SPIRAL ANTENNA NBN HOT-ELECTRON BOLOMETER MIXER AT SUBMM FREQUENCIES

We have studied the phonon-cooled hot-electron bolometer (HEB) as a qu asioptical mixer based on a spiral antenna designed for 0.3-1 THz freq uency band and fabricated on sapphire and high resistivity silicon sub strates. HEB devices were produced from superconducting 3.5-5 nm thick NbN films with a critical temperature 10-12 K and a critical current density of approximately 10(7) A/cm(2) at 4.2 K. For these devices we reached a DSB receiver noise temperature below 1500 K, a total convers ion loss of L-t = 16 db in the 500-700 GHz frequency range, an IF band width of 3-4 GHz and an optimal LO absorbed power of approximate to 4 mu W. We experimentally analyzed various contributions to the conversi on loss and obtained an RF coupling factor of about 5 dB, internal mix er loss of 10 db and IF mismatch of 1 dB.