JPH11243233A - Superconducting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a superconducting device sharing a Josephson junction, realizing a low inductance superconducting wiring loop, and improving the junction characteristic and uniformity of the Josephson junction for the manufacture of an integrated circuit using oxide superconducting Josephson junction. SOLUTION: This superconducting device 18 is formed by laminating a lower superconducting electrode layer 12 and an oxide interlayer insulation layer 13 comprising an oxide superconductor practically represented by REBa2 Cu3 O7-δ (RE: Rare-earth elements excluding Pr, δ: 0 to 0.5) on a substrate 11. The laminated film is selectively etched, a recess 15 is formed, the side face 15b has a given angle to the face of the substrate, the bottom face 15a reaches at least the surface of a lower superconducting electrode layer 14, and a Josephson junction is formed by having a barrier layer 16 and an upper superconducting electrode layer 17 laminated in the recess 15. For the barrier layer, an oxide having a composition of RE'Ba2 Cu3 Ox (RE': Rare-earth element having a ion radius smaller than that of the rare-earth element RE of the oxide superconductor electrode, x: 6 to 8) and a cubic crystal structure similar to a simple perovskite structure can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting element composed of an oxide superconductor, and more particularly to a superconducting element suitable for a Josephson junction element for constructing a logic circuit or the like using a single flux quantum as an information medium. About.

[0002]

2. Description of the Related Art Conventionally, as a device constituting a superconducting integrated circuit, a tunnel type Joseph having a laminated structure using a metal superconductor such as Pb or Nb and sandwiching an insulating layer thin enough to allow a superconducting pair to tunnel. Son junctions are known. Such a conventional tunnel-type Josephson element requires an extremely low-temperature operation close to the liquid helium temperature. Also, such a tunnel type Josephson device has a hysteresis inherent in the current-voltage characteristic,
When a logic circuit is manufactured, it has a problem such as a complicated circuit configuration, and has not yet been widely used.

[0003] Under such circumstances, in recent years, oxide materials exhibiting superconductivity at a high temperature equal to or higher than the temperature of liquid nitrogen have been discovered. Oxide superconductors have a superconducting gap that is about an order of magnitude larger than conventional metal superconductors, and can be laminated with oxide materials that exhibit a wide range of properties from metallic conduction to eclipse. For this reason, the SNS (superconducting-voltage) which has no hysteresis in the current-voltage characteristic and has a high output voltage.
A normal-superconducting) type Josephson junction can be realized. If such a Josephson junction can be used to construct an integrated circuit using single flux quanta as an information medium, there is no need to operate at least at extremely low temperatures as compared with the case where a conventional metal superconductor is used. Further, since a much higher speed operation is possible due to the large output voltage, a wide range of applications is expected.

[0004] The development of Josephson junctions using oxide superconductors is proceeding in two main directions.
One is to utilize the function of the grain boundary generated inside the oxide superconductor thin film as a barrier.
One is to form a Josephson junction by artificially inserting a thin film of a normal conductor or an insulator between two superconducting electrodes, as in the case of a conventional metal superconductor. The former is relatively easy to fabricate, but has poor controllability of junction characteristics due to the use of amorphous crystal grain boundaries, and is difficult to apply to integrated circuits. For this reason, the development of the latter junction using various barrier materials has been activated.

FIG. 12 shows one structural example of a Josephson junction in which an oxide superconductor and a barrier material are laminated. In this bonding, first, an oxide superconducting thin film to be the lower superconducting electrode 2 and an interlayer insulating layer 3 are laminated on the substrate 1, and then one end surface 2a thereof has a predetermined inclination angle α with the substrate surface. The barrier layer 4 and the oxide superconducting thin film serving as the upper superconducting electrode 5 are laminated and formed so as to cover the inclined end face 2a by etching. This joining structure is hereinafter referred to as an inclined joining.

In the inclined junction, one dimension of the junction is determined by the thickness of the oxide superconductor thin film used for the lower superconducting electrode 2 and the inclination angle of the inclined end face (etched surface) 2a, so that miniaturization is easy. At the same time, since the oxide superconducting thin film to be the upper superconducting electrode 5 can be continued as it is on the substrate surface exposed by etching, the oxide superconducting thin film can be used as it is as a wiring. I have. These features are expected to be of great advantage in fabricating integrated circuits.

[0007]

However, FIG.
When an attempt is made to actually fabricate a single flux quantum logic circuit (SFQ logic circuit) with a tilted junction as shown in FIG. There is a problem in that the formation of the superconducting wiring is restricted, and the loop inductance cannot be reduced sufficiently.

That is, the SFQ logic circuit is based on the operation of taking one flux quantum in and out of a loop formed by a Josephson junction and a superconducting wiring. For this, 1
One of the product of the critical current I _c of the Josephson junctions included in the inductance L and the loop of the loop, should be designed to 0.5 to 1.5 times the magnitude of the magnetic flux quantum ^{_{Φ 0 (= 2.07 × 10 15}} Wb) is there. Considering the strictest condition of L · I _c = 0.5Φ ₀ , L must be 10 pH for I _c = 100 μA and 1 pH for 1 mA.

The inductance L per unit length of the superconducting wiring on the ground plane is represented by d as the thickness of the interlayer insulating layer, t _g and t _s as the ground plane, the thickness of the superconducting wiring, and λ _L as the penetration distance into London. , L = μ ₀ / Kw [d + λ _L coth (t _g / λ _L ) + λ _L co
th (t _s / λ _L )]. Here, w is a wiring width, and K is a fringe coefficient. As a realistic circuit, w = 1μm, d = 0.2μ
m, t _s = t _g = 0.2 μm, and K = 1.5, L
Is 0.6pH / μm.

FIG. 13 is a plan view showing an example of a superconducting loop manufactured by using an inclined junction. Note that FIG.
In the above, X is a Josephson junction. Assuming such a square superconducting loop, the length of the wiring that constitutes one loop must be about six times the wiring width.
Therefore, the minimum value of inductance is 3.6pH. As a result, I _c of the Josephson junction for constituting the SFQ circuit needs to be set below 0.28MA.

Meanwhile, if it is attempted to operate the SFQ logic circuits at high temperatures, in order to reduce the probability of the circuit by thermal noise malfunctions, it is necessary to increase the I _c. As an example,
10 A circuit consisting of ⁴ junctions at 100K at 10K and 20K
When operated with GHz clock, the probability of malfunction is one year
Estimating the minimum critical current value required to make it less than or equal to one yields values of about 0.17 mA and 0.33 mA, respectively. Therefore, when a plane loop as shown in FIG. 13 is used,
The temperature at which integrated circuits can be safely operated is up to about 10K. Refrigerators that can cool down to 10K are large and expensive, and cannot take full advantage of using high-temperature superconductors.

