JP2003264319A - High temperature superconducting josephson junction and superconducting electronic device having it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high temperature superconducting Josephson junction in which a variation in characteristics of Josephson junction is suppressed and the characteristics and reliability of a product employing the Josephson junction can be enhanced, and a superconducting electronic device employing it. <P>SOLUTION: The inventive high temperature superconducting Josephson junction sandwiches a barrier layer 5 by two superconductors 2 and 4 wherein the superconductors 2 and 4 contain one or more kinds of elements selected from among Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, one or more kinds of elements selected from among Ba, Sr and Ca, Cu and oxygen, and the barrier layer 5 contains one or more kinds of elements selected from among La, Nd, Sm and Eu, and one or more kinds of elements selected from among Y, Gd, Dy, Ho, Er, Tm, Yb and Lu. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-temperature superconducting Josephson junction and a superconducting device having the same, and particularly when applied to a superconducting device such as a chip having a plurality of Josephson junctions. A high-temperature superconducting Josephson junction capable of improving the characteristics and reliability of a product using this chip by reducing the variation of the Son-junction, and a superconducting device having the high-temperature superconducting Josephson junction Is.

[0002]

2. Description of the Related Art Superconductors have (1) zero electrical resistance,
(2) Perfect diamagnetism, (3) Josephson effect, and other properties that other materials do not have, so power transport, generator, fusion plasma confinement, magnetic levitation vehicle, magnetic shield, ultra high Sensitive magnetic sensor, microwave high speed communication device,
Wide application to high-speed computers is expected.
Conventionally, the superconducting transition temperature (Tb) of NbTi, Nb ₃ Sn
Only superconductors with low c) were known, but 198
In 6 years Bednorz and Mueller
Discovered a copper oxide high temperature superconductor (La _1-x Ba _x ) ₂ CuO ₄ having a superconducting transition temperature (Tc) of about 30 K (JGBednorz and KAMueller: Z. Phys. B64,
189 (1986)).

After that, YBa₂Cu₃O_y(Tc = 90
K), Bi₂Sr₂Ca₂Cu₃O_y(Tc = 110K),
Tl₂Ba₂Ca₂Cu₃O_y(Tc = 125K), HgB
a₂Ca ₂Cu₃O_y(Tc = 135K) etc.
Oxide high temperature superconductivity having superconducting transition temperature (H-Tc)
The body was reported, and now the manufacturing process, physical properties,
Many studies have been made and reported on applications and the like.
Among them, YBa₂Cu₃O_yHigh temperature superconductor is Tl or Hg
It does not contain harmful elements such as
Since it is a superconductor, it can be used for electronic devices and wire rods.
It is regarded as the most promising material for materials.

As an application example to an electronic device, there is a Josephson element utilizing the Josephson effect, but this element requires a Josephson junction fabrication technique using a thin film technique. As Josephson junctions for oxide high-temperature superconductors, bicrystal junctions, bi-epitaxial junctions,
Josephson junctions with various structures such as step edge junction, bridge junction, ramp edge junction, and laminated junction have been proposed (Susumu Takada: Applied Physics 62, 443 (1993)). Among them, the ramp edge junction has a structure in which a tunnel barrier layer is obliquely formed between a pair of high-temperature oxide superconductors, the tunnel barrier layer has a large driving capability during switching, and the critical current is a factor for controlling the thickness of the tunnel barrier layer. It is promising because it can be changed (Mitsuo Hidaka, Tetsuro Sato, Shuichi Tahara: Applied Physics 67 1167 (1998)).

One of the indicators showing the performance of the Josephson junction
Is the IcRn product. This IcRn product is a certain temperature
Maximum value of current that can flow in superconducting state at
(Critical current value: Ic), the superconducting state is broken and the state is normal.
Standardized the resistance (Rn) when the condition is reached.
Qualitatively, the signal magnitude during switching is qualitatively
It is an index that shows the quality. The larger this IcRn product, the faster
Can be operated. The above lamp edge joint is
A large IcRn product is obtained compared to the Josephson junction of the structure
To be An example of this ramp edge junction is a tunnel
PrBa for the barrier layer₂Cu₃O_y(PBCO)
YBa is used for the high temperature superconductor that becomes the electrode.₂Cu ₃O_y(YBC
O) has been proposed.

On the other hand, the laminated junction has a structure in which an oxide high temperature superconductor layer, a tunnel barrier layer, and an oxide high temperature superconductor layer are sequentially laminated, and research is continued as a structure advantageous for future large-scale integration. ing. In these ramp edge junctions and laminated junctions, P is used as a tunnel barrier layer.
rBa ₂ Cu ₃ O _y (PBCO) layer, Nb-doped SrTi
An O ₃ layer, a damaged layer during the process, etc. are used. Here, in order to form a tunnel barrier layer, a case where a thin film is deposited is called an "artificial barrier", and a case where a surface damage layer caused by ion irradiation during the process is used without depositing a thin film is referred to as a "process barrier". It is called a Josephson junction (IEJ: Interface-Engineered Junction) using a damaged layer.

This IEJ has the advantage that a large tunneling current can be obtained because the junction layer is extremely thin, and is actively studied (BH Moeckly et al., Appl. Phys. L).
ett.71, 2526 (1997)). It has been confirmed by a transmission electron microscope (TEM) that an extremely thin layer of about 1 to 2 nm is formed in the above-mentioned lamp edge junction, and this extremely thin layer functions as a Josephson junction. However, the detailed structure has not yet been elucidated (for example, JG Wen et al., "Advances
in Superconductivity XII "-Proc.ISS'99, p.984, (19
99.10.17-19), Y. Soutome et al., "Advances in Super
conductivity XII "-Proc.ISS'99, p.990, (1999.10.17-
19)).

