JP2656364B2 - Superconducting element manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a superconducting element using an oxide superconductor, and more particularly to a method for manufacturing a superconducting element having a bridge-type Josephson junction. It relates to a manufacturing method.

(Prior art) Conventionally, a tunnel-type Josephson junction has been known in which a superconducting element is made of a metal superconductor such as Pb or Nb and a thin insulating layer sandwiched by a pair of superconducting elements is sandwiched. I have. Such a conventional tunnel-type Josephson device needs to operate at a very low temperature close to the temperature of liquid helium. In addition, since it exhibits current-voltage characteristics having hysteresis peculiar to a tunnel-type Josephson junction, it has a problem such as a complicated circuit configuration and has not been widely used.

On the other hand, as a Josephson junction element using a metal superconductor and having no hysteresis characteristics, the development of a so-called bridge type junction, in which a main electrode consisting of a pair of metal superconductors is connected by a thin and thin metal superconductor, is also being developed. ing. However, such a bridge-type junction requires a very low-temperature operation close to the temperature of liquid helium and obtains a large output voltage because the superconducting gap of the metal superconductor is small, as in the case of the tunnel-type junction described above. It was difficult to do so, and it did not contribute to the industry.

Under such circumstances, an oxide superconducting material exhibiting superconducting properties at a high temperature equal to or higher than the temperature of liquid nitrogen has recently been discovered and has attracted much attention. Having this oxide superconductor,
If a Josephson junction can be manufactured, there is great expectation that at least a cryogenic operation is not required as compared with a Josephson junction formed using the above-mentioned conventional metal superconductor.

(Problems to be Solved by the Invention) However, the oxide superconducting material has an essential problem that its surface is easily degraded in the air and its coherence length is small, and the oxide superconducting material exhibits a clear Josephson characteristic. It was difficult to produce a perfect junction. In other words,
The development of a Josephson junction using the oxide superconductor having a high critical temperature is expected to have a great impact on industry, but the development of a bonding structure for making this practical, and a method of manufacturing the same have been developed. Was an issue.

The present invention has been made in view of such a point,
It is an object of the present invention to provide a method of manufacturing a bridge-type Josephson junction device that exhibits good Josephson characteristics, has a large output voltage, and does not exhibit hysteresis characteristics.

[Structure of the Invention] (Means for Solving the Problems) In the method for manufacturing a superconducting element of the present invention, a step of laminating and forming a different kind of conductive material thin film on an oxide superconducting thin film; A step of selectively etching and removing a part of the conductive material thin film stack, a step of burying an insulating material in a region removed by the selective etching, and covering at least a part of the buried insulating material, And a step of laminating and disposing a conductive material so as to have electrical contact between the superconducting material and the conductive material thin film laminate separated from each other by the embedded insulating material.

(Operation) According to the present invention, in manufacturing a required superconducting element, a structure in which another conductive material layer is coated and laminated on an oxide superconductor layer first is adopted. For this reason, the deterioration of the surface is easily and reliably prevented, and even if left undisturbed in the air, the possibility of forming a metamorphic layer that does not exhibit the required superconducting properties is completely prevented.

In addition, in the present invention, the electrical connection between the island-shaped oxide superconductor and the conductive material thin film laminate region involved in the Josephson junction and formed at minute intervals by selective etching is also minimized. Since the gaps are arranged on the surface of the insulator buried so as to form a substantially flat surface, stable wiring can be performed.

Thus, according to the present invention, it is possible to manufacture a Josephson superconducting element having no hysteresis characteristics and a wide application range.

(Example) Hereinafter, an example of the present invention will be described.

First, the basic configuration or conditions of the present invention will be described prior to the description of specific examples.

