JP2012199235A - Method of introducing nano-scale crystal defect into high temperature superconducting oxide thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple method for introducing a controlled crystal defect in a (RE)BCO thin film.SOLUTION: On top of a high temperature superconducting oxide thin film, deposited on a substrate, which consists primarily of a rare earth oxide expressed by a general formula (RE)BaCuO(where, RE represents one kind of atom selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er and Yb) is placed a porous alumina self-supporting film. And, by using the alumina film as a mask, argon ion milling is applied, whereby a nano-scale crystal defect is introduced into the high temperature superconducting oxide thin film.

Description

  The present invention relates to a method for introducing nanoscale crystal defects into a high-temperature superconducting oxide thin film.

  A superconductor can flow a large current with zero electric resistance in a superconducting state, but an electric resistance is generated when a current larger than a predetermined current value (critical current) flows. As the current is further increased, the temperature of the superconductor rises due to the generated heat and becomes a normal conducting state, resulting in a larger electrical resistance. Taking advantage of the characteristics of such superconductors, the resistance is normally zero, and in principle, a large resistance is generated in the event of a short circuit in a power transmission cable or power system with no loss to suppress an increase in accident current. New power equipment (current limiter) can be made. And the high temperature superconducting oxide thin film which implement | achieves these is used as the most important material.

High-power superconducting oxides with high critical current per unit width (critical surface current) are required for power transmission cables and thin-film current limiters that use superconducting thin films. It is necessary to produce a thin film. Since the critical surface current is the product of the critical current density (critical current per unit cross section, J _c ) and the film thickness, it is desirable that both are large.

In recent years, the general formula (RE) Ba ₂ Cu ₃ O _x (wherein RE represents one atom selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Yb) (hereinafter referred to as “RE”). The manufacturing process technology of a superconductor composed of a high-temperature superconducting oxide represented by “(RE) BCO”) has made remarkable progress. As a result, large bulk bodies having a high critical current density and oriented crystal orientation, tape wires exceeding a length of 10 m by vapor deposition on a metal tape substrate, and the like are also manufactured.

(RE) BCO thin films can be formed on a substrate by pulsed laser deposition (PLD), vacuum deposition, various sputtering methods, chemical vapor deposition (CVD), MBE, coating pyrolysis ( Various methods such as MOD method are used.
Defects in the thin film naturally introduced in the formation of this (RE) BCO thin film, for example, point defects such as oxygen vacancies, fine impurities, linear defects such as dislocations, and planar defects such as crystal grain boundaries It is known that it acts as a pinning to limit the movement of the magnetic flux, and in the (RE) BCO film, the crystal defects are perpendicular to the film surface, that is, parallel to the c-axis of the (RE) BCO crystal. When the magnetic field is applied perpendicularly to the film surface, the critical current density _Jc is improved.

Therefore, by controlling the pinning introduced during deposition, in order to improve the J _c of the resulting (RE) BCO thin films, by applying a nanostructured control the film growth, the artificial crystal defects in YBCO films Process development to introduce a high density has been made, and a target exchange method for film formation by a pulse laser deposition method (PLD method) and a mixed target method have been tried.
For example, Non-Patent Document 1, the mixed target method BaZrO _3, BaZrO ₃ is in YBCO thin film, has been shown to form a plurality of pillar-shaped particles having a diameter of 5 to 10 nm, also in non-patent document 2 significant improvement in J _c has been reported to be obtained by producing a multi-layer film YBCO and pinning Y ₂ BaCuO ₅ targets by depositing alternately.

However, it is extremely difficult to control the density of dislocations that are naturally introduced by variously changing the deposition conditions during the (RE) BCO deposition. In addition, although the crystal grain boundary also acts as pinning, in general, since the crystal grain boundary exists randomly, it is extremely difficult to control J _c by controlling the tilt angle of the crystal grain boundary.
As described above, it is difficult to control the pinning that is naturally introduced during film formation. Therefore, it is important to artificially pin the film so as to improve J _c of the obtained (RE) BCO thin film. It has become a challenge.
In order to solve this problem, for example, Non-Patent Document 3 reports that columnar defects are introduced by heavy ion irradiation to YBCO.

