Münster 1997 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 19: Postersitzung III: Josephsonkontakte(1-25), SQUIDs, Sensoren, Detektoren(26-37), Supraleitung in Hochfrequenz und Elektronik(38-45), Präparation und Dotierung von HTSL(46-53), NMR und Ultraschall in HTSL(54-60), Thermodynamik, Magnetismus(61-68), Transporteigenschaften von HTSL(69-73), Spektroskopie, Ramanstreuung, param. Meissner-Effekt in HTSL(74-84), n-dotierte HTSL(85-91)
TT 19.16: Poster
Donnerstag, 20. März 1997, 15:30–19:00, Z1
Fabrication of NbN-MgO-NbN junctions integrated in low-loss Al transmission lines for THz mixers — •M. SCHICKE, B. PLATHNER, and K.-H. GUNDLACH — Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, F-38406 St. Martin d’Hères
NbN tunnel junctions are of great interest for THz heterodyne receivers because their large gap voltage of 5 mV implies an upper frequency limit of 4Δ/h = 2.6 THz as compared to the 1.4 THz of Nb. However, due to the high ac losses in NbN films for frequencies above the NbN gap frequency, 2Δ/h = 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. This process permits the realization of hybrid mixer chips 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 [1]. NbN films on quartz substrates with and without intermediate layers of Al and Nb have Tc > 15 K and ρN = 100 … 130 µ Ω ·cm. Nb buffers should prevent the possible formation of insulating AlN at the Al-NbN interfaces. We fabricated the first NbN junctions sandwiched between Al layers. Both evaporated and sputtered Al were employed. Critical-current densities of up to 60 kA/cm2 and subgap resistances Rsg ≈ 4 · RN were achieved.
[1] B. Plathner et al., to appear in Appl. Phys. Lett., 23 Dec. 1996