4.7-THz Superconducting Hot Electron Bolometer Waveguide Mixer

Abstract

We present the first superconducting hot electron bolometer (HEB) waveguide mixer operating at 4.7 THz. The 5.5-nm-thick, 300-nm-long, and 3600-nm-wide NbN HEB microbridge is integrated into a normal metal (Au) planar circuit on a 2 $\mu$ m thick silicon substrate. This circuit is integrated in a 24 $\mu$ m $\,\times\,$ 48 $\mu$ m $\,\times\,$ 21 $\mu$ m waveguide cavity and a 14 $\mu$ m $\, \times \,$ 7 $\mu$ m $\, \times \,$ 200 $\mu$ m substrate channel, which is directly machined into a CuTe alloy block. The power spectrum of the HEB mixer, measured with a Fourier transform spectrometer, is in good agreement with the results of 3-D EM circuit simulation. Measured mixer performance shows a state-of-the-art double sideband noise temperature of 1100 K, averaged over the IF bandwidth of 0.2–3.5 GHz. The 3-dB noise roll-off is 3.5 GHz. This mixer is used in the German REceiver for Astronomy at Terahertz frequencies (GREAT) at the airborne Stratospheric Observatory for Far Infrared Astronomy (SOFIA).