On the other hand, a superconducting motor using an Nb-based low-temperature superconducting wire and using a superconducting coil formed by the superconducting wire as a field winding (field coil) is known. In such a superconducting motor, a superconducting field coil is cooled to a temperature lower than the critical temperature to be superconducting so that a large field current flows and the field is strengthened to achieve a large output.
In Non-Patent Document 4, since the porous alumina self-supporting film (see Non-Patent Document 5 below), which has been developed by nanotechnology and has been researching the production of various nanostructures, has determined the size and distribution of the pores. , A material that can be used to introduce an artificial pin, a method of directly producing the porous alumina film on an Nb-based low-temperature superconducting thin film, and then producing columnar defects of the artificial pin by Ar ion milling is attempted, it has been reported to be successful in improving the J _c than introducing columnar defects in the process.

JLMacManus-Driscoll, SRFoltyn, QXJia, H.Wang, A.Serquis, L.Civale, B.Maiorov, MEHawley, MPMaley and DEPeterson, “Strongly enhanced current conductors in superconducting coated conductors of YBa2Cu3O7-x + BaZrO3 Nat. Matls. 3, 439 (2004). T.Haugan, P.N.Barnes, R.Wheeler, F.Meisenkothenand M.Sumption, “Addition of nanoparticle dispersions to enhance flux pinningof the YBa2Cu3O7-x superconductor,” Nature 430, 867 (2004). L. Civale, “Vortex pinning and creepin high-temperature superconductors with columnar defects,” Supercond. Sci. Technol. 10, A11 (1997). RBDinner, APRobinson, SLSahonta, JHDurrell, JLMacManus-Driscoll and MGBlamire, “High density magneticpinning centres via porous alumina templates,” Poster presentation at VortexMatter in Nanostructured Superconductors (Vortex VI), Rhodes, Greece, 17-24September 2010; RBDinner, APRobinson, SCWimbush, JLMacManus-Driscolland MGBlamire, “Depairing critical current achieved in superconducting thinfilms with through-thickness arrays of artificial pinning centers,” Supercond. Sci. Technol. 24 (2011) 055017. O.Rabin, P.R.Herz, Y.M.Lin, A.I.Akinwande, S.B.Cronin and M.S.Dresselhaus, “Formation of Thick Porous Anodic Alumina Filmsand Nanowire Arrays on Silicon Wafers and Glass,” Adv. Func. Matls. 13, 631 (2003).

As mentioned above, artificial pinning methods such as the film-forming target exchange method and mixed target method should be introduced into the thin film by controlling the distribution and density of crystal defects so that the maximum J _c can be obtained. In practice, however, the distribution of crystal defects introduced into the superconducting matrix is random, and the size of the defects is difficult to control.
In addition, with respect to research for introducing columnar defects into a (RE) BCO thin film by a simple method, methods other than the heavy ion irradiation have not been developed yet. However, in principle, heavy ion irradiation is complicated, and there is a problem that it is difficult to scale up in manufacturing.
As described above, in the (RE) BCO thin film, there is no method for easily introducing controlled crystal defects having a large area.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a simple method for introducing controlled crystal defects in a (RE) BCO thin film.

In order to enable control of crystal defects, the present inventors considered applying the method of introducing nano defects to the Nb thin film described in Non-Patent Document 4 to a (RE) BCO superconducting thin film. An attempt was made to produce porous alumina directly on a RE) BCO superconducting thin film.
However, the acid solution used in the anodization process could not be realized to dissolve (RE) BCO.
Therefore, the present inventors have further studied, and instead of directly producing anodized aluminum on a (RE) BCO thin film, a porous alumina free-standing film having a protective layer made of PMMA (polymethyl methacrylate) is used. The knowledge that it can be achieved by using was obtained.

The present invention has been completed based on these findings, and according to the present invention, the following inventions are provided.
[1] General formula (RE) Ba ₂ Cu ₃ O _{7 formed} on a substrate (wherein RE is one selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb) By placing a porous alumina film on a high-temperature superconducting oxide thin film mainly composed of a rare earth oxide represented by the following, and performing argon ion milling using the alumina film as a mask, A method of introducing nanoscale crystal defects into the high-temperature superconducting thin film.
[2] The method according to [1] above, wherein the porous alumina membrane has an average pore size of 60 to 120 nm.
[3] The method according to [1] above, wherein the porous alumina film has a thickness of 1 to 5 μm and has a polymethyl methacrylate protective film thereon.
[4] The method according to any one of [1] to [3], wherein the high-temperature superconducting oxide thin film is formed by any one of a large area PLD method, a fluorine-free MOD method, and a co-evaporation method. .
[5] A superconductor having a high critical current density obtained by causing nano-sized controlled crystal defects in the high-temperature superconducting oxide thin film by the method according to any one of [1] to [4] above .

