JPH0582842A - Superconducting wiring - Google Patents

Abstract

PURPOSE:To eliminate faulty states wherein superconducting junctions, resistor components, and so forth are generated on the interface between superconducting lines, by providing the buffer layer made of the semiconductor, which has a long-range proximity effect, between the superconducting lines made of oxide superconductors, whose orientation characteristics are different from each other. CONSTITUTION:On an SrTiO3 substrate 10, a first superconducting line 1 made of a Y1Ba2Cu3O7-x oxide superconductor thin film, which is subjected to c axis orientation, an SrTiO3 insulation layer 4 and a second superconducting line 2 made of a Y1Ba2Cu3 O7-x oxide superconductor thin film, which is subjected to c axis orientation are laminated successively. Between the superconducting lines 1, 2 and a superconducting interlayer wiring 3, La1.5Ba1.5Cu3O7-y layers 5 are respectively formed. The oxide superconductor, which is in contact with the layer 5, has a long-range proximity effect. As a result, between the superconducting lines 1, 2 and the superconducting interlayer wiring 3, superconducting currents flow respectively. Also, on the interface between the superconducting lines 1, 2 and the layer 5, and similarly, on the interface between the superconducting interlayer wiring 3 and the layer 5, superconducting junctions, resistor components, and so forth do not exist. Therefore, the superconducting wiring has a satisfactory characteristic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to superconducting wiring.
More specifically, a superconducting field effect type device including a first superconducting conductive line formed of a c-axis oriented oxide superconducting thin film and a second superconducting conducting line formed of an a-axis oriented oxide superconducting thin film. Regarding the device.

[0002]

2. Description of the Related Art Applications of superconductors to electronic equipment are roughly divided into two types. That is, a superconducting element that uses a superconductor and operates on a principle different from that of a conventional semiconductor element, and a superconducting wiring that uses a superconductor for an electric line in an electronic device. It is considered that by replacing the currently used semiconductor element with a superconducting element, it is possible to dramatically improve the performance of electronic equipment. The use of superconducting elements in combination with superconducting wiring gives a higher effect, while
It has been found that electronic devices can be speeded up only by superconducting wiring. In particular, when a superconducting conductive line is used as the signal line, it is possible to transmit a signal having a higher frequency than before, which leads to speeding up of electronic equipment. Further, since signal attenuation is reduced, it is possible to reduce the number of amplifiers and the like, which has an effect of reducing power consumption.

On the other hand, in recent years, research on oxide superconductors having a high critical temperature has progressed, and oxide superconductors are being put to practical use in addition to conventional metal superconductors. There are many types of oxide superconductors, but a typical one has a critical temperature of 80K.
Before and after Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconductor, critical temperature is 10
There are Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _y based oxide superconductors around 0 K and Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _z based oxide superconductors with a critical temperature around 120 K. Both oxide superconductors have a critical temperature well above that of metallic superconductors.

[0004]

It is known that oxide superconductors have crystal anisotropy in their superconducting properties, and in particular, the critical current density Jc is a direction perpendicular to the c-axis of oxide superconductor crystals. Is known to be the largest. Therefore, when the oxide superconductor is used for the superconducting wiring, the direction in which the current flows matches the direction in which the critical current density of the oxide superconducting crystal is maximum to form the superconducting wiring.

FIG. 2 shows a sectional view of an example of superconducting wiring using an oxide superconductor. The superconducting wiring of FIG. 2 is a two-layer wiring used in an integrated circuit or the like formed of an oxide superconductor, and is a lower superconducting conductive wire formed on a substrate 10 and having an insulating layer 4 disposed therebetween. The path 1 and the upper superconducting conductive line 2 are connected by a superconducting interlayer wiring 3. A horizontal superconducting current flows through the superconducting lines 1 and 2.
Therefore, c-axis oriented oxide superconducting thin films capable of flowing a larger current in the horizontal direction are used for the superconducting conductive lines 1 and 2. On the other hand, in the superconducting interlayer wiring 3,
Since the superconducting current in the vertical direction flows, the superconducting interlayer wiring 3
Is composed of an oxide superconducting thin film with a-axis orientation (or b-axis orientation, which will be hereinafter represented by the more general a-axis orientation).

