Development of THz Nb diffusion-cooled hot electron bolometer mixers

We summarize our research activities on THz Nb diffusion-cooled hot electron bolometer (HEB) mixers, carried out at Space Research Organization Netherlands (SRON) and Delft University of Technology. This paper will include our understanding on the device physics of diffusion-cooled HEB mixers, noise and IF bandwidth measurements of waveguide mixers around 0.7 THz, and in particular recent measurements of Nb quasi-optical mixers at 0.64 and 2.5 THz. The waveguide devices demonstrate a receiver noise temperature of 900 K at 0.7 THz. The quasi-optical mixers show 1200 K at 0.64 THz and 4500 K at 2.5 THz and a maximum IF bandwidth of at least 5 GHz.