  The present invention has succeeded in introducing pinning into a (RE) BCO thin film. Thereby, a (RE) BCO thin film having a high critical surface current can be produced. This method is simpler than conventional heavy ion irradiation, and can be introduced into a thin film by accurately controlling the distribution and density of artificial pins. Moreover, it can be used many times until the porous alumina free-standing film is broken, and is an efficient method.

Schematic diagram showing the positional relationship between a porous alumina free-standing film and a superconducting oxide thin film Scanning electron micrographs of (a) upper surface and (b) cross section of a commercially available porous alumina free-standing film (Nanomaterials) without PMMA film It is the scanning electron micrograph of the surface of the YBCO thin film processed by Ar-ion milling with the YBCO thin film after film formation (As-grown), (a), (b) is a photograph of a sample (a), (c), (d) is a photograph of sample (b), and (e) and (f) are photographs of ampoule (c). Samples (a), with respect to the film thickness of the YBCO thin film (b) and (c), in 77.3 K, is a graph showing changes in critical current density _{J c,} □, the critical current density of the As-grownYBCO film, ● indicates the critical current density of the YBCO thin film after being processed by argon ion milling using a porous alumina free-standing film. Scanning electron micrographs of the surface of as-grown sample (a) and sample (b) after argon ion milling. It is an AFM photograph of an as-grown sample (a) and a sample (b) after argon ion milling, and (c) and (d) are AFM photographs after each etching. It is a diagram showing a J _c distribution mapping in 77.3K samples (5 × 5mm ^2), ◆ the As-grown, □ after argon ion milling, ▲ shows after annealing.

  The method of the present invention does not directly produce anodized alumina on a (RE) BCO thin film, but separately prepares a porous alumina free-standing film on the (RE) BCO thin film, and then Ar ions Etching is performed by milling. Then, by Ar ion milling, a pattern similar to the hole pattern of the porous alumina free-standing film is etched into the (RE) BCO thin film under the porous alumina free-standing film.

  FIG. 1 is a diagram for explaining a method of introducing nanoscale crystal defects in a high-temperature superconducting thin film according to the present invention, and is a method for forming porous alumina on a superconducting thin film formed on a substrate. The film is a film obtained by anodizing an Al film, on which a PMMA (polymethyl methacrylate) layer as a protective film is provided, and through this PMMA layer, Ar (argon) The ion milling process is schematically shown.

The present invention is the first attempt to introduce controlled nano-defects into a (RE) BCO thin film prepared by PLD method, fluorine-free MOD method, and co-evaporation method, and by using this simple method, A controlled crystal defect is introduced into the (RE) BCO thin film, and the critical current (critical surface current) per unit width of the thin film can be greatly improved.
The method of the present invention is a simpler method than conventional heavy ion irradiation, and can be introduced into a thin film by accurately controlling the distribution and density of artificial pins. Moreover, it can be used many times until the porous alumina free-standing film is broken, and is an efficient method.
Further details will be described below.

The high-temperature superconducting oxide thin film used in the present invention is a rare earth oxide represented by the general formula (RE) Ba ₂ Cu ₃ O ₇ (RE = Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb). Is the main component.
As the substrate for forming the thin film, a sapphire substrate, SrTiO ₃ (STO) substrate, LaAlO ₃ (LAO) or the like is used.
The substrate is also provided with a buffer layer such as CeO ₂ , Y ₂ O ₃ , YSZ (yttria stabilized zirconia) for lattice matching and prevention of diffusion.

  As a method for forming the (RE) BCO thin film of the present invention on these substrates, pulse laser deposition (PLD), vacuum deposition, various sputtering methods, chemical vapor deposition (CVD), MBE, coating, etc. Various methods such as a thermal decomposition method (MOD method) are used, and among these, a pulse laser deposition method (PLD method), a fluorine-free MOD method, and a co-evaporation method are preferably used.

