JP2736062B2 - Method for producing oxide superconductor thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for producing an oxide superconductor thin film used for various superconductor devices and the like. (Prior Art) In recent years, since it was announced that Ba-La-Cu-O-based layered perovskite-type oxides may have a high critical temperature, research on oxide superconductors has been performed at a famous place. (Z.Phys.B Condensed Matter 64,189-193 (198
6)). Among them, LnBa ₂ Cu ₃ O _7-δ having an oxygen deficiency represented by a Y—Ba—Cu—O system (δ represents an oxygen vacancy, usually 1 or less, and Ln is Y, La, Sc, Nd, Sm, Eu, Gd, Dy, H
At least one element selected from o, Er, Tm, Yb and Lu: part of Ba can be replaced by Sr or the like. The critical temperature of the defective perovskite-type oxide superconductor indicated by) is 90K.
Because of the above and high temperature higher than the boiling point of liquid nitrogen, it is attracting attention as a very promising material. (Phys. Rev. Lett.vo
l.58 No.9,908-910). In order to use such an oxide superconductor as various electronic devices, thinning techniques of the oxide superconductor have been studied in various places. As a method of depositing an oxide superconductor as a thin film on a substrate, a method using a conventional thinning technique, a method using a vapor deposition method, a sputtering method, or the like, or a method using an oxide superconductor powder as a paste. Attempts have been made to form a film by applying and baking a solution or a solution of a thermally decomposable compound of each element constituting the oxide superconductor. (Problems to be Solved by the Invention) Among the above-mentioned methods, however, for example, in a normal sputtering method or a vacuum evaporation method using a sintered body of an oxide superconductor as a target or an evaporation source, the substrate temperature is low. Due to the high temperature, there is a problem that it is difficult to control the composition of the formed film components, that is, the reproducibility of the oxide superconductor film is poor. In addition, a magnetron sputtering method with a high film formation rate and high purity of the obtained film has been attempted, but the crystallinity of the obtained oxide superconductor film is low, and after forming the film, the film is further subjected to a high temperature of about 900 ° C. Unless heat treatment is performed, there is a problem that sufficient superconductivity is not exhibited. In addition, in the method of applying and baking a paste of oxide superconductor powder or a compound solution of each constituent element, it is difficult to control the film thickness, or it cannot be uniformly crystallized, and a partially different phase is formed, There are problems such as low superconductivity. The present invention has been made to solve such a problem, and an object of the present invention is to provide a method for producing an oxide superconductor thin film having excellent reproducibility and excellent crystallinity. [Constitution of the Invention] (Means for Solving the Problems) In the first method for producing an oxide superconductor thin film of the present invention, when forming an oxide superconductor thin film on a base material, At the same time each element produced by heating and evaporating each metal element constituting the body is caused to collide with the base material at a predetermined ratio, and at the same time, oxygen ions are formed as an ion beam in excess of the stoichiometric ratio of the oxide superconductor. By supplying, the oxide superconductor thin film is formed.
Further, in the second method for producing an oxide superconductor thin film, in forming an oxide superconductor thin film on a substrate, each element produced by heating and evaporating each metal element constituting the oxide superconductor is described. Ionization, and then accelerated by an electric field to collide with the substrate at a predetermined ratio, while simultaneously supplying oxygen ions as an ion beam in excess of the stoichiometric ratio of the oxide superconductor, The method is characterized in that the oxide superconductor thin film is formed. Although many oxide superconductors are known, it is practically preferable to use a rare-earth-element-containing provskite-type oxide superconductor having a high critical temperature. The oxide superconductor containing a rare earth element and having a perovskite structure here may be a superconducting state,
LnBa ₂ Cu ₃ O _7-δ (Ln is Y, La, Sc, Nd, Sm, Eu, Gd, D
At least one element selected from rare earth elements such as y, Ho, Er, Tm, Yb, and Lu is represented by δ, which is an oxygen deficiency, usually 1 or less; and part of Ba can be replaced with Sr. ) And oxides having a perovskite structure in a broad sense such as a layered ovskite type having an oxygen deficiency and a layered ovskite type such as an Sr—La—Cu—O system. Rare earth elements are also defined in a broad sense and include Sc, Y and La-based elements. As a typical system, in addition to Y-Ba-Cu-O system, Y is Yb, Ho,
Sc-Ba substituted with rare earths such as Dy, Eu, Er, Tm, and Lu
-Cu-O-based, Sr-La-Cu-O-based and the like. The method for producing the oxide superconductor thin film of the present invention will be described in more detail. First, each metal element constituting the target oxide superconductor is heated and evaporated to produce a group of each element. As the evaporation source, a single metal or oxide of each element can be used. Particularly, the use of a pure metal having high purity is preferable because the composition can be easily controlled. Next, the group of each element is ionized by, for example, passing through a plasma, and the group of ionized elements is accelerated by an electric field to collide with a substrate.