In order to form a loop having a smaller inductance by using the inclined junction, it is conceivable to adopt a three-dimensional configuration whose cross-sectional structure is shown in FIG. In the configuration of FIG. 14, the loop inductance can be reduced to about twice the inductance per unit area. That is, 1.
2pH is feasible. In this case, the junction I _c is 0.84 mA
It is expected that the operating temperature of integrated circuits can be increased to 50K.

However, since the actual logic circuit requires not independent loops but loops connected to each other, the configuration of FIG. 14 cannot form an entire circuit. As the simplest example, consider a flux quantum transfer circuit whose equivalent circuit is shown in FIG. In FIG. 15, X ₁ , X ₂ , X ₃ , X ₄ and X ₅ are Josephson junctions and L
Is the inductance of the superconducting wiring. In this circuit 2
A superconducting loop containing two Josephson junctions is connected to share one junction. It is impossible to connect the loops shown in FIG. 14 by sharing one junction, and the circuit shown in FIG. 15 cannot be formed.

As can be seen from the above simple example, in order to manufacture an SFQ logic circuit using a conventional inclined junction, a planar loop structure must be adopted at least in part.
As a result, the upper limit of the critical current value of the Josephson junction is defined, so that it has been impossible to achieve a sufficiently high-temperature operation. In other words, integrated circuits using graded Josephson junctions composed of oxide superconductors are expected to exhibit high performance in principle, but can be applied to SFQ integrated circuits that are expected to be used in actual applications. In order to achieve this, a bonding structure capable of reducing the inductance of the wiring loop is required.

As described above, in the conventional superconducting element having a Josephson junction, the inductance of the wiring loop can be reduced in order to remove the restriction on the critical current value of the Josephson junction and enable high-temperature operation. It is an issue to develop a joining structure and a manufacturing technique thereof.

On the other hand, in order to further miniaturize the superconducting element, it is necessary to improve the bonding characteristics itself. In improving the junction characteristics and controllability thereof Josephson junction critical current I _c of the Josephson junctions is an important factor.

[0017] Recently, as one of the techniques for increasing the critical current I _c of the Josephson junction, to 400 to ℃ in a state close to vacuum the oxide superconducting thin film of YBa ₂ Cu ₃ O _7-δ composition 500
When heated to a temperature of ℃, it was found that the crystal structure changed and a phase having a cubic simple perovskite structure without superconducting properties was formed, and this cubic phase was used as a barrier layer. Josephson junctions have been reported. This change in crystal structure, to produce easily by giving the plasma damage to the YBa ₂ Cu ₃ O _7-δ, the surface layer by heat-treating YBa ₂ Cu ₃ O _7-δ film to damage the surface only This was changed to a cubic phase and used as a barrier layer (BH Moecklyand K. Char, Extended Abst
racts of 6th International Superconductive Electro
nics Conference (Berlin, June 1997), vol.1, p.8-p.1
0).

This method is interesting as a new method for fabricating a Josephson junction using an oxide superconductor. According to the result of the additional test performed by the present inventors, the plasma damage region is continuous from the surface in the depth direction. Therefore, it was found that the boundary between the cubic phase after the heat treatment and the superconducting phase was not clearly formed. In such a structure, the critical current as a Josephson junction becomes low because the superconductivity gradually deteriorates toward the surface.

The present invention has been made to address such a problem, and has as its object to basically improve the characteristics of a Josephson junction.
Another object of the present invention is to provide a superconducting element that realizes a superconducting loop having a three-dimensional configuration and connects such loops while sharing a Josephson junction, thereby enabling a high-temperature operation of the Josephson junction. Also the second
To, by increasing the critical current I _c of the Josephson junction, and its object is to provide a superconducting device which aimed at improving characteristics of the Josephson junction.

[0020]

According to a first aspect of the present invention, a first superconducting element is formed on a substrate and directly or via an oxide thin film on the substrate.
₂ Cu ₃ O _7-δ (where RE is at least one element selected from rare earth elements other than Pr, and δ is a number from 0 to 0.5; the same shall apply hereinafter) A lower superconducting electrode layer made of an oxide superconductor, an interlayer insulating layer formed on the lower superconducting electrode layer, and a laminated film of the lower superconducting electrode layer and the interlayer insulating layer, and a side surface provided on the substrate surface. With a predetermined inclination angle with respect to the bottom surface, the bottom surface reaching the substrate surface or the oxide thin film surface, a barrier layer formed so as to cover the side surface and the bottom surface of the depression, and provided on the barrier layer. REBA
It is characterized by comprising an upper superconductive electrode layer made of an oxide superconductor having a substantially composition represented by ₂ Cu ₃ O _7-δ.

In the first superconducting element, a barrier layer and an upper superconducting electrode layer are formed in a recess provided in a laminated film of a lower superconducting electrode layer and an interlayer insulating layer. In such a concave portion, the junction is continuously formed so as to make a round around the periphery, and constitutes one Josephson junction as a whole. Therefore, by forming a plurality of concave portions arranged linearly, it is possible to realize a circuit in which superconducting loops having a three-dimensional structure share one junction and are connected. According to the superconducting loop having the three-dimensional structure, the inductance of one loop can be sufficiently reduced, so that it is possible to realize a superconducting circuit that can operate at a temperature sufficiently higher than the temperature of liquid helium. The second superconducting element of the present invention is formed on a substrate and directly or via an oxide thin film on the substrate and substantially expressed by REBa ₂ Cu ₃ O _7-δ , as described in claim 2. A lower superconducting electrode layer made of an oxide superconductor having a composition to be formed,
An interlayer insulating layer formed on the lower superconducting electrode layer, a laminated film of the lower superconducting electrode layer and the interlayer insulating layer, and a side surface having a predetermined inclination angle with respect to the substrate surface; A recess reaching the lower superconducting electrode layer,
A barrier layer formed so as to cover the side surface and the bottom surface of the concave portion; and REBa ₂ Cu ₃ provided on the barrier layer.
And an upper superconducting electrode layer made of an oxide superconductor having a composition substantially represented by O _7-δ .

Similarly, in the second superconducting element, one Josephson junction is formed as a whole in the recess. Therefore, by arranging a plurality of recesses in a straight line, the same as in the first superconducting element. , Three-dimensional superconducting loop 1
A circuit in which two junctions are shared and connected can be realized.

Further, in the second superconducting element, the recess is formed so that the bottom partly bites into the lower superconducting electrode layer, whereby the sandwich-type joint formed on the bottom of the recess and the inclined part formed on the side are formed. A mold and a similar joint can coexist. In this case, the Josephson current is mainly carried by the junction on the inclined side surface, and a characteristic in which the contribution of the sandwich junction is added to the normal conductance can be realized. Therefore, it is possible to suppress the occurrence of hysteresis in the current-voltage characteristics.
On the other hand, when the concave portion is formed with precision control so that the bottom surface coincides with the surface of the lower superconducting electrode layer, the joining on the side surface is not formed and only the sandwich-type joining portion on the bottom surface can be used. That is, it is possible to form a substantially sandwich-type laminated junction.

