Hot-electron direct detectors: feasibility of NEP H 10 -20 WHz at submillimeter waves Boris S. Karasik a) and William R. McGrath Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 Michael E. Gershenson Dept. of Physics & Astronomy, Rutgers University, Piscataway, NJ 08854 Andrew V. Sergeev Dept. of Electrical and Computer Engineering, Wayne State University, Detroit, MI 48202 Recently, we have presented a concept for a hot-electron direct detector (HEDD) capable of counting single millimeter-wave photons [1]. Such a detector meets the needs of future space far-infrared missions (NEP £ 10 -19 W/ Ö Hz) and can be used for background-limited detector arrays on the Space InfraRed Interferometric Telesope, the 10-meter space telescope and Submillimeter Probe of the Evolutionof Cosmic Structure [2]. The detector is based on a microbridge (1-μm-long) transition edge sensor fabricated from an ultra-thin film of a superconductor with the critical temperature T c = 0.1-0.3 K. A very strong temperature dependence of the electron-phonon coupling allows adjustment the electron-phonon scattering time, t e-ph , to the desired time constant of the detector (t =10 -4 -10 -3 s) at T = 0.1 K. Further adjustment of t eph is possible due to the electron-mean-free-path dependence of t e-ph . The microbridge contacts are made from a superconductor with a higher critical temperature (Nb); these contacts will block the thermal diffusion of hot carriers into the contacts because of the Andreev reflection (see Fig. 1). The low electron-phonon heat conductance, high thermal resistance of the contacts, and small heat capacity of electrons in a micron-size bridge determine the noise equivalent power of ~ 10 20 – 10 21 W/ Ö Hz at T = 0.1 K, which is 10 2 to 10 3 times better than that of state-of-the-art bolometers. By exploiting the negative electro-thermal feedback, the detector time constant can be made as short as 10 -5 -10 -4 s without sacrificing sensitivity. Fig. 1 Our recent measurements [3] addressed the attainability of the low NEP in realistic low-T c materials. For an optimized bolometer one would expect the intrinsic noise to be dominated Hot file:///C|/Nadia/space_detectors/karasik.htm (1 of 6) [8/21/2001 5:43:44 PM]