Superconducting TiN films grown by directional reactive evaporation

TL;DR

This paper introduces a new reactive evaporation method to grow disordered superconducting TiN films with tunable properties, enabling fabrication of RF devices with high quality factors for quantum circuit applications.

Contribution

It presents a novel directional reactive evaporation technique for TiN film growth, allowing precise control over superconducting properties and enabling complex device fabrication.

Findings

Sheet resistance up to 1361 Ω/□ for 10nm films

Superconducting transition temperature (Tc) of 0.77K

High quality factors (Q=300-2200) in RF devices

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 to 3.1*10^-5 mbar} and film thickness d from 10nm to 300nm. For 10nm thick films, the sheet resistance reaches 1361 \Omega/\square and T_c = 0.77K, which translates into an estimate for the sheet inductance as large as L_\square = 2.4nH/\square. Benefiting from the directionality of reactive evaporation, we fabricated RF test devices with micron-sized dimensions using a resist mask and a lift-off process, which would be impossible 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 = 300-2200. The loss is likely due to the presence of titanium oxynitride in the morphological composition of our films. The flexibility of the lift-off process suggest applications of reactively-evaporated TiN for making supporting structures around quantum circuits, such as readout resonators or compact on-chip filters.