A third superconducting element of the present invention is formed on a substrate and directly or via an oxide thin film on the substrate.
A lower superconducting electrode layer comprising an oxide superconductor having a composition substantially represented by REBa ₂ Cu ₃ O _7-δ ; and a lower superconducting electrode layer formed so as to cover at least a part of the lower superconducting electrode layer. RE'Ba containing a rare earth element RE 'having a smaller ionic radius than the rare earth element RE used for the body
₂ Cu ₃ O _x (where RE ′ is at least one element selected from rare earth elements, and the rare earth element RE
Represents a rare earth element with a smaller ionic radius, x is 6 to 8
And a barrier layer having a cubic structure similar to a simple perovskite structure, which is composed of an oxide having a composition substantially represented by the formula:
And an upper superconducting electrode layer made of an oxide superconductor having a composition substantially represented by Ba ₂ Cu ₃ O _7-δ or RE′Ba ₂ Cu ₃ O _7-δ .

The superconductor having the REBa ₂ Cu ₃ O _7-δ composition has such a property that as the ionic radius of the rare earth element increases, the stability in a low oxygen concentration atmosphere increases. The conversion of the crystal structure from a layered perovskite structure showing superconductivity to a cubic structure not showing superconductivity was performed by leaving the material in a low-oxygen concentration atmosphere where the layered perovskite structure was unstable in a certain temperature range. What happens sometimes. Accordingly, by appropriately setting the temperature and the oxygen concentration, only the oxide layer containing the rare-earth element RE ′ having a small ionic radius as a constituent element can be selectively made to have a cubic structure similar to a simple perovskite structure. Since a clear boundary can exist between the barrier layer of the cubic layer and the lower superconducting electrode layer based on the difference in the ionic radius of the rare earth element, a high-performance Josephson junction can be formed with good reproducibility. It is possible to obtain.

[0026]

Embodiments of the present invention will be described below.

FIG. 1 is a view showing the structure of an embodiment of the first superconducting element of the present invention. FIG. 1 (a) is a plan view of the superconducting element, and FIG. It is sectional drawing along. In FIG. 1, reference numeral 11 denotes a substrate, on which an oxide superconductor layer is formed as a lower superconducting electrode layer 12. Note that an oxide superconductor layer serving as a ground plane and a thin film made of an oxide insulator are provided in this order on the substrate 11, and the lower superconducting pole layer 12 may be formed on the oxide thin film serving as the insulating layer. .

On the lower superconducting electrode layer 12 composed of an oxide superconductor layer, an interlayer insulating layer 1 composed of an oxide insulator or the like is formed.
3 are formed. The lower superconducting electrode layer 1
A concave portion 15 whose bottom surface 15 a reaches the surface of the substrate 11 (or the surface of the oxide thin film) is provided in the laminated film 14 of the second and the interlayer insulating layers 13. Each side surface 15b of the recess 15
Is at a predetermined angle with respect to the surface of the substrate 11, for example, 15 to 30.
It is inclined at an angle of about °. In other words, each end face exposed to the concave portion 15 of the lower superconducting electrode layer 12 is an inclined end face.

The above-mentioned concave portion 15 can be formed by ion milling using an appropriate mask such as a resist, for example. That is, etching is performed by irradiating the laminated film 14 of the lower superconducting electrode layer 12 and the interlayer insulating layer 13 with ions inclined at an appropriate angle with respect to the substrate surface. At this time, by rotating the substrate 11, each side surface 15b of the recess 15 can be an inclined surface. The recess 15 may have a truncated pyramid shape or a truncated cone shape.

Bottom surface 15a and side surface 15b of recess 15
Are each covered with a barrier layer 16. In other words, a barrier layer 16 is formed on the laminated film 14 including the lower superconducting electrode layer 12 and the interlayer insulating layer 13, including the inside of the recess 15, and the barrier layer 16 is made of an oxide superconductor. An upper superconducting pole layer 17 is formed. These form a superconducting element 18 having a Josephson junction formed around the recess 15.

The lower superconducting electrode layer 12 and the upper superconducting electrode layer 17 are represented by a general formula: REBa ₂ Cu ₃ O _7-δ (where RE is Y, La, Nd, Eu, Gd, Tb, Y
b, at least one element selected from rare earth elements other than Pr, such as Lu, where δ is a number from 0 to 0.5). is there. The reason why Pr is excluded from the rare earth elements is that a substance in which RE is entirely occupied by Pr does not exhibit superconductivity.

The barrier layer 16 may be composed of any of an insulator and a normal conductor. The constituent materials of the barrier layer 16 include the lower superconducting electrode layer 12 to the upper superconducting electrode layer 1.
It is preferable to use an oxide material for epitaxially growing up to 7 to obtain a Josephson junction having good characteristics.

[0033] Particularly, PrBa ₂ Cu ₃ O _7-δ is a layered perovskite oxide having no superconducting properties, REBa weakened superconductivity by doping an impurity element such as _{Co 2 Cu 3 O 7-δ} , Furthermore it is preferred to use a non-superconducting oxide such as lower superconducting electrode layer 2 and the conductive oxide such as insulating oxide and CaRuO _3, such as the pseudo-SrTiomikuron ₃ lattice-matched. Further, RE'Ba ₂ C by a third superconducting element of the present invention described later.
An oxide having a composition substantially represented by u ₃ O _x and having a cubic structure similar to a simple perovskite structure can be applied to the barrier layer 16.

At first glance, the superconducting element 18 of this embodiment can be seen from FIG. 1B only as having two inclined junctions formed opposite to each other, but the fundamental difference from the conventional inclined junction is as follows. The point is that the joining structure with the barrier layer 16 interposed therebetween is continuously formed around the recess 15. The joint formed continuously around the periphery of the concave portion 15 constitutes one Josephson junction as a whole. The second point different from the conventional inclined junction is that the upper superconducting electrode layer 17 is not automatically extended to the surface of the interlayer insulating layer on the substrate surface or the ground plane, and the upper superconducting electrode layer 17 The termination can be achieved only on the insulating layer 13.

By using the Josephson junction whose structure is shown in FIG. 1, a circuit having a small loop inductance can be easily formed. FIG. 2 is a cross-sectional view schematically showing the structure of a magnetic flux quantum transfer circuit formed by arranging the Josephson junctions shown in FIG. 1 in a straight line.

The circuit structure shown in FIG. 2 is such that a plurality of recesses 15 are formed in a laminated film 14 of a lower superconducting
(15-1, 15-2, 15-3...) Are linearly arranged and formed on the laminated film 14 including the inside of each of the recesses 15-1, 15-2, 15-3. The barrier layer 16 and the upper superconducting electrode layer 17 are sequentially formed.

