetism and superconductivity are adjacent in the phase diagram is a common property of oxide superconducting materials, and although the mechanism of the development of the high superconducting critical temperature Tc is not clear, it is thought that there is a deep relationship. . On the other hand, as shown in the phase diagram shown in FIG. 4, the CrRe alloy transforms from an antiferromagnetic material to a superconducting material when the antiferromagnetic material Cr is alloyed with Re and its concentration increases. In other words, increasing the Re concentration in the CrRe alloy causes the antiferromagnetic order to disappear and superconductivity to appear, which is equivalent to increasing the amount of oxygen in the oxide superconducting material. Furthermore, considering that the antiferromagnetic order of the oxide superconducting material is realized on the two-dimensional surface of CuO, it is possible to
A high superconducting critical temperature Tc can be obtained by the laminated structure of an e-alloy thin film and a thin film made of a different material, thereby achieving the above-mentioned first objective. It goes without saying that the metal that can be alloyed with Cr is not limited to the above-mentioned Re, as long as the antiferromagnetic order disappears and superconductivity appears. It is also sufficient for the antiferromagnetic material to be transformed from an antiferromagnetic material to a superconducting material by mixing different materials, such as Cr--Mo alloy, Mn. Needless to say, the material is not limited to Cr, such as γ-Fe. In addition, as a material different from the above-mentioned CrRe alloy and laminated thereon, an insulator which is a material that alleviates the interaction between adjacent CrRe alloy thin films in the laminated structure, such as SiO
x, AlOx, MgO, or when the wave function seeped out of the metal due to bonding forms an exciton, the exciton energy gives the upper limit of the superconducting critical temperature Tc, and it is a material that achieves a sufficiently high superconducting critical temperature Tc. Semiconductors, such as S i , G e , A Q 1-
xGaxAs. Preferred are InSb, InAs, or metals that are carrier-rich materials, such as Au, Ag, Cu.
In addition, the thickness of the CrRe alloy thin film in the laminated structure and the thickness of the thin film made of a different material need to be sufficient to realize the two-dimensionality of the CrRe alloy, so that the thin film does not become island-like. If coverage is obtained, the former is 1000 Å
The latter is sufficient, but preferably 500 Å or less, more preferably 50 Å or less, and the latter is sufficient even if it is 1000 Å or more, but preferably 500 Å or less, more preferably 5
It shall be 0A or less. In a Josephson device consisting of a pair of superconducting electrodes and a Josephson tunnel barrier film existing between the superconducting electrodes, the Josephson tunnel barrier film is used as a magnetoelectric material, and an electric field is generated in the magnetoelectric material. Form a gate electrode. This realizes a three-terminal superconducting element. Furthermore, the magnetic moment generated from the magnetoelectric effect by applying the gate voltage effectively acts on the Josephson tunnel barrier film without being hindered by the Meissner effect of the superconducting electrode, so a superconducting element with a large amplification factor where the effect of the gate voltage is sufficiently exerted is created. This makes it possible to achieve the above second objective. An alloy containing at least Cr is used as a superconducting electrode, and then its surface is oxidized. Cr contained in the generated oxide
Since 2O is a magnetoelectric material, a connection structure between a superconducting material and a magnetoelectric material has been realized, thereby achieving the third hundredth objective. Examples of the alloy containing at least Cr include the above-mentioned CrR5 alloy. Furthermore, a surface oxide film containing this Cr2O was added to a thickness of 100 Å.
