Increasing integration scale of superconductor electronics beyond one million Josephson junctions
Sergey K. Tolpygo, В.К. Семенов
Abstract
Abstract We review the existing fabrication processes for superconductor digital electronics and describe approaches to increasing the scale of integration of superconducting digital circuits from the current level of about one million Josephson junctions (JJs) on a 1-cm 2 chip toward ten million JJs per chip. We present designs of ac-clocked Single Flux Quantum (SFQ) shift registers, convenient benchmarking circuits, in a 250-nm-linewidth superconductor electronics fabrication process developed recently at MIT Lincoln Laboratory (MIT LL). For shift registers using resistively shunted JJs with Josephson critical current density, J c of 100 μA/μm 2 , we achieved a record-high circuit density of 4.2·10 6 JJs per cm 2 , a factor of three higher than the previous record obtained in the MIT LL 350-nm-linewidth SFQ5ee process. Using self-shunted JJs with J c of 600 μA/μm 2 , we increased this record circuit density to 7.4·10 6 JJs per cm 2 .