Resist-Free Shadow Deposition Using Silicon Trenches for Josephson Junctions in Superconducting Qubits

Abstract

Superconducting qubit fabrication innovations continue to be explored to achieve higher performance. Despite improvements to base layer fabrication and processing, resist-based Josephson junction (JJ) schemes have largely remained unchanged. The polymer mask during deposition causes chemical contamination and limits in situ and ex situ surface preparation, junction materials, and scalability. Here, we demonstrate a resist-free approach to junction fabrication based on etched silicon trenches that is compatible with standard silicon microfabrication processes and easily integrated into existing innovations in qubit base layer fabrication and chemical processing. We fabricate Al-AlOx-Al JJs and qubits using this method, measuring median energy relaxation times up to 188 μs. We find minimal contamination at the substrate–metal interface and fluctuations of energy relaxation on a 45 h time scale that are narrow and normally distributed. The method widens the process window for substrate preparation and new materials platforms.