JPH02120229A - Production of superconducting thin film of oxide - Google Patents

Abstract

PURPOSE:To periodically synthesize superconducting thin films of Bi-based oxide as single crystal film on a substrate at low temperature by sputtering ionic beam against four kinds of targets in the order of Bi2O3, SrO, CuO, CaO, CuO, CaO, CuO, SrO and Bi2O3. CONSTITUTION:In the above-mentioned method, periodic structure of (Bi.O)2 atomic layer/(Sr.Ca.Cu.O) perovskite type structure 1 (Bi.O)2 atomic layer ...is artificially laminated and grown in a specific direction of axis c in a crystal structure of Bi-based oxide superconductor. Then four kinds of targets are successively and periodically sputtered in the order of (Bi.O) layer, (Sr) layer, (Cu.O) layer, (Ca) layer, (Cu.O) layer, (Ca) layer. (Cu.O) layer, (Sr) layer and (Bi.O) layer. Consequently, a thin film of Bi-based superconductor single crystal is laminated and grown. Thickness of laminated film of each layer is 5Angstrom (Bi.O) layer, 10Angstrom (Sr.Ca.Cu.O) layer in total in the case of 80K phase of Bi base and 13Angstrom in the case of 110K phase. The substrate temperature in the lamination is 500-800 deg.C.

Description

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

(Prior Art) Superconducting thin films are indispensable for applications such as quantum magnetic interference devices using Josephson junctions, superconducting LSI wiring, and superconducting active devices. In recent years, starting with the Y-based oxide superconductor with a critical temperature of 90 degrees discovered by Chu et al. of Hughston University in the United States in February 1982, the critical temperature uox,
Bi-based oxide superconductors, as well as TI-based oxide superconductors with critical temperatures of 12O and oxides with critical temperatures exceeding liquid nitrogen temperatures, were developed by Cheng et al. of the University of Arkansas in the United States. Superconductors were discovered one after another. As a result, superconducting application devices that conventionally had to use liquid He can now be realized using liquid nitrogen, and in particular, the thinning of these oxide superconductors is due to quantum magnetism due to Josephson junctions that operate above the liquid nitrogen temperature. Interference elements, superconducting LSI wiring, superconducting active elements, etc. have been realized, and their applications can be widely used. Now, Bi-based superconductor thin films have conventionally been produced basically by the following three methods.

The first method is, for example, Applied Physics Letter (
Appl, Phys, Lett,) Volume 53.427
Using the magnetron sputtering method as shown in
By forming a film using a single target consisting of R, Ca, and Cu, and then heat-treating this film at 880°C in oxygen, a C-axis oriented film exhibiting zero resistance was obtained in 83. There is.

The second method is, for example, Applied Physics Letters (Appl, Phys, Lett,) Vol. 53.
．． As shown on page 337, film formation was performed using a pulsed laser and a single target as in the first method, and later on 875
A superconducting thin film of 80 °C was obtained by heat treatment in oxygen at 80 °C.

Furthermore, as a third method, for example, Applied Physics Letter (Appl, Phys, Lett,)
Bi, Sr, Ca, C as in Volume 53, page 624
A zero-resistance superconducting film was obtained in 35 by simultaneously evaporating u from independent vapor deposition sources and performing heat treatment in oxygen at 860°C after film formation.

(Problem that the invention sought to solve) However, in both cases, the conventional superconducting film manufacturing method requires high-temperature heat treatment of 850°C or higher to create a superconducting film, and the film is C-axis oriented. The surface of the material is rough, and although the onset of superconductivity appears to be 110 K, the final zero resistance temperature is low, making device application difficult. Further, in order to improve the homogeneity of the Josephson junction, it is desirable to use a single crystal film.

An object of the present invention is to provide a method for synthesizing this Bi-based oxide superconducting thin film as a single crystal film on a substrate at a low temperature.

(Means for solving the problem) The present invention uses Bi2O3, SrO+ C as a target.
A method for manufacturing an oxide superconducting thin film by ion beam sputtering using four types of targets of a0pCuO, the targets being B12O31 SrO, C
ub.

Cab, Cub, Cab, Cub, SrO,B
A method for producing an oxide superconducting thin film characterized by using i2O3 in this order and periodically growing it in layers by ion beam sputtering; A method for producing a superconducting thin film and using (Bi) instead of bismuth oxide as a target.
2O3)1-x(Pbo)x (0<x≦0.1)
This is a method for manufacturing the oxide superconducting thin film using the following composition.

