JPH042695A - Oxide single crystal base, production thereof and superconductor device using the same - Google Patents

Abstract

PURPOSE:To stabilize superconductive critical temperature and superconductive critical electric current with good matching of lattice by making an oxide superconductive thin film to epi-growth on a specific single crystal base. CONSTITUTION:At least a species of impurity selected from Ca in a molar ratio of 0.00001-0.1 to Sr, Nd in a molar ratio of 0.00001-0.1 to La and Cr in a molar ratio of 0.00001-0.1 to Ga is added to a compound having a composition of SrLaGaO4 and K2NiF4-type crystal structure to form a single crystal base. Then, an oxide superconductive thin film expressed by the formula (delta=0-1; Ln is Yb, Er, Y, Ho, Gd, Eu or Dy) and having all lattice constants within 3.76-3.92Angstrom or within 6.32-5.54Angstrom .

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an oxide superconductor, a supersemiconductor device using the same, and a method for manufacturing the same.

(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, Nb3 is deposited on a substrate by plasma sputtering.
There is a Ge 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 burdens due to the need for liquefaction and cooling equipment.
Furthermore, because helium resources are extremely scarce, this has become a major problem that hinders the practical application of superconductors in the 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, other single crystals for substrates include sapphire, ys
z, silicon, gallium arsenide, LiNb0a, GG
GSLaGaOa, LaA10a, etc. are attracting attention.

However, MgO single crystal substrate or SrTi
03 In the conventional thin film formation method using a single crystal substrate as a substrate, it is not possible to stably increase the superconducting critical current 1c), and there are problems in that 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; (n) no deterioration of film quality due to interdiffusion with the substrate during epitaxial film growth; (m) high melting point, as 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~l, Ln:Yb, Er, Y,
Ho, Gd, Eu, Dy), Bi-Sr--Ca-C
Many oxides have been reported, including u-0-based oxide thin films and Tl-Ba-Ca-Cu-0-based oxide thin films.

The lattice constants a and b of these oxides are all 3
．． It ranges from 76 to 3.92 people. Also, if we change the 45@ coordinates, J 2 a and J2b can also be seen as fundamental lattices, and in this case, the lattice constants a and b are 5.
It is said that there were 32 to 5,54 people.

On the other hand, magnesium oxide (MgO), which is currently a widely used substrate material, has a -4°203 lattice constant difference of 7 to 11%, which makes it difficult to form good epitaxial growth films. was extremely difficult to obtain. This is sapphire, ysz.

The same was true for silicon, gallium arsenide, L i NbO3, 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, and it is only possible to obtain crystals with an etch bit density of more than 105 pieces/C-. It is difficult to obtain a high quality epitaxial film on a poor substrate. Furthermore, it was also impossible to obtain large-sized substrates.

Furthermore, the L a G a Oa single crystal has a lattice constant of a-5
゜496, b-5,5548, which is expected to have good lattice matching with the oxide superconductor, or because a phase transition occurs around 150℃, the crystal contains twins. There are problems, and the removal of twins is a major issue when putting LaGaO3 single crystal into practical use as a substrate for superconducting thin films.

Also, for LaAlO3 single crystal, the lattice constant a-b
-3.788 people, perhaps due to good lattice matching with oxide superconductors, but the melting point is extremely high at 2100°C, making it extremely difficult to create a single crystal, and there are twins within 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 films, and are easy to obtain single crystals. There is nothing that meets the conditions,
There was a problem that it was impossible to obtain a stable super-semiconductor device.

Therefore, the present inventor has proposed a SrLaGaO4tl crystal (Japanese Patent Application No. 323739/1983).

The present invention improves this SrLaGaO4 single crystal to provide a single crystal substrate material that can form even better epitaxial superconducting thin films, solves the instability of superconductivity of oxide thin films, and solves the problem of superconducting devices. The purpose is to provide high-quality superconductor thin films that can be applied to

[Structure of the invention]

(Means for Solving the Problem) Therefore, in the present invention, the composition is SrLaG as the substrate material.
In a compound having a crystal structure of 2NiF4 type, which is aO4, the molar ratio to strontium (Sr) is 0.0.
0001 to 0.1 mol of calcium (Ca), neodymium (Nd) and gallium (Ga) with a molar ratio of 0.00001 to 0.1 mol to lanthanum (1,a).
) is added with one or more types of chromium (Cr) in a molar ratio of 0.00001 to 0.1 mol.

Then, an oxide superconducting thin film is formed on this substrate by epitaxial growth.

(Function) By using the SrLaGaO4 single crystal substrate doped with impurities in this way, an oxide superconducting thin film with extremely good characteristics can be formed.

This is thought to be because the addition of impurities makes the substrate surface chemically active and allows formation of a good epitaxially grown film.

By the way, the SrLaGaO4 sintered body is K2N1F4
It has a type crystal structure with a lattice constant of a-3,843, and has good lattice matching to all oxide superconducting thin films.

As mentioned above, the lattice constants a and b of currently reported high-temperature oxide superconductors range from 3.76 to 3.92A.

