JPH05152626A - Superconducting device and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an excellent tunnel junction in a superconducting device while the productivity of the device is improved. CONSTITUTION:This superconducting device comprises a superconducting thin film 3 having the composition of Ba1-xKxBiO3 (0.2<x<0.5) formed on a substrate 1 and a metallic or superconducting layer 5 formed on an insulating layer 4 composed of potassium superoxide (KO2 formed as a result of the oxidation of excessive potassium (K) precipitated at the time of forming the thin film 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting device having a tunnel type junction structure used for a micromixer, a superconducting transistor and the like, and a method for manufacturing the same.

[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 consisting of N (S is a superconducting thin film, I is an insulating layer, and N is a normal conductor). In this case, after forming an insulating layer such as MgO on the S layer, the superconducting thin film or the normal conducting layer is formed. The body is laminated.

[0004]

By the way, in the tunnel junction, it is better that the I layer has a smaller film thickness within the coherence length. For example, if a bismuth-based superconducting material is used, the coherence length is short. Due to this, it is necessary to set the thickness of the I layer to 1 to 1.5 nm or less. However, when an attempt is made to form a thin I layer, pinholes are generated due to irregularities on the superconducting thin film, and a good tunnel junction has not been obtained with a device using an oxide superconducting material under the present circumstances. FIG. 10 shows the tunnel conductance in the tunnel junction using the conventional oxide superconducting material. As is clear from FIG. 10, the nonlinearity is weak and the leak is large.

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 favorable tunnel junction while improving productivity.

[0006]

A superconducting device according to a first aspect of the present invention is a Ba _{1 -x} formed on a substrate.
It is formed by oxidizing a superconducting thin film having a composition of K _x BiO ₃ (0.2 <X <0.5), and excess potassium (K) deposited on the superconducting thin film when the thin film is formed. And an insulating layer having a composition of potassium superoxide (KO ₂ ) and a metal layer or a superconducting layer formed on the insulating layer.

Further, in the method for manufacturing a superconducting device according to the second aspect of the present invention, Ba _1-x K _x BiO is formed on the substrate.
_A superconducting thin film having a composition of ₃ (0.2 <X <0.5) was prepared using a target having a composition in which potassium (K) was excessive with respect to the substrate temperature, and excess potassium ( K) is precipitated and the potassium (K) is oxidized to form an insulating layer having a composition of potassium superoxide (KO ₂ ) on the superconducting thin film, and a metal layer or a superconducting layer is formed on the insulating layer. It is characterized by forming a tunnel type junction.

A superconducting device according to a third aspect of the present invention is a Ba _1-x K _x BiO ₃ (0.
2 <X <0.5), and a superconducting thin film (KO ₂ ) formed by oxidizing excess potassium (K) deposited when the thin film is formed on the superconducting thin film. ) A first insulating layer having a composition, a second insulating layer having a magnesium oxide (MgO) composition formed on the first insulating layer, and a metal layer or a superconducting layer formed on the second insulating layer. And,

Furthermore, in the method for manufacturing a superconducting device according to the fourth aspect of the present invention, a Ba _1-x K _x BiO film is formed on a substrate.
_A superconducting thin film having a composition of ₃ (0.2 <X <0.5) was prepared using a target having a composition in which potassium (K) was excessive with respect to the substrate temperature, and excess potassium ( K) is precipitated and the potassium (K) is oxidized to form a first insulating layer having a composition of potassium superoxide (KO ₂ ) on the superconducting thin film, and magnesium oxide (K) is formed on the first insulating layer. After the second insulating layer having a composition of MgO) is laminated and formed, a metal layer or a superconducting layer is formed on the second insulating layer to form a tunnel junction.

Also, in the method for manufacturing a superconducting device according to the fifth aspect of the present invention, after introducing argon gas and oxygen gas into the apparatus, a plasma atmosphere is provided inside the apparatus.
In a method of manufacturing a superconducting device in which a superconducting thin film having a composition of Ba _1-x K _x BiO ₃ (0.2 <X <0.5) is formed on a substrate, a gas inside the apparatus at the time of introducing gas during the formation of the superconducting thin film The pressure is set to 40 to 120 Pa, and the temperature of the substrate is heated to 300 ° C. or higher and 500 ° C. or lower, and potassium (K) is added to the substrate temperature of the substrate.
A superconducting thin film is formed by using a target having a composition that results in excess of K, and excess potassium (K) is deposited on the superconducting thin film. ₂ ) It is characterized by forming an insulating layer having a composition.

