JP3015393B2 - Method for producing oxide superconductor thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a method for producing an oxide superconductor thin film.

(Prior Art) In order to apply an oxide superconductor having a high critical temperature, which has recently attracted attention, to an electronic device, it is essential to make the oxide superconductor thinner. Attempts have been made to form such a thin film of oxide superconductor by a sputtering method, an evaporation method, or the like.

When forming an oxide superconductor thin film by these methods, the crystallization is promoted by forming the film on a substrate heated to a high temperature of 600 ° C. or higher, or the oxide superconductor is formed on a substrate in a low temperature state. After depositing the components, 900
Generally, heat treatment is performed in an oxygen atmosphere at about ° C to crystallize.

However, the temperature history of the oxide superconductor thin film at a high temperature by the formation method described above causes the oxide superconductor to be in a polycrystalline state by causing disordered grain growth,
In addition, the formation of a reaction layer between the thin film and the substrate is caused to cause problems such as deterioration of superconductivity.

(Problems to be Solved by the Invention) As described above, when the oxide superconductor experiences a high temperature state in the process of forming the thin film, polycrystallization of the oxide superconductor and deterioration of superconductivity are caused. In addition, if the film is formed at a reduced substrate temperature, the film cannot be sufficiently crystallized, and the superconductivity is significantly deteriorated. On the other hand, in order to apply an oxide superconductor to an electronic device, a single crystal epitaxially grown film having excellent superconductivity is indispensable.

For this reason, it is an important subject to sufficiently crystallize the oxide superconductor thin film by a low-temperature process in applying the oxide superconductor thin film to the device. Also, when actually applying an oxide superconductor thin film to an electronic device,
Coexistence with a semiconductor is indispensable, and therefore crystallization in a low-temperature process becomes even more important.

The present invention has been made to address such a problem, and provides a thin-film oxide superconductor that promotes crystallization of an oxide superconductor in a low-temperature process and enables application to an element. The purpose is to do so.

[Constitution of the Invention] (Means for Solving the Problems) That is, the oxide superconductor of the present invention is a thin-film oxide superconductor formed on a single-crystal adherend substrate, The oxide superconductor thin film is inclined at an angle of 3 to 8 degrees from any one of the (100) crystal plane, the (110) crystal plane, and the (111) crystal plane of the single crystal body. The film is formed on the oxide superconductor thin film forming surface of the substrate to be formed.

Many oxide superconductors are known.In the present invention, oxide superconductors having a perovskite-type structure containing a rare earth element, and oxide superconductors such as Bi-based, Tl-based, and Pb-based Has been applied.

The oxide superconductor containing a rare earth element and having a perovskite structure may be any material capable of realizing a superconducting state, and is a RE M ₂ Cu ₃ O _7-δ system (RE is Y, La, S
M is at least one element selected from rare earth elements such as c, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu;
a, Sr, at least one element selected from Ca, δ represents an oxygen vacancy, usually a number of 1 or less, and part of Cu is Ti, V, C
Replaceable with r, Mn, Fe, Co, Ni, Zn, etc. )) And the like.

The Bi-based oxide superconductor is represented by a chemical formula: Bi ₂ Sr ₂ Ca ₂ Cu ₃ Ox (I): Bi ₂ (Sr, Ca) ₃ Cu ₃ Ox (II) And the Tl-based oxide superconductor includes a chemical formula: Tl ₂ Ba ₂ Ca ₂ Cu ₃ Ox …… (III): Tl ₂ (Ba, Ca) ₃ Cu ₂ Ox …… (IV) Are represented.

Examples of the method for forming the oxide superconductor thin film in the present invention include an electron beam evaporation method, a laser evaporation method,
Cluster ion beam method, magnetron sputtering method,
Various known thin film forming methods such as an ion beam sputtering method and a plasma CVD method can be applied.

The substrate to be used in the present invention is a single crystal (10
0) A plane inclined from 3 to 8 degrees from any one of the crystal plane, the (110) crystal plane and the (111) crystal plane, for example, a polished surface as a surface on which the oxide superconductor thin film is formed. is there. MgO, S
Examples thereof include a single crystal of an oxide such as rTiO ₃ , Y-stabilized ZrO ₂ , LiAlO ₃ , and LaAlO _3, and a single crystal of a semiconductor such as Si and GaAs.

The polishing direction is not particularly limited as long as the polishing surface to be the oxide superconductor thin film forming surface is inclined within a range of 3 degrees to 8 degrees from any one of the crystal planes described above. It is more preferable to select the (100) crystal plane or the (110) crystal plane of the above-mentioned material as the designated crystal plane. This is because excellent lattice constant matching with the oxide superconductor is achieved, and epitaxial growth is easier.

