A 665 GHz WAVEGUIDE RECEIVER USING A TUNED 0.5μm Nb/AlOx/Nb SIS TUNNEL JUNCTION

We report recent results on a 580-740 GHz SIS heterodyne receiver employing a tuned 0.50μm Nb/AlOx/Nb SIS tunnel junction. The receiver has been successfully installed at the Caltech Submillimeter Observatory, Hawaii. Results of an untuned device in the same waveguide block were presented at the fifth International THz Conference. Since the mixer is meant to be operated near the supercodunting gap frequency of niobium (24/h ≈ 690 GHz), special has been taken to minimize the absorption loss in the rf matching network. To this effect we propose the use of a RF matching network that constitutes a hybrid between the well know ”end-loaded” stub and radial stub matching networks. We have measured uncorrected DSB receiver temperatures as low as 160K from 680to 702 GHz, 200K at 725GHz and 120K from 585-640 GHz. The uncorrected mixer noise temperature at 702 GHz is about 125K, of which 62K can be directly contributed to the front end optics loss. Mixer conversion loss at 702 GHz is 7dB, of which≈ 0.9dB is due to the absorption loss in the Nb film. This results in a corrected mixer noise temperature of 63K, ≈ 1.7 times the quantum noise limit.