JPH0244024A - Production of thin oxide superconducting film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 Paul Chu of Hyuston College and others 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 Tl-Ba-Ca-Cu oxide superconductor discovered in February 1988 by Sheng et al., an American Arkansas dog, contains a superconducting phase exhibiting 125K, making its application to thin film devices even more realistic. It has become.

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 125, and contamination of the superconducting phase in the 100 of 2 is unavoidable. Compared to Y-based oxide superconductors, this Tl-based oxide superconductor has characteristics such as no structural changes due to oxygen vacancies and is stable against moisture and other atmospheres, 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 of
Applied Physics (JJAP 27 No.
5 (1988) L849-851) describes a method using high-frequency magnetron sputtering.

This device consists of a single TI Ba Ca
This method uses a CuO compound ceramic target 16 and sputters it to form a film on a room temperature magnesium oxide substrate. 8 is a substrate holder, 10 is a gate valve, 11 is a pump, and 12 is a vacuum chamber. The film immediately after being deposited on a room temperature substrate is amorphous and has semiconductor-like electrical characteristics. By annealing this film in an oxygen atmosphere at a high temperature of about 9406C, a thin film exhibiting superconducting properties of about 100°C can be obtained, but a crystal structure showing a superconducting transition temperature of about 125°C as shown in Figure 2 cannot be obtained. . This is T.I.
The thermal equilibrium transition from the amorphous state of five types of atoms to the superconducting crystal structure of 125 in which Ba, Ca, Cu, and O atoms form a regular layered structure is extremely difficult. It shows that it is difficult. Also,
Even if a superconducting phase appears at 110, a thin film containing a superconducting phase at 80 will result, and the superconducting critical current of the film will 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 TI-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 125 phase and a 100 phase is formed. Further, this heat treatment temperature requires high temperature treatment of about 0 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 Tl-Ba-Ca-Cu-0 based oxide superconducting film grown in a single phase with 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 uses thallium oxide (Tl2O3) and barium-calcium-copper oxide (Ba-Ca-Cu-0) as vapor deposition sources, and deposits T1□03 on a substrate by four people. Ba-Ca-Cu
-0x14 This is a method for producing an oxide superconducting thin film in which a single-phase oxide superconducting thin film with a superconducting transition temperature of 125 is obtained by fabricating an amorphous multilayer periodic structure in groups of 14 and then annealing this film. After the final heat treatment, the Tl-Ba-Ca-Cu-0 oxide superconducting film, which has conventionally been made by single-target sputtering or co-evaporation, has 18 superconducting phases and a periodic structure. The melting point of the oxide is about 940°C, and the superconducting phase and 10
0 competes with the superconducting phase to grow.

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 125 superconducting phase from the beginning, the 80 phase and the 110 phase phase are phased in the heat treatment process. Avoiding the competition of single phase 1
By obtaining a phase superconducting thin film in No. 10 and at the same time reducing the distance of atomic movement required to form a crystal structure, the required heat treatment temperature is lowered.

(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 T1□o3 target 3 and a Ba-Ca-C
A u-0 (composition ratio 2:2:3) target 4 is sputtered. The complete field of view of the sputtered particles 3' and 4' is restricted by the top plate 5, and the shutters are alternately operated while monitoring the film thickness using shutters 6, 7 and a crystal oscillator film thickness gauge 15 driven from the outside of the vacuum chamber. 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 is 4X10-'torr, and oxygen gas is locally blown at 2X10-3torr to promote oxidation near the substrate.
The oxygen partial pressure was 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 00OV 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 Tl-Ba-Cu-0x when V was 120 mA was IA/sec.

Under the above conditions, 4 people (B
A total of 200 cycles of 14 a-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 (TI
-0) and (Ba-Ca-Cu-0) layers, the periodic length is approximately 1
It can be seen that a multilayer periodic structure of eight people is created. Also X
Since a halo pattern is observed in the line mid-angle diffraction region, the film is an amorphous multilayer periodic structure film. By subjecting this amorphous multilayer periodic structure film to heat treatment at 800°C for 1 hour in an oxygen atmosphere, a thin film exhibiting a superconducting transition temperature (zero resistance) of 125K was obtained. FIG. 4 shows the X-ray diffraction pattern of the film after heat treatment. The X-ray diffraction pattern is 37
It shows the C-axis orientation with the fundamental period of humans, and each peak is (0,
It is found that the superconducting thin film is a single-phase superconducting thin film because no other different phases are observed. At the same time, whereas the conventional method required heat treatment at 890°C, which is the same as in the synthesis of bulk ceramics, a superconducting thin film was synthesized in 125 using heat treatment at 800°C.

(Effects of the Invention) As described above, by applying the present invention, a film exhibiting superconductivity at 125 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 structure. Figure 3.4 shows the X-ray diffraction pattern. In the figure, 1.2...Ion source, 3...Tl□03 target, 4...Ba-Ca-Cu oxide target, 5...
・Top plate, 6, 7... Shutter, 8... Board holder, 9... Heater, 10... Gate valve, 11
...Vacuum pump, 12-1. vacuum chamber, 1
3... Electron gun for reflected high-energy electron beam diffraction, 14.
...Screen, 15...Crystal resonator film thickness monitor, 1
6...Target. Figure 1

Claims (1)

[Claims] (1) Amorphous Tl_2O_
3 and Ba_2Ca_2Cu_3O_x, and then heat-treating this film to obtain a single-phase oxide superconducting thin film.