By the way, in the lamp edge joining or the lamination joining, when the parameters at the time of production are improper and the thickness of the joining layer becomes extremely thin, and it becomes difficult to control the thickness, some places of the joining layer are short-circuited. It happens that it ends up. The current-voltage characteristic (IV characteristic) at the joint changes depending on the thickness of the joint. When the thickness of the bonding layer is too thick, the superconducting current cannot flow, and therefore the current-voltage characteristic (IV characteristic) at the bonding portion is obtained.
Indicates simply the characteristics as a resistor as shown in FIG.

If the thickness of the bonding layer is appropriate,
As shown in FIG. 4B, the superconducting current can tunnel the junction layer without generating a voltage within the range of the critical current value Ic. In this case, when a current exceeding the critical current value Ic is passed, a sudden voltage is generated. The IV characteristic in the state where the voltage is generated gradually approaches a straight line passing through the origin. The IV characteristic of this Josephson junction is RSJ (Resistivel
y Shunted Junction) characteristic. When the bonding layer is too thin and short-circuited, as shown in FIG.
A voltage is gradually generated at a current of the critical current value Ic or more. This phenomenon is that a voltage is induced by the movement of the magnetic flux, so this IV characteristic is FF (Flux Flo
w) Called a property.

[0010]

By the way, in order to realize a superconducting device using the Josephson effect, a Josephson junction having the above-mentioned RSJ characteristics and having an appropriate critical current value Ic and IcRn product is used. Although it is necessary to fabricate a large number, there is a problem that the Josephson junction has a large variation and the stability and reliability of the characteristics are not sufficiently satisfied under the present circumstances.
In particular, since the critical current value Ic is sensitive to the junction structure and the manufacturing process, there is an urgent need to establish a technique for suppressing the variation in the critical current value Ic.

When considering the industrial application of Josephson junctions, a technique for producing a plurality of Josephson junctions operating with appropriate characteristics with good reproducibility is essential. For large-scale integration in the future, it is necessary to fabricate many Josephson junctions with small variations in characteristics. So far, Josephson junctions using oxide high-temperature superconductors with high superconducting transition temperature (Tc) have been studied for the purpose of realizing superconducting devices with high operating temperature. , Demonstration of circuit operation was limited to very small ones.

[0012] For example, according to J. Talvacchio et al., In order to operate a circuit having 100 junctions or more, it is necessary to suppress characteristic variation to 10% or less in standard deviation (σ) (J. Talvacchio et al. ., IEEE Trans. Appl. Sup
ercond. 7, 2051 (1997)), recently, a lamp-edge type Josephson junction that satisfies this characteristic has been reported.

Also, Satoh et al. Use YBa ₂ Cu ₃ O _yx for the superconducting electrode and (La _0.3 Sr _0.7 ) for the insulating layer.
(Al _0.65 Ta _0.35 ) O _y was used to obtain a standard deviation (σ) of 8% (at 4.2 K) at 100 junctions (T. Satoh et al., IEEE Trans. Appl. Supercond. 9). ,
3141 (1999), JP 2000-150974 A).
According to Satoh et al., 2 between two superconducting electrodes
Good bonding characteristics are achieved by forming a uniform barrier layer with a thickness of nm or less and mixing La into the interface from the insulating layer during etching. However, the amount of La mixed in is so small that it cannot be confirmed even with an analytical transmission electron microscope that analyzes using characteristic X-rays generated by irradiating an electron beam with a beam diameter of about 1 nm (JG
Wen et al., Appl. Phys. Lett. 75 (1999)).

[0014], Hitoshi Saotome, YBa ₂ to the superconducting electrode
Using Cu ₃ O _yx and CeO ₂ for the insulating layer, the standard deviation (σ) at 100 junctions was 7.9% (at 4.2K) (May May, et al., 62nd Academic Meeting of Applied Physics) Proceedings of the lecture No.1 p.195 14a-G-7 (2001.9 / 11-14)).
They did not use any material containing La, and achieved this value by a structure and process in which La was not mixed between two superconducting electrodes. Thus, in the conventional Josephson junction, the standard deviation (σ) is 8 at 100 junctions.
Although about 100% has been obtained, this level is not sufficient to achieve integration of 100 junctions or more,
There is a strong demand for Josephson junctions that can achieve smaller characteristic variations with a larger number of junctions.

The present invention has been made in order to solve the above problems, and the dispersion of the characteristics of the Josephson junction is small, and the characteristics and the reliability of the product using the Josephson junction can be improved. An object of the present invention is to provide a high temperature superconducting Josephson junction and a superconducting device having the same.

[0016]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors to improve the stability of a metastable phase in a Josephson junction, the barrier layer was La, Nd, Sm, Eu.
One or more elements selected from Y, G
A cation containing one or more elements selected from d, Dy, Ho, Er, Tm, Yb, and Lu and having an ionic radius of 0.0947 nm or more when 6-coordinated with oxygen is positive. It has been found that when the ion atomic ratio is 35 to 65%, the stability can be improved without impairing the characteristics, and thus the variation in the characteristics within the chip can be suppressed.

