JPH04147681A - Supedconducting junction - Google Patents

Abstract

PURPOSE:To manufacture a superconducting junction of stable performance with good reproducibility by constituting the junction from the thin film of an oxide superconductor, which is formed on a substrate having a square pillar-shaped protrusion with the bottom face perpendicular to a film-forming surface and one side face almost perpendicular to the film-forming surface in the manner of crossing the protrusion and of which the part on the side face of the protrusion almost perpendicular to the film-forming surface is thin. CONSTITUTION:In the title superconducting junction, e.g. a substrate surface is first etched by Ar ion milling so that a square pillar-shaped protrusion is formed on a substrate 4. Then, the substrate 4 with the protrusron 40 formed thereon is heated to 590-650 deg.C so that there is formed the thin film 1 of an oxide superconductor in the shape of crossing the protrusion 40 of the substrate 4. When the oxide superconductive thin film 1 is formed at the substrate temperature, there is formed an oxide superconductive thin film 1 composed of c-axis oriented oxide superconductor crystal. The cross section of the protrusion 40 is rectangular and its side face 41 is perpendicular to the film-forming surface of the substrate 4. Also, the protrusion 40 is 150nm in height and 10mum in maximum width. The oxide superconductive thin film 1 is divided into superconductive layers 11 and 12 of about 300nm thickness and a weakly combined part 13 on the side face 41 of the protrusion 40. The thickness of the weakly combined part 13 is about 10nm.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to superconducting junctions. More specifically, the present invention relates to a novel superconducting junction using an oxide superconductor.

There are various configurations for realizing superconducting junctions, such as conventional Josephson junctions, and the most preferred structure is a tunnel-type junction in which a thin non-superconductor is sandwiched between a pair of superconductors.

However, superconducting junctions in which a pair of superconductors are weakly coupled, such as a point contact type or a microbridge type, also exhibit the Josephson effect, although the characteristics are different. Generally, such a superconducting junction has a very fine structure, and the above-mentioned superconductors and non-superconductors are composed of so-called thin films.

For example, when realizing a tunnel-type superconducting junction using an oxide superconductor as a superconductor, a first oxide superconducting thin film, a non-superconducting thin film, and a second oxide superconducting thin film are laminated in order on a substrate. do.

Depending on the purpose, non-superconductors include insulators such as MgO,
Semiconductors such as Si and metals such as Au are used, and each constitutes a superconducting junction with different characteristics.

The stiffness of a non-superconductor in a tunnel-type superconducting junction is determined by the coherence length of the superconductor.

Oxide superconductors have very short coherence lengths, so
In a tunnel-type superconducting junction using an oxide superconductor, the thickness of the non-superconductor must be approximately several nm.

Furthermore, both point-contact type superconducting junctions and microbridge type superconducting junctions require very fine processing to achieve weak coupling between a pair of superconductors.

On the other hand, in consideration of the operating characteristics of a superconducting junction, each layer constituting the superconducting junction must have good crystallinity and be a single crystal or a polycrystal with an orientation very close to that of a single crystal.

Problems to be Solved by the Invention In the tunnel type superconducting junction described above, a first oxide superconducting thin film, a non-superconducting thin film, and a second oxide superconducting thin film each having good crystallinity must be laminated. It is difficult to stack a very thin non-superconducting thin film with good crystallinity on top of an oxide superconducting thin film, and it is difficult to form an oxide superconducting thin film with good crystallinity on top of this non-superconducting thin film. This is extremely difficult due to the characteristics of oxide superconductors.

Further, even if the above-mentioned laminated structure was realized, the interface between the oxide superconductor and the non-superconductor was not good and desired characteristics could not be obtained.

On the other hand, the fine processing required to realize point-contact type superconducting junctions and micro-bridge type superconducting junctions is extremely difficult, and it has not been possible to produce superconducting junctions with stable performance with good reproducibility.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a superconducting junction with a novel configuration using an oxide superconductor, which solves the problems of the prior art described above.

Means for Solving the Problems According to the present invention, on a substrate having a rectangular prism-shaped protrusion whose bottom surface is perpendicular to the film-forming surface and whose one side is approximately perpendicular to the film-forming surface, there is provided a substrate with a protrusion extending across the protrusion. A superconducting junction is provided, wherein a portion of the quadrangular prism-shaped protrusion on a side surface substantially perpendicular to the film formation surface is formed of a thin oxide superconductor thin film.

Function The superconducting junction of the present invention is composed of an oxide superconducting thin film formed on a substrate having a square prism-shaped protrusion. That is, in the superconducting junction of the present invention, a first superconducting layer and a second superconducting layer integrally formed of an oxide superconducting thin film are weakly bonded at a portion above the protrusion of the substrate. The portion of the square prism-shaped protrusion of the oxide superconducting thin film formed on the side surface substantially perpendicular to the substrate film formation surface is thin, resulting in a weak coupling having a structure similar to a so-called microbridge type.

The superconducting junction of the present invention preferably uses a C-axis oriented thin film of an oxide superconductor. This is because the critical current density and coherence length in the direction perpendicular to the C axis of the oxide superconductor are large. When the superconducting junction of the present invention is made of a C-axis oriented oxide superconducting thin film, the main current flows in a direction perpendicular to the C-axis, so it has better characteristics.

