JOSEPHSON IC

PURPOSE:To obtain the titled device which can keep stable action with a switching speed of 5ps or less and is suitable for the increase in integration, by a method wherein the junction current density in each case of using Nb oxide for the tunnel barrier layer and using Al oxide or Al and Al oxide is made specific. CONSTITUTION:An Nb film for example is formed on an Si substrate 1, and the lower electrode 2 is provided by processing this film with a photo resist as a mask. Next, an SiO film is formed by resistance heating evaporation, and the insulation layer 3 is produced by processing the lift-off method using a photo resist as a stencil mask. Then, the tunnel barrier layer 4 and the upper electrode 5 are provided on the surface of the lower electrode 2. Further, an Mo thin film is formed and then processed by ion etching into a resistor. The junction current density is 1X10 A/m -1.25X10 A/m in the case of using Nb oxide for the barrier layer 4 and 4X10 A/m -3X10 A/m in the case of Al oxide or Al and Al oxide.