JPH042694A - Oxide single crystal base, production thereof and superconductor device using the same - Google Patents

Abstract

PURPOSE:To stabilize superconductivity by making a specific oxide superconductive thin film to perform epi-growth on a base made of Ca-La-Ga system oxide single crystal having K2NiF4-type crystal structure. CONSTITUTION:An oxide superconductive thin film having a chemical composition expressed by formula II (delta=0-1; Ln is Yb, Er, Y, Ho, Gd, Eu or Dy) and having all of lattice constants a and b are within 3.76-3.92Angstrom or 5.32-5.54Angstrom is made to epi-growth on a Ca-La-Ga system oxide single crystal base having K2NiF4-type crystal structure and expressed by formula I (-0.05<x, y, z<0.05; -0.2<w<0.2) formed by Czochralski method or zone-melting method, etc.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an oxide single crystal substrate, a super semiconductor device using the same, and a manufacturing method thereof, and particularly relates to the composition of the single crystal substrate. .

(Prior art) Superconductivity is said to be the most unique property among the various electromagnetic properties exhibited by substances, and is characterized by complete conductivity,
Future developments in applications are expected by utilizing the respective properties such as perfect diamagnetism and quantization of magnetic flux.

Electronic devices that utilize such superconducting phenomena are expected to have a wide range of applications, including high-speed switches, high-sensitivity detection elements, and high-sensitivity magnetometers.

As a superconductor often used in conventional superconducting devices, for example, Nb3G is deposited on a substrate by plasma sputtering.
There is a thin film. This critical temperature is at most 23° and can only be used at liquid helium temperatures. However, the use of liquid helium increases cooling costs and technical burden due to the need for liquefaction and cooling equipment, and furthermore, helium resources are extremely scarce.
This has become a major problem that hinders the practical application of superconductors in industrial and consumer fields.

Therefore, various attempts have been made to obtain superconductors with high critical temperatures.In particular, recent research on oxide superconducting thin films has been remarkable, and the superconducting critical temperature has exceeded 77°K. It became possible to operate using nitrogen as a refrigerant.

Conventionally, such oxide superconducting thin films have mainly been produced using MgO heated to a high temperature by sputtering or vapor deposition.
A method has been adopted in which it is formed on a single crystal substrate or a 5rTi03 single crystal substrate.

In addition, sapphire, ys
z, silicon, gallium arsenide, LiNb0a, GG
GSLaGaO3, LaAlO3, etc. are attracting attention.

However, MgO single crystal substrate or 5rTi03
Conventional thin film formation methods that use single-crystal substrates have problems in that the superconducting critical current (JC) cannot be stably increased and the superconducting critical temperature (Tc) is unstable. Ta.

By the way, in order to produce an excellent epitaxial film, it is necessary for the substrate material to have the following conditions.

(1) good lattice matching with the thin film crystal; (II) no deterioration of film quality due to interdiffusion with the substrate during epitaxial film growth; (m) high melting point because the substrate material is heated to high temperature; (IV) A single crystal with good crystallinity is available; (V) It has electrical insulation properties.

On the other hand, as a high critical temperature oxide superconductor, LnBa
CuO(δ-0-1, Ln:Y2 3
7-δ b, Er, Y, Ho, Gd, Eu, Dy), BiS
r-Ca-Cu-0 based oxide thin film, Tl-Ba-Ca
Many oxides, such as -Cu-0-based oxide thin films, have been reported.

The lattice constants a and b of these oxides are all 3
,76 to 3.92 people. Also, by changing the 456 coordinates, J 2 a and J2b can be seen as fundamental lattices, and in this case, the lattice constants a and b are 5.
It is expressed as 32 to 5.54 people.

On the other hand, the currently widely used substrate material is magnesium oxide (MgO), which has a lattice constant difference of 7 to 11%, which makes it possible to form a good epitaxial growth film. was extremely difficult to obtain. This is sapphire, ysz.

The same was true for silicon, gallium arsenide, L 1Nb03 , and GGG.

