Heterodyne measurements of a NbN superconducting hot electron mixer at terahertz frequencies

The performance of a NbN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixer is investigated in the 0.65-3.12 THz frequency range. Th e device is made from a 3 nm thick NbN film on high resistivity Si and inte grated with a planar spiral antenna on the same substrate. The in-plane dim ensions of the bolometer strip are 0.2x2 mu m. The best results of the DSB noise temperature at 1.5 GHz IF frequency obtained with one device are: 130 0 K at 650 GHz, 4700 K at 2.5 THz and 10,000 K at 3.12 THz, The measurement s were performed at 4.5 K ambient temperature. The amount of local oscillat or (LO) power absorbed in the bolometer is about 100 nW. The mixer is linea r to within 1 dB compression up to the signal level 10 dB below that of the LO, The intrinsic single sideband conversion gain measured at 650 GHz is - 9 dB, the total conversion gain is -14 dB.