Inductance and mutual inductance of superconductor integrated circuit features with sizes down to 120 nm. Part I

TL;DR

This paper presents detailed measurements and analysis of inductance and mutual inductance in superconductor integrated circuits with feature sizes down to 120 nm, including effects of ground plane perforations, vias, and magnetic flux trapping.

Contribution

It provides new empirical data and analysis on inductance characteristics of superconductor IC features at nanometer scales, utilizing advanced fabrication processes and comparison with inductance extraction software.

Findings

Inductance varies with ground plane perforations and via configurations.

Flux trapping in ground moats affects coupling between inductors.

Process parameter variations influence inductance values.

Abstract

Data are presented on inductance of various features used in superconductor digital integrated circuits such as microstrip and stripline inductors with linewidths down to 120 nm and different combinations of ground plane layers, effect of perforations of various sizes in the ground planes and their distance to the inductors on inductance, inductance of vias of various sizes between adjacent layers and composite vias between distant superconducting layers. Effects of magnetic flux trapping in ground plane moats on coupling to nearby inductors are discussed for circuit cooling in a residual field of several configurations. Test circuits used for the measurements were fabricated in a new 150-nm node of a fully planarized process with eight niobium layers, SC2 process, developed at MIT Lincoln Laboratory for superconductor electronics and in its 250-nm node SC1, as well as in the standard fabrication process SFQ5ee. The SC2 process utilizes 193-nm photolithography in combination with plasma etching and chemical mechanical planarization of interlayer dielectrics to define inductors with linewidth down to about 100 nm on critical layers. All other processes use 248 nm photolithography. Effects of variation of process parameters on circuit inductors are discussed. The measured data are compared with the results of inductance extraction using software packages InductEx and wxLC. Part II is devoted to mutual inductance of various closely spaced features in integrated circuits, meanders, and transformers.