JPH0243358A - Production of thin superconducting film - Google Patents

Abstract

PURPOSE:To easily produce the thin superconducting film having the high critical temp. by using Cu, Cr, Ca metals and Bi2O3 as evaporating sources at the time of forming a Bi-Sr-Ca-Cu oxide having a specific compsn. as a thin film by a vacuum vapor deposition device. CONSTITUTION:The Bi2O3 is used together with the Cu, Sr, Ca metals as the evaporating sources at the time of forming the oxide having the compsn. expressed by the formula consisting of Bix(Sr1-xCax)bCu1-a-bOy where a: 0.2-0.35, b: 0.4-0.5, x: 0.3-0.7, y: 0.8-1.2 as the thin film by using the vacuum vapor deposition device. The temp. of the substrate on which the thin film is to be formed is preferably set at about 800-900 deg.C. The thin superconducting film consisting of the Bi-Sr-Ca-Cu oxide having the high critical temp. is easily formed in this way.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to B1-8r-Ca-Cu having a high critical temperature.
This invention relates to a method for producing superconducting thin films mainly composed of oxides.

(Prior Art) In recent years, as oxide superconducting materials having a high critical temperature (Tc), La-based materials with a Tc of 40 and Tc of 90 have been used.

Y-based materials have been developed and are attracting much attention in the field of materials science. Afterwards, many studies were conducted on these oxide superconducting materials, and Maeda et al.
We discovered that a superconductor with a Tc of 110 exists in a-Cu oxides (Japanese Journal of Applied Physics (Jpn)).

J, Appl, Phys, 27 (1988) L2
09)). However, in this Bi-based material, Tc of 110
In addition to the phase with Tc of 85, there is also a phase with Tc of 110. The zero resistance temperature observed by Maeda et al. was much lower than 100, because the phase with

However, if this 110 T. If it were possible to increase the ratio of the phase with 100% to 100% or higher and obtain a superconducting state, conventional superconducting materials with low critical temperatures would have to use expensive liquid helium as a coolant. On the other hand, this new B1-8r-Ca-Cu based oxide superconducting material can use inexpensive liquid nitrogen as a refrigerant. It can be used in many applications such as superconducting magnet wire, high-speed computer elements, and sensors.

As mentioned above, this B1-8r-Ca-Cu based oxide superconducting bulk material is characterized in that it is difficult to form a phase having a Tc of 110. On the other hand, by heat-treating a thin film created by sputtering at a temperature of 800° C. to 900° C., a superconducting thin film whose electrical resistance becomes zero at 100 KQ degrees has been obtained.

(Problems to be Solved by the Invention) The Bi-8r-Ca-Cu based oxide superconducting material has T as described above in 110. In addition to the superconducting phase with a T of 85. There exists a superconducting phase with . Among these, the superconducting phase with a Tc of 110 is formed at a very high temperature in a thermal equilibrium state of 8608C to 895°C, and the formation rate is very slow, making it extremely difficult to fabricate. . On the other hand, 8
T for 5. Superconducting phases with a Therefore, when a thin film is created by a process of heat treatment at high temperature after film formation (as in the conventional method), a superconducting phase with a Tc of 85 is preferentially formed. Superconducting phases with T of 85 are difficult to form, and even if they are formed, T of 85. There was a problem that it would become a mixed phase with the superconducting phase with Therefore, when superconducting transitions are observed using electrical resistance measurements, they often show two-step superconducting transitions. That is, after showing a small transition at 110, 85
It shows a large superconducting transition near , and becomes completely superconducting. In addition, in some reported cases, a thin film made by sputtering and heat-treated at 800°C to 9000°C becomes completely superconductive near 100, but two-phase The transition width was very wide due to the mixture of

On the other hand, if a vacuum evaporation process is used to form a thin film on a substrate heated to around 850°C, where a phase with a Tc of 110 is stable, a T of 110K can be obtained. It is possible that a superconducting phase can be formed preferentially. However, as the substrate temperature increases, a problem arises in that Bi is depleted from the film. For this reason, it becomes extremely difficult to achieve a desired composition in the thin film, resulting in the problem that good superconducting properties cannot be obtained.

The present invention solves the problems of the prior art and provides a method for manufacturing a B1-8r-Ca-Cu based oxide superconducting thin film having a high critical temperature.

(Means for solving the problems) The present invention provides Bia(Sr□-xCax), Cu0-a-b
Represented by the formula O9, a=0.2-0.35, b=0
．． 4-0.5, x=0.3~0.7, y=o, s~1
．． B1-8r-, which is characterized by using Bi2O3 as well as Cu, Sr, and Ca metals as evaporation sources when producing a thin film of the oxide having the composition No. 2 by vacuum evaporation.
This is a method for producing a Ca-Cu-based superconducting thin film. Also, the above B
When producing a 1-8r-Ca-Cu based superconducting thin film by vacuum evaporation, it is desirable to heat the substrate temperature to 800°C to 900°C.

(Function) In the Bi-8r-Ca-Cu based oxide superconducting thin film,
The range of a is 0.2 to 0.35, and the range of b is 0.4 to 0.
5. The range of X is 0.3-0.7, the range of y is 0.8-1
．． The reason why it is limited to 2 is because if it is outside this range, the proportion of the superconducting phase will be extremely small, making it impossible to obtain a superconducting thin film exceeding 100K. In addition, Cu as an evaporation source,
The reason for using Bi2O3 in addition to Sr and Ca metals is that when the substrate temperature during film formation is raised, if Bi gold metal is used as an evaporation source, it will not enter the Bi gold metal film, which has a low melting point, and the purpose is to improve the composition of the thin film. This is because the deviation will be larger than the composition, and the superconducting properties will deteriorate significantly. Furthermore, the substrate temperature during vapor deposition is 110 T for Bi-based superconducting materials. Since the phase with a Tc of 85 is a stable phase at high temperatures, if it is deposited at a substrate temperature lower than 800°C, a phase with a Tc of 85 or an amorphous phase is likely to be formed. becomes difficult to obtain. Furthermore, if the deposition is performed at a substrate temperature higher than 900° C., the thin film becomes difficult to adhere to the substrate because this substrate temperature is higher than the melting point of the Bi-based superconducting material.

(Example) An example of the present invention will be described in detail below. In this example, a quaternary simultaneous vapor deposition apparatus was used to produce a thin film of B1-8r-Ca-Cu-based oxide superconducting material. The quaternary simultaneous vapor deposition apparatus of this embodiment has four resistance heating sources as heating sources for the vapor deposition material.

At this time, the heating source may be an electron beam heating source, a laser heating source, a sputter evaporation source, or other such heating source. In this example, Cu is used as the evaporation material.
, Sr, and Ca metals, Bi2O3 was used. 40 cc of each evaporated material can be prepared in a crucible.

A (100) MgO single crystal substrate was used as the substrate. The substrate is 5rTt03. Materials such as ZrO2 and sapphire may be used.The size of the substrate is 50 mm x 25 mm and 0.2 mm thick. The board is
It can be heated up to 950°C using a heater.

When preparing a thin film, first set the vacuum chamber to 10-8
Evacuate to Torr level vacuum. After that, oxygen gas is introduced into the chamber so that the degree of vacuum becomes 1X10' Torr. The vacuum level in the chamber is 10-5 Torr.
Any other degree of vacuum may be used as long as it is on the order of ~10 −3 Torr. However, at this time, it is necessary to introduce oxygen gas near the substrate so that the oxygen partial pressure near the substrate becomes about two orders of magnitude higher. This is because the desired Bi-based oxide superconductor structure cannot be formed unless the oxygen partial pressure on the substrate surface during film formation is high to a certain extent.

The substrate is heated by the heater to a temperature of 750°C to 9°C.
It is maintained at 20°C. In this state, current is passed through the heater of the resistance heating source to raise the temperature of the evaporation source to the desired temperature and evaporate each material.

When each material reached the desired evaporation rate, the substrate shutter was opened and a thin film was produced on the substrate. The evaporated atoms ejected from each evaporated material become mixed with each other near the substrate, and also react with oxygen gas, so that they adhere as a homogeneous oxide thin film on the heated substrate. The thickness of the produced thin film was 1000 Å or more. Since the thin film lacks oxygen in the as-deposited state, it was heat-treated at about 500°C in an oxygen gas stream for several hours. At this time, the heat treatment may be performed at other temperatures. The composition of the obtained thin film was investigated by EPMA.

When the structure of the thin film thus prepared was examined by X-ray diffraction, the material falling within the scope of the present invention had a T of 110. It was found that it is composed of a superconducting phase with .

In this example, thin films were produced under the conditions and compositions shown in Table 1, including materials outside the scope of the present invention. In addition, the produced thin film has an oxygen content of 0.8 to 1.2.
It was within the range of Table 1 also shows the T of the thin film evaluated by electrical resistance measurement. are also shown at the same time. As seen in the table, the composition is a = 0.2-0.35
．． b = 0.4-0.5. Thin films 1, 2, 3, 4, 5, 9, 12, 14 within the range of x = 0.3 to 0.7
, 16, 18.21 are T of 100 or more in any of the thin films. is obtained. Also, the substrate temperature is 800°
Films 24, 25, 26 which are in the range C to 900 C also have a T of over 100. It can be seen that this is an extremely excellent superconducting thin film. Furthermore, in this example, in addition to Cu, Sr, and Ca metals, as evaporation materials,
When Bi gold metal was used, the Bi concentration in the thin film was significantly reduced, making it impossible to obtain a high To.

B1-8r-C synthesized by the conventional manufacturing method in this way
T of a-Cu-based oxide superconducting thin film. Compared to the relatively low value of 10OK or less, the manufacturing method according to the present invention has
Among the methods shown in Table 1, which have good superconducting properties and are very excellent methods, the ones marked with an x are outside the scope of the present invention.

Table 1 (Effects of the Invention) As explained in detail above, the method for producing a superconducting thin film according to the present invention is characterized in that B1-8r-Ca-
A Cu-based oxide superconducting thin film can be easily obtained, and its effects are significant.

Claims (1)

[Claims] (1) Bi_a(Sr_1_−_xCa_x)_bCu
It is expressed by the formula _1_-_a_-_bO_y, where a is 0.
2-0.35, b is 0.4-0.5, x is 0.3-0.
7. When forming an oxide with a composition in which y is 0.8 to 1.2 into a thin film using a vacuum evaporation device, Cu, Sr, and C are used as an evaporation source.
A method for producing a superconducting thin film, characterized by using Bi_2O_3 together with a metal.