Furthermore, 5rTi03 has a smaller difference in lattice constant from the oxide superconducting thin film than MgO, 0.4 to 4%, and has excellent lattice matching. However, 5rTi03 is currently only produced by the Bernoulli method, and its crystallinity is extremely poor.

Only crystals with a tipit density of more than 105/C- can be obtained, and it is difficult to obtain a high quality epitaxial film on such a substrate with poor crystallinity. In addition, it was impossible to handle large-sized boards manually.

Furthermore, the LaGaO3 single crystal has a lattice constant a-5°496
It is expected that it will have a good lattice matching with the oxide superconductor, but since a phase transition occurs around 150°C, there is a problem that twins will be included in the crystal. Therefore, the removal of twins is a major issue in the practical application of L a Ga 03 single crystals as substrates for superconducting thin films.

Also, for LaAlO3 single crystal, the lattice constant a-b
-3.788 people, and good lattice matching with oxide superconductors is expected, but because the melting point is extremely high at 2100°C, it is extremely difficult to produce a single crystal, and there are twins in the crystal. There was a problem that it included.

(Problems to be Solved by the Invention) As described above, the materials conventionally used as substrates for superconducting thin films have good lattice matching with the above-mentioned superconducting thin film, and are easy to obtain as single crystals. There is nothing that meets the conditions,
There was a problem that a stable super-semiconductor device could not be obtained.

Therefore, the present inventor developed 5rLaGa0 as a single crystal substrate that has good lattice matching with superconducting thin films and can be easily formed.
4 single crystal substrate (patent application No. 63-323739) and 5r
NdGaO+ (Japanese Patent Application No. 1249930) is proposed.

The present invention was made in view of the above-mentioned circumstances, and provides a single crystal substrate material capable of forming even better epitaxial superconducting thin films, solves the instability of superconductivity of oxide thin films, and solves the superconducting instability of oxide thin films. The purpose is to provide high-quality superconductor thin films that can be applied to conduction devices.

[Structure of the invention]

(Means for Solving the Problem) Therefore, in the present invention, as a substrate material, calcium-
A lanthanum-gallium based oxide single crystal substrate is used.

Ca La Ga 0 1-x 1-y I-z 4-v(-0,0
5<x<0.05, -0.05<y<0.0
5. −.

, 05 <z <0.05. −0.2<W<0.2
) Then, an oxide superconducting thin film is formed on this substrate by epitaxial growth.

(Function) As a result of various experiments, the present inventor synthesized CaLaGa04 and learned that it can be an extremely good substrate for an oxide superconductor.

This single crystal has a K2NiF4 type crystal structure, with lattice constants of g-3, 81 and c-12, 12. When we change the coordinates by 45'', a becomes 5°39 people.

As mentioned above, the lattice constants a and b of currently reported high-temperature oxide superconductors are 3.76 to 3°92 (depending on the coordinate system, it is also believed to be 5.32 to 5.54). .

Therefore, the lattice constant of CaLaGaO4 is in the above range 3,
76 to 3.92 people, and if we rotate the coordinate system by 45 degrees, J 2 a can be seen as a basic lattice,
a-5.40 people, but the lattice constant is 5.32~ when J2a of the oxide superconductor thin film is regarded as the fundamental lattice.
It is also within the range of 5.54 people. In this way Ca L
The difference in lattice constant between the aG a 04 single crystal and the oxide superconductor thin film is extremely small. Furthermore, the crystal structure is extremely similar, and the lattice matching with the 5rNd Ga 04 single crystal oxide superconductor thin film is extremely excellent, satisfying all of the above-mentioned conditions.

However, there have been no reports on CaLaGaO4 single crystals, and it was unclear whether it was possible to produce CaLaGaO4 single crystals.

Therefore, the present inventors conducted various studies on single crystallization of CaLaGa04, and as a result, succeeded in a single crystal production test.

