JPH0492816A - Production of thin-film superconductor - Google Patents

Abstract

PURPOSE:To excellently obtain a thin film having a crystal structure of a Pb- based superconductor by specifying oxygen partial pressure in a preparation atmosphere. CONSTITUTION:A thin-film superconductor containing principal components composed of Pb, at least one element (A) selected from alkaline earth metallic elements, at least one element (Ln) selected from rare earth elements and Cu is formed on a substrate heated at 400-600 deg.C by regulating the oxygen partial pressure in a preparation atmosphere to <=0.1Pa and using a molecular-beam epitaxial, electron beam vacuum deposition, ion beam sputtering or laser vacuum deposition method.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing an oxide superconductor thin film having a high critical temperature. discovered an oxide superconductor with a perovskite-like structure.9 Since then, superconductivity has been confirmed in various oxide systems. Superconducting ceramics 4
It was discovered that superconductivity has a critical temperature of about L70 [R, J, Cava, B,
8') ori' (Batlogg), J, J,
Krajewski, L.
W, Rupp, L, F, Six
Schnee IIlayer, T.
ν1-Siegrist, R,B,
77 van Dover, P
, v Luci x (Marsh), W, F, to a,
Peck, Jr.
(Gallagher), S.H.
larum), J.H. Marshall
ll), RoC, Farrow,
J, V, Waszczak, R
, Hull and P.

