Analysis of the fabrication process of Nb/Al-AlN/sub x//Nb tunnel junctions with low R/sub n/A values for SIS mixers

Abstract

Abstract-We characterize the fabrication process of superconductor-insulator-superconductor junctions (SIS) based on a Nb/Al-AlN /Nb tri-layer. Utilization of the AlN tunnel barrier, produced by Al nitridation in a nitrogen glow discharge, enables us to produce high quality SIS junctions with low values (the product of junction resistance and area). Analyzing the correlation of junction resistance and plasma properties, it is concluded that the mechanism of tunnel barrier formation is based on nitrogen implantation into the Al layer with subsequent diffusion of nitrogen, stimulated by plasma heating. The latter process plays a dominant role since values are well correlated with the power dissipated on the substrate surface. An SIS mixer using this technology and electron-beam lithography has been successfully fabricated.

High quality Nb-based tunnel junctions for high frequency and digital applications

“…It is well known that using a simple exposure of sputtered Al surface into N atmosphere one cannot get a continuous 1051-8223/03$17.00 © 2003 IEEE AlN layer of sufficient thickness to be used as a tunnel barrier [1]. Several successful attempts of Al nitridation have been made using a glow discharge in nitrogen atmosphere [1]- [4]. Following this idea we grow an AlN tunnel barrier just after Al deposition using rf magnetron discharge.…”

“…T HE idea of utilizing SIS tunnel junctions for heterodyne mixing at THz frequencies has received remarkable support due to recent developments of Nb-Al-AlN-Nb tunnel junctions with low values (where , are junction normal-state resistance and area respectively) down to 1 m [1]- [4]. Use of sub-micrometer size Nb-Al-AlN-Nb tunnel junctions in combination with low loss NbN or NbTiN tuning circuits will result in significant improvement of 1 THz receiver sensitivity.…”

Shot noise in YBCO bicrystal Josephson junctions

“…These resonances may cause a deviation of from value. Fiske steps can be also observed in Josephson junctions with small damping such as SIS tunnel junctions [12]. Therefore, we assume that tunneling is a dominant mechanism of the current flow in the tested YBCO bicrystal junctions.…”

Superconducting detectors and mixers for millimeter and submillimeter astrophysics

“…The HEB data are from [236], [285]- [296]. metal circuits [227], [228], higher gap superconductors such as NbN or NbTiN [229]- [237], and very high current density AlN-barrier junctions [221], [233], [238], [239]. At present, SIS mixers have been successfully operated at frequencies up to 1.25 THz-the latest result for the Herschel/HIFI 1.2-THz SIS mixer is 530 K (DSB) uncorrected, and below 400 K after correction for the LO beamsplitter [280].…”