JPH012212A - Method for manufacturing superconducting composite oxide thin 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 a method for producing a superconducting 19 composite oxide thin film, in particular,
The present invention relates to a method for producing a superconducting composite oxide thin film with excellent uniformity and stability.

[Prior art] Many substances that exhibit superconductivity have been known in the past, and among alloy systems, Nb-based alloys such as Nb3Ge and NbN exhibit a high superconducting critical temperature (hereinafter referred to as Tc), and Nb
It was reported about 10 years ago that Ge has a Tc of 23.6 [Applied Phys.
s Let-ters, 23.480 (1973)
] Until recently, no substance with higher Tc was known.

On the other hand, in the composite oxide system, it has been reported that LiTi0a has a Tc of 13.7;
r-4als Research Bulletin,
8+ 777 (1973)], its Tc is low and its practicality as a superconducting material is low.

Superconducting materials have a wide range of applications, and the main area of development is in magnet applications.Superconducting magnets have zero electrical resistance, so they can generate a strong magnetic field with only a small amount of power required for cooling. becomes possible. Therefore, it can be expected to be applied to fields that require a strong magnetic field, such as nuclear fusion, magnetic levitation trains, MHD power generation, accelerators, and motors. In the power field, applications include generators, power storage, and power transmission lines, and in the electronics field, computer elements such as logic and memory (Josephson elements)
, a sensor that detects weak magnetic fields (quantum interference device)
It has applications in microwave devices that can be used in millimeter-wave band mixers and oscillators.

Superconducting materials used in such applications are required to have a high Tc, and the search for material F4 is currently continuing. If a material with high Tc is developed,
Instead of expensive and resource-problematic liquid helium (boiling point 4.2K), it is now possible to use liquid nitrogen (boiling point 77.3K), which is inexpensive and resource-rich, as a refrigerant, and its uses are increasing. is expected to expand even further.

Recently, it has been reported that rare earth hydroxides of the Ba-La-Cu-0 system have a Tc as high as 30 [Ze
I-tschrift fjir Physik, B
64.189 (1986)], even higher TC (
Y-Ba-Cu-0-based rare earth composite oxide has been reported as a substance with
Review Letters 58.908 (1
987)].

[Problems to be solved by the invention] Superconducting thin films are used in the electronics field, such as devices and sensors, and are characterized by high speed, high sensitivity, and high precision, but in order to satisfy these characteristics, uniform film quality is required. and stability are necessary.

Thin films of Pb, Nb-based metals, alloys, and intermetallic compounds may undergo compositional changes due to oxidation, resulting in a problem in that their properties deteriorate or change.

Furthermore, the processing process for these thin films is limited due to their composition, and T
Due to the low c, practical applications are limited and problematic.

Recently, composite oxides with high Tc have been proposed, but the production of thin films with uniform modification and stability has not yet been completed.

[Means for Solving the Problem] As a result of extensive research to solve the above-mentioned problems, the present inventors have discovered that a uniform and stable superconducting thin film having a high Tc can be produced by reactive sputtering. This discovery led to the completion of the present invention.

That is, the method for producing a composite material of the present invention is a method for producing a superconducting composite oxide thin film, which is characterized by sputter linking onto a substrate using a molten rare earth-copper composite oxide as a target.

The method for producing a superconducting composite oxide thin film of the present invention will be described in detail below.

First, the superconducting composite oxide of the present invention will be explained.

As a superconducting composite oxide, Li-Ti-0 system (Te1
3.7K), Ba-(Pb-Bi)-0 system (Te1
3K), Rb-W-0 series (Tc 6.4K), and copper-based composite oxides. Li-Ti-0 series, B
Since a-(Pb-Bi)-0 and Rb-W-0 complex oxides have low Tc, they are expensive and require the use of liquid helium, which is a scarce resource, limiting their practical use. I end up getting beaten up. - Since some of the cuprous composite oxides have Tc higher than that of liquid nitrogen, they can be made into superconductors by using liquid nitrogen, which is a low-cost and abundant resource, as a refrigerant, which is more preferable from an industrial perspective. Become something.

The superconducting copper-based composite oxide has the general formula %, where , is at least one selected from Ca, Sr, and Ba, and M2 is 5cSY, La, Ce, P.
r,, Nds Pm, Sm, Eu5Gd's Tb,
, Dy, Ilo, , Er, Tm-yb, and Lu. Furthermore, the composition ratios of a, b, and x are as follows: 0.5≦a≦3 0.02≦X≦0.91.0≦
It is preferable that b≦4.0 because it produces a superconducting composite oxide with high Tc.

Next, a method for manufacturing the superconducting composite oxide layer will be explained.

