TY - JOUR
T1 - Characterization of different type of Nb-AlOx based Josephson tunnel junctions
AU - Adelerhof, D.J.
AU - Houwman, E.P.
AU - Fransen, P.B.M.
AU - Veldhuis, D.
AU - Flokstra, J.
AU - Rogalla, H.
PY - 1991
Y1 - 1991
N2 - Three types of Josephson tunnel junctions, standard Nb/Al,AlOx/Nb, symmetric Nb/Al,AlOx/Al/Nb, and Nb/Al,AlOx/AlOx/Nb containing a double-oxide layer were investigated by means of temperature-dependent I-V measurements, conductance-voltage measurements, noise analysis, and Auger electron spectroscopy scanning across the edge of a sputtered crater profile. In standard junctions, frequently small leakage currents have been observed as well as resistance fluctuations, leading to telegraph noise. Both effects can be related to the direct contact between the AlOx and the Nb counter electrode. Leakage currents larger than 0.01% of the theoretical maximum critical current have not been observed in any of the symmetric junctions. The sub-gap current of these junctions is dominated by single- and two-particle tunneling. The SNAP process that was used to define the junction areas affects the tunnelling mechanisms below the sum-gap voltage, probably by the introduction of barrier inhomogeneities at the edges of the junctions. The AlOx barrier in symmetric and asymmetric junctions cannot completely be represented by a trapezoidal barrier shape. The metal-insulator interface between Al and AlOx in both junction types is probably not very sharp, which might be due to oxygen diffusion. The metal-insulator interface between AlOx and Nb in standard junctions can be represented by a step-wise increase of the potential barrier, indicating that this interface is very distinct. The AlOx barrier in double-oxide layer junctions is not homogeneous and probably contains low barrier channels
AB - Three types of Josephson tunnel junctions, standard Nb/Al,AlOx/Nb, symmetric Nb/Al,AlOx/Al/Nb, and Nb/Al,AlOx/AlOx/Nb containing a double-oxide layer were investigated by means of temperature-dependent I-V measurements, conductance-voltage measurements, noise analysis, and Auger electron spectroscopy scanning across the edge of a sputtered crater profile. In standard junctions, frequently small leakage currents have been observed as well as resistance fluctuations, leading to telegraph noise. Both effects can be related to the direct contact between the AlOx and the Nb counter electrode. Leakage currents larger than 0.01% of the theoretical maximum critical current have not been observed in any of the symmetric junctions. The sub-gap current of these junctions is dominated by single- and two-particle tunneling. The SNAP process that was used to define the junction areas affects the tunnelling mechanisms below the sum-gap voltage, probably by the introduction of barrier inhomogeneities at the edges of the junctions. The AlOx barrier in symmetric and asymmetric junctions cannot completely be represented by a trapezoidal barrier shape. The metal-insulator interface between Al and AlOx in both junction types is probably not very sharp, which might be due to oxygen diffusion. The metal-insulator interface between AlOx and Nb in standard junctions can be represented by a step-wise increase of the potential barrier, indicating that this interface is very distinct. The AlOx barrier in double-oxide layer junctions is not homogeneous and probably contains low barrier channels
U2 - 10.1109/20.133880
DO - 10.1109/20.133880
M3 - Article
SN - 0018-9464
VL - 27
SP - 3153
EP - 3153
JO - IEEE transactions on magnetics
JF - IEEE transactions on magnetics
IS - 27
ER -