JPH054898A - Production of bi-based oxide superconductor film - Google Patents

Abstract

(57) [Summary] [Structure] When manufacturing a Bi-based oxide superconducting film by electron beam multi-source deposition, one of the IIa group elements that are constituent elements of the oxide superconductor to be manufactured as a deposition source Pb oxides containing more than one element (eg Ca ₁₀ PbOx
Etc.) and an oxide (crystal) made of at least one element of the IIa, IIIa and IVa group elements as the substrate, the substrate temperature of 500 to 800 ° C., and the degree of vacuum on the substrate surface of 1 to 10
^The film is formed under the condition of ^-3 Torr. [Effect] During vapor deposition, the rapid decrease in vapor deposition rate, which has been a problem in the past, and subsequent temporal changes are suppressed, making it easy to form a high-Tc single-phase superconducting film exhibiting a high critical temperature (Tc). It can be manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a Bi-based oxide superconducting film, and more particularly, to easily producing a superconducting film having a high critical temperature (Tc) (hereinafter referred to as a high Tc phase film). Regarding the method.

[0002]

_2. Description of the Related Art The superconductivity of Bi-based oxide superconductors increases with the increase of CaCuO ₂ layers in unit cells. However, the high Tc phase (Bi ₂ Sr ₂ Ca ₂ Cu), which has the highest Tc and has three CaCuO ₂ layers,
_{In order} to produce a superconductor (bulk material) of ₃ O _X ), it is necessary to strictly control the composition and the heat treatment temperature. Usually, a low Tc (80k) low Tc phase or Tc Even lower (2
0k) can only be produced in a mixture with the semiconductor phase
(For example, Jpn.J.Appl.Phys.27 (1988) L209), and
The volume ratio occupied by the high Tc phase is also small.

This tendency is the same in the case of producing an oxide superconducting film, and strict control of the film forming composition is essential to obtain a high Tc phase film, and the substrate of each element constituting the superconducting film is required. It is desirable to control the deposition rate on each element. As one of the methods, a multi-source vacuum vapor deposition method, in which a plurality of electron guns are used and elements forming a film can be individually vapor-deposited, is considered promising.

In general, the method of controlling the composition of a film in the multi-source deposition method uses the same number of film thickness sensors as the number of evaporation sources, and the irradiation energy amount for each evaporation source during film formation based on the measured values. Method, a film thickness sensor is provided at the substrate position in advance before vapor deposition, and the vapor deposition rate with respect to the irradiation energy amount, irradiation time, etc. is obtained in advance for each vapor deposition source (for example, Jpn.J.Appl.Phys. 28 (1989)
L1217-L1219), and can be roughly divided into. But,
In the method (1), the apparatus system becomes expensive, the film forming chamber becomes large, and an error occurs due to the evaporation flow received by each film thickness sensor from another evaporation source. Furthermore, since each film thickness sensor cannot be installed at the substrate position, it is difficult to accurately grasp the evaporation amount. Further, in the method (1), since the evaporation amount obtained in advance is different from that during film formation, the reproducibility of the film formation composition ratio is poor.

Further, it is difficult to stably produce a Bi-based oxide superconducting film having a predetermined composition by such electron beam multi-source deposition method for the following reasons.

(A) Constituent element of Bi-based oxide superconductor
Since the difference between the melting point and the boiling point of the group IIa element is small at 900 ° C. or less, local heating by the electron beam causes bumping (splash), which tends to make the evaporation amount unstable.

(B) Due to the change in shape of the electron beam irradiation surface due to the introduced gas during the film formation, the evaporation amount sharply decreases with the passage of time at a constant heating output.

[0008]

As described above, the method of producing a Bi-based high Tc phase superconducting film, which requires a strict composition control by the electron beam multi-source deposition method, is a method which has been used so far. It can be said that it is extremely difficult to follow.

An object of the present invention is to provide a method for easily producing a Bi-based oxide superconducting film composed of a high Tc phase single phase in an electron beam multi-source deposition method.

[0010]

[Means for Solving the Problems] Regarding the production of Bi-based oxide superconductors, the following facts are already known.

(1) When a group IIa element and an alloy mainly composed of these elements are used as the evaporation source, the evaporation amount with respect to a constant electron beam heating output is unstable because bumping easily occurs, and the electron beam The shape of the irradiation surface changes with time, and thus is significantly reduced.