In the present invention, as a starting point in manufacturing a superconducting element, another conductive material is laminated and formed on an oxide superconducting film. Here, as another conductive material to be laminated, a noble metal such as Au, Ag, or Pt, which has good electrical contact with the oxide superconductor and is chemically stable, or a material containing these as a main component Preferred alloys. By forming or manufacturing this laminated structure without exposing the surface of the superconductor layer to the atmosphere, further improvement in characteristics can be expected.

Further, in the present invention, after the superconductor-conductive material laminated film at the portion where the bridge-type junction is formed or formed is removed by etching, it is necessary to form a thin and thin bridge portion that fills and connects that portion with an insulating material. There is. If the bridge portion has a structure crossing a step, a problem such as so-called step disconnection occurs, and a superconducting element cannot be manufactured with high yield.

In the present invention, the conductive material of the bridge portion used can be arbitrarily selected as long as it can exhibit a proximity effect with the oxide superconductor. By using the noble metal or the like used for the laminated structure, contact with the main electrode portion can be greatly improved. Alternatively, a metal superconductor that exhibits superconducting characteristics at a very low temperature can be used as the bridge material.

In the manufacturing method according to the present invention, a stacked structure of an oxide superconductor and another conductive material is first formed. The conductive material to be coated is formed so as to have good electrical contact with the oxide superconductor, so that the superconducting property oozes to the surface of the oxide superconductor by the proximity effect.

Therefore, it is desirable that the thickness of the conductive material to be coated be thin in order to effectively exert the proximity effect, but at the same time, since this conductive material film also has a function as a protective film on the surface of the oxide superconductor, a pinhole or the like is required. To a thickness that does not cause The surface covered with the conductive material film functioning as such a protective film becomes chemically stable and does not deteriorate in the subsequent manufacturing steps.

In the manufacturing method according to the present invention, the main electrode portion forming the bridge junction is formed by an etching technique using the lithography means for the superconductor-conductive material laminated film. That is, since the bridge junction requires a small distance between the main electrodes, it is realistic to use the electron beam exposure method in the current technology. According to the current electron beam exposure technology, patterning of 0.1 μm is relatively easy, and it is expected that further reduction will be possible in the future.

After the resist is exposed and developed in the patterning, etching can be easily performed by using an ion milling method or the like. In the method of the present invention, particularly after the etching step, while leaving the resist used for the etching, an insulating material such as SiO or BaF ₂ is vapor-deposited, and the groove formed by the etching (etching removed portion)
And to flatten the surface after lift-off. By going through this flattening step, subsequent formation of a bridge portion can be performed on a flat surface,
It is possible to form a thin and thin bridge portion necessary for obtaining a large output voltage with a good yield.

As described above, the bridge portion is formed by the lithography process and the lift-off process using the resist. Also in this case, it is practical to use an electron beam exposure step in the current state of the art. Further, as a material for forming the bridge portion, a metal or the like having good contact characteristics with the main electrode is preferably used. That is, in order for the bridge junction to exhibit the Josephson characteristic, it is necessary to generate a proximity effect in which the superconducting characteristic leaks into the bridge material from the main electrode. However, as long as the proximity effect can be effectively exerted, an intervening layer for the purpose of increasing the output voltage may be intentionally formed between the laminated film and the bridge portion.

Next, a specific example of the present invention will be described with reference to FIGS. 1 (a) to 1 (e), 2 and 3. FIG.

1 (a) to 1 (e) schematically show an embodiment of a method for manufacturing a superconducting element of the present invention.

First, YBa ₂ Cu ₃ O ₇ as an oxide superconductor and Au as a conductive material are prepared, and sequentially and sequentially formed in a film shape on a substrate 1, for example, a SrTiO ₃ plate by a multi-source sputtering method in the same vacuum vessel. Then, a laminated structure of the oxide superconductor 2 and the conductive material 3 having a structure as shown in cross section in FIG. 1A was formed. At this time, the film 2 of YBa ₂ Cu ₃ O ₇ is made of a substrate (SrT
iO ₃ ) 1 was heated to 650 ° C. in an Ar—O ₂ mixed gas atmosphere, and after forming YBa ₂ Cu ₃ O ₇ , the temperature of the substrate 1 was changed to 2 ° C.
With the temperature lowered to about 00 ° C., the Au film 3 was laminated at a thickness of 500 ° in an Ar atmosphere.