The PLD (Pulsed Laser Deposition) method irradiates the surface of the target (substance that becomes the material of the thin film) with a pulsed laser beam having a high energy density, thereby instantaneously peeling off the material on the target surface and generating plasma. This is a method of producing a thin film by depositing the atoms and molecules formed on a substrate arranged to face the target. (Refer to “Manufacturing superconducting thin film using laser light irradiation”, AIST TODAY, National Institute of Advanced Industrial Science and Technology, 2006, Vol. 6-11, P12-15)
The large area PLD method has a longer distance between the target and the substrate than the normal PLD (maximum 14 cm; the normal PLD is about 3 to 5 cm), so the composition is intentionally shifted from the stoichiometric composition to the Y-rich. Therefore, it has been reported that an appropriate amount of vacancies can be introduced into the YBCO thin film on the sapphire substrate to greatly improve the critical film thickness for crack generation to 1,000 nm or more (K. Develos-Bagarinao, H. Yamasaki, Y. Nakagawa, H. Obara and H. Yamada, “Microcrack-free thick YBCO / CeO ₂ / Al ₂ O ₃ films prepared by a large-area pulsed laser deposition system,” Physica C 392-396, 1229 (2003)). In the present invention, it is particularly preferably used.

In addition, the MOD method (Metalorganic deposition, also referred to as “coating pyrolysis method”) is a method in which a precursor solution of (RE) BCO superconducting material is applied on a linear substrate, particularly a tape-like substrate, and then at about 500 ° C. It is calcined and thermally decomposed, and the resulting pyrolyzed product (MOD calcined film) is crystallized by heat treatment (main firing) at a higher temperature (for example, around 800 ° C.) to obtain a superconductor. Compared with the vapor phase method (evaporation method, sputtering method, pulsed laser deposition method, etc.) that is mainly manufactured in vacuum, the manufacturing equipment is simple, and in this respect, cost reduction is expected. In addition, it has features such as easy handling of large areas and complex shapes.
In the MOD method, there is a method of using a metal compound solution of a fluorine-containing organic acid such as trifluoroacetic acid as a precursor solution for a superconducting material. However, this method has a problem that dangerous hydrogen fluoride gas is generated during the heat treatment process. is there. Therefore, a method using a metal organic compound containing no fluorine as a superconductor precursor is a fluorine-free MOD method. (See Toshiya Kumagai and two other authors, “Preparation of Superconducting Films by Coating Pyrolysis,” Surface Technology, Japan Surface Technology Association, 1991, Vol. 42, No. 5, P500-507).

The co-evaporation method is a film-forming method improved from the MBE method (molecular beam epitaxy method), in which a reactive gas is introduced in the vicinity of the substrate, and the molecular beam from the evaporation source reacts with the reactive gas in the vicinity of the substrate surface. This is a method for growing a thin film on a substrate.
The YBCO membrane currently on the market is based on this method.

  Ion milling means a processing method using an ion beam. In the present invention, the (RE) BCO thin film is etched by argon ion milling. An argon ion milling apparatus is a semiconductor manufacturing apparatus or the like. What is generally used can be used as it is.

In the present invention, the porous alumina used as the etching mask is a nanostructure having a pore size of nanometer size and nano-sized pores in a direction perpendicular to the substrate, and anodizing aluminum (Japanese Patent Publication No. 6-37291). Films made by anodizing aluminum can be controlled in the pore size range from several nanometers to several tens of nanometers depending on the production conditions, and since the film composition is alumina, considerable heat resistance and corrosion resistance are expected. There is an advantage that you can.
As an example, FIG. 2 shows scanning electron micrographs of a (a) upper surface and (b) cross section of a commercially available porous alumina free-standing film (Nanomaterials), which is not provided with a PMMA film on the surface.

In the present invention, the thickness of the porous alumina free-standing film used as a mask is 1 to 5 μm, preferably 1 to 2 μm.
Since the porous alumina free-standing film is very fragile at the above thickness, it is preferably used by coating PMMA (polymethyl methacrylate) on the film to a thickness of 2 to 4 μm in order to support it mechanically.

In addition, the porous alumina free-standing film used in the present invention has a pattern of holes formed on the underlying (RE) BCO thin film by Ar ion milling. Therefore, the pore size of the porous alumina free-standing film to be used is a size necessary for forming nanoscale crystal defects in the (RE) BCO thin film, and is 60 to 120 nm, preferably 100 nm. Used.
Moreover, the shape is columnar, and in order to allow Ar ions to pass through without hindrance, a continuous hole along the thickness of the porous alumina free-standing film is used.

EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to this Example.
(Sample preparation)
The following three samples were prepared.
Sample (a): Large YBCO film R surface produced by the area PLD method (1 1 02) is CeO ₂ buffer layer for on the sapphire substrate was cut and polished so that the surface of the diffusion preventing lattice-matched ( Film thickness: 30 nm) was formed by a large area PLD method, and was annealed for a short time at a high temperature (1050 ° C.) in oxygen in order to planarize the surface of the CeO ₂ layer. On this CeO ₂ buffer layer, a YBCO thin film was formed to a thickness of 500 nm by the large area PLD method.

Sample (b): A CeO ₂ buffer layer (30 nm) was produced by electron beam evaporation on a YBCO film SrTiO ₃ (STO) substrate produced by a fluorine-free MOD method . A YBCO thin film having a thickness of 780 nm was formed on the CeO ₂ buffer layer by a fluorine-free MOD method.

Sample (c): Commercially available YBCO film A commercially available co-evaporation method is used to form a CeO ₂ buffer layer (30 nm) and a YBCO thin film (300 nm) on a sapphire substrate (manufactured by THEVA (Germany)). Was used.

Example 1
For each of samples (a) to (c), the surface morphology after film formation (as-grown), that is, before argon ion milling, was observed with a scanning electron microscope (SEM), an atomic force microscope (AFM), or the like. .
On the left side of FIG. 3, the results of as-grown scanning electron microscope observation are shown.
(a), (c) and (e) are photographs of samples (a), (b) and (c), respectively.

Next, a porous alumina free-standing film was placed on each of the above samples, and argon ion milling was performed.
The used porous alumina free-standing film has an area of 5 mm square, and the surrounding Al film is about 2.5 mm. The hexagonal holes are about 90-100 nm and the thickness is 1-2 μm.
Argon milling equipment is manufactured by Hakuto Co., Ltd. (model: 3-IBE, sample chamber vacuum: atmospheric pressure to 6 × 10 ⁻⁴ Pa, beam diameter: 3 cm, beam acceleration voltage: 300 V, ion current density: 1 cm 1 mA per ² (at an incident angle of 0 °) was used, the argon gas flow rate was 5.0 sccm, and the pressure in the sample chamber was specified as 4 × 10 ⁻² Pa. The beam voltage was 300 V, and the incident angle was Warming up was performed in 2 minutes until the beam was stabilized at 0 °, and etching was performed for 15 to 60 minutes, and the in-plane rotation speed of the sample stage was specified as 4.0 rpm.

With respect to the sample treated by argon ion milling, the surface morphology was again observed with SEM and AFM and compared with the as-grown surface morphology.
The right side of FIG. 3 shows the result of scanning electron microscope observation after argon ion milling.
(b), (d) and (f) are photographs after milling sample (a) for 30 minutes, photographs after milling (b) for 15 minutes, and (c) after milling for 30 minutes, respectively. In each case, the white arrows indicate the damaged areas.
As shown in FIG. 3, a damaged area of milling due to ions on the surface of the sample subjected to argon ion milling was confirmed. The range of the damage area depends on the milling time.

(Example 2)
With respect to samples (a) to (c), the critical current density J _c was measured by the third harmonic induction method. In the third harmonic induction method, a pickup coil was placed on the sample surface, an alternating current was passed through the coil, and the third harmonic voltage (V ₃ ) induced in the coil was measured. Then, the average electric field (E _av ) and J _c in the superconducting thin film were obtained from the current value (I _th ) when V ₃ began to occur. This (J _c, E _av ) pair is measured three times while changing the frequency of the alternating current, an EJ characteristic curve is obtained, and the electric field reference is _calculated from the power law relation E = E _c (J / J _c ) ⁿ finally sought _{J c} using _{(E c = 1μV / cm)} . A pickup coil having an inner diameter of 0.8 mm and an outer diameter of 2.2 mm was used. (Details of the induction method are described in the literature: H. Yamasaki, Y. Mawatari, Y. Nakagawa, T. Manabe, M. Sohma, “Automatic Measurement of the Distribution of Jc and n-Values in Large-Area Superconducting. Films Using Third-Harmonic Voltages, "IEEE Trans.Appl.Supercond.vol.17 no.2, p.3487-3490, 2007)
The result is shown in FIG.
As shown in FIG. 4, the critical current (critical surface current) per unit width was improved by the effect of ion milling. At 77.3K, the sample (a) formed by the large area PLD method is about 5 to 9%, the sample (b) formed by the co-evaporation method is about 13 to 18%, the sample formed by the fluorine-free MOD method (c ) improvement of J _c was obtained of approximately 21 to 71%.

