28.07.2016
Doctoral Dissertation

5 August 2016 M.Sc. Juhani Julin (Faculty of Mathematics and Science, Physics)

Juhani Julin defends his dissertation in Physics "Fabrication, Electrical Characterization and 1/f-Noise Study of Submicron Sized Superconductive Tunnel Junctions" on 5 August 2016.

Juhani Julin photo: Pauliina ToivolaM.Sc. Juhani Julin defends his dissertation in Physics "Fabrication, Electrical Characterization and 1/f-Noise Study of Submicron Sized Superconductive Tunnel Junctions". Opponent Dr. Clemens Winkelmann (Université Grenoble Alpes, France) and custos Professor Ilari Maasilta. The Dissertation will be conducted in English.

Abstract

This thesis presents results focused on fabrication and electrical characterization of superconducting tunnel junctions and Josephson junctions, e.g. measuring the current-voltage response and 1/f noise from different samples at different temperatures. Junctions were fabricated inside a vacuum chamber where metal evaporation through a resist mask was used to create submicron-sized junctions. The tunneling barrier was common between all different samples, i.e. in-situ oxidized aluminium between the metal depositions.

Different material combinations were used, e.g. Al-AlOx-Al, Al-AlOx-Al:Mn and Al-AlOx-Nb. The manganese doping in aluminium (Al:Mn) suppresses the superconductivity making the Al:Mn parts normal, while pure aluminium is superconducting, creating a normal metal-insulator-superconductor (NIS) device.

The qualities of junctions were improved, if possible, by vacuum thermal annealing at 400 C, which was found both to stabilize aluminium and aluminium-manganese based junctions and to reduce the characteristic 1/f noise in them, which are desired results, since for most applications it is important to have a junction with stable parameters over long time and 1/f noise is limiting the sensitivity of many devices. However, the procedure is not for granted, since most other NIS material combinations didn't survive the annealing treatment.

We studied Al-AlOx-Nb junctions at cryogenic temperatures (~100 mK) either as a SIS' device, or as a NIS device by suppressing the superconductivity of aluminium with magnetic field, and observed excess sub-gap current, which could not be explained by standard tunneling theory with the Dynes model.

Further information:
Juhani Julin, tel. 040 805 4449, juhani.julin@phys.jyu.fi

More information

Juhani Julin

None

juhani.julin@phys.jyu.fi