JPH01203218A - Production of thin oxide superconducting film - Google Patents

Abstract

PURPOSE:To increase transition temp. and to reduce unevenness by successively vapor-depositing Ln (Y or lanthanoid), Ba and Cu as metals in a prescribed ratio to form a unit layer, laminating such layers on a substrate and treating the resulting laminated film under prescribed conditions. CONSTITUTION:Ln, Ba and Cu as metals are successively vapor-deposited in 1:2: 3 ratio in the number of atoms. to form a unit layer and such layers are laminated on a substrate. The resulting laminated film is heated in vacuum or in an atmosphere in which no chemical reaction takes place between the metals. By the heating, counter diffusion is caused between the layers and a uniform alloy is formed. This alloy is heat-treated in gaseous oxygen.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing an oxide superconducting thin film.

[Prior Art] Superconductivity is a phenomenon in which electrical resistance becomes τ below a certain temperature. Figure 3 shows typical resistance/temperature characteristics. The temperature at which resistance begins to decrease is the onset superconducting transition temperature "eo"
The temperature at which n+ becomes completely zero is the photoresistance superconducting transition temperature Tce
It is called nd. By the way, Ln, [1a2Cu30
It was discovered that an oxide with the composition formula 7-d (Ln is Y (yttrium) or a lanthanide element) is a superconductor with a higher superconducting transition temperature than any previously known substance. Now that its superconducting transition temperature Te@nd has exceeded the boiling point of liquid nitrogen, 77, the possibility of its application is attracting more and more attention. In order to apply this oxide superconductor to electronic devices, superconducting wiring, etc., thin film formation technology is essential.

Several methods have been reported as techniques for forming these oxide superconductor thin films. Broadly speaking, these methods include sputtering methods and vapor deposition methods.

As a typical example of the sputtering method, see Reference (1) 'Y.

Enomoto et al: Japan
se Journal of 8ppliedP
hysics, vol, 26. No, 7. p, 1
There is a method described in No. 1248,1. The manufacturing method according to this document will be explained below.

A sintered body made of Y-Ba-Cu-0 is used as the target material. First, by sputtering a target in a mixed gas of oxygen and argon,
A thin film made of Y-Da-Cu-0 is formed on an rTi03 substrate. The superconductivity of oxide superconductors is extremely sensitive to the composition, and even a slight deviation will cause a decrease in the superconducting transition temperature and loss of superconductivity. Therefore, if the atomic ratio of the elements in the formed thin film is The composition of the target is adjusted to an appropriate atomic ratio such that :Ba:Cu-1:2:3. Since it will not become a superconductor as it is, by removing it from the sputtering equipment after forming the thin film and applying appropriate heat treatment in oxygen gas, the superconducting transition temperature Tcend, defined as the temperature at which the electrical resistance drops, will reach 77 or higher. A thin film is produced. However, since the rate of sputtering from the target differs depending on each element, the composition ratio on the target surface changes as sputtering progresses, and as a result, the atomic ratio of the thin film formed on the substrate changes to Y:Ba:C.
It deviates from u=1:2:3. Therefore, Tcend
It has a serious drawback that the value is significantly lower than 77 and there is no reproducibility at all.

As a typical example of the vapor deposition method, see Document (2) rR, [l.

Laibowitz; Physical Revi
ew It, vol, 35. No.

16, p, 8821. There is a method described in The manufacturing method according to this document will be explained below.

Three metals, Y, Ba, and Cu, are loaded into separate hearths, and the three metals are simultaneously vapor-deposited using three independent electron beam sources. At that time, 101' Torr
An atmosphere of about .tau. of oxygen is introduced into the vacuum apparatus, and the deposition is performed in this background gas atmosphere. moreover,
By heating the substrate to about 450° C., oxidation progresses during vapor deposition.

Even if the film is co-deposited in an oxygen atmosphere, the amount of oxygen contained in the film is insufficient, so after the deposition is complete, heat treatment is performed at a temperature of 900 to 950°C in an electric furnace with oxygen gas flowing. . However, in this method, three metals are deposited simultaneously in an oxygen atmosphere, and the temperatures of the substrate and film thickness monitor are different, so Y, Ba, and Cu are deposited as in the former sputtering method.
It has the major drawback that it is difficult to accurately and reproducibly control the atomic ratio of There is.

