Superconducting titanium nitride films grown by directional reactive evaporation

Abstract

We report a novel method of growing strongly disordered superconducting titanium nitride (TiN) thin films by reactive electron-beam deposition. The normal state sheet resistance and superconducting critical temperature (Tc) can be tuned by controlling the deposition pressure in the range of 1.1×10−6–3.1×10−5mbar. For 10nm thick films, the sheet resistance (R□) reaches 1361Ω/□ and Tc=0.77K, which translates into an estimate for the sheet inductance as large as L□=2.4nH/□. Benefiting from the directionality of reactive evaporation, we fabricated RF test devices with micrometer-sized dimensions using a resist mask and a lift-off process, which would be difficult with sputtering or atomic layer deposition methods. The spectroscopic measurements result in consistent sheet inductance values in two different device geometries, and the quality factors ranged from Q = 300 to 2200. The loss is possibly due to the presence of titanium oxynitride (TiNxOy) in the morphological composition of our films. The flexibility of the lift-off process suggests applications of reactively evaporated TiN for making supporting structures around quantum circuits, such as readout resonators or compact on-chip filters.