First, the method for producing a superconducting copper-based composite oxide of the present invention is as follows:
For example, rare earth compounds such as rare earth oxides and rare earth hydroxides, barium oxide, barium carbonate, strontium oxide,
A method of mixing a predetermined amount of an alkaline earth metal compound such as strontium carbonate, and a copper compound such as cupric oxide or cupric carbonate and heating it to cause a solid phase reaction, rare earth elements, alkali such as strontium, barium There is a method in which an aqueous solution of oxalate is added to a mixture of aqueous solutions of soluble compounds such as chlorides and nitrates of earth metals and copper to cause coprecipitation, followed by heating and reaction. Furthermore, after producing a mixture of two of these metal compounds by a coprecipitation method, a predetermined composite oxide can also be obtained by mixing the mixture with other metal compounds.

The heating reaction conditions vary depending on the composition, but from 600℃ to 1
It is preferable to conduct the treatment at 200° C. for 0.5 hours to one week in a predetermined atmosphere.

Next, the rare earth-copper composite oxide melt-molded target used in the present invention will be explained. The rare earth-copper-based composite oxide melt-molded target of the present invention is characterized by containing the composite oxide produced as described above and a raw material for producing the composite oxide.

The method for producing the rare earth-copper composite oxide molten target of the present invention includes, for example, applying a slurry in which a rare earth-copper composite oxide is suspended in ethanol to a platinum plate, and then heating the composite oxide. A rare earth-copper composite oxide molten target can be obtained by melting and solidifying the material. Alternatively, a rare earth-copper composite oxide may be placed in a platinum crucible and melted by resistance heating or high-frequency heating to form a liquid, and then placed in a mold and molded into a predetermined shape to be used as a target. Furthermore, a raw material mixture of the composite oxide or a raw material obtained by melt-molding and dividing into a plurality of parts can also be used as the target.

The substrate used in the present invention may be any substrate as long as it has heat resistance that can withstand heat treatment during and after sputtering. For example, to rare earth oxides such as lanthanum oxide, yttrium oxide, etc.1201, sapphire, partially stabilized zirconia, magnesia, silicon, 5rTiO1
, BaTiO3, silicon carbide, aluminum nitride, gold,
Copper, platinum coated quartz, silver coated sapphire, etc. can be used.

Various shapes can be used depending on the field of application.

Next, a method for producing a composite oxide thin film by reactive sputtering according to the present invention will be explained.

The manufacturing method of the present invention uses the above-mentioned rare earth-copper composite oxide molten target and substrate, and uses, for example, an oxygen partial pressure of 0. I
Reactive sputtering is performed in the presence of oxygen at Torr.

If the oxygen partial pressure exceeds 5 Torr, it is not preferable because a dense film cannot be obtained and the film formation rate is reduced.

Therefore, a suitable sputtering atmosphere is in the presence of oxygen at 5 Torr or less, preferably ITo
The atmosphere is below rr. Further, it is preferable to mix an inert gas such as Ars He in order to increase sputtering efficiency.

Next is the substrate temperature, which affects the crystallinity of the thin film and the amount of gas mixed in. The substrate temperature during sputtering is 5
At temperatures above 00° C., the film formation rate is low, but the resulting thin film is homogeneous, crystalline, and dense, which is preferable. Also, the substrate temperature is 50
If the temperature is below 0°C, the resulting thin film will tend to be amorphous due to the large amount of gas mixed in, but it can be made into a crystalline and homogeneous film by heat-treating it at a temperature of 500 to 1000°C in a predetermined atmosphere after sputtering. . At this time, in the present invention, the heat treatment temperature is 500°C to 1000°C, more preferably 750°C to 950°C. If the heat treatment temperature is less than 500°C, the crystallization of the thin film will not be sufficient;
If the temperature is higher than 0°C, the composite oxide on the substrate will flow and the film thickness will be disturbed, which is not preferable.

Further, by performing heat treatment in a predetermined atmosphere, it is possible to crystallize the thin film and adjust the oxygen content. For example, the oxygen content of the thin film can be increased by heat treatment under conditions of high oxygen partial pressure. Since the cooling rate after heat treatment may affect the crystal structure, crystal grain size, oxygen content, etc. of the thin film, it is preferable to cool the thin film at a predetermined cooling rate. In addition, multi-stage aging may be used, in which heat treatment is performed at a predetermined temperature for crystallization, and then heat treatment is performed at another predetermined temperature for a predetermined time and in a predetermined atmosphere, and then cooled at a predetermined cooling rate in order to transform the crystal phase. can.

As a heating method in the heat treatment, for example, a method may be used in which the thin film is heated together with the substrate in an electric furnace, or a method in which laser light or infrared light is focused and irradiated onto the thin film to heat part or all of the thin film. can.

Next, it is preferable to grow the film at a film forming rate of 10 to 500 people/min. A film forming rate of less than 10 persons/min is disadvantageous because it takes a long time to obtain a predetermined film thickness and productivity decreases. Further, a film forming rate of 500 persons/min or more is not preferable because the resulting film is non-uniform and pinholes are likely to be generated.

Examples of sputtering methods used in the present invention include high frequency sputtering, magnetron sputtering, and bias sputtering.