This single crystal can be created by Czochralski pulling method, zone melting method, etc., and the composition range of the single crystal obtained in this way is Ca1□ l-ya Ga 0 1-z 4-v (-0, 05<x<0.05, -0.05<y
<0.05-0.05 <z <0.05 -0.
It was confirmed that 2<W<0.2).

Ca La Ga1- obtained in this way
x 1-y 1-z 04-w By using a single crystal substrate, an oxide superconducting thin film is epitaxially grown on this substrate by sputtering, vacuum evaporation, etc., and a superconductor with good superconductivity is produced. We were able to obtain a thin film.

(Example) Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

First, a method for manufacturing CaLaGaO4 single crystal will be described.

441.96gr of CaCO3 (purity 9999%),
763.43g La2O3 (99.99% purity) and 439.22g Ga203 (99.999% purity)
After mixing, calcining at 1000℃ and decarboxylation treatment,
It was crushed and press-molded.

The molded body thus formed was heated to 1200°C in the atmosphere.
Approximately 1450g of C80,96
A L a +, 02G a 1.0204.02 sintered body was obtained.

This sintered body was placed in an iridium crucible or a platinum crucible having an external diameter of 80 + nm, a height of about 80 mm, and a wall thickness of 2 cm, and was melted by high-frequency heating. When an iridium crucible was used here, a nitrogen atmosphere containing 0.5 to 2% oxygen was used. In addition, when using Shirokane Rutsuho, 10 to 2
A nitrogen atmosphere containing 1% oxygen was used. Note that oxygen was added here in order to prevent decomposition and evaporation of gallium oxide.

In this way, Cao96L a , , 2G
After melting the 2044o2 sintered body, using the Czochralski pulling method, Ca L a G a
04 single crystal was grown.

As a seed crystal, 5rTi03 [10
0] single crystal or a [100] single crystal of 5rLaGaC)+, and after obtaining the CaLaGa04 single crystal, the single crystal of the [100] orientation of the crystal was used as a seed crystal. The crystal pulling conditions are the pulling speed lff
1m/Hr, crystal rotation speed 3Orpm, diameter 30mm
, a [100 co-axis single crystal with a length of 70 mm could be obtained.

In this way, the formed C a L a G a
Argon/oxygen (mixing ratio 1:1) was used using a (001) simple crystal substrate 1 made by slicing a 04 single crystal into a wafer shape.
A YBa2 Cu30 thin film 2 with a thickness of 1000 nm was deposited by RF magnetron sputtering in an atmosphere of . Here, the target and 7-δ have a composition of YBa2 Cu30 after film formation.
A sintered body adjusted so that -δ is used is used. The conditions at this time were a gas pressure of 10 Pa, an electric power of 300 W, and a substrate temperature of 600°C.

After the deposition, annealing was performed at 900° C. for 1 hour in an oxygen atmosphere.

Using the superconducting thin film pattern 2 thus formed on the CaLaGa0+ single crystal substrate 1 as a basic structure, a device such as a superconductor memory device can be formed.

Here, as shown in the figure, gold (Au) electrodes 31, 32, 33 are then formed by vapor deposition through an electrode forming mask.
．． The zero resistance temperature Te01 and the superconducting critical current J at 7-δ at 77° were measured using the four-probe method.

4 is a stabilized power supply, and 5 is a voltmeter.

YBa2 formed on this CaLaGaO4 single substrate 1
The zero resistance temperature TcO of Cu30 superconducting thin film is 8
7°, and the superconducting critical current Jc at 77° is 6X
This shows an extremely good result of 1.05A/c-.

For comparison, Sr, which has been conventionally used as a substrate,
(100) simple crystals of TiO3 and 5rLaGao4
(100) YB U2 under the same conditions using a simple crystal
A CU30.7-δ thin film was deposited. Table 1 shows the results of measuring the superconducting critical current Jc at zero resistance temperatures Tc01 and 77 at this time.

Table 1 As is clear from the results, when CaLaGa04 single crystal is used as a substrate, both T and J are excellent. This means that the CaLaGa04 single crystal substrate is
This is thought to be due to the excellent crystallinity and uniformity of the film.

