JPH081970B2 - Method for manufacturing thin film superconducting device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a superconducting element, particularly a superconducting element using a composite compound thin film having a weakly bonded portion.

2. Description of the Related Art Hitherto, as superconductors, niobium nitride (NbN), niobium 3 germanium (Nb ₃ Ge), etc. have been known as A15 type binary compounds. Also, various superconducting elements using these materials have been proposed. However, the superconducting transition temperature Tc of these materials was only 24K. Further, as a perovskite compound, a Ba-Pb-Bi-O-based compound (Japanese Patent Laid-Open No. SHO11-29100) is used.
No. 60-173885) is known, and many superconducting devices using this material have been studied. However, the Tc of this material was as low as 13K, which made practical application difficult. However, T
A Ba-La-Cu-O system high-temperature superconductor with c of 30-40K has been proposed [JG Bednorz and KAMuller, zeitshrift fur physi
k B) -Condensed Matter 64,189-193 (1986)]. Furthermore, in the recently proposed Y-Ba-Cu-O system, Tc of more than 90K has been reported [MKWu et al., Physical Review Letters Vol.58, No.
9,908-910 (1987)], the boiling point of liquid nitrogen (77K) became higher, and its practical application has become promising.

Problems to be Solved by the Invention A compound compound material represented by a Y-Ba-cu-O system is formed as a thin film high-temperature superconductor by using a thin film forming method such as a sputtering method. However,
It is considered difficult to realize a new element because the process technology for producing an element using this superconducting thin film has not been established. The inventors believe that this composite compound is an oxide, and that its superconducting properties can be controlled by precise control of the oxygen atomic weight, and studied the hydrogen ion irradiation effect for controlling the oxygen amount by hydrogen ions, and based on this, Has invented a method for manufacturing a new superconducting device using a complex compound material.

Means for Solving Problems A method of manufacturing a superconducting device using a composite compound thin film according to the present invention is, for example, A, B, Cu in which the molar ratio of elements as a composite compound is 0.5 ≦ (A + B) /Cu≦2.5. Is characterized in that a structure having at least two or more superconducting electrodes and weakly bonded portions is formed by partially irradiating the oxide coating with hydrogen ions.

Where A is Sc, Y and lanthanum series element (atomic number 57
To 71), B represents at least one element of Group IIa elements such as Ba, Sr, Ca, Be and Mg.

Action In the method for manufacturing a thin film superconducting element according to the present invention, since the composite compound superconductor is made into a thin film, a homogeneous superconductor is used as compared with a conventional sintered body, and hydrogen ions are added to this thin film. By irradiating with, the irradiation region becomes a weakly coupled portion, so that a very highly accurate thin film superconducting element can be easily realized by the manufacturing method of the present invention.

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

In FIG. 1, the composite compound superconductor coating 2 is formed on the substrate 1 by, for example, a sputtering method, and heat-treated in an oxygen atmosphere or by implanting oxygen ions,
It is a thin film that exhibits superconductivity or has a higher Tc (Fig. (A)).

Further, a weakly bonded portion 5 is formed by irradiating a part of the coating film 2 with hydrogen ions 4 (FIG. 7B). However, the present inventors have confirmed that this weakly bonded portion 5 exhibits any of the properties of a normal conductor, a hand conductor, and an insulator depending on the concentration of hydrogen ions implanted. In this case, if there are two superconducting electrodes, that is, a two-terminal element, a weak coupling type or tunnel type Josephson element is obtained.

In FIG. 1, in order to form the superconductor coating, A-
The composite compound of B-Cu-O is deposited on the substrate by a physical vapor deposition method such as thermal evaporation such as electron beam evaporation or laser beam evaporation. In this case, the composition formula of the superconductor A-B-Cu-O has not been clearly determined yet, but it is said to be oxygen-deficient perovskite (A, B) ₃ Cu ₃ O ₇ . The present inventors have confirmed that if the element ratio in the produced coating is in the range of 0.5 ≦ (A + B) /Cu≦2.5, the superconducting phenomenon is found even if there is some difference in the critical temperature. The method of forming the composite compound film is not limited to the physical vapor deposition method, but may be a chemical vapor deposition method such as atmospheric pressure or reduced pressure chemical vapor deposition method, plasma chemical vapor deposition method, photochemical method. The present inventors have confirmed that the vapor phase growth method is also effective if the ratios of the components A, B and Cu are matched.

The inventors have confirmed that there is an optimum temperature range for the substrate when depositing the composite compound coating on the surface 3 of the substrate 1. That is, the optimum substrate temperature range is 100-100
It is 0 ° C. If the temperature is 100 ° C. or lower, the adhesion of the composite oxide film to the surface of the substrate will be poor. Further, at 1000 ° C. or higher, the deviation from the structural ratio of the components AB and Cu in the composite oxide coating becomes large.

Furthermore, the present inventors have found that the temperature of the substrate when depositing the composite compound film is optimally in the range of 500 to 900 ° C. in view of the function of this type of vapor deposition apparatus and the reproducibility of the properties of the composite compound film. confirmed. In this case, the formed composite compound film is composed of amorphous or microcrystal.