It goes without saying that the above-mentioned three-terminal type Josephson device with a gate electrode can be realized by forming a superconducting electrode thereon and forming a gate electrode on the oxide film containing Cr2O. Nb-AM-AIOK-Nb Josephson element is A1
20x is a Josephson tunnel barrier film, Nb and A
It has been evaluated as a highly reliable superconducting element due to its good bonding properties between L and ANO*, and the high stability of the high melting point gold gNb material compared to InPb alloy. A lower superconducting electrode made of Nb is formed using a forming machine, and a metal containing A2, such as Afl-Tb, AM-Gd, or Al-Dy, is formed into a film, and then this is oxidized, and an electric field is applied to the upper superconducting electrode made of Nb and this oxide. This creates a usable gate electrode. TbAnO, GdA Q Ox, or DyAnO is a magnetoelectric material, and Nb, Al, and A 110 x exhibit good bonding properties, so the magnetoelectric effect can be used and the Josephson material has high reliability. element,
That is, a three-terminal type superconducting element can be realized, thereby achieving the fourth objective. The magnetoelectric material GdA Q O, has a lattice constant a-axis = 5.2
47A, b-axis = 5.304A, c-axis = 7.447m orthorhombic perovskite crystal structure, DyAlO, has lattice constants a-axis = 5.21m, b-axis = 5.31m, c-axis = 7 .4
It has an orthorhombic perovskite crystal structure. Oxide superconducting material La1. aasro, tacu04 has lattice constant a axis = 3.78 people (1,41 lines a = 5.33 people), C
Axis = 13.23 large tetragonal 2NiF, type crystal structure,
YB a2Cu, O. is the lattice constant a-axis = 3.82 people (1,41*a=:5.3
9 people), b axis = 3.89A (1,41*b = 5.49
A), Orthorhombic oxygen-deficient perovskite crystal structure with c-axis = 11.68A. Bi, 5rzCaN-1CuNO2N+*+Z is the lattice constant a-axis ~ b-axis ~ 5.4 people, T Q 2 B a, C
an-I CUNO2N+4+Z takes lattice constants a-axis ~ b-axis ~ 5.4 people. Therefore, GdAl○s + D y
The lattice constant mismatch between A +203 and the above-mentioned oxide superconducting material is as small as about 3%, making it possible to bond the two without impairing crystallinity, making it possible to bond the magnetoelectric material Gd.
AlO,. If DyAlO is provided with a gate electrode that can be used to generate an electric field, a superconducting element utilizing the magnetoelectric effect can be realized, thereby achieving the fifth objective. In the above description, GdAl○ is used as the magnetoelectric material. Although DyAQO is given as an example, these materials can be used as long as they have a similar crystal structure to oxide superconducting materials and have a lattice mismatch of 10% or less, more preferably 5% or less, and even more preferably 5% or less. Needless to say, there is no limit.

【Example】

Hereinafter, the present invention will be explained in detail with reference to Examples. 1st
A first embodiment of the present invention will be described with reference to the drawings. This example is an example in which a laminated structure made of metallic superconducting materials was manufactured. Using vacuum evaporation method. Clean sapphire substrate 1 (c-side) with hot phosphoric acid. After surface treatment, CrRe alloy 2. A laminated thin film was formed by alternately depositing Si3. The ultimate vacuum in the deposition chamber is approximately 1
It is 0-11 Torr. All depositions use electron beam evaporation, Cr and Re are simultaneously deposited, and R
The e concentration was 30%, that is, Cr, Re, etc., and the total film thickness was 1500 with a cycle of CrRe alloy/S i =50λ/100A. FIG. 1 shows a cross-sectional view of the obtained metallic superconducting material. Next, the temperature dependence of resistivity was measured using the usual four-terminal measurement method. As a result, the superconducting critical temperature Tc obtained is reported to be Cr. R
e. It was recognized that the superconducting critical temperature Tc was improved by two-dimensional stacking. Next, a second embodiment of the present invention will be explained using FIG.