As described above, the superconducting conductive lines 1 and 2,
If an oxide superconducting thin film having a different orientation from that of the superconducting interlayer wiring 3 is used, the interfaces 11, 12, 21 and 22 become grain boundaries, causing a problem. For example, when the crystal grain boundary at the interface is a superconducting junction, only a tunnel current flows at the interface, so the current capacity is limited. Also,
The superconducting junction at the interface makes the input / output characteristics non-linear. Even if the interface is not a superconducting junction, Joule heat is generated due to the electrical resistance of the interface, the superconductivity of the superconducting wiring is lost, and the superconducting conductive line and the superconducting interlayer wiring affect each other and their composition deteriorates. There is something to do.

In order to prevent the above-mentioned problems from occurring at the interface between the superconducting conductive line and the superconducting interlayer wiring, A
It has been proposed to form a noble metal layer such as u or Ag so that the interface does not become a grain boundary of the oxide superconductor.
However, since the noble metal layers such as Au and Ag have electric resistance, Joule heat may be generated and the superconductivity of the superconducting wiring may be lost.

Therefore, an object of the present invention is to provide a superconducting wiring that solves the above-mentioned problems of the prior art.

[0009]

According to the present invention, a first superconducting line formed of an oxide superconducting thin film made of an oxide superconducting crystal with c-axis orientation, and an electrical connection to the first superconducting wiring. A second superconducting line composed of an oxide superconducting thin film made of an oxide superconducting crystal with a-axis orientation connected to the first superconducting line, the first superconducting line and the second superconducting line. Provided is a superconducting wiring characterized in that an oxide superconductor comprises a buffer layer composed of an oxide semiconductor exhibiting a long-distance proximity effect, between the electric conductor and the electric line.

[0010]

The superconducting wiring of the present invention comprises a first superconducting line made of a c-axis oriented oxide superconducting thin film and a second superconducting line made of an a-axis oriented oxide superconducting thin film. The main feature is that the oxide superconductor is provided with a buffer layer composed of an oxide semiconductor exhibiting a long-distance proximity effect. The superconducting wire of the present invention comprises a first superconducting conductive line formed of a c-axis oriented oxide superconducting thin film and a second superconducting line formed of an a-axis oriented oxide superconducting thin film by the buffer layer. Since the interface between them is not the crystal grain boundary of the oxide superconductor, various problems at the interface of the conventional superconducting wiring can be suppressed.

The long distance proximity effect of oxide superconductors means that when a specific insulator or semiconductor is sandwiched between a pair of oxide superconductors, the distance between oxide superconductors is much wider than usual. Is a phenomenon in which a superconducting current flows. The buffer layer of the superconducting wiring of the present invention is an oxide semiconductor exhibiting the above long-distance proximity effect.
La _1.5 Ba _1.5 Cu ₃ O _7-y , La _1.5 Ca _1.5 Mn ₃ O _{7-z and the} like are preferable. Since the composition of each of these oxide semiconductors is close to that of the oxide superconductor, the characteristics of the oxide superconducting thin film are not deteriorated even if they are diffused into the oxide superconducting thin film. Also,
When the buffer layer made of the above semiconductor is formed between the first superconducting conductive line and the second superconducting conductive line, the anisotropy of the first and second superconducting conductive lines is compensated. Further, in the superconducting wiring of the present invention, a superconducting current flows in the buffer layer made of the semiconductor due to the long distance proximity effect. Therefore, even if the buffer layer made of the above semiconductor is formed, the original characteristics of the superconducting wiring are not deteriorated at all.

In the superconducting wiring of the present invention, the buffer layer preferably has a thickness of about 50 to 500 nm. This is because if the thickness of the buffer layer is less than 50 nm, the effect of the buffer layer is not sufficient, and if the thickness of the buffer layer exceeds 500 nm, it becomes difficult for superconducting current to flow in the buffer layer. In this case, the thickness of the buffer layer means the thickness of the buffer layer between the first and second superconducting wires.

The present invention can be applied to any oxide superconductor, but the Y ₁ Ba ₂ Cu ₃ O _{7 -X} oxide superconductor is preferred because it can stably obtain a high quality thin film with good crystallinity. .. Further, the Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x oxide superconductor is particularly preferable because its superconducting critical temperature Tc is high.

Hereinafter, the present invention will be described in more detail by way of examples, but the following disclosure is merely examples of the present invention and does not limit the technical scope of the present invention.

