AIP/123-QED Photon-noise limited sensitivity in titanium nitride kinetic inductance detectors

We demonstrate photon-noise limited performance at sub-millimeter wavelengths in feedhorn-coupled, microwave kinetic inductance detectors (MKIDs) made of a TiN/Ti/TiN trilayer superconducting film, tuned to have a transition temperature of 1.4 K. The lumped-element detector design enables dual-polarization sensitivity. The devices are fabricated on a silicon-on-insulator (SOI) wafer. Micro-machining of the SOI wafer backside creates a quarter-wavelength backshort optimized for ef-ficient coupling at 250 µm. Using frequency read out and when viewing a variable temperature thermal source, we measure device noise consistent with photon noise when the incident optical power is>1 pW, corresponding to noise equivalent powers> 4×10−17 W/√Hz. This sensitivity makes these devices suitable for broadband photometric applications at these wavelengths