JPH04144993A - Substrate for forming oxide superconductor thin film - Google Patents

Abstract

PURPOSE:To facilitate the growth of an oxide superconductor thin film by changing the crystal-mixing ratio of a mixed crystal thin film in a substrate comprising a silicon single crystal and a La1-xNdxGaO3 mixed crystal thin film layer formed on the silicon single crystal towards the direction of film thickness. CONSTITUTION:An intermediate layer La1-xNdxGaO3 on a single crystalline Si (100) formed by MBE method to prepare a substrate. La, Nd, Ga2O3 are prepared as evaporation sources, and the partial pressure of oxygen in a chamber during the formation of the film is fixed to 2X10<-4> Torr. The temperatures of the evaporation sources are controlled by a computer to change the mixed crystal composition of the formed film. The thin film of a NdGaO3 composition is first formed on a single crystalline Si in a thickness of 156Angstrom at a substrate temperature of 715 deg.C. The mixed crystal thin film of La0.2Nd0.8GaO3 is subsequently formed in a thickness of 156Angstrom , and the mixed crystal thin film of La0.6 Nd0.4GaO3 mixed thin film is finally formed to provide the subject substrate.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides LnBavCusOx, I, nBatcu
a(lx(Ln: Y, I, a.

Ce, Nd, Ps+ F, u, Gd, Tb,
Dy+ Ho, Hr+ Tm, yb, I, u, etc.
The present invention relates to a substrate for forming an oxide superconductor thin film such as YBCO (hereinafter, this oxide will be referred to as YBCO).

(Prior Art) In order to hybridize a superconductor with a semiconductor device, it is considered to be an essential condition that a superconducting thin film such as YBCO can be formed on a Si single crystal substrate.

By the way, in order to form a superconducting thin film, it is necessary to maintain the substrate temperature at a high temperature of 600 to 800°C, but since Si and Y)IcO react significantly at this high temperature, it is difficult to form a crystalline substrate in Si. It is not possible to directly form a Y 11 CO superconducting thin film on. Therefore, thin films with relatively high chemical stability such as ZrO or 5rTiOs are
i (formed as an intermediate layer in the It crystal), and its
Attempts have been made to form superconducting thin films in -.

Furthermore, looking at the matching of the crystal lattices of the substrate and superconducting thin film, for example, YBatCusOx has a; 3.82 people;
It is orthorhombic with b3.89 people and c=11.68 people,
Since Si is a cubic crystal system with a=5.43 people, hypothetically,
Even if an epitaxial layer could be formed directly on a crystal substrate, a mismatch in the lattice constants between the Si single crystal and the YBCO thin film would cause lattice strain, and the properties of the superconducting thin film would be insufficient. 2. Even in the conventional technology of sandwiching a thin film of 0..5rTi (13, etc.) as an intermediate layer, it is impossible to expect that the interlayer thin film of ZrL, 5rTiO+, etc. Since a large number of defects are introduced, the crystallinity of the superconducting thin film formed on this intermediate layer thin film cannot be said to be sufficient, and the superconducting properties cannot be maximized.

(Problems to be Solved by the Invention) Therefore, the present invention solves the above-mentioned drawbacks and solves the problem of S i 11
Oxide superconducting thin film formation that enables the growth of high-quality oxide superconducting thin films by reducing or completely eliminating mismatches in lattice constants between crystals and intermediate layer thin films, and between intermediate layer thin films and superconducting thin films. The aim is to provide a substrate for

(Means for Solving the Problems) The present invention provides an S41+1 crystal formed in 1, a+-
A crystallized film layer conductive thin film forming substrate consisting of xNdxGaO+ΔSi crystal thin film layer, characterized in that the mixed crystal ratio of the mixed crystal thin film is changed stepwise or continuously in the film thickness direction. This is a substrate for forming superconducting thin films.

(Function) In order to eliminate the mismatch in lattice constant between the S i it crystal and the superconducting thin film, the present inventors have developed an intermediate layer III
After various studies on A, 1, a + XNdxGao
It was discovered that the mixed material (-C) eliminates the mismatch described in (1) and also functions as a buffer layer that suppresses the reaction between Sl and YBCO.

