High quality Nb-based tunnel junctions for high frequency and digital applications

TLDR

These junctions may have a good potential in Josephson junction arrays and Single‑Flux‑Quantum applications (RSFQ). The study aims to achieve ultimate performance of integrated sub‑mm receivers at 1 THz by developing low‑R_n/S AlN tunnel junctions and proposes a new approach to realize overdamped Nb/AlO_x/Nb junctions. New fabrication techniques, including electron‑beam lithography with chemical‑mechanical polishing, were optimized to produce Nb/AlN/Nb junctions with 0.03 µm² area and to implement the overdamped Nb/AlO_x/Nb design. High‑quality Nb/AlN/Nb junctions with R_j/R_n = 16 and R_n/S = 10 Ω µm² were demonstrated, and the dependence of key parameters on current density and circuit geometry was characterized.

Abstract

A number of new fabrication techniques are developed and optimized in order to fit the requirements of contemporary superconducting electronics. To achieve ultimate performance of integrated submm receivers with operational frequency of 1 THz, tunnel junctions with AlN tunnel barrier having a R/sub n/S value as low as 1 /spl Omega//spl mu/m/sup 2/ have been developed. High quality characteristics of Nb/AlN/Nb tunnel junctions with R/sub j//R/sub n/=16 and R/sub n/S=10 /spl Omega//spl mu/m/sup 2/ have been demonstrated. Electron Beam Lithography (EBL) in combination with Chemical Mechanical Polishing (CMP) has been incorporated to produce Nb/AlN/Nb junctions with 0.03 /spl mu/m/sup 2/ area. A new approach to obtain overdamped Nb/AlO/sub x//Nb tunnel junctions has been proposed and realized. The dependencies of the main parameters of novel junctions on the current density and circuit geometry have been studied. These junctions may have a good potential in Josephson junction arrays and Single-Flux-Quantum applications (RSFQ).