Understanding and controlling growth of transition metal nitrides for next-generation superconducting quantum devices

Superconducting transition metal nitrides such as niobium nitride (NbN), titanium nitride (TiN) and their alloys are key for next-generation quantum devices due to their promising superconducting properties and compatibility with semiconductor processes. Precise control of thin film growth is crucial to ensure accurate structure, stoichiometry, and defect concentration, which influence device performance.

We present an extensive analysis of NbN, TiN, and NbTiN thin films deposited using DC reactive sputtering in a cluster tool system at Berkeley Lab’s Molecular Foundry. Structural, chemical, and electrical characterization shows how crystallinity and composition affect the superconducting properties. Process parameters such as substrate choice, deposition temperature, and nitrogen partial pressure are explored to understand their role in achieving epitaxial nitride films. We also report on the relationship of key superconducting properties such as critical temperature, upper critical field and superconducting gap to structure and stoichiometry, paired with quality factor measurements obtained from resonator structures. This work offers a systematic approach for synthesis and optimization of high-quality superconducting nitrides thin-films essential for superconducting quantum circuits.