Stress Accommodation in Nanoscale Dolan Bridges Designed for Superconducting Qubits

TL;DR

This paper introduces a stress-relief mask design for Josephson junctions in superconducting qubits, significantly improving fabrication yield by reducing bridge fracture during processing.

Contribution

A novel lithography mask with stress-relief channels that decreases lateral stress and enhances the survivability of Dolan bridges in Josephson junction fabrication.

Findings

Stress-relief channels reduce lateral stress by over 70%.

Achieved 100% yield in fabricating over 100 Josephson junctions.

Improved robustness of Dolan bridges during device processing.

Abstract

Josephson junctions are the principal circuit element in numerous superconducting quantum information devices and can be readily integrated into large-scale electronics. However, device integration at the wafer scale necessarily depends on having a reliable, high-fidelity, and high-yield fabrication method for creating Josephson junctions. When creating Al/AlOx based superconducting qubits, the standard Josephson junction fabrication method relies on a sub-micron suspended resist bridge, known as a Dolan bridge, which tends to be particularly fragile and can often times fracture during the resist development process, ultimately resulting in device failure. In this work, we demonstrate a unique Josephson junction lithography mask design that incorporates stress-relief channels. Our simulation results show that the addition of stress-relief channels reduces the lateral stress in the Dolan bridge by more than 70% for all the bridge geometries investigated. In practice, our novel mask design significantly increased the survivability of the bridge during device processing, resulting in 100% yield for over 100 Josephson junctions fabricated.