That is, the high temperature superconducting Josephson junction of the present invention is a Josephson junction in which a barrier layer is sandwiched between two superconductors, and the superconductors are Y, L.
a, Nd, Sm, Eu, Gd, Dy, Ho, Er, T
Containing one or more elements (RE) selected from m, Yb and Lu, one or more elements (AE) selected from Ba, Sr and Ca, Cu and oxygen (O) The barrier layer includes one or more elements (RE1) selected from La, Nd, Sm, and Eu, and Y,
It is characterized by containing one or more elements (RE2) selected from Gd, Dy, Ho, Er, Tm, Yb and Lu.

In the barrier layer, the proportion of cations having an ionic radius of 0.0947 nm or more when 6-coordinated with oxygen (O) is preferably in the range of 35 to 65% in terms of cation atomic ratio. It is desirable that the barrier layer be edge-joined or laminated-joined with the two superconductors.

The superconducting device of the present invention is characterized by comprising at least one high temperature superconducting Josephson junction of the present invention.

Here, the characteristic variation in the chip will be described in more detail. In general, characteristic variations within a chip are due to non-uniformity caused by subtle changes in fabrication conditions. The barrier layer at the junction is known to be a very thin metastable phase (JGWen et a
L., Appl. Phys. Lett. 75, 2470 (1999)). Reducing the variation in the characteristics of the Josephson junction is nothing but to produce this unstable metastable phase stably with good reproducibility. This is a strict requirement to precipitate a non-equilibrium metastable phase in a very thin layer.

Up to now, most of the researches on high temperature superconducting Josephson junctions have been carried out by using YBa ₂ as a superconducting material.
Cu ₃ O _y has been used. Wen et al., YBa ₂ Cu ₃
When the composition of the junction portion in the lamp edge type Josephson junction using O _y was measured using an analytical transmission electron microscope, it was Y: Ba: Cu = 30: 43: 27 (JGWen et al., Appl. Phys. Lett. 75, 2470 (199
9)). On the other hand, according to the study of the phase diagram of the Y-Ba-Cu-O system, it is already known that there is no stable phase having such a cation ratio (for example, DMDeLeeuw et al., Phys.
ica C 152, 39 (1988)).

The barrier layer existing at the bonding interface has a thickness of about 2 nm.
It is said to be a crystal phase having a perovskite type structure having the following extremely thin thickness. This perovskite structure is represented by the chemical formula ABO ₃ , and the A site atom (A atom) is surrounded by 12 oxygen atoms, and the B site atom (B atom) is surrounded by 6 oxygen atoms. There is. A cation having a relatively large ionic radius occupies the A site and a small cation occupies the B site.

Here, Y: Ba: Cu = 30: 43: 2
Consider that cations mixed in a ratio of 7 form a perovskite structure together with oxygen. Considering the ionic radius, it is not difficult to imagine that Ba with a large ionic radius will occupy the A site and Cu with a small ionic radius will occupy the B site. Therefore, an intermediate ionic radius between Ba and Cu is considered. The Y with must be distributed to both sites in equal proportions. When this Y is regularly arranged, delicate heat treatment control is required.

Further, it is very difficult for Y to occupy a 12-coordinated site, and there is a possibility that it may be precipitated as a stable phase such as Y ₂ O ₃ in some places. It is a factor that reduces the controllability and reliability of the characteristics. In fact, it has been confirmed that Y ₂ O ₃ is precipitated at the interface portion of the Josephson junction, which has poor characteristics. It is considered that such precipitation of a different phase is one of the causes because there is not enough element having a relatively large size that can occupy the 12-coordinated site near the interface.

There is also an example in which the barrier layer has a perovskite structure represented by Y _1-x BaCu _x O _y and having a lattice constant of 0.41 to 0.43 nm, but the composition is determined by using an analytical transmission electron microscope. As a result, the ratio of Ba: Y + Cu was 1:
It turned out that it was off from 1. As a result, Y becomes A
If it does not enter the site, it is easily considered to precipitate as Y ₂ O ₃ .

When considering the electro-neutral principle of a perovskite type substance, for example, Y _1-x BaCu _x O _y (= B
a (Y _1-x Cu _x ) O _y ), the valence of Ba is +
Since the valence of 2, Y is +3 and does not take the mixed valence, C
The valence of u becomes +2 or more, or oxygen is deficient. In any case, it is considered to be chemically unstable. Furthermore, the lattice constant of the YBa ₂ Cu ₃ O _y high temperature superconductor is a≈b≈c / 3≈0.38-
It is 0.39 nm, which is smaller than 0.41 to 0.43 nm. Considering these factors, the composition is Y: Ba: Cu.
= 30:43:27 barrier layer is Y _1-x BaCu _x O
_Even if the perovskite structure represented by _y has a lattice constant of 0.41 to 0.43 nm, its stability remains a problem.

In the present invention, in the Josephson junction in which the barrier layer is sandwiched between two superconductors, the barrier layer is one or more elements (RE1) selected from La, Nd, Sm and Eu. ), And Y, Gd, Dy,
By containing one or more elements (RE2) selected from Ho, Er, Tm, Yb, and Lu, the element (RE1) that constitutes the barrier layer is the element (RE1) that constitutes the superconductor ( Since RE) is an element having a relatively large ionic radius, it easily occupies the A site of the perovskite structure. On the other hand, the element (RE2) forming the barrier layer easily occupies the B site of the perovskite structure.

Therefore, for example, Y _1-x BaCu _x O _y
In (= Ba (Y _1-x Cu _x ) O _y ), a part of Ba is replaced with the element (RE1), so that the element (RE1)
Has a valence of +3, which increases the stability of the perovskite structure, which is considered from the neutrality principle of electricity. Further, since the element (RE1) has a smaller ionic radius than Ba, the lattice constant of the perovskite structure becomes small, and YBa ₂ C
Improves lattice matching with a superconductor having a crystal structure similar to that of u ₃ O _y .

