JP3102936B2 - Superconducting device and manufacturing method thereof - Google Patents

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 junction structure used for a micromixer, a superconducting transistor, and the like, and a method of 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
Bismuth-based oxide superconducting materials and yttrium-based oxide superconducting materials having a high density have been proposed.

When a superconducting device is manufactured using the above-described oxide superconducting material, for example, a tunnel junction having a constant operating voltage and excellent circuit operation stability is used. This tunnel type junction is SIS or SI
It has a sandwich structure composed of N (S is a superconducting thin film, 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, the superconducting thin film or the normal conducting The body is laminated.

[0004]

By the way, in the above-mentioned tunnel junction, the thickness of the I layer is preferably as small as possible within the coherence length. For example, when a bismuth-based superconducting substance or the like is used, the coherence length is short. For this reason, it is necessary to set the thickness of the I layer to 1 to 1.5 nm or less. However, if an attempt is made to form a thin I layer, pinholes are generated due to irregularities on the superconducting thin film, and at present, good tunnel junctions cannot be obtained with a device using an oxide superconducting substance. FIG. 10 shows the tunnel conductance in a tunnel junction using a conventional oxide superconducting material. As is clear from FIG. 10, the nonlinearity is weak and there are many leaks.

[0005] The present invention has been made in view of the present situation, and has as its object to provide a superconducting device capable of obtaining a good tunnel junction while improving productivity.

[0006]

According to a first aspect of the present invention, there is provided a superconducting device comprising a Ba _1-x substrate formed on a substrate.
A superconducting thin film having a composition of K _x BiO ₃ (0.2 <X <0.5), and formed by oxidizing excess potassium (K) deposited on the superconducting thin film when the thin film is formed. An insulating layer having a composition of potassium superoxide (KO ₂ ), and a metal layer or a superconducting layer formed on the insulating layer.

Furthermore, the method of manufacturing a superconducting device according to the second aspect of the invention, on a substrate, Ba _1-x K _x BiO
_{3 A} superconducting thin film having a composition of (0.2 <X <0.5) is formed using a target having a composition in which potassium (K) becomes excessive with respect to the substrate temperature, and excess potassium (K) is formed on the superconducting thin film. K) is deposited, and the potassium (K) is oxidized to form an insulating layer 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.

[0008] A superconducting device according to a third aspect of the present invention is a superconducting device comprising Ba _1-x K _x BiO ₃ (0.
2 <X <0.5), and a superoxide thin film (KO ₂ ) formed by oxidizing excess potassium (K) deposited on the superconducting thin film when the thin film is formed. A) 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 comprising.

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

Further, in a method of manufacturing a superconducting device according to a fifth aspect of the present invention, after introducing an argon gas and an oxygen gas into an apparatus, the inside of the apparatus is converted into a plasma atmosphere.
In a method for 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 in an apparatus at the time of introducing a gas when forming the superconducting thin film is used. The pressure is set to be 40 to 120 Pa, and in a state where the temperature of the substrate is heated to 300 ° C. or more and 500 ° C. or less, a superconducting thin film is formed using a target having a composition in which potassium (K) becomes excessive with respect to the substrate temperature . And depositing excess potassium (K) on the superconducting thin film, and oxidizing the potassium (K) to form an insulating layer having a potassium superoxide (KO ₂ ) composition on the superconducting thin film. And

A superconducting device according to a sixth aspect of the present invention is a superconducting device comprising a Ba _1-x Rb _x BiO formed on a substrate.
_{3 A} superconducting thin film having a composition of (0.2 <X <0.5), and a superoxide film formed by oxidizing excess rubidium (Rb) deposited upon forming the thin film 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.

