JPS5821880A - Manufacture of oxide superconductive thin film - Google Patents

Abstract

PURPOSE:To enable to obtan a thin oxide superconductive film by sputtering a powder mixture of the oxides of lithium and titanium as a target in argon gas. CONSTITUTION:Li, Ti and the oxides of these elements are combined to produce an Li1+XTi2-XO4, which is mixed to form a composition of -0.25<=X<=0.2. The mixture powder is hot pressed at approx. 900 deg.C in inert or reduced atmosphere, and is then annealed as a target. the mixture is sputtered in the argon gas and is accumulated in a thin film on a sapphire substrate.

Description

[Detailed Description of the Invention] The present invention relates to a method for manufacturing an oxide superconducting thin film, which is necessary when applying superconductors such as Li1+ and T + 2-x O4 to devices using superconductivity. It is.

L j 1 + This means that the composition is -0,25≦X≦02
In the range x, superconducting transition occurs, and in the range x<:0.2, it exhibits insulating properties. This is for example.

In order to be able to create tunnel-type Josephson junctions using oxides with the same crystal structure,
Since the difference in coefficient of thermal expansion between the superconductor and the insulator is small, there is a possibility that the stability against heat cycles, which has been a problem with the above-mentioned bonding elements in the past, can be greatly improved. However,
A sintering method, a hot press method, a swaging method, a melting method, and the like have been tried as methods for manufacturing the L I 1+X T 12-A04 superconductor.

All of the products produced by these methods were in the form of lumps, and no products in the form of thin films were obtained.

The object of the present invention is to obtain TJ i1+X T I 2 x which could not be obtained with the prior art as explained above.
An object of the present invention is to provide a manufacturing method capable of obtaining an oxide superconducting thin film made of 04.

One of the above objects is the method for producing an oxide superconducting thin film of the present invention, which is represented by Li ++ and a powder mixture of two or more selected from the group consisting of lithium, titanium, lithium oxides, titanium oxides, oxides containing both lithium and titanium, or the like. Sputtering is performed using the reacted powder product or its sintered body as a target in an atmosphere of argon gas or a mixed gas containing argon gas and a small amount of hydrogen gas at an atmospheric gas pressure of 1 to 1oPa and a power of approximately 25o-4soW. By forming an oxide thin film on the substrate surface, the oxide thin film is
When it crystallizes at a temperature of 40° C. to form an oxide superconducting thin film, it becomes more stable.

According to the manufacturing method of the present invention, it is possible to manufacture a superconducting thin film composed of L11+xTi2-x04, which could not be obtained using conventional techniques.

The sputtering target in the present invention can be manufactured as follows. For example, the raw material powder is 1.

(a) Li, Ti, TiO2; (b) Li20
．． Ti, TiO2; (c) Li20. T+20s
, Too. ;(d) LI2TI205, T'+20s
With an appropriate combination such as; L11+1T i2
In what is indicated by x 04, -〇, 25≦X≦
Blend and mix to obtain a composition of 02. L obtained by reacting this mixed powder or mixed powder at a temperature of about 900°C in an inert atmosphere or a reducing atmosphere.
i1. -xTi2-x04 powder can be used as a target, but it is not suitable for obtaining good film quality and for increasing the film deposition rate.

For that purpose, chunks are best. The simplest one is L l 14-X T I 2 x 04, which is produced by treating the above mixed powder or reacted powder at a temperature of about 900°C in an inert atmosphere or a reducing atmosphere.
It is a sintered body.

In sputtering in the present invention, it is desirable to use the TI,F magnetron sputtering method in order to reduce the composition deviation between the composition of the target and the composition of the formed thin film. As the atmospheric gas in this case, argon gas or a mixed gas of argon gas and a small amount of hydrogen gas is used. The sputtering conditions depend on the equipment used, so I cannot say anything about them, but generally the atmospheric pressure is 1 to 10 Pa, and the input power is 2.
50-450W, anode voltage 22-3.2 kV,
Appropriately, the anode current is about 180 to 250 mA.

