On the concept of a normal metal hot-electron microbolometer for space applications

We present a theoretical analysis and experimental evaluation of a hot-electron microbolometer with normal metal absorber for ultrasensitive detecting infrared and submillimeter waves. The basic version of the antenna coupled microbolometer makes use of a hot-electron effect in the thin film resistive strip and Andreev reflection of hot electrons at SN interface between the strip and superconducting antenna. A value of NEP=5/spl middot/10/sup -18/ W/Hz/sup 1/2/ for the thermal fluctuation noise and the thermal time constant t=0.2 /spl mu/s at 300 mK have been estimated for one of the realized devices with thermal conductance G/spl ap/6/spl middot/10/sup -12/ W/K. At 100 mK, the thermal conductance has been decreased to G/spl ap/7/spl middot/10/sup -14/ W/K, that gives estimations for the thermal NEP=2/spl middot/10/sup -19/ W/Hz/sup 1/2/ and the time constant t=5 /spl mu/s. An advanced version of the microbolometer includes also additional SIN junctions connected to the resistive strip for electronic cooling the absorber. Such microbolometer is intended as a detector of millimeter and submillimeter wave radiation for space applications.