Normal metal - insulator - superconductor thermometers and coolers with titanium-gold bilayer as the normal metal
Räisänen, I., Geng, Z., Kinnunen, K., & Maasilta, I. (2018). Normal metal - insulator - superconductor thermometers and coolers with titanium-gold bilayer as the normal metal. In J. Bylander, T. Löfwander, & M. Misiorny (Eds.), LT28 : Proceedings of the 28th International Conference on Low Temperature Physics (pp. 012090). Journal of Physics : Conference Series, 969. Institute of Physics Publishing. doi:10.1088/1742-6596/969/1/012090
Julkaistu sarjassaJournal of Physics : Conference Series
We have fabricated superconductor - insulator - normal metal - insulator - superconductor (SINIS) tunnel junctions in which Al acts as the superconductor, AlOx is the insulator, and the normal metal consists of a thin Ti layer (5 nm) covered with a thicker Au layer (40 nm). We have characterized the junctions by measuring their current-voltage curves between 60 mK and 750 mK. For comparison, the same measurements have been performed for a SINIS junction pair whose normal metal is Cu. The Ti-Au bilayer decreases the SINIS tunneling resistance by an order of magnitude compared to junctions where Cu is used as normal metal, made with the same oxidation parameters. The Ti-Au devices are much more robust against chemical attacks, and their lower tunneling resistance makes them more robust against static charge. More significantly, they exhibit significantly stronger electron cooling than Cu devices with identical fabrication steps, when biased close to the energy gap of the superconducting Al. By using a self-consistent thermal model, we can fit the current-voltage characteristics well, and show an electron cooling from 200 mK to 110 mK, with a non-optimized device. ...