Development of phonon-cooled NbTiN HEB heterodyne mixers for THz applications

Phonon-cooled hot electron bolometer (HEB) mixer elements are promising heterodyne detectors for THz frequencies. The current development status of niobium-titanium nitride (NbTiN) HEB mixers for THz receivers, for example for the GREAT receiver on SOFIA, is presented for both waveguide and quasi-optical mixers. Waveguide mixers are based on 2 μmd thick silicon nitride membranes which are suspended in a substrate channel and quasi-optical mixers are based on an extended hemispherical silicon lens integrated with logarithmic spiral antennas. The measured DSB receiver noise temperature is 1000 K for waveguide and 2000 K for quasi-optical mixers at 800 GHz RF and 1 GHz IF. The HEB devices are fabricated at KOSMA and consist of a 4-5 nm thin NbTiN film.