JPH0283986A - Superconducting diode - Google Patents

Abstract

PURPOSE:To form a barrier layer between first and second superconductor layers with excellent controllability by a method wherein the material of the barrier layer has at least two elements, Cu and O, in common with the materials of the other layers. CONSTITUTION:A barrier layer 3 is formed between a first superconductor layer 2 and a second superconductor layer 3. The layers 2, 4 and 3 are made of same type materials such as (La1-x)2CuO4. The composition of the layer 3 is properly made to be different, for instance x=0.02, from the compositions of the layers 2 and 4 so as not to show superconductivity (so as to show insulating properties in this case). With this constitution, the layer 3 between the layers 2 and 4 can be formed with excellent controllability. In other words, a barrier height V can be determined by the difference in carrier concentration between the barrier layer and the superconductors and, by changing the carrier concentration, the excellent controllability can be provided. Therefore, the barrier height can be formed with excellent controllability and reproducibility and the shape, particularly the thickness, of the barrier can be predetermined freely.

Description

[Detailed Description of the Invention] [Summary] Regarding a superconducting diode, it is possible to form a barrier layer between a first superconductor layer and a second superconductor layer made of an oxide superconductor with good controllability. The purpose of the present invention is to provide a superconducting diode that has an insulating or semiconductor layer between a first superconductor layer made of an oxide superconductor and a second superconductor layer made of an oxide superconductor. A barrier layer having electrical conductivity is formed, and the barrier layer is made of two of the constituent elements containing Cu, 0 constituting the first superconductor layer and the second superconductor layer.
Construct so that at least the elements of species or higher are common.

[Industrial application field]

The present invention relates to a superconducting diode that is a so-called two-terminal element using a superconductor, and more specifically, a superconducting diode that is constructed using an oxide superconductor and that can form a barrier layer with good controllability. It concerns diodes.

In recent years, oxide superconductors (also called oxide ultrahigh temperature conductors) whose critical temperature exceeds the boiling point of liquid nitrogen (77K) have been discovered, and superconductivity phenomena using this oxide superconductor, for example in the electronics field, have been discovered. is expected to be used.

The devices conventionally used in the field of superconducting electronics are Josephson devices based on Josephson junctions, which have the advantages of high speed and low power consumption, so there is a desire to realize this in high-temperature superconductors as well. Here, the Josephson device usually has a thin insulating film that allows electron tunneling sandwiched between electrodes made of a superconductor. In addition, it is believed that any technology capable of realizing a superconducting diode having a structure using an oxide superconductor, not just a device using a Josephson junction, would be industrially useful.

[Conventional technology]

Hereinafter, a conventional superconducting diode using a Josephson junction using a low-temperature superconductor will be specifically explained with reference to the drawings.

FIG. 7 is a cross-sectional view showing the structure of a conventional superconducting diode.

In this figure, 21 is a substrate made of Si, for example, and 22
23 is an insulating film made of, for example, 5 iOz, and 23 is a first superconductor layer made of, for example, Nb, which functions as a base electrode. 24 is a barrier layer made of AAOx, for example;
25 is a second superconductor layer made of Nb, for example, and functions as a counter electrode. 26 is, for example, SiO
An interlayer insulating film consisting of □, 27 is a contact hole, 28
is a wiring layer made of Nb, for example.

Note that here, the Josephson junction is the first superconductor layer 23
, a barrier layer 24 and a second superconductor layer 25.

Next, the manufacturing method will be briefly explained.

First, the substrate 21 is oxidized by, for example, a thermal oxidation method to form an insulating film 22, and then Nb is deposited on the insulating film 22 by, for example, a sputtering method to form a first superconductor layer 23. Next, a thin layer of AA is deposited on the base electrode 23 by, for example, a sputtering method, and this A1 is oxidized to form a barrier layer 24. After that, Nb is deposited on the barrier layer 24 by, for example, a sputtering method to form a second superconductor. body layer 25
form. After that, the superconductor layer 25 and the barrier layer 24 are etched by reactive dry etching using CF4+5%0□.
etching. Next, the base electrode 23 is processed by reactive dry etching using CF4+5%0□. Then, an interlayer insulating film 26 is formed by depositing SiO□ on the entire surface by, for example, the CVD method, and the second superconductor layer 2
After forming a contact hole 27 by selectively etching the interlayer insulating film 26 on the layer 5, a wiring layer 28 is formed so as to make contact with the second superconductor layer 25 through the contact hole 27. , a superconducting diode having the structure shown in FIG. 7 is completed.