This example is an example of a superconducting element in which an alloy containing Cr, CrRe alloy, is used as a superconducting electrode, and its oxide is used as a magnetoelectric material. The vacuum evaporation apparatus used in this example consists of two vacuum chambers: a evaporation chamber with an ultimate vacuum of about 10''''11 Torr, and a sample exchange chamber into which oxygen gas can be introduced. A sapphire substrate 1 (R side) was used as the substrate, and after cleaning the surface with hot phosphoric acid, Cr was deposited simultaneously using the electron beam evaporation method as in the first embodiment of the present invention. Re3゜membrane 20
00λ film was formed to form the lower superconducting electrode 4. Next, after transporting to the exchange chamber, 1 atm of oxygen gas was introduced to oxidize the surface, forming an oxide containing magnetoelectric materials Cr, O, and forming the Josephson tunnel barrier H5 (No. 5
Figure (a)). Next, this substrate was transported to the vapor deposition chamber again, and Cr7°Re was deposited in the same manner as in the method for forming the lower superconducting electrode 4. A film of 200 OA was deposited to form an upper superconducting electrode 6. After applying the resist, the resist was patterned using a normal photolithography method, and then the upper superconducting electrode 6 was processed using an ion milling method to form a Josephson junction 7 with an area of 5 μm×5 μm. Next, using photolithography again, PSG (PSG is Phosphos) was deposited on the Josephson tunnel barrier film 5 by chemical vapor deposition.
(l+), which stands for ilicata glass, is about 10
The gate electrode 8 was formed using the 00A type (FIG. 5(b)). The current-voltage characteristics between the superconducting electrodes 4 and 6 of the three-terminal superconducting element thus obtained are shown in FIG. 5(c) using the gate voltage Vg as a parameter. When Vg=OV, the maximum superconducting current is lm=100μA, but when Vg=0. I
At V, rm=10 μA, and it can be confirmed that the superconducting current can be controlled by the gate voltage. In this example, the Josephson tunnel barrier film is made of magnetoelectric material, so
The magnetic moment generated by applying the gate voltage directly acts on the Josephson current, and this results in a three-terminal superconducting element with a higher amplification factor than a three-terminal superconducting element in which the Josephson tunnel barrier film and magnetoelectric materials are different. realizable. Next, a third embodiment of the present invention will be described using FIG. 6. This example is an example of a superconducting element in which the superconducting electrode is made of Nb. Using a DC sputtering device with a dual target consisting of a target Gcl consisting of Nb and a target consisting of Aff, 2 Nb was deposited on a Si substrate l in an Ar atmosphere.
000λ film was formed to form the lower superconducting electrode 4. After sufficiently cooling without exposing to the atmosphere, Gd and Afl were deposited to a thickness of 8oλ. Next, 99.999% high purity oxygen gas was introduced into the vacuum chamber, and a magnetoelectric material GdAlOx was formed to form the Josephson tunnel barrier film 5. After evacuation, the upper superconducting electrode 6 was formed by depositing 200 OA of Nb by direct current sputtering in an Ar atmosphere in the same manner as the lower superconducting electrode 4 (FIG. 6(a)). Thereafter, similarly to the second embodiment of the present invention, photolithography was used to provide a gate electrode that can be used to generate an electric field in the magnetoelectric material, thereby realizing a three-terminal superconducting element. FIG. 6(b) shows the dependence of the current-voltage characteristic between the superconducting electrodes 4° and 6 on the gate voltage Vg. This confirms a three-terminal superconducting element with a higher amplification factor. In this example, G d A 10 * is used as the Josephson tunnel barrier film 5.
