JPS63274024A - Manufacture of superconductive membrane - Google Patents

Abstract

PURPOSE:To manufacture a superconductive material membrane of a high critical temperature and an even composition by carrying out a physical vacuum evaporation with a specific alloy as a vacuum evaporation source, together with O or O2 ion beams, to form the membrane. CONSTITUTION:An alloy including an element alpha selected from groups IIa and IIIa in the periodic table, an element beta selected from groups IIa and IIIa in the periodic table including the same element as the alpha, and an element gamma selected from groups Ib, IIb, IIIb, IVa, and VIIIa in the periodic table is used as a vacuum evaporation source, and together with O or O2 ion beams, a physical vacuum evaporation is carried out to form a membrane. An alloy made by mixing Y and Ba, and mixing Cu in an excessive amount, for example, is used, the alloy target 2 and a substrate 5 are installed in a chamber 1, the inside of the chamber 1 is evacuated to a vacuum, a current is applied to a heater 6, the substrate temperature is heated to apply a high frequency power to an RF electrode and an ion generating electrode, and the membrane is produced in a forming speed 0.3 Angstrom /sec. As a result, it is made possible to produce a membrane of a superconductive oxide with the Tc much higher than the conventional superconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing superconducting thin films. More specifically, the present invention relates to a method for producing a superconducting thin film having a high superconducting critical temperature and having a uniform composition.

BACKGROUND OF THE INVENTION Superconductivity, which is said to be a phase transition of electrons, is a phenomenon in which the electrical resistance of a conductor becomes zero under certain conditions and exhibits complete diamagnetic properties. That is, under superconductivity, there is no power loss at all even when current is passed through a superconductor, and a high-density current continues to flow forever. For example, if superconducting technology is applied to power transmission, it will be possible to significantly reduce the approximately 7% power transmission loss that currently occurs with power transmission. In addition, applications as electromagnets for generating high magnetic fields include, for example, MHD in the field of power generation technology.
Along with power generation and electric motors, it is expected to be a technology that advantageously promotes the realization of nuclear fusion reactions, which are said to consume more electricity than the amount of electricity generated. In addition, N
It is expected to be used in M R1 pi meson therapy, high energy physical experiment equipment, etc.

Apart from the use in large-scale devices as described above, other uses of superconducting materials include the production of various superconducting elements. A typical example is an element that utilizes the Josephson effect, in which a quantum effect appears macroscopically due to an applied current when superconducting materials are weakly bonded together. Tunnel junction type Josephson devices are expected to be extremely high-speed switching devices with low power consumption because the energy gap of superconducting materials is small.

Furthermore, since the Josephson effect on electromagnetic waves and magnetic fields appears as a precise quantum phenomenon, it is expected that Josephson elements will be used as ultra-sensitive sensors for magnetic fields, microwaves, radiation, etc.

Furthermore, as the degree of electronic circuitry increases, the power consumption per unit area reaches the limit of cooling capacity. Therefore, there is a need for the development of superconducting elements for ultra-high-speed computers.

Problems to be Solved by the Invention On the other hand, despite various efforts, the superconducting critical temperature Tc of superconducting materials has not been able to exceed 23K of Nb3Ge for a long time. , B
Sintered materials of KJiF type oxides such as al2Cub or (La, Sr]2cu04 have been discovered as superconducting materials with high T. The possibility of realizing non-low temperature superconductivity has greatly increased.These materials So, 30 to 50
This is a dramatically higher T than the conventional method. was observed, 7
Tc values above 0 have also been observed. However, these superconducting materials are sintered materials, and microscopically they tend to have unreacted particle portions or have non-uniform compositions and structures, so they cannot be directly applied to electronic devices.

In addition, in order to apply it to various electronic devices, it is necessary to have a thin film structure and finely control the composition and structure.

Furthermore, it is expected that a long superconducting material will be manufactured by vapor-depositing a superconducting material onto a metal or other wire or tape-like material, and a superconducting material vapor-deposition technique is also required for such manufacturing.

However, to date, it has not been possible to form thin films with desired compositions and crystal structures using simple physical vapor deposition.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above and to provide a method for producing a thin film of a superconducting material having a high critical temperature Te and having a uniform composition and structure.

