Superconducting Computing

The quest for superconducting computers began soon after demonstration of the first Josephson junction switching element. An initial attraction was the ability to switch at the then extremely rapid rates of 100+ GHz. Semiconductor-based computers won that early battle by reducing transistor sizes sufficiently to allow switching at GHz rates without cooling to liquid helium temperatures (~4 kelvins), but are now approaching hard limits to further improvement.
Historical highlights include:

• 1911  Superconductivity discovered
• 1957  BCS theory of superconductivity
• 1962, 1963  Josephson effect predicted, observed
• 1969-1983  IBM Josephson junction computer effort
• 1983  Nb/AlOx/Nb trilayer Josephson junctions
• 1981+  Japanese development efforts
• 1985  Rapid single flux quantum (RSFQ) logic developed in Russia
• 1998  RSFQ T-flip flops operated at up to 770 GHz
• 2001  FLUX-1 microprocessor chip fabricated with 65,759 Josephson junctions
• 2007  64-kb hybrid Josephson-CMOS memory demonstrated with 600 ps access time
  
  

FLUX-1R1 Chip 8-bit, scalable microprocessor prototype 4 superconductor layers 4 kA/cm2 Josephson junction critical current density 65,759 Josephson junctions 10.3 x 10.6 mm chip Designed to operate at 20 GHz Source: 2002 NGST/SUNY-Stony Brook/JPL




Energy efficiency is now very important. Computing systems based on superconducting electronic circuits have the potential for significant energy savings. Research and development areas include:

• Logic circuits
• Memories
• Interconnects between low-temperature components
• Interconnects  for system Input and output
• System architecture
• Design tools and fabrication technology for superconductive electronics
• Component packaging and system integration
• Cryogenic cooling systems
  
  
For further information please contact:
Marc Manheimer
Laboratory for Physical Sciences
8050 Greenmead Road
College Park, MD 20740