Improving Transmon Qubit Performance with Fluorine-based Surface Treatments

TL;DR

This paper demonstrates that fluorine-based surface treatments on silicon substrates significantly improve transmon qubit energy relaxation times by reducing surface-related microwave losses, highlighting the importance of materials analysis in qubit performance enhancement.

Contribution

It introduces fluorine-based wet etching as an effective surface treatment to enhance transmon qubit coherence by removing residues and reducing microwave loss at the metal-substrate interface.

Findings

Median T1 time improved to 334 microseconds

Surface treatments effectively remove germanium residue

Enhanced qubit quality factor Q=6.6×10^6

Abstract

Reducing materials and processing-induced decoherence is critical to the development of utility-scale quantum processors based on superconducting qubits. Here we report on the impact of two fluorine-based wet etches, which we use to treat the silicon surface underneath the Josephson junctions (JJs) of fixed-frequency transmon qubits made with aluminum base metallization. Using several materials analysis techniques, we demonstrate that these surface treatments can remove germanium residue introduced by our JJ fabrication with no other changes to the overall process flow. These surface treatments result in significantly improved energy relaxation times for the highest performing process, with median $T_1=334~\mu$s, corresponding to quality factor $Q=6.6\times10^6$. This result suggests that the metal-substrate interface directly underneath the JJs was a major contributor to microwave loss in these transmon qubit circuits prior to integration of these surface treatments. Furthermore, this work illustrates how materials analysis can be used in conjunction with quantum device performance metrics to improve performance in superconducting qubits.