Title :
Fabrication of Nb/Al-Nx/NbTiN junctions for SIS mixer applications
Author :
Bumble, B. ; LeDuc, H.G. ; Stern, J.A. ; Megerian, K.G.
Author_Institution :
Jet Propulsion Lab., California Inst. of Technol., Pasadena, CA, USA
fDate :
3/1/2001 12:00:00 AM
Abstract :
We discuss fabrication and characteristics of superconductor-insulator-superconductor (SIS) junctions which typically exhibit a 3.5 mV sum-gap voltage. Junctions have a sub-gap to normal state resistance ratio of RSG/RN=27 for resistance-area products down to RNA=8 Ω μm2 and high quality junctions have been produced with RNA products as low as 4 Ω μm2. The device structure incorporates a Nb base electrode, a tunnel barrier formed by plasma nitridation of a thin Al proximity layer, and a NbTiN counter-electrode. Results for all Nb junctions with high current density aluminum-nitride barriers are also shown. Nitridation of the aluminum layer is investigated by control of the dc floating potential on a separate rf driven electrode in the vacuum process chamber. Devices are integrated to a mixer antenna structure incorporating NbTiN as a ground plane. The wire circuit layer can be either normal metal or NbTiN. Annealing results show improved I-V characteristics with increased RNA products. Recent receiver measurements employing these junctions exhibit low noise performance up to 900 GHz
Keywords :
aluminium compounds; annealing; niobium; niobium compounds; nitridation; submillimetre wave mixers; superconducting device noise; superconducting microwave devices; superconductor-insulator-superconductor mixers; titanium compounds; type II superconductors; 3.5 mV; I-V characteristics; Nb base electrode; Nb-AlN-NbTiN; Nb/Al-Nx/NbTiN junctions; NbTiN counter-electrode; SIS mixer applications; annealing; dc floating potential; fabrication; low noise performance; mixer antenna structure; nitridation; plasma nitridation; resistance-area products; rf driven electrode; sub-gap/normal state resistance ratio; sum-gap voltage; superconductor-insulator-superconductor junctions; thin Al proximity layer; tunnel barrier; wire circuit layer; Current density; Electrodes; Fabrication; Josephson junctions; Niobium; Plasma density; Plasma devices; RNA; Superconducting devices; Voltage;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
