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TEION KOGAKU (Journal of Cryogenics and Superconductivity Society of Japan)

Recent Progress in Superconducting Digital Electronics-Recent Status on the Development of Low-power Superconducting Network Devices-

S. Hasuo

Published Jan 1, 2008• 0 citations
Publisher

Abstract

In recent years, the development of superconducting digital electronics has been making rapid progress. A variety of digital circuits based on Single-Flux Quantum (SFQ) device technology such as high-speed switching circuits for router systems and high-speed sampling oscilloscope systems have been demonstrated. These achievements have been mainly based on the NEDO project, “Development of Low-power Superconducting Network Devices”. This paper describes these recent progress and future prospects of superconducting digital electronics.

DOI
10.2221/jcsj.43.236

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FOREWORD

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Special Section on Progress & Trend of Superconductor-based ComputersIt is our great pleasure to have a Special Section entitled "Progress & Trend of Superconductor-based Computers" in IEICE Transactions on Electronics.Superconducting devices based on Josephson junctions exhibit low power consumption and fast switching.Superconducting transmission lines are free of dispersion up to several hundred GHz.Unique logic circuits such as fast single flux quantum (SFQ) circuits and ultralow power adiabatic quantum-flux parametron (AQFP) logic circuits were proposed and have been improved.These circuits have been well developed based on not only their theoretical advantage but also reliable design and fabrication technology of superconducting integrated circuits.Recently, strong interest on quantum computing motivates the development of superconducting quantum-bits, control and readout circuits, and their integration.In this Special Section, seven invited papers and a contributed one describe these topics: two papers for SFQ, four for AQFP, and two for key devices for quantum circuits.Finally, I would like to appreciate activities of all authors, reviewers, and members in editorial committee for completing this special section.