In the present invention, l;a+-xNdxGaOs shown in FIG.
Using the dependence of the lattice constant of the mixed crystal material on the composition of the Si
1 of the intermediate layer so that the region of the intermediate layer in contact with the 'tl crystal has a lattice constant that is the same as or extremely close to the crystal lattice of the Si single crystal. Select the mixed crystal ratio X of the a+-xNdxGaOs mixed crystal material, and similarly select the mixed crystal ratio X for the region of the intermediate layer in contact with the superconducting thin film, step by step between the two regions, Alternatively, by continuously changing the mixed crystal ratio At the same time, the lattice constant within the intermediate layer can also be changed gradually in response to the mixed crystal ratio X, which changes stepwise or continuously, so internal stress is also alleviated during this time, forming a high-quality superconducting thin film. Now you can.

The substrate for forming a superconducting thin film of the present invention is M B 14
It can be produced by any film forming method such as a laser sputtering method or a laser sputtering vapor deposition method.

(Example) An intermediate layer Cat-J is formed on the lit crystal Si (+00) plane.
A substrate was fabricated by forming dxGaOs using the M1 silicon method. As an evaporation source, 1, a + N d + G av
03 and set the oxygen partial pressure in the chamber to 2XI during film formation.
The temperature of the evaporation source was fixed at O-' Torr, and the mixed crystal composition of the film was changed by controlling the temperature of the evaporation source using a computer. First, a thin film having a composition of 1idGaO was formed on single crystal Si to a thickness of 156 layers. At this time, the temperature of the E plate was 715°C. Next, a mixed crystal thin film of do, 5Ga (13) was formed with a film thickness of 156 on Lao, y, and finally 1.ao, 5Nd
o, aGaOa mixed crystal thin film was formed to a thickness of 154.

For comparison, ZrOx on top of single crystal 5i (10G)
, 5rTiO1, and NdGa0+ were prepared.

-1- The substrate of the embodiment described above and a Si substrate without an intermediate H layer,
And, a superconducting thin film YHatCusOx was formed by laser evaporation using the 1λ plate of Comparative Example 2 and an excimer laser (^rP 193 ns). The deposition conditions for the superconducting thin film are such that the energy density of the ekinoma laser is set to 1
”/C1, change the oxygen partial pressure in the chamber/desire to IXI (
I"'r(l r r, 3XIO"Torr during cooling,
] The λ plate temperature was set at 670°C.

Regarding the tiI superconducting thin film, the superconducting properties are as follows:
Critical temperature (Tc), critical current density (Jc) at 77K
) was investigated.

Table 1 Characteristic values are not shown for those with superconducting thin films formed, but this means that Tc and Jc could not be observed due to reaction deterioration. The examples of the present invention show higher values of both Tc and Jc than the comparative examples. It can be seen that the lattice constants of the Si single crystal/intermediate layer thin film/superconducting thin film interfaces obtained in this example have extremely good matching as shown in FIG.

Note that Figure 1 shows the intermediate layer Lao, tNdo, and 5GaOs.
The illustration is shown with layers omitted.

(Effects of the Invention) By adopting the above configuration, the present invention achieves 5iIl
1. Between the crystal and the superconducting thin film. a+-xNtLxGaO
+ A strained superlattice can be interposed, making it extremely easy to grow an oxide superconducting thin film with excellent superconducting properties, and facilitating the production of a hybrid device of a Si semiconductor and a superconductor.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the crystal lattice matching state of the intermediate layer thin film and superconducting thin film produced on Si single crystal in the example, and FIG. 2 is a diagram showing the state of crystal lattice matching of the intermediate layer La+-
FIG. 2 is a diagram showing the dependence of the lattice constant on the mixed crystal composition for a Ga03 mixed crystal material. Figure 1

Claims (1)

[Claims] La_1_-_xNd_xG formed on Si single crystal
An oxide superconducting thin film comprising a substrate for forming an oxide superconducting thin film comprising an aO_3 mixed crystal thin film layer, wherein the mixed crystal ratio of the mixed crystal thin film is changed stepwise or continuously in the film thickness direction. Substrate for formation.