Characterization of a tantalum-aluminum-based kinetic inductance detector for far-infrared space applications

Future far-infrared space observatories equipped with cryogenic telescopes require ultra-sensitive detectors to enable measurements limited only by the sky background. We present the design, fabrication, and characterization of a superconducting kinetic inductance detector (KID) at 4.3 THz. The lumped-element KID comprises a tantalum interdigitated capacitor and a 100-nm-wide aluminum-line inductor connected in parallel. The inductor acts also as a low-volume absorber. We achieved photon-noise-limited performance with a noise equivalent power of 1.9 × 10−19 W/Hz referenced to absorbed blackbody power at a modulation frequency of 300 Hz. Under optical loading above 1.83 fW, the detector remains stable with white-noise spectra extending down to ∼100 mHz.