If the atmospheric pressure is too high, it may not be possible to form a thin film, and if the atmospheric pressure is too low, there may be large composition deviations. If the input power is large, the surface of the thin film will become rough.

The thin film after sputtering is amorphous or partially crystallized, has high electrical resistivity, and does not undergo superconducting transition. Therefore, heating is performed at a temperature of about 860 to 940° C. in an inert atmosphere or a reducing atmosphere. As a result, a spinel structure appears, and the thin film undergoes a superconducting transition.

It is necessary to select the substrate material so that the Li 1+X T 12 x O4 thin film and the substrate do not react during heating.

Hereinafter, the present invention will be explained in detail with reference to an example and a graph showing the superconducting transition characteristics of a thin film produced thereby.

Harm J Famine - Raw material powder TJ i2 T + 205 and T i 20
Weigh out 1 mol of s each.

After performing wet mixing using ethyl alcohol and agate stone for about 5 hours, the ethyl alcohol was removed by drying, and the mixed powder was further mixed for about 30 minutes using an agate mortar. 6
Hot pressing was performed at a temperature of about 900° C. for an hour in a mixed gas atmosphere of argon gas and hydrogen gas. In order to prevent cracks, subsequent annealing was performed at the same temperature.

The 100φ Li T; 20° sintered body produced in this manner was used as a target. Sputtering was performed using a planar RF magnetron spankling device.

Argon gas was used as the atmospheric gas, and the temperature was 50 to 60 at 330 W under various atmospheric gas pressures of 1 to 9 Pa.
Thin films were deposited on sapphire substrates at 100-300° C. for minutes. The thickness of the obtained thin film was 1 to 1.5 μm, and the film formation rate was 170 to 260 A/min.

These thin films were pale blue-black to blue-black in color, and were amorphous or partially crystallized.

When the sample was crystallized in hydrogen gas at a temperature of 900°C, all of the crystals exhibited a blue-black color and a spinel phase began to grow.Q The sputtering atmosphere gas pressure was 1.3.6°9 Pa.
The electrical resistivity at low temperature of the above thin film manufactured under each pressure was measured and shown in the graph.
It is a diagram.

As can be seen from the graph in Figure 1, the atmospheric gas pressure is 6~
In the case of 9 Pa, the superconducting transition temperature of the thin film at low temperature is 10.9 to 11 iK, the transition width is 06 to 7 K, and these values are the stoichiometry of bulk produced by other methods. It is equivalent to the stoichiometric composition L + 'r 1204.

As explained above, the present invention using the sputtering method has made it possible to manufacture oxide superconducting thin films necessary for application to superconducting devices and the like.

[Brief explanation of drawings]

FIG. 1 shows the pressure of argon gas, which is the atmospheric gas for sputtering, in an embodiment of the present invention. This is a graph showing the measured values of the electrical resistivity at low temperatures of various oxide superconducting thin films manufactured at different temperatures in the range of 1 to 9 Pa. Patent applicant Junnosuke Nakamura, patent attorney representing Nippon Telegraph and Telephone Public Corporation

Claims (1)

[Claims] In what is represented by Ll 14-x Tl2-X 04 . -025≦X≦02, and selected from the group consisting of lithium, titanium, oxides of lithium, oxides of titanium, and oxides containing both lithium and titanium. Targeting a powder mixture formed by mixing two or more types, a powder product obtained by reacting the same, or a sintered body thereof, in an atmosphere of argon gas or a mixed gas containing argon gas and a minimum amount of hydrogen gas, Atmospheric gas pressure approximately 1 to 1o I'a
. Par7 - Form an oxide thin film on the substrate by sputtering at about 250-450W. Next, the oxide thin film is crystallized at a temperature of about 860 to 940°C to form a superconducting thin film.