In the superconducting circuit having such a structure, a Josephson junction is formed on each side surface of each of the concave portions 15-1, 15-2, and 15-3 (the inclined end surface exposed to the concave portion of the lower superconducting electrode layer 12). each superconducting loop Z ₁ comprising two Josephson junctions, Z ₂ ... are formed between adjacent recesses (15-1 and 15-2, and 15-2 and 15-3). Here, since the junction formed in each recess 15 constitutes one Josephson junction as the whole recess as described above, each superconducting loop Z ₁ , Z ₂ is formed as shown in the equivalent circuit of FIG. A single Josephson junction is shared and connected.

In FIG. 15, L ₁ , L ₂ ... Are the inductances of the superconducting wirings, X ₁ , X ₂ , X ₃ are the Josephson junctions, and the junction X ₁ corresponds to the recess 15-1.
Bonding X ₂ are recesses 15-2, bonding X ₃ corresponds to the recess 15-3.

As described above, the plurality of recesses 15-1, 1-5 are formed in the laminated film 14 of the lower superconducting electrode layer 12 and the interlayer
5-2, 15-3... Are arranged linearly, and a common upper superconducting pole layer 17 including the inside of each recess 15-1, 15-2, 15-3. It is possible to realize a circuit in which three-dimensional superconducting loops Z ₁ , Z _2, ... Share one junction and are connected. Then, according to the superconducting loops Z ₁ and Z ₂ having a three-dimensional structure, the inductance of one loop can be sufficiently reduced, so that a superconducting circuit capable of operating at a temperature sufficiently higher than the liquid helium temperature, for example, An ultra-high-speed logic circuit (SFQ logic circuit) using a single magnetic flux quantum as an information medium can be realized.

Next, an embodiment of the second superconducting element of the present invention will be described with reference to FIGS.

In the superconducting element 19 shown in FIG. 4, a lower superconducting electrode layer 12 and an interlayer insulating layer 13 are sequentially formed on a substrate 11 in the same manner as the superconducting element 18 shown in FIG. A recess 20 is formed. Here, the concave portion 20 in this embodiment is similar to the concave portion 15 shown in FIG. 1 in that each side surface 20b is inclined at a predetermined angle (for example, about 15 to 30 °) with respect to the substrate surface. The bottom surface 20a is provided so as to reach the lower superconducting electrode layer 12 unlike the concave portion 15 shown in FIG.

The bottom surface 20a of the recess 20 may be formed so as to partially penetrate the lower superconducting electrode layer 12 as shown in FIG. 4B, or as shown in FIG. It may be formed so as to coincide with the layer 12. The configuration other than the shape of the recess 20, for example, the shape and constituent material of each layer is the same as the superconducting element 18 shown in FIG.

As shown in FIG. 4B, in the superconducting element 19 having the recess 20 formed so that the bottom surface 20a partially penetrates into the lower superconducting electrode layer 12, as shown in FIG. a junction X _a sandwich type formed on the bottom surface 20a of the inclined and the similar junction X _B coexist formed on the side surface 20b. That is, FIG.
In contrast to the structure shown in FIG.
Is formed not only along the side surface 20b, but also on the bottom surface 20a.

For example, in the SFQ logic circuit, it is necessary to use an oxide superconductor layer having a c-axis orientation (a crystal orientation in which the c-axis of the crystal axis stands upright on the substrate surface) in order to reduce the London penetration depth of the superconducting pole layer. There is. When a sandwich-type junction is formed on such a superconducting layer, a large critical current density cannot be obtained as a Josephson junction unless the barrier layer is made sufficiently thin due to conduction anisotropy. On the other hand, in the case of a sandwich type junction, the normal conductance is relatively large.

[0045] In the inclined similar Josephson junctions are allowed to coexist and junction X _B sandwich type junction X _A and the side surface 20b of the bottom surface 20a, the Josephson current is mainly borne by the junction X _B of the inclined side surface 20b , the normal conducting conductance can be achieved is applied properties contributed sandwich type junction X _a. In such a junction, since the McCumber coefficient is small, no hysteresis occurs in the current-voltage characteristics. This facilitates the fabrication of SFQ logic circuits.

[0046] The bonding portion of the bottom surface 20a X _A and the side 20
For even b Josephson junctions are allowed to coexist and junction X _B of, similarly to the joint shown in FIG. 1, for constituting the single Josephson junction as a whole recess, superconducting loop conformation is one A circuit connected by sharing a junction can be realized. Therefore, it is possible to realize an SFQ logic circuit or the like that can operate at a temperature sufficiently higher than the liquid helium temperature.

On the other hand, as shown in FIG. 5, in the superconducting element 19 'in which the concave portion 20 is formed by precisely controlling the bottom surface 20a to coincide with the surface of the lower superconducting electrode layer 12, as shown in FIG. Is not formed on the bottom surface 2b.
It can only be a sandwich type junction X _A of 0a. That is, it is possible to form a substantially sandwich-type laminated junction.

A sandwich type Josephson junction has an N
In the case where a conventional metal superconductor such as b is used, it is generally manufactured. In that case, after laminating the lower superconducting electrode layer, the barrier layer and the upper superconducting electrode layer, only the portion to be joined is formed. In this case, etching is performed until the barrier layer or the lower superconducting electrode layer is exposed, the exposed portion is covered with an interlayer insulating layer, and then a wiring layer that contacts the upper superconducting electrode layer of the junction is formed. Attempts have been made to apply a similar process to oxide superconductors, but in oxide superconductors where it is necessary to epitaxially grow all layers, an interlayer dielectric layer grows abnormally around the junction, There have been problems such as insufficient coating.

[0049] Match the bottom surface 20a of the recess 20 on the surface of the lower superconducting electrode layer 12, a superconducting element 19 which is only a sandwich type junction X _A of the bottom surface 20a 'is surely solve the problems related to coating of the interlayer insulating layer This is what made it possible. Then, as in the case of the junction shown in FIG. 1, one Josephson junction is formed as a whole recess, so that a circuit in which a superconducting loop having a three-dimensional structure shares one junction and is connected can be realized. Therefore, it is possible to realize an SFQ logic circuit or the like that can operate at a temperature sufficiently higher than the liquid helium temperature.

Next, an embodiment of the third superconducting element of the present invention will be described with reference to the manufacturing process diagram of FIG.

First, as shown in FIG.
A lower superconducting electrode layer 24 is formed on an oxide thin film as an interlayer insulating layer 23 formed on the oxide superconducting layer as the ground plane 22. The lower superconducting electrode layer 24 has a general formula: REBa ₂ Cu ₃ O _7-δ (where RE is Y, La, Nd, Eu, Gd, Tb, Y), as in the above-described embodiment.
b, at least one element selected from rare earth elements other than Pr such as Lu, and δ is a number of 0 to 0.5).

