JPH0244029A - Production of thin oxide superconducting film - Google Patents

Abstract

PURPOSE:To easily produce a superconducting film having a single phase by forming an amorphous Bi2O3-Sr2Ca2Cu3Ox film having a multilayered periodic structure on a substrate and by heat-treating this film. CONSTITUTION:A Bi2O3 target 3 and a Sr-Ca-Cu-O (2:2:3 ratio of Sr:Ca:Cu) target 4 are arranged in a vacuum chamber 12 provided with Kaufmann type ion sources 1, 2. The scattering range of sputtered particles 3', 4' is limited with a top plate 5 and an amorphous Bi2O3-Sr2Ca2Cu3Ox film having a multilayered periodic structure is formed on a substrate by alternately opening shutters 6, 7. The film is then heat-treated at a prescribed temp. in an oxygen atmosphere to obtain a thin superconducting film having a high superconduction transition temp. of the 110K order. This superconducting film having a single phase is easily produced.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to oxide superconducting thin films.

(Prior art) Superconducting thin films are indispensable for manufacturing Josephson devices and quantum magnetic interferometers by forming Josephson junctions, and various types of thin films have been made in the past. Initially, Josephson elements using materials such as lead were manufactured by simple sputtering or vacuum evaporation. Lead-based thin films use liquid helium as a coolant, but its boiling point is 4.2K.
On the other hand, there are drawbacks such as the critical temperature of the thin film being 7.2, which is a small temperature margin, and the large number of variations in bonding, making it difficult to obtain stable operation. For this reason, niobium (Nb)-based thin films, which have a higher superconducting critical temperature than lead, have come to be used. Niobium thin film or niobium nitride thin film are each 9
．． 23, and has a superconducting critical temperature of 15.7. This niobium or niobium nitride thin film was obtained by ultra-high vacuum evaporation or reactive sputtering using argon and nitrogen gas against a niobium target. All of the above were superconducting thin films that required the use of liquid He as a coolant, but the Y-Ba-Cu based oxide superconductor discovered in February 1987 by Ball Chu et al. It attracted a lot of attention as a material with a conduction transition temperature of 93K, which achieved superconductivity using liquid nitrogen as a coolant.

Furthermore, the B1-8r-Cu-Cu-based oxide superconductor discovered by Maeda et al. at the Institute of Metal Materials Research, Ministry of International Trade and Industry in January 1988, contains a superconducting phase exhibiting 110K, making its application to thin film devices even more realistic. It has become a thing.

However, in the method of producing a bulk sintered body in high-temperature thermal equilibrium, it is extremely difficult to obtain a superconducting phase in a single 110, and the superconducting phase cannot be avoided in the 80 of 2. Ta. Compared to Y-based oxide superconductors, this Bi-based oxide superconductor has characteristics such as no structural change due to oxygen vacancies and is stable against atmospheres such as moisture, making it extremely suitable for device applications. It's promising. An example of manufacturing this Bi-based superconducting thin film is given in Japanese Journal Op.
Applied Physics (JJAP 27 No.
4 (1988) L643-645) describes a method using high-frequency magnetron sputtering.

This device consists of a single B1-8r-Ca as shown in Figure 2.
This method uses a -Cu-0 compound ceramic target 16 and sputters it to form a film on a magnesium oxide substrate at a substrate temperature of about 200 to 600°C. 8 is a substrate holder, 10 is a gate valve, 11 is a pump, 12
is a vacuum chamber. When a low-temperature substrate with a substrate temperature of about 200° C. is used, the film immediately after deposition is amorphous and has semiconductor-like electrical characteristics. This film was heated to 890°C.
By annealing in a high temperature oxygen atmosphere of about 8.
Although a thin film exhibiting superconductivity on the order of 0 is obtained, a crystal structure exhibiting a superconducting transition temperature of 110 is not obtained. Also 6
When using a high-temperature substrate at about 00°C, a film exhibiting superconductivity at about 80°C can be obtained even immediately after film formation, and by annealing it in a high-temperature oxygen atmosphere at about 890°C, In general, although a superconducting phase can be obtained at 110, the final zero resistance is still around 80. This is Bi
, Sr, Ca, Cu, and O atoms form a regular layered structure to form a superconducting crystal structure of 110. It is extremely difficult to transition from an amorphous mixture of five types of atoms in thermal equilibrium. This shows that it is difficult to Furthermore, even if a superconducting phase appears at 110, the film becomes a thin film containing a superconducting phase at 80, and the superconducting critical current of the film does not increase.

Furthermore, since each grain in the film has different superconducting properties, there are problems such as non-uniformity in device properties when the film is microfabricated to form a superconducting device such as a Josephson junction. Furthermore, the heat treatment temperature is 900°C.
The degree of occurrence is very high and it becomes a major hindrance in the industrial production process.

(Problems to be Solved by the Invention) In the method of obtaining a Bi-based superconducting film by annealing an amorphous or incompletely crystalline phase at high temperature by single-target sputtering or co-evaporation, A mixed phase of a phase at 110 and a phase at 80 is formed. Further, this heat treatment temperature requires high temperature treatment of about 880 to 900°C, which is not preferable in terms of the device manufacturing process. Furthermore, the film after heat treatment becomes a C-axis oriented film, but its in-plane orientation is random.

An object of the present invention is to provide a method for manufacturing a B1-8r-Ca-Cu-0 based oxide superconducting film epitaxially grown in a single phase and C-axis orientation at a lower temperature and easier than conventional methods. There is a particular thing.

(Means for solving the problem) The present invention is based on bismuth oxide (Bi203) and strontium-calcium-copper oxide (Sr-Ca-Cu-Ox).
Bi203 was deposited on a magnesium oxide substrate using
(for example, 4 people) and Sr-Ca-Cu-Ox (14 people), and by later annealing this film, a single-phase oxide superstructure with a superconducting transition temperature of 110 This is a method for producing an oxide superconducting thin film to obtain a conductive thin film, in which a bismuth oxide epitaxial layer with a rock salt type crystal structure is formed as a first layer on a magnesium oxide substrate, after which the periodic structure is formed, and after final heat treatment. a
This is a method for producing an epitaxial oxide superconducting thin film in which the , b, and c axes are aligned. B1-8, which has conventionally been performed by single target sputtering or co-evaporation
In the r-Ca-Cu-0 oxide superconducting film, the superconducting phase has an 18-person periodic structure and the melting point is about 900°C111
At 0, a superconducting phase is formed at about 890°C, and at 80, a superconducting phase is formed at about 840°C. For this reason, during normal firing of ceramics, the superconducting phase is formed first at 80, and the superconducting phase grows competitively at 110 at a temperature close to the melting point. In the present invention, the growth of the thin film is controlled on the order of a monoatomic layer, and by making the film have an Akylphus periodic structure with the same period as the 110 superconducting phase from the beginning, the 80 phase and the 110 phase are phased in the heat treatment process. By avoiding the competition between 110 and 110, a phase superconducting thin film is obtained in a single-phase 110, and at the same time, the required heat treatment temperature is lowered by reducing the distance of atomic movement required to form a crystal structure.

Furthermore, B as a buffer layer on the magnesium oxide substrate.
By heteroepitaxially growing i2O3, (Bi-0)/(Sr-Ca-
The amorphous multilayer film of Cu-0) can be made into an epitaxial single crystal thin film through a heat treatment process.

(Example) FIG. 1 shows a dual ion beam sputtering apparatus used to manufacture this multilayer periodic structure thin film. The vacuum chamber 12 is equipped with two Kaufmann type ion sources 1 and 2, each with a Bi2O3 target 3. Sr-Ca-C
A u-0 (composition ratio 2:2:3) target 4 is sputtered. The sputtered particles 3', 4' are restricted in their divergent field of view by the top plate 5, and the film thickness is monitored by shutters 6 and 7 driven from the outside of the vacuum chamber and by a crystal resonator film thickness meter 15, and the shutters are rotated alternately. A multilayer periodic structure is formed by opening and closing. 9 is a heater, 13 is an electron gun,
14 is a screen. At this time, the degree of vacuum in the chamber was 4X10-'torr, and oxygen gas was locally blown at a partial pressure of 2X10-torr near the substrate to promote oxidation. The substrate temperature was 200° C., and rotation was applied at 60 rpm to avoid as much as possible the film thickness distribution within the substrate surface. Inside the chamber, a neutralizer neutralizes Ar+ emitted from the ion source. Set the output of ion source 1 to 1.
When the voltage is 000V and 70mA, the film formation rate of Bi2O3 is 0.51/see, and the output of the ion source 2 is 100O
The film formation rate of Sr-Ca-Cu-Ox when V was 120 mA was LA/sec.

Under the above conditions, 4 people from Bi layer (Bi203) layer (
A total of 200 cycles of 14 Sr-Ca-Cu-0) layers were formed on a magnesium oxide (100) surface. FIG. 3 shows the X-ray diffraction pattern immediately after this film formation. X-ray diffraction of the film shows long-period reflections up to the second order on the low-angle side, (B
It can be seen that a multilayer periodic structure with a periodic length of approximately 18 people is formed by the (i-0) and (Sr-Ca-Cu-0) layers. Further, since a halo pattern is observed in the X-ray medium angle diffraction region, the film is an amorphous multilayer periodic structure film. This amorphous multilayer periodic structure film was heated to 800°C in an oxygen atmosphere.
A thin film exhibiting a superconducting transition temperature (zero resistance) of 107 K was obtained by performing the heat treatment for 1 hour. X of the film after heat treatment
The line diffraction pattern is shown in FIG. The X-ray diffraction pattern is 3
It shows a C-axis orientation with a fundamental period of 7 people, and each peak is (0
, On), and no other different phases are observed, indicating that it is a single-phase superconducting thin film. At the same time, the temperature is 890°C, which is the same as bulk ceramic synthesis using the conventional method.
However, a superconducting thin film was synthesized in 110 by heat treatment at 800°C.

Next, bismuth oxide is heteroepitaxially grown as a buffer layer on the magnesium oxide substrate. In this example, the substrate temperature is 450° C., the oxygen gas partial pressure near the substrate is 2×1O−2 torr, and 500A is grown. In this case, γ-type cubic bismuth oxide grows in alignment with the orientation of the manesia substrate. After that, the substrate temperature was lowered, and an amorphous multilayer periodic structure film was formed according to the above example, and heat treatment was applied to form the epitaxially grown B1.
A superconducting thin film was obtained in -8r-Ca-Cu-0 system 110.

(Effects of the Invention) As described above, by applying the present invention, an epitaxial film exhibiting superconductivity in 110 and consisting of a single phase can be easily obtained, which is very effective in practice.

[Brief explanation of the drawing]

FIG. 1 is a schematic structural diagram of an ion beam sputtering apparatus using dual ion sources, in which the present invention is implemented. FIG. 2 shows a conventionally used high frequency magnetron sputtering device. Figure 3.4 shows the X-ray diffraction pattern. In the figure, 1, 2... Ion source, 3... Bi2O3 target, 4... Sr-Ca-Cu oxide target, 5...
・Top plate, 6, 7... Shutter, 8... Board holder, 9... Heater, 10... Gate valve, 11
... Vacuum pump, 12 ... Vacuum chamber, 1
3100 reflection high energy electron diffraction electron gun, 14.
...Screen, 15...Crystal resonator film thickness monitor, 1
6-Bi-8r-Ca-Cu oxide target.

Claims (2)

[Claims] (1) Bismuth oxide (Bi_2O_3) and strontium/calcium/copper oxide (Sr_2Ca_2Cu_3)
Amorphous B is deposited on the substrate using O_x) as a target.
A method for producing an oxide superconducting thin film, which comprises producing a multilayer periodic structure of i_2O_3 and Sr_2Ca_2Cu_3O_x, and then heat-treating this film to obtain a single-phase oxide superconducting thin film. (2) A γ-phase cubic Bi oxide epitaxial layer is formed as a first layer on a magnesium oxide substrate, and amorphous Sr_2Ca_2Cu_3O_x and Bi_
A method for producing an oxide superconducting thin film, which comprises producing an epitaxial oxide superconducting thin film by preparing a 2O_3 multilayer periodic structure and heat-treating it.