However, TbAlOx, which is an oxide magnetoelectric material containing the same Al as GdAlOX, or DyA +20
It goes without saying that even if 8 is used, the same effect as in this embodiment can be obtained. Further, in this example, by forming a film of metal Gd and All and then oxidizing it, G d A
Although nOx was formed, it goes without saying that a superconducting element similar to this example can also be obtained by forming GdAfl◯8 by using a high frequency sputtering method using GdAlO as a sputtering target. Further, Cr is a stable material that is used as an MS material for magnetic disks and one surface is covered with Cr oxide. Therefore, if this is used as a Josephson tunnel barrier film, a stable Josephson device can be realized. Furthermore, since cr203 is a magnetoelectric material, by providing a gate electrode thereon as in this example, a three-terminal superconducting element in which the Josephson tunnel barrier film is made of a magnetoelectric material can be obtained. It goes without saying that this can be achieved. Next, a fourth embodiment of the present invention will be described using FIG. 7. This example is an example of a superconducting element in which the superconducting electrode is made of an oxide superconducting material. Using a high-frequency magnetron sputtering device with dual targets of DyBa2Cu, sOx and DyADOx, Ar:02=1:1 was deposited on the 5rTiO substrate l.
．． The lower superconducting electrode 4 was formed by 2000 people depositing DyBa2Cu30x under conditions of a pressure of 30 m Torrt and a substrate temperature of 730°C. Subsequently, a magnetoelectric material DyAlO was formed at a thickness of 100 Å without exposing it to the atmosphere to form the Josephson tunnel barrier film 5. Next, similarly to the lower superconducting electrode 4, D
yBa, Cu, and Ox were deposited by 2000 people to form the upper superconducting electrode 6 (FIG. 7(a)). Thereafter, similarly to the second embodiment of the present invention, photolithography was used to provide a gate electrode that can be used to generate an electric field in the magnetoelectric material, thereby realizing a three-terminal superconducting element. FIG. 7(b) shows the dependence of the current-voltage characteristics between the superconducting electrodes 4 and 6 on the gate voltage Vg. This confirms that a three-terminal superconducting element with a high amplification factor has been realized. still,
In this example, DyBa2Cu, Ox and D y A Q
Ox was continuously formed into a film, but in order to prevent mutual diffusion between the two, there was a layer of A u y A g y with a thickness of 1 μm or less between the two.
A superconducting element similar to this example can also be obtained by forming a thin film made of at least one member selected from the metal group consisting of P d + P t or a composite thereof. The above metals, especially A
u gives the degree of spread of the Cooper pair. The coherence length of superconductivity is estimated to be approximately 1 μm, which is extremely long and comparable to the film thickness, making it effective as a diffusion prevention layer. Furthermore, the second aspect of the present invention. Third. A three-terminal superconducting element having the structure shown in FIG. 8 was manufactured using each material of the fourth example, and a high amplification factor was also obtained with this element.

【Effect of the invention】

As explained above, according to the present invention, a metal antiferromagnetic material is alloyed with a different metal, and a thin film of a superconducting material and a thin film of a different material are layered. , a structure similar to an oxide superconductor having a high superconducting critical temperature Tc can be obtained, thereby making it possible to realize a high superconducting critical temperature Tc. In addition, in a Josephson device consisting of a pair of superconducting electrodes and a Josephson tunnel barrier film between them, the Josephson tunnel barrier film is made of a magnetoelectric material, and a gate electrode that can be used to generate an electric field in the magnetoelectric material is also used. will be established. As a result, the magnetic moment generated by the gate voltage directly acts on the Josephson current, resulting in a superconducting element with a higher amplification factor than a three-terminal superconducting element in which the Josephson tunnel barrier film and magnetoelectric material are configured separately. It becomes possible.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a superconducting material laminated structure according to the first embodiment of the present invention, FIG. 2 is a cross-sectional view of a three-terminal superconducting element using a conventional magnetoelectric material, and FIG. Superconducting material Y
