Future cold space borne observatories for the far infrared, such as the Origins Space Telescope, require large arrays of extremely sensitive detector operating in a 1-10 THz band. We present the design, fabrication and characterisation of microwave kinetic inductance detectors (MKIDs) with a high optical coupling efficiency and a noise equivalent power NEP = 4 ⋅ 10^-20 W/√Hz, measured using a thermal calibration source band-pass filtered in a narrow band around 1.55 THz. The devices are antenna-coupled NbTiN-aluminium hybrid MKIDs, optimised for a low NEP, high responsivity and super-THz operation. Key is the use of a very small aluminium volume of ~5 μm3 for radiation absorption, increasing the responsivity by capacitively loading the NbTiN coplanar waveguide section of the resonator and using a thin membrane for the aluminium coplanar waveguide where the THz radiation is absorbed.
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