JPH03197319A - Production of superconductor of thin film - Google Patents

Abstract

PURPOSE:To obtain a superconductor of thin film having excellent superconducting characteristics in good reproducibility by oxidizing a sputtering deposited film of specific compound oxide consisting essentially of Nd2CuO4 type crystal structure on a substrate. CONSTITUTION:A sputtering deposited film of compound oxide consisting of a main component of Nd2CuO4 type crystal structure shown by the formula on a substrate is oxidized to give the objective superconductor material of thin film. In the formula, A is Nd, Sm or Pr; B is Ce or Th; X is 0.06<=x<=0.08. Crystallizability of the film of sputtering deposition, especially of the film treated at 750-1,000 deg.C substrate temperature is enough to provide superconducting characteristics, further crystallizability can be increased by heating the film in the atmosphere or in an atmosphere containing >=10<-3> atmospheric pressure at 900-1,100 deg.C for a given time and further excellent superconducting properties can be obtained.

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a thin film of an oxide superconductor having a high critical temperature, particularly a method for manufacturing a thin film superconductor having an Nd2CuOa type crystal structure. Conventional technology Ba is an oxide superconductor with a high superconducting transition temperature.
-ta-Cu-0 superconductor discovered

【C! Ishi-ni-shi-Norf rnd k-mi]ra (J
, G. Bednorzand, A. Mulle)
r, fuishishi 1 lift fuishishi 1r
itsh-rifLfur Physik B)-Co
ndensed Matter, vol, 64, 18
9-193 (1986)], since then many new oxide superconductors have been discovered. By the way, recently, Nd-Ce-Cu, which has a different charge transport carrier in the normal conductive state from these conventional oxide superconductors, has been developed.
A new oxide superconductor with an a-type crystal structure represented by -0ζ has been discovered.
Stingray f5ri h4- ・? Shitous, home (Y,
Tokura, H., Takagi and S. υchida), 24f+-(Nature)vol
, 337, 345-347 (1989)]. Although the details of the superconducting mechanism of this type of material are not clear,
The transition temperature may be even higher, and promising applications such as the realization of new devices are expected. Problems to be Solved by the Invention However, with current technology, Nd-Ce-Cu-0 based materials can only be formed through the process of sintering, so they can only be obtained in the form of ceramic powder or blocks. On the other hand, when putting this type of material into practical use,
Although there is a strong demand for processing into thin films, it is extremely difficult to fabricate thin films with good superconducting properties using conventional techniques. The present invention aims to solve the problems of the prior art. Means for solving rRa The present invention provides a method for solving rRa using (A + -yB
An oxidation treatment is performed on a sputter-deposited film of a composite oxide represented by (here, A is Nd, S+s,
At least one element of Pr, B represents at least one element of Ce and Th, and X is 0.06≦
x≦0. 08) is a method for producing a thin film superconductor. Effect of the present invention The main component of the present invention is (
A + -x B +e ) 2 C1304 rel l1 M compound +7) In order to fabricate a superconducting thin film, a highly crystalline Wi film is basically formed on a suitable substrate using a sputter deposition method. , which attempts to control superconducting properties by adjusting the oxygen content. EXAMPLES Examples of the present invention will be described below with reference to the drawings. The present inventors fabricated a thin film of this oxide superconductor having the Nd2CuOa type crystal structure by sputter deposition, and investigated in detail the relationship between the fabrication conditions and the superconductivity of FILM. As a sputtering target, a sintered body obtained by heat-treating an oxide containing He element, B element, and Cu at high temperature in the atmosphere was used. However, AC, iNd,
At least one of Ss and Pr, B is Ce
, Th, and as a result, on a single crystal substrate heated to 400°C to 1000°C,
For example, a thin film of Nd+, esCe@, +5 Cubs, N
A crystallized fII film was obtained by sputtering a target film containing d, Ce, and Cu. Especially SrT
iO3, BaTiO3, LaAlO3, LaGao
When a single crystal with a perovskite crystal structure of grade 3 is used as a substrate, Nd is applied along its crystal axis.
The inventors have discovered that the crystal axes of +, 5sCe@, and +sCL+04 are oriented and a thin film with good crystallinity can be obtained. Furthermore, in the case of producing a normal oxide thin film, an inert gas such as argon and oxygen or an oxidizing gas are mixed in approximately equal proportions and used as a snoken gas. However, Nd2Cu
For oxide superconductors with an Oa-type crystal structure, if the partial pressure of oxygen or oxidizing gas in the sputtering gas is extremely low, they will have good superconductivity, that is, almost the same as that of ceramic materials. The present inventors have discovered that the following can be obtained with good reproducibility. The cause of this is not clear at present, but it is said that a reducing atmosphere is good for sintering ceramics made of this type of material, and by lowering the oxygen partial pressure during sputter deposition, unnecessary oxygen is removed from the thin film. or the composition of the thin film is Nd+, 8sCes, +
It seems that good results are obtained because 5CuOa-y and an appropriate amount of oxygen vacancies are introduced. Furthermore, it has been found that good superconducting properties can be obtained even when using only an inert gas that does not contain any oxygen or oxidizing gas. It was confirmed that argon is relatively easy to use as an inert gas and gives good results. The reason for these is that although a certain amount of oxygen is required to create the Nd2CuO4 type crystal structure, it is thought that the oxygen can be sufficiently supplied from the target. Sputter-deposited films, especially when the substrate temperature is 750°C to 10°C.
Although the crystallinity of the film at 00°C is sufficient to obtain superconducting properties, it is further heated in the air or in an atmosphere containing oxygen at 10-3 atmospheres or higher in the temperature range of 900°C to 1100°C for a certain period of time. It was confirmed that by doing so, it was possible to improve crystallinity and obtain even better superconducting properties. Additionally, it has been found that rapid cooling to room temperature or lower after heat treatment reduces the oxygen content and facilitates subsequent reduction treatment. In addition, the present inventors have found that optimal superconducting properties can be obtained by performing an appropriate reduction treatment and reducing the oxygen content to an optimal value lower than the stoichiometric ratio by introducing oxygen vacancies. I found it. The method of reduction treatment is in vacuum or # cable partial pressure 10
It has been found that heating in an inert gas atmosphere such as argon at a pressure of -3 atmospheres or less is effective. At this time, the amount of oxygen desorbed or the amount of defects strongly depends on the oxygen diffusion process. In other words, the appropriate processing temperature range for heating is 500°C to 900°C, but the required closing during processing is also affected by the film thickness and surface condition of the superconductor, but the higher the processing temperature, the more I found out that it only takes a short amount of time. However, if the closing time during processing is not long, the superconductivity will be impaired, and it was found that there is an optimum closing time for each processing temperature. However, with this type of reduction treatment method, especially when the treatment temperature is high, the amount of reduction may be too large and the minimum necessary oxygen may be deficient, or the oxygen concentration distribution in the film may be non-equilibrium or uneven. The present inventors believe that oxidation treatment not only promotes crystallization at high temperatures as described above, but also ultimately reduces the oxygen concentration. It has been found that in order to obtain the best superconducting properties by uniformly adjusting the optimum value, it is very effective to carry out the process in the temperature range of 400°C to 600°C. Also,
On the other hand, the present inventors have also discovered that oxidation treatment in the temperature range of 600° C. to 900° C. is effective in the sense of applying excessive oxygen and causing the superconductivity to be lost. Oxidation treatment methods include heating for a certain period of time in the air or in an atmosphere containing oxygen at 10-3 atmospheres or more, and oxidation treatment by irradiating oxygen ions or oxygen atoms to a temperature of about 300℃. We have discovered that the process can be performed selectively at relatively low temperatures. More detailed examples will be described below. Using an oxide ceramic sintered body containing Nd, Ce, and Cu as a target, strontium titanate (100
) A thin film was fabricated on the surface of the substrate by high-frequency planar magnetron scattering. This target is Nd2
A sintered body obtained by heat-treating O3, CeO2, and C[10] at 1050° C. for 8 hours in the atmosphere was used. Although pure argon gas was used as the sputtering gas, a thin film with good crystallinity could be formed. The reason for this seems to be that a certain amount of oxygen is required to create an NdzCuOa type crystal structure, and that oxygen is most suitably supplied from the target. When the temperature of the substrate during vapor deposition was 400°C to 1000°C, signs of superconductivity were observed in the electrical resistance of the thin film at low temperatures, but especially in thin films formed at 750°C to 1000°C, zero resistance was observed. was confirmed to be about 20%, and the crystallinity was also good and the reproducibility was excellent. More specific examples will be shown below in order to better understand the content of the present invention. Nd+, 5sCe@, +sCu”0x (using D oxide ceramic sintered body as a target, M2O, or SrTiO3 (100) or (110
) A thin film was formed on a single-crystal substrate. Sputtering power 160W, sputtering gas pressure 3 x 10-'To
A thin film with a thickness of about 0.5 to 0.8 μm was obtained by performing interleaved sputter deposition for about 1 hour under conditions of rr. The sputtering gas was pure argon gas, and the substrate temperature was varied to investigate the relationship between crystallinity and superconducting properties. After the above process, we investigated the composition of the thin film and found that the ratio of metal elements was Nd:Ce:Cu=1.85:
The ratio was almost stoichiometric, 0.15:1.0. The crystal structure of the thin film was also investigated by X-ray diffraction. As a result, it was found that when a 5rTiO3 (100) substrate was used as the substrate, the formed thin film had an N d2 Cuo a type crystal structure in which the C axis was oriented perpendicular to the substrate. When using a 5rTiO3 (110) substrate,
A thin film with a (103) plane was grown, a (110) plane was grown on the MgO (100) plane, and a (100) plane was grown on the (110) plane. Substrate temperature from 750℃ to 1000℃
The crystallinity of the film at ℃ is sufficient to obtain superconducting properties.
It was confirmed that the crystallinity could be improved by heating in an interval of 1 to 2 hours, and even better superconducting properties could be obtained. It has been found that a thin film crystal structure in which the C-axis is oriented perpendicular to the substrate is suitable for providing excellent superconducting properties. In that sense, as a substrate, 5rTiOi
(100) In addition to the substrate, BaTiO3, LaA IO3,
It was confirmed that a single crystal (100) substrate having a perovskite crystal structure such as LaGaO3 is superior. Some of the thin films obtained showed superconducting properties after film formation or after the heat treatment described above to promote crystallization, but the superconducting properties could be further enhanced by an appropriate reduction treatment. We also found that it is possible to improve the superconducting properties of materials that did not exhibit superconducting properties. It has also been found that rapid cooling to room temperature or lower after heat treatment reduces the oxygen content and facilitates subsequent reduction treatment. It has been found that heating in a vacuum or in an atmosphere of an inert gas such as argon with an oxygen partial pressure of 10@-3 atm or less is effective for the reduction treatment. Figure 1 shows the temperature dependence of the electrical resistance of a typical thin film with a film thickness of 5000A when heated in vacuum by varying the processing temperature and opening during processing.
Curve 11 is before reduction treatment, curve 12, 13, 14 is 60
Curve 15 was treated at 0° C. for 2, 16, and 522 hours, respectively, and curve 15 was treated at 800° C. for 2 hours. The processing time required to obtain excellent superconducting properties with a critical temperature of 22 or higher is 8 to 30 hours at 600°C and 100°C at 800°C.
It was leap time at ~3 o'clock. From this, the amount of oxygen desorbed or lost strongly depends on the oxygen diffusion process, and the appropriate treatment temperature range for heating is 500°C to 900°C, but the optimal opening during treatment is Although it is influenced by the film thickness and surface condition of the superconductor, we found that the higher the processing temperature, the shorter the processing time, but the optimum opening range is narrower. The above-mentioned sample subjected to the 52-hour step reduction treatment was further subjected to an oxidation treatment by heat treatment in an oxygen atmosphere of 1 atm. Figure 2 shows the temperature dependence of electrical resistance.0 songs $92
1, 22.23 are 400℃, 600℃, 70℃ respectively
It was processed at 0°C in 5 hour intervals. For those treated at 400°C, both critical temperature and critical W'full current density recovered to their maximum values, and it was confirmed that improvements in critical temperature and critical current density were also observed for those treated at 600°C. . Furthermore, it was confirmed that the superconducting property itself could be lost when treated at 700°C. Furthermore, as a means of oxidation treatment, for example, ECRIil
We have discovered that by using an i* plasma generator, superconducting thin films can be efficiently oxidized using efficiently ionized high-energy oxygen ions and neutral oxygen atoms. It was confirmed that the treatment temperature at that time is sufficient at a low temperature from room temperature to 300° C., and that the oxidation treatment can be performed selectively by using a mask or the like. In this case as well, it is possible to improve the superconducting properties of a product whose superconducting properties have been degraded by the above-mentioned 522-time step reduction treatment, and it is also possible to cause the superconducting properties themselves to be lost under strongly oxidizing conditions. It was confirmed. Note that this result also applies to combinations containing S+s, Pr, or at least one of these instead of Nd, and combinations containing T11 or at least one of these instead of Ce.
It was confirmed that they were the same. Effects of the Invention The present invention has made it possible to obtain a high-quality, high-performance thin film superconductor having an Nd2CuOa type crystal structure with good reproducibility. The manufacturing method of the present invention is essential for applications such as devices using this type of substance, and the present invention has great industrial value.

[Brief explanation of drawings]

FIG. 1 is a graph showing the temperature dependence of electrical resistance due to reduction treatment of a thin film superconductor manufactured in one embodiment of the present invention, 2nd page! 1 is a graph showing the temperature dependence of electrical resistance due to oxidation treatment of a thin film superconductor manufactured in an example of the present invention.

Claims (4)

[Claims] (1) Oxidation treatment is performed on a sputter-deposited film of a composite oxide whose main component is (A_1_-_xB_x)_2CuO_4 having an Nd_2CuO_4 type crystal structure (here, A is Nd, S , B represents at least one element among Ce and Th, and x is a numerical value in the range of 0.06≦x≦0.08). Method for manufacturing superconductors. (2) As a method of oxidation treatment, in the atmosphere or 10^-
^400℃~11 in an atmosphere containing oxygen of 3 atmospheres or more
2. The method for producing a thin film superconductor according to claim 1, wherein the heating is performed at a temperature range of 00° C. for a certain period of time. (3) As a pre-oxidation process, 5 % of
3. The method for producing a thin film superconductor according to claim 1, wherein the reduction treatment is performed by heating at a temperature range of 00C to 900C for a certain period of time. (4) Claim 1, characterized in that the method of oxidation treatment is irradiation with oxygen ions or oxygen atoms.
Or the method for producing a thin film superconductor according to 3.