(2) Bi-based oxide superconductor (bulk material) is
A high Tc phase is difficult to form even if it is manufactured by a normal solid phase method (a method of mixing oxide raw material powders containing each element in an arbitrary composition ratio and sintering at high temperature), and a low Tc phase or a semiconductor phase is generated. It becomes a mixture with. However, when Pb oxide is added to the above mixed powder and sintered, the volume fraction of the high Tc phase easily increases without strict composition control (Phys. Rev. B38 (1988) 893).

On the other hand, the present inventors have obtained the following findings.

(3) When the Pb oxide containing one or more IIa group elements is evaporated by electron beam irradiation,
Pb evaporates stably at a constant rate.

Based on the above-mentioned facts (1) to (3), the present inventors have decided to use a Group IIa element as a vapor deposition source for Group IIa element in order to obtain a Bi-based oxide superconducting film consisting of a high Tc phase single phase. It was confirmed that it was effective to use the element-Pb-O sintered body, and the present invention was completed.

The gist of the present invention is to use, as a vapor deposition source, a Pb oxide containing at least one element of the IIa group elements which are constituent elements of the oxide superconductor to be produced, and IIa as a substrate, The substrate temperature is set using an oxide single crystal or polycrystal composed of one or more elements of the IIIa and IVa group elements.
500 to 800 ° C., under the condition of a vacuum degree of 10 ⁰ to 10 ^-3 Torr on the substrate surface, method of manufacturing the Bi-based oxide superconducting film, characterized by forming a film by an electron beam multi-source evaporation method " It is in.

The above-mentioned Pb oxide contains Sr, Ca, Bi and the like which are constituent elements of the Bi-based oxide superconductor, and specifically, Sr ₅ PbOy, Ca ₂ PbO ₄ , Ca ₇ Bi. ₃ Pb ₃ O ₁₆ and the like.

As the substrate, if it is a single crystal or a polycrystal of an oxide composed of one or more elements of the IIa, IIIa and IVa group elements, those usually used in the vapor deposition method can be used. ..

[0019]

In the present invention, the use of an oxide (single crystal or polycrystal) made of at least one element of the IIa, IIIa and IVa elements as the substrate is due to the lattice constant with the oxide superconductor. This is because the difference is relatively small and the crystallinity of the film formation is high.

The substrate temperature is limited to 500 to 800 ° C.
If the substrate temperature is below 500 ° C, the deposited film will become amorphous,
This is because when the temperature exceeds 800 ° C, a superconducting phase is not formed due to precipitation of Ca or Cu oxides.

[0021] In addition, when the degree of vacuum is less than 10 ⁰ Torr,
The mean free path of each evaporated particle (atom, molecule) is extremely short at 0.1 mm or less, and the size of the reaction chamber is restricted, making it difficult to introduce multiple electron guns, shutters, and other substrates into the chamber. Becomes Also, the degree of vacuum is 10 ^-3 To
If it exceeds rr, the oxidizing atmosphere becomes thin, and the introduction of oxygen into the generated film becomes insufficient, making it difficult to manufacture the oxide superconducting film. Therefore, the degree of vacuum on the substrate surface is 10 ^0. ~ 10 ^-3
Limited to Torr.

One of the reasons why the source of the IIa group element, which is a constituent element of the oxide superconducting film, is a Pb oxide containing this element is that the deposition rate is rapidly decreased by the oxidation of the electron beam irradiation surface, and This is because it is possible to suppress the subsequent change in the deposition rate with time.

FIG. 1 shows, as a vapor deposition source, only Ca, Sr, and Ca.
-Pb-Ox and Sr-Pb-Oy is a diagram showing the temporal change of each deposition rate when performing vacuum deposition by electron beam irradiation, from this figure Pb oxide as a deposition source It was found that the rapid decrease in the deposition rate and the subsequent temporal change were considerably suppressed in the case of the presence.

Another reason for using Pb oxide is the ratio of the group IIa element to Pb (weight ratio, hereinafter simply referred to as Sr / Pb,
Ca / Pb, etc.) depends on the composition of the Pb oxide used as a vapor deposition source and the electron beam heating output, and by appropriately selecting them, the ratio of Group IIa element to Pb in the vapor deposited film can be set to a predetermined value. Because you can do it.

