Fabrication of Ta/TaOx/Nb Junctions for Superconducting Qubits with Reactive Magnetron Sputtering

The dominant source of noise in superconducting qubits comes from its

material constituents. Although AlOx is still widely used as the dielectric in

Josephson Junctions, its amorphous structure hosts two level system (TLS)

defects. These TLS defects have dipoles that dissipate energy by coupling with

the resonant microwave electric field, limiting coherence times. In this work,

we explore an alternate Josephson junction stack, Ta/TaOx/Ta/Nb, with the

aim of reducing materials-induced noise. The barrier(TaOx) is grown with

controlled reactive magnetron sputtering with optimized control parameters,

and the asymmetric gap along with higher gap of Ta and Nb in comparison to

Al suppresses quasiparticle noise. The devices are fabricated with overlap

process using subtractive etching to define their features. XPS, TEM and

AFM results of the oxide, device fabrication flow and preliminary

characterization of the devices will be presented.