IEICE Transactions on Electronics•May 31, 2022•0 citations
In recent years, the development of superconducting digital electronics has been making rapid progress. A variety of digital circuits based on Single-Flux Quantum (SFQ) device technology such as high-speed switching circuits for router systems and high-speed sampling oscilloscope systems have been demonstrated. These achievements have been mainly based on the NEDO project, “Development of Low-power Superconducting Network Devices”. This paper describes these recent progress and future prospects of superconducting digital electronics.
Superconducting devices have intrinsically superior characteristics to those of semiconductor devices. Presently, we can fabricate more than twenty thousand junctions on one chip using niobium technology. We have demonstrated the operation of a network system with a superconducting interconnection chip using voltage-state logic. Single flux quantum devices are promising for future superconducting applications because the clock frequency of SFQ logic is higher than that of voltage-state. We have proposed a high-end switch based on hybrid architecture using optical devices, semiconductors and SFQ devices. To demonstrate the high-speed operation of SFQ circuits, we developed an arbiter circuit that uses SFQ components and the arbiter circuit operates at 60 GHz. We also have developed a high Tc superconducting (HTS) SFQ sampler system for observing ultra-fast signal waveforms. In addition, we will discuss the prospects of future superconducting devices based on the fabrication technologies we developed.
Single-flux quantum logic (SFQ) circuits, in which a flux quantum is used as an information carrier, have the possibility for opening the door to a new digital system operated at over 100-GHz clock frequency at extremely low power dissipation. The SFQ logic system is a so-called pulse logic, which is completely different from the level logic for semiconductors like CMOS, so circuit design technologies for SFQ logic circuits have to be newly developed. Recently, much progress in basic technologies for designing SFQ circuits and operating circuits at high speeds has been made. With advances in these design tools, large-scale circuits including more than several thousand junctions can be easily operated with the clock frequency of more than several tens of gigahertz. High-end routers and high-end computers are possible applications of SFQ logic circuits because of their high throughput nature and the low power dissipation of SFQ logic. In this paper, recent advances of SFQ circuit design technologies and recent developments of switches for high-end routers and microprocessors for high-end computers that are considered possible applications for SFQ logic will be described.
Single flux quantum (SFQ) logic circuits, in which a single flux quantum is used for an information carrier, have a possibility to open a new digital system operated with over 100 GHz clock frequencies at extremely low power dissipations. Recently, much progress in basic technologies for designing SFQ circuits and operating circuits with high speeds has been done. By taking advancements in these designing tools, circuits including more than several thousands junctions easily operated with the clock frequency of more than several tens GHz. Applications of SFQ circuits such as high performance computers, high end router and high end servers are being developed in the world taking advantages of the high through-put nature and the low power dissipation of the SFQ logic.
The authors argue that superconducting digital electronics is the future trend for high-speed and low-power applications. Low-T/sub c/ technology based on stable Nb-AlO/sub x/-Nb tunneling junctions has been successful in constructing most of the digital circuit logic elements. A four-stage shift register constructed with latching logic operated up to 4 GHz with a power consumption of about 60 mu W per gate. A 12-b analog-digital coverter constructed with a single flux quantum (SFQ) logic showed proper operation with the total power dissipated being only about 100 mu W. Fabrication of Josephson tunneling junctions with high-T/sub c/ materials has been tougher than with low-T/sub c/ materials. However, recently developed very high speed rapid single flux quantum (RSFQ) logic circuits can be applied to weak link type junctions fabricated with YBa/sub 2/Cu/sub 3/O/sub 7-x/ films. Simulations of the various circuits with weak link type junctions, e.g., shift registers, analog-digital converters, etc., show fast operation and reasonable margins. Applications of similar concepts can be applied to NbN circuits operating at above 10 K.>
I describe the fundamental technologies concerning the single flux quantum (SFQ) logic circuits. Recent remarkable progress in the computer-aided-design (CAD) tool, which is based on the cell-based design technique, enables us to make SFQ integrated circuits. Although the circuit demonstrated so far has 2, 300 Josephson junctions at most, this number will increase because the CAD tool is advancing. The on-chip test system has also been developed to test the high-speed nature of the SFQ circuit. For example, the shift-register employed as a circuit under test operates correctly at 55GHz. I also describe the potential applications of the SFQ circuits. An analog-to-digital converter utilizing the high-speed nature and high sensitivity in the SFQ circuits will be applicable to the front end of the future base stations, which require broad band width, high sensitivity, and flexibility. Packet switches used in the future high-end router need high throughput and functionality. Only SFQ-based packet switches can meet these requirements. Another potential application is a high-end server. We have studied micro-architectures of a processor executing the Java Byte Codes directly and a multiprocessor system constructed by connecting the processors and memories via the ultra-broad-band SFQ network switches. Throughout the study, we employ the concept of the complexity-reduction (CORE), in which the high-speed nature of the SFQ circuits is used for the reduction of the circuit scale or simplification of the micro-architecture; the multiprocessor system has high performances. These clear applications promote rapid technological progress in the SFQ technology, though we must make every endeavor to find new application fields.
Special Section on Progress & Trend of Superconductor-based ComputersIt is our great pleasure to have a Special Section entitled "Progress & Trend of Superconductor-based Computers" in IEICE Transactions on Electronics.Superconducting devices based on Josephson junctions exhibit low power consumption and fast switching.Superconducting transmission lines are free of dispersion up to several hundred GHz.Unique logic circuits such as fast single flux quantum (SFQ) circuits and ultralow power adiabatic quantum-flux parametron (AQFP) logic circuits were proposed and have been improved.These circuits have been well developed based on not only their theoretical advantage but also reliable design and fabrication technology of superconducting integrated circuits.Recently, strong interest on quantum computing motivates the development of superconducting quantum-bits, control and readout circuits, and their integration.In this Special Section, seven invited papers and a contributed one describe these topics: two papers for SFQ, four for AQFP, and two for key devices for quantum circuits.Finally, I would like to appreciate activities of all authors, reviewers, and members in editorial committee for completing this special section.