Detailed Characterization of Quasi-Optically Coupled Nb Hot Electron Bolometer Mixers in the 0.6-3 THz Range

Two type of Nb diffusion-cooled HEB mixers have been studied. One uses a twin-slot antenna designed for 700 GHz, and has a bridge length of 200 nm. This device is fabricated using an in situ-process for the interface between the bridge and the cooling pads. An uncorrected receiver noise temperature of 1200 K at 640 GHz and an IF bandwidth of 5 GHz have been measured. The second device uses a log-periodic antenna designed for a wide RF bandwidth. However, there is a misalignment of the Nb bridge with respect to the Au cooling pads. Receiver noise temperatures at 0.64, 1.9, and 2.5 THz have been measured. We are able to link the geometry feature to the measured properties. 1