Abstract: A photodetecting device having Josephson junctions, comprises an insulating substrate, a polycrystalline superconductor film formed on the insulating substrate such that Josephson junctions are formed at grain boundaries, the superconductor film having a first region subjected to light illumination, and second and third regions formed contiguously at both sides of the first region such that a width of each of the second and third regions is wider than that of the first region, an input circuit for supplying a predetermined bias current between the second and third regions, and an output circuit for detecting a change in voltage between the second and third regions, one terminal of said input circuit and one terminal of said output circuit being commonly grounded, wherein the superconductor film comprises BaPb.sub.1-x Bi.sub.x O.sub.3 (where 0.32.ltoreq.x.ltoreq.0.35). This simple photodetecting device can detect an optical signal at high speed with high sensitivity.

Abstract: A tunneling Josephson junction is disclosed in which first and second superposed superconducting electrode layers are formed of thin films of oxide superconducting materials having a perovskite structure of BaPB.sub.1-x Bi.sub.x O.sub.3. A barrier layer interposed between these superconducting electrode layers is a thin film of long service life which is stable and breakdown free under heat cycles from room temperature to ultra low temperatures. This film is made of an oxide with perovskite structure which has the same crystal structure and thermal expansion coefficient as those of the first and second superconducting layers for functioning as an insulator or a semiconductor. The oxide with perovskite structure may be BaSnO.sub.3, Ba.sub.1-y Sr.sub.y Pb.sub.1-x Bi.sub.x O.sub.3 (wherein 0.ltoreq.x.ltoreq.0.3, y>0.3) or BaPb.sub.1-x (A.sub.1-y Bi.sub.y)O.sub.3 (wherein A is at least one member selected from the group consisting of V, Nb, Ta and Sb; 0.1.ltoreq.x.ltoreq.0.3; and 0.ltoreq.y.ltoreq.0.5).