[Example] Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 Yttrium chloride, barium nitrate and copper nitrate each at 1 mo7/j! Dissolved in ion-exchanged water to a concentration of . Yttrium chloride aqueous solution I, barium nitrate aqueous solution 21, and nitrium MIPj311 were taken to prepare a mixed aqueous solution. Next, 957 g of oxalic acid dihydrate (1.1 times the stoichiometric amount) was added to the aqueous solution to coprecipitate yttrium, barium, and steel oxalate. The obtained precipitate was filtered, washed with water, and then dried at 100'C. followed by 930℃
The sample was calcined for 2 hours in oxygen at a temperature of .

10 g of the obtained composite oxide was suspended in 7 g of methyl ethyl ketone to form a slurry, and the slurry was coated on a platinum disk with a diameter of 4 inches. The coated platinum disk has a temperature of 0 at 1050℃.
．． After heating and melting for 5 hours, it was used as a target.

Sputtering is done by magnetron sputtering.
A composite oxide thin film was formed on a sapphire plate (50 x 50 x 1 mm). As for the sputtering conditions, the atmosphere was 0□50%-Ar50% mixed gas as the flow gas, and the total pressure during sputtering was 5 x 10-3T.
It was kept at orr. Further, sputtering was performed for 4 hours at a substrate temperature of 200°C.

The composite oxide thin film was then heated in oxygen at a temperature of 930°C for 6 hours, and then heated at a rate of -500°C/hour for 5 hours.
Cooled to 80°C. It was then heated at a temperature of 580°C for 1 hour and then cooled at a rate of -50°C/hour.

In addition, electrodes were attached to the composite oxide thin film, the film was placed in a taliostat, and its electrical resistance was measured, and it was found to be a superconducting thin film having a Tc (zero resistance temperature) of 95K.

Example 2 Yttrium oxide 22.6g, barium nitrate 104.5g
After mixing 47.7 g of cupric oxide in a ball mill for 2 hours, the mixture was heated at a temperature of 900°C in oxygen for 12 hours, and -50'
A composite oxide was obtained by cooling at a cooling rate of C/hour.

The obtained tips were placed in a mold and compression molded at a pressure of 100℃ + r/cd, then placed in a platinum plate; A disc-shaped composite oxide sintered body was used as a target.

Platinum plate (50 x 40 x
A composite oxide thin film was formed on the 0.1 m1). The conditions for sputtering are 0!30%-^r70%Y
Combination gas was used as a flow gas, and the total pressure during sputtering was maintained at I x 10-'' Torr.The substrate temperature was set to 100°C and sputtering was performed for 2 hours.Then, after heating at a temperature of 930°C in oxygen for 5 hours, , -900
It was cooled to 580°C at a rate of °C/hour. Then 580℃
After heating in oxygen for 6 hours at a temperature of -50°C/hour.

The obtained composite oxide thin film had a thickness of 8,000 mm and was a homogeneous film. After cutting, the temperature dependence of magnetic susceptibility was measured using a vibrating magnetometer, and the diamagnetic transition temperature of magnetic susceptibility was 90°C.

Example 3 33.7 g of neodymium oxide, 104.5 g of barium nitrate
, 47.7 g of cupric oxide were mixed in a ball mill for 2 hours, heated in oxygen at a temperature of 920°C for 2 hours, and then -100
A composite oxide was obtained by cooling at a rate of °C/hour.

500 g of the obtained powder was placed in an MgO crucible and melted in a high frequency melting furnace to form a liquid. The composite oxide melt was placed in an iron mold, cooled and solidified, and then cut into a 4 inch diameter to obtain a target.

A composite oxide thin film was formed on a partially stabilized zirconia substrate (50 x 40 x 1 x 1) by magnetron sputtering.

The conditions for sputtering are 0□20%-Ar
An 80% mixed gas was used as the flow gas, and the total pressure during sputtering was maintained at 5 x 10-'Torr. Further, sputtering was performed for 4 hours at a substrate temperature of 250°C. The mixture was then heated at 930°C for 6 hours under oxygen, and then cooled to 580°C at a rate of -900°C/hour.

Then, after heating at a temperature of 580°C for 6 hours, -50°C/
Cooled at a rate of 100 hrs.

The obtained composite oxide thin film had a thickness of 7,200 mm and was a homogeneous film.

When an electrode was attached to the thin film and the electrical conductivity was measured in a cryostat, it was found that Tc (zero resistance temperature) was 92.

[Effects of the Invention] As explained above, the method for producing a superconducting composite oxide thin film of the present invention provides a superconducting composite oxide thin film having uniform film quality and stability, and is extremely useful industrially. be.

Patent applicant: Asahi Kasei Industries, Ltd.

Claims (1)

[Claims] A method for producing a superconducting composite oxide thin film, which comprises sputtering onto a substrate using a rare earth-copper composite oxide molten molded body as a target.