This paper presents the fabrication and characterization of superconducting qubit components from titanium nitride (TiN) and aluminum nitride (AlN) layers to create Josephson junctions and superconducting resonators in an all-nitride architecture. Our methodology comprises a complete process flow for the fabrication of TiN/AlN/TiN junctions, characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), ellipsometry and DC electrical measurements. We evaluated the sputtering rates of AlN under varied conditions, the critical temperatures of TiN thin films for different sputtering environments, and the internal quality factors of TiN resonators in the few-GHz regime, fabricated from these films. Overall, this offered insights into the material properties critical to qubit performance. Measurements of the dependence of the critical current of the TiN
IAlN
ITiN junctions yielded values ranging from 150
μAto 2
μA, for AlN barrier thicknesses up to ca. 5 nm, respectively. Our findings demonstrate advances in the fabrication of nitride-based superconducting qubit components, which may find applications in quantum computing technologies based on novel materials.
Lossy dielectrics are a significant source of decoherence in superconducting quantum circuits. In this report, we model and compare the dielectric loss in bulk and interfacial dielectrics in titanium nitride (TiN) and aluminum (Al) superconducting coplanar waveguide resonators. We fabricate isotropically trenched resonators to produce a series of device geometries that accentuate a specific dielectric region's contribution to the resonator quality factor. While each dielectric region contributes significantly to loss in TiN devices, the metal–air interface dominates the loss in the Al devices. Furthermore, we evaluate the quality factor of each TiN resonator geometry with and without a post-process hydrofluoric etch and find that it reduced losses from the substrate–air interface, thereby improving the quality factor.
Over the past decades, high-coherence mechanical resonators have been continuously pushed to new limits, using techniques such as dissipation dilution and clamp-tapering to enhance their quality factor beyond intrinsic material limitations. Today, these mechanical resonators are often fabricated from silicon-nitride, silicon-carbide or aluminum. Recently, however, interest in novel material platforms has grown, especially those allowing for the integration within superconducting circuits. Among these, superconducting nitrides stand out as particularly promising due to their high transition temperatures compared to elementary superconductors. Here, we introduce them as nanomechanical resonators and report on the fabrication and characterization of highly stressed, doubly clamped niobium titanium nitride (NbTiN) nanostring resonators. Using optical interferometry, we determine the elastic properties and mechanical quality factor from room temperature to 13 K. We observe high tensile stress up to 0.81 GPa along with a Young's modulus of 181 GPa and an intrinsic mechanical quality factor up to 850. With these favorable mechanical properties, NbTiN constitutes a promising material platform for future applications in cavity electro- and nanomechanics.
© 2020 Author(s). Lossy dielectrics are a significant source of decoherence in superconducting quantum circuits. In this report, we model and compare the dielectric loss in bulk and interfacial dielectrics in titanium nitride (TiN) and aluminum (Al) superconducting coplanar waveguide resonators. We fabricate isotropically trenched resonators to produce a series of device geometries that accentuate a specific dielectric region's contribution to the resonator quality factor. While each dielectric region contributes significantly to loss in TiN devices, the metal-air interface dominates the loss in the Al devices. Furthermore, we evaluate the quality factor of each TiN resonator geometry with and without a post-process hydrofluoric etch and find that it reduced losses from the substrate-air interface, thereby improving the quality factor.