Inductorless Fast Phase Logic: Enabling Two-Order-of-Magnitude Density Scaling for Superconductor VLSI

TL;DR

This paper introduces a novel superconductor logic family called Fast Phase Logic (FPL) that enables two-order-of-magnitude density scaling and reduced power consumption, with potential applications in high-performance computing.

Contribution

The paper presents FPL, a new superconductor logic family with a fabrication process supporting higher density, faster operation, and lower power, advancing superconductor VLSI technology.

Findings

FPL can achieve two orders of magnitude higher integration density than RSFQ.

FPL reduces supply current by five times compared to conventional logic.

Architectural study shows FPL's advantages in FFT circuit performance.

Abstract

Fast phase logic (FPL) is a novel digital superconductor electronic (SCE) logic family that employs multiple junction types, including switching 0-Josephson junctions (0-JJs), non-switching 0-JJ stacks, and $\pi$-JJs. FPL enables flexible, automatable cell layouts, faster pulse propagation, reduced bias current via phase-shifting $\pi$-JJs, and minimized inductive loops, thereby reducing susceptibility to trapped flux and crosstalk. A fabrication process to support FPL is proposed. NbTiN superconductors offer small grain sizes, smooth surfaces, and thermal stability up to 400~$^\circ$C, while high-$J_c$, self-shunted JJs enable compact devices. AlN dielectrics provide good crystal matching to NbTiN, improving superconducting properties. Projections indicate that FPL, combined with the proposed process, can achieve a two-order-of-magnitude increase in integration density over conventional RSFQ logic and a five-fold reduction in supply current. The increased density reduces latency and improves computational throughput, while NbTiN-based devices provide higher output voltage and impedance, improving compatibility with CMOS circuits. Further fabrication advancements, such as higher-$J_c$ NbTiN-based JJs, higher processing temperatures, and stacked JJ structures, could enhance FPL implementation and scalability toward very large-scale integration (VLSI). FPL has the potential to significantly advance SCE technology, with near-term applications in accelerator cores for signal processing and artificial intelligence, and long-term potential in supercomputing. Its advantages are evaluated through an architectural study of a fast Fourier transform (FFT) circuit, with comparisons to CMOS and SFQ technologies.