Abstract
We demonstrate low-noise heterodyne mixing with NbN/AlN/NbN tunnel junctions in the submillimeter-wave region. The prepared junction size was 1 μm in diameter and the current density was about 20 kA/cm2, supplying a small ωCJRN product (ωCJRN=3 at 300 GHz). The mixer used a lens-coupled log-period antenna and an integrated tuning circuit which incorporated a radial short stub tuner for resonating out the junction capacitance. The junctions showed good dc I–V characteristics, excellent submillimeter-wave responses and sensitive heterodyne mixing responses. From 254 to 350 GHz the average receiver noise temperature measured using the standard Y-factor method was about 250 K double sideband (DSB). The lowest receiver noise temperature, 200 K (DSB), was obtained around 303 GHz.
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