Low-noise heterodyne mixing with NbN microbolometers at 800 GHz

Abstract

Mixer performance of NbN transition edge microbolometers was investigated in a frequency range from 795 to 813 GHz. The devices consist of a parallel array of 3 NbN lines with submicron length patterned by e-beam lithography in a self-aligned process. The heterodyne mixer response was proven by means of two superposed oscillator signals at the receiver input and the observation of a discrete line in the output spectrum. Receiver noise temperatures, Trec, were determined by the hot/cold load Y-factor method in a quasioptical receiver at 4.2 K. The accessible intermediate frequency (IF) band was 1000 to 1750 MHz. We have compared devices with a NbN film thickness of 100 and 50 Å. Lowest receiver noise temperatures were obtained at 800 GHz. Uncorrected Trec values around 900 K were measured for both devices at a 1000 MHz IF frequency. For higher IF frequencies, Trec increased much less in the 50 Å device than in the 100 Å device. At 800 GHz and 1750 MHz IF frequency, Trec was only 1180 K. This result indicates that in an optimized NbN bolometric mixer the IF frequency band can extend to reasonable high values for radioastronomical applications.

SIS and bolometer mixers for terahertz frequencies

“…A similar value has been deduced from experiments at 800 GHz (Lehnert et al 1998) applying the so-called isotherm technique proposed by Ekström et al (1994). The optimum LO power for an SIS mixer at 800 GHz is approximately 450 nW and increases with the square of the LO frequency, whereas the LO power for the bolometer should be frequency independent.…”

“…Figure 21 shows a NbN bolometer integrated in a dipole antenna (Lehnert et al 1998). To obtain the right resistance R N ≈ 100 the 5 nm thick and 0.4 µm long bridge should be 2.5 µm wide.…”

Low noise NbN superconducting hot electron bolometer mixers at 1.9 and 2.5 THz

“…Currently, for frequencies beyond 1 THz, superconducting hot electron bolometers (HEBs) appear to be the only option for low noise heterodyne mixing elements. Phonon-cooled HEBs, based on thin superconducting NbN with a fast electronphonon cooling time, are particularly promising because they combine a high sensitivity with a reasonably large intermediate frequency (IF) roll-off [1][2][3][4][5][6]. However, these detectors have not yet reached the ultimate sensitivity limit set by quantum noise: hω/k B , in which h is the Planck constant, ω is the angular frequency and k B is the Boltzmann constant.…”

Imaging of thermal domains in ultrathin NbN films for hot electron bolometers

“…Ultrathin NbN films have recently gained much attention for use in THz hot electron bolometer (HEB) mixers and fast photon counting detectors (see e.g. [1,2,3,4]). NbN HEB mixers are short microbridges (typical length and width of order 1 µm and a few nm thickness) with contacts to antenna and dc leads.…”