1. Field of the Invention
The present invention relates to a superconducting device for use in a high speed superconducting circuit such as a calculator, a high sensitivity magnetic sensor, or a passive element of an optical or ultrahigh frequency superconducting circuit, and relates to a method of producing the device.
2. Description of the Prior Art
Conventionally, in producing a flat type junction of an anisotropic superconducting thin film (e.g., an oxide high temperature superconductor), a technique of providing a stepped portion or a V-shaped groove as a discontinuous portion on a substrate on which the thin film is to be grown is used to control the crystal orientation of the thin film and to thereby achieve a grain boundary junction.
However, in order to make both sides of the junction area have an identical substrate surface height, at least three angled portions are produced, which results in growth of a plurality of grain boundaries or junctions in one junction area. Therefore, due to a variation of link or characteristics between the junctions, reproducibility of junction characteristics with regard to noise and the like is significantly degraded.
Aside from the above-mentioned method, there is a method of obtaining a junction through lithography using an electron or ion beam. By patterning a fine V-shaped groove on a substrate surface by irradiation of the substrate surface with such an electron or ion beam, a junction can be obtained while the height of the substrate surface is kept constant except for the junction area. However, in such a case, it is difficult to reduce the width (diameter) of the beam to a value smaller than the coherence length of the superconductor, which consequently causes a problem that a plurality of uncontrolled junctions are formed in the fine V-shaped groove, resulting in a non-homogeneous junction area.
There is also a technique of locally disturbing the crystallinity of a substrate by irradiating the substrate with such a weak beam that forms no grooves. This technique, however, has the same drawback as described above.
As described above, with the method utilizing the lithography technique, it is difficult to achieve a single junction in one junction area, which reduces the controllability of the junction characteristics.
As another technique which does not utilizes the lithography technique, there is a bicrystal technique by which two substrates are adhered to each other, which technique cannot integrate junctions.
Among the conventional techniques, the technique utilizing the lithography technique has an advantage in formation of plural junctions on the same substrate as well as formation of the junctions in arbitrary positions. This technique, however, has a drawback that it is impossible to make every area have only a single junction.
On the contrary, the bicrystal technique which can easily obtain a single controlled junction has a drawback that it is not appropriate for integration.