Next, an oxide layer 25 serving as a barrier layer after heat treatment is formed so as to cover at least a part of the lower superconducting electrode layer 24. Here, the oxide layer 25 is a rare earth element R in the oxide superconductor used as the lower superconducting electrode layer 24.
A rare earth element RE 'having a smaller ionic radius than E, a general formula: RE'Ba ₂ Cu ₃ O _7-δ (wherein RE' is at least one element selected from rare earth elements containing Y, (It is a rare earth element having an ionic radius smaller than that of the rare earth element RE)).

For example, if the lower superconducting electrode layer 24 is made of NdBa
_{When 2} Cu ₃ O _7-δ is used, YBa ₂ Cu ₃ O containing Y having a smaller ionic radius than Nd as the rare earth element RE ′ is used.
_The oxide layer 25 is formed by _7-δ . Such a stacked structure is subjected to heat treatment for converting the crystal structure of the oxide layer 25 from a layered perovskite structure to a structure similar to a simple perovskite structure having a cubic structure.

In general, a superconductor having a REBa ₂ Cu ₃ O _7-δ composition has such a property that the stability under a low oxygen concentration atmosphere increases as the ionic radius of the rare earth element RE increases. The conversion of the superconducting layered perovskite structure from a layered perovskite structure to a cubic structure occurs when a material is left under a low oxygen concentration atmosphere where the layered perovskite structure becomes unstable in a certain temperature range. is there.
Therefore, by appropriately setting the temperature and the oxygen concentration,
Although the oxide layer 25 containing the rare earth element RE 'having a small ionic radius as a component, that is, the RE'Ba ₂ Cu ₃ O _7-δ layer becomes unstable, the R as the lower superconducting electrode layer 24 becomes unstable.
EBa ₂ Cu ₃ O _7-δ can be kept stable.

The present invention utilizes such characteristics of the oxide superconductor. By performing the heat treatment step in which the temperature and the oxygen concentration are controlled as described above, FIG.
As shown in (b), only the RE'Ba ₂ Cu ₃ O _7-δ layer is a barrier layer 26 having a cubic structure similar to a simple perovskite structure which does not exhibit superconducting properties, that is, the general formula: RE'Ba ₂ Cu ₃ The barrier layer 26 has a composition substantially represented by O _x (where x represents a number of 6 to 8) and is made of an oxide having a cubic structure. The amount of oxygen in the oxide constituting the barrier layer 26 may fluctuate during the phase transition from the layered perovskite structure to the cubic crystal, and the value of x is in the range of 6 to 8. In this case, the thickness of the region to be converted to the cubic structure is the thickness of the original oxide layer 25, that is, RE'Ba ₂
The lower superconducting electrode layer 2 is determined by the thickness of the Cu ₃ O _7-δ layer, and is composed of a cubic layer and a REBa ₂ Cu ₃ O _7-δ layer thereunder.
4, there will be a clear boundary.

Thereafter, barrier layer 26 having a cubic structure is formed.
As shown in FIG. 8C, REBa ₂ Cu ₃ O
By forming the upper superconducting pole layer 27 made of an oxide superconductor having a composition substantially represented by _7-δ or RE'Ba ₂ Cu ₃ O _7-δ , the superconducting layer having a sandwich type Josephson junction is formed. An element 28 is obtained. The joining structure is not limited to a simple laminated structure, but can naturally be applied to an inclined joining.

In a conventional Josephson junction in which a barrier layer is formed by subjecting the surface of a conventional YBa ₂ Cu ₃ O _7-δ layer to a plasma treatment after applying plasma damage to change only the surface layer to a cubic phase, As described above, since the plasma damage region is formed continuously from the surface in the depth direction, the boundary between the cubic phase and the superconducting phase after heat treatment is not clearly formed, and the superconducting characteristics gradually increase toward the surface. To deteriorate,
The critical current as a Josephson junction is low.

On the other hand, in this embodiment, REBa
₂ Cu ₃ O _7-δ on the basis of the difference in stability under low oxygen concentration atmosphere based upon the ionic radius of the rare earth element of the oxide superconductor in composition, only RE'Ba ₂ Cu ₃ O _7-δ layer Since the structure is converted to a cubic structure similar to a simple perovskite structure that does not exhibit superconductivity, a clear structure is formed between the barrier layer 26 and the lower superconducting electrode layer (RE′Ba ₂ Cu ₃ O _x layer having a cubic structure) 24. Boundaries can exist. Therefore, it becomes possible to obtain a Josephson junction having a good critical current.

The region once converted to the cubic structure is extremely stable, and furthermore, REBa _2, which exhibits superconducting characteristics, is formed thereon.
The structure is not destroyed even after the step of depositing the Cu ₃ O _7-δ film. For this reason, the superconductor serving as the upper superconducting electrode layer 27 includes the REB used for the lower superconducting electrode layer 24.
The same material as a ₂ Cu ₃ O _7-δ may be used, or a material having a different rare earth element from the lower superconducting electrode layer 24, for example, RE′Ba ₂ Cu ₃ O _7-δ may be used. Good.

[0060]

Next, an embodiment of the present invention will be described.

Embodiment 1 FIG. 9 is a perspective view showing a partial cross section of a main part structure of an integrated circuit manufactured by applying the first superconducting element of the present invention. In the figure, reference numeral 31 denotes a substrate made of a single crystal of SrTiO ₃ , the surface of which is coincident with the (100) plane. This SrT
On the iO ₃ single-crystal substrate 31, a thickness 2 composed of an oxide superconductor whose composition is substantially represented by YBa ₂ Cu ₃ O _7-δ
The 50 nm ground plane 32 is formed in an orientation (c-axis orientation) such that the c-axis of the crystal structure stands upright on the substrate surface.

On the ground plane 32, a thickness of 250 nm
The oxide insulator layer 33 made of the SrTiO ₃ thin film was formed. In forming these layers, a multi _- source sputtering method was used, and a YBa ₂ Cu ₃ O _7-δ film was formed at a substrate temperature of 800 ° C. in an atmosphere of an Ar / O ₂ mixed gas of 20 mTorr.
The rTiO ₃ film was formed under a condition of a substrate temperature of 680 ° C. in an atmosphere of an Ar / O ₂ mixed gas of 10 mTorr.

Next, using the same film forming conditions as those described above, a 200 nm-thick YBa to be the lower superconducting electrode layer 34 is formed.
Sr serving as ₂ Cu ₃ O _7-δ film and interlayer insulating layer 35 thereon
TiO ₃ films were sequentially formed. The thickness of the SrTiO ₃ film serving as the interlayer insulating layer 35 was 250 nm.

Thereafter, the above-mentioned laminated film is taken out of the sputtering apparatus, a pattern of a positive resist is formed at a predetermined position by an ordinary optical exposure method, and the interlayer insulating layer 35 and the lower part of the interlayer insulating layer 35 are formed by ion milling using the resist as a mask. The superconducting electrode layer 34 is continuously etched until the surface of the insulator layer 33 on the ground plane 32 is exposed, so that the side surface forms an angle of 25 degrees with respect to the substrate surface, and a square shape of 1 μm on a side. A small hole (recess) 36 was formed.

