JPH02120231A - Production of superconducting thin film of oxide - Google Patents

Abstract

PURPOSE:To readily laminate and grow a superconducting thin film of Bi-based oxide showing superconductivity at about 107K on a substrate at low temperature by sputtering ionic beam against four kinds of targets in the order of Bi2O3, SrO and CuO, CaO and CaO, CaO and CuO, SrO and CuO and Bi2O3. CONSTITUTION:In the above-mentioned method, periodic structure of (Bi.O)2 atomic layer/(Sr.Ca.Cu.O) perovskite type structure/(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. For example, in obtaining Bi-based 110K superconducting phase, sputtering is periodically carried out in the order of (Bi.O) layer (Sr.Cu.O) layer (Ca.Cu.O) layer (Ca.Cu.O) layer (Sr.Cu.O) layer (Bi.O) layer. In the operation, the substrate temperature is 500-800 deg.C and partial pressure of O2 gas on the substrate is maintained at >=2X10<-4>Torr so that an epitaxially grown superconducting thin film of Bi-hased oxide is obtained.

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, and the critical temperature of 110 degrees discovered by the aforementioned researchers of the Inorganic Materials Research Institute. 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, developed by Z, Z, 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 oxide superconducting thin film as a single crystal film on a substrate at a low temperature.

(Means for Solving the Problems) The present invention uses Bi2O3, SrO, and Ca as targets.
b.

A method of manufacturing an oxide superconducting thin film by ion beam sputtering using four types of CuO targets, the targets being B12O3r SrO and Cub.

CaO and CuO, CaO and CuO, SrO and CuO
A method for manufacturing an oxide superconducting thin film characterized by periodic layered growth by ion beam sputtering using +B12O3 in this order, and (Bi2O3)1-x(PbO)x instead of bismuth oxide as a target. (However, 0<x≦0.1) A method for producing the oxide superconducting thin film, and a method for producing the oxide superconducting thin film by introducing radio frequency (RF) into a vacuum container during the film formation process. It's a method.

In this method, two atomic layers of (Bi-0)/(Sr-Ca-Cu
-0) Perovskite type layer/(Bi-0) two atomic layer...
・A periodic structure is artificially layered and grown, for example, a superconducting phase (Bi-0 layer → (Sr-Cu
-01m -+(Ca-Cu-0 sho-(Ca-Cu-0
) layer - + (SrCu.O) layer - + (Bi-0) layer → in order, and in the case of superconducting phase at 80, (Bi-0) layer, (S
r-Cu.O) layer, (Ca-Cu-O) layer.

This is a method for growing a Bi-based superconductor single crystal thin film in a layered manner by sequentially combining four types of targets in the order of (Sr-Cu.0) layer and (Bi.0) layer and sputtering them periodically.

The laminated film thickness of each layer is (Bi-0) 5 layers, (Sr-Ca,
Cu, O) layers are laminated by a total of 10 people in the case of Bi-based 80 phase, and 13 people in the case of 110 phase. As desirable conditions, if the substrate temperature is maintained at 500° C. to 800° C. and the oxygen gas partial pressure on the substrate is maintained at 2×10’ Torr or more, an epitaxially grown Bi-based oxide superconducting thin film is synthesized. 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. Additionally, bismuth oxide, or strontium, calcium and copper oxides can be grown heteroepitaxially on the substrate, forming an initial epitaxial layer of about 10 to 10
By growing about 0, a single-crystal Bi-based oxide superconducting thin film is grown in the subsequent film growth process. 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 (SrTiO3) 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 apparatus, in which the vacuum chamber 12 is equipped with four Kaufmann type ion sources 1, 2, 16, and 17, each with Bi
A 2O3 target 3, a SrO target 4, a CaO target 18, and a CuO target 19 are sputtered. The sputtered particles 3', 4' have a divergent field of view restricted by the top plate 5, and are measured by four crystal oscillator film thickness gauges (1 in Fig. 1(a)).
While monitoring the film thickness using step 5), a multilayer periodic structure is formed by alternately opening and closing four shutters (6 and 7 in FIG. 1(a)) driven from outside the vacuum chamber.

