Structural and electrical properties of ultrathin niobium nitride films grown by atomic layer deposition

S Linzen, M Ziegler, Oleg Astafiev, M Schmelz, U Hübner, M Diegel, E Il’ichev, H-G Meyer

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We studied and optimized the properties of ultrathin superconducting niobium nitride films fabricated with a plasma-enhanced atomic layer deposition (PEALD) process. By adjusting process parameters, the chemical embedding of undesired oxygen into the films was minimized and a film structure consisting of mainly polycrystalline niobium nitride with a small fraction of amorphous niobium oxide and niobium oxo-nitrides were formed. For this composition a critical temperature of 13.8 K and critical current densities of 7×106 A cm–2 at 4.2 K were measured on 40nm thick films. A fundamental correlation between these superconducting properties and the crystal lattice size of the cubic δ-niobium-nitride grains were found. Moreover, the film thickness variation between 40 and 2 nm exhibits a pronounced change of the electrical conductivity at room temperature and reveals a superconductor–insulator-transition in the
vicinity of 3 nm film thickness at low temperatures. The thicker films with resistances up to 5kΩ per square in the normal state turn to the superconducting one at low temperatures. The perfect thickness control and film homogeneity of the PEALD growth make such films extremely promising candidates for developing novel devices on the coherent quantum phase slip effect.
Original languageEnglish
Article number035010
Pages (from-to)1-4
Number of pages4
JournalSuperconductor Science and Technology
Issue number3
Early online date6 Jan 2017
Publication statusPublished - 30 Jan 2017

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