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Applied Superconductivity

Performance of quasi-optical SIS mixer with NbN/AlN/NbN tunnel junctions and NbN tuning circuit at 760 GHz

Yoshinori Uzawa, Zhen Wang, Akira Kawakami

Published Jul 1, 1998• 12 citations
Publisher
DOI
10.1016/s0964-1807(98)00120-3

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The low-noise performance of a waveguide SIS mixer with NbN/AlN/NbN tunnel junctions and an NbN/MgO/NbTiN tuning circuit on an MgO substrate was demonstrated at frequencies above the gap frequency of Nb. To design the mixer, the complex refractive index of the MgO substrate was measured by using a THz time-domain spectrometer. The superconductive properties of NbTiN films on MgO were examined in detail. An uncorrected receiver noise temperature of 262 K (DSB) at 820 GHz was achieved in an IF bandwidth of 4-12 GHz at a bath temperature of 4.2 K. By comparing the measured and calculated conversion gains, the loss in the NbN/MgO/NbTiN tuning circuit was estimated to be 0.98 dB at 810 GHz.

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SIS Mixers Based on NbN Techniques for ALMA Band 10

Mahoto Takeda, Yoshinori Uzawa, Zhen Wang

We designed, fabricated, and tested SIS mixers based on NbN techniques and estimated the specific capacitance of NbN/AlN/NbN tunnel junctions, which were fabricated by DC-magnetron sputtering, by measuring DC-SQUID resonance steps. In the mixers, NbN/AlN/NbN junctions and NbN/Si O2/Al tuning circuits were used for investigating receiver performance at frequencies greater than 900 GHz. The specific capacitance of the junction was estimated at 120 fF/ mum2with a critical current density of 12 kA/cm2. The resonance frequencies generated in the tuning circuits linearly changed with respect to the tuning lengths up to at least 1.1 THz. We found that an input-circuit structure, which we used, is a factor that degrades receiver noise at frequencies greater than 900 GHz.

IEEE Transactions on Applied Superconductivity•Jun 1, 2007•7 citations
The low-noise performance of a waveguide SIS mixer with NbN/AlN/NbN tunnel junctions and an NbN/MgO/NbTiN tuning circuit on an MgO substrate was demonstrated at frequencies above the gap frequency of Nb. To design the mixer, the complex refractive index of the MgO substrate was measured by using a THz time-domain spectrometer. The superconductive properties of NbTiN films on MgO were examined in detail. An uncorrected receiver noise temperature of 262 K (DSB) at 820 GHz was achieved in an IF bandwidth of 4-12 GHz at a bath temperature of 4.2 K. By comparing the measured and calculated conversion gains, the loss in the NbN/MgO/NbTiN tuning circuit was estimated to be 0.98 dB at 810 GHz.
We designed, fabricated, and tested SIS mixers based on NbN techniques and estimated the specific capacitance of NbN/AlN/NbN tunnel junctions, which were fabricated by DC-magnetron sputtering, by measuring DC-SQUID resonance steps. In the mixers, NbN/AlN/NbN junctions and NbN/Si O2/Al tuning circuits were used for investigating receiver performance at frequencies greater than 900 GHz. The specific capacitance of the junction was estimated at 120 fF/ mum2with a critical current density of 12 kA/cm2. The resonance frequencies generated in the tuning circuits linearly changed with respect to the tuning lengths up to at least 1.1 THz. We found that an input-circuit structure, which we used, is a factor that degrades receiver noise at frequencies greater than 900 GHz.