9 is a heater, 13 is an electron gun for RHEED, 14 is RHE
This is the ED screen. At this time, the degree of vacuum in the chamber was 4×10 torr, and oxygen gas was blown locally near the substrate to promote oxidation at an oxygen partial pressure of 2×10 torr. The substrate temperature was 620° C., and the substrate was rotated at 60 rpm to avoid film thickness distribution within the substrate surface as much as possible. Inside the chamber, a neutralizer neutralizes Ar emitted from the ion source. Ion source 1 output 600v
, the film formation rate of Bi2O3 is 0.2A when it is 30mA.
/5ee-c available, ion source 2.16 (7) Output 6
00V.

The film formation rates of both SrO and CaO at 40 mA were 0.181/sec. When the output of the ion source 17 was 600V and 30mA, the CuO film formation rate was 0.
It was 2A/sec.

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 period length of 36 was formed under conditions of a substrate temperature of 62 O'C1 and an oxygen gas partial pressure of I.times.10 Torr while checking the RHEED pattern during film formation. For example, when 5rCuO is grown on an MgO substrate, the 5uCuO as a buffer layer is heteroepitaxially aligned with the orientation of the MgO substrate. In this case, there are 10 5rCuO layers. After a buffer time of 4 minutes after the formation of the heteroepitaxial layer, BiO is epitaxially grown by 6 people. After an additional 2 minutes of buffering time, SrO
, CuO by two people at the same time, buffer time 2 minutes, C
ab, CuO was treated by 4 people at the same time, 2 people at a time for 2 minutes, and SrOCuO was treated by 2 people at the same time.
Periodic layered film formation was repeated under the following settings: 2 people using O, 2 minutes of buffer time, 6 people using BiO, 2 minutes of buffer time.

Here, when performing simultaneous sputtering, the output of each ion source is adjusted so that the sputtering end times are the same. Furthermore, the reason why the set value is set longer than the periodic length of the superconducting phase in the Bi system 110 is to take into account the probability of adhesion of sputtered particles to the film surface.

The RHEED diffraction spots are streak-like, indicating that the film surface has good flatness and that epitaxial growth continues. FIG. 2 shows the X-ray diffraction pattern of the film when this artificial period length of 18 people was repeated 15 times and the total film thickness was 300 people. From this X-ray diffraction pattern, 36 people (18 people x 2) Bi-based superconductor
It can be seen that the layer in Figure 10 is clearly oriented along the C axis. It was confirmed that the electrical resistance of this film had an onset at 110K and became superconducting at 107K. The above is Bi
This is one example of a method for synthesizing an ultra-thin epitaxial superconducting thin film having the phase 110, and Table 1 shows other film formation results. In the same way, 6 people (Bi-0) and (S
By setting the r-CaCu-0) layer to 10 people, B
A superconducting phase film was also easily produced in i-based 80. It is also possible to use BiO as a buffer layer, and a single crystal film could be synthesized by performing the above-described process.

Table 1 In these processes, the appropriate temperature for the film properties, substrate temperature, and oxygen gas partial pressure near the substrate is 500 to 800°C; below 5006°C, crystallinity is poor and superconducting properties cannot be obtained; At temperatures above .degree. C., a non-superconducting phase grows due to a composition shift in the film and copper being reduced. Oxygen partial pressure should be at least 2X10 to grow crystals.
rr is necessary. 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. Furthermore, by applying a bias potential to the RF plasma and accelerating oxygen ions to 10V to 80V and irradiating the substrate with the oxygen ions, the film could be grown. Improvement in surface flatness 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 as a target (Bi2O
3) An epitaxial film was produced using 1-x(PbO)x (0<x<0.1). The oxygen gas partial pressure during film formation is l
It is fixed at Xl0-2 Torr. 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;
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 the drawing]

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
aO target, 19 is a CuO target.

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 and CuO, CaO and CuO, CaO and CuO, SrO
A method for manufacturing an oxide superconducting thin film, which comprises periodically growing layers on a substrate by ion beam sputtering using CuO and Bi_2O_3 in this order. (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: