LOW-NOISE IN A DIFFUSION-COOLED HOT-ELECTRON MIXER AT 2.5 THZ

The noise performance of a Nb hot-electron bolometer mixer at 2.5 THz has been investigated. The devices are fabricated from a 12-nm-thick N b film, and have a 0.30 mu mX0.15 mu m in-plane size, thus exploiting diffusion as the electron cooling mechanism. The rf coupling was provi ded by a twin-slot planar antenna on an elliptical Si lens. The experi mentally measured double sideband noise temperature of the receiver wa s as low as 2750+/-250 K with an estimated mixer noise temperature of approximate to 900 K. The mixer bandwidth derived from both noise band width and IF impedance measurements was approximate to 1.4 GHz. These results demonstrate the low-noise operation of the diffusion-cooled bo lometer mixer above 2 THz. (C) 1997 American Institute of Physics.