[Problems to be Solved by the Invention] Both of the above two methods for forming oxide superconducting thin films have the fatal drawback that accurate control of the atomic ratio, which has the greatest effect on the superconducting properties of the thin film, cannot be reproducibly performed. are doing. As a superconducting thin film formation method that can solve this drawback, there is a method in which three metals are deposited in a stacked manner as described in the literature (3) 'B, Y, T
saur et al;
ics Letters, vol, 51. No.1
1. +1.858J, and also in the literature (4
) "Masashi Yamaki et al.: Proposed in Japanese Patent Application No. 52-268343 J.

In the method in document (3), first, Y, Ba and Cu
The three metals are arranged in the order of Cu-+Ba-+Y: Y:Ba:
Laminated vapor deposition is performed so that the composition ratio of Cu is 1:2:3. Laminate deposition is performed six times with this laminated structure as one unit.

After the deposition, oxidation is progressed by heat treatment in an electric furnace with oxygen gas flowing therein, and an oxide superconducting thin film is obtained. The superconducting transition temperature of this oxide superconducting thin film
The top data reported is 1 in 72 when using yttrium stabilized zirconia (YSZ) as a substrate and 40 when using sapphire as a substrate. In either case, Teana is 77 or less.

In literature (4), Yb (ytterbium) is used instead of Y from the viewpoint of complete solid solution with Ba;
An oxide superconducting thin film is obtained by heat-treating a laminated vapor-deposited film consisting of three metals, Ba, Cu, and Cu in oxygen. As a result, the superconducting transition temperature Tc@nd has increased, and the top data is 75 when MgO is used as a substrate. However, this value does not exceed the boiling point of liquid nitrogen temperature, 77K, which is two criteria for application.

FIG. 4 shows Tcon and Tcend of 10 samples of the same lot that were deposited in layers and annealed in oxygen.

Tcon does not vary much, but Tcend is 50K
It has the drawback that it varies widely from 75K to 75K and has poor reproducibility. The reason for this is thought to be as follows.

When producing an oxide superconducting thin film by heat-treating the above-mentioned metal laminated vapor-deposited film in oxygen gas, mutual diffusion and oxidation of metals progress simultaneously during the heat treatment. Therefore,
Yb, A portion is formed in which the atomic ratio of Ba and Cu deviates from the composition ratio of 1:2:3. Therefore, it is thought that Tcend decreases. Since the diffusion phenomenon of a mixture of oxide and metal differs slightly from sample to sample, variations in i' can and poor reproducibility between samples in the same lot are also due to the same cause.

The purpose of the invention is to solve the above-mentioned problems and to improve the superconducting transition temperature T e l! II d is greater than or equal to 77, and
It is an object of the present invention to provide a method for manufacturing an oxide superconducting R film that can suppress variations in superconducting transition temperature not only between samples manufactured in the same lot but also between samples in different lots.

[Means for Solving the Problem] In order to achieve such an object, the present invention provides a method in which the atomic ratio of Y or lanthanide metal, Ba and Cu is 1.
: A three-layer deposited layer formed by individually sequentially depositing each metal in a ratio of 2:3 is set as one unit, and the stacked unit is stacked and deposited on the substrate once or multiple times,
It is characterized by heating the deposited film in an atmosphere where chemical reactions with the respective metals do not occur or in a vacuum to cause interdiffusion in the stacked deposited films to form a uniform alloy, and then heat-treating in oxygen gas. .

[Function 1 In the wood invention, the composition ratio of 1:2:3 is increased in the plane direction and depth by heat treatment at a temperature at which the laminated deposited films sufficiently interdiffuse and form an alloy in an atmosphere that does not react with the laminated metal. After making the Ln1Ba2CLI30t-d (Ln
(Y or lanthanoid elements) can be formed with good reproducibility. Therefore, it is possible to produce an oxide superconducting thin film that has a high superconducting transition temperature and less variation in superconducting properties.

[Examples] The present invention will be explained in detail below using Examples. The oxide superconducting thin film is manufactured in steps ① to ②.

(2) Load Y (or lanthanide metal), Ba, and Cu into separate hearths for electron beam evaporation.

■MgO, 5rTiCh, ZrO, YSZ or to ℃
M layers of three metals are sequentially deposited on a substrate made of 205 or the like by electron beam evaporation. Each membrane Noah is Y
(or lanthanoid metal), Ba, and Cu so that the atomic ratio is 1:2:3. In this example, the overall J depth of this three-layer laminated film was selected to be in the range of about 10 to 200 nm. Although all stacking orders were tried, there was no change in the superconducting properties. Therefore, any stacking order may be used.