A superconducting device according to a sixth aspect of the present invention is a Ba _1-x Rb _x BiO formed on a substrate.
₃ (0.2 <X <0.5), and superoxide formed by oxidizing excess rubidium (Rb) deposited when the thin film is formed on the superconducting thin film. An insulating layer having a rubidium (RbO ₂ ) composition and a metal layer or a superconducting layer formed on the insulating layer are provided.

Further, in the method for manufacturing a superconducting device according to the seventh aspect of the present invention, Ba _1-x Rb _x Bi is formed on the substrate.
A superconducting thin film having a composition of O ₃ (0.2 <X <0.5) was prepared using a target having a composition in which rubidium (Rb) was excessive with respect to the substrate temperature, and the excess rubidium was formed on the superconducting thin film. By depositing (Rb) and oxidizing this rubidium (Rb), an insulating layer having a rubidium superoxide (RbO ₂ ) composition is formed on the superconducting thin film,
A metal layer or a superconducting layer is formed on this insulating layer to form a tunnel junction.

A superconducting device according to an eighth aspect of the present invention is a Ba _1-x Rb _x BiO film formed on a substrate.
₃ (0.2 <X <0.5), and superoxide formed by oxidizing excess rubidium (Rb) deposited when the thin film is formed on the superconducting thin film. A first insulating layer having a rubidium (RbO ₂ ) composition, a second insulating layer having a magnesium oxide (MgO) composition formed on the first insulating layer, and a metal formed on the second insulating layer A layer or a superconducting layer.

According to a ninth aspect of the present invention, there is provided a method of manufacturing a superconducting device, wherein Ba _1-x Rb _x BiO is formed on a substrate.
_A superconducting thin film having a composition of ₃ (0.2 <X <0.5) was prepared using a target having a composition in which rubidium (Rb) was excessive with respect to the substrate temperature, and excess rubidium ( Rb) is precipitated and this rubidium (Rb) is oxidized to form a first insulating layer of a rubidium superoxide (RbO ₂ ) composition on the superconducting thin film, and magnesium oxide (Rb) is formed on the first insulating layer. MgO)
After the second insulating layer having the composition is laminated and formed, a metal layer or a superconducting layer is formed on the second insulating layer to form a tunnel junction.

Further, in the method for manufacturing a superconducting device according to the tenth aspect of the present invention, after introducing argon gas and oxygen gas into the apparatus, a Ba _1-x Rb _x BiO ₃ gas atmosphere is created in the apparatus. In a method for manufacturing a superconducting device in which a superconducting thin film having a composition of (0.2 <X <0.5) is formed on a substrate, a gas pressure in the apparatus at the time of introducing gas during the superconducting thin film formation is 40 to 120 Pa. And the temperature of the substrate is heated to 300 ° C. or higher and 500 ° C. or lower, a superconducting thin film is formed using a target having a composition in which rubidium (Rb) becomes excessive with respect to the substrate temperature of the substrate, and the superconducting thin film is formed. It allowed precipitating excess rubidium (Rb) on the thin film, by oxidizing the rubidium (Rb), a superconducting thin film on the superoxide rubidium (RBO ₂₎ absolute composition And forming a layer.

[0016]

According to the present invention, excess potassium (K) is deposited on the surface of the Ba _1-x K _x BiO ₃ oxide superconductor. The deposited potassium (K) is oxidized to form a potassium superoxide (KO ₂ ) insulator layer on the surface of the oxide superconductor. Since this potassium superoxide (KO ₂ ) insulator layer is deposited and formed on the surface, it is densely formed on the oxide superconductor, and there is no possibility of pinholes even if there are irregularities on the superconductor surface. Therefore, a very good tunnel junction without leakage can be formed.

Further, according to the present invention, Ba _1-x Rb _x B
iO ₃ excess on the surface of the oxide superconductor rubidium (R
b) precipitates. The deposited rubidium (Rb) is oxidized, and rubidium superoxide (Rb) is formed on the surface of the oxide superconductor.
O ₂ ) An insulating layer is formed. Since this rubidium superoxide (RbO ₂ ) insulator layer is formed by being deposited on the surface, it is densely formed on the oxide superconductor, and there is no risk of pinholes even if there are irregularities on the superconductor surface.
Therefore, a very good tunnel junction without leakage can be formed.

