Structural and electrical characterization of NbO2 thin film vertical devices grown on TiN-coated SiO2/Si substrates

TL;DR

This study investigates the electrical switching behavior of NbO2 thin films grown on TiN-coated substrates, revealing how growth conditions influence composition, leakage current, switching speed, and oscillation frequency.

Contribution

It provides new insights into how growth pressure affects NbO2/Nb2O5 composition and electrical properties of vertical devices, advancing understanding of their switching mechanisms.

Findings

Higher growth pressure increases NbO2 content and improves switching performance.

Leakage current is dominated by trap-assisted Poole-Frankel conduction.

Films with higher NbO2 content exhibit faster switching and higher oscillation frequencies.

Abstract

We report on the electrical properties of polycrystalline NbO2 thin film vertical devices grown on TiN coated SiO2/Si substrates using pulsed laser deposition. First, we analyzed the thickness and contact size dependences of threshold switching of NbO2 films grown in 10 mTorr Ar/O2 mixed growth pressure, where 25.1%/74.9% of NbO2/Nb2O5 surface composition content was estimated by ex-situ x-ray photoelectron spectroscopy. The leakage current properties in the insulating state were dominated by trap-charge assisted Poole-Frankel conduction mechanism. The threshold switching and self-sustained current oscillatory behavior of films with different NbO2/Nb2O5 composition ratios was measured and analyzed. The second film was grown in lower (1 mTorr) growth pressure which resulted in a higher (34.2%/65.8%) NbO2/Nb2O5 film surface composition. The film grown in higher growth pressure demonstrated lower off-state leakage current, faster switching and self-sustained oscillations with higher frequency than the film grown in lower growth pressure.