Low-noise SIS mixer for far-infrared radio astronomy

Abstract

We present a low noise SIS mixer developed for the 1.2 THz band of the heterodyne spectrometer of the Herschel Space Observatory. The device of this design will be among the first SIS mixers flown in space at Herschel. The developed SIS mixer has a quasi-optical design, with a double slot planar antenna and an extended spherical lens made of pure Si. The SIS junctions are Nb/AlN/NbTiN with the critical current density of about 30 KA/cm2 and with the junction area of a quarter of a micron square. For the ease of the Josephson current suppression, the SIS junctions are diamond-like shaped. The simultaneous suppression of the Josephson currents in the two SIS junctions is a particular advantage of the used shape. A low loss Nb/Au micro-strip transmission line is used for the first time in the mixer circuit well above the gap frequency of Nb.Using the new mixer we demonstrated the minimum uncorrected Double Sideband receiver noise of 550 K (Y=1.34). The minimum receiver noise corrected for the local oscillator beam splitter and for the cryostat window is 330 K, about 6 hν/k, apparently for the first time in the THz frequencies range.

THz radiation sensors

“…6) which is near the Nb gap fre− quency (n Nb »0.65-0.7 THz). It seems that they are the best solution for the ground−based radio−astronomy in the wave− length region n < 1 THz [103]. Above this frequency, the Nb has losses like a normal metal.…”

“…Above this frequency, the Nb has losses like a normal metal. Another frequency limit for Nb devices is near n = 1.7 n Nb = 1.0-1.1 THz and, more− over, above this frequency the bias voltage region, where re− verse quantum assisted tunnelling does not occur, is shrink− ing rapidly, and this bias region is non−existent at 2n Nb [103], though theoretically the Nb SIS frequency band is limited by Nb doubled band frequency (2n Nb »1.3 THz) [104]. However, there exists one more reason preventing to build wide frequency band SIS mixer.…”

Development of Low Noise THz SIS Mixer Using an Array of Nb/Al-AlN/NbTiN Junctions

“…2(a). It is similar to one used in our work on 1.2 THz SIS mixer [11]. The mixer housing components are: the base frame, the IF and DC bias board, and the IF and DC connectors.…”

Noise temperature and beam pattern of an NbN hot electron bolometer mixer at 5.25 THz

“…Quasioptical radiation coupling scheme using a twin slot antenna in combination with a dielectric lens has been successfully applied to heterodyne mixers 4,12 up to 1.9 THz in the Herschel space observatory. We choose a spiral antenna in combination with a silicon lens in this work because it is broad band and can work at the high end of THz frequencies.…”