JPH02267121A - Oxide superconducting 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 [Field of Industrial Application] The present invention relates to a superconducting thin film used for 5QUIDs, Josephson devices, superconducting transistors, electromagnetic wave sensor device wiring, electrodes, antennas, etc.

[Prior art] As is well known, oxide superconducting materials whose critical temperature significantly exceeds the liquid nitrogen temperature of 77 K and are expected to be applied to general society are P.
Compared to conventional superconducting materials such as N b and N b 33 n, the becoherence length is shorter. Also, due to the crystal structure, the anisotropic pressure is strong. For example, looking at the coherence length, the C-axis direction is a,
It is 1/3 to 1/10 of the b-axis direction. Therefore, epitaxial growth is essential for applying oxide superconducting materials to thin film devices that require high critical current densities or suppress potential barriers such as grain boundaries. In order to perform epitaxial growth, it is necessary to match the lattice of the substrate and the superconducting material, and in general, PHYSICAL REVIEW VOL
, 38 No. 1 (1988) 765-767,
APPL Engineering ED FHYS Engineering C8 LETTER3VO
L, 53 No. 17 (1988) 1654-1
656, single crystal substrates such as MgO were used.

[Problems to be Solved by the Invention] However, the single crystal oxide substrate used for forming conventional oxide superconducting thin films is limited to crystals with a diameter of approximately 5 cmφ or less, even though MgO can have a relatively large diameter. It was getting worse. Moreover, its production required complicated control and a long time. Therefore, unlike semiconductors, they have had problems such as not being able to be produced as efficiently as possible, the shape of the element being limited, and manufacturing costs being high.

In addition, when directly attaching an oxide superconducting thin film using a single-crystal silicon wafer (which can be made into a large-diameter single-crystal silicon wafer (which can be obtained up to approximately 20 cm in diameter), it reacts with the silicon wafer and becomes a low critical temperature phase, or in severe cases, a superconducting phase. It broke down and became a semiconductor phase or an insulator phase. Even if a superconductor phase is obtained, the crystal will naturally not grow well epitaxially.

The present invention is intended to solve these problems, and its purpose is to provide an oxidation method that enables large diameters, high critical current densities, and suppresses grain boundary barriers, has no limitations on applications, and is excellent in mass production. The aim is to obtain superconducting thin films at low cost.

[Means for Solving the Problems] In order to solve the above problems, the oxide superconducting thin film of the present invention is made of a Bi film formed on a single crystal silicon wafer substrate.
-M-Cu-0 system or Bi-Pb-M-Cu-0 system oxide superconducting thin film (here M represents alkaline earth) between the single crystal silicon wafer substrate and the oxide superconducting thin film When the composition is expressed as CaoxFy in parts, x<0. 2.1
．． It is characterized by forming an intermediate layer satisfying 6≦y≦2.

If the values of x and y are out of this range, the intermediate layer will not have a good crystal structure, and the oxide superconducting thin film formed thereon will not be a good epitaxially grown film.

Furthermore, the composition range is more preferably that X is O to 0.05 and y is 1.9 to 2.

[Example] The present invention will be explained below with reference to Examples.

Example-1 First, CaoxF was deposited on a single crystal silicon wafer substrate.
A Y film is formed to a thickness of 400 to 500 nm using a reactive vapor deposition method. Hereinafter, this film will be referred to as an intermediate layer.

The film formation conditions were: Ca metal was used as the evaporation source, and the substrate temperature was 480°C.
1 Initial vacuum degree 2*1O-6Torr, film formation rate 17~2
0 nm/min. Fluorine is supplied to the film by converting CF4 gas into plasma and introducing it into the chamber. (The degree of vacuum after introduction was on the order of 10-' Torr) The obtained intermediate layer was analyzed by X-ray diffraction and RHEED and was found to be an epitaxially grown film. Also ESC
According to analysis by A and SIMS (using CS ions), a trace amount of oxygen was found in the film, although it was not intentionally introduced.

Next, B i 1.97P b 0.2S r 2. O.C.
a 2.03Cu3.05CI superconducting film with a thickness of 1'50 nm
Formed. The film forming conditions were B1-Pb alloy, Sr, and
Ca and Cu metals were used (evaporation was performed by electron beam for B1-Pb alloy and Knudsen cell for other metals), vacuum degree 3 to 6 * 1 O-5 Torr, substrate temperature 6
80°C1 film deposition rate 20-35 nm/mi
n, and oxygen is supplied by irradiating the substrate with oxygen plasma activated by microwaves during film formation.

Next, an annealing treatment is performed at 500° C. in an oxygen atmosphere for 15 hours to obtain an oxide superconducting thin film. However, as-gro
In some cases, a superconducting film can be obtained using wn, and annealing treatment is performed as necessary.