A superconducting diode using the conventional low-temperature superconductor described above can obtain good Josephson junction characteristics such as high speed and low power consumption. Josephson junction and SIS
(Abbreviation for 5uper In5ulator 5uper)
upper-Semicon-ducter-3upper
In order to realize the bonding, the barrier layer between the superconducting electrodes may be formed with good controllability, and specifically, the barrier height and thickness of the barrier layer may be appropriately controlled.

Here, the barrier height of the barrier layer indicates the height of the barrier against the passage of electrons when an energy diagram is drawn. The thickness of the barrier layer can be appropriately controlled by, for example, the oxidation time of A2.

[Problem to be solved by the invention]

However, although it is possible to obtain good Josephson junction characteristics in superconducting diodes using such conventional low-temperature superconductors, it is possible to obtain good Josephson junction characteristics; Superconductor layer 23 and second superconductor layer 2
5, and form a barrier layer with good controllability (barrier height and thickness of the barrier layer) between the first superconductor layer 23 and the second superconductor layer 25 made of this oxide superconductor. The problem was that it was extremely difficult.

Specifically, in the first superconductor layer 23 and the second superconductor layer 25 made of Nb, good superconducting properties can be obtained even if polycrystals are used, whereas with oxide superconductors, When a polycrystalline material is used, the grain boundaries, which should not normally have Josephson junctions, become a kind of Josephson junction, making it impossible to obtain the desired superconducting properties. In addition, for crystal growth of oxide superconductors, the temperature is usually 900°C.
This requires a high substrate temperature (or heat treatment temperature), and due to the high temperature, diffusion occurs between the barrier layer and the superconductor electrode, creating a thick reacted layer, resulting in a thin barrier due to the intended tunneling. It is not possible to form layers. Therefore, using an oxide superconductor,
It is extremely difficult to form Josephson junctions and other superconducting diodes, and the characteristics of the resulting devices are not reproducible.

Therefore, an object of the present invention is to provide a superconducting diode in which a barrier layer between a first superconductor layer and a second superconductor layer made of an oxide superconductor can be formed with good controllability. It is said that

[Means to solve the problem]

In order to achieve the above object, the superconducting diode according to the present invention has the following features:
An insulating or semiconductive barrier layer is formed between a first superconductor layer made of an oxide superconductor and a second superconductor layer made of an oxide superconductor, and the barrier layer The layer includes two elements called Cu and 0 among the constituent elements including Cu and O that constitute the first superconductor layer and the second superconductor layer.
It is composed of at least one or more elements in common.

In the present invention, the barrier layer comprises a first superconductor layer and a second superconductor layer.
Among the constituent elements including Cu and 0 constituting the superconductor layer, at least two or more elements Cu and O are common to the first superconductor layer and the second superconductor layer. The constituent elements constituting the layer may include Cu, 0, and the barrier layer may also contain the elements Cu, 0, and the constituent elements constituting the barrier layer may be the first This includes cases in which all constituent elements including CLJ and 0 are common to the superconductor layer and the second superconductor layer.

[Function] The present invention provides an insulating or semiconducting barrier between a first superconductor layer made of an oxide superconductor and a second superconductor layer made of an oxide superconductor. A barrier layer is formed such that at least two or more elements Cu and 0 among the constituent elements including Cu and 0 forming the first superconductor layer and the second superconductor layer are in common. It is composed of

Therefore, the barrier height can be formed with good controllability and reproducibility, and the shape and especially the thickness of the barrier layer can be freely set, making it possible to form the barrier layer with good controllability. It becomes like this.

(Example) Hereinafter, the present invention will be explained based on the drawings.

1 to 3 are diagrams for explaining one embodiment of a superconducting diode according to the present invention, FIG. 1 is a cross-sectional view showing the structure of one embodiment, and FIG. 2 is an operating principle of one embodiment. A diagram explaining
FIG. 3 is a diagram showing a schematic potential diagram for a carrier in one embodiment.

