Characterization of NbN/AlN/NbN tunnel junctions fabricated without intentional heating

Abstract

We have fabricated by SNEP process Nb/AI/NbN/AIN/NbN Josephson junctions with the gap voltage V, = 2A!e IZ: 4.0 mV, subgap leakage R,,/R, IZ: 6.0, current density measured at the gap current rise J, = 1.5 kA/cm2. The (111)-textured NbN with transition temperature T, 16 K have been deposited at ambient substrate temperature. Phase composition and structure of the NbN films were investigated by X-ray diffraction analysis (XRD). It was found that the films have a structure close to the cubic 6-NbN (JCPDS card N38-11556) and the phase composition and intrinsic stress in NbN depend on Ar and N2 partial pressure during DC maguetroln sputtering. Cross-sectional TEM analisys showed that in -s'itu depositoin of thin AI layer in the base Nb/AI/NbN electrode provides effective planarization of its surface and the result in improvement of tunnel junction parameters.

Stationary properties of SINIS double-barrier Josephson junctions

“…In summary, we can formulate the main technological tendencies for obtaining a highest value of the I C R N parameter for double-barrier structures. The first is a means of reduction of the pt product during the formation of the barrier with simultaneous surface planarization of the bottom electrode [15]. The second is the possibility of reduction of the proximity effect in the composite electrodes by reducing the thickness of the Al layers without degrading the weaklink-type IVC behaviour of the junctions.…”

Double-barrier junction based dc SQUID

“…This is realized, as in Ref. [8], by depositing the base electrode as a base plate of 100 nm thick Nb, a 4 nm Al layer and a 40 nm Nb top plate (as thin as possible for smoothness). To make the ®rst barrier, a 5 nm Al layer is ®rst deposited.…”

Epitaxial NbN/AlN/NbN tunnel junctions on Si substrates with TiN buffer layers

“…[13][14][15] However, because the superconducting properties of NbN films are dependent on the crystal structures of the film, 16,17 it is difficult to fabricate high-quality NbN tunnel junctions on substrates other than MgO. Despite several attempts to develop NbN tunnel junctions using Si substrates, 18,19 to date, there have been no reports of junctions with a high quality similar to that of epitaxial NbN junctions fabricated on MgO substrates. Therefore, to enable practical application of NbN junctions in superconducting electronics, it is important to develop epitaxial NbN tunnel junctions on Si or other substrates.…”