Low-loss, high-coherence airbridge interconnects fabricated by single-step lithography

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 that enables the fabrication of nanoscale airbridges with just one step of electron-beam lithography. By optimizing a multilayer resist stack with a triple-exposure-dose scheme and a thermal reflow step, we achieve burr-free, suspended metallic bridges with sub-micron 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 T₁, 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.