Torehe'-(Trevor), Nat+-(Nat
ure), Vol. 336. 211-214
(1988)] As a result of detailed analysis, this material has a layered structure similar to other high-temperature oxide superconductors, and has a perovskite structure unit).
(A, Ln) Two layers of CuO* are adjacent to PbO-Cu-
Even if the structure is sandwiched between PbO block layers, the ideal chemical composition is (P bpc u ) (A, Ln) s C
u t Ox, and as a representative substance (PbpCu
)S r s (Y, Ca )CueO- is known, and the problem that the invention seeks to solve.However, with current technology, Pb-A-Ln-Cu-0-based materials can only be formed through the process of sintering. 1. Only available in ceramic powder or block form. % -4, When this type of material is put into practical use, it is strongly desired to process it into a thin film (unlike other oxide superconductors, it is extremely difficult to process this type of material into a thin film). A method for producing a thin film superconductor according to the present invention, which is a method for solving problems that are considered difficult to solve.The main component is lead (
Pb), alkaline earth element (A), rare earth element (Ln)
, oxide superconductor thin film Pb-A-L made of copper (Cu)
In the production of n-Cu-○, it is necessary to reduce the oxygen partial pressure in the production atmosphere to 0.1 Pa or less.In the production of conventional oxide superconducting thin films, it is important to promote oxidation of the thin film, and it is possible to As long as the power to increase the oxygen partial pressure in the fabrication atmosphere is ＼ or instead of normal oxygen molecules, active acid sites with higher oxidizing ability atomic acid sites are manufactured using ozone. When applied to a certain Pb-based superconductor Pb-A-Ln-Cu-○, the present inventors were unable to obtain the crystal structure of a superconductor in a thin film (despite being an oxide material). By extremely lowering the oxygen partial pressure in the production atmosphere, they discovered that a thin film with a crystalline structure of a Pb-based superconductor could be obtained surprisingly well below a certain oxygen partial pressure. It is not certain whether a thin film structure can be formed when the partial pressure is low. It is thought that this is because the valence of the metal element in the PbO-CuPbO block layer is low, and excessive oxidation will destroy the structure of the block layer. It is better to have a moderately low oxygen partial pressure.The upper limit is about 0.1 Pa.9 Also, this type of material has a relatively low base temperature during fabrication4.
We also discovered that it can be fabricated at temperatures between 00 and 600 degrees Celsius.We also confirmed that if the substrate temperature were higher than this, the Pb element in the film would re-evaporate, so it was confirmed that the crystal structure of a Pb-based superconductor could not be obtained. In particular, when producing thin films of this type by sputtering deposition, a mixture of oxygen and inert gas is normally used as the sputtering gas for oxide thin films, but if only an inert gas that does not contain oxygen is used, a good Pb-based film can be produced. MBB must be confirmed that a superconducting thin film can be obtained.
When producing thin films of this type using high-vacuum deposition equipment such as electron beam evaporation, ion beam sputtering, or laser evaporation, active acid black with strong oxidizing power, which is often used in the production of ordinary oxide superconductor thin films, is used. Atomic acid black It was confirmed that there is no need to use a special gas such as ozone, and that it can be produced in a high vacuum of 10-2 Pa or less near the substrate. Examples of particularly effective examples In order to provide a deeper understanding of the content of the invention by the present inventors, the following is an explanation using specific examples. Example 1 Using a high-frequency magnetron sputtering device, A sputtering target (YoPb5S r
tY+, a6cam, 〒cu*, SO6 diameter 80mm
A disk of MgO single crystal (10
0) On the plane substrate E, under sputtering gas of 0.5 Pa,
A 1.% thin film was prepared by sputtering discharge at 100 W, and about 2,000 P bers were deposited in about 30 minutes.
Thin films of aYs, sCa@, and 5cusQx were formed. The characteristics of the films produced were investigated by changing the argon/oxygen mixing ratio in the sputtering gas. Figure 1 (a), (b), (c)
G-02/Ar=1/3 (oxygen partial pressure 0.125Pa:
The X-ray diffraction patterns of thin films made with sputtering gases of sample a), Oe/A r = 174 (oxygen partial pressure 0.1 Pa: sample b), and pure argon (sample C) are shown, respectively. The film of sample a prepared at an oxygen partial pressure of 0.125 Pa is an insulator, and the X-ray pattern shows the appearance of other layers. Pb shown as
Although it was confirmed that the structure of a Pb-based superconductor was formed, in the case of sample C, in which oxygen was further reduced and a sputtering gas containing only pure argon was used, a Pb-based superconducting thin film with good C-axis orientation was obtained. 9. The lattice constant of this film is c=15.7
There are 5 people, and there is no connection with Pb-based superconducting ceramics.
From this result, it was found that the crystal structure of a Pb-based superconductor can be obtained when the oxygen partial pressure during sputter deposition is 0.1 Pa or less. The thin film showed superconducting transition even in its original state (reproducibility and characteristics improved by heat treatment at 300°C for 30 minutes in air).
c) are the characteristics of sample b and sample C, respectively.
Sample B showed superconductivity at 50, and sample C showed superconductivity at 85.When sputter deposition of Pb-based superconductor was performed using only inert gas without oxygen in the sputtering gas, sample C showed superconductivity at 85. It was found that a good crystal structure and superconducting properties can be obtained as shown in Table 3. Also, the substrate temperature at which superconducting properties can be obtained Example 2 MBE device, which was 400 to 600°C, lower than conventional oxide superconductors A Pb-3r-Y-Ca-Cu-0 thin film was prepared using Pb-3r-Y-Ca-Cu-0 thin film using PbO compound, Sr metal, Y metal, Ca metal, and Cu metal as raw materials. Each element can be evaporated individually
After the vapor deposition chamber was evacuated to below 10-'Pa, vapor deposition was performed on the MgO substrate heated to 550°C. Step 9: During film formation, oxygen gas is introduced into the deposition chamber.The degree of vacuum near the substrate is 1.
A thin film with the crystal structure of a Pb-based superconductor can be obtained at a pressure of 0-2 Pa or less. A very small amount of oxygen is sufficient without using oxygen. Also, the structure of a Pb-based oxide superconductor can be obtained without introducing oxygen gas.
It is thought that this is because oxygen from bO is supplied to the membrane.
Therefore, if oxides are used as raw materials in such high vacuum evaporation equipment, there is no need to use oxygen gas in the production of Pb-based superconducting thin films, making it possible to easily produce thin films.
At this time, the degree of vacuum near the substrate is a fairly high vacuum of 10-'Pa, and precise structural control such as atomic layer control is possible. It was confirmed by backscattered electron diffraction that the obtained thin film was an epitaxial thin film whose c axis was oriented perpendicularly and whose crystal orientation was aligned with that of the Mgo substrate. Effects The method for producing a thin film superconductor according to the present invention ζL This is the first method that makes it possible to produce a Pb-based oxide superconducting thin film, which could not be obtained in the past.Especially for producing thin films of this type of material (
We discovered that it does not require much oxygen and can be synthesized at relatively low temperatures, making it possible to easily produce superconducting thin films using simple equipment.Therefore, we have developed a method for producing thin film materials that is optimal for device applications. can also provide

[Brief explanation of the drawing]

Figure 1 shows Pb-3r-Y-C in one embodiment of the present invention.
a - X-ray diffraction pattern of Cu-0 thin film Fig. 2 is a temperature characteristic diagram of electrical resistance in the thin film obtained in the same example. l) Figure ma(k)

Claims (4)

[Claims] (1) The main components are lead (Pb) and alkaline earth elements (A
), rare earth element (Ln), and copper (Cu) in the production of an oxide superconductor thin film, a method for producing a thin film superconductor, characterized by reducing the oxygen partial pressure in the production atmosphere to 0.1 Pa or less. . Here, A represents at least one element among alkaline earth elements, and Ln represents at least one element among rare earth elements. (2) The method for producing a thin film superconductor according to claim 1, characterized in that the temperature of the substrate during production is maintained at 400°C to 600°C. (3) The method for producing a thin film superconductor according to claim 1, wherein the thin film is formed using sputtering vapor deposition, and the sputtering gas used at that time is only an inert gas. (4) Thin film production is performed using molecular beam epitaxy (MBE), electron beam evaporation, ion beam sputtering, or laser evaporation, and the degree of vacuum near the substrate is 10
2. The method for producing a thin film superconductor according to claim 1, wherein the pressure is ^-^2 Pa or less.