High-Q superconducting microwave resonators using MBE titanium nitride
arXiv:2607.15230
The authors use molecular beam epitaxy to grow high-quality TiN thin films on sapphire, achieving very low X‑ray rocking curve widths and superconducting coplanar waveguide resonators with internal quality factors exceeding 10^6 at the single‑photon level and over 2×10^7 at high photon numbers.
Abstract
Using molecular beam epitaxy, we have realized thin films of titanium nitride (TiN) on c-plane sapphire that exhibit the lowest observed full-width at half maximum X-ray rocking curve width of 18 arcsec. Though the (111) oriented TiN exhibits an abrupt and crystalline interface with sapphire, for the first time we observe sub-surface defects in the sapphire substrate, which nucleate structural defects in the epitaxial TiN layer. Using quarter-wavelength coplanar waveguide (CPW) resonators in a 3 \textmu m/6 \textmu m/3 \textmu m gap/strip/gap lines in a hanger geometry, we find the internal quality factor of the TiN resonators to be in the single-photon limit at 5.8 GHz and 10 mK, rising to at . The results are of high interest for applications of superconducting TiN in several areas, and provide a path towards epitaxial Josephson junctions with crystalline barriers in the future for high coherence qubits.
8 pages and 5 figures