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

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.