Proximity-coupled Ti/TiN multilayers for use in kinetic inductance detectors

Abstract

We apply the superconducting proximity effect in TiN/Ti multi-layer films to tune the critical temperature, T_C, to within 10 mK with high uniformity (less than 15 mK spread) across a 75 mm wafer. Reproducible T_C’s are obtained from 0.8 to 2.5 K. These films had high resistivities, > 100 µΩ cm, and internal quality factors for resonators in the GHz range, on the order of 100 k and higher. Trilayers of both TiN/Ti/TiN and thicker superlattice films were prepared, demonstrating a well controlled process for films over a wide thickness range. Detectors were fabricated and shown to have single photon resolution at 1550 nm. The high uniformity and controllability coupled with the high quality factor, kinetic inductance, and inertness of TiN make these films ideal for use in frequency multiplexed kinetic inductance detectors and potentially other applications such as nanowire detectors, transition edge sensors, and associated quantum information applications.