Gain bandwidth of NbN hot-electron bolometer terahertz mixers on 1.5μm Si3N4∕SiO2 membranes

The gain bandwidth of NbN hot-electron bolometer terahertz mixers on electrically thin Si3N4∕SiO2 membranes was experimentally investigated and compared with that of HEB mixers on bulk substrates. A gain bandwidth of 3.5GHz is achieved on bulk silicon, whereas the gain bandwidth is reduced down to 0.6–0.9GHz for mixers on 1.5μm Si3N4∕SiO2 membranes. We show that application of a MgO buffer layer on the membrane extends the gain bandwidth to 3GHz. The experimental data were analyzed using the film-substrate acoustic mismatch approach.