Further, by laminating an insulating layer of magnesium oxide (MgO) composition on an insulating layer of potassium superoxide (KO ₂ ) or rubidium superoxide (RbO ₂ ), an insulating layer barrier stable even in the atmosphere. Is formed, and a very good tunnel junction with no leakage can be formed.

[0019]

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, which is SrTiO ₃ (1
SIN (S is a superconducting thin film,
The structure is such that I is an insulating layer and N is a normal conductor. Above S layer 3
And the N layer 5 has a thickness of about 1000Å, and the S layer 3 is B
The a _0.6 K _0.4 BiO ₃ or Ba _0.6 Rb _0.4 BiO ₃ to N layer 5 is made of Au or the like. On the other hand, the I layer 4 has a thickness of about 40Å and is made of Ba _0.6 K _0.4 BiO ₃ or Ba _0.6 Rb.
_{When 0.4} BiO ₃ is formed, it is composed of potassium superoxide (KO ₂ ) or rubidium superoxide (RbO ₂ ) formed by oxidizing potassium (K) or rubidium (Rb) deposited on the surface.

Here, the superconducting device having the above structure was manufactured as follows. First, as the S layer 3, Ba _0.6 K
_The case of using _0.4 BiO ₃ will be described.

The substrate 1 is ultrasonically cleaned in ethyl alcohol, then boiled and dried. Next, after mounting the cleaned substrate 1 in an RF-magnetron sputtering apparatus equipped with a sputtering target having a composition in which potassium (K) becomes excessive with respect to the substrate temperature, the apparatus internal pressure is set to 10
^Evacuate until the pressure reaches ^-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.

Thereafter, 50 to 150 W is applied between the positive and negative electrodes of the device.
After the plasma is generated in the apparatus by applying the discharge power of 300, the substrate 1 is heated to 300 by the heating apparatus in the apparatus.
Heat to ℃ ~ 500 ℃.

Then, after performing pre-sputtering for 0.5 to 2 hours, the shutter in the apparatus is opened and the main sputtering is started in a state where the substrate 1 is heated to 300 to 500 ° C.
As a result, the formation of the S layer 3 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 the Ar gas is stopped, the introduction state of the O ₂ gas is maintained, and the temperature is kept at 350 ° C. or higher for about 1 hour. After that, the temperature is lowered and the substrate 1 is cooled in an O ₂ gas atmosphere.

Ba _0.6 K _0.4 B formed by this sputtering
When forming the S layer 3 composed of iO ₃ , excess potassium (K) is deposited on the surface of the S layer 3. Then, potassium is precipitated in the S layer 3 surface (K) is oxidized in an O ₂ atmosphere, potassium deposited on the surface (K) is potassium superoxide in O ₂ atmosphere over all 300 ℃ (KO ₂₎ becomes , An I layer 4 made of potassium superoxide (KO ₂ ) is formed.

If desired, an I layer may be further laminated.

An N layer 5 of Au or the like is provided on the I layer 4 by EB vapor deposition or vapor deposition.

Further, in the case of the SIS structure, the following method other than the method of forming the S layer by the same method as the above-mentioned sputtering method after forming the I layer 4 made of potassium superoxide (KO ₂ ). There is.

If Nb or Pb is laminated on Au, the Nb or Pb becomes superconducting, and the coherence length is several thousand Å (4.2K). Therefore, Au having a thickness of 1000 Å or less is sufficiently superconducting. It becomes a state. That is, when Nb / Au is used, a Josephson junction having a SIS structure is obtained.

The Josephson junctions of this structure, when forming the S layer 3 made of Ba _0.6 K _0.4 BiO ₃ on the substrate 1, 300 ° C. The potassium is precipitated in the S layer 3 surface (K)
I becomes potassium superoxide (KO ₂ ) in the above O ₂ atmosphere I
After forming the layer 4, 500 Å of Au is laminated by resistance heating. Then, it is obtained by depositing Nb at 2Å / sec for 15 minutes by the MBE method and stacking 1800Å Nb.

