NbN-MgO-NbN tunnel junctions integrated in aluminum strip lines for terahertz quasiparticle mixers

M Schicke*, B Plathner, KH Gundlach, M Aoyagi, S Takada, P Dieleman, JBM Jegers, TM Klapwijk, H van de Stadt

*Bijbehorende auteur voor dit werk

    OnderzoeksoutputAcademicpeer review

    Samenvatting

    NbN tunnel junctions are of great interest for THz heterodyne receivers because their large gap voltage of V-gap approximate to 5 mV implies an upper frequency limit of 4 Delta/h approximate to 2.6 THz as compared to 1.4 THz of Nb. However, due to the high ac losses in NbN films for frequencies above the NbN gap frequency, 2 Delta/h approximate to 1.3 THz, NbN matching circuits cannot be used. Lower losses are achieved with normal metals such as Al. Both for waveguide mixers and quasioptical mixers, quartz substrates are preferred. We report on a room-temperature fabrication process for NbN-MgO-NbN junctions with surfaces below 1 mu m(2) integrated in Al strip lines on quartz substrates. Appropriate plasma conditions for NbN-film deposition are obtained through the use of a second Nb target which acts as a selective nitrogen pump. NbN films on quartz substrates with and without an intermediate layer of Al have T-c > 15 K and rho(N) = 100 - 130 mu Omega.cm. Nb buffers should prevent the possible formation of insulating AIN at the Al-NbN interfaces. We fabricated the first NbN junctions sandwiched between Al layers. Sputtered Al were employed. Critical-current densities of up to 60 kA/cm(2) and subgap resistances R-sg approximate to 5.R-N were achieved. The I-V curves show various structures below the gap voltage. We discuss here the observation of a distinct steep step at eV = 2 Delta/3.

    Originele taal-2English
    TitelAPPLIED SUPERCONDUCTIVITY 1997, VOLS 1 AND 2
    RedacteurenH Rogalla, DHA Blank
    Plaats van productieBRISTOL
    UitgeverijIOP PUBLISHING LTD
    Pagina's377-380
    Aantal pagina's4
    ISBN van geprinte versie0-7503-0487-1
    StatusPublished - 1997
    Evenement3rd European Conference on Applied Superconductivity (EUCAS 1997) - , Netherlands
    Duur: 30-jun-19973-jul-1997

    Publicatie series

    NaamINSTITUTE OF PHYSICS CONFERENCE SERIES
    UitgeverijIOP PUBLISHING LTD
    ISSN van geprinte versie0951-3248

    Other

    Other3rd European Conference on Applied Superconductivity (EUCAS 1997)
    LandNetherlands
    Periode30/06/199703/07/1997

    Citeer dit