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Each embodiment of a high temperature superconducting Josephson junction and a superconducting device having the same according to the present invention will be described.

[First Embodiment] FIG. 1 shows a first embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a lamp edge type high temperature superconducting Josephson junction according to the embodiment of the present invention, in which reference numeral 1 is a substrate
Is a first superconductor, 3 is an interlayer insulating layer, 4 is a second superconductor,
5 is a barrier layer.

The end portion of the first superconductor 2 is edge-processed with respect to the substrate 1 to form an edge surface 2a which is inclined at a predetermined angle with respect to the substrate surface. Similarly to the first superconductor 2, the interlayer insulating layer 3 has its end portion obliquely edge-processed with respect to the substrate 1 to form an edge surface 3a flush with the edge surface 2a of the first superconductor 2.

The second superconductor 4 is formed so as to cover the entire first superconductor 2 and the interlayer insulating layer 3 at the Josephson junction portion, and has an extremely thin thickness at the interface with the edge surface 2a of the first superconductor 2. Barrier layer 5 is formed. As a result, a ramp-edge type Josephson junction in which the barrier layer 5 is sandwiched between the two superconductors 2 and 4 is formed.

The substrate 1 is an insulative substrate whose surface is a flat surface having an extremely high degree of flatness. For example, (La _0.3 S
r _0.7 ) (Al _0.65 Ta _0.35 ) O ₃ etc. (La _1-x Sr _x ).
(Al _1-y Ta _y ) O ₃ , MgO, SrTiO ₃ (ST
O), an inorganic insulating material such as NdGaO _3, LaAlO ₃ is preferably used.

The first superconductor 2 and the second superconductor 4 are
Y, La, Nd, Sm, Eu, Gd, Dy, Ho, E
One or more elements (Re) selected from r, Tm, Yb and Lu, one or more elements (Ae) selected from Ba, Sr and Ca, Cu and oxygen ( It is a copper oxide high temperature superconductor containing O) and is a perovskite type ceramics.

These first superconductor 2 and second superconductor 4
As long as the above composition satisfies the above conditions, the superconductors 2 and 4 may have the same composition or different compositions. This copper oxide high temperature superconductor is, for example, Y _3-xy Ba _x La _y
Cu ₃ O _z (YBLCO), YBa ₂ Cu ₃ O _y (YBC
O), NdBa ₂ Cu ₃ O _y (NdBCO), YbBa ₂ C
_{u 3 O y (YbBCO),} Yb 3-xy Ba x La y Cu 3 O z
Etc. are preferably used.

The interlayer insulating layer 3 is composed of the first superconductor 2 and the second superconductor 2.
It is made of an insulating material sufficient to cut off between the superconductors 4. For example, CeO ₂ , (La _0.3 Sr _0.7 ) (Al
_0.65 Ta _0.35 ) O ₃ etc. (La _1-x Sr _x ) (Al _1-y Ta
_y ) O ₃ , SrTiO ₃ (STO), CaSnO _{3 and the} like are preferably used.

The barrier layer 5 is an extremely thin layer having a composition different from that of the first superconductor 2 and the second superconductor 4, and La, N
one or more elements (RE1) selected from d, Sm and Eu, and Y, Gd, Dy, Ho, Er, Tm,
It is an oxide compound containing one or more elements (RE2) selected from Yb and Lu. Examples of the oxide-based compound include Y _3-xy Ba _x La _y Cu ₃
O _z (YBLCO), (Y, Yb) _1-xyz Ba _x La _y C
_{u z O w, Nd 1-} xyz Y x Ba y Cu z O w and the like. The barrier layer 5 may contain other elements such as an alkali metal and a transition metal by using an artificial barrier method or the like.

The ratio of cations having an ionic radius of 0.0947 nm or more when 6-coordinated with oxygen (O) in this barrier layer is in the range of 35 to 65% in terms of cation atomic ratio. The composition of the barrier layer can be quantitatively analyzed by using an analytical transmission electron microscope having an electron beam diameter of about 1 nm or less. However, in this embodiment, the data of the ionic radius is based on the paper of Shannon (RDS
hannon, ActaCryst. A32 p.751 (1976)).

Next, a method of manufacturing the lamp edge type high temperature superconducting Josephson junction of this embodiment will be described with reference to FIG. First, as shown in FIG. 2A, a first superconductor layer 11 and an interlayer insulating layer 12 are sequentially formed on a substrate 1 by RF sputtering, CVD, reactive CVD, etc., and spin-coated. A photoresist 13 is formed on the interlayer insulating layer 12 by a method or the like. Next, the photoresist 13 is patterned by the photolithography method, and the patterned photoresist is subjected to a reflow process to form the mask 14 having a gentle sloped end 14a.

Next, as shown in FIG. 2B, the mask 14 is used to perform etching treatment on the interlayer insulating layer 12 and the first superconductor layer 11 by Ar ion (Ar ⁺ ) irradiation 15, to thereby make Josephson The end portions of the interlayer insulating layer 12 and the first superconductor layer 11 at the joint portion are made to have a gentle slope. As a result, the inclined surface of the first superconductor layer 11 is A
Damaged by the r ion (Ar ⁺ ) irradiation 15 results in an extremely thin damaged layer 16. Then, the mask 14 is removed using an ashing device.

