Process for preparing Josephson junction device having weak link of artificial grain boundary

A method for manufacturing a Josephson junction device comprising the steps of:

• wet-etching at least a portion of a principal surface of a single crystalline substrate so that the principal surface includes a first and a second region, of which at least a lattice distance of an exposed lattice of said first region is slightly different from a lattice distance of an exposed lattice of said second region, and,
• forming an oxide superconductor thin film on the first and second regions of the principal surface so that the oxide superconductor thin film includes first and second portions respectively positioned on the first and the second regions of the substrate, said first and said second portions of said oxide superconductor thin film being constituted of single crystals of the oxide superconductor, wherein a lattice of said first portion is oriented at an angle of 45.degree. to a lattice of the second portion, and so that the oxide superconductor thin film has a grain boundary between said first and second portions, which constitutes a weak link of the Josephson junction.