JOSEPHSON LSI FABRICATION TECHNOLOGY USING NBN/MGO/NBN TUNNEL-JUNCTIONS

We have developed Josephson LSI fabrication technology using NbN/MgO/NbN tunnel junctions. 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 Tc of 15 K was obtained. The reproducibility of the MgO deposition rate was improved. The 10-bit 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-bit words. The total access time was measured to be 710 ps. The uniformity and the reproducibility of the critical current density in the LSI chip were improved. The application of the NbN/MgO/NbN tunnel junction to the Josephson LSI fabrication technology was demonstrated.