Josephson device, method of forming Josephson device and superconductor circuit

A Josephson device comprising:

• a substrate having a surface;
• a first superconducting electrode layer formed on the surface of the substrate;
• an insulator formed on the first superconducting electrode layer and having a penetration hole penetrating the insulator layer in a direction taken along a thickness of the insulator layer;
• a barrier layer deposited on the first superconducting electrode layer and within the penetration hole;
• and
• a second superconducting electrode layer filling the penetration hole and covering the barrier layer and the insulator layer,
• wherein said first and second superconducting electrode layers are made of an oxide superconductor material having (RE)1(AE)2Cu3Oy as a main component, where an element RE is at least one element selected from a group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and an element AE is at least one element selected from a group consisting of Ba, Sr and Ca;
• and
• said barrier layer is made of a material that includes the element RE, the element AE, Cu and oxygen, where in cations within the material forming the barrier layer, a Cu content is in a range of 35 At. % to 55 At. % and an RE content is in a range of 12 At. % to 30 At. %, and the barrier layer has a composition different from compositions of the first and second superconducting electrode layers.