The substrate temperature during film formation by this MBE method is 150.
When performed at ˜300 ° C., the transition temperature Tc of Nb is 9.2 K and works as a Josephson junction of SIS structure at 9 K or less. Pb can also be formed by the same method.

FIG. 6 shows the results of examining the tunnel conductance in the tunnel junction using the oxide superconducting material according to the present invention. As is clear from FIG. 6, according to the present invention, there is no interface damage, a good interface is obtained, and a good conductance is obtained.

FIG. 7 is a sectional view showing a second embodiment of the superconducting device according to the present invention, which is SrTiO ₃ (1
SIN (S is a superconducting thin film,
The structure is such that I is an insulating layer and N is a normal conductor. Above S layer 3
And the N layer 5 has a thickness of about 1000Å, and the S layer 3 is B
The a _0.6 K _0.4 BiO ₃ or Ba _0.6 Rb _0.4 BiO ₃ to N layer 5 is made of Au or the like.

On the other hand, the I layer 4 is made of Ba _0.6 K _0.4 BiO.
₃ or Ba _0.6 Rb _0.4 BiO ₃ , potassium superoxide (KO ₂ ) or rubidium superoxide (RbO ₂ ) formed by oxidizing potassium (K) or rubidium (Rb) deposited on the surface when forming ₃ or Ba _0.6 Rb _0.4 BiO _3. ), And a second insulating layer 42 made of magnesium oxide (MgO) laminated on the first insulating layer 41 by RF magnetron sputtering or EB vapor deposition. ..

Second layer composed of magnesium oxide (MgO)
For the insulating layer 42, amorphous MgO or polycrystalline MgO is used. When amorphous MgO is used, even if there are irregularities on the first insulating layer 41, the amorphous MgO is smoothly laminated on the surface and the surface of the amorphous MgO is flattened.
An N layer or the like can be easily laminated on the gO surface.

A superconducting device having the above structure was manufactured as follows. A case where Ba _0.6 K _0.4 BiO ₃ is used as the S layer 3 will be described.

Ba _0.6 is sputtered on the substrate 1.
The S layer 3 made of K _0.4 BiO _{3 is} formed, and when the S layer 3 is formed,
Excess potassium (K) is deposited on the surface of the S layer 3 to form the first insulating layer 41 made of potassium superoxide (KO ₂ ), which is the same as that of the first embodiment described above, and therefore the description thereof is omitted here. Then, a method for forming the second insulating layer 42 on the first insulating layer 41 will be described.

After placing a solidified MgO sintered body or powder as a sputtering target in the sputtering apparatus, Ar gas was introduced into the sputtering apparatus and the gas pressure in the apparatus was set to 1 to 10 Pa. ..

After that, the substrate 1 is kept at room temperature for 50 to 10
Amorphous MgO is deposited by applying an RF output of 0 W. The film forming rate is 2 to 40 Å / min, and the second insulating layer 42 made of amorphous MgO having a thickness of about 20 to 40 Å is laminated on the first insulating layer 41 made of potassium superoxide (KO ₂ ).

An N layer 5 of Au or the like having a film thickness of 2000 Å is provided on the second insulating layer 42 by EB vapor deposition or vapor deposition.

By the way, the tunnel junction using only potassium superoxide (KO ₂ ) as the insulating layer in the first embodiment can obtain an effective conductance exhibiting a strong nonlinearity as shown in FIG. As shown in FIG. 8, there are cases where fairly weak ones are produced. On the other hand, as in the second embodiment shown in FIG. 7, potassium superoxide (K
By stacking a MgO film on O ₂ ), as shown in FIG.
A device showing a strong nonlinearity at V was obtained with good reproducibility.

Now, Ba _0.6 K _0.4 B by sputtering
The sputtering target used when forming the S layer 3 made of iO ₃ is a barium compound (for example,
BaCO ₃ , BaO, Ba (NO) ₂ ), a potassium compound (for example, KO ₂ , K ₂ CO ₃ , KNO ₃ ) or a bismuth compound (for example, Bi ₂ O ₃ ) in excess of potassium (K) with respect to the substrate temperature. After mixing in the following proportions, it is fired in a nitrogen gas atmosphere (600 to 700 ° C.) for 2 to 5 hours and in an oxygen gas atmosphere (400 to 500 ° C.) for 2 to 5 hours, and further, 1 to
It was prepared by pressing at a pressure of 3 ton / cm ² .

