Low-noise submillimeter-wave NbTiN superconducting tunnel junction mixers

We have developed a low-noise 850 GHz superconductor-insulator-superconduct or quasiparticle mixer with NbTiN thin-film microstrip tuning circuits and hybrid Nb/AlN/NbTiN tunnel junctions. The mixer uses a quasioptical configu ration with a planar twin-slot antenna feeding a two-junction tuning circui t. At 798 GHz, we measured an uncorrected double-sideband receiver noise te mperature of T-RX=260 K at 4.2 K bath temperature. This mixer outperforms c urrent Nb SIS mixers by a factor of nearly 2 near 800 GHz. The high-gap fre quency and low loss at 800 GHz make NbTiN an attractive material with which to fabricate tuning circuits for SIS mixers. NbTiN mixers can potentially operate up to the gap frequency, 2 Delta/h similar to 1.2 THz. (C) 1999 Ame rican Institute of Physics. [S0003- 6951(99)02651-0].