When the obtained oxide superconducting thin film was analyzed by X-ray diffraction and RHEED, it was found to be an epitaxially grown film.

Example 2 Under the conditions of Example 1 in Table 1, oxygen was also introduced into the chamber to change the amount of oxygen in the film to form a CaOxFy film. However, the oxygen supply is not in the form of plasma. Table 1 shows the values estimated by ESCA, AES, S-MS analysis (number of samples n-7), etc. of the composition of the intermediate layer obtained under conditions of different amounts of introduced oxygen. Next, Bi25r2Ca2Cu3
The film forming conditions for forming a 0y film of 1100nm using the MBE method are as follows: Bi, Sr, Ca, and Cu metals are used as the evaporation source, and the degree of vacuum is 3.
~6*1O-5Torr (during film formation), substrate temperature 600~
The temperature is 680° C. and the film formation rate is 20 to 35 nm/min. Oxygen is supplied by irradiating the substrate with oxygen plasma activated by microwaves during film formation.

Next, the critical temperature and critical current density of the obtained oxide superconducting thin film were measured by a four-probe method. The measurement temperature was 77K, and the measurement atmosphere was helinium gas.

For cooling, Daikin Industries cryogenic refrigerator UV204SR is used.
It was used.

The results are shown in Table 2 (Example-1) and Table 3 (Example 2). a, b, c, d are comparative examples; a:
B1-3 r-C directly on single crystal silicon wafer substrate
a: When a Cu-0 thin film is formed, b: When MgO single crystal is used for the substrate, c: d: When the composition range of the intermediate layer deviates from the conditions of the present invention.

As can be seen from Table 2, the oxide superconducting thin film according to the present invention has a large diameter even when a large-diameter silicon wafer is used as a substrate.
The high critical current density is close to that obtained when using a gO single crystal substrate. The reason why Comparative Example a does not become superconducting is because the deposited material reacts with the silicon wafer over the entire film and does not adopt the crystal structure of the superconducting material. In the present invention, since this reaction can be suppressed, superconducting properties can be obtained even when the film is formed as thin as 1100 nm.

This is because lattice matching with the oxide superconducting material shown in Table 3 cannot be achieved. In other words, the composition of the intermediate layer, expressed as CaOxFy, needs to satisfy x<0.2.1.6≦y≦2.

More preferably, CaF2 containing a small amount of oxygen is preferred, as can be seen from the fact that B has the highest critical current density among the examples. The effect of oxygen introduction also suppresses the occurrence of cracks in the film.

Table 4 shows the price of a single crystal silicon wafer substrate and a conventionally commonly used MgO single crystal substrate.

Table 4 Also, when the composition of the intermediate layer deviates from the range of the present invention, the critical current density sharply decreases as shown in Table 3.

This is because the crystal structure of the intermediate layer becomes unstable due to the composition being out of the appropriate range, and the single-crystal silicon wafer substrate formed on it has a large diameter of 4 inches (approximately 10 cmφ), approximately twice that of the MgO single-crystal substrate. However, the price is about 1
/20. By employing a single crystal silicon wafer substrate in this way, it is possible not only to increase the diameter but also to significantly reduce costs.

[Effects of the Invention] As described above, according to the present invention, it is possible to epitaxially grow an oxide superconducting thin film even if a single-crystal silicon wafer, which can have a large diameter, is used as a substrate, while suppressing reactions with the substrate. Because of this, a high critical current density can be obtained. Furthermore, despite the large diameter, the price of the board is much lower.

Therefore, there are no limitations on usage due to shape or critical current density.
Oxide superconducting thin films with excellent mass productivity can be obtained at low cost.

The oxide superconducting thin film obtained by the present invention can be used as it is, or after being subjected to microfabrication, formation of a protective film, lamination of other materials, etc., 5QUID, Josephson device, superconducting transistor, electromagnetic wave sensor, magnetic sensor, element wiring, current It can be applied to control elements, magnetic flux quantum memories, optical switch elements, magnetic shields, antennas, etc.

that's all Applicant: Seiko Epson Corporation Attorney Kisanbe Tsuchi Suzuki and 1 other person

Claims (1)

[Claims] Bi formed on a single crystal silicon wafer substrate
- M-Cu-O system or Bi-Pb-M-Cu-O system oxide superconducting thin film (here M represents alkaline earth) between the single crystal silicon wafer substrate and the oxide superconducting thin film. When the composition is expressed as CaO_xF_y, x<0.2,
An oxide superconducting thin film characterized by forming an intermediate layer in which 1.6≦y≦2.