In ion milling, Ar ions were incident on the substrate surface at an angle of 50 degrees, and the substrate was rotated at a constant speed during etching. The reason that the side surface of the concave portion 36 formed by this etching process forms a relatively gentle angle with respect to the substrate surface is that the resist mask is also etched and receded during milling, and the inclination angle changes the incident angle of Ar ions. Can be controlled.

After the completion of the etching, the resist used as a mask with an organic solvent is removed.
Irradiation was performed at an accelerating voltage of about 00 eV for 10 minutes to clean the etched end face. Thereafter, the sample is mounted again on the multi-source sputtering apparatus, and PrBa ₂ Cu ₃ O _7-δ serving as the barrier layer 37 is provided.
Film and YBa ₂ Cu ₃ O to be the upper superconducting electrode layer 38
_{The 7-δ} films were continuously laminated. The thickness of the barrier layer 37 is 10n
m, and the thickness of the upper superconducting electrode layer 38 is 300 nm.

After the formation of the above-mentioned laminated film, a pattern of a positive resist is formed at a predetermined position by an ordinary optical exposure method,
Using the resist as a mask, the upper superconducting electrode layer 38 and the barrier layer 37 were etched by ion milling until the surface of the interlayer insulating layer 35 was exposed, thereby completing the device structure shown in FIG.

As a result of evaluating the electrical characteristics of a large number of the junctions manufactured as described above, it was found that all the junctions had a temperature of 4.2K and 60K.
The characteristic of the Josephson junction was clearly shown between the above, and the I _c · R _n product, which is an index indicating the performance of the junction, reached about 1.5 mV at 4.2 K and about 0.3 mV even at 50 K. Also, the 48 junctions fabricated on the same wafer I _c and R _n together distribution is small, it was confirmed that fit in about 10% as the standard deviation.

Embodiment 2 FIG. 10 is a perspective view showing a partial cross section of a main structure of an integrated circuit manufactured by applying the second superconducting element of the present invention.
The Josephson junction used in the second embodiment is different from the first embodiment in that it includes a sandwich type junction in which a lower superconducting electrode layer 34, a barrier layer 37, and an upper superconducting electrode layer 38 are vertically stacked.

The fabrication of the device of the second embodiment is similar to that of the first embodiment.
Similarly to the above, film formation by multi-source sputtering and etching by Ar ions were used. First, a 250 nm-thick ground plane 32 made of an oxide superconductor whose composition is substantially represented by YBa ₂ Cu ₃ O _7-δ and a 250 nm-thick SrTiO ₃ film are formed on a SrTiO ₃ single crystal substrate 31. Thickness to become oxide insulator layer 33 and lower superconducting electrode layer 34
A 200 nm YBa ₂ Cu ₃ O _7-δ film was continuously laminated using the same sputtering apparatus.

Next, a 50 nm thick SrTiO ₃ thin film which is to constitute a part of the interlayer insulating layer 35 was deposited, and the sample was taken out of the vacuum apparatus. The conditions for forming these layers were the same as those in Example 1 described above. Thin SrTiO ₃ film
In the subsequent step of separating the lower superconducting electrode layer on the wafer into several island regions, the lower superconducting electrode layer 34
Is used to prevent the deterioration of.

Next, a pattern of a positive resist is formed at a predetermined position on the above-mentioned laminated film by a usual optical exposure method.
Using this resist as a mask, the thin SrTiO ₃ film and the lower superconducting electrode layer 34 are etched until the surface of the insulator layer 33 on the ground plane 32 is exposed by ion milling. It separated into island-like areas. Thereafter, an SrTiO ₃ film having a thickness of 250 nm was deposited on the entire surface of the wafer to form an interlayer insulating layer 35.

Next, a pattern of a positive resist is formed also by the usual optical exposure method, and the side surface forms an angle of about 25 degrees with respect to the substrate surface by ion milling using the resist as a mask. A small hole (recess) 39 having a square shape of 2 μm was formed in the interlayer insulating layer 35. Also in this etching step, Ar ions were incident at an angle of 50 degrees with respect to the substrate surface, and the substrate was rotated at a constant speed during the etching. This etching process was performed until the surface of the lower superconducting electrode layer 34 was exposed, and the resist mask after the etching was removed with an organic solvent.

Next, the etching end face is cleaned by irradiating Ar ions accelerated to 100 eV for 10 minutes, and thereafter, PrBa serving as a barrier layer 37 is formed by using a multi-source sputtering apparatus.
YBa to be ₂ Cu ₃ O _7-δ film and upper superconducting electrode layer 38
₂ Cu ₃ O _7-δ films were continuously laminated. The thickness of the barrier layer 37 was 10 nm, and the thickness of the upper superconducting electrode layer 38 was 300 nm.

Finally, the upper superconducting electrode layer 38 was processed into a predetermined pattern by a usual optical exposure method and ion milling to complete the superconducting circuit shown in FIG. FIG.
In the above, a part of the junction structure formed on the lower superconducting electrode layer
Are connected in common.

The Josephson junction thus manufactured exhibited an I _c · R _n product of about 1 mV at a temperature of 4.2 K. This value was slightly lower than that of the device of Example 1 described above, while the characteristic distribution of the 48 junctions in the wafer was:
It was confirmed that a very uniform Josephson junction could be obtained with a small standard deviation of 8%.

Example 3 FIG. 11 is a sectional view showing a manufacturing process and a structure of an embodiment of the third superconducting element of the present invention. FIG. 11 shows, in order, manufacturing steps of an element structure in which the third superconducting element of the present invention is combined with the first superconducting element. The procedure of manufacturing the superconducting element in the third embodiment is as follows.

First, as shown in FIG.
The N _{3 is} deposited on the iO ₃ single crystal substrate 41 by multi-source sputtering.
250 nm-thick ground plane layer 42 made of an oxide superconductor whose composition is substantially represented by dBa ₂ Cu ₃ O _7-δ
And then a 50 nm thick SrTiO ₃ layer, 200 mm thick
An interlayer insulating layer 43 having a three-layer structure of a PrBa ₂ Co _0.2 Cu _2.8 O _7-δ layer having a thickness of 50 nm and a SrTiO ₃ layer having a thickness of 50 nm.
Were laminated.

