HOT-ELECTRON QUASI-OPTICAL NBN SUPERCONDUCTING MIXER

Hot electron superconductor mixer devices made of thin NbN films on SiO2-Si3N4-Si membrane have been fabricated for 300-350 GHz operation. The device consists of 5-10 parallel strips each 5 mu m long by 1 mu m wide and are coupled to a tapered slot-line antenna The IV characteristics and position of optimum bias point were studied in the temperature range 4.5-8 K. The performance of the mixer at higher temperatures is closer to that predicted by theory for uniform electron heating. The intermediate frequency bandwidth versus bias has also been investigated At the operating temperature 4.2 K a bandwidth as wide as 0.8 GHz has been measured for a mixer male of 6 nm thick film. The bandwidth tends to increase with operating temperature. The performance of NbN mixer is expected to be better for higher frequencies where the absorption of radiation should be more uniform.