Next, the substrate 1 on which the stacked structure of the oxide superconductor 2 and the conductive material 3 is formed is taken out of the vacuum vessel, and two layers of resist 4 for electron beam exposure are applied, and a line pattern having a width of about 0.2 μm is drawn by electron beam. After that, a portion is selectively removed by an ion beam milling method using Ar ions to partition an oxide superconductor-conductive material stack as shown in cross section in FIG. 1 (b). The groove 5 to be formed was formed.

After the ion beam milling process, a SiO film (layer) 6 is vapor-deposited and formed to a predetermined thickness in a vacuum device while leaving the resist 4 (FIG. 1 (c)). An insulator is buried in the groove 5 that has been etched away, and Fig. 1 (d) shows this state in cross-section, where the contact between the SiO film 6 and the side wall of the oxide superconductor 2 is good. Good surface flatness was obtained.

Next, the bridge forming portion is patterned by an electron beam exposure method so as to cross the insulator buried portion 5 'formed in a line shape, and Au3' serving as a bridge is formed to a width of 0.2 μm by a lift-off process using a resist. Formed, FIG. 1 (e)
A Josephson junction type superconducting element structure as shown in section in FIG.

FIG. 2 shows the results of measuring the current-voltage characteristics at 10 ° K of the thus obtained Josephson junction type superconducting element. From Fig. 2, the critical current at the junction is about 50
It was confirmed that a good characteristic of 4 mV as a product of μA and IcRn was obtained.

A superconducting element having a dc SQUID (superconducting magnetic flux quantum interferometer) structure having a configuration shown in plan view in FIG. 3 was produced by using the same production method as that for producing the above-mentioned Josephson junction type superconducting element. Thus, the manufactured dc SQUID structure superconducting element shows a clear periodic response to the magnetic field,
The voltage modulation depth exhibited a performance reaching 500 μV or more.

[Effects of the Invention] As described above, according to the present invention, a bridge-type Josephson junction device that can operate at a high temperature using an oxide high-temperature superconductor can be easily and stably provided (with good reproducibility). Can be manufactured. In other words, it operates at a high temperature of about liquid nitrogen temperature and shows no hysteresis in current-voltage characteristics, making it ideal for SQUID (superconducting magnetic flux quantum interferometer) applications. It is suitable for manufacturing a Josephson element, which is an essential element for realizing it. Thus, it can be said that the manufacturing method of the present invention greatly contributes to providing a superconducting element which is extremely useful in industry.

[Brief description of the drawings]

1 (a) to 1 (e) are cross-sectional views schematically showing an embodiment of forming a bridge type junction by a method for manufacturing a superconducting element according to the present invention, and FIG. 2 is a sectional view showing a method for manufacturing a superconducting element according to the present invention. FIG. 3 is a plan view showing the structure of a dc SQUID superconducting element manufactured by the method for manufacturing a superconducting element according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Support substrate 2 ... Oxide superconductor 3 ... Conductor film 3 '... Bridge part 4 ... Resist layer 5 ... Oxide superconductor-conductor film lamination etching removal area | region (groove) 6 ... Insulator 6 ': Area buried with insulator

Claims (1)

(57) [Claims] A step of laminating and forming a different kind of conductive material thin film on the oxide superconducting thin film; a step of selectively etching and removing a part of the formed superconductive material-conductive material thin film laminate; Embedding an insulating material in a region removed by selective etching; and covering at least a part of the buried insulating material, and
Stacking and disposing a conductive material so as to make electrical contact between the superconducting material and the conductive material thin film laminate separated from each other by the embedded insulating material.