In addition, when the crystallinity of the surface of the superconducting thin film prepared in this way was observed by reflection high-speed electron diffraction, it was found that CaL
In the superconducting thin film produced on the aG a 04 single crystal substrate, a sharp streak-like diffraction pattern showing the (001) orientation could be obtained, indicating that a good epitaxially grown film was formed.

In addition, the target material was changed to LnBa2Cu307-δ(
δ-0~l, Ln: Yb, Er, Y, Ho.

CaLaGa0 as above as Gd, Eu, Dy)
4 A superconducting thin film fabricated on a single-crystal substrate under the same conditions as above also yielded a shabby streak-like diffraction pattern showing the (001) orientation, indicating that a good epitaxially grown film was formed. Ta.

For CaLaGa04 single crystal, when the (001) plane is used, an epitaxial film of the (001) plane of the superconducting thin film is easily formed, but when the (100) plane and (110) plane are used, the epitaxial film is easily formed. (100) plane of superconducting thin film,
An epitaxial film having a (110) plane can be formed.

Example 2 Next, as a second example of the present invention, a (001) CaLaGaO4 single crystal substrate formed by the same method as Example 1 was prepared.
R on the surface under an atmosphere of argon/oxygen (mixing ratio 2°1)
Bi25r2Ca2Cu30 1o-a was deposited to a thickness of 1000 by F magnetron sputtering.

Here, the target has a composition of Bi25r after film formation.
2Ca2Cu,0. -6 was used.

The conditions at this time were a gas pressure of 5 Pa and an electric power of 200 W.

The substrate temperature was 600°C.

After the deposition, annealing was performed at 900° C. for 1 hour in an oxygen atmosphere.

B f 2 S r 2 Ca produced in this way
Electrodes were formed on the 2 Cu 30 10-11 thin film in the same manner as in Example 1, and the zero resistance temperature Tc01 and the superconducting critical current Jc at 77° were measured using the four-terminal method.

The results are shown in Table 2.

Table 2 As is clear from the results, both Teo and Je are excellent when CaLaGa04 single crystal is used as a substrate. This is because CaLaGaO4 single crystal substrate has excellent film crystallinity and uniformity, so Bi25r2C
It is considered that in the case of forming the a2Cu30+o-a thin film, an excellent thin film similar to that in Example 1 could be obtained.

Note that this single crystal substrate is made of Bj2Sr2Ca2CLl
30 +o-,s Part of the Bi element in the thin film was replaced with pb 8 11. P bO,2S r2 Ca2CU3
0t.

Even when a 6-thin film was formed, stable Te0sJe could be obtained.

Furthermore, when the (001) plane of the CaLaGa0+ single crystal is used, an epitaxial film of the (001) plane of the superconducting thin film is easily formed, but when the (100) plane and (110) plane are used, the epitaxial film is easily formed. The (100) plane of the conductive thin film, (
110) plane can be formed.

Example 3 Next, as a third example of the present invention, R was applied to a (001) simple crystal substrate of CaLaGa04 formed in the same manner as in Example 1 in an atmosphere of argon/oxygen (mixing ratio 1:1).
YB a2 Cu307-6 was deposited to a thickness of 1000 by F magnetron sputtering. Here, the target has a film composition of T12 Ba2 Ca2 after film formation.
The one adjusted to be Cu30 is used. The conditions at this time were gas pressure of 10 Pas, power of 80 W, and substrate temperature of 600°C.

After deposition, it was wrapped with gold foil and 905% in an oxygen atmosphere.
Annealing was performed at ℃ for 10 minutes. The purpose of wrapping with gold foil is to prevent evaporation of thallium.

TI2 Ba2 Ca2 Cu produced in this way
30 The zero resistance temperature Tc01 of the thin film and the superconducting critical current Jc at 77°K were measured using the four-terminal method.

The results are shown in Table 3.

Table 3 In this case as well, as is clear from the results in Table 3 above, C
It can be seen that when a L a G a 04 single crystal is used as a substrate, both Tc0sJc are excellent.