In these figures, 1 is a substrate made of, for example, 5rTiO+, and 2 is a first superconductor layer made of an oxide superconductor of, for example, (La+-XSr,)zCub, which functions as a Heath electrode. , 3 is, for example, an insulating barrier layer made of an oxide of (La+-xsrx) 2 Cu Oa, where X is 0.02 and the thickness is, for example, 15 nm. For example, 4 is (La+-
A second superconductor layer made of an oxide superconductor of x Srx )z Cu1t, which functions as a counter electrode, and X is preferably about 0.075 as a value that shows good superconducting properties. . Reference numerals 5a and 5b are electrodes made of, for example, Al1, which have a thickness of, for example, 1 μm, and have the function of passing a current through the device from the outside.

Next, the principle of operation will be explained using FIG. 2.

The first superconductor layer 2 and the second superconductor layer 4 have a function of exhibiting superconducting properties at the temperature used, and the barrier layer 3
is a constituent element containing Cu, 0 (1, a+-x S rx
)z Cubs oxide (La+-x
5r In this case, it exhibits insulating properties. Note that the first superconductor layer 2, the barrier layer 3 and the second
Ideally, the superconductor layer 4 is made of a single single crystal, and the first superconductor layer 2, Hanoa layer 3, and second superconductor layer 4 are made of at least similar crystals. has a structure,
They can be considered to be the same type of substance, except for the difference in conductivity, such as superconductivity and insulating properties (or semiconductor-like conductivity), due to differences in composition and the way the atomic planes are stacked.

Next, a schematic potential diagram for carriers will be explained using FIG.

Note that here, V is the barrier height, which is determined by the difference in carrier concentration of the superconductor.

As shown in FIG. 3, this diagram shows the potential change from the first superconductor N2 to the second superconductor layer 4 of the device shown in FIG. Since the first superconductor layer 2 and the second superconductor layer 4 have a higher carrier concentration than the barrier layer 3, their potential is lower. On the other hand, since the barrier layer 3 is a region with a lower carrier concentration than the first superconductor layer 2 and the second superconductor layer 4, the potential for carriers is high. This barrier layer 3 with high potential functions as a barrier against carriers. Note that the carrier concentration can be changed by appropriately changing the composition ratio of the constituent elements.

That is, in the above embodiment, the barrier layer 3 is formed between the first superconductor layer 2 and the second superconductor layer 4, and the barrier layer 3 is formed between the first superconductor layer 2 and the second superconductor layer 4. Layer 4 and barrier layer 3 (L
Since they are made of the same type of material, a+-xSr*)zCuO4, the barrier layer 3 between the first superconductor layer 2 and the second superconductor layer 40 can be formed with good controllability. Specifically, the controllability is improved because, in conventional systems, the barrier height is determined at the hetero-interface between the semiconductor (or insulator) and the superconducting metal, as shown in Figure 3. As shown, the barrier height (2) can be determined by the difference in carrier concentration in the superconductor, and excellent controllability can be achieved by appropriately changing the value of the carrier concentration. Furthermore, since an oxide superconductor with a large superconducting energy gap is used, there is an advantage that large nonlinearity can be obtained at higher temperatures.

Therefore, the barrier height is 'Ml? 211 and can be formed with good reproducibility, and the shape of the barrier, especially the thickness, can be freely set. For example, by continuously changing the composition of the material of the barrier layer 3, it is possible to create a slope in the profile of the barrier layer 3.

