PT Journal
AU Hajenius, M
   Yang, ZQ
   Gao, JR
   Baselmans, JJA
   Klapwijk, TM
   Voronov, B
   Gol'tsman, G
TI Optimized sensitivity of NbN hot electron bolometer mixers by annealing
SO IEEE Trans. Appl. Supercond.
JI IEEE Trans. Appl. Supercond.
PY 2007
BP 399
EP 402
VL 17
IS 2
DI 10.1109/TASC.2007.898064
DE NbN HEB mixers
AB We report that the heterodyne sensitivity of superconducting hot-electron bolometers (HEBs) increases by 25-30% after annealing at 85degC in high vacuum. The devices studied are twin-slot antenna coupled mixers with a small area NbN bridge of 1 mum times 0.15 mum, above which there is a SiO 2 passivation layer. The mixer noise temperature, gain, and resistance versus temperature curve of a HEB before and after annealing are compared and analysed. We show that the annealing reduces the intrinsic noise of the mixer by 37% and makes the superconducting transition of the bridge and the contacts sharper. We argue that the reduction ofthe noise is mainly due to the improvement of the transparency of the contact/film interface. The lowest receiver noise temperature of 700 K is measured at a local oscillator frequency of 1.63 THz and at a bath temperature of 4.2 K.
ER