Furthermore, the manufacturing method of the seventh superconductor device according to the aspect of the invention, on a substrate, Ba _1-x Rb x Bi
A superconducting thin film having a composition of O ₃ (0.2 <X <0.5) is formed using a target having a composition in which rubidium (Rb) is excessive with respect to the substrate temperature, and excess rubidium is formed on the superconducting thin film. (Rb) is deposited, and the rubidium (Rb) is oxidized to form an insulating layer having a composition of super rubidium oxide (RbO ₂ ) on the superconducting thin film,
A metal layer or a superconducting layer is formed on the insulating layer to form a tunnel junction.

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

According to a ninth aspect of the present invention, there is provided a method for manufacturing a superconducting device, comprising _: forming a substrate on a substrate by using Ba _{1 -x} Rb _x BiO
_{3 A} superconducting thin film having a composition of (0.2 <X <0.5) is formed using a target having a composition in which rubidium (Rb) is excessive with respect to the substrate temperature, and excess rubidium (Rb) is formed on the superconducting thin film. Rb) is precipitated, and the rubidium (Rb) is oxidized to form a first insulating layer having a super rubidium oxide (RbO ₂ ) composition on the superconducting thin film, and a magnesium oxide (RbO ₂ ) is formed on the first insulating layer. MgO)
After laminating a second insulating layer having a composition, a metal layer or a superconducting layer is formed on the second insulating layer to form a tunnel junction.

Further, in a method of manufacturing a superconducting device according to a tenth aspect of the present invention, after introducing an argon gas and an oxygen gas into the apparatus, the inside of the apparatus is set to a plasma atmosphere, and Ba _{1 -x} Rb _x BiO _{3 is used.} In the method of manufacturing a superconducting device in which a superconducting thin film having a composition of (0.2 <X <0.5) is formed on a substrate, the gas pressure in the apparatus at the time of gas introduction during the production of the superconducting thin film is 40 to 120 Pa. In a state where the temperature of the substrate is heated to 300 ° C. or more and 500 ° C. or less, a superconducting thin film is formed using a target having a composition in which rubidium (Rb) is excessive with respect to the substrate temperature and the substrate temperature. 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]

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

According to the present invention, Ba _1-x Rb _x B
Excess rubidium (R) is added to the surface of the iO ₃ oxide superconductor.
b) precipitates. The precipitated rubidium (Rb) is oxidized, and the rubidium oxide (Rb) is superposed on the surface of the oxide superconductor.
O ₂ ) An insulator layer is formed. The rubidium superoxide (RbO ₂ ) insulator layer is formed by being deposited on the surface, so that it is formed densely on the oxide superconductor, and there is no possibility that pinholes will be generated even if the superconductor surface has irregularities.
Therefore, a very good tunnel junction without leakage can be formed.

Further, an insulating layer having a composition of magnesium oxide (MgO) is laminated on an insulating layer of potassium superoxide (KO ₂ ) or rubidium superoxide (RbO ₂ ), so that an insulating layer barrier which is stable even in the atmosphere. Is formed, and a very good tunnel junction without leakage can be formed.

[0019]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view showing a first embodiment of a superconducting device according to the present invention, wherein SrTiO ₃ (1
SIN (S is a superconducting thin film,
I is an insulating layer, and N is a structure in which a main body portion 2 of a sandwich structure composed of a normal conductor is formed. S layer 3
And the N layer 5 has a thickness of about 1000 °, and the S layer 3 has a thickness of B
The N layer 5 is made of Au or the like from a _0.6 K _0.4 BiO ₃ or Ba _0.6 Rb _0.4 BiO ₃ . On the other hand, the I layer 4 has a thickness of about 40 ° and is Ba _0.6 K _0.4 BiO ₃ or Ba _0.6 Rb.
When forming _0.4 BiO ₃ , 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, a superconducting device having the above structure was manufactured as follows. First, as the S layer 3, Ba _0.6 K
_The case where _0.4 BiO ₃ is used will be described.

