Development of Nb/Au bilayer HEB mixer for space

In this paper we propose to use a metal-superconductor bilayer as an RF detecting element for a diffusion-cooled hot electron bolometer mixer. The motivation is to engineer a superconducting material with a low transition temperature, Tc, (below Tc of commonly used Nb) and higher diffusion constant. With this it is expected to improve the overall HEB mixer performance, i.e. obtain lower noise and wider intermediate frequency bandwidth as well as reduce a local oscillator power requirement. We report our initial experimental results. A couple of Nb/Au bilayer films with different thickness combinations have been fabricated on either glass or Si substrates. The measured sheet resistance and transition temperature of the bilayers are close to those desired for the fabrication of HEB mixers. 1