In addition, in the above embodiment, the first superconductor layer 2 and the second superconducting four-body layer 4 are formed by (La+-x S rx ) z Cu
The barrier layer 3 is composed of the constituent element O4, and the barrier layer 3 is composed of the constituent element O4, which constitutes the first superconductor layer 2 and the second superconductor layer 4.
La+-x S rw )2 CIJO4 and the case where the barrier layer 3 is composed of the same components as the first superconductor layer 2 and the second superconductor layer 2 have been described, but the present invention is not limited to this. Of the constituent elements including Cu and 0 constituting the superconductor layer 4, it is sufficient that at least two or more elements, CU and 0, are common; for example, the first superconductor layer 2 and the second superconductor layer 4 may be made of (La+-x S rx )z Cu0a, and the barrier layer 3 may be made of insulating Laz Cub. In addition, the first superconductor layer 2, the second superconductor layer 4, and the barrier layer 3 are made of Bi, Sr, Can-I C
In this case, the first superconductor layer 2 and the second superconductor layer 4 are made of B with n=3.
iz Srz Ca2Cu=o□, and the barrier layer 3 can be made of n-1 BizSr and CuO□.

In the above embodiment, the first superconductor layer 2, the second superconductor layer 4, and the barrier layer 3 are (La1-x S rx ) 2C
Although a case has been described in which the first superconductor layer 2 is made of a constituent element called ubs and the carrier concentration is appropriately changed by changing the compositional acid ratio of the constituent elements, the present invention is not limited to this. The second superconductor layer 4 and the barrier layer 3 are B
It may be constructed of az YCu30n, and the carrier concentration may be changed appropriately by changing the ix of oxygen. In this case, when X is close to 7, it becomes a superconductor, and when X is close to 0, it becomes an insulator. Specifically, as shown in FIG. 4, a superconducting diode with a Brehner structure can be realized, and a first superconductor layer 2a and a second superconductor layer 4a
For example, the oxygen amount . In this device, a first superconductor layer 2a and a second superconductor layer 4
If the distance (spacing) a is sufficiently short, it becomes a planar weakly coupled Josephson device, and if the distance between the first superconductor layer 2a and the second superconductor layer 4a is long, the SN junction becomes 2 This type of element can be easily realized by selective oxidation methods such as plasma oxidation.

It is also possible to realize a super low four diode as shown in FIG. 5, which has almost the same structure as the one shown in FIG.
, and the parameter y of the composition of the barrier layer 3b starts from the left side of the figure and starts from y = 0.075, and the parameter y of the composition of the barrier layer 3b
It changes continuously up to the rightmost value y = 0.02. Therefore, as shown in FIG. 6, the shape of the potential becomes an asymmetrical triangle, and as a result, the current-voltage characteristics can be rectified.

In the above embodiment, for example, (La+-x S rx ) z
Although the case where X of CUOa is set to x=0.02 and the barrier layer 3 is configured to have an insulating function has been described, the present invention is not limited to this, and has a semiconductor-like electrosensitive function. It may be configured as follows.

〔Effect of the invention〕

According to the present invention, it is possible to easily control (form) a barrier layer between a first superconductor layer made of an oxide superconductor and a second superconductor layer made of an oxide superconductor. It has the effect of being able to.

[Brief explanation of the drawing]

FIGS. 1 to 3 are diagrams illustrating an embodiment of a superconducting diode according to the present invention. 4... Second superconductor layer, 5a, 5b... electrode. /--~・ Agent Patent Attorney Igatasada Figure 2 is a diagram explaining the operating principle of one embodiment, Figure 3 is a diagram showing a schematic potential diagram for the carrier of one embodiment, Figure 4 and FIG. 5 is a sectional view showing the structure of another embodiment, FIG. 6 is a schematic potential diagram for the carrier of the other embodiment shown in FIG. 5, and FIG. 7 is a sectional view showing the structure of the conventional example. It is a diagram. 1...Substrate, 2...First superconductor layer, 3...Barrier layer, Cross-sectional view showing the structure of one embodiment Fig. 1 Other embodiments Fig. 4 is a sectional view showing the structure of another embodiment. Fig. 5 is a diagram illustrating the operating principle of the 'AA example. FIG. 6 shows a schematic potential diagram for carriers of other embodiments shown in No. 5 UjJ.
Figure 7 is a sectional view showing the structure of a conventional example.

Claims (1)

[Claims] An insulating or semiconductive barrier layer is formed between a first superconductor layer made of an oxide superconductor and a second superconductor layer made of an oxide superconductor, and the barrier layer The layer is made of two of the constituent elements containing Cu and O that constitute the first superconductor layer and the second superconductor layer.
A superconducting diode characterized by having at least one or more elements in common.