Fabrication of Superconducting Nb–AlN–NbN Tunnel Junctions Using Electron-Beam Lithography

Mikhail Yu Fominsky,Valery P Koshelets,Pavel N Dmitriev,Artem M Chekushkin,Lyudmila V Filippenko

doi:10.3390/electronics10232944

Mikhail Yu Fominsky, Valery P Koshelets + Show 3 more

Open Access

https://doi.org/10.3390/electronics10232944

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Journal: Electronics	Publication Date: Nov 26, 2021
Citations: 8	License type: CC BY 4.0

Affiliation: Institute of Radio-Engineering and Electronics

Abstract

Mixers based on superconductor–insulator–superconductor (SIS) tunnel junctions are the best input devices at frequencies from 0.1 to 1.2 THz. This is explained by both the extremely high nonlinearity of such elements and their extremely low intrinsic noise. Submicron tunnel junctions are necessary to realize the ultimate parameters of SIS receivers, which are used as standard devices on both ground and space radio telescopes around the world. The technology for manufacturing submicron Nb–AlN–NbN tunnel junctions using electron-beam lithography was developed and optimized. This article presents the results on the selection of the exposure dose, development time, and plasma chemical etching parameters to obtain high-quality junctions (the ratio of the resistances below and above the gap Rj/Rn). The use of a negative-resist ma-N 2400 with lower sensitivity and better contrast in comparison with a negative-resist UVN 2300-0.5 improved the reproducibility of the structure fabrication process. Submicron (area from 2.0 to 0.2 µm2) Nb–AlN–NbN tunnel junctions with high current densities and quality parameters Rj/Rn > 15 were fabricated. The spread of parameters of submicron tunnel structures across the substrate and the reproducibility of the cycle-to-cycle process of tunnel structure fabrication were measured.

Highlights

One of the most successful areas of superconducting electronics is the development of low-noise terahertz receivers [1,2]
Submicron tunnel junctions are necessary to realize the ultimate parameters of SIS receivers, which are used as standard devices on both ground and space radio telescopes around the world
Heterodyne SIS receivers are used as standard devices on most ground-based and space radio telescopes around the world [4,5]

Summary

Introduction

One of the most successful areas of superconducting electronics is the development of low-noise terahertz receivers [1,2]. To implement the ultimate parameters of SIS mixers, it is necessary to create and optimize a reproducible and reliable technology for the fabrication of nanostructures with a tunnel barrier thickness on the order of 1 nm with an extremely high current density and low leakage currents [6,7,8]. To match the waveguide elements of the high-current-density mixer with the receiving antenna, the area of the SIS junctions must be substantially less than a square micrometer. This article describes the technology of SIS tunnel structure fabrication of submicron sizes using direct electron-beam lithography (EBL) and subsequent plasma chemical etching for the manufacture of high-quality tunnel structures with good reproducibility and minimal deviation of parameters along the substrate. The measurements were carried out using an automated system for measuring the current–voltage characteristics and electrophysical parameters of the SIS tunnel junctions IRTECON [14]

Sputtering Equipment and Technology Processes

Conclusions