JPH03232723A - Superconductor - Google Patents

Abstract

PURPOSE:To obtain a lamination type superconductor capable of showing the critical temperature of the superconductive oxide itself by laminating a silicon substrate, an oxide ground layer having a spinel type crystal structure and an oxide superconductor layer in order. CONSTITUTION:(a) A substrate (Silicon is suitable), (b) an oxide ground layer [a layer having spinel type crystal structure, composed of oxide represented by AB2O4 (A is Zn or Mg; B is Fe, Al or Ga) and having 200Angstrom -1mum, especially 500-2000Angstrom thickness] and (c) an oxide superconductor layer [especially oxide superconductor thin film of Y (or Er)-Ba-Cu-O-based oxide, Bi-Sr-Ca-Cu-O-based oxide, etc., having 1000Angstrom -1mum, especially 1000-4000Angstrom thickness] are laminated in that order to obtain the objective superconductor applicable to a device composed of combined semiconductors such as a superconductive transistor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a stacked superconductor having an oxide superconducting layer containing yttrium, barium, or the like. In particular, the present invention relates to Y (or Er)-Ba-Cu-0 system, B1-5
The present invention relates to a stacked superconductor having a thin film of an oxide superconductor such as r-Ca-Cu-0. These superconductors can be applied to the electronics field, especially to the superconducting transistor field.

[Prior art]

Conventionally, substrates for forming Y-based, Bi-based, etc. oxide superconductor layers include S r T x Oa single crystal substrates, MgO
Single crystal substrates, SiO substrates, glass substrates, silicon substrates, etc. are used.

However, when considering applying the oxide superconducting layer to the electronics field by combining it with a semiconductor, it is preferable to use silicon as the substrate.

However, when silicon is used as a substrate, its critical temperature is considerably lower than that of superconducting oxides.

This is because the substrate is heated or annealed to form a superconducting oxide thin film on the silicon substrate.
It is subject to a thermal history at high temperatures of 0°C to 800°C, and at these high temperatures, a mutual diffusion phenomenon occurs between silicon and superconducting oxide, which deteriorates the superconducting properties of the oxide layer and the properties of the silicon substrate. This is thought to be caused by.

In order to avoid such adverse effects of the superconducting properties of the superconducting layer, the thickness of the superconducting layer must be increased.

In order to solve the problems associated with increasing the film thickness, MgO, ZrO2, Ca
F2. A method of providing an intermediate layer made of a single crystal of Pt or the like and oriented along the -axis has been considered, but the results are still unsatisfactory.

〔the purpose〕

An object of the present invention is to provide a layered superconductor that can exhibit the critical temperature inherent to the superconducting oxide itself.

Another object of the present invention is to provide a stacked superconductor in which silicon and superconducting oxide do not adversely affect each other when silicon is used as a substrate.

〔composition〕

The present invention provides a substrate with a general formula (Tadashi) having a spinel type crystal structure, where A is Zn or Mg, B is Fe, and A
At least one element selected from the group consisting of Q + Ga. ) The present invention relates to a superconductor characterized in that an oxide underlayer and an oxide superconducting layer shown in the following are laminated in this order.

The thickness of the oxide base layer is 200 to 1 μm, especially 500 μm.
The number of people is preferably 2000 to 2000, and the thickness of the superconducting layer is 1000.
1 μm to 1 μm, particularly preferably 1000 to 4000 people.

The substrate is 5rTiO, which has been used conventionally.
, MgO, etc., or polycrystalline silicon can also be used, but silicon single crystal is most preferred in the present invention, and the crystal planes are (1,1,1), (100), (1
10) Surfaces are used.

Next, an oxide having a spinel crystal structure having the general formula AB, 04 will be explained.

A is a divalent metal ion, B is a trivalent metal ion, A is Mg, Zn, and B is selected from the group consisting of Fe, Al, and Ga.

If it contains Fe, it is preferable not to have ferromagnetism*
ZnFe20. exhibits antiferromagnetism at extremely low temperatures and is paramagnetic above that temperature. For non-magnetic materials, Z n Ga2
0. , Mg Ga, 04, etc.