By the way, the deposition amount of potassium (K) varies depending on the substrate temperature even if the sputtering target composition has the same amount of potassium (K). That is, the higher the substrate temperature, the greater the amount of potassium (K) deposited.

For example, when the substrate temperature Ts is 400 ° C., the composition of the sputtering target is Ba _0.6 K _x BiO.
By using X = 0.25 to 0.35 in ₃ , it is possible to obtain a BKBO thin film having a good resistance temperature characteristic. The superconducting transition temperature Tc at this time is 26 K to 28 K, and the resistivity just above Tc of the superconducting semiconductor is 2 to 3 mΩ · cm.
It is a degree.

Further, the amount of potassium (K), that is, the amount of potassium (K) deposited on the surface is changed by changing the above X. For example, when X = 0.25 to 0.27, potassium (K) hardly precipitates. When X = 0.27, the precipitation of potassium (K) starts.

After the film formation, as described above, since the film is kept in the O ₂ atmosphere at 350 ° C. or higher for about 1 hour, the excess potassium (K) deposited on the surface is entirely potassium superoxide (K). Exist in the form of KO ₂ ).

When X = 0.25 to 0.27,
Even if potassium (K) does not precipitate, the potassium (K) on the outermost surface is oxidized and potassium superoxide (K)
It becomes potassium superoxide of O ₂ ).

FIG. 4 shows that when 0.25 and <x <0.27,
FIG. 5 is a conceptual diagram of film growth when 0.28 <x <0.35. In these figures, the white circles indicate the KO ₂ layer and the black circles indicate the BKBO molecule.

Due to these facts, the thickness of the potassium superoxide (KO ₂ ) layer on the surface is about 3Å when the thickness is X to 0.25 to 0.27.

When precipitation occurs, (X to 0.2
8 to 0.35) Potassium superoxide (K)
It forms a dense oxide of O ₂ ). In either case,
Since the distribution of K on the surface is very uniform, the potassium superoxide (KO ₂ ) oxide layer is formed with a uniform thickness.

FIG. 3 shows the results of measuring the composition amount of X, that is, K, and the thickness of the potassium superoxide (KO ₂ ) oxide layer with Ba _0.6 K _x BiO ₃ as the sputtering target composition. As shown in FIG. 3, the precipitation point of K (X = 0.2
7) Above, there is a substantially proportional relationship between the amount of X and the thickness of the potassium superoxide (KO ₂ ) layer.

The relational expression is Where D is the thickness of potassium superoxide (KO ₂ ) and x is K
Is the amount.

For example, when x = 0.3, D (0.
3) = It is possible to form a uniform barrier of 17Å.
However, when x <0.35, K starts to be distributed in an island shape, so that a uniform potassium superoxide (KO ₂ ) film cannot be formed.

In forming the potassium superoxide (KO ₂ ) layer, only the first surface layer of the BKBO layer may be damaged, but that layer is the smallest barrier layer. In conventional oxide-based superconductors, since there is no such spontaneous oxide barrier layer, it is necessary to form an artificial oxide barrier layer such as MgO or SrTiO ₃ .

The S layer 3 was examined by the X-ray diffraction method, and the results are shown in FIG. As is clear from FIG.
It was confirmed that the S layer was oriented almost completely in the (110) direction. Moreover, the width of the peak is similar to that of a substrate having a single crystal structure. From this, it can be seen that the film quality of the S layer is good.

Further, it was confirmed from the photograph obtained by the RHEED method that the S layer 3 was epitaxially grown.

Next, as the S layer 3, Ba _0.6 Rb _0.4 BiO is used.
_The case of using ₃ will be described.

First, the substrate 1 is ultrasonically cleaned in ethyl alcohol, then boiled and dried. Next, after mounting the cleaned substrate 1 in an RF-magnetron sputtering device equipped with a sputtering target having a composition in which rubidium (Rb) is excessive with respect to the substrate temperature, the internal pressure of the device is 10 ^-4 ~. Vacuuming is performed until the pressure reaches 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 apparatus by applying the discharge power of 300, the substrate 1 is heated to 300 by the heating apparatus in the apparatus.
Heat to ℃ ~ 500 ℃.