Then, as shown in FIG. 2C, the first superconductor layer 11 and the interlayer insulating layer 12 are formed by a laser deposition method or the like.
A second superconductor layer 17 is formed on top. By forming this second superconductor layer 17, the damaged layer 16 generated on the inclined surface of the first superconductor layer 11 reacts with the first superconductor layer 11 and the second superconductor layer 17 to react with each other. It becomes the barrier layer 5.

Finally, an electrode made of a conductive material such as gold (Au) is formed at a predetermined position on each of the first superconductor layer 11 and the second superconductor layer 16 by a vapor deposition method, a sputtering method or the like. As described above, the lamp edge type Josephson junction in which the extremely thin barrier layer 5 is sandwiched between the two superconductors 2 and 4 can be easily manufactured by using the IEJ method.

According to the ramp edge type high temperature superconducting Josephson junction of this embodiment, the barrier layer 5 is formed of La, Nd,
One or more elements (RE1) selected from Sm and Eu, and Y, Gd, Dy, Ho, Er, Tm,
Since the element (RE1) contains one or more elements (RE2) selected from Yb and Lu, the element (RE1) easily occupies the A site, and the element (RE2) easily occupies the B site. The stability of can be increased.

Since the barrier layer 5 contains the element (RE1) and the element (RE2), the lattice matching between the barrier layer 5 and the two superconductors 2 and 4 can be improved, and A stable Josephson junction can be realized. As described above, it is possible to obtain a Josephson junction that exhibits good RSJ characteristics and has extremely small variations in the critical current values Ic and IcRn products.

By forming a large number of ramp-edge type high temperature superconducting Josephson junctions of this embodiment on one chip, it is possible to obtain a superconducting device having extremely small variations in the critical current values Ic and IcRn products.

[Second Embodiment] FIG. 3 shows a second embodiment of the present invention.
FIG. 4 is a cross-sectional view showing a stacked high temperature superconducting Josephson junction of the embodiment of FIG. 1, in which a first superconductor 2 and an interlayer insulating layer 3 are sequentially formed on a substrate 1, and a portion corresponding to the Josephson junction of the interlayer insulating layer 3 is formed. An opening 3b is formed, a second superconductor 4 is formed on the interlayer insulating layer 3 and on the first superconductor 2 exposed in the opening 3b, and Ar is formed on the surface of the first superconductor 2 exposed in the opening 3b. The damaged layer generated by the ion (Ar ⁺ ) irradiation reacts with the first superconductor 2 and the second superconductor 4 to form an extremely thin barrier layer 5.

As described above, the Josephson junction of this embodiment is different from the Josephson junction of the first embodiment described above in the structure of the Josephson junction. The Josephson junction of the present embodiment can be easily manufactured by the IEJ method, like the Josephson junction of the first embodiment described above. The stacked high temperature superconducting Josephson junction of the present embodiment can also achieve the same effects as the ramp edge high temperature superconducting Josephson junction of the first embodiment described above.

[0048]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

1. Lamp edge type high temperature superconducting Josephson
Junction (Example 1) Y was added to the first superconductor._0.9Ba_1.9La_0.2Cu₃
O_yTo the second superconductor as YBa₂Cu ₃O_yOn the substrate (L
a_0.3Sr_0.7) (Al_0.65Ta_0.35) O₃(Hereinafter, LS
Lamp (abbreviated as AT) using the IEJ method.
An edge type Josephson junction was prepared.

First, the first superconductor was formed on the LSAT substrate by the off-axis RF sputtering method, and LSAT as an interlayer insulating layer was further formed thereon to a film thickness of 200 nm. Next, a photoresist was applied on the interlayer insulating layer by the spin coating method, followed by patterning by the photolithography method, and a reflow treatment was performed so that the edges of the photoresist had a gentle slope. Next, acceleration voltage 400V, ion current 50
The interlayer insulating layer and the first layer are irradiated by Ar ion irradiation under the condition of mA.
The superconductor was etched. Ar ion irradiation was performed while rotating the substrate with the incident direction inclined at 30 ° with respect to the substrate surface.

As a result, a gentle slope was formed on the interlayer insulating layer and the first superconductor. The surface of this slope is Ar
It is covered with a layer damaged by ion irradiation. The remaining resist was removed by an ashing device, and then a second superconductor was formed on the interlayer insulating layer and the first superconductor by a laser deposition method. Further, gold (Au) was vapor-deposited and subjected to appropriate patterning to form an electrode having a predetermined shape, whereby a sample of Example 1 was obtained.

In this sample, all 10 Josephson junctions formed on the substrate showed RSJ type IV characteristics. The IcRn product at 4.2K is 2.1 to
The critical current value Ic was 2.6 mV and was about 0.9 mA.
Further, the critical current value Ic was measured for 100 Josephson junctions connected in series formed on the same substrate, and the average value (X) and standard deviation (σ) were obtained. The variation (σ / X) of the critical current value Ic was 7.0%.

When the barrier layer was observed using an analytical transmission electron microscope having an electron beam diameter of about 1 nm, most of the thickness was 1 nm or less. Further, when the composition analysis of 20 points of the barrier layer was performed using this analytical transmission electron microscope, Y: Ba: La: Cu = 1
It was 9: 39: 12: 30. Here, an atom having an ionic radius of 0.0947 nm or more when 6-coordinated with oxygen is B
a and La accounted for 51% of the cation atomic ratio.

