DIGITAL APPLICATIONS OF SUPERCONDUCTING NIOBIUM FILMS

In this paper we describe the performance of Josephson circuits made with superconducting niobium films. Niobium Josephson integrated circuits are much more uniform, stable, and reproducible than those made of lead alloys. We have developed a Josephson circuit fabrication process using Nb/AlO(x)/Nb Josephson junctions, niobium wiring, SiO2 insulators, and molybdenum resistors. Stress-free deposition is important for fabricating small junctions with niobium films. During insulator deposition, junction temperatures were kept under 150-degrees-C to prevent the niobium and Al-AlO(x) from mixing. Using this process, we fabricated an 8-bit digital signal processor (DSP) based on the well-known complementary metal-oxide-semiconductor DSP, and confirmed its processing speed of 1 gigaoperation per second with a 12 mW power dissipation. Josephson devices fabricated with this niobium film process are faster and have lower power consumption than semiconductor devices.