[10a-PA5-1~29] 11 Superconductivity (Poster)

▲ [10a-PA5-4] Niobium Based SIS Junctions with Aluminum Nitride Barrier

〇Matthias Kroug¹, Shohei Ezaki¹, Akihira Miyachi¹, Wenlei Shan¹ (1.National Astronomical Observatory of Japan)

Keywords:SIS junction, niobium, aluminum nitride

Niobium Superconducting-Insulator-Superconductor (SIS) tunnel junctions are most commonly fabricated from the layer stacks Nb/Al/AlO_x/Nb or Nb/Al/AlN_x/Nb, which are asymmetric with respect to the barrier. We have fabricated and characterized junctions using the symmetric layer stack Nb/Al/AlN_x/Al/Nb. The ultra-thin AlN_x barrier is formed by exposing the Al overlayer on the Nb base electrode to the afterglow region of a nitrogen plasma. Our experiments show that for the high current density regime, e.g. j_c > 10 kA/cm², junctions based on the symmetric layer stack have significantly lower sub-gap leakage than those made from the asymmetric layer stack. The mm-sized junctions, defined by optical lithography, have current densities up to 50 kA/cm² and quality factors of R_sub-gap/R_normal = 15 or greater. Sharpness of the non-linearity and high gap voltage of V_gap ~ 2.8 mV are maintained as long as the thickness of the Al layers do not exceed 4 nm.