Josephson LSI fabrication technology using NbN/MgO/NbN tunnel junctions

Josephson LSI fabrication technology using NbN/MgO/NbN tunnel junctions has been developed. The deposition process of the NbN electrode was investigated to obtain high uniformity of the electrical properties. The deposition process of the MgO tunnel barrier was investigated to obtain high reproducibility of the Josephson critical current density. The NbN film with high T/sub c/ of 15 K was obtained. The reproducibility of the MgO deposition rate was improved. The 10-b instruction 128-word ROM unit chip was successfully fabricated using the NbN/MgO/NbN junction LSI technology with the 3- mu m design rule. The READ operation test was performed for a few 10-b words. The total access time was measured to be 710 ps. The uniformity and reproducibility of the critical current density in the LSI chip were improved.