Cryogenic Memories for RSFQ Ultra-High-Speed Processor

The gap between logic speed and memory access is a growing problem in all computing systems and it is exacerbated for ultra-high speed processors such as the proposed cryogenic Rapid Single Flux Quantum (RSFQ) logic working at 50 .100 GHz. The Superconducting Technology Assessment (STA) Panel considered two levels in a hierarchy of cryogenic memory located off of the processor chip. The first level of off-chip memory would be located on the MCM at 4 Kelvin (4 K) with the processor chip in order to minimize propagation-time delays. We are planning for a 1 Mb memory for this stage. The second-level memory would be much larger and could be located on a more efficient refrigerator stage at 40-77 K.