These have a lattice constant of 8.2 to 8.4 chromaticity.

On the other hand, YlB a2Cu, Ox, Bi25 r, Ca2
What is the lattice constant of superconductors such as Cu and Ox?

3.83 to 3.88 people, 5.4 people. Further, the lattice constant of Si is 5.41.

In the present invention, it is preferable to epitaxially grow the superconducting thin film on the underlying layer, but there are several conditions, one of which is the fitting of the lattice constant, as well as thermal expansion coefficient, stress, elements of the underlying layer, and superconductivity. There are bonding states of elements in the conductive layer, etc. Preferably, the underlayer is oriented along the C-axis of a spinel structure on the Si substrate, and the superconducting layer is also a film oriented along the c-axis. Si, spinel (A B
z O4) - The crystal structure of the superconducting layer belongs to the cubic system, and even if it does not lead to epitaxial growth, -
It is fully possible to form an axially oriented film.

As for thin film production methods, the base layer is produced by the usual RF sputtering method or the facing target sputtering method, and the superconducting film is produced by plasma evaporation method (a filament and a grid are provided on the evaporation source, thereby removing oxygen gas and evaporated substances. It is manufactured by a method in which the plasma is made into a plasma state. It is necessary to heat the Si substrate at 400° C. to 650° C. to form a base film and a superconducting film as-depo.

〔Example〕

10m x 10.5m Si substrate [crystal plane (100
)) ZnGa by facing target sputtering,
O, prepare a membrane. Target is Zn:Ga:O=1:
A sintered target with a composition adjusted to approximately match the ratio of 2:4 is used.

Using a mixed gas of Ar and 02, the oxygen partial pressure is 1 mt.
orr to 5mtorr (0, l Pa to IPa
), and the substrate temperature was in the range of 450°C to 600°C. The input power was 0.8 A and 1.5 KV, the substrate heating temperature was 550° C., and the oxygen partial pressure was 2 mtorr.

The ratio of Ar and 02 was 4:1.

The thin film thus obtained was C-axis oriented according to the results of X-ray diffraction, had a thickness of 1000 mm, and had a flat film surface.

Next, the vacuum chamber was previously drawn to 10-3 to 10-'Pa, and oxygen gas was introduced. The pressure at that time is 10-1 to 1
0-''Pa.The evaporation source of the electron gun contains Y metal, Ba
Metal and Cu metal were each placed in a royal gun, and each material was evaporated at an accelerating voltage of 10 KV. The previously prepared ZnGa
The heating temperature was 550° C. using a 2O2 film-coated 81 substrate. On the other hand, a power of 400 W was applied to the tungsten filament provided on the evaporation source to cause thermionic electrons to be emitted. The thermoelectrons are further absorbed by a positive voltage of 1 (IOV) applied to a mesh grid provided above.
It is being pulled and captured here. During this time, the oxygen and evaporated material are partially ionized and a plasma is generated in this region.

However, the board is grounded.

The thickness of the thus obtained film was 2000 mm, the orientation axis was the C axis, and the film surface was smooth and dense.

The critical temperature was found to be approximately 80°C from electrical resistance and magnetic susceptibility measurements.

[Effects] By using the base layer with the AB204 spinel crystal structure described above, the critical temperature can be increased and the film quality can be improved compared to a superconducting thin film deposited directly on a Si substrate, and it can also be used for superconducting transistors, etc. It has become possible to apply this technology to devices that combine these semiconductors.

Furthermore, the substrate heating temperature was also lowered.

Claims (1)

[Claims] 1. Substrate, general formula AB_2O having a spinel crystal structure
_4 (In the formula, A is Zn or Mg, and B is at least one element selected from the group consisting of Fe, Al, and Ga.) Oxide base layer and oxide superconducting layer represented by A conductor characterized by being laminated in this order. 2. The superconductor according to claim 1, wherein the substrate is silicon.