After ultrasonic cleaning the substrate 1 in ethyl alcohol, it is boiled and dried. Next, the washed substrate 1 is mounted 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.
Vacuum is performed until the pressure becomes ^-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
At 0:50, 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 apparatus.
After the plasma is generated in the apparatus by applying discharge power of
Heat to 500C to 500C.

Thereafter, after pre-sputtering is performed for 0.5 to 2 hours, the main sputtering is started by opening the shutter in the apparatus while the substrate 1 is heated to 300 ° C. to 500 ° C.
Thus, the formation of the S layer 3 is started. At this time, since the film formation rate is 500 ° / hr, the main sputtering is performed for about 2 hours. After the main sputtering, the shutter is closed and the plasma is turned off. Thereafter, the introduction of the Ar gas is stopped, and the state of the introduction of the O ₂ gas is maintained and maintained at a temperature of 350 ° C. or higher for about one hour. Thereafter, the temperature is lowered, and the substrate 1 is cooled in an O ₂ gas atmosphere.

Ba _0.6 K _0.4 B by this sputtering
When forming the S layer 3 made 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 Then, an I layer 4 made of potassium superoxide (KO ₂ ) is formed.

If necessary, an I layer may be further laminated.

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

In the case of using the SIS structure, the following method is used in addition to the method of forming the S layer by the same method as the 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 (4.2 K). Therefore, Au having a thickness of 1000 Å or less can be sufficiently superconducting. State. That is, when Nb / Au is used, a Josephson junction having an 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 which becomes potassium superoxide (KO ₂ ) in the above O ₂ atmosphere
After the layer 4 is formed, Au is laminated at 500 ° by resistance heating. Then, Nb is formed at a rate of 2 ° / sec for 15 minutes by MBE, and 1800 ° of Nb is laminated.

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

FIG. 6 shows the result 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 damage to the interface, a good interface is obtained, and good conductance is obtained.

FIG. 7 is a sectional view showing a second embodiment of the superconducting device according to the present invention, wherein SrTiO ₃ (1
SIN (S is a superconducting thin film,
I is an insulating layer, and N is a structure in which a main body portion 2 of a sandwich structure composed of a normal conductor is formed. S layer 3
And the N layer 5 has a thickness of about 1000 °, and the S layer 3 has a thickness of B
The N layer 5 is made of Au or the like from a _0.6 K _0.4 BiO ₃ or Ba _0.6 Rb _0.4 BiO ₃ .

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. ) And a second insulating layer 42 of magnesium oxide (MgO) formed on the first insulating layer 41 by RF magnetron sputtering or EB vapor deposition. .

The second made of magnesium oxide (MgO)
The insulating layer 42 is made of amorphous MgO or polycrystalline MgO. When amorphous MgO is used, even if there are irregularities on the first insulating layer 41, amorphous MgO is smoothly laminated on the surface and the amorphous MgO surface is flattened.
Lamination of an N layer or the like on the gO surface can be easily performed.

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

Ba _{0.6 is} deposited on the substrate 1 by sputtering.
A S layer 3 made of K _0.4 BiO _{3 is} formed as a forming element.
Excess potassium (K) is deposited on the surface of the S layer 3 and the method of forming the first insulating layer 41 made of potassium superoxide (KO ₂ ) is the same as that of the first embodiment described above, and the description is omitted here. Then, a method of forming the second insulating layer 42 on the first insulating layer 41 will be described.

After a MgO sintered body or a solidified powder was placed 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. .

Thereafter, the substrate 1 is kept at room temperature,
An amorphous MgO film is formed by applying an RF output of 0 W. The second insulating layer 42 of amorphous MgO of about 20 to 40 ° is laminated on the first insulating layer 41 of potassium superoxide (KO ₂ ) at a deposition rate of 2 to 40 ° / min.

On the second insulating layer 42, an N layer 5 made of Au or the like having a thickness of 2000 Å is formed by EB evaporation or evaporation.