FIG. 2 and FIG. 3 respectively use Ca-Pb-based oxides and Sr-Pb-based oxides having various compositions,
Ca / Pb when evaporation is performed by changing the electron beam heating output
(Fig. 2) and Sr / Pb (Fig. 3). As is clear from these figures, by selecting an appropriate Pb oxide and controlling the heating output of the electron beam, Ca / Pb or Sr / Pb can be changed over a wide range.

As described above, the method of the present invention is characterized in that the Pb oxide containing the group IIa element, which is a constituent element of the oxide superconductor, is used as a vapor deposition source, and thereby the composition is strictly controlled. It is possible to easily control the composition of the oxide without using a high Tc phase single phase to obtain a Bi-based oxide superconducting film.

[0027]

Example A Bi-based oxide superconducting film having the target composition shown in Table 1 was prepared, and the film composition, crystal structure and superconducting properties were investigated.

As a vapor deposition source for each constituent element, pure metals were used in both the conventional example and the present invention example for Bi and Cu. Further, regarding Sr, pure metal was used in the conventional example, Sr ₅ PbOy was used in the present invention example, pure metal was used in Ca in the conventional example, and Ca ₂ PbO ₄ was used in the present invention example. Four electron guns were used, and the electron beam heating output was fixed in the range of 2 to 3 kW for Bi and Cu, and 4 to 6 kW for Sr and Ca. A magnesium oxide single crystal plate was used as the substrate, and vapor deposition was performed at a substrate temperature of 720 ° C. and an oxygen partial pressure on the substrate surface of 10 ⁻² Torr. The film composition was analyzed by ICP spectroscopy.

The investigation results are shown in Table 1, FIG. 4 and FIG.

[0030]

[Table 1]

As is clear from Table 1, in the example of the present invention,
Even if the composition was not strictly controlled, an oxide film having the target composition was easily obtained within a composition deviation of 12%.

FIG. 4 shows the conventional example No. 3 and the invention example No. 6 in Table 1.
In the X-ray diffraction pattern of, the peak of the high Tc phase (H in the figure) was observed in both the conventional example and the example of the present invention. In, low Tc phase (L in the figure) and semiconductor phase (S in the figure) peaks were observed.

FIG. 5 shows the results of a survey on superconducting properties. In the conventional example, the electrical resistance was zero at 82K (the point where the vertical axis intersects the horizontal axis represents zero). Shows that the film has only a high Tc phase single phase with a critical temperature of over 100K.

The atomic weight ratio of each element constituting the high Tc phase is B
i (Pb): Sr: Ca: Cu = 2: 2: 2: 3, and in the example of the present invention, a high Tc phase film is obtained although the composition ratio is slightly deviated. That is, according to the method of the present invention, it is possible to easily obtain a Bi-based oxide superconducting film composed of a high Tc phase single phase without performing strict composition control.

[0035]

EFFECTS OF THE INVENTION In producing a Bi-based oxide superconducting film, by applying the method of the present invention in which a Pb oxide containing a group IIa element that is a constituent element of this oxide is used as a vapor deposition source, it is possible to easily obtain a high Tc. It can be a superconducting film composed of a single phase.

[Brief description of drawings]

FIG. 1 is a diagram showing a temporal change in a deposition rate when a Pb oxide containing a group IIa element is used as a deposition source.

FIG. 2 shows electron beam heating output and Ca / in vapor deposition film when Ca-Pb based oxides having various compositions are used as vapor deposition sources.
It is a figure which shows the relationship of Pb (weight ratio).

FIG. 3 shows electron beam heating output and Sr / in the deposited film when Sr—Pb based oxides having various compositions are used as the deposition source.
It is a figure which shows the relationship of Pb (weight ratio).

FIG. 4 is a diagram showing an X-ray diffraction pattern of a Bi-based oxide superconducting film obtained in an example.

FIG. 5 is a diagram showing superconducting properties of Bi-based oxide superconducting films obtained in Examples.

Claims (1)

Claim: What is claimed is: 1. As a vapor deposition source, a Pb oxide containing one or more elements of the IIa group elements which are constituent elements of the oxide superconductor to be produced is used, and the substrate is IIa. , an oxide single crystal or polycrystalline consisting of one or more elements of III a and IVa group elements, a substrate temperature of 500 to 800 ° C., under the condition of a vacuum degree of 10 ⁰ to 10 ^-3 Torr on the substrate surface 2. A method of manufacturing a Bi-based oxide superconducting film, which comprises forming the film by an electron beam multi-source deposition method.