Challenges and the Status of Superconducting Single Flux Quantum Technology
Naveen Kumar Katam, Jamil Kawa and Massoud Pedram
ABSTRACT
Design and manufacturing of superconductive electronics have been evolving over the past three decades with significant progress made in related fields. Rapid single flux quantum (RSFQ) logic circuits have become popular among superconductive logic families and its energy-efficient variants (ERSFQ and eSFQ) have shown promise as an ultra lowpower and high-speed circuit fabric. SFQ circuits have been demonstrated at tens of GHz with an energy consumption of an attojoule per gate. There are many differences between SFQ and conventional CMOS circuits. SFQ logic circuits are based on the manipulation of the quantized magnetic flux pulses. Most of the logic gates are sequential in nature requiring the clock to be distributed to every logic gate. SFQ logic gates have no gain and hence splitters are needed to drive multiple fanouts. Design and successful demonstration of a controllable superconducting switch and a compact reliable memory element have evaded researchers so far. This paper starts by describing key differences between SFQ logic and conventional CMOS and concludes by listing key challenges that must be overcome to achieve the very large scale integration of SFQ circuits and make the demonstration of a superconductive CPU a reality.
Keywords: Cryogenic computing, ERSFQ, Josephson junctions, superconductive electronics.
