Low-Loss, High-Coherence Airbridge Interconnects Fabricated by Single-Step Lithography

TL;DR

This paper presents a simplified, single-step lithography process for fabricating nanoscale airbridges that improve device performance without adding loss, enabling better integration in quantum and nano-electronic devices.

Contribution

A novel single-step electron-beam lithography method for creating high-quality, nanoscale airbridges with enhanced mechanical stability and minimal loss in quantum devices.

Findings

Achieved sub-200 nm, smooth, suspended metallic bridges.

No measurable additional loss in qubit relaxation time T1.

2.5-fold enhancement of dephasing time T2* in superconducting qubits.

Abstract

Airbridges are essential for creating high-performance, low-parasitic interconnects in integrated circuits and quantum devices. Conventional multi-step fabrication methods hinder miniaturization and introduce process-related defects. We report a simplified process for fabricating nanoscale airbridges using only a single electron-beam lithography step. By optimizing a multilayer resist stack with a triple-exposure-dose scheme and a thermal reflow step, we achieve smooth, suspended metallic bridges with sub-200-nm features that exhibit robust mechanical stability. Fabricated within a gradiometric SQUID design for superconducting transmon qubits, these airbridges introduce no measurable additional loss in the relaxation time $T_1$, while enabling a 2.5-fold enhancement of the dephasing time $T_2^*$. This efficient method offers a practical route toward integrating high-performance three-dimensional interconnects in advanced quantum and nano-electronic devices.