In addition to this, however, this type of coating exhibits semiconducting properties, and superconductivity is not seen even at liquid He temperature (4K). Moreover, it was confirmed that the film had a high resistance when left in the air and was a very unstable and unreliable film.

The present inventors have proposed that a composite compound film of this kind is heat-treated at a high temperature of 700 ° C. or higher in an atmosphere of an oxidizing gas such as oxygen, or is treated with oxygen-io generated by the discharge of a gas containing at least oxygen. Superconductivity occurs,
It has been found that long-term stability is also greatly improved. It has been found that when treating with this oxygen ion, heating the substrate improves the superconducting properties. The optimum heating temperature was 200-800 ° C. When the temperature is higher than this, the resistivity becomes high, the characteristics of the coating become unstable, and steep superconductivity is not exhibited.

The present inventors have found that by subjecting the superconducting thin film obtained by these oxygen treatments to hydrogen treatment, the superconducting thin film can be controlled to exhibit the properties of a normal conductor, a semiconductor, or an insulator as described above. .

The hydrogen treatment is realized by ionizing hydrogen molecules by plasma discharge or the like and irradiating the superconducting thin film with the hydrogen ions. In other words, by reducing the oxygen by irradiating hydrogen ions to a superconductor optimized to control the amount of oxygen by oxidation treatment and exhibiting superconductivity, the optimum condition of oxygen for superconductivity is destroyed and superconductivity disappears. is there.

Hydrogen is a light element, and by heating the substrate to about 100 to 500 ° C. at the time of irradiation, it is possible to perform processing with good uniformity even when accelerated by irradiation with a low accelerating voltage. It has the advantage of not causing significant damage to the.

Also, when irradiating hydrogen ions accelerated at a high voltage of 30 KV or more, the region of the superconducting thin film to be processed is finely controlled, and precise and fine reduction processing is possible, and the Josephson device that requires submicron processing It becomes easy to fabricate such devices.

(Specific Example) YBa ₂ Cu ₃ O ₇ sintered by high-frequency planar magnetron sputtering using the sapphire single crystal R-plane as the substrate 1.
The target was sputter-deposited in a mixed gas atmosphere of Ar and O ₂ and deposited as a crystalline YBa ₂ Cu ₃ O ₇ coating on the substrate to form a layered structure.

In this case, the gas pressure is 0.5 Pa and the sputtering power is 150.
W, sputtering time 1 hour, film thickness of 0.5 μm, substrate temperature 700 ° C. The formed film was heated to 500 ° C. and subjected to oxygen ion treatment. The processing time was 10 minutes in a vacuum chamber of 5 × 10 ⁻⁴ Torr. The film thus obtained showed superconductivity and its transition temperature was 90K.

In this embodiment, the film thickness of the coating film 2 is 0.5 μm, but it was confirmed that superconductivity occurs even when the film thickness is 0.1 μm or less, or 10 μm or more.

Further, a weakly bonded portion 5 could be formed with good controllability by forming a mask pattern on the superconductor coating 2 using a resist or the like and partially irradiating it with hydrogen ions 4. In this case, the resist is preferably PMMA for electron beams that can be developed only with an organic solvent, or a negative resist. Usually, many of these resists are deteriorated when heated to 200 ° C. or higher and cannot function as resists, but the element manufacturing method by hydrogen ion irradiation of the present invention is effective because it hardly raises the substrate temperature. Is.

The hydrogen ion irradiation method as described above is shown in FIGS.
An apparatus having the configuration shown in the figure was used.

First, hydrogen gas is introduced into the ion source 6 shown in FIG. 2, and a high frequency signal is applied to the electrodes 7 and 8 facing each other with this gas interposed therebetween to generate plasma. A magnetic field generation source 9 for forming a magnetic field is arranged in this plasma, and efficiently generated hydrogen ions are supplied to a substrate table 11 on which a substrate 10 having a composite compound superconductor film formed thereon is arranged and a plasma of the ion source. By applying a voltage between them, hydrogen ions are extracted from the ion source and irradiated on the partially masked superconducting film 2 on the substrate 1 of the substrate table 11. The portion without the mask is irradiated with hydrogen ions to form a weak bond. At this time, when the voltage applied between the plasma and the sample table is 2 KV or less, the surface of the coating film 2 in the part without the mask is sputtered, but the oxygen reduction treatment can be effectively performed on the inside of the coating film. confirmed.

FIG. 3 shows that hydrogen gas is introduced into the vacuum chamber 12, microwave is introduced into this gas to generate discharge, plasma is generated, and a magnetic field 13 is applied to the plasma to increase the ionization efficiency of hydrogen ions. It was used as a source. In this case, when a microwave source 14 of 2.45 GHz is used as the microwave source 14 and the magnetic field strength is set to about 875 Gauss, cyclotron resonance of electrons occurs, so that the ionization efficiency of hydrogen increases.
The hydrogen ion extracted by this ion source is used for the sample table 15
The structure is such that the composite compound superconducting film arranged above is irradiated. In this case, it was found that high-energy hydrogen ions efficiently ionized by microwaves form a weakly bonded portion in the mask-free portion of the coating with good controllability with respect to the partially masked superconducting coating.