(Example 3)
Except that the argon ion milling time was changed to 30 minutes, in the same manner as in Example 1, the dependence of the damage area caused by argon ion milling on the sample (b) was determined by using a scanning electron microscope and an atomic force microscope (AFM). (Scan area: 5 μm × 5 μm).
FIG. 5 shows the results of scanning electron microscope observation. (A) and (b) show an as-grown sample and a sample after argon ion milling, respectively.
FIG. 6 is an AFM image (scan area: 5 μm × 5 μm), and (a) and (b) show an as-grown sample and a sample after argon ion milling, respectively.
As shown in the AFM image of FIG. 6, the surface morphology of the sample subjected to argon ion milling basically looks similar to the as-grown sample for the fine structure, but as shown by the white arrow, the sputter The remains of are observed.

Example 4
Next, the sample in Example 3 was etched with a 0.15 vol% Br-ethanol solution for 2-3 seconds, and the presence of defects was confirmed by AFM observation.
FIGS. 6C and 6D show the results of the as-grown sample and the sample after argon ion milling, respectively.
6C and 6D, natural defects or defects introduced by milling appear as etch pits observed by AFM (indicated by white arrows). Compared with As-grown, it was found that the density of etch pits in the argon ion milled sample increased by about 3 times.

(Example 5)
The distribution of critical current density (J _c ) at 77.3 K of As-grown (♦) and after argon ion milling (□) of a YBCO film (film thickness 700 nm) produced by the fluorine-free MOD method was measured.
FIG. 7 is a diagram showing _Jc distribution mapping. Grid positions 1 to 9 on the horizontal axis are “1 to 3” in order from the left of the upper stage of the sample (5 × 5 mm ² ) shown in the figure, The positions correspond to “4 to 6” in order from the left and “7 to 9” in order from the left in the lower row.
As shown in FIG. 7, the MOD sample having a higher J _c value (1.7 MA / cm ² or more) showed no change in J _c or deterioration after argon ion milling. This is considered that the film | membrane was damaged by ion irradiation.
It is known that superconducting thin film can recover superconducting properties and crystallinity by annealing with oxygen heat treatment in superconducting thin films (Yijie Li, S. Linzen, F. Machalett, F. Schmidl, P. Seidel, “Recovery of superconductivity and recrystallization. of ion-damaged YBa ₂ Cu ₃ 0 _7-x films after thermal annealing treatment, “Physica C vol. 243, pp. 294-302, 1995).
Thus, after the ion milled sample was subjected to oxygen heat treatment annealing at 450 ° C., the distribution of critical current density (J _c ) was measured in the same manner.
The distribution of critical current density (J _c ) of the sample after the annealing treatment is shown by ▲ in FIG.
As can be seen from the results, it was possible to improve the value and uniformity of J _{c in} the self-magnetic field by applying the annealing treatment to a sample of about 5 × 5 mm ² .

Claims (5)

A general formula (RE) Ba ₂ Cu ₃ O _{7 formed} on a substrate (wherein RE is an atom selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Yb) A porous alumina film is placed on the high-temperature superconducting oxide thin film mainly composed of the rare earth oxide represented by the following formula, and argon ion milling is performed using the alumina film as a mask. A method of introducing nanoscale crystal defects into a thin film.   The method according to claim 1, wherein an average pore diameter of the porous alumina membrane is 60 to 120 nm.   The method according to claim 1, wherein the porous alumina film has a thickness of 1 to 5 μm and has a polymethyl methacrylate protective film thereon.   The method according to claim 1, wherein the high-temperature superconducting oxide thin film is formed by any one of a large area PLD method, a fluorine-free MOD method, and a co-evaporation method.   A superconductor having a high critical current density obtained by causing nanosized controlled crystal defects in the high-temperature superconducting oxide thin film by the method according to any one of claims 1 to 4.