After that, after performing pre-sputtering for 0.5 to 2 hours, in the state where the substrate 1 is heated to 300 to 500 ° C., the shutter in the apparatus is opened to start the main sputtering.
As a result, the formation of the S layer 3 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 the Ar gas is stopped, the introduction state of the O ₂ gas is maintained, and the temperature is kept at 350 ° C. or higher for about 1 hour. After that, the temperature is lowered and the substrate 1 is cooled in an O ₂ gas atmosphere.

Ba _0.6 Rb _0.4 by this sputtering
When forming the S layer 3 made of BiO ₃ , excess rubidium (Rb) is deposited on the surface of the S layer 3. Then, rubidium which is deposited in the S layer 3 surface (Rb) is oxidized in an O ₂ atmosphere, rubidium deposited on the surface (Rb) is superoxide rubidium in all 300 ° C. or more O ₂ atmosphere (Rb
O ₂ ), and I made of rubidium superoxide (RbO ₂ ).
Layer 4 is formed. An N layer 5 of Au or the like is provided on the I layer 4 by EB vapor deposition or vapor deposition.

In the case of the SIS structure, after the I layer 4 made of rubidium superoxide (RbO ₂ ) is formed,
The S layer may be formed by the same method as the above-mentioned sputtering method, or Au may be laminated on the I layer 4 and Nb or Pb may be laminated thereon in the same manner as in the above-mentioned embodiment.

In the case of the second embodiment shown in FIG. 7,
After forming the I layer made of rubidium superoxide (RbO ₂ ), the second insulating layer made of amorphous MgO may be provided by the method described above.

The above sputtering target is
Barium compound (for example, BaCO ₃ , BaO, Ba
(NO) ₂ ), a rubidium compound (for example, RbO ₂ , R
b ₂ CO ₃ , RbNO ₃ ), a bismuth compound (for example, Bi ₂
O ₃ ) is mixed at a ratio of rubidium (Rb) excess with respect to the substrate temperature, and then a nitrogen gas atmosphere (600 to 70) is mixed.
2 hours at 0 ° C., oxygen gas atmosphere (400-500)
(° C.) for 2 to 5 hours, and further pressed at a pressure of 1 ton / cm ² .

As in the case of potassium described above, the deposition differs depending on the substrate temperature even with the same amount of rubidium (Rb). That is, the higher the substrate temperature, the more the amount of rubidium (Rb) deposited.

For example, when the substrate temperature Ts is 400 ° C., the composition of the sputtering target is Ba _0.6 Rb _x Bi.
By using X = 0.25 to 0.35 for O ₃ , a BRbBO thin film having good resistance temperature characteristics can be obtained. The superconducting transition temperature Tc at this time is 26K to 30K.
And the resistivity just above Tc of the superconducting semiconductor is 2-3 mΩ.
・ It is about cm.

As in the case of potassium, the amount of rubidium (Rb) deposited on the surface is changed by changing the amount of rubidium (Rb), that is, the above X. For example,
When X = 0.25 to 0.27, rubidium (Rb) is hardly deposited. When X = 0.27, the precipitation of rubidium (Rb) starts.

After the film formation, as described above, since the film is kept in an O ₂ atmosphere at 350 ° C. or higher for about 1 hour, excess rubidium (Rb) deposited on the surface is entirely rubidium superoxide ( It exists in the form of RbO ₂ ).

When X = 0.25 to 0.27,
Even when rubidium (Rb) is not deposited, the rubidium (Rb) on the outermost surface is oxidized to become rubidium superoxide (RbO ₂ ).

When x = 0.3, D (0.3) = 17
A uniform barrier of Å can be formed. However, x
When <0.35, Rb begins to be distributed in an island shape, so that a uniform rubidium superoxide (RbO ₂ ) film cannot be formed.

Also in the formation of the rubidium superoxide (RbO ₂ ) layer, only the first surface layer of the BRbBO layer may be damaged as described above, but that layer becomes the minimum barrier layer.

As a result of examining the S layer 3 by an X-ray diffraction method, it was confirmed that the S layer was oriented almost completely in the (110) direction. Moreover, the width of the peak is similar to that of a substrate having a single crystal structure. From this, it can be seen that the film quality of the S layer is good.

Further, it was confirmed from the photograph obtained by the RHEED method that the S layer 3 was epitaxially grown.