Therefore, the lattice constant of SrLaGaO4 is within the above range 3.
This is approximately the median value of 76 to 3.92 people.

Also, if we rotate the coordinate system by 45 degrees, J 2 a can be seen as the fundamental lattice, and it can also be seen as a-5,40A, but if /2a of the oxide superconductor thin film is seen as the fundamental lattice, The lattice constant is also in the range of 5.32 to 5.54 people. As described above, the difference in lattice constant between the S rLaGa04 single crystal and the oxide superconductor thin film is extremely small. In addition, the crystal structure is extremely similar, and the lattice matching with the SrLmGa04 single crystal oxide superconductor thin film is extremely excellent.
It meets all of the conditions mentioned above.

Therefore, the present inventors conducted various studies on single crystallization of SrLaGaO4, and as a result of creating a mixed crystal single crystal with added impurities, they found that the crystallinity decreased and the difficulties in crystal growth technology increased. We have found impurities that can improve the surface condition without any impurities, and the limit for their addition.

The impurity elements Ca, Nd, and Cr all have the effect of slightly decreasing the lattice constant, but the above amounts are not large enough to affect lattice matching.

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

Example 1 First, Sr r -Cax L a H-N d
A method for manufacturing a yG a 1Cr,04 single crystal will be described.

570, llgr of 5rCOa (99.99% purity), 20.34gr of CaCO3 (99.99% purity), and 629.08gr of La203 (99.99% purity)
and 34.19gr of Nd2O3 (99.99% purity)
, 350.49 gr of Ga20a (purity 99.999
%) and 24°72gr Cr2O3 (purity 99.99
%) were mixed, calcined at 1000°C, decarboxylated, pulverized, and press-molded.

The molded body thus formed was heated to 1300°C in the atmosphere.
About 1500 g of S r 0.
95Ca o, osL a 0.95N d O, O9
Ga 0.92C "...O4 sintered body was obtained.

This sintered body was placed in an iridium crucible or a platinum crucible having an external diameter of 80 W, a height of about 80 ms, and a wall thickness of 2 mm, 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 a platinum crucible, 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 S r 0.95Cao, 05L a
o, eqN dO,05G a 0.92Cr o
After melting the oso a sintered body, a single crystal was grown using the Czochralski pulling method.

As a seed crystal, a single crystal of SrLaGaO4 was used. The crystal pulling conditions are a pulling speed of 1 sv/H.
r, crystal rotation speed 25 rpm, diameter 3011, length 70
-1 [100] axis single crystal could be obtained.

The thus formed SrLaGaO4 single crystal containing Ca, Nd, and Cr as impurities was sliced into a wafer-like (001) opposite crystal substrate 1, and argon/oxygen (mixing ratio 1:1) was used. YBa2C with a thickness of 1000A was formed by RF magnetron sputtering in an atmosphere.
A uaO thin 7-δ film 2 was deposited. Here, the target used was one whose composition ratio was adjusted to 7-δ so that the composition ratio after film formation was YBa2CuaO. Further, the film forming conditions at this time were a gas pressure of 10 Pa, 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.

Gold (Au) is deposited by vacuum evaporation using an electrode forming mask.
Electrodes 31 to 33 are formed.

The zero resistance temperature Tc01 and the superconducting critical current Jc at 77° of the YBa2Cua O7-δ thin film thus produced were measured using a four-probe method as shown in the figure. Here, 4 is a stabilized power supply, and 5 is a voltmeter.

The results are shown in Table 1.

For comparison, S containing Ca, Nd, and Cr as impurities
Using rLaGaO4 single crystal as a substrate, Y
A Ba2Cu30 thin film was deposited.

Table 1 shows the zero resistance temperature T eOs and 77
The results of measuring the superconducting critical current Jc at °C are shown.

Table 1 As is clear from the results, by adding Ca, Nd, and Cr as impurities, the zero resistance temperature To can be lowered. It can be seen that the superconducting critical current JC is improved at , and 77°.

When the molar ratio of each element is less than 0.00001, no effect is observed, and when the molar ratio is more than 0.1, cracks and cells tend to form in the crystal.

Note that these impurities may be used alone or in combination of two or three types.

Example 2 Next, as a second example of the present invention, Sr containing Ca, Nd, and Cr as impurities was formed in the same manner as in Example 1.
A LaGaO4 single crystal was sliced into a wafer shape (0
01) Argon/oxygen (mixing ratio 2:
]) B i2 S r2 Ca2 Cu with a film thickness of 1000 nm by RF magnetron sputtering method in an atmosphere of
30 was deposited.

As a target, the composition ratio after film formation is Bi25r2Ca
The composition ratio was adjusted to 2Cu30. The film forming conditions at this time were a gas pressure of 5 Pa and a power of 20 Pa.
The temperature was 0W and the substrate temperature was 600°C.

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

Bi25r2 Ca2Cu30 produced in this way
A gold electrode was formed on the thin film in the same manner as in Example 1, and the superconducting critical current J at zero resistance temperature Tc01 and 77°
c was measured using the four-terminal method.