The PrB used in the middle of the interlayer insulating layer 43
The a ₂ Co _0.2 Cu _2.8 O _7-δ layer is made of ordinary PrBa ₂ C
a part of Cu of u ₃ O _7-δ substituted with Co,
It is an insulator having a higher resistivity than PrBa ₂ Cu ₃ O _7-δ . Since PrBa ₂ Co _0.2 Cu _2.8 O _7-δ is a material having a relatively small relative dielectric constant of about 30 at a low temperature, it is convenient for producing a transmission line having a high signal propagation speed. In the third embodiment, the interlayer insulating layer 43 has a three-layer laminated structure because a small dielectric constant of PrBa ₂ Co _0.2 Cu _2.8 O _7-δ is used and the DC leakage current is reduced to a sufficiently small value. In order to keep.

On the interlayer insulating layer 43, the same sputtering apparatus is used to form a 200 nm thick N
SrT serving as dBa ₂ Cu ₃ O _7-δ film and interlayer insulating layer 45
iO ₃ films were sequentially laminated. In consideration of the process described later, in the third embodiment, the thickness of the SrTiO ₃ insulating layer 45 is
500 nm.

After the above-mentioned laminated film is formed, the sample is taken out of the vacuum vessel of the sputtering apparatus, and as shown in FIG. It was produced by an optical exposure method. In Example 3, the window had a square shape with a side of 1.5 μm.

Next, using this resist 46 as a mask,
The substrate surface was irradiated with Ar ions at an angle of 50 degrees to etch the interlayer insulating layer 45. At the time of this etching, the substrate was rotated so that the angle formed by the side surface after etching with respect to the substrate surface was 25 degrees. This etching is not performed until the interlayer insulating layer 45 in the window portion is completely removed.
The process was terminated when the SrTiO ₃ layer having a thickness of nm remained, and the remaining resist was removed with a solvent to produce a structure as shown in FIG. 11C.

Thereafter, the entire surface of the wafer is
Ar ion irradiation was performed at an angle of 40 degrees, and etching was performed on the entire surface while substantially maintaining the surface shape of FIG. By the first etching step, the SrTiO ₃ insulating layer 4
In the region where 5 is thinned, the lower superconducting electrode layer 4
Etching proceeds to 4, and a structure as shown in FIG. 11D can be formed. The reason why the etching process is divided into two stages in the third embodiment is to prevent the side surface of the lower superconducting electrode layer 44 exposed by the etching from being contaminated by the organic solvent for removing the resist.

Next, the wafer is mounted on the sputtering apparatus again, and YBa ₂ Cu ₃ O having a thickness of 10 nm for forming a barrier layer.
_{A 7-δ} layer 47 was deposited on the entire surface of the wafer (FIG. 11).
(E)). Thereafter, the sample is heat-treated in the same sputtering apparatus under the conditions of an oxygen partial pressure of 1 × 10 ⁻⁵ Torr and a substrate temperature of 480 ° C. for 45 minutes to form the YBa ₂ Cu ₃ O _7-δ layer 47 into a cubic barrier layer. 48 (FIG. 11F). Under these heat treatment conditions, since the lower superconducting electrode layer 44 and the NdBa ₂ Cu ₃ O _7-δ layer as the ground plane 42 are stable, the crystal structure does not change.

The pressure in the sputtering apparatus was set to YBa ₂ Cu ₃ O
_The conditions for forming the _7-δ thin film were changed, and as shown in FIG. 11 (g), an upper superconducting electrode layer 49 whose composition was substantially represented by YBa ₂ Cu ₃ O _7-δ was formed on the entire surface of the wafer. rear,
The element structure shown in FIG. 11H was completed by processing the upper superconducting electrode layer 49 by an optical exposure method and ion milling.

In the Josephson junction fabricated in Example 3, the product of I _c · R _n at a temperature of 4.2 K was as large as 1.8 mV,
In 48 of the joint in the same wafer, the distribution of I _c is the standard deviation is very small as about 5% has been confirmed.

This uniformity of characteristics is sufficient for realizing a highly integrated logic circuit. However, at a temperature of 20 K or less, a slight hysteresis characteristic is observed in the current-voltage characteristic, and the characteristic is applied to the SFQ circuit. It is suggested that the normal conductance of the junction needs to be increased in order to achieve this. Such a junction conductance can be adjusted by manufacturing the second superconducting element of the present invention using the method for manufacturing a barrier layer described in this embodiment.

[0088]

As described above, according to the first and second superconducting elements of the present invention, a superconducting wiring loop having a three-dimensional configuration having a small inductance value is connected by sharing one Josephson junction. Can be manufactured.
Therefore, it is possible to realize an ultra-high-speed logic circuit that operates at a sufficiently high temperature as compared with the liquid helium temperature, for example, using a single flux quantum as an information medium. Further, the third aspect of the present invention
According to this superconducting element, a Josephson junction having a high I _c · R _n value and an extremely small characteristic distribution in a wafer can be manufactured, and a highly integrated logic circuit can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main structure of an embodiment of a first superconducting element of the present invention, wherein (a) is a plan view thereof and (b)
FIG. 3A is a cross-sectional view along the line AA in FIG.

FIG. 2 is a cross-sectional view showing one configuration example of a superconducting circuit using the superconducting element shown in FIG.

FIG. 3 is an equivalent circuit diagram of the superconducting circuit shown in FIG.

FIGS. 4A and 4B are diagrams showing a main part structure of an embodiment of the second superconducting element of the present invention, wherein FIG. 4A is a plan view thereof and FIG.
FIG. 3A is a cross-sectional view along the line AA in FIG.

FIG. 5 is a cross-sectional view showing a main structure of another embodiment of the second superconducting element of the present invention.

6 is a diagram for explaining a state of formation of a junction in the superconducting element shown in FIG.

FIG. 7 is a view for explaining a state of formation of a junction in the superconducting element shown in FIG.

FIG. 8 is a sectional view showing a manufacturing process and a main part structure of an embodiment of the third superconducting element of the present invention.

FIG. 9 is a partial cross-sectional perspective view schematically illustrating the structure of the superconducting integrated circuit according to the first embodiment of the present invention.

FIG. 10 is a partially sectional perspective view schematically showing a structure of a superconducting integrated circuit according to a second embodiment of the present invention.

FIG. 11 is a cross-sectional view schematically showing a manufacturing process of the superconducting element according to the third embodiment of the present invention.

FIG. 12 is a cross-sectional view schematically illustrating a structure of a conventional inclined Josephson junction.

FIG. 13 is a plan view schematically showing one structural example of a superconducting wiring loop to which a conventional inclined junction is applied.

FIG. 14 is a cross-sectional view schematically showing another structural example of a superconducting wiring loop to which a conventional inclined junction is applied.

FIG. 15 is an equivalent circuit diagram of a circuit used for transferring a flux quantum in a single flux quantum logic circuit.

[Explanation of symbols]

 11, 21 ... substrate 12, 24 ... lower superconducting electrode layer 13 ... interlayer insulating layer 15, 20 ... recess 16 ... barrier layer 17, 27 ... upper superconducting electrode layer 18, 19, 19 ', 28 ... ... Superconducting element 26 ... Barrier layer made of oxide having cubic structure

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[Procedure amendment]

[Submission date] February 15, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction contents]

[0020]

According to a first aspect of the present invention, a first superconducting element is formed on a substrate and directly or via an oxide thin film on the substrate.
₂ Cu ₃ O _7-δ (where, RE is at least one element selected from rare earth elements other than Pr, and δ is from 0 to 0.
The number 5 is shown. The same shall apply hereinafter), a lower superconducting electrode layer made of an oxide superconductor having a composition substantially represented by the following formula, an interlayer insulating layer formed on the lower superconducting electrode layer, and the lower superconducting electrode layer and the interlayer insulating layer. And the side surface forms a predetermined inclination angle with respect to the substrate surface, and the bottom surface covers the substrate surface or the oxide thin film surface, and the side surface and the bottom surface of the concave portion are covered. One that is formed and is continuous around the periphery of the recess
And an upper superconducting pole layer made of an oxide superconductor having a composition substantially represented by REBa ₂ Cu ₃ O _7-δ provided on the barrier layer. It is characterized by.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

In the first superconducting element, a barrier layer and an upper superconducting electrode layer are formed in a recess provided in a laminated film of a lower superconducting electrode layer and an interlayer insulating layer. In such a concave portion, the junction is continuously formed so as to make a round around the periphery, and constitutes one Josephson junction as a whole. Therefore, by forming a plurality of concave portions arranged linearly, it is possible to realize a circuit in which superconducting loops having a three-dimensional structure share one junction and are connected. According to the superconducting loop having the three-dimensional structure, the inductance of one loop can be sufficiently reduced, so that it is possible to realize a superconducting circuit that can operate at a temperature sufficiently higher than the temperature of liquid helium. The second superconducting element of the present invention is formed on a substrate and directly or via an oxide thin film on the substrate and substantially expressed by REBa ₂ Cu ₃ O _7-δ. A lower superconducting electrode layer made of an oxide superconductor having a composition to be provided, an interlayer insulating layer formed on the lower superconducting electrode layer, and a laminated film of the lower superconducting electrode layer and the interlayer insulating layer, and The side surface forms a predetermined angle of inclination with respect to the substrate surface, and the bottom surface bites into the lower superconducting electrode layer .
Formed so as to cover the side surface and the bottom surface of the concave portion, and continuously around the concave portion.
And a top superconducting pole layer made of an oxide superconductor having a composition substantially represented by REBa ₂ Cu ₃ O _7-δ provided on the barrier layer. It is characterized by doing.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

Further, in the second superconducting element, a concave portion is formed such that the bottom surface partially bites into the lower superconducting electrode layer.
Therefore, a sandwich-type joint formed on the bottom surface of the concave portion and a joint similar to the inclined type formed on the side surface can coexist. In this case, the Josephson current is mainly carried by the junction on the inclined side surface, and a characteristic in which the contribution of the sandwich junction is added to the normal conductance can be realized. Therefore, it is possible to suppress the occurrence of hysteresis in the current-voltage characteristics .

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0041

[Correction method] Change

[Correction contents]

In the superconducting element 19 shown in FIG. 4, a lower superconducting electrode layer 12 and an interlayer insulating layer 13 are sequentially formed on a substrate 11 in the same manner as the superconducting element 18 shown in FIG. A recess 20 is formed. Here, in the concave portion 20 in this embodiment, each side surface 20b has a predetermined angle (for example, about 15 to 30 °) with respect to the substrate surface.
Is different from the concave portion 15 shown in FIG.
It is provided so as to bite into lower superconducting electrode layer 12.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0042

[Correction method] Change

[Correction contents]

The tail, configurations other than the shape of the recess 20, for example for such each layer of the shape and the material, which is similar to the superconducting device 18 shown in FIG.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0047

[Correction method] Change

[Correction contents]

On the other hand, as shown in FIG. 5, in the superconducting element 19 'in which the concave portion 20 is formed by precisely controlling the bottom surface 20a to coincide with the surface of the lower superconducting electrode layer 12, as shown in FIG. Is not formed on the bottom surface 2b.
Only becomes sandwich joint X _A of 0a.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0048

[Correction method] Deleted

[Procedure amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0049

[Correction method] Deleted

Claims (3)

[Claims] 1. A substrate, which is formed directly or via an oxide thin film on the substrate, and wherein REBa ₂ Cu ₃ O _7-δ (where RE is at least one element selected from rare earth elements other than Pr) , Δ
Represents a number from 0 to 0.5), a lower superconducting electrode layer made of an oxide superconductor having a composition substantially represented by the formula: an interlayer insulating layer formed on the lower superconducting electrode layer; A concave portion provided in a laminated film of a layer and an interlayer insulating layer, wherein a side surface forms a predetermined inclination angle with respect to the substrate surface, and a bottom surface reaches the substrate surface or the oxide thin film surface; And a barrier layer formed so as to cover the bottom surface, and an upper superconducting electrode layer provided on the barrier layer and comprising an oxide superconductor having a composition substantially represented by REBa ₂ Cu ₃ O _7-δ. A superconducting element comprising: 2. A substrate, and REBa ₂ Cu ₃ O _7-δ (where RE is at least one element selected from rare earth elements other than Pr) formed on the substrate directly or via an oxide thin film. , Δ
Represents a number from 0 to 0.5), a lower superconducting electrode layer made of an oxide superconductor having a composition substantially represented by the formula: an interlayer insulating layer formed on the lower superconducting electrode layer; A concave portion provided on a laminated film of a layer and an interlayer insulating layer, wherein a side surface forms a predetermined inclination angle with respect to the substrate surface and a bottom surface reaches the lower superconducting electrode layer; and covers a side surface and a bottom surface of the concave portion And an upper superconducting pole layer made of an oxide superconductor having a composition substantially represented by REBa ₂ Cu ₃ O _7-δ provided on the barrier layer. A superconducting element characterized by the following. 3. A substrate, and REBa ₂ Cu ₃ O _7-δ formed directly or on an oxide thin film on the substrate, wherein RE is at least one element selected from rare earth elements other than Pr. , Δ
Represents a number from 0 to 0.5), a lower superconducting electrode layer made of an oxide superconductor having a composition substantially represented by the following: and the oxide is formed so as to cover at least a part of the lower superconducting electrode layer. RE 'including a rare earth element RE' having a smaller ionic radius than the rare earth element RE used for the superconductor.
Ba ₂ Cu ₃ O _x (where RE ′ is at least one element selected from rare earth elements and represents a rare earth element having an ion radius smaller than that of the rare earth element RE, and x is 6
A barrier layer made of an oxide having a composition substantially represented by the following formula (1) and having a cubic structure similar to a simple perovskite structure: REBa ₂ Cu ₃ O _A superconducting electrode layer comprising an oxide superconductor having a composition substantially represented by _7-δ or RE'Ba ₂ Cu ₃ O _7-δ .