[0015]

Example A superconducting wire of the present invention was produced. The process will be described with reference to FIG. First, on a SrTiO ₃ (110) substrate 10 as shown in FIG. 1 (a), a first c-axis oriented Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film as shown in FIG. 1 (b) was formed. Superconducting line 1, SrTiO ₃ insulating layer 4 and c-axis oriented Y ₁ Ba ₂ Cu
The second superconducting conductive line 2 of ₃ O _7-X oxide superconducting thin film is sequentially laminated. Various sputtering methods and MBE can be used to form a c-axis oriented Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film.
Any method such as a method, a vacuum vapor deposition method, a CVD method can be used. The main film forming conditions for forming a film by the sputtering method are shown below. Substrate temperature 700 ° C Sputtering gas Ar 90% O ₂ 10% Pressure 5 × 10 ^-2 Torr Film thickness 400nm For the substrate 10 and insulating layer 4, use Mg instead of SrTiO _3.
O can also be used.

Next, as shown in FIG. 1 (c), first and second
Of the portion 30 to form a superconducting layer interconnects for connecting the superconducting electric line is processed by reactive ion etching with a Cl-based gas, as shown in FIG. _{1 (d), La 1.5 Ba} 1.5 Cu 3 O 7-y oxide The semiconductor layer 5 is laminated by the sputtering method. La _1.5 Ba
La _1.5 Ca _1.5 Mn ₃ O _7-z may be used instead of _1.5 Cu ₃ O _7-y . The main conditions for forming the La _1.5 Ba _1.5 Cu ₃ O _7-y oxide semiconductor layer by the sputtering method are shown below. Substrate temperature 700 ℃ Sputtering gas Ar 50% O ₂ 50% Pressure 5 × 10 ^-2 Torr Film thickness 100nm

Finally, as shown in FIG. 1 (e), a-axis orientation Y ₁ Ba ₂ C
The superconducting interlayer wiring 3 is formed from the u ₃ O _{7 -X} oxide superconducting thin film to complete the superconducting wiring of the present invention. a-axis orientation Y
The main film forming conditions for forming the ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film by the MBE method are shown below. Substrate temperature 630 ℃ Pressure 5 × 10 ^-5 Torr Film thickness 400nm

In the above superconducting wiring of the present invention, La _1.5 Ba _{1.5 is provided} between the superconducting conductive lines 1 and 2 and the superconducting interlayer wiring 3.
A Cu ₃ O _7-y layer 5 is formed. Since the oxide superconductor in contact with La _1.5 Ba _1.5 Cu ₃ O _7-y exhibits the long-distance proximity effect, a superconducting current flows between the superconducting conductive lines 1 and 2 and the superconducting interlayer wiring 3. In addition, the superconducting conductive lines 1 and 2
The interface with the La _1.5 Ba _1.5 Cu ₃ O _7-y layer 5 and the superconducting wiring 3
The interface with the La _1.5 Ba _1.5 Cu ₃ O _7-y layer 5 is well formed, and there is no superconducting junction or resistance component. Therefore, the superconducting wiring of the present invention has good characteristics.

[0019]

As described above, according to the present invention,
High-performance superconducting wiring is provided. In the superconducting field effect element of the present invention, the superconducting conductive lines composed of oxide superconductors having different orientations do not directly contact each other, and the buffer layer is formed of a semiconductor exhibiting a long-distance proximity effect. Therefore,
There are no problems such as superconducting junctions or resistance components occurring at the interface between superconducting conductive lines formed of oxide superconductors having different orientations.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a step of producing a superconducting wire of the present invention.

FIG. 2 is a diagram illustrating a configuration of superconducting wiring.

[Explanation of symbols] 1, 2 superconducting conductive line 3 superconducting interlayer wiring 4 insulating layer

Claims (1)

[Claims] 1. A first superconducting conductive line composed of an oxide superconducting thin film composed of c-axis oriented oxide superconducting crystals,
A second superconducting line formed of an oxide superconducting thin film made of an a-axis oriented oxide superconducting crystal electrically connected to the first superconducting line. A superconducting wiring comprising a buffer layer made of an oxide semiconductor, in which an oxide superconductor exhibits a long-distance proximity effect, between the superconducting conductive line and the second superconducting conductive line.