Superconducting Digital Circuit Design With an Open Source and Freeware Tool Chain

Superconducting digital circuits have been around for decades, but recent projects that exploit such circuits for low-power, high-performance computing are rapidly maturing superconducting circuit technologies. As a result of increasing circuit complexity, there is renewed focus on superconducting digital circuit design tools. Until now, most computer-aided design (CAD) tool development for superconducting electronics (SCE) circuit design has been based on calibrating semiconductor tools, rather than creating new technology-specific tools for the SCE circuit design. The recent development shows bias toward large and expensive CAD tools. These tools, or modules developed for commercial semiconductor CAD tools, require users to have access to an expensive commercial semiconductor CAD software, which places it out of the reach of new entrants or small research groups in SCE. In this paper, the open-source tools that can be used as alternatives to form an SCE design tool chain are described. All the design stages in an SCE integrated circuits design flow, from circuit specification down to layout design, are noted in this paper. Each stage is discussed and the available open-source tools are described. The inherent disadvantages of these open-source tools are also pointed out. A design example is then provided to demonstrate a complete open source and freeware tool chain.

I. Introduction

Superconducting electronics (SCE) design has become a key topic of research in the quest to develop faster yet low-power beyond-CMOS alternatives for power-hungry supercomputers and data centers [1]. As the barrier of physical limitations on semiconductor electronics approaches, the SCE technology is an increasingly viable option for the next major leap in high-performance computing [2] . Several superconducting logic families have emerged in the process, such as rapid single flux quantum (RSFQ) [3], energy-efficient RSFQ [4], energy-efficient SFQ [5], reciprocal quantum flux [6], and adiabatic quantum flux parametron (AQFP) [7].