The tunnel junction using only potassium superoxide (KO ₂ ) in the first embodiment as an insulating layer can obtain an effective conductance exhibiting strong nonlinearity as shown in FIG. As shown in FIG. 8, there is a case where something very weak can be made. On the other hand, as in the second embodiment shown in FIG.
By laminating an MgO film on O ₂ ), as shown in FIG. 9, 2-3 me corresponding to the energy gap of BKBO is formed.
A device exhibiting strong nonlinearity at V was obtained with good reproducibility.

[0043] 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 ), potassium compounds (eg, KO ₂ , K ₂ CO ₃ , KNO ₃ ) and bismuth compounds (eg, Bi ₂ O ₃ ) are excessively potassium (K) with respect to the substrate temperature. After mixing at a certain ratio, the mixture is baked 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.
It was prepared by pressing at a pressure of 3 ton / cm ² .

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

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 , a BKBO thin film having good resistance temperature characteristics can be obtained. 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 about.

When the amount of potassium (K), that is, X, changes, the amount of potassium (K) deposited on the surface changes. For example, when X = 0.25 to 0.27, potassium (K) hardly precipitates. If X exceeds 0.27, precipitation of potassium (K) 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 one hour, any excess potassium (K) deposited on the surface is entirely potassium superoxide (K). KO ₂ ).

In the case of X = 0.25 to 0.27,
Even when potassium (K) does not precipitate, potassium (K) on the outermost surface is oxidized to form potassium superoxide (K).
O ₂ ) becomes potassium superoxide.

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, open circles indicate KO ₂ layers, and black circles indicate BKBO molecules.

For these reasons, the thickness of the potassium superoxide (KO ₂ ) layer on the surface is about 3 ° in the case of X to 0.25 to 0.27.

When there is precipitation, (X to 0.2
8-0.35) Maximum of about 40 ° is potassium superoxide (K
A dense oxide of O ₂ ) is formed. In each 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 _× BiO ₃ as the sputtering target composition. As shown in FIG. 3, the precipitation point of K (X = 0.2
7) Above, an almost proportional relationship is established 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
Quantity.

For example, when x = 0.3, D (0.
3) A uniform barrier of = 17 ° can be formed.
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 the formation of the potassium superoxide (KO ₂ ) layer, only the first surface of the BKBO layer may be damaged, but this layer is the minimum barrier layer. In a conventional oxide-based superconductor, since there is no spontaneous oxide barrier layer, it is necessary to form an artificial oxide barrier layer such as MgO or SrTiO ₃ .

FIG. 2 shows the result of the examination of the S layer 3 by the X-ray diffraction method. As is clear from FIG.
It was confirmed that the S layer was oriented almost completely in the (110) direction. The width of the peak is similar to that of a substrate having a single crystal structure. This indicates that the film quality of the S layer is good.

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

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

First, the substrate 1 is ultrasonically cleaned in ethyl alcohol, and then boiled and dried. Next, the substrate 1 which is the cleaning, after mounting in the RF- magnetron sputtering apparatus sputtering target composition rubidium (Rb) becomes excessive is attached to the substrate temperature, device internal pressure 10 ^-4 to Vacuum is performed until the pressure becomes 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
At 0:50, 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 apparatus.
After the plasma is generated in the apparatus by applying discharge power of
Heat to 500C to 500C.

Thereafter, after presputtering is performed for 0.5 to 2 hours, the main sputtering is started by opening the shutter in the apparatus while the substrate 1 is heated to 300 ° C. to 500 ° C.
Thus, the formation of the S layer 3 is started. At this time, since the film formation rate is 500 ° / hr, the main sputtering is performed for about 2 hours. After the main sputtering, the shutter is closed and the plasma is turned off. Thereafter, the introduction of the Ar gas is stopped, and the state of the introduction of the O ₂ gas is maintained and maintained at a temperature of 350 ° C. or higher for about one hour. Thereafter, the temperature is lowered, and the substrate 1 is cooled in an O ₂ gas atmosphere.