(Comparative Example 1) A ramp edge type Josephson junction was produced by the method of IEJ using YBa ₂ Cu ₃ O _y as the first superconductor and the second superconductor. First, the first off-axis RF sputtering method was used to form a first layer on the LSAT substrate.
A superconductor and LSAT as an interlayer insulating layer on the superconductor.
Was formed into a film having a thickness of 200 nm. Then, in the same manner as in Example 1, a gentle slope was formed on the interlayer insulating layer and the first superconductor, and the second superconductor was formed thereon.

In this sample, all ten Josephson junctions formed on the substrate showed RSJ type IV characteristics. The IcRn product at 4.2K is 2.0 to
2.4 mV, the critical current value Ic was about 0.8 mA.
When the critical current value Ic was measured for 100 Josephson junctions connected in series formed on the same substrate, the variation (σ / X) was 9.7%.

When the barrier layer was observed using an analytical transmission electron microscope with an electron beam diameter of about 1 nm, most of the thickness was 1 nm or less. Further, when the composition analysis of 20 points of the barrier layer was performed using this analytical transmission electron microscope, Y: Ba: Cu = 30: 4.
It was 1:29. The La content of this barrier layer was below the detection limit, and was hardly mixed. Also,
In some places of the barrier layer, a disordered portion of the lattice having a thickness of 3 nm or more was observed. Therefore, when the composition of this portion was analyzed, it was found that Y ₂ O ₃ and Y ₂ Ba ₂ O ₅ were precipitated. The frequency of occurrence of these precipitates was higher than that in Example 1.

(Embodiment 2) In the same manner as in Embodiment 1, the first
Using Y _0.9 Ba _1.9 La _0.2 Cu ₃ O _y as the superconductor and YbBa ₂ Cu ₃ O _y as the second superconductor, a ramp edge type Josephson junction was produced by the IEJ method. However, MgO was used for the substrate and CeO ₂ was used for the interlayer insulating layer.

In this sample, all 10 Josephson junctions formed on the substrate showed RSJ type IV characteristics. The IcRn product at 4.2K is 2.1 to
The critical current value Ic was 2.5 mV and was about 0.9 mA.
Further, when the critical current value Ic was measured for 100 Josephson junctions connected in series formed on the same substrate, the variation (σ / X) was 6.8%.

When the barrier layer was observed using an analytical transmission electron microscope in the same manner as in Example 1, the thickness was almost 1 nm or less, and the composition was (Y + Yb): Ba: L.
It was a: Cu = 20: 38: 10: 32. here,
Atoms having an ionic radius of 0.0947 nm or more when 6-coordinated with oxygen were Ba and La, and accounted for 48% of the cation atomic ratio.

(Comparative Example 2) In the same manner as in Example 2, IE
A lamp edge type Josephson junction was manufactured by the method of J. However, YBa ₂ Cu ₃ O _y containing no La was used for the first superconductor. In this sample, all 10 Josephson junctions formed on the substrate showed RSJ type IV characteristics. IcR at 4.2K
The n product is 1.4 to 1.9 mV, and the critical current value Ic is about 0.6.
It was mA. Also, the critical current value I for 100 Josephson junctions connected in series formed on the same substrate
When c was measured, the variation (σ / X) was 18.
It was 6%.

When the barrier layer was observed using an analytical transmission electron microscope, a large number of disordered portions of the lattice having a thickness of 3 nm or more were observed. When the composition was analyzed by selecting a thin portion of the barrier layer with a thickness of 1 nm or less, (Y + Y
b): Ba: Cu = 30: 34: 36. Here, the ionic radius when 6-coordinated with oxygen is 0.0947n
The atom of m or more was Ba, and the cation atomic ratio was 34%.

Example 3 NdBa ₂ C was used as the first superconductor.
u ₃ O _y , YBa ₂ Cu ₃ O _y as the second superconductor, and a lamp edge type by an artificial barrier method in which Y ₂ Cu ₂ O ₅ is thinly formed before forming the second superconductor. A Josephson junction was created.

First, the off-axis RF sputtering method was used to deposit a first superconductor on a MgO substrate and further deposit CeO ₂ as an interlayer insulating layer thereon to a thickness of 200 nm. Then, in the same manner as in Example 1, a gentle slope was formed on the interlayer insulating layer and the first superconductor. After that, Y ₂ Cu ₂ O ₅ was formed into a film of about 3 nm on them by a laser deposition method, and a second superconductor was formed thereon.

In this sample, all 10 Josephson junctions formed on the substrate showed RSJ type IV characteristics. Further, the IcRn product at 4.2K is 1.9 to
The critical current value Ic was 2.3 mV and was about 0.8 mA.
Further, when the critical current value Ic was measured for 100 Josephson junctions connected in series formed on the same substrate, the variation (σ / X) was 7.5%.

When the barrier layer was observed using an analytical transmission electron microscope in the same manner as in Example 1, most of the thickness was 1 nm or less and the composition was Nd: Ba: Y: C.
u = 15: 36: 20: 29. Here, the atoms having an ionic radius of 0.0947 nm or more when 6-coordinated with oxygen were Nd and Ba, and accounted for 51% of the cation atomic ratio.

Comparative Example 3 In the same manner as in Example 3, IE
A lamp edge type Josephson junction was manufactured by the method of J. However, the sample was prepared by omitting the step of depositing Y ₂ Cu ₂ O ₅ . In this sample, 10 formed on the substrate
Four of the junctions showed FF type IV characteristics and were not Josephson junctions. The remaining 6 showed RSJ type IV characteristics and were Josephson junctions. In these Josephson junctions, the IcRn product at 4.2K was 0.4 to 0.8 mV, and the critical current value Ic was about 0.1 mA.

