JPH0432276A - josephson junction element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a device having a Josephson junction, and more specifically, to a device having a Josephson junction, and more specifically to a device having a crystal anisotropy in critical current density or coherence length such as a high temperature superconductor. Regarding the Josephson junction device used.

Note that the present invention can be applied to any device that utilizes the Josephson effect, such as a 5QUID, an infrared detector, a mixer, a three-terminal device, and a computer.

<Prior art> Many proposals and reports have already been made regarding di-Sefson junction devices using high-temperature superconductor thin films such as YBCO (for example, Akinobu Irie et al.
,al,,Japanese Journal of A
pplied Physics Vol, 28. No.1
0,0ctober, 1989.1) IP, L1816
-1819), and most of those currently realized utilize grain boundary bonding.

The reason for this is that the coherence length of high-temperature superconductors is short by several orders of magnitude, so it is impossible to create a shape that artificially produces the Josephson effect, whether it is a tunnel type or a weakly coupled type. .

<Problem to be solved by the invention> By the way, in the Josephson junction using grain boundaries,
Because grain boundaries, which cannot be controlled artificially, are used, there are many variations in important factors such as the position of the bond, critical temperature of the bond, critical current density, and critical current. It is not possible to obtain an element with specific characteristics.

An object of the present invention is to provide a grain boundary Josephson junction element that can be manufactured with good reproducibility and has high performance.

<R1! Means for Solving> The configuration for achieving the above object will be described with reference to FIG. 1 corresponding to the embodiment. A second plane 12 intersecting at an obtuse angle θ is formed on the surface of the substrate 1, and a thin wire 2 made of a superconducting thin film having crystal anisotropy in critical current density and coherent length is formed between the first and second planes. It is characterized by being formed to cross the intersection line 3 of 11 and 12.

<Function> In general, high-temperature superconductor thin films such as YBCo,
Crystal anisotropy exists in the critical current density and coherence length, and the critical current density is particularly large in the direction perpendicular to the C-axis.

It is also known that the critical current density changes depending on the mutual bonding state of crystals (PHYSICALRf!
VIEW LETTER5, Vol 61. No, 2.
There is also a report that a good 5QUID was obtained using a YBCOI film with a naturally occurring Josephson junction in which the C axis was shifted by several degrees (Current 1nYBCOBridge by
MO-CVD Th1n Fila+, by Tsu
tomu Yamashita et al.)
.

The present invention takes advantage of this fact.

That is, a thin wire 2 made of a superconducting thin film such as a high-temperature superconducting thin film having crystal anisotropy in critical current density and coherent length is placed on a substrate 1 with first and second surfaces 11 intersecting each other at an obtuse angle θ. 12 so that the crystal axis direction of the FF film thin wire 2 on the first and second surfaces 11 and 12 is formed so as to cross the intersection line 3 of the FF film, as schematically shown in FIG. angle θ
This makes it possible to forcibly shift the grain by a certain amount, and it is possible to artificially form a so-called sub-grain boundary in this part. In other words, by forcibly lowering the critical current density in this portion, it is possible to artificially obtain weak coupling.

<Embodiment> FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, in which (a) is a plan view of the main part, and (b) is a sectional view taken along the line AA.

The surface of the Mg0 (100) base Fi1 has a first plane 11 that is a plane parallel to the bottom surface, and a curved surface that intersects this plane at an obtuse angle θ and gradually becomes parallel to the bottom surface as it moves away from the intersection. A second surface 12 is formed.

A C-axis oriented YBCO high temperature superconductor thin film wire 2 having a minute width dimension is formed so as to cross the intersection line 3 of the first and second surfaces 11 and 12. Note that both ends of this thin wire 2 are connected to electrode parts 4 and 5 made of the same YBCO high temperature superconductor thin film.

The structure described above can be manufactured by the following procedure.

First, in order to form first and second surfaces 11 and 12 that intersect at an angle θ on the surface of the MgO (100) substrate 1, a resist is applied to the flat substrate so as to cover the first surface 11. After patterning, the surface of the substrate is milled by Ar ion milling. At this time, by adjusting the milling conditions, it is possible to obtain a curved second surface 12 in which the angle at the intersection is relatively steep and gradually approaches parallel to the bottom surface as it moves away from the angle. .

Next, with the substrate 1 heated to 550 to 650°C,
YB across the intersection line 3 of the first and second surfaces 11 and 12
A CO thin film is formed.

As a result, a YBCO thin film with C-axis orientation perpendicular to the substrate surface is grown in each portion.

According to the structure of the embodiment of the present invention as described above, the first surface 11 of the YBCO high temperature superconductor thin film thin wire 2 is shown in FIG. The C axis direction of the upper part and the same <C of the part near the intersection line 3 on the second surface 12 of the YBCO high temperature superconductor thin film thin wire 2
As shown by the arrows in the figure, they are offset from each other by an angle (π-θ) with respect to the axial direction. Therefore, a discontinuous portion of the crystal is formed here, and a so-called sub-grain boundary 20 is obtained. The critical current density in this sub-grain boundary 20 portion is significantly lower than in other portions, and therefore the YBCO high temperature superconductor thin film thin wire 2 is weakly bonded in this portion, resulting in a Josephson junction.

The sub-grain boundary 2o formed in this part can be artificially controlled by the intersection angle θ of the two planes, the width and film thickness of the YBCO high temperature superconductor vR film thin wire 2, etc., and the desired critical current can be achieved with good reproducibility. We can obtain a Josephson junction with

In addition to the above-mentioned MgO, the material for the substrate is 5
rTiO, (100), (110), YSZ, 00
Any material may be used as long as it does not damage the high temperature superconductor thin film used.

Moreover, it goes without saying that any superconductor thin film may be used as long as it has strong crystallinity.

Furthermore, the crystal axis direction of the superconductor thin film is not particularly limited to the C-axis, and may be in other directions.

<Effects of the Invention> As explained above, according to the present invention, two planes intersecting at an obtuse angle are formed on the substrate surface, and a superconductor with crystal anisotropy is formed so as to cross the line of intersection of the two planes. Since thin film wires are formed, a discontinuous surface where the crystal axis direction changes sharply occurs in the superconductor thin film on this intersection line, and a subgrain boundary is artificially formed. Therefore, it is necessary to use a high temperature superconductor thin film, etc. However, it is artificially■.

5QUID, etc., which can control dynamic resistance R, etc., can be produced stably and with good reproducibility.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a schematic explanatory diagram of its operation. 1...Substrate 11...First surface 12...Second surface 2...YBCO high temperature superconductor thin film thin wire 20...
Subgrain boundary 3...Intersection line Patent applicant Representative of Shimadzu Corporation Patent attorney Nishi 1) Shin

Claims (1)

[Claims] A second plane intersecting the first plane at an obtuse angle is formed on the substrate surface, and a thin wire made of a superconducting thin film having crystal anisotropy in critical current density and coherent length is formed on the substrate surface. A Josephson junction element formed to cross a line of intersection between first and second surfaces.