The results are shown in Table 2.

Table 2 As is clear from the results, by adding Ca, Nd, and Cr as impurities, the zero resistance temperature Teos
It can be seen that the superconducting critical current JC at 77° and 77° is improved.

It is considered that in the case of forming the Bi25r2Ca2Cu, O thin film as described above, an excellent thin film similar to that in Example 1 could be obtained.

Example 3 Next, as a third example of the present invention, Sr containing Ca, Nd, and Cr as impurities was formed in the same manner as in Example 1.
The LaGaOa single crystal was sliced into wafers (0
01) Argon/oxygen (mixing ratio 11) on a simple crystal substrate
) film thickness by RF magnetron sputtering method in an atmosphere of 000 T 12 Ba2 Ca2Cu
30 was deposited.

As a target, the composition ratio after film formation is T128a2C
A material adjusted to have a2 Cu30 was used. Further, the film forming conditions at this time were a gas pressure of 10 Pa, electric 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 for 0 minutes at °C. The purpose of wrapping with gold foil is to prevent thallium from evaporating.

TI2 Ba2 Ca2 Cu produced in this way
30 A gold electrode was formed on the thin film in the same manner as in Examples 1 and 2, and the superconducting critical current Jc at zero resistance temperatures Te01 and 77 was measured using the four-terminal method.

The results are shown in Table 3.

Table 3: In this case, the above is also true! As is clear from the results in Table 3, C
It can be seen that by adding a, Nd, and Cr as impurities, the zero resistance temperature T, o, and superconducting critical current Jc at 77@ are improved.

As described above, it is considered that in the case of forming the T12 Ba2 Ca2 Cua O thin film, an excellent thin film similar to that in Examples 1 and 2 could be obtained.

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

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

Further, in the above embodiment, the case where the reference plane orientation is the (001) plane has been described, but the same effect can be obtained when the (100) (110) plane is used.

In addition, in the above example, Ca, Nd, and Cr were added as impurities, but in addition, Ba and Mg were added as impurities.

Effects are also seen when AJ, Fe, Si, Ce, Pr, and Zr are added to Na, although there is no clear effect when Ca, Nd, and Cr are added.

〔Effect of the invention〕

As explained above, according to the present invention, when forming a superconducting thin film, the composition is SrLaGaO as a substrate material.
C in a compound having a 2NiF4 type crystal structure
An oxide single crystal substrate doped with α, Nd, and Cr is used, and an oxide superconducting thin film is formed on this substrate by epitaxial growth, resulting in good lattice matching and stable superconducting critical temperature. It becomes possible to provide a superconductor with a high and stable superconducting critical current.

[Brief explanation of drawings]

The figure is a diagram showing a method for measuring a superconductor according to an embodiment of the present invention. 1...Sr added with Ca, Nd, and Cr
LaGaO4 substrate, 2 ・Y Ba 2 Cu 30
Thin film, 317-δ ~34... Electrode, 4... Stabilized power supply, 5... Voltmeter. Applicant's agent Takahisa Kimura 1---, Al board 2-1-Mi&8mNWIE 31-34---Au electrical packaging 4---? Standardized immersion 5-voltmeter diagram

Claims (6)

[Claims] (1) K_2NiF_ whose composition is SrLaGaO_4
Strontium (S
calcium (Ca) having a molar ratio of 0.00001 to 0.1 mol to r), neodymium (having a molar ratio of 0.00001 to 0.1 mol to lanthanum (La)
Nd), the molar ratio to gallium (Ga) is 0.000
1. A single-crystal substrate characterized by adding one or more of chromium (Cr) in an amount of 0.01 to 0.1 mol. (2) K_2NiF_ whose composition is SrLaGaO_4
Strontium (S
calcium (Ca) having a molar ratio of 0.00001 to 0.1 mol to r), neodymium (having a molar ratio of 0.00001 to 0.1 mol to lanthanum (La)
Nd), the molar ratio to gallium (Ga) is 0.000
0.01 to 0.1 mole of chromium (Cr), and an oxide superconducting thin film formed on the substrate. Semiconductor equipment. (3) K_2NiF_ whose composition is SrLaGaO_4
Strontium (S
calcium (Ca) having a molar ratio of 0.00001 to 0.1 mol to r), neodymium (having a molar ratio of 0.00001 to 0.1 mol to lanthanum (La)
Nd), the molar ratio to gallium (Ga) is 0.000
01 to 0.1 mol of chromium (Cr) is added to the single crystal substrate; A method for manufacturing a super-semiconductor device, comprising the step of epitaxially growing an oxide superconducting thin film having a thickness of 92 Å or in the range of 5.32 to 5.54 Å. (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) Claim (3) characterized in that the superconducting thin film forming step is a step of forming a Bi-Sr-Ca-Cu-O based oxide thin film.
A method of manufacturing the supersemiconductor device described above. (6) Claim (3) characterized in that the superconducting thin film forming step is a step of forming a Tl-Ba-Ca-Cu-O based oxide thin film.
A method of manufacturing the supersemiconductor device described above.