When the barrier layer was observed using an analytical transmission electron microscope, a large number of disordered portions of the lattice having a thickness of 3 nm or more were observed. When a thin portion of the barrier layer having a thickness of 1 nm or less was selected and its composition was analyzed, Nd: Ba:
It was Y: Cu = 33: 39: 7: 21. Here, atoms having an ionic radius of 0.0947 nm or more when 6-coordinated with oxygen were Nd and Ba, and accounted for 72% of the cation atomic ratio.

(Example 4) In the same manner as in Example 3, a ramp edge type Josephson junction was manufactured by an artificial barrier method. However, NdBa ₂ Cu ₃ O _y was used for the first superconductor and the second superconductor, and Y ₂ BaCuO ₅ was thinly formed before forming the second superconductor.

In this sample, all 10 Josephson junctions formed on the substrate showed RSJ type IV characteristics. The IcRn product at 4.2K is 2.1 to
The critical current value Ic was 2.5 mV and about 1.0 mA.
Further, when the critical current value Ic was measured for 100 Josephson junctions connected in series formed on the same substrate, the variation (σ / X) was 7.3%.

When the barrier layer was observed using an analytical transmission electron microscope in the same manner as in Example 1, most of the thickness was 1 nm or less, and the composition was Nd: Ba: Y: C.
u = 19: 34: 22: 25. Here, atoms having an ionic radius of 0.0947 nm or more when 6-coordinated with oxygen were Nd and Ba, and accounted for 53% of the cation atomic ratio.

(Comparative Example 4) In the same manner as in Example 4, a ramp-edge type Josephson junction was manufactured by an artificial barrier method. However, before depositing the second superconductor,
Nd ₄ Ba ₂ Cu ₂ O ₁₀ was deposited instead of Y ₂ BaCuO ₅ . In this sample, out of the 10 junctions formed on the substrate, 3 junctions showed FF type IV characteristics and were not Josephson junctions. The remaining 7 joints are R
It showed an SJ type IV characteristic and was a Josephson junction. In these Josephson junctions, the IcRn product at 4.2K was 0.5 to 1.1 mV, and the critical current value Ic was about 0.1 mA.

When the barrier layer was observed using an analytical transmission electron microscope, a large number of disordered portions of the lattice having a thickness of 3 nm or more were observed. When a thin portion of the barrier layer having a thickness of 1 nm or less was selected and its composition was analyzed, Nd: Ba:
Cu was 29:37:34. Here, the atoms having an ionic radius of 0.0947 nm or more when 6-coordinated with oxygen were Nd and Ba, and accounted for 66% of the cation atomic ratio.

2. Laminated high-temperature superconducting Josephson junction (Example 5) Y _0.9 Ba _1.9 La _0.2 Cu ₃ was used as the first superconductor.
The O _y, using YbBa ₂ Cu ₃ O _y to the second superconductor, IE
A laminated Josephson junction was produced by the method of J.
However, MgO was used for the substrate and CeO ₂ was used for the interlayer insulating layer.

First, the first superconductor and the interlayer insulating layer were each formed to a film thickness of 200 nm by the off-axis RF sputtering method. Next, a photoresist was applied on the interlayer insulating layer by spin coating, and then patterning was performed by photolithography to produce a mask. Then, using this mask, the interlayer insulating layer was subjected to etching treatment by Ar ion irradiation under the conditions of an acceleration voltage of 400 V and an ion current of 50 mA, and an opening was formed in a portion of the interlayer insulating layer corresponding to the Josephson junction. A damaged layer is formed on the exposed surface of the first superconductor by Ar ion irradiation. Then, a second superconductor was deposited on the interlayer insulating layer and on the exposed surface of the first superconductor by a laser deposition method.

In this sample, all 10 Josephson junctions formed on the substrate showed RSJ type IV characteristics. Also, the IcRn product at 4.2K is 1.2 to
The critical current value Ic was 1.6 mV and was about 0.3 mA.
Further, when the critical current value Ic was measured for 10 Josephson junctions formed on the same substrate, the variation (σ / X) was 9.8%.

When the barrier layer was observed using an analytical transmission electron microscope with an electron beam diameter of about 1 nm, most of the thickness was 1 nm or less. Further, when the composition analysis of 20 points of the barrier layer was performed using this analytical transmission electron microscope, (Y + Yb): Ba: La:
Cu was 20: 37: 10: 33. Here, the atoms having an ionic radius of 0.0947 nm or more when 6-coordinated with oxygen were Ba and La, and accounted for 47% of the cation atomic ratio.

Example 6 An artificial barrier method in which YBa ₂ Cu ₃ O _y is used for the first superconductor and the second superconductor, and thin Nd ₂ CuO ₄ film is formed before the second superconductor film is formed. A lamp-edge type Josephson junction was prepared by. Here, the film thickness of Nd ₂ CuO ₄ was variously changed, and the influence of this thickness on the Josephson junction was investigated.

First, the first superconductor was deposited on the MgO substrate by the off-axis RF sputtering method, and CeO ₂ was further deposited thereon to a film thickness of 200 nm as an interlayer insulating layer. Then, in the same manner as in Example 1, a gentle slope was formed on each of the interlayer insulating layer and the first superconductor. After that, Nd ₂ CuO ₄ was formed into a film with a film thickness of about 0.5 to 50 nm by a laser deposition method, and a second superconductor was formed thereon. As described above, nine kinds of samples (Nos. 1 to 9) having different film thicknesses of Nd ₂ CuO ₄ were obtained.