Means for Solving the Problems The present invention has been completed as a result of repeated various experiments and studies in order to solve the above-mentioned problems. One element α selected from the elements, one element β selected from the elements of group 11a and 111a of the periodic table that include the same elements as α, and one element β of the periodic table 1b, I[b, llIb, I' A thin film is formed by physical vapor deposition using an alloy containing at least one element T selected from Group Va and Group A elements as a vapor deposition source and a 0 or 02 ion beam.

action The above superconducting thin film is General formula: (αl-Xβx)r, O.

(However, α, β, and γ are the elements defined above, X is the atomic ratio of β to α+β, and 0.1≦X≦0.9, and y and 2 are (α+−xj9x) 1, the atomic ratio is 0.4≦y≦3.0.1≦2≦5). Jx)rYoZ For example, in the case of Ba-Y-Cu-0 system, it is considered to be a mixed phase mainly consisting of Ba2Y+CuaOt-x (X is 1 or less).

The thin film is preferably a perovskite oxide or a pseudo-perovskite oxide.

Pseudo-perovskite refers to a structure similar to perovskite, and includes, for example, an oxygen-deficient perovskite type, an orthorhombic type, and the like.

The alloy used as a vapor deposition source in the present invention is Ba-Y-Cu
, Ba-La-Cu or Sr-La-Cu are preferred.

The atomic ratio of α and β in the vapor deposition source used in the method of the present invention can be appropriately selected depending on the types of α, β, and T described above. Y
-Ba, La-Ba5Sr-Ba, Y/(Y+Ba) is preferably 0.06 to 0.94, more preferably 0.1 to 0.4, and Ba/(Y+Ba) is preferably 0.06 to 0.94, more preferably 0.1 to 0.4. La+Ba) is 0.04 to 0.96
Sr/(La+Sr) is preferably in the range of 0.03 to 0.95, more preferably 0.08 to 0.45, and Sr/(La+Sr) is preferably in the range of 0.03 to 0.95.
．． It is more preferable that it is 05-0.1. If the atomic ratio of the vapor deposition source deviates from the above range, the superconducting critical temperature of the vapor deposited film will not reach the desired value. Further, the atomic ratios of Da, Sr, La5Y, and Cu in the vapor deposition source are determined according to the atomic ratios of [3aSSr, La, Y, and Cu in the target thin film. For example, Ba5Y and Cu sources for vapor deposition.

The ratio is determined based on the atomic ratio of Ba, Y, and Cu in the thin film to be formed, and is adjusted according to the vapor deposition efficiency of Ba, Y, and Cu.

This is based on Ba, Sr, and L, which are the constituent components of the thin film of the invention.
This is because the melting points, etc. of the oxides of a, Y, and Cu are different, and therefore the vapor deposition efficiency is different.

That is, unless the elemental ratio of the vapor deposition source is appropriately selected, the thin film will not have the desired elemental ratio. Further, in the case of sputtering, the atomic ratio of the vapor deposition source (target) can be calculated and determined from the sputtering coefficient of each metal oxide, the vapor pressure on the substrate, and the like.

According to a preferred embodiment of the present invention, a 0 or 02 ion beam is directed toward the substrate during the physical vapor deposition. The ion source is preferably capable of differential pumping and is preferably of a cold cathode type. Inside the ion source is 1.7 x 10-
It is preferable to flow 02 gas in the range of ~8.3 X 1O-3 Torr, and the discharge voltage of the ion source is 0.
．． A range of 8 to 10 kV is preferred. Moreover, the acceleration voltage of the ion source is preferably in the range of 50V to 40kV.

Furthermore, according to a preferred embodiment of the present invention, the physical vapor deposition atmosphere includes Ar and 02, the partial pressure of A is 1, OX
10-5~1. It is preferable that OX is within the range of 10-'Torr, and the 02 partial pressure is 1.0X10-5
It is preferably within the range of 1.0 x 1 O-3 Torr.

Furthermore, according to a preferred embodiment of the present invention, during the physical vapor deposition, the substrate is heated to a temperature in the range of 230 to 1410°C using a heater. The substrate is MgO single crystal or SrTi
O3 single crystal is preferred, but glass, quartz, Si, stainless steel or ceramics can also be used.

