JP3081386B2 - Method for manufacturing oxide superconductor and method for manufacturing superconducting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an oxide superconductor and a method for manufacturing a superconducting device using the same, and in particular, to Ba _1-x K _x BiO ₃ (0.2 <x <0.5).
(Hereinafter referred to as BKBO).

[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
A bismuth-based superconducting material having a high level has been proposed.

When a superconducting device is manufactured using the above-described superconducting material, for example, a tunnel junction having a constant operating voltage and excellent circuit operation stability is used. This tunnel junction has a sandwich structure composed of SIS (S is a superconducting thin film and I is an insulating layer). In this case, when the bismuth-based superconducting material is used for the S layer, the coherence length is short. , I layer need to be set to 1 to 1.5 nm or less.

Accordingly, the applicant has previously proposed a superconducting device using a superconducting material having a composition of BKBO and a long coherence length as a superconducting material (for example, see Japanese Patent Application No. 3-285621). .

FIG. 6 shows the structure of the proposed superconducting device.
Shown in This superconducting device is a superconducting transistor using a tunnel junction. A superconducting thin film 2 of BKBO composition is formed on a SrTiO ₃ single crystal substrate 1 doped with Nb in a range of 0.08% by weight to 0.5% by weight. Is formed by sputtering, and this Nb-doped SrTi
A good semiconductor-superconductor junction is obtained by the O ₃ single crystal substrate 1 and the superconducting thin film 2.

The BKBO is annealed in an oxygen (O ₂ ) atmosphere and then exposed in a dry atmosphere, whereby an insulating barrier is naturally formed on the surface of the BKBO. Used as a layer.
A superconducting base transistor can be formed by depositing an emitter layer 4 made of gold (Au) or the like on the insulating barrier 3 by vapor deposition.

In the device described above, an insulating barrier (hereinafter referred to as a natural barrier) naturally formed on the surface of the BKBO is used as a barrier layer of a tunnel junction corresponding to an emitter / base.

According to the present invention, the natural barrier used in the above device was analyzed by XPS or the like. That is, the substrate temperature 4 on the SrTiO ₃ (110) substrate
B with a film thickness of 1500 ° and Tc28K epitaxially grown by rf-magnetron sputtering at 00 ° C.
The surface of the KBO thin film, that is, a natural barrier was analyzed by XPS or the like. The result is shown in FIG. FIG. 5 shows the XPS depth profile of the BKBO thin film. As is apparent from FIG. 5, an altered layer a composed of a K compound layer such as K ₂ CO ₃ or KOH is formed up to about 10 約 from the surface. A mixed layer (non-stoichiometric layer) b in which Ba is relatively deficient with respect to Bi and K is formed from the lower part of the altered layer a to about 100 °. This mixed layer b is made of Bi ₂ O ₃ , B
Ba and B are i ₂ O ₄ .H ₂ O, KBiO _2, etc.
Low-Tc temperature B relatively lacking with respect to i and K
It has been found that the KBO layer is formed in this order from the surface side.

It is believed that the altered layer a and the insulating layer constitute a natural barrier.

[0010]

The above-mentioned natural barrier is a good tunnel barrier and can form a tunnel junction. However, the Tc of BKBO having a high Tc temperature, which is free from Ba deficiency and has no composition deviation, is 28 K
On the other hand, the low-Tc temperature BKBO lacking Ba has a Tc of about 20 K, and the presence of the low-Tc temperature BKBO lowers the operating temperature of the device.

The device preferably has a higher operating temperature, and it is desired to use BKBO having a high Tc temperature.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned demands, and has improved a surface layer portion of a BKBO thin film to provide a high-T
It is intended to provide a BKBO at a temperature c.

[0013]

According to the present invention, there is provided a method of manufacturing an oxide superconductor, comprising the steps of forming a Ba _1-x K _x BiO _{3 layer} on a substrate.
(Where x is 0.2 <x <0.5) Ba is added to the surface layer of the oxide superconducting thin film having the composition to correct the composition deviation of the superconductor in the surface layer portion. .

Further, the method of manufacturing an oxide superconductor according to the present invention is characterized in that the composition of Ba _1-x K _x BiO ₃ (where x is 0.2 <x <0.5) formed on the substrate After forming a BaO film on the surface of the oxide superconducting thin film, heat treatment is performed, Ba is added to the surface layer portion of the oxide superconducting thin film, and the composition deviation of the superconductor in the surface layer portion is corrected. .

Further, the method for manufacturing an oxide superconductor according to the present invention comprises a Ba _1-x K _x BiO ₃ (where x is 0.2 <x <0.5) composition formed on a substrate. Ba is ion-implanted into the surface layer of the oxide superconducting thin film, heat treatment is performed, Ba is added to the surface layer portion of the oxide superconducting thin film, and the composition deviation of the superconductor in the surface layer portion is corrected. I do.

[0016] In the method of manufacturing superconducting devices of this _{invention, Ba 1-x K x BiO} 3 formed on the substrate (here, x is, 0.2 <x <0.5) a composition oxide A BaO film is formed on the surface of the superconductor thin film, heat treatment is performed, an insulating film is provided on the surface of the oxide superconductor thin film, and the oxide superconductor is formed on the insulating film.

Further, the method of manufacturing a superconducting device according to the present invention relates to a method of manufacturing an oxide superconducting device having a composition of Ba _1-x K _x BiO ₃ (here, 0.2 <x <0.5) formed on a substrate. Ba is ion-implanted into the surface layer of the body thin film, heat-treated, an insulating film is formed on the oxide superconductor thin film, and the oxide superconductor is formed on the insulating film. .

[0018]

By injecting or diffusing Ba into the surface layer of the BKBO oxide superconductor thin film, Ba is added to the composition deviation region where Ba is lost. As a result, the high Tc28K
A BKBO thin film having a Tc temperature is obtained.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a method of manufacturing a BKBO thin film according to the present invention will be described with reference to FIG.

An SrTiO ₃ single crystal substrate 1 doped with 0.05 to 0.5% by weight of Nb is prepared. Then, the single crystal substrate 1 is washed with trichlene, acetone and methanol. Washing is performed by ultrasonication in trichlene for 10 minutes, ultrasonic wave in acetone for 10 minutes, and ultrasonic wave in methanol for 10 minutes.
Pickle each minute. After the cleaning is completed, the substrate is dried in a vacuum oven at 120 ° C. for 10 minutes, and then set in a sputtering chamber.

Then, a BKBO thin film 2 is formed on the single crystal substrate 1 by rf-sputtering. In this film formation, first, the sputtering chamber is evacuated to vacuum and 1 ×
After reaching 10 ⁻⁵ Pa, the substrate temperature is set to 380 to 400 ° C.

The gas flow rate is set to O ₂ : Ar = 1: 1,
While flowing gas of 80 Pa in total, 100 W of BKBO
Sputtering. BKBO target is BKBO
This was a powder target obtained by hardening the powder by pressing, and the sputtering rate was 0.1 ° / sec. Under these conditions 300
When the sputtering is performed for 0 second, the BKBO superconducting thin film 2 of 500 to 1000 ° is formed. This BKBO film has Tc = 28 K and R ₃₀₀ = 100 μΩcm, and a superconducting thin film having very good superconducting properties can be obtained (FIG. 1).
(See (a)).

After the sputtering, the natural barrier 3 is formed by exposing to a dry atmosphere (see FIG. 1B). The surface of the BKBO thin film thus formed has a K compound layer a of about 10 ° and a composition shift region b of about 100 ° as shown in FIG.

Subsequently, the substrate 1 on which the BKBO thin film 2 is formed is put into a vacuum chamber, and when the degree of vacuum in the vacuum chamber reaches 1 × 10 ⁻⁵ Pa, the substrate temperature is reduced to 210 to 3 Pa.
By raising the temperature to 00 ° C. and maintaining the temperature for about 30 minutes to 1 hour, the K compound layer a is decomposed. Thereafter, a BaO film 6 having a thickness of several Å is formed on the BKBO thin film 2 by electron beam evaporation (see FIG. 1C).

Then, at 400 ° C. in an oxygen (O ₂ ) atmosphere.
Anneal at a temperature of By this heat treatment, Ba is diffused and added to the region of the surface layer where Ba is deficient, and the surface layer is partially crystallized. By this treatment, the compositional deviation of the Ba deficiency in the surface layer portion of the BKBO thin film is eliminated, the surface layer of BKBO is reformed, and B
A KBO thin film is obtained.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. The second embodiment uses an apparatus capable of forming a BKBO thin film and depositing BaO in the same chamber. That is, as described above, SrT
After the BKBO thin film 2 is formed on the iO ₃ single crystal substrate 1 (see FIG. 2A), BaO having a thickness of several 膜厚 is formed in the same chamber.
A thin film 6 is formed on the BKBO thin film 2 by electron beam evaporation (see FIG. 2B).

After that, as described above, in an O ₂ atmosphere, 40
After annealing at 0 ° C., B on the surface layer portion of the BKBO thin film
Eliminates the composition deviation of a defect.

Next, a third embodiment of the present invention will be described with reference to FIG. A BKBO thin film 2 is formed on an SrTiO ₃ single crystal substrate 1 by rf-sputtering in the same manner as described above (see FIG. 3A).

Subsequently, a dose of 10 ¹⁵ / cm is applied to the surface of the BKBO thin film 2 at an acceleration voltage of several KeV (10 KeV or less).
^{About two} times Ba is implanted by ion implantation 9. From the depth profile of FIG. 5 described above, it can be seen that 20 to 30% of Ba is missing from the surface to several hundred degrees.

Considering high temperature Tc BKBO having a thickness of 100 ° of 1 cm ² , V = 1 × 10 ⁻¹² m ³
Becomes

The BKBO unit cell volume V _BKBO can be expressed as follows. V _BKBO = (4.28 °) ³ = 7.84 × 10 ^-29 (m ³ )

The BKBO existing at a thickness of 100 ° is as follows. V / V _BKBO = 1.28 × 10 ¹⁶ (pieces) Therefore, 1.28 × 10 ¹⁶ (pieces) of BKBO is 100Å
Exists in the thickness. In the case of high-temperature BKBO, since Ba is ~ 0.6 per unit cell, Ba exists 7.68 × 10 ¹⁵ within a thickness of 100 °.

As described above, since 20 to 30% of Ba is deficient, in order to obtain high-temperature BKBO, the dose amount is 7.68 × 10 ¹⁵ × 0.2 to 0.3 = 1. .5
4 to 2.3 × 10 ¹⁵ (pieces) / cm ² . Therefore, the dose may be set to about 10 ¹⁵ / cm ² .

Subsequently, annealing is performed in an oxygen atmosphere (see FIG. 3C). In this annealing, the ion implantation is performed one time.
Since it is considered that the implantation is performed to a depth of up to 00 °, the BKBO film is reformed at a reforming temperature of the BKBO film of about 400 ° C., and a BKBO thin film having a high temperature Tc is obtained. This annealing can also remove the K compound layer on the surface of the BKBO thin film at the same time.

Next, an example of manufacturing a stacked type Josephson junction having an SIS structure using BKBO according to the present invention will be described with reference to FIG. In this embodiment, until the BKBO thin film 2 is reformed, that is, the SrTiO ₃ single crystal substrate has BK
The steps of forming the BO thin film 2 and adding the deficient Ba, and FIGS. 4 (a) to 4 (d) are the same as those in the method shown in FIG. The reference numerals are used and the description is omitted.

