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High-Speed Rapid-Single-Flux-Quantum Multiplexer and Demultiplexer Design and Testing

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Doctoral thesis

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Superconductor electronics excel for high operation speed and low power consumption. Rapid-Single-Flux- Quantum RSFQ circuits in which information is stored in superconductor loops as tiny magnetic flux quanta and transferred as several picosecond-wide voltage pulses with quantized area, are demonstrated to work at a few tens of gigahertz with the current niobium process and has the potential to work up to a few hundred gigahertz with technology scaling. A large superconductor RSFQ system or a hybrid system combined with the low-power high-density cryogenic CMOS memory can be realized with a multi-chip module MCM packaging technique. The goal of this thesis project is to design and to experimentally demonstrate 20-50 GHz operation of a 18 demultiplexer DEMUX and an 81 multiplexer MUX. DEMUX and MUX are important interface circuits that are required to take advantage of the ultra-high speed of the RSFQ logic. They are required to interface the superconductor and the lower-speed semiconductor circuits in a hybrid system. In a superconducting MCM system, the DEMUX and MUX can be used to convert the data rate between chips. The speed of RSFQ circuits scales with the process technology. An analysis is done to show that the maximum speed of RSFQ circuits is proportional to the shunted Josephson junctions critical current times its shunt resistance value IcR. Furthermore, IcR is proportional to the square root of the junctions critical current density Jc exp 12 in the low-Tc niobium process. Superconductor integrated circuits using a micron niobium fabrication technology can operate up to 30- 40 GHz. Combining the possible larger process variations caused by the reduced feature size and thinner junction barrier layer, operation of DEMUX and MUX circuits at 50 GHz is taken as a reasonable and challenging design goal.

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  • Electrical and Electronic Equipment
  • Quantum Theory and Relativity

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