(2) The above-mentioned three-layer laminated structure is set at IRI-position, and this unit is laminated and deposited on the substrate once or multiple times. If this unit is to be laminated on the substrate only once, this step is completed in step (2).

②After vapor deposition, heat treatment is performed in a gas (inert gas, nitrogen gas, carbon dioxide, etc.) that does not react with the laminated vapor deposited film or in a vacuum to create a uniform alloy. The temperature increase rate and temperature decrease rate are 10°C/h to 1000°C/h. If the heat treatment temperature is high, the necessary treatment time will be short, whereas if the temperature is low, it will take a long time to achieve uniformity. From a practical point of view, the heat treatment temperature is 4
The temperature is preferably 00°C or higher, and the heat treatment conditions can be selected from 400°C to 800°C and from 10 minutes to several hours.

■Then, heat treatment is performed in an electric furnace flowing oxygen gas. The temperature increasing rate is 10°C/h to 1000°C/h, and the temperature decreasing rate is 10°C/h to 500°C/h. The lower limit of the heat treatment temperature is 700°C. From a practical point of view, the heat treatment temperature is 75
The temperature is preferably 0°C or higher, and the heat treatment conditions can be selected from 750°C to 950°C and from 10 minutes to several hours.

FIG. 3 shows the experimental results of the resistance and temperature of the typical oxide superconducting thin film obtained in this example. Y as a lanthanide metal
b, and MgO was used as the substrate. The stacking order is Yb→Ba-
+(:u, and the film thickness d0 of the stacked unit of three metals is 2
00 nm, and the number of laminations n in the lamination unit was 3. Therefore, the film thickness d of the entire laminated film is d=d, n=600 nm. Yb, Da and Cu are non-reactive gases,
In this example, nitrogen gas was used. The heat treatment temperature in nitrogen gas for 1 hour was 800° C. for 2 hours. The temperature raising/lowering rate was 500°C/h.

As shown in Figure 1, the superconducting transition temperature T at which the resistance becomes zero
cand is 79 degrees, exceeding the boiling point of nitrogen temperature 77 degrees.

Figure 2 shows 1.
Tea□ and Tccnd of 0 samples are shown. The data variation is very small and the rcend is 77 for all test slopes.
It's beyond. This shows that the variation in data is extremely small, not only between samples made in the same lot, but also between samples made in different lofts. It is obvious at a glance that the effect of introducing step (2) in the above-mentioned embodiment is great.

The results obtained above have been explained by specifying conditions such as using Yb as the lanthanide metal and MgO as the substrate, but the same results can be obtained not only with this combination but also with the contents described in the examples. Ta. In addition, in this example, in the heat treatment in a gas that does not react with the laminated vapor-deposited metal, it was explained that the heat treatment in oxygen gas was performed after lowering the temperature to room temperature. Of course, after heat treatment, the gas may be switched to oxygen gas and heat treatment in oxygen gas may be started without lowering the temperature.

Furthermore, in this example, a method using an electron beam was explained as a metal deposition method, but it is of course possible to fabricate an oxide superconducting thin film using resistance heating evaporation, high frequency heating evaporation, or sputter evaporation. .

[Effects of the Invention] As explained above, in the present invention, an oxide superconducting thin film having a resistance superconducting transition degree of 7 or more at a boiling point of 77 at a nitrogen temperature can be produced with good reproducibility and with little variation. This has the effect of opening up a wide range of applications to electronic devices and superconducting interconnects that operate at liquid nitrogen temperatures.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the resistance/temperature characteristics of an oxide superconducting thin film according to an embodiment of the present invention, FIG. 2 is a diagram showing temperature characteristics of an oxide superconducting thin film according to an embodiment of the present invention, and FIG. FIG. 4 is a diagram showing the temperature characteristics of an oxide superconducting thin film produced by a conventional manufacturing method.

Claims (1)

[Claims] (1) One unit is a three-layer deposited layer formed by depositing Y or lanthanide metal, Ba, and Cu in sequence in an atomic ratio of 1:2:3. The laminated units are laminated one or more times on a substrate, and the deposited film is heated in an atmosphere or vacuum in which chemical reactions with the respective metals do not occur to cause interdiffusion in the laminated deposited film. A method for producing an oxide superconducting thin film, which comprises forming a uniform alloy and heat-treating it in oxygen gas.