[0076]

As described above, according to the present invention, potassium (K) or rubidium (Ba) deposited on the surface of a Ba _1-x K _x BiO ₃ or Ba _1-x Rb _x BiO ₃ oxide superconductor ( Rb) is oxidized and an insulating layer of potassium superoxide (KO ₂ ) or rubidium superoxide (RbO ₂ ) is formed on the surface of the oxide superconductor. Since this potassium superoxide (KO ₂ ) or rubidium superoxide (RbO ₂ ) insulator layer is formed by being deposited on the surface, it is densely formed on the oxide superconductor and even if there are irregularities on the superconductor surface. There is no risk of pinholes. Therefore, a very good tunnel junction without leakage can be formed.

By stacking an insulating layer of magnesium oxide (MgO) on an insulating layer of potassium superoxide (KO ₂ ) or rubidium superoxide (RbO ₂ ), a stable insulating layer barrier is formed even in the atmosphere. As a result, a very good tunnel junction without leakage can be formed with good reproducibility.

[Brief description of drawings]

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

FIG. 2 is a graph showing an X-ray diffraction pattern of an S layer.

FIG. 3 is a graph showing the relationship between the amount of K in the sputtering target composition and the thickness of a potassium superoxide (KO ₂ ) oxide layer.

FIG. 4 is a conceptual diagram of film growth when a composition amount of K of a sputtering target composition is 0.25 and <x <0.27. It is a conceptual diagram of film growth in the case of 0.28 <x <0.35.

FIG. 5 is a conceptual diagram of film growth when the composition amount of K in the sputtering target composition is 0.28 <x <0.35.

FIG. 6 is a graph showing tunnel conductance in a tunnel type junction using the oxide superconducting material according to the present invention.

FIG. 7 is a sectional view showing a second embodiment of the present invention.

FIG. 8 is a graph showing tunnel conductance in a tunnel type junction using an oxide superconducting material according to the first example of the present invention.

FIG. 9 is a graph showing tunnel conductance in a tunnel type junction using an oxide superconducting material according to the second embodiment of the present invention.

FIG. 10 is a graph showing tunnel conductance in a tunnel type junction using a conventional oxide superconducting material.

[Explanation of symbols]

 1 Substrate 2 Main Body 3 S Layer 4 I Layer 5 N Layer 41 First Insulating Layer 42 Second Insulating Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuro Usuki, 2-18, Keihan Hondori, Moriguchi City Sanyo Electric Co., Ltd. (72) Inventor Junnobu Yoshiza, 2-chome, Keihan Hondori, Moriguchi Sanyo Electric Co., Ltd. Inside the company

Claims (10)

