Improved Flux QubitsBased onTantalum

Recently, there have been considerable efforts to improve the design and fabrication of superconducting qubits with a focus on material platforms. The use of tantalum on sapphire has led to increased relaxation and coherence times of qubits [1]. However, to realize scalable qubits compatible with industrial fabrication processes, the quality of materials and interfaces on Si substrates must be improved. We present our results on a new process for superconducting circuits using superconducting Ta films on Si substrates. The growth of Ta on Si is characterized via XPS, XRD and ToF-SIMS analysis. We then apply microscopy methods on the film to characterize the microstructure at designed surfaces and interfaces. Subsequently, we outline our process for the fabrication of superconducting qubits using Ta on Si with special attention to interfaces, as well as roughness of designed features on the chip. We present our work on several types of designs, including resonators and flux qubits. The study gives new insight into the material engineering of Ta and shows potential for improving coherence times in superconducting qubits.

[1] A. P. M. Place et al., “New material platform for superconducting transmon qubits with coherence times exceeding 0.3 milliseconds,” Nat. Commun. 12, (2021)