Resolving Power of Visible to Near-Infrared Hybrid β-Ta/NbTiN Kinetic Inductance Detectors

Kevin Kouwenhoven, Daniel Fan, Enrico Biancalani, Steven A. H. de Rooij, Tawab Karim, Carlas S. Smith, Vignesh Murugesan, David J. Thoen, Jochem J. A. Baselmans, Pieter J. de Visser

Submitted on 12 July 2022


Kinetic Inductance Detectors (KIDs) are superconducting energy-resolving detectors, sensitive to single photons from the near-infrared to ultraviolet. We study a hybrid KID design consisting of a beta phase tantalum (β-Ta) inductor and a NbTiN interdigitated capacitor (IDC). The devices show an average intrinsic quality factor Qi of 4.3×105 ± 1.3 ×105. To increase the power captured by the light sensitive inductor, we 3D-print an array of 150×150 μm resin micro lenses on the backside of the sapphire substrate. The shape deviation between design and printed lenses is smaller than 1μm, and the alignment accuracy of this process is δx=+5.8±0.5 μm and δy=+8.3±3.3 μm. We measure a resolving power for 1545-402 nm that is limited to 4.9 by saturation in the KID's phase response. We can model the saturation in the phase response with the evolution of the number of quasiparticles generated by a photon event. An alternative coordinate system that has a linear response raises the resolving power to 5.9 at 402 nm. We verify the measured resolving power with a two-line measurement using a laser source and a monochromator. We discuss several improvements that can be made to the devices on a route towards KID arrays with high resolving powers.


Comment: 11 pages, 9 Figues, Journal Paper

Subjects: Physics - Instrumentation and Detectors; Astrophysics - Instrumentation and Methods for Astrophysics; Condensed Matter - Superconductivity