PT Unknown
AU Hajenius, M
   Baselmans, JJA
   Gao, JR
   Klapwijk, TM
   de Korte 2, PAJ
   Voronov, B
   Gol’tsman, G
TI Increased bandwidth of NbN phonon cooled hot electron bolometer mixers
SE Proc. 15[super:th] Int. Symp. Space Terahertz Technol.
PY 2004
BP 381
EP 386
DE NbN HEB mixers; IF bandwidth
AB We study experimentally the IF gain bandwidth of NbN phonon-cooled hot-electron-bolometer (HEB) mixers for a set of devices with different contact structures but an identical NbN film. We observe that the IF bandwidth depends strongly on the exact contact structure and find an IF gain bandwidth of 6 GHz for a device with an additional superconducting layer (NbTiN) in between the active NbN film and the gold contact to the antenna. These results contradict the common opinion that the IF bandwidth is determined by the phonon-escape time between the NbN film and the substrate. Hence we calculate the IF gain bandwidth of a superconducting film using a two-temperature model. We find that the bandwidth increases strongly with operating temperature and is not limited by the phonon escape time. This is because of strong temperature dependence of the phonon specific heat in the NbN film.
ER