The supply amount of each element is acceptable even if it slightly deviates from the stoichiometric ratio of the target oxide superconductor, but in order to form a higher-purity oxide superconductor thin film, It is important to control the supply amount of the gas accurately. At the same time as the supply of each metal element, oxygen ions are supplied in excess of the stoichiometric ratio of the target oxide superconductor. The supply of the oxygen ions is performed, for example, in the form of a beam using an ion gun. The supply amount of the oxygen ions is, for example, about 0 to 100 atoms to 1 atom of Ln in the case of a defect perovskite-type oxide superconductor represented by LnBa ₂ Cu ₃ O _7-δ. is there. In this way, by depositing a group of metal elements constituting the oxide superconductor and supplying an excessive amount of oxygen, an oxide superconductor thin film can be formed with good reproducibility. As the substrate used in the present invention, the linear expansion coefficient in the plane direction is preferably in the range of ^{5 × 10 -6 / K~25 × 10} -6 / K. If the coefficient of linear expansion in the surface direction of the substrate is out of the range of 5 × 10 ⁻⁶ / K to 25 × 10 ⁻⁶ / K, the difference in coefficient of linear expansion with the oxide superconductor becomes too large, and It is easy to peel off from Examples of such a base material include the following. (Base material) (linear expansion ^{_{coefficient) LiNbO 3 15.4 × 10 -6 /}} K LiTaO 2 16.1 × 10 -6 〃 SrTiO ₃ 11.2 × 10 ^-6 〃 ZrO ₂ 8 × 10 ^-6 〃 Al ₂ O ₃ 8 × 10 ^{- 6} 〃 MgO 13 × 10 ^-6 〃 Ag 19.3 × 10 ^-6 〃 Pd 12 × 10 ^-6 〃 The shape of the substrate is not limited to the substrate shape. It is also possible to use. (Operation) In the present invention, the oxide superconductor thin film is formed by a so-called cluster ion beam method in which each metal element constituting the film is made to fly as a group, thereby forming a film. By hitting the substrate with
This group of elements diffuses on the base material, resulting in an excellent film formation rate. Further, in the present invention, since the crystallinity of the oxide superconductor is improved by supplying an excessive amount of oxygen, even if the temperature of the substrate is lower than that of a conventional sputtering method, for example, 500 ° C. to 700 ° C. An oriented oxide superconductor thin film can be formed with good reproducibility even at about ° C, and an oxide superconductor thin film having excellent superconducting properties can be obtained without performing heat treatment after this film formation step. (Example) Next, an example of the present invention is described. Example First, using 3N purity Y, Ba and Cu as evaporation sources,
These were housed independently in three crucibles arranged in a vacuum vessel. On the other hand, a 10 mm × 10 mm × 1 mm MgO substrate was used as a substrate to be attached, and this was set at a predetermined position in a vacuum vessel. Then, the inside of the vacuum vessel is evacuated to about 1 × 10 ⁻⁵ Torr, and each of the above-mentioned crucibles is heated by a heater to evaporate a group of each element, and the group of each element is passed through an ionization section. The ionized elements were further accelerated by an electric field (acceleration voltage: 1 kV) and supplied to the substrate. The supply amounts of these elements are Y, B
a, Cu were adjusted so that the atomic ratio was 1: 2: 3. Simultaneously with the supply of each element, oxygen ions were supplied as an ion beam by an ion gun onto the substrate such that the atomic ratio of oxygen was 10. This series of operations was performed for 100 minutes to form an oxide superconductor thin film. The substrate temperature during this operation was set to 600 ° C. When the crystal phase of the oxide superconductor thin film thus obtained was identified by chemical analysis and X-ray diffraction, it was a single phase of Y ₁ Ba ₂ Cu ₃ O _6.8 phase, which is the conductor phase. It was excellent. The thickness was 1 μm. When the superconducting properties of this oxide superconductor thin film were measured, good results were obtained with a critical temperature of 85 K and a critical current density of 2 × 10 ⁴ A / cm ² . On the other hand, as a comparison with the present invention, a film was formed under the same conditions except that the supply amount of oxygen in the above example was set to 7 in atomic ratio, and the characteristics of the film were measured. However, a superconducting state was not obtained. Was. From the identification of the crystal phase, it was found that the amount of oxygen was small, so that the phase was not a superconductor phase. [Effects of the Invention] As is clear from the above examples, according to the first method for producing an oxide superconductor thin film of the present invention, reproducibility can be achieved without performing heat treatment for crystallization after film formation. An oxide superconductor thin film excellent in superconductivity can be obtained. According to the second method for producing an oxide superconductor thin film of the present invention, ions of each constituent metal element are caused to fly as a group, and oxygen is supplied in excess of the stoichiometric ratio. An oxide superconductor thin film having excellent reproducibility and excellent superconducting properties can be obtained without being subjected to a heat treatment for crystallization after film formation, as well as being excellent in speed and crystallinity.

Claims (1)

(57) [Claims] In forming the oxide superconductor thin film on the base material, simultaneously colliding each element generated by heating and evaporating each metal element constituting the oxide superconductor on the base material at a predetermined ratio, A method for manufacturing an oxide superconductor thin film, comprising forming the oxide superconductor thin film by supplying oxygen ions as an ion beam in excess of the stoichiometric ratio of the oxide superconductor. 2. In forming the oxide superconductor thin film on the base material, a group of each element generated by heating and evaporating each metal element constituting the oxide superconductor is ionized, and then accelerated by an electric field to accelerate the base material. Forming an oxide superconductor thin film by supplying oxygen ions as an ion beam in excess of the stoichiometric ratio of the oxide superconductor at the same time as bombarding the oxide superconductor at a predetermined ratio. Of manufacturing superconductor thin film. 3. 3. The method according to claim 1, wherein the oxide superconductor is a perovskite-type oxide superconductor containing a rare earth element. 4. The oxide according to claim 1 or 2, wherein the oxide superconductor contains a rare earth element, Ba and Cu in an atomic ratio of substantially 1: 2: 3. Manufacturing method of superconductor thin film. 5. The oxide superconductor has an oxygen-defective perovskite structure represented by LnBa ₂ Cu ₃ O _7-δ (Ln represents at least one element selected from rare earth elements, and δ represents an oxygen defect). 3. The method for producing an oxide superconductor thin film according to claim 1 or 2, wherein the method is a superconductor.