Superconductor-normal metal hot electron microbolometer with capacitive coupling. 

 

M. Tarasov, M. Fominsky, A.Kalabukhov, L. Kuzmin

Chalmers University of Technology, Gothenburg, Swqden

Institute of Radio Engineering and Electronics, Moscow, Russia

M.Lomonosov Moscow State University, Moscow, Russia

 

Capacitive coupled normal metal hot electron microbolometer with superconducting electrodes (CCNHEB) is a further development of the concept of a normal metal hot electron microbolometer with Andreev mirrors (ANHEB).  It was proposed to avoid frequency and energy limitation of ANHEB in which Andreev mirrors are effective for relatively long absorbers and energies below the superconductor energy gap.  Another advantage of CCNHEB is much easier layout in which same tunnel junctions provide both thermal insulation and temperature sensing.  Samples were fabricated with absorber made of bilayer of Cr and Al to match the impedance of antenna to the absorber resistance.  Electrodes were made of Al and tunnel junctions are formed over the Al oxide layer.  Bolometers are integrated with log-periodic and double-dipole planar antennas.  Temperature response of bolometer structures was measured at temperatures down to 256 mK.  In our experiment we observed dV/dT=1.7 mV/K that corresponds to responsivity S=0.4*10⁹ V/W and for amplifier noise V_n=3nV/Hz^1/2 the technical noise equivalent power is NEP=7.5*10^-18 and intrinsic one corresponding to the SIN noise V_n=0.5 nV/Hz^1/2  NEP=V_n/S=1.2*10^-18.  For microwave evaluation of bolometer we use a black body radiation source comprising of thin NiCr film deposited on thin sapphire substrate and suspended on nylon support fibers.  Source was placed in front of CCNHEB attached to extended hemisphere sapphire lens. 

Voltage response of CCNHEB on temperature variation DVT and blackbody radiation DV249mV.