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NbTiN BASED TUNING STRUCTURES FOR BROADBAND Nb-Al2O3-Nb SIS MIXERS FROM 640 GHz– 800 GHz

Authors:
S. Glenz, S. Haas, C.E. Honingh, K. Jacobs
Abstract:
We present measurements with a prototype waveguide SIS mixer for band 2 (640 GHz – 800 GHz) of HIFI (Heterodyne Instrument for FIRST). The Nb/Al2O3/Nb junctions have an RnA product from 12–18 [Omega]µm². These junctions are embedded in microstrip circuits tuning out the device capacitance using a NbTiN ground layer and various top conductor materials such as NbTiN, Nb and Al. The NbTiN films are fabricated by DC magnetron sputtering which is optimized for a minimum value of the DC resistivity and for a high critical temperature by varying the sputter pressure, sputter power and Ar:N2 flow. Typical NbTiN film parameters for device fabrication are [rho] = 120 µ[Omega]cm and Tc = 14.5 K. The best uncorrected noise temperatures we measured so far are for devices with NbTiN/SiO2/Nb tuning. At 4.2 K bath temperature, a standard Y-factor measurement yields uncorrected receiver noise temperatures of 350 K at 642 GHz and 500 K at 810 GHz for 1.5 GHz intermediate frequency. We discuss the effect of the various tuning circuit materials on the mixer performance. In addition, measurements at IF’s between 4 GHz and 8 GHz will be presented.
Categories:
SIS Mixers
Year:
2001
Session:
1
Full-text:
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Page Number(s):
1-10