In the present invention, a substrate is irradiated with a 0 or 02 ion beam during physical vapor deposition. By this irradiation, the oxygen concentration contained in the vapor deposited film becomes appropriate, so that the crystal structure of the vapor deposited film is also improved and the Tc value is improved. Ion beam is 0
Preferably, there are only two ion beams, and for this purpose the ion source is preferably of the cold cathode type. In addition, in the ion source, 1,7 xlo-5 to 8.3 XIO2To
It is preferable to flow 0□ gas in the range of rr. That is,
If the 0□ gas flow rate is less than 1.7 x 10-5 Torr, the 0□ ion beam will be insufficient, and the
This is because if it exceeds r, it becomes excessive and the desired thin film modification effect is not observed.

Since the pressure of this ion f source is different from that inside the chamber, the ion source must be capable of differential pumping.

The discharge voltage of the ion source is preferably in the range of 0.8 to 10 kV. That is, if the discharge voltage is less than 0.8 kV, sufficient ions will not be generated, and if it exceeds 10 kV, the excited state of the ions will become unstable. In addition, the ion acceleration voltage is 50
A range of V to 40 kV is preferred. That is, if the accelerating voltage is less than 50 V, a sufficient amount of oxygen will not be taken into the thin film, and if it exceeds 40 kV, the price of the device will become expensive, leading to an increase in cost.

The physical vapor deposition method of the present invention includes vacuum vapor deposition method, ion 7'L
/- Either the Tink method or the ion beam sputtering method can be used. The vapor deposition atmosphere contains Ar and 02, and the Ar partial pressure is 1. OXl0-5~1. OXl0
-2Torr range, 02 partial pressure is 1.0X10
-5 to 1, OX 1O-3Torr is preferable.

That is, when the Ar partial pressure is less than 1.0X10' Torr, discharge is difficult to occur;
When the value exceeds 1, the mean free path of gas molecules, ions, etc. in the chamber becomes too short, making it impossible to deposit an oxide having the desired superconducting properties. Also, 0□ partial pressure is 1. O
When X is less than 1O-5 Torr, the crystallinity of the deposited film is poor and it is difficult to obtain a perovskite-type oxide or a pseudo-perovskite-type oxide.The higher the 02 partial pressure, the better the crystallinity. Above OX 1O-3 Torr, the deposition rate decreases significantly.

According to a preferred embodiment of the present invention, it is preferable to use an MgO single crystal or SrTiO3 single crystal substrate with the (001) plane as the film forming surface.

Further, according to a preferred embodiment of the present invention, the substrate is heated to 230 to 1410°C using a heater. By heating the substrate, the thin film undergoes an action similar to sintering, and becomes a suitable perovskite-type oxide or pseudo-perovskite-type oxide. However, if the substrate temperature is too high, it becomes difficult to control the composition of the deposited film, and the desired perovskite-type oxide or pseudo-perovskite-type oxide cannot be obtained.

Next, the apparatus used to carry out the method of the present invention will be explained. FIG. 1 is a schematic diagram of an ion beam sputtering apparatus used for producing the superconducting oxide thin film of the present invention.

The apparatus shown in FIG. 1 includes a chamber 1, a target (evaporation source) 2 placed in the chamber 1, a magnetron electrode 3 placed so as to surround this coupe, and a high-frequency power source 4 placed side by side. , a group vji, 5 which is provided facing the raw material target 2 and on whose surface a thin film is to be formed. The chamber 1 is connected to a vacuum pump (not shown) through an exhaust hole 8, so that the interior thereof can be evacuated.

An ion source 10 capable of differential pumping is installed in the chamber 1 facing the substrate 4, and the ion source 10 includes an introduction hole 9 for taking in 0□ gas, an exhaust hole 8, and a cold cathode ion generating electrode 11.
, an ion extraction electrode 12.

A heating heater 6 is attached to the substrate 5, and the temperature of the substrate can be adjusted. Further, the chamber 1 is provided with an atmospheric gas introduction hole 9 .

EXAMPLES The present invention will be explained below using examples, but it goes without saying that the technical scope of the present invention is not limited to these examples in any way.

A superconducting thin film was produced using the ion beam sputter link apparatus shown in FIG.

The film forming conditions for each example are shown in Table 1.

