IF bandwidth and noise temperature measurements of NbNHEB mixers on MgO substrates

We report the fabrication and testing of hot electron bolometric mixers with an ultrathin NbN film as heterodyne receivers operating at the terahertz frequencies. We found that the qualities of NbN strip are usually degraded by the damages resulting from fabrication process, We have developed a fabrication process for reducing the damages in NbN films. We also fabricated HEB mixers with a new structure In order to study the IF bandwidth determined by the original qualities of NbN thin films, Investigations at 100 GHz revealed that the widest IF bandwidth of 2.0 GHz was obtained by a mixer based on 2.8 nm-thick NbN film An usual type of HEB mixer based on the 2.8 nm-thick NbN film was also fabricated and evaluated. The receiver noise temperature at 900 GHz was 780 K, the absorbed LO power was about 400 nW, and the conversion gain was -13 db.