In addition to this, hydrogen gas is introduced into the vacuum chamber, a high frequency is applied to the parallel electrodes to discharge the gas, and a superconductor film partially masked is placed in this discharge plasma for hydrogen treatment. You can also

Also, in FIG. 2, it was confirmed that hydrogen treatment by an ordinary ion implantation technique using an accelerating voltage of several tens of KV or more, etc. is sufficient to form a structure that does not cause superconductivity because it destroys the crystal structure.

The details of changes in superconducting properties due to changes in constituent elements A and B of this type of composite compound superconductor (A, B) ₃ Cu ₃ O ₇ are not clear. However, it is true that A is trivalent and B is bivalent. Although Y has been described as an example of the A element, Sc, La, and lanthanum series elements (atomic number)
57-71) does not change the essential characteristics of the invention only to the extent that the superconducting transition temperature changes.

Also in the B element, the change of the group IIa element such as Sr, Ca, Ba changes the superconducting transition temperature by about 10K, but does not essentially change the characteristics of the present invention.

EFFECTS OF THE INVENTION The method of manufacturing a thin film superconducting element according to the present invention is characterized in that a thin film superconductor is partially irradiated with hydrogen ions. The irradiation effect of hydrogen ions is well controlled and easy to process. Therefore, a thin film superconducting device having a very high precision weak coupling portion is realized by the present invention.

As described above, according to the method of manufacturing a thin film superconducting element of the present invention, it can be integrated with a device such as Si or GaAs, and is practically used for manufacturing various superconducting devices such as a Josephson element. In particular, the transition temperature of this type of compound superconductor may reach room temperature, and the practical range is wide, and the industrial value of the present invention is high.

[Brief description of drawings]

FIG. 1 is a cross sectional view showing the basic concept of a method for manufacturing a thin film superconducting element according to an embodiment of the present invention, and FIGS. 1 ... Substrate, 2 ... Composite compound superconductor coating, 3 ... Surface, 4 ... Hydrogen ion, 5 ... Weak bond, 6 ... Ion source, 7,8 ... Electrode, 9,13 ... Magnetic field source, 10, 16 ...
… Substrate, 11, 15 …… Substrate stand, 12 …… Vacuum chamber, 14 …… Microwave source.

Claims (13)

[Claims] 1. A superconductor coating using a composite compound,
A method for manufacturing a thin film superconducting element, which comprises irradiating with hydrogen ions to form a weakly bonded portion in the coating, and forming a structure in which the coating is separated into at least two regions by the weakly bonded portion. 2. An oxide containing an element A, an element B and Cu having a molar ratio of elements of 0.5 ≦ (A + B) /Cu≦2.5 is used as the complex compound. Method for manufacturing thin film superconducting device of. Where A is Sc, Y and a lanthanide series element (atomic number 57
To 71), B represents at least one element of the IIa group elements. 3. The method for manufacturing a thin film superconducting element according to claim 1, wherein the width of the irradiation region of hydrogen ions is about 0.2 μm or less. 4. A PMMA as a mask pattern for forming a weakly coupled portion.
The method for producing a thin film superconducting element according to claim 1, wherein an electron beam resist of acrylic resin type such as CMS or the like, or a styrene resin type electron resist such as CMS or a negative resist for photolithography is used. 5. The method for producing a thin film superconducting element according to claim 1, wherein the composite compound coating film is heated during hydrogen ion irradiation. 6. The method for producing a thin film superconducting element according to claim 1, wherein plasma generated by discharging a gas containing at least hydrogen in a vacuum chamber is used as a hydrogen ion source. 7. The method for producing a thin film superconducting element according to claim 6, wherein a plasma processing apparatus by plasma decomposition using microwaves is used as the hydrogen ion source apparatus. 8. A method for manufacturing a thin film superconducting element according to claim 7, wherein electron cyclotron resonance absorption is used as the hydrogen ion source device. 9. A method in which hydrogen ions generated by electric discharge in a vacuum chamber are irradiated by accelerating by applying a voltage between the plasma in the vacuum chamber and a sample stage on which a composite compound film is installed. A method of manufacturing a thin film superconducting device according to claim 6. 10. An electrode installed at a predetermined potential between a plasma generated by applying a high-frequency voltage to hydrogen gas and a sample stage to irradiate hydrogen ions. Item 9. A method for manufacturing a thin film superconducting device according to item 9. 11. The method for producing a thin film superconducting element according to claim 9, wherein a direct current voltage of 2 KV or less is applied between the plasma and the sample stage. 12. The method for producing a thin film superconducting element according to claim 9, wherein the composite compound film is provided in plasma generated by applying a high frequency voltage to hydrogen gas. 13. The method for manufacturing a thin film superconducting element according to claim 9, wherein a voltage of 30 KV or more is applied between the hydrogen ion source and the sample stage.