Example 1 As raw material target 2, Y and Ba were mixed at a molar ratio of 1:2, and Cu was mixed at a molar ratio of Y, Ba, and Cu of 1:2:3.
An alloy prepared by mixing 10% by weight in excess of the amount was used, and the (001) plane of the λIgo single crystal was used as the film-forming surface for the substrate 5.

First, the alloy target 2 and the substrate 5 are placed in the chamber 1.
was installed. Next, the inside of the chamber 1 is evacuated to a vacuum, and 4.
02 of 5 x 10-'Torr and 6.0 x 10'T
orr's Ar was introduced. The inside of the ion source 10 was similarly evacuated, and then 02 of 3.0×10' Torr was introduced.

The heater 6 is energized and the substrate temperature is heated to 680°C.
High frequency power was passed through the RF main electrode ion generating electrode. At the same time, a voltage was also applied to the ion extraction electrode. Each power and voltage is RF main power 45W/c++f,
The discharge voltage of the ion generation electrode was 1.6 kV, and the acceleration voltage applied to the ion extraction/extraction electrode was 620V. At this time,
The thin film was produced at a deposition rate of 0.3 persons/second. The film forming conditions are shown in Table 1.

Example 2 As raw material target 2, L'ASBa was used at a molar ratio of 1:2
The molar ratio of Cu to La, Ba, and Cu was 1:
An alloy prepared by mixing 10% by weight more than the 2:3 ratio was used, and the (001) plane of the MgO single crystal was used as the film-forming surface for the substrate 5. The film-forming procedure was the same as in Example 1, and the film-forming conditions are shown in Table 1.

Example 3 As raw material target 2, La and Sr were used in a molar ratio of 1:2.
[The molar ratio of U to La, Sr, and Cu is 1=
Using an alloy prepared by mixing 10% by weight in excess of the 2:3 ratio, the substrate 5 is made of 5rTiOa single crystal (00
1) surface was used as the film-forming surface. The film-forming procedure was the same as in Example 1, and the film-forming conditions are shown in Table 1.

Next, samples were prepared to measure the resistance of each of the obtained thin films. In the sample for resistance measurement, a pair of A1 electrodes were further formed by vacuum deposition on both ends of the thin film formed on the substrate 5, and lead wires were soldered to the AI electrodes.

Table 1 shows the film forming conditions and the measurement results of the obtained TCs Tcf (temperature at which the electrical resistance becomes completely zero).

As a result, it was found that the method of the present invention can appropriately control the crystal structure and oxygen concentration of the thin film and form a superconducting thin film with excellent properties.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, the present invention makes it possible to form a superconducting oxide into a thin film having a much higher Tc than conventional superconductors. Therefore, the present invention is useful in the field of applying superconductors and bodies as thin film devices, such as Ma-tisoo's switching elements called Josephson devices, Anacker's memory devices, and even superconducting quantum interferometers. It is effective when used for applications such as SQtllD).

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an example of a sputtering apparatus used to carry out the method of the present invention. (Main reference numbers) 1...Chamber, 2...Raw material target, 3
...RF main electrode 4..High frequency power supply, 5..Substrate, 6..Heater, 8..Exhaust hole,
10...Ion source, 12...Ion extraction electrode

Claims (26)

