JPH05183204A - Superconducting device - Google Patents

Abstract

PURPOSE:To provide a superconducting device which can prevent the occurrence of polarons and in which an excellent tunnel type junction can be obtained. CONSTITUTION:The title device is constituted of a superconducting oxide layer 1, insulating layer 3 formed on the layer 1, and metallic layer 4 formed on the layer 3 and a metallic layer 2 is provided between the layers 1 and 3 for preventing the diffusion of polarons.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a microwave mixer,
The present invention relates to a tunnel-type junction structure superconducting device used for a superconducting transistor or the like.

[0002]

2. Description of the Related Art In recent years, the progress of superconducting electronics in Japan has been remarkable, and the transition temperature Tc has been increased accordingly.
A high bismuth-based oxide superconducting material and a yttrium-based oxide superconducting material have been proposed.

When a superconducting device is manufactured using the above oxide superconducting material, for example, a tunnel type junction having a constant operating voltage and excellent stability in circuit operation is used. This tunnel type junction is SIS or SI
It has a sandwich structure composed of N (S is a superconductor, I is an insulating layer, and N is a normal conductor). In this case, after providing an insulating layer such as MgO on the S layer, a superconductor or a normal conductor is formed. The body is laminated. In the sandwich structure made of SIS or SIN, a material such as MgO, SrTiO ₃ or the like having a good matching of lattice constant and thermal expansion coefficient is used as the insulating layer.

However, Mg used as the insulating layer
In ionic crystals such as O and SrTiO ₃ and in insulating materials having a high dielectric constant, there is a problem that polarons are generated, the insulating characteristics are deteriorated, and a good tunnel junction cannot be obtained.

The present invention has been made in consideration of the present situation, and an object thereof is to provide a superconducting device capable of obtaining a good tunnel junction while improving productivity.

[0006]

A superconducting device according to a first aspect of the present invention is an oxide superconducting layer, an insulating layer formed on the superconducting layer, and an insulating layer formed on the insulating layer. A superconducting device including a metal layer, characterized in that a metal layer for preventing polaron diffusion is provided between the oxide superconductor layer and the insulating layer.

Furthermore, a superconducting device according to a second aspect of the present invention is an oxide superconductor layer, an insulating layer formed on the superconductor layer, and an oxide superconductor formed on the insulating layer. A superconducting device comprising layers,
It is characterized in that a metal layer for preventing polaron diffusion is provided between at least one of the oxide superconductor layers and the insulating layer.

[0008]

Function: Metal does not generate polaron and can pass superconducting conductors. Therefore, the insulating characteristics of the tunnel junction element are improved, and the superconducting characteristics are hardly deteriorated, so that a good tunnel junction can be formed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a first embodiment of a superconducting device according to the present invention, in which a sandwich structure made of SIN (S is a superconductor, I is an insulating layer, N is a normal conductor) is formed. Has become. The S layer 1 and the N layer 4 have a thickness of about 1000Å, and the S layer 1 is B layer.
i ₂ Sr ₂ Ca ₁ Cu ₂ O _x , Ba _0.6 K _0.4 BiO ₃ or Y
_{The 1} Ba ₂ Cu ₃ O _x to N layer 5 is made of Au or the like. On the other hand, the I layer 3 has a thickness of about 40Å
It is selected from TiO ₃ .

The feature of the present invention is that S
The metal layer 2 having a film thickness of 100 to 300Å is provided between the layer 1 and the I layer 3.

As the metal layer 2, Al, Ga, In, T of rare earth, titanium group, vanadium group, chromium group, manganese group, iron group, platinum group, copper group, zinc group and boron group are used.
1, Sb, Bi, and lanthanoids of the carbon group and the nitrogen group may be selected.

The metal layer 2 does not generate polarons and is capable of passing superconducting conductors. Therefore, the insulating characteristics of the tunnel junction element are improved, and the superconducting characteristics are hardly deteriorated, so that a good tunnel junction can be formed.

Here, the superconducting device having the above structure was manufactured as follows. Bi ₂ Sr ₂ Ca ₁ as the S layer ₁
The case of using Cu ₂ O _x (hereinafter referred to as BSCCO) will be described.

A single crystal BSCCO substrate 1 is prepared, and this B
A metal layer 2 made of Au having a film thickness of 100 to 300 Å on the SCCO substrate 1 by EB vapor deposition or vapor deposition by resistance heating.
To provide. The metal layer 2 may have any thickness as long as it can uniformly cover the surface of the BSCCO substrate 1.

After providing the metal layer 2 on the substrate 1, the substrate 1 is placed in a vacuum chamber. And MgO as a source
The melt was put into a vacuum chamber, and the back pressure was set to 1 × 10 ⁻⁹ Torr in the vacuum chamber.

After that, the substrate is kept at 250 ° C. or lower, in this embodiment, room temperature, and an amorphous MgO film is formed by an EB gun. The film forming rate is 6 Å / min, and the I layer 3 made of amorphous MgO of about 20 to 40 Å is laminated.

An N layer 4 of Au or the like having a film thickness of 2000 Å is provided on the I layer 3 by EB vapor deposition or vapor deposition by resistance heating.

FIG. 2 shows the conductance of the tunnel junction in this embodiment. As shown in FIG. 2, the S layer 1
By providing the metal layer 2 for preventing the diffusion of polaron between the insulating layer 3 and the insulating layer 3, it is possible to reproducibly obtain a device exhibiting a strong nonlinearity at 20 to 30 meV corresponding to the energy gap of BSCCO. On the other hand, the conductance of the conventional tunnel junction in which the metal layer is not provided between the S layer 1 and the insulating layer 3 has only a large amount of leakage and weak nonlinearity as shown in FIG.

FIG. 4 is a sectional view showing a second embodiment of a superconducting device according to the present invention, which has a structure in which a sandwich structure composed of SIS (S is a superconductor, I is an insulating layer) is formed. There is. The S layers 1 and 5 have a thickness of about 1
000Å and the S layer is Bi ₂ Sr ₂ Ca ₁ Cu
₂ O _x , Ba _0.6 K _0.4 BiO ₃ or Y ₁ Ba ₂ Cu ₃ O _x . On the other hand, the I layer 3 has a thickness of about 40Å and is composed of MgO and SrTiO ₃ .

Then, the S layer 1 and the I layer 3 and the I layer 3 and the S layer
Between the layers 6, the metal layers 2 and 5 each having a film thickness of 100 to 300 Å
Is provided.

The superconducting device having the above structure was manufactured as follows. A case where BSCCO is used as the S layers 1 and 6 will be described.

A single crystal BSCCO substrate 1 is prepared, and this B
A metal layer 2 made of Au having a film thickness of 100 to 300 Å on the SCCO substrate 1 by EB vapor deposition or vapor deposition by resistance heating.
To provide.

After providing the metal layer 2 on the substrate 1, the substrate 1 is placed in a vacuum chamber. And MgO as a source
The melt was put into a vacuum chamber, and the back pressure was set to 1 × 10 ⁻⁹ Torr in the vacuum chamber.

After that, the substrate is kept at 250 ° C. or lower, in this embodiment, room temperature, and an amorphous MgO film is formed by an EB gun. The film forming rate is 6 Å / min, and the I layer 3 made of amorphous MgO of about 20 to 40 Å is laminated.

A metal layer 5 made of Au and having a film thickness of 100 to 300 Å is provided on the I layer 3 by EB vapor deposition or vapor deposition by resistance heating.

Thereafter, an S layer 6 made of BSCCO having a film thickness of 1000 Å is provided on the metal layer 5 by a vapor deposition method or a sputtering method. Here, a case where the S layer 6 is formed by a sputtering method will be described. After mounting in the rf-magnetron sputtering device equipped with the sputtering target, vacuuming is performed until the internal pressure of the device becomes 10 ⁻⁴ to 10 ⁻⁶ Pa.

Next, Ar gas and O ₂ gas are introduced into the apparatus. At this time, the ratio of Ar gas to O ₂ gas is 5
It was set to 0:50 and the gas pressure in the apparatus was set to 80 Pa.

Then, 50 to 150 W is applied between the positive and negative electrodes of the device.
After the plasma is generated in the device by applying the discharge power of, the substrate is heated to 500 ° C. by the heating device in the device.
Heat to ~ 700 ° C.

Then, after performing pre-sputtering for 0.5 to 2 hours, the shutter in the apparatus is opened and the main sputtering is started while the substrate is heated to 500 to 700 ° C.
As a result, the formation of the S layer 6 is started. At this time, since the film forming rate is 500 Å / hr, the main sputtering is performed for about 2 hours. After the end of the main sputtering, the shutter is closed and the plasma is turned off. After that, the introduction of Ar gas is stopped and the introduction state of O ₂ gas is maintained and maintained at a temperature of 600 ° C. or higher for about 1 hour. After that, the temperature is lowered and the substrate is cooled in an O ₂ gas atmosphere to form the superconducting device shown in FIG.

FIG. 5 shows the conductance of the tunnel junction in this embodiment. As shown in FIG. 5, the S layer 1
By providing the metal layer 2 for preventing the diffusion of polaron between the insulating layer 3, the S layer 6, and the insulating layer 3, a device showing a strong nonlinearity at 20 to 30 meV corresponding to twice the energy gap of BSCCO can be obtained. It can be reproducibly obtained.
On the other hand, the conductance of the conventional tunnel junction in which the metal layer is not provided between the S layer 1 and the insulating layer 3 has only a large amount of leakage and weak nonlinearity as shown in FIG.

In the embodiment shown in FIG. 4, metal layers 2 and 5 are provided between the S layer 1 and the I layer 3 and between the I layer 3 and the S layer 6, respectively. The same effect can be obtained by providing a layer.

In the above-mentioned embodiments, BSCCO is used as the S layer, but Y ₁ Ba ₂ Cu ₃ O _x , Ba
The same effect can be obtained by using an oxide superconductor other than BSCCO such as _0.6 K _0.4 BiO ₃ .

Further, although Au was used as the metal layer 2 in the above-mentioned embodiments, in addition to Au, rare earths, titanium group, vanadium group, chromium group, manganese group, iron group, platinum group, copper group, zinc are used. Group, boron group Al, Ga, In, T
Alternatively, a metal selected from Sb, Bi, lanthanoids of carbon group 1, carbon group, and nitrogen group may be used.

As described above, according to the present invention, the metal layer provided between the oxide superconductor and the insulating layer does not generate polaron and can pass the superconducting conductor. .. Therefore, the insulating characteristics of the tunnel junction element are improved, and the superconducting characteristics are hardly deteriorated, so that a good tunnel junction can be formed.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a graph showing tunnel conductance in the tunnel type junction according to the first embodiment of the present invention.

FIG. 3 is a graph showing tunnel conductance in a conventional tunnel junction.

FIG. 4 is a sectional view showing a second embodiment of the present invention.

FIG. 5 is a graph showing tunnel conductance in the tunnel junction according to the first embodiment of the present invention.

FIG. 6 is a graph showing tunnel conductance in a conventional tunnel junction.

[Explanation of symbols]

 1 S Layer 2 Metal Layer 3 I Layer (Amorphous Material) 4 N Layer 5 Metal Layer 6 S Layer

Claims (3)

[Claims] 1. A superconducting device comprising an oxide superconductor layer, an insulating layer formed on the superconductor layer, and a metal layer formed on the insulating layer, the oxide superconductor comprising: A superconducting device, characterized in that a metal layer for preventing polaron diffusion is provided between the layer and the insulating layer. 2. A superconductor device comprising an oxide superconductor layer, an insulating layer formed on the superconductor layer, and an oxide superconductor layer formed on the insulating layer.
A superconducting device, characterized in that a metal layer for preventing polaron diffusion is provided between at least one of the oxide superconductor layers and the insulating layer. 3. The rare earth metal, titanium group, vanadium group, chromium group, manganese group, iron group, platinum group, copper group, zinc group, boron group Al, Ga, In, Tl, carbon group, The superconducting device according to claim 1 or 2, wherein the superconducting device is selected from nitrogen group Sb, Bi, and lanthanoids.