Thereafter, for each sample, the IV characteristic, the critical current value Ic, the variation σ / X of the critical current value Ic, (Nd +
Ba): (Y + Cu) was determined and summarized in Table 1. In addition,
The IV characteristics and the critical current value Ic were measured for 10 Josephson junctions formed on the substrate. I
For -V characteristics, "FF", "RSJ", "resistance"
Displayed in any type of As for the variation σ / X, the critical current value I at 4.2K for 100 Josephson junctions formed on the same substrate
c was measured and the variation σ / X was determined.

[0080]

[Table 1]

According to Table 1, the film thickness of Nd ₂ CuO ₄ is 1 to
It was found that RSJ type IV characteristics were exhibited in the range of 20 nm, and the variation σ / X was smaller than 10% in the range of the film thickness of 2 to 5 nm. In particular, the sample with a film thickness of 2 to 3 nm exhibits RSJ type IV characteristics and the variation σ
It was found that / X was smaller than 8% and the effect of suppressing the variation in characteristics was small. In addition, atoms with an ionic radius of 0.0947 nm or more when 6-coordinated with oxygen are Nd and B.
However, the variation σ / X is 1 when the sum of Nd and Ba (Nd + Ba) is 35 to 65% in terms of cation atomic ratio.
It was found to be smaller than 0%.

[0082]

According to the high temperature superconducting Josephson junction of the present invention, the superconductors sandwiching the barrier layer are made of Y, La and N.
d, Sm, Eu, Gd, Dy, Ho, Er, Tm, Y
one or more elements selected from b and Lu (R
E), one or more elements (AE) selected from Ba, Sr and Ca, Cu and oxygen (O) are contained, and the barrier layer is selected from La, Nd, Sm and Eu. And at least one element (RE2) selected from Y, Gd, Dy, Ho, Er, Tm, Yb, and Lu (RE2). Therefore, the lattice matching between the barrier layer and the two superconductors can be improved, and a more stable Josephson junction can be realized. Therefore,
It is possible to obtain a Josephson junction exhibiting excellent RSJ characteristics and having extremely small variations in the critical current values Ic and IcRn products. Further, by limiting the constituent elements of the superconductor and the barrier layer as described above, a plurality of Josephson junctions with small characteristic variations can be manufactured with good reproducibility.

According to the superconducting device of the present invention, since one or more high-temperature superconducting Josephson junctions of the present invention are provided, it is possible to suppress variations in the characteristics of the Josephson junction within one superconducting device. The electric characteristics and reliability of this superconducting device can be improved. Therefore, it is possible to improve the electrical characteristics and reliability of the product using this superconducting electronic device. Further, it is possible to reproducibly manufacture a superconducting device having one or more Josephson junctions with small characteristic variations.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a ramp edge type high temperature superconducting Josephson junction according to a first embodiment of the present invention.

FIG. 2 is a process diagram showing a method for manufacturing a ramp-edge type high temperature superconducting Josephson junction according to the first embodiment of the present invention.

FIG. 3 is a sectional view showing a laminated high temperature superconducting Josephson junction according to a second embodiment of the present invention.

FIG. 4 is a diagram showing IV characteristics of a joint part, (a)
FIG. 4 is a diagram showing respective IV characteristics in the case of showing resistance, (b) showing RSJ characteristics, and (c) showing FF characteristics.

[Explanation of Codes] 1 substrate 2 first superconductor 2a edge surface 3 interlayer insulating layer 3a edge surface 3b opening 4 second superconductor 5 barrier layer 11 first superconductor layer 12 interlayer insulating layer 13 photoresist 14 mask 14a edge portion 15 Ar ion (Ar ⁺ ) irradiation 16 Damage layer 17 Second superconductor layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yuki Wakana             Foundation law, 1-14-3 Shinonome, Koto-ku, Tokyo             International Superconductivity Technology Center             Conducting Engineering Laboratory (72) Inventor Keiichi Tanabe             Foundation law, 1-14-3 Shinonome, Koto-ku, Tokyo             International Superconductivity Technology Center             Conducting Engineering Laboratory F term (reference) 4M113 AA06 AA16 AA25 AA37 AD36                       AD37 AD67 AD68 BA04 BA07                       BA11 BA15 BA23 BB07 BC04                       BC08 CA34

Claims (4)

[Claims] 1. A Josephson junction in which a barrier layer is sandwiched between two superconductors, wherein the superconductors are Y, La, Nd, Sm, Eu, Gd,
1 selected from Dy, Ho, Er, Tm, Yb, Lu
One or more elements, one or more elements selected from Ba, Sr and Ca, Cu and oxygen (O) are contained, and the barrier layer is selected from La, Nd, Sm and Eu. 1 or 2 or more elements and Y, Gd, Dy, H
A high-temperature superconducting Josephson junction comprising one or more elements selected from o, Er, Tm, Yb and Lu. 2. The barrier layer is characterized in that the proportion of cations having an ionic radius of 0.0947 nm or more when 6-coordinated with oxygen (O) is 35 to 65% in terms of cation atomic ratio. The high temperature superconducting Josephson junction according to claim 1. 3. The high temperature superconducting Josephson junction according to claim 1, wherein the barrier layer is formed by edge joining or laminated joining with the two superconductors. 4. A superconducting device comprising one or more high temperature superconducting Josephson junctions according to claim 1, 2 or 3.