Development of Phonon-Cooled NbTiN HEB Heterodyne Mixers for GREAT

The current development status of NiobiumTitanium Nitride (NbTiN) HEB mixers, for example for the GREAT receiver on SOFIA, is presented for both waveguide and quasi-optical mixers for 0.8, 1.9 and 2.7 THz LO frequency. For the waveguide mixers at 0.8 and 1.9 THz the HEBs are made on 2μm thick silicon nitride membranes which are suspended in a substrate channel perpendicular to the waveguide. For the quasi-optical mixer at 2.7 THz the devices are fabricated on Si-substrates and are integrated into spiraland doubleslot antennas and used with an extended hemispherical silicon lens. Our measurements show that the waveguide/membrane mixers work well at both 800 GHz and 1.9 THz. To increase the required IF bandwidth we are developing thin NbN films. The first results of the NbN thin film development are presented in the paper.