The above-mentioned superconducting bonding of the present invention is performed by sputtering an oxide superconducting thin film onto a substrate having a protrusion having the above-described shape.
It can be produced by forming a film using a BE method, a vacuum evaporation method, or a laser ablation method. In this case, the material particles (molecules,
It is preferable to supply and deposit a gas). This is because when the material particles are supplied in this manner, the oxide superconducting thin film is deposited thinly on the surface of the protrusion that is substantially perpendicular to the substrate film formation surface.

The following procedure is used to fabricate the superconducting junction of the present invention. First, for example, the surface of the substrate is etched by Ar ion milling to form a square prism-shaped protrusion on the substrate. Next, the substrate on which the protrusion is formed is heated to 590 to 650° C. to form a thin film of oxide superconductor having a shape that crosses the protrusion of the substrate. When an oxide superconducting thin film is formed at this substrate temperature, an oxide superconducting thin film composed of C-axis oriented oxide superconducting crystals is formed. A superconducting element using the superconducting junction of the present invention is completed by processing the shape of the oxide superconducting thin film and providing electrodes as necessary.

In the superconducting junction of the present invention, any oxide superconductor can be used, but Y-Ba-Cu-0-based oxide superconductors can stably yield high-quality thin films with good crystallinity. preferable. Moreover, Bi-3r-Ca-Cu-0 based oxide superconductor is particularly preferable because its superconducting critical temperature Tc is high.

Further, the superconducting junction of the present invention includes MgO, 5rTi03,
It is also preferable to fabricate on an oxide substrate such as YSz. This is because it is easy to form a C-axis oriented thin film of an oxide superconductor on a specific surface of these substrates.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the following disclosure is merely an example of the present invention and does not limit the technical scope of the present invention in any way.

EXAMPLE FIG. 1(a) and Co., Ltd. show a schematic diagram of an example of the superconducting junction of the present invention. (Figure 1(a) is a plan view, Figure 2, etc.)
is a sectional view taken along line A-A in FIG. 1(a).

The superconducting junction shown in FIG. 1 is composed of an oxide superconducting thin film 1 formed across a square prism-shaped protrusion 40 provided on a substrate 4. The superconducting junction shown in FIG. The cross section of the protrusion 40 is rectangular,
The side surface 41 is perpendicular to the film-forming surface of the substrate 4. Further, the height of the protrusion 40 is 150 nm, and the maximum width is 10 μm.

The oxide superconducting thin film 1 is divided into superconducting layers 11 and 12 with a thickness of about 300 nm and a weak coupling portion 13 on the side surface 41 of the protrusion 40 . The thickness of the weak coupling portion 13 is approximately IQ nm.

Example 1 A superconducting junction of the present invention having the configuration shown in FIG. 1 was fabricated.

First, on the (100) plane of the MgO substrate, A
The protrusions 40 were formed by r-ion milling.

Acceleration voltage 700V Cathode current 50mA Vacuum degree 3 XIO'TorrAr gas flow rate
20 SCCM Next, by laser ablation method, Y1 with C-axis orientation
A Ba2Cu3O7-x superconducting thin film was formed across the protrusion 40. The main film forming conditions are shown below.

Laser Excimer laser (Wavelength 193 nm) Laser output: 1.5 J/cfft.

Pulse frequency: 17 Substrate temperature: 675° C. Pressure: 400 mTorr (02 only) Film thickness: 200 nm Terminals were provided to the superconducting junction of the present invention produced as described above, and the characteristics were measured. Cooled to 85K, frequency 15GHz
, when microwaves with an output of 0.2 mW were applied, 31
A Shapiro step was observed at a voltage point that is a multiple of μV, confirming that Josephson coupling was realized.

Example 2 The superconducting junction of the present invention having the configuration shown in FIG.
It was produced using a -Ca-Cu-0 based oxide superconductor. First, Ar ion milling was performed on the (100) plane of an MgO substrate under the following conditions to form protrusions 40.

Accelerating voltage: 700V Cathode current: 50mA Vacuum degree: 3 x 10-'TorrAr gas flow rate: 20SCCM Next, by laser ablation method, B1 with C-axis orientation was removed.
25r2Ca2CU3 C1+ superconducting thin film at protrusion 40
It was formed to cross the. The main film forming conditions are shown below.

Laser Excimer laser (wavelength: 193 nm) Laser output: 1.5 J/crl, Pulse frequency: IHz Substrate temperature: 650°C Pressure: 400 mTorr (02 only) Film thickness: 200 nm Terminals were provided to the superconducting junction of the present invention prepared as described above to determine its characteristics. It was measured. Cooled to 90K, frequency 11G&,
When a microwave with an output of 0.1W was applied, the result was 22.7
A Shapiro step was observed at a voltage point that is a multiple of μV, confirming that Josephson coupling was realized.

As described in detail, according to the present invention, a superconducting junction with a novel configuration can be realized using an oxide superconductor. Since the superconducting junction of the present invention is composed of an oxide superconductor formed integrally, it is easy to manufacture, and it is easy to obtain one with excellent characteristics.

The present invention further promotes the application of superconducting technology to electronic devices.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a superconducting junction of the present invention. [Main reference number] ・Oxide superconducting thin film, ·substrate

Claims (1)

[Claims] Formed on a substrate having a square prism-shaped protrusion whose bottom surface is perpendicular to the film-forming surface and whose one side is substantially perpendicular to the film-forming surface so as to cross the said protrusion; A superconducting junction characterized in that a portion on a side surface substantially perpendicular to the film formation surface is composed of a thin film of a thin oxide superconductor.