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

Abstract

We studied and optimised 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 minimised 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.

Improved critical temperature of superconducting plasma-enhanced atomic layer deposition of niobium nitride thin films by thermal annealing

“…Extremely interesting results (Tc: ~14 K for the ~30 nm thick film) have been reported using TBTDEN/H 2 [15,18] or TBTDEN/H 2 /N 2 [17,19]. Several authors [14,18] reported that the films may contain relatively high amounts of oxygen and carbon, up to 50 at%. However, high impurity levels make it difficult to make definite conclusions on the relationship between material properties and the superconductivity.…”

Superconducting properties of very high quality NbN thin films grown by pulsed laser deposition

“…NbN thin films are generally fabricated by reactive magnetron sputtering [4], high-temperature chemical vapor deposition technique (HTCVD) [5] or atomic layer deposition (ALD) [6]. Olaya et.…”

“…[5] fabricated 40 nm thin NbN film with T c = 16.8 K at sapphire by using of high-temperature chemical vapor de-position technique with the high substrate temperature (T s ) of 1300 • C, which makes this technology unusable for the preparation of heterostructures. On the other hand, Linzen [6] reported the fabrication of high quality 40 nm thick NbN film deposited by plasma-assisted ALD with relatively lower substrate temperature of T s = 350 • C on sapphire, but with lower T c of 13.8 K.…”

Compositional and electrical properties of Cr, Nb, Cr/Nb, CrNbN, and CrN/NbN multilayers grown using the d.c. magnetron sputtering technique

“…It is important to note that TMN are attractive because of the combination of properties that makes them very suitable and reliable for different technological applications. From the perspective of electrical behavior, one TMN widely studied is niobium nitride (NbN), which exhibits very attractive electrical properties, mainly related to its superconducting behavior . Regarding this nitride, studies have mainly focused on determining the relationship between its electrical behavior and its microstructural state.…”

“…From the perspective of electrical behavior, one TMN widely studied is niobium nitride (NbN), which exhibits very attractive electrical properties, mainly related to its superconducting behavior. 13 Regarding this nitride, studies have mainly focused on determining the relationship between its electrical behavior and its microstructural state. For example, Wang et al 14 reported that, at certain synthesis parameters, the NbN films, with the highest quality single crystal structure, exhibited the best superconducting properties.…”