# A self-aligned nano-fabrication process for vertical NbN-MgO-NbN Josephson junctions

## TL;DR

This paper introduces a novel self-aligned fabrication process for vertical NbN-MgO-NbN Josephson junctions, enabling scalable, high-performance superconducting circuits with customizable impedance.

## Contribution

It presents a new self-aligned process for fabricating vertical NbN-MgO-NbN Josephson junctions with a wide range of sizes and impedance options, suitable for complex microwave circuits.

## Key findings

- Junctions have high gap voltages (> 4 mV)
- Low sub-gap leakage currents observed
- Process supports a broad range of junction areas

## Abstract

We present a new process for fabricating vertical NbN-MgO-NbN Josephson junctions using self-aligned silicon nitride spacers. It allows for a wide range of junction areas from 0.02 um^2 to several 100 um^2. At the same time, it is suited for the implementation of complex microwave circuits with transmission line impedances ranging from < 1 Ohm to > 1 kOhm. The constituent thin films and the finished junctions are characterized. The latter are shown to have high gap voltages (> 4 mV) and low sub-gap leakage currents.