[Claims] (1) One element α selected from the elements of groups IIa and IIIa of the periodic table, one element β selected from the elements of groups IIa and IIIa of the periodic table that include the same elements as α, and the periodic table
Forming a thin film by physical vapor deposition using an alloy containing at least one element γ selected from group Ib, IIb, IIIb, IVa, and VIIIa elements as a deposition source and using an O or O_2 ion beam in combination. A method for producing a superconducting thin film characterized by: (2) The oxide superconducting thin film has the general formula: (α_1_−_xβ_x)γ_yO_z (where α, β, and γ are the elements defined above, x is the atomic ratio of β to α+β, and 0.1≦ x≦0.9, and y and z are 0 when (α_1_−_xβ_x) is 1
．． 4≦y≦3.0, 1≦z≦5 atomic ratio) The method for producing a superconducting thin film according to claim 1, wherein the oxide is an oxide having a composition represented by the following. . (3) The method for producing a superconducting thin film according to claim 1 or 2, wherein the vapor deposition source is an alloy of Ba, Y, and Cu. (4) The method for producing a superconducting thin film according to claim 1 or 2, wherein the vapor deposition source is an alloy of Ba, La, and Cu. (5) The method for producing a superconducting thin film according to claim 1 or 2, wherein the vapor deposition source is an alloy of Sr, La, and Cu. (6) The method for producing a superconducting thin film according to claim 3, wherein the atomic ratio Y/(Y+Ba) of the vapor deposition source is in the range of 0.06 to 0.94. (7) The atomic ratio Ba/(La+Ba) of the vapor deposition source is 0.04
5. The method for producing a superconducting thin film according to claim 4, wherein the superconducting thin film is in the range of 0.96 to 0.96. (8) The atomic ratio Sr/(La+Sr) of the vapor deposition source is 0.03
6. The method for producing a superconducting thin film according to claim 5, wherein the superconducting thin film is in the range of 0.95 to 0.95. (9) Atomic ratio Y/(Y+Ba) of vapor deposition source is 0.1 to 0
．． 4. The method for producing a superconducting thin film according to claim 6, characterized in that: (10) The atomic ratio Ba/(La+Ba) of the vapor deposition source is 0.0
8 to 0.45, the method for producing a superconducting thin film according to claim 7. (11) The atomic ratio Sr/(La+Sr) of the vapor deposition source is 0.0
9. The method for producing a superconducting thin film according to claim 8, wherein the ratio is from 5 to 0.1. (12) The atomic ratio of Ba-Y-Cu, Ba-La-Cu, or Sr-La-Cu in the evaporation source is
a-Y-Cu, Ba-La-Cu or Sr-La-C
Based on the atomic ratio of u, Ba-Y-Cu, Ba-La
The method for producing a superconducting thin film according to any one of claims 1 to 11, wherein the method is adjusted depending on the vapor deposition efficiency of -Cu or Sr-La-Cu. (13) The method for producing a superconducting thin film according to any one of claims 1 to 12, characterized in that the O or O_2 ion beam is irradiated toward a substrate. (14) Claims 1 to 1, characterized in that the physical vapor deposition apparatus is equipped with an ion source capable of differential pumping.
The method for producing a superconducting thin film according to any one of Item 3. (15) The method for producing a superconducting thin film according to any one of claims 1 to 14, characterized in that a cold cathode ion source is used as the ion source. (16) 1.7×10^-^5 to 8 in the above ion source
．． 16. The method for producing a superconducting thin film according to any one of claims 1 to 15, characterized in that O_2 gas in a range of 3 x 10^-^3 Torr is flowed. (17) Adjust the discharge voltage of the ion source to 0.8 to 10k.
17. The method for producing a superconducting thin film according to any one of claims 1 to 16, characterized in that the voltage is in the range of V. (18) Set the acceleration voltage of the ion source to 50V to 40k.
18. The method for producing a superconducting thin film according to any one of claims 1 to 17, characterized in that the voltage is in the range of V. (19) The evaporation atmosphere contains Ar and O_2, and the Ar partial pressure is 1.0×10^-^5 to 1.0×10^-^2T
19. The method for producing a superconducting thin film according to claims 1 to 18, wherein the superconducting thin film is within the range of orr. (20) O_2 partial pressure of the above vapor deposition atmosphere is 1.0×10^
20. The method for producing a superconducting thin film according to claim 19, wherein the torr is within the range of -^5 to 1.0 x 10^-^3 Torr. (21) The superconducting thin film according to any one of claims 1 to 20, wherein the physical vapor deposition is a vacuum evaporation method, an ion blating method, or an ion beam sputtering method. How to make (22) The method for producing a superconducting thin film according to any one of claims 1 to 21, wherein the substrate is heated by a heater during vapor deposition. (23) The heating temperature of the substrate during vapor deposition is 230 to 14
23. The method for producing a superconducting thin film according to claim 22, wherein the temperature is in the range of 10°C. (24) As the substrate, MgO single crystal or SrTi
24. The method for producing a superconducting thin film according to any one of claims 1 to 23, characterized in that an O_3 single crystal is used. (25) The method for producing a superconducting thin film according to claim 24, wherein the film-forming surface of the MgO single crystal or SrTiO_3 single crystal substrate is a (001) plane. (26) Claims 1 to 25, characterized in that the substrate is one selected from the group consisting of glass, quartz, Si, stainless steel, and ceramics.
A method for producing a superconducting thin film according to any one of the above.