In this method, two atomic layers of (Bi-0)/(Sr-CaCu-
0) Perovskite type layer/(Bi-0) two atomic layer...
The periodic structure of (Bi・
O) layer, (Sr) layer, (Cu・O) layer, (Ca)
Bi-based super This is a method of growing superconductor single crystal thin films in layers. Furthermore (B
i-0) layer, (Sr) layer, (Cu-0) layer, (C
a) layer, (Cu-0) layer, (Sr) layer, (Bi-
0) Sputtering may be performed around layer j.

The laminated film thickness of each layer is (Bi, O) 5 layers, (Sr-Ca-
The Cu-0) layer is laminated by a total of 10 people in the case of Bi-based 80 phase, and 13 people in the case of 110 phase. Preferably, the substrate temperature is maintained at 500 DEG C. to 800 DEG C., and the partial pressure of oxygen gas on the substrate is maintained at 2.times.10' Torr or more to synthesize an epitaxially grown Bi-based oxide superconducting thin film. At this time, it is desirable to provide a relaxation time of 10 seconds or more between each lamination process, during which time migration of sputtered particles on the surface and modification of the crystallinity of the laminated film occur. Furthermore, bismuth oxide, strontium, calcium, and copper oxides can be grown heteroepitaxially on a substrate, and by growing an epitaxial layer of approximately 10 to 100 layers at the initial stage, a single crystal Bi-based oxide can be formed by the subsequent film growth process. An oxide superconducting thin film is grown. Furthermore, by introducing RF into the vacuum chamber, sputtered particles can be activated and the crystallization temperature of the film can be lowered, and oxygen is also ionized, thereby promoting oxidation of each constituent element. Furthermore, by accelerating oxygen ions generated from RF or an oxygen ion source to IOV~80V and irradiating the film growth surface, oxidation and migration on the film growth surface are promoted, improving the crystallinity of the film and flattening the film surface. Improves oiliness. Furthermore, by substituting part of Bi with Pb, the superconducting properties are improved and the transition becomes sharper. These epitaxial films can be synthesized on any substrate of magnesium oxide (MgO) single crystal, strontium titanate (SrTtO3) single crystal, yttrium stabilized zirconia (ysz) single crystal, or zirconia (Zr02) single crystal.

(Example) FIG. 1 shows an ion beam sputtering apparatus used to manufacture a multilayer periodic structure thin film. FIG. 1(a) is a front view of the device, and FIG. 1(b) is a top view. Vacuum chamber 12
is equipped with four Kaufmann type ion sources 1.2.16°17, each with 3 B12O3 targets, 4 SrO targets, 18 CaO targets, and 1 CuO target.
Sputter 9. The divergent field of view of the sputtered particles 3' and 4'' is limited by the top plate 5, and four crystal oscillator film thickness gauges (
While monitoring the film thickness using 15) in Figure 1(a), a multilayer periodic structure is formed by alternately opening and closing four shutters (6 and 7 in Figure 1(a)) driven from outside the vacuum chamber. Ru.

9 is a heater, 13 is an electron gun for RHEED, 14 is RHE
This is the ED screen. Vacuum degree inside the chamber: 4X1
0 torr, and oxygen gas is blown around the substrate to promote oxidation at a local oxygen partial pressure of 2×10 torr. Also, in order to avoid the film thickness distribution within the substrate plane as much as possible,
It gives rpm rotation. Inside the chamber, a neutralizer neutralizes Ar emitted by the ion source. B12 when the output of ion source 1 is 600v and 30mA.
The film formation rate of o3 is 0.2 people/see, and the ion source 2
SrO when the output of ゜16 is 600■, 40mA,
The deposition rate of CaO was 0.18 A/sec, and when the output of the ion source 17 was 600 V and 30 mA, the deposition rate of CuO was 0.2 people/see.

Next, an example of film formation of a superconducting phase in Bi-based 110 using an Mg0 (100) substrate will be shown. A film with a periodic length of 36 was formed under the conditions of a substrate temperature of 620° C. and an oxygen gas partial pressure of I×10 Torr near one substrate, while checking the RHEED pattern during film formation.

For example, when 5uCuOxe is grown on an MgO substrate, Mg
5uC as a buffer layer by matching the substrate orientation of O
uO becomes heteroepitaxial. 5rCu in this case
There are 10 people in the O layer. After heteroepitaxial layer deposition 4
After a slow period of minutes, BiO is grown epitaxially by 6 people.