Figure 4 is the phase diagram of Ba2Cu and Ox, Figure 4 is the phase diagram of CrRe alloy, Figures 5 (a) and (b) are cross-sectional views of the superconducting element of the second embodiment of the present invention, Figure 6 (a), jI7 (a) is a cross-sectional view of a superconducting element according to the third and fourth embodiments of the present invention, and FIG. 5 (C), FIG. 6 (b), and FIG. Second. Third. A current-voltage characteristic diagram of the device of the fourth embodiment, and FIG. 8 is a sectional view of the device of a modification of the present invention. Explanation of symbols 10.・Substrate, 2...CrRe alloy, 3...Si,
4... Lower superconducting electrode, 5... Josephson tunnel l wall film, 6... Upper superconducting electrode, 7... Josephson junction, 8... Gate electrode. Ta/Tacha 3 r”il 'r'Ba-x, KotLJ OHx Treatment 41 Yor', -Toba 1K)

Claims (1)

[Scope of Claims] 1. A superconducting element comprising at least a laminated structure of a metal superconducting material and a material different from the metal superconducting material, the metal superconducting material comprising an antiferromagnetic material and the antiferromagnetic material. A superconducting element characterized by being made of an alloy of a ferromagnetic material and a different metal. 2. The superconducting element according to claim 1, wherein the antiferromagnetic material is Cr, Cr-Mo alloy, Mn_2_y-Fe
A superconducting element characterized by being at least one member selected from the group consisting of: 3. The superconducting element according to claim 1, wherein the antiferromagnetic material is Cr, and the metal different from the antiferromagnetic material is Re. 4. In the superconducting element according to claim 1, the material different from the metal superconducting material is SiO_x, AnO_x, Mg
O_x, Si, Ge, Al_1_-_xGa_xAs, InSb, InAs,
A superconducting element characterized by being at least one member selected from the group consisting of Au, Ag, and Cu. 5. A superconducting element comprising at least a pair of superconducting electrodes, a Josephson tunnel barrier film existing between the superconducting electrodes, and means for generating and using an electric field in the Josephson tunnel barrier film, A superconducting device characterized in that the Josephson tunnel barrier film is made of a magnetoelectric material. 6. The superconducting element according to claim 5, wherein at least one of the pair of superconducting electrodes is made of a metal containing Cr, and the Josephson tunnel barrier film contains at least Cr oxide. element. 7. The superconducting element according to claim 5, wherein at least one of the pair of superconducting electrodes is made of Nb, and the Josephson tunnel barrier film is made of an oxide containing at least Al. . 8. The superconducting element according to claim 7, wherein the oxide containing at least Al is TbAlO_x, GdAlO
A superconducting element characterized by being at least one member selected from the group consisting of __x and DyAlO_x. 9. The superconducting element according to claim 5, wherein at least one of the pair of superconducting electrodes is made of an oxide superconducting material, and the Josephson tunnel barrier film is at least an oxide having a perovskite crystal structure. Features of superconducting elements. 10. The superconducting element according to claim 9, wherein the oxide superconductor is (La_1_-_xM_x)_2CuO_
4_−_δ(0≦x≦1, δ≧0, M=Ca, Sr, B
a) or LnBa_2Cu_3O_7_-_δ(δ≧
0, Ln=Y, La, Nd, Sm, Eu, Gd, Dy,
Ho, Er, Tm, Yb, Lu) or Bi-Sr-(
Ca_1_-_yY_y)-Cu-O(y≧0) or Tl-Ba-Ca-Cu-O or Ln'_2_-_xCe_xCuO_4_-_δ(0≦
x≦2, δ≧0;
A superconducting element characterized by being _x. 11. The method for manufacturing a superconducting element according to claim 6, comprising at least the steps of forming the metal containing Cr, and forming the Cr oxide by oxidizing the Cr. A method for manufacturing a superconducting element. 12. The method for manufacturing an oxide superconducting element according to claim 7 or 8, comprising the step of forming the Nb, Al and the A
A method for manufacturing a superconducting element, comprising at least the steps of forming a composite metal other than Al, and forming an oxide containing at least Al by oxidizing the composite metal. 13. A superconducting material laminated structure comprising a metal superconducting material and a material different from the metal superconducting material, the metal superconducting material comprising an alloy of an antiferromagnetic material and a metal different from the antiferromagnetic material. A superconducting material laminated structure characterized by: