Study of IF Bandwidth of ${\hbox{MgB}}_{2}$ Phonon-Cooled Hot-Electron Bolometer Mixers

A noise bandwidth (NBW) of 6-7 GHz was obtained for hot-electron bolometer (HEB) mixers made of 10 nm MgB
₂
films. A systematic investigation of the (IF) gain bandwidth as a function of the MgB
₂
film thickness (30, 15, and 10 nm) is also presented. The gain bandwidth (GBW) of 3.4 GHz was measured for a 10 nm film, corresponding to a mixer time constant of 47 ps. For 10 nm films a reduction of the GBW was observed with the reduction of the critical temperature (
Tc
). Experimental data were analyzed using the two-temperature model. From the theoretical analysis, the electron-phonon time (τ
_{e - ph}
), the phonon escape time (τ
_esc
) and the electron and phonon specific heats (c
_e
, c
_ph
) were extrapolated giving the first model for HEB mixers of MgB
₂
films.