As shown in FIG. 4D, a molecular beam epitaxy (M
BE) or the like to form an MgO insulating film 7 (FIG. 4E)
reference).

Subsequently, using rf-sputtering,
By epitaxially growing the BKBO thin film 8 on the MgO insulating film 7, a stacked Josephson junction using the BKBO thin film is obtained (see FIG. 4F).

In the embodiment shown in FIG.
Is shown by providing a BaO film, but a Josephson junction having an SIS structure may be similarly formed on the thin film to which Ba is added by ion implantation.

[0039]

As described above, according to the present invention, the deficiency of Ba on the surface of a BKBO thin film can be corrected, so that a BKBO film having a high temperature Tc can be obtained, and a stacked type It is possible to form a Josephson junction.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a method of manufacturing a BKBO thin film according to the present invention for each step.

FIG. 2 is a sectional view showing a second embodiment of FIG. 2 for each step of the method of manufacturing a BKBO thin film according to the present invention.

FIG. 3 is a sectional view showing a third embodiment of FIG. 3 for each step of the method of manufacturing a BKBO thin film according to the present invention.

FIG. 4 is a cross-sectional view showing an embodiment of a method for manufacturing a superconducting device using a BKBO thin film according to the present invention for each step.

FIG. 5: BKBO formed on SrTiO ₃ single crystal substrate
FIG. 4 is a characteristic diagram showing a depth profile of a thin film.

FIG. 6 is a schematic diagram showing a superconducting transistor using a BKBO thin film.

[Explanation of symbols]

1 SrTiO ₃ single crystal substrate 2 BKBO thin film 3 natural barrier 4 the emitter electrode 6 BaO film 7 MgO insulating layer 8 BKBO film 9 ion implantation (Ba)

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tatsuro Usuki 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Junnobu Yoshizato 2-18 Keihanhondori, Moriguchi-shi, Osaka No. Sanyo Electric Co., Ltd. (56) References JP-A-63-261177 (JP, A) JP-A-2-260677 (JP, A) JP-A-1-192181 (JP, A) JP-A-3- 122003 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 39/00 H01L 39/22-39/24 JICST file (JOIS)

Claims (5)

(57) [Claims] 1. Ba _1-x K _x BiO ₃ formed on a substrate
(Where x is 0.2 <x <0.5) Ba is added to the surface layer of the oxide superconducting thin film having the composition to correct the composition deviation of the superconductor in the surface layer portion. Manufacturing method of oxide superconductivity. 2. Ba _1-x K _x BiO ₃ formed on a substrate
(Here, x is 0.2 <x <0.5) After forming a BaO film on the surface of the oxide superconductor thin film having the composition, heat treatment is performed, and Ba is added to the surface layer portion of the oxide superconductor thin film. And a method of correcting the composition deviation of the superconductor in the surface layer portion. 3. Ba _{1 -x} K _x BiO ₃ formed on a substrate
(Where x is 0.2 <x <0.5) Ba is ion-implanted into the surface layer of the oxide superconducting thin film having the composition, and then heat treatment is applied to the surface layer portion of the oxide superconducting thin film. B
a) adding a to correct the composition deviation of the superconductor in the surface layer portion. 4. Ba _{1 -x} K _x BiO ₃ formed on a substrate
(Here, x is 0.2 <x <0.5) After forming a BaO film on the surface of the oxide superconductor thin film having a composition and performing a heat treatment, an insulating film is formed on the surface of the oxide superconductor thin film. Provided,
A method for manufacturing a superconducting device, comprising forming an oxide superconductor on the insulating film. 5. A Ba _1-x K _x BiO layer formed on a substrate.
₃ (Here, Ba is ion-implanted into the surface layer of the oxide superconductor thin film having a composition of 0.2 <x <0.5), and after heat treatment, an insulating film is formed on the oxide superconductor thin film. And forming an oxide superconductor on the insulating film.