A 850-GHZ WAVE-GUIDE RECEIVER EMPLOYING A NIOBIUM SIS JUNCTION FABRICATED ON A 1-MU-M SI3N4 MEMBRANE

Citation
Jw. Kooi et al., A 850-GHZ WAVE-GUIDE RECEIVER EMPLOYING A NIOBIUM SIS JUNCTION FABRICATED ON A 1-MU-M SI3N4 MEMBRANE, IEEE transactions on microwave theory and techniques, 46(2), 1998, pp. 151-161
Citations number
33
Categorie Soggetti
Engineering, Eletrical & Electronic
ISSN journal
00189480
Volume
46
Issue
2
Year of publication
1998
Pages
151 - 161
Database
ISI
SICI code
0018-9480(1998)46:2<151:A8WREA>2.0.ZU;2-T
Abstract
We report on a 850-GHz superconducting-insulator-superconducting (SIS) heterodyne receiver employing an RF-tuned niobium tunnel junction wit h a current density of 14 kA/cm(2), fabricated on a 1-mu m Si3N4 suppo rting membrane, Since the mixer is designed to be operated well above the superconducting gap frequency of niobium (2 Delta/h approximate to 690 GHz), special care has been taken to minimize niobium transmissio n-line losses, Both Fourier transform spectrometer (FTS) measurements of the direct detection performance and calculations of the IF output noise with the mixer operating in heterodyne mode, indicate an absorpt ion loss in the niobium film of about 6.8 dB at 822 GHz. These results are in reasonably good agreement with the loss predicted by the Matti s-Bardeen theory in the extreme anomalous limit, From 800 to 840 GHz, we report uncorrected receiver noise temperatures of 518 or 514 K when we use Callen & Welton's law to calculate the input load temperatures , Over the same frequency range, the mixer has a 4-dB conversion loss and 265 K +/-10 K noise temperature, At 890 GHz, the sensitivity of th e receiver has degraded to 900 K, which is primarily the result of inc reased niobium film loss in the RF matching network, When the mixer wa s cooled from 4.2 to 1.9 K, the receiver noise temperature improved ab out 20% 409-K double sideband (DSB), Approximately half of the receive r noise temperature improvement can be attributed to a lower mixer con version loss, while the remainder is due to a reduction in the niobium film absorption loss. At 982 GHz, we measured a receiver noise temper ature of 1916 K.