JPH0555651A - Manufacture of josephson device - Google Patents

Abstract

PURPOSE:To obtain a Josephson device which can be easily manufactured by chamfering an MgO board in a various direction, disposing an oxide superconducting thin film on the board, and forming a weak connection according to the growing direction dependency of the film and the angle of the board. CONSTITUTION:A board 10 is formed of an MgO board in such a manner that the surfaces A and C have a plane (100) and the surface B is formed to incline 45 deg. with respect to the surface A and has a plane (110). A thin oxide superconducting film 11 such as a YBCO film, a BSCCO film, etc., is laminated to be formed on the board 10 by a CVD method. The film 11 to be deposited on the surfaces A and C of the board 10 is grown perpendicularly to a C axis on the board 10. The film 11 to be deposited on the surface B is grown in parallel with the C axis on the board 10. Accordingly, superconducting electron pairs easily flow parallel to the surfaces A and C of the board 10. However, the pairs scarcely flow in parallel with the film on the surface B to form a weak bond type Josephson junction. Accordingly, an element can be easily formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a Josephson device utilizing weak coupling partially formed in a superconductor.

[0002]

2. Description of the Related Art As a weakly coupled Josephson element, there is a bridge type Josephson element. FIG. 4 shows a general bridge type Josephson device. In this device, a constriction 22 having a length d is formed in a superconductor thin film 21 to weaken the superconducting property of that portion and weakly couple it, and a voltage terminal 2 is formed in a portion without a constriction.
3, 24 and current terminals 25, 26 are provided. The length d of the constriction 22 is about the coherence length of the material of the thin film 21, and is several thousand Å in the case of a superconductor such as Nb or Pb.

By the way, Ln-Ba-Cu-O (Ln is a rare earth element) known as a high critical temperature superconductor has a coherence length of about 1/100 of Nb, Pb, etc. It is impossible to make a Josephson device. However, in such an oxide superconductor, grain growth generally occurs during film growth to form grain boundaries. Therefore, weak bonds, that is, grain boundary Josephson bonds, are formed in various places inside the film. There is a problem that the critical current density does not increase due to this weak coupling, but various devices have been prototyped using this grain boundary Josephson coupling.

FIG. 5 shows an example. FIG. 5 is a SQUID using an oxide superconductor, particularly Ln-Ba-Cu-O.
(Superconducting quantum interferometer), which is an element in which two bridge type Josephson elements are connected in parallel, and voltage terminals 35 and 36 and current terminals 37 and 38 are provided in two portions 33 that sandwich two constrictions 34. Has been.

[0005]

[Problems to be Solved by the Invention] Ln-Ba-Cu-O
In the superconductor of the system, as described above, very weak coupling is likely to occur. However, Bi-Sr-Ca-Cu-O (BS with a critical temperature higher than 10 K higher than that of the Ln-Ba-Cu-O system
CCO) -based or Bi-Pb-Sr-Ca-Cu-O
In the (BPSCCO) based superconductor, grain boundary Josephson characteristics are not observed although grain growth occurs during film growth.

Therefore, the element shown in FIG.
It is not made with CO. Further, in order to operate an element as shown in FIG. 4 which is not a grain boundary Josephson element, fine processing of a coherence length is necessary, which is difficult with the current technology.

An object of the present invention is to solve the above-mentioned problems and provide a Josephson device which is easy to manufacture.

[0008]

According to the method for manufacturing a Josephson element of the present invention, the MgO substrate is chamfered in various orientations, and the oxide superconducting thin film is deposited on this substrate to form the oxide superconducting thin film. It is characterized in that weak bonds are formed depending on the growth direction dependence of the substrate and the angle of the substrate.

[0009]

In the oxide superconducting thin film deposited on the MgO (100) surface, the c-axis grows perpendicular to the substrate. Also (10
The plane inclined at 45 ° to the (0) plane is in the direction of the MgO (110) plane, and the oxide superconducting thin film deposited on that plane grows parallel to the c-axis.

In the superconducting thin film having the c-axis grown perpendicular to the substrate, the superconducting pair easily flows in parallel to the film surface, but in the superconducting thin film having the c-axis grown parallel to the substrate, the superconducting pair runs in the direction parallel to the film surface. Becomes difficult to flow.