Ba _0.6 Rb _0.4
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 made of Au or the like is provided on the I layer 4 by EB evaporation or evaporation.

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

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

Further, the sputtering target is
Barium compounds (eg, BaCO ₃ , BaO, Ba
(NO) ₂ ), a rubidium compound (for example, RbO ₂ , R
b ₂ CO ₃ , RbNO ₃ ), bismuth compounds (for example, Bi ₂
O ₃₎ a were mixed in a ratio to become excessive rubidium (Rb) to the substrate temperature, Chissogasu atmosphere (600-70
0 ° C.) for 2 to 5 hours in an oxygen gas atmosphere (400 to 500
C.) for 2 to 5 hours, and then pressed at a pressure of 1 to ³ ton / cm ² .

As in the case of potassium, the precipitation differs depending on the substrate temperature even with the same amount of rubidium (Rb). That is, the higher the substrate temperature, the greater 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 with 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 the above-mentioned potassium, the amount of rubidium (Rb) deposited on the surface changes by changing the amount of rubidium (Rb), that is, the above X. For example,
When X = 0.25 to 0.27, rubidium (Rb) hardly precipitates. When X exceeds 0.27, 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, any excess rubidium (Rb) deposited on the surface is completely removed from the super rubidium oxide (Rb). RbO ₂ ).

In the case of X = 0.25 to 0.27,
Even when rubidium (Rb) does not precipitate, rubidium (Rb) on the outermost surface is oxidized into rubidium superoxide (RbO ₂ ).

When x = 0.3, D (0.3) = 17
均一 A uniform barrier can be formed. Where x
At <0.35, since Rb starts to be distributed in an island shape, a uniform rubidium superoxide (RbO ₂ ) film cannot be formed.

In the formation of the rubidium superoxide (RbO ₂ ) layer, only the first layer on the surface of the BRbBO layer may be damaged in the same manner as described above, but this layer becomes the minimum barrier layer.

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

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

[0076]

As described above, according to the present invention, potassium (K) or rubidium (K) or rubidium (B) deposited on the surface of a Ba _1-x K _x BiO ₃ or Ba _1-x Rb _x BiO ₃ oxide superconductor is obtained. Rb) is oxidized to form an insulating layer of potassium superoxide (KO ₂ ) or rubidium superoxide (RbO ₂ ) on the surface of the oxide superconductor. Since the potassium superoxide (KO ₂ ) or rubidium superoxide (RbO ₂ ) insulator layer is deposited and formed on the surface, it is densely formed on the oxide superconductor, and even if the superconductor surface has irregularities. 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, it is possible to form a very good tunnel junction having no leak with good reproducibility.

[Brief description of the 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 a relationship between a composition amount of K in a sputtering target composition and a thickness of a potassium superoxide (KO ₂ ) oxide layer.

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

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

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

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Main part 3 S layer 4 I layer 5 N layer 41 1st insulating layer 42 2nd insulating layer

Continuing on the front page (72) Inventor Tatsuro Usuki 2--18 Keihanhondori, Moriguchi-shi Sanyo Electric Co., Ltd. (72) Inventor Junnobu Yoshizato 2-18-18 Keihanhondori, Moriguchi-shi Sanyo Electric Co., Ltd. (56 References JP-A-3-68181 (JP, A) JP-A-57-126185 (JP, A) JP-A-3-122003 (JP, A) Applied Physics Letters vol. 58, no. 1, p. 95 (1991) Physical Review B vol. 44, p. 12521 (1991) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 39/22 ZAA H01L 39/24 ZAA JICST file (JOIS)

Claims (10)