Here, the reason why the inclination angle of the polished surface is set in the above range is as follows. If the angle of the polished surface from the crystal plane is less than 3 degrees, crystallization at low temperature cannot be sufficiently promoted, and if this angle exceeds 8 degrees, the film surface becomes rough and polycrystalline. This is because

In the present invention, the substrate temperature at the time of forming the oxide superconductor thin film is not particularly limited, but can be set to 600 ° C. or lower. This is achieved by lowering the crystallization temperature of the oxide superconductor by making the thin film formation surface a polished surface at a predetermined angle. By setting the substrate temperature at a low temperature of 600 ° C. or lower, a single crystal film that has been successfully epitaxially grown can be obtained.

(Operation) In the oxide superconducting thin film of the present invention, a polished surface inclined from 3 to 8 degrees from a predetermined crystal plane of the single crystal body is used as an oxide superconductor thin film forming surface, and the polished surface is formed on the polished surface. It is a film formed. Here, when the polished surface is considered at the atomic level, it has a step at the atomic layer level. Considering that the film formation process starts crystal growth with some kind of defect such as a kink as a nucleus, the polished surface has many crystal growth nuclei. Therefore, the crystal growth is promoted even in the low-temperature process, and it is possible to obtain a sufficiently crystallized thin-film oxide superconductor.

(Example) Next, an example of the present invention is described.

Examples 1 to 4 First, a single crystal of SrTiO ₃ was used
As shown in the figure, the (100) crystal plane 2 of the SrTiO ₃ single crystal 1
3 degrees, 4 degrees, 7 degrees, polishing at each angle θ of 8 degrees,
A single-crystal substrate having the polished surface 3 as a surface on which an oxide superconductor thin film was formed was manufactured. The normal vector of the polished surface was such that the direction of the projection vector on the (100) plane was the [010] direction or the [001] direction.

Next, a Y-Ba-Cu-O-based oxide superconductor thin film was formed on each of the single crystal substrates by a reactive sputtering method under the following conditions. The sputtering gas used was an argon mixed gas containing 50% oxygen gas, the sputtering pressure was set to 0.65 Pa,
An oxide having a basic composition of Y: Ba: Cu = 1: 2: 3 was sputtered on the polished surface 3 of the single crystal substrate heated to 550 ° C. to form a film having a thickness of 0.3 μm.

After film formation in this manner, each thin film was annealed at 500 ° C. for 1 hour in an oxygen gas stream of 1 atm.

The composition of each oxide superconductor thin film thus obtained is
It was confirmed by X-ray diffraction that it was Y ₁ Ba ₂ Cu ₃ O _7-δ . Further, the temperature change of the resistance of each Y-based oxide superconductor thin film was measured to determine the transition temperature (Tc). In addition, the surface condition was observed. Table 1 shows the results.

Further, as a comparison with the present invention, SrTi in which the inclination angle θ of the polished surface in the above embodiment was set to 0 °, 2 °, 9 °, and 10 °
O ₃ single-crystal substrates were prepared, and a Y-based oxide superconductor thin film was formed under the same conditions as in the above examples. The transition temperature was measured and the surface state was observed for these films. Table 1 also shows the results.

As is clear from Table 1, each oxide superconductor thin film obtained in each of Examples 1 to 4 exhibited a transition temperature equal to or higher than the temperature of liquid nitrogen, and had a smooth and single-crystal surface state. On the other hand, the oxide superconductor thin films according to Comparative Examples 1 and 2 did not show a superconducting state, or at a very low temperature. Further, the oxide superconductor thin films according to Comparative Examples 3 and 4 did not decrease the transition temperature so much, but the film surface was roughened and polycrystallized, and could not be put to practical use as an electronic device or the like. In these, the diffraction images of the oxide superconductor thin films according to the examples were sharp streak-like by high-speed reflection electron diffraction, whereas the diffraction images of the oxide superconductor thin films according to Comparative Examples 3 and 4 were ring-shaped. Was also confirmed.

In each of the above embodiments, the example in which the manufacturing method of the present invention is applied to the Y-based oxide superconductor has been described. However, by forming a film on a polished surface in the same manner as in the above-described embodiment, other rare earth-based The method of the present invention can be applied to the production of all oxide superconductor thin films such as and superconducting oxides.

[Effects of the Invention] As described above, according to the present invention, since a film is formed on a polished surface including many nuclei for crystal growth during film formation,
Crystal growth is greatly promoted, and an oxide superconductor thin film which is sufficiently crystallized and has excellent superconductivity can be obtained even on a substrate in a low temperature state.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a single crystal substrate shown in one embodiment of the present invention. 1 ... single crystal, 2 ... (100) crystal face, 3 ... polished face.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-82576 (JP, A) JP-A-64-52323 (JP, A) JP-A-1-95411 (JP, A) JP-A-1-95411 175115 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 1/00-23/08

Claims (1)

(57) [Claims] 1. An oxide superconductor thin film forming surface of a substrate to be formed of a single crystal body is formed by a (100) crystal plane and a (110) crystal plane of the single crystal body.
A plane inclined from 3 ° to 8 ° from any one of the crystal planes selected from the crystal plane and the (111) crystal plane; A method for producing an oxide superconductor thin film, comprising forming an oxide superconductor thereon.