Therefore, a kind of weak-coupling Josephson junction is formed by planes having different crystal orientations.

Further, the boundaries between the planes having different crystallographic orientations are angled to the substrate, and the film deposited thereon forms grain boundaries and also constitutes a grain boundary effect type Josephson junction.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the present invention.

A MgO substrate is used as the substrate 10, and the A and C faces have a (100) face. The B surface is formed so as to be inclined by 45 ° with respect to the A surface, and the B surface has a (110) surface.

An oxide superconducting thin film 11 such as a YBCO film or a BSCCO film is laminated on the substrate 10 by a CVD method having a good step coverage.

As described above, since the A-plane and C-plane of the substrate 10 have the (100) plane, the oxide superconducting thin film 11 deposited thereon grows with the C-axis perpendicular to the substrate 10.

Since the B-face of the substrate 10 has the (110) face, the C-axis of the deposited oxide superconducting thin film 11 grows parallel to the substrate 10.

Therefore, the A and C planes of the substrate 10 are a and b in the figure.
The superconducting pair easily flows in the plane direction, that is, parallel to the film surface. However, in the B plane, the superconducting pair is unlikely to flow in the direction parallel to the film plane, and a weak coupling type Josephson junction is formed in the A plane → B plane → C plane.

Further, the boundaries between the A and B surfaces and the B and C surfaces are
Since the substrate 10 is angled, the superconducting thin film 11 deposited on top of it forms grain boundaries. Therefore, a grain boundary effect type Josephson junction is also deposited.

In FIGS. 2 and 3, a thin portion corresponding to the constriction of the bridge-type junction or the contact portion of the point contact type junction is partially formed to form a Josephson junction. FIG. 6 is a process drawing showing a method of forming a film.

A method of manufacturing the weak coupling type Josephson device will be described with reference to FIGS.

First, Mg having a (100) plane as a substrate
An O substrate 40 is prepared.

As shown in FIG. 2A, the substrate 40 is irradiated with the charged particle beam 60. The irradiation region 41 of the beam 60 is removed, and the recess 42 is formed.

Subsequently, as shown in FIG. 2B, the beam diameter is narrowed and the substrate 40 is further irradiated with the beam 60.

As shown in FIG. 2C, this beam 60
The irradiation region 43 is removed and a recess 44 is formed.

As described above, by gradually narrowing the beam diameter and irradiating the substrate 40 with the beam 60, a precise and continuous step 45 is formed as shown in FIG.

As shown in FIG. 3A, an oxide superconducting thin film 50 of YBCO, BSCCO or the like is deposited on the MgO substrate 40 having the step 45 formed therein by a sputtering method or the like.

As shown in FIG. 3B, a weak coupling portion is formed in a portion surrounded by a dotted line to form a Josephson junction element.

According to this method, the weak coupling portion can be formed in series, and the serialization can improve the impedance. Also, any number of serializations is possible.

Further, if the distance between the weak couplings can be precisely controlled and the voltage standard use and size are controlled by serialization, a high impedance single junction operating element can be formed by the coherence operation.

[0031]

As described above, according to the present invention, a weakly coupled Josephson junction is formed on the planes having different crystal orientations, and the grain boundary effect type Josephson junction is formed at the boundary between the planes having different crystal orientations. Since the junction is configured, it is possible to provide a Josephson junction element that can be easily manufactured without the need for performing fine processing.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a manufacturing process in which a step is formed on a substrate to form a weakly coupled Josephson element.

FIG. 3 is a cross-sectional view showing a manufacturing process in which a step is formed on a substrate to form a weakly coupled Josephson element.

FIG. 4 is a cross-sectional view showing a bridge-type Josephson element.

FIG. 5 is a plan view of an SQID using an oxide superconductor.

[Explanation of symbols]

 10 MgO substrate 11 Oxide superconductor thin film

Claims (1)

[Claims] 1. A MgO substrate is faced in various orientations and an oxide superconducting thin film is deposited on this substrate to form weak bonds depending on the growth direction dependence of the oxide superconducting thin film and the angle of the substrate. A method of manufacturing a Josephson device, characterized in that