[Claims] 1. Ba _1-x K _x BiO ₃ formed on a substrate
A superconducting thin film having a composition of (0.2 <X <0.5) and potassium superoxide formed by oxidizing excess potassium (K) deposited on the superconducting thin film when the thin film is formed. A superconducting device comprising an insulating layer having a (KO ₂ ) composition and a metal layer or a superconducting layer formed on the insulating layer. 2. A Ba _1-x K _x BiO ₃ (0.2
A superconducting thin film having a composition of <X <0.5) is prepared using a target having a composition in which potassium (K) becomes excessive with respect to the substrate temperature, and excess potassium (K) is deposited on the superconducting thin film. , By oxidizing this potassium (K), potassium superoxide (KO ₂ ) is formed on the superconducting thin film.
A method of manufacturing a superconducting device, comprising forming an insulating layer having a composition, forming a metal layer or a superconducting layer on the insulating layer, and forming a tunnel junction. 3. Ba _1-x K _x BiO ₃ formed on a substrate
A superconducting thin film having a composition of (0.2 <X <0.5) and potassium superoxide formed by oxidizing excess potassium (K) deposited on the superconducting thin film when the thin film is formed. A first insulating layer having a (KO ₂ ) composition, a second insulating layer having a magnesium oxide (MgO) composition formed on the first insulating layer, and a metal layer formed on the second insulating layer. Alternatively, a superconducting device including a superconducting layer. 4. A Ba _1-x K _x BiO ₃ (0.2
A superconducting thin film having a composition of <X <0.5) is prepared using a target having a composition in which potassium (K) becomes excessive with respect to the substrate temperature, and excess potassium (K) is deposited on the superconducting thin film. , By oxidizing this potassium (K), potassium superoxide (KO ₂ ) is formed on the superconducting thin film.
A first insulating layer having a composition is formed, and a second insulating layer having a magnesium oxide (MgO) composition is laminated on the first insulating layer, and then a metal layer or a superconducting layer is formed on the second insulating layer. Forming a tunnel-type junction, and manufacturing a superconducting device. 5. After introducing argon gas and oxygen gas into the apparatus, the inside of the apparatus is made into a plasma atmosphere, and Ba _1-x K _x
In a method of manufacturing a superconducting device in which a superconducting thin film having a composition of BiO ₃ (0.2 <X <0.5) is formed on a substrate, a gas pressure in the apparatus at the time of introducing gas during the formation of the superconducting thin film is 40 to 120 Pa. In such a state that the temperature of the substrate is heated to 300 ° C. or higher and 500 ° C. or lower, a superconducting thin film is formed using a target having a composition in which potassium (K) is excessive with respect to the substrate temperature substrate temperature. A superconducting device characterized by forming an insulating layer having a potassium superoxide (KO ₂ ) composition on the superconducting thin film by depositing excess potassium (K) on the superconducting thin film and oxidizing the potassium (K). Manufacturing method. 6. Ba _1-x Rb _x BiO formed on a substrate
₃ (0.2 <X <0.5), and superoxide formed by oxidizing excess rubidium (Rb) deposited when the thin film is formed on the superconducting thin film. A superconducting device comprising an insulating layer having a rubidium (RbO ₂ ) composition and a metal layer or a superconducting layer formed on the insulating layer. 7. A Ba _1-x Rb _x BiO ₃ (0.
A superconducting thin film having a composition of 2 <X <0.5) is prepared using a target having a composition in which rubidium (Rb) is excessive with respect to the substrate temperature, and excess rubidium (Rb) is deposited on the superconducting thin film. This is rubidium (R
By oxidizing b), an insulating layer having a composition of rubidium superoxide (RbO ₂ ) is formed on the superconducting thin film, and a metal layer or a superconducting layer is formed on this insulating layer to form a tunnel junction. And a method for manufacturing a superconducting device. 8. Ba _1-x Rb _x BiO formed on a substrate
₃ (0.2 <X <0.5), and superoxide formed by oxidizing excess rubidium (Rb) deposited when the thin film is formed on the superconducting thin film. A first insulating layer having a rubidium (RbO ₂ ) composition, a second insulating layer having a magnesium oxide (MgO) composition formed on the first insulating layer, and a metal formed on the second insulating layer A superconducting device comprising a layer or a superconducting layer. 9. A Ba _1-x Rb _x BiO ₃ (0.
A superconducting thin film having a composition of 2 <X <0.5) is prepared using a target having a composition in which rubidium (Rb) is excessive with respect to the substrate temperature, and excess rubidium (Rb) is deposited on the superconducting thin film. This is rubidium (R
b) is oxidized to form a first insulating layer having a rubidium superoxide (RbO ₂ ) composition on the superconducting thin film, and a _second insulating layer having a magnesium oxide (MgO) composition is formed on the first insulating layer. Is formed, and then a metal layer or a superconducting layer is formed on the second insulating layer to form a tunnel-type junction, which is a method for manufacturing a superconducting device. 10. After introducing argon gas and oxygen gas into the apparatus, the inside of the apparatus is made into a plasma atmosphere and Ba _{1 -x}
In a method of manufacturing a superconducting device in which a superconducting thin film having a composition of Rb _x BiO ₃ (0.2 <X <0.5) is formed on a substrate, a gas pressure in the apparatus at the time of introducing gas during the formation of the superconducting thin film is 40 to Set to 120 Pa,
In the state where the temperature of the substrate is heated to 300 ° C. or higher and 500 ° C. or lower, a superconducting thin film is formed using a target having a composition in which rubidium (Rb) is excessive with respect to the substrate temperature of the substrate, and the superconducting thin film is excessively formed on the superconducting thin film. A method for producing a superconducting device, comprising depositing rubidium (Rb) and oxidizing the rubidium (Rb) to form an insulating layer having a composition of rubidium superoxide (RbO ₂ ) on the superconducting thin film.