(57) [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 a potassium superoxide formed by oxidizing excess potassium (K) deposited upon forming the thin film on the superconducting thin film. A superconducting device comprising an insulating layer having a composition of (KO ₂ ) and a metal layer or a superconducting layer formed on the insulating layer. 2. The method according to claim 1, wherein 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) is excessive with respect to the substrate temperature, and excess potassium (K) is deposited on the superconducting thin film. By oxidizing the potassium (K), potassium superoxide (KO ₂ ) is formed on the superconducting thin film.
A method for 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 a potassium superoxide formed by oxidizing excess potassium (K) deposited upon forming the thin film on the superconducting thin film. A first insulating layer of (KO ₂ ) composition, a second insulating layer of magnesium oxide (MgO) formed on the first insulating layer, and a metal layer formed on the second insulating layer Or a superconducting device comprising a superconducting layer. 4. A substrate comprising 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) is excessive with respect to the substrate temperature, and excess potassium (K) is deposited on the superconducting thin film. By oxidizing the 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 formed on the first insulating layer, and then a metal layer or a superconducting layer is formed on the second insulating layer. And forming a tunnel-type junction. 5. After introducing an argon gas and an oxygen gas into the apparatus, the inside of the apparatus is turned into a plasma atmosphere, and Ba _1-x
In a method for manufacturing a superconducting device in which a superconducting thin film having a composition of K _x BiO ₃ (0.2 <X <0.5) is produced on a substrate, the gas pressure in the apparatus at the time of gas introduction during the production of the superconducting thin film is 40 to Set to 120Pa,
In a state where the temperature of the substrate is heated to 300 ° C. or more and 500 ° C. or less, a superconducting thin film is formed using a target having a composition in which potassium (K) is excessive with respect to the substrate temperature , and excess potassium (K) is formed on the superconducting thin film. A method for manufacturing a superconducting device, comprising: forming an insulating layer having a composition of potassium superoxide (KO ₂ ) on a superconducting thin film by depositing K) and oxidizing the potassium (K). 6. Ba _1-x Rb _x BiO formed on a substrate
_{3 A} superconducting thin film having a composition of (0.2 <X <0.5), and a superoxide film formed by oxidizing excess rubidium (Rb) deposited upon forming the thin film 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. On a substrate, 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. At first, this rubidium (R
b) is oxidized to form an insulating layer of rubidium superoxide (RbO ₂ ) composition on the superconducting thin film, form a metal layer or a superconducting layer on the insulating layer, and form a tunnel junction. A method for manufacturing a superconducting device. 8. Ba _1-x Rb _x BiO formed on a substrate
_{3 A} superconducting thin film having a composition of (0.2 <X <0.5), and a superoxide film formed by oxidizing excess rubidium (Rb) deposited upon forming the thin film on the superconducting thin film. A first insulating layer of rubidium (RbO ₂ ) composition, a second insulating layer of magnesium oxide (MgO) 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 substrate comprising 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. At first, this rubidium (R
b) is oxidized to form a first insulating layer having a superconducting rubidium oxide (RbO ₂ ) composition on the superconducting thin film, and a _second insulating layer having a magnesium oxide (MgO) composition being formed on the first insulating layer. And forming a metal layer or a superconducting layer on the second insulating layer to form a tunnel-type junction. 10. After introducing an argon gas and an oxygen gas into the apparatus, the inside of the apparatus is turned into a plasma atmosphere and Ba _1-x
In a method for 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, the gas pressure in the apparatus at the time of gas introduction at the time of producing the superconducting thin film is 40 to 40. Set to 120Pa,
In a state where the temperature of the substrate is heated to 300 ° C. or more and 500 ° C. or less, a superconducting thin film is formed using a target having a composition in which rubidium (Rb) is excessive with respect to the substrate temperature and the substrate temperature, and the superconducting thin film is formed on the superconducting thin film. A method of manufacturing a superconducting device, comprising forming an insulating layer having a composition of rubidium superoxide (RbO ₂ ) on a superconducting thin film by depositing rubidium (Rb) and oxidizing the rubidium (Rb).