A scalable non-superconducting tunnel junction technology

TL;DR

This paper introduces a CMOS-compatible, wafer-scale fabrication method for non-superconducting TiW/Al-AlOx/TiW tunnel junctions, enabling scalable integration into cryogenic and quantum systems with validated performance down to 20 mK.

Contribution

It presents a novel, scalable, non-superconducting tunnel junction technology based on TiW alloy, overcoming previous integration and scalability challenges.

Findings

Successful wafer-scale fabrication of TiW/Al-AlOx/TiW junctions

Validated performance in Coulomb blockade thermometers down to 20 mK

Demonstrated compatibility with CMOS processes

Abstract

Tunnel junctions are one of the key elements of chip-scale microsystems serving various technologies from classical microelectronics to quantum information. Aluminium and its oxide (AlOx) have dominated cryogenic tunnel junction technology for decades due to the high quality of AlOx barriers and Al superconducting properties below 1.2 K. However, many applications require non-superconducting junctions, either standalone or in combination with superconducting technology, motivating efforts to suppress Al superconductivity through magnetic fields, doping, or proximity effects -- approaches that so far suffered from integration compatibility and scalability issues. Here, we present a CMOS-compatible normal-metal tunnel junction technology based on TiW alloy and AlOx barriers. We demonstrate wafer-scale fabrication of TiW/Al-AlOx/TiW junctions and validate their performance in Coulomb blockade thermometers operating down to 20 mK, confirming robust normal-state behavior. This TiW-based architecture offers a scalable solution for non-superconducting tunnel junctions across a broad temperature range, enabling integration into advanced cryogenic, quantum and nanoelectronic chip-level systems.