This is because the Ca L a G a 04 single crystal substrate has excellent film crystallinity and uniformity.
It is considered that in the case of forming a 2Cu30 thin film, an excellent thin film similar to that in Examples 1 and 2 could be obtained.

Also in this case, when the (001) plane of the Ca L a G a 04 single crystal is used, the (00
1) epitaxial film is easily formed, but (10
When the 0) plane and the (110) plane are used, epitaxial films of the (100) plane and the (110) plane of the superconducting thin film can be formed, respectively.

Note that the present invention is not limited to these examples and can be applied to the formation of other oxide superconducting thin films.

Further, regarding the composition of the oxide single crystal substrate, in addition to the composition of the embodiment, it is also effective to add a small amount of impurities such as Sr, Nd, and Cr.

Furthermore, in the above embodiments, the RF magnetron sputtering method was used to form the superconducting oxide thin film, but the method is not limited to this, and may include vacuum evaporation method, multi-dimensional evaporation method, molecular beam epitaxy (MBE method), MSD method etc. may be used.

〔Effect of the invention〕

As explained above, according to the present invention, when forming a superconducting thin film, Ca-La-Ga having a 2NiF4 type crystal structure as shown in the following formula is used as a substrate material.
Ca La Ga 0 L-x I-y l-z 4-w (-0,0
5<x<0.05, -0.05<y<0.0
5 -0.05 < z < 0.05. −0.2<ν
<0.2), it is possible to provide a superconductor with good lattice matching, stable and high superconducting critical temperature, and stable superconducting critical current.

[Brief explanation of the drawing]

The figure is a diagram showing a method for measuring a superconductor according to an embodiment of the present invention. 1-...Ca L a G a 04 substrate, 2...Y
B a2Cu30 thin film, 31-34-=electrode, 4
... Stabilized power supply, 5... Voltmeter.

Claims (6)

[Claims] (1) A calcium-lanthanum-gallium-based oxide single crystal substrate characterized by having a K_2NiF_4 type crystal structure as shown in the following formula. Ca_1_-_xLa_1_-_yGa_1_-_zO
_4_-_w(-0.05<x<0.05, -0.05
<y<0.05, -0.05<z<0.05, -0.2
<w<0.2) (2) It is characterized by comprising a calcium-lanthanum-gallium-based oxide single crystal substrate having a K_2NiF_4 type crystal structure as shown in the following formula, and an oxide superconducting thin film formed on this substrate. A super-semiconductor device. Ca_1_-_xLa_1_-_yGa_1_-_zO
_4_-_w(-0.05<x<0.05, -0.05
<y<0.05, -0.05<z<0.05, -0.2
<w<0.2) (3) A step of preparing a calcium-lanthanum-gallium oxide single-crystal substrate having a K_2NiF_4 type crystal structure as shown in the following formula, and forming a substrate with lattice constants a and b of 3.76 on the single-crystal substrate. ~3.92 Å or 5.3
1. A method for manufacturing a supersemiconductor device, comprising a superconducting thin film forming step of epitaxially growing an oxide superconducting thin film having a thickness in the range of 2 to 5.54 Å. Ca_1_-_xLa_1_-_yGa_1_-_zO
_4_-_w(-0.05<x<0.05, -0.05
<y<0.05, -0.05<z<0.05, -0.2
<w<0.2) (4) The superconducting thin film forming step is a step of forming an oxide superconducting thin film having a composition ratio expressed by the following formula. Production method. LnBa_2Cu_3O_7_-_δ (δ=0 to 1, Ln: Yb, Er, Y, Ho, Gd, E
u, Dy) (5) The superconducting thin film forming step includes Bi-Sr-Ca-
4. The method of manufacturing a super-semiconductor device according to claim 3, wherein the step is to form a Cu-O-based oxide thin film. (6) The superconducting thin film forming step includes Tl-Ba-Ca-
4. The method of manufacturing a super-semiconductor device according to claim 3, wherein the step is to form a Cu-O-based oxide thin film.