After another 1 minute buffer time, 2 people applied SrO, 1 minute buffer time, 2 people applied CuO, 2 people applied CaO, 1 minute buffer time,
2 people for CuO, 1 minute buffer time, 2 people for CaO, 1 minute buffer time, 2 people for CuO, 1 minute buffer time, 2 people for SrO, 1 minute buffer time, 6 people for BiO, 1 minute buffer time, Repeat periodic layered film deposition using the settings.

Here, the reason why the set value is set longer than the periodic length of the superconducting phase of the Bi system 110 is to take into account the probability of adhesion of sputtered particles to the film surface. RHEED diffraction spots are streak-like and the film surface has good flatness;
Furthermore, it can be seen that epitaxial growth continues. This artificial period length of 18 people is repeated 15 times for a total film thickness of 30
Figure 2 shows the X-ray diffraction pattern of the membrane when 0 people were present. From this X-ray diffraction pattern, 36 people (18 people x
It can be seen that 110Ki of the Bi-based superconductor (2) is formed with a neat C-axis orientation. The electrical resistance of this film is 1
It was confirmed that it has an onset at 10K and becomes superconducting at 107K. The above is an example of a method for synthesizing an ultra-thin epitaxial superconducting thin film having a Bi-based 110 phase, but Table 1 shows other film formation results. In similar means, (B
6 people for i-0) layer, 10 people for (Sr-Ca-Cu・0) layer
By setting it as human, we were able to easily create a superconducting phase film in Bi-based 80. It is also possible to have BiO as a buffer layer, and a single crystal film is synthesized by performing the above-mentioned process.In these processes, the film characteristics, substrate temperature, and oxygen gas partial pressure near the substrate are The appropriate substrate temperature is 500 to 800°C; below 500°C, crystallinity is poor and superconducting properties cannot be obtained; above 8006°C, a non-superconducting phase grows due to film composition deviation and copper reduction. It ends up. Oxygen partial pressure should be at least 2X10 t for crystal growth.
orr is required. Furthermore, by introducing RF into the vacuum chamber, sputtered particles are activated within the RF coil and at the same time oxygen plasma is generated. By performing the same growth as above in this environment, it was confirmed that the superconducting critical temperature of the film was improved, and by applying a bias potential to the RF plasma to accelerate oxygen ions to IOV ~ 80cm and irradiating the substrate with the oxygen ions. An improvement in the flatness of the film surface was observed. A similar flatness improvement effect was also observed by separately installing an oxygen ion gun in the vacuum chamber as a source of accelerated oxygen ions.

Next, instead of bismuth oxide, Torr was fixed as the target. The superconducting properties are improved up to x = 0.1 (Tc increases to 5 to 15), but above this the quality of the single crystal film deteriorates due to the generation of different phases in the film, so it is not practical. It becomes irrelevant.

The above has described an epitaxial film synthesized on a magnesium oxide (MgO) single crystal substrate, but strontium titanate (SrTiO3) single crystal, yttrium stabilized zirconia (YSZ) single crystal, zirconia (Zr0
2) Single crystals could be similarly synthesized on any substrate.

(Effects of the Invention) As described above, by applying the present invention, it is possible to easily synthesize a single-phase epitaxial film that exhibits superconductivity at about 107°C at a low temperature, which is extremely useful for applications to devices, etc. It is valid.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are schematic structural diagrams of an ion beam sputtering apparatus in which the present invention is implemented. FIG. 2 is an X-ray diffraction diagram. In the figure, 1.2.16.17 is an ion source, 3 is a Bi
2O3 target, 4 is 5rCaCuO oxide target, 5 is top plate, 6 and 7 are shutters, 8 is substrate holder, 9 is heater, 10 is gate valve, 11 is vacuum pump, 12 is vacuum chamber, 13 is reflection height Electron gun for energy electron diffraction (RHEED), 14 is RHEE
D screen, 15 is crystal resonator film thickness monitor, 18 is C
The aO target and 19 are CuO targets.

Claims (3)

[Claims] (1) Bi_2O_3, SrO, Ca as targets
A method for producing an oxide superconducting thin film in which ion beam sputtering is performed using four types of targets, O and CuO, in a predetermined order, the targets being Bi_2O_3 and Sr.
O, CuO, CaO, CuO, CaO, CuO, SrO
, Bi_2O_3 in the order of ion beam sputtering to periodically grow layers on a substrate. (2) Instead of bismuth oxide as a target (Bi
_2O_3)_1_-_x(PbO)_x (0<
The method for producing an oxide superconducting thin film according to claim 1, characterized in that x≦0.1). (3) Radio frequency (RF) is applied inside the vacuum container during the film formation process.
3. A method for producing an oxide superconducting thin film according to claim 1 or 2, characterized in that: