\textbf{Structural and electrical characterization of NbO}$_{\mathrm{\mathbf{2}}}$\textbf{ vertical devices grown on TiN coated SiO}$_{\mathrm{\mathbf{2}}}$\textbf{/Si substrate}

Due to its relatively high MIT temperature (1081 K) and current-controlled negative differential resistance, NbO$_{\mathrm{2}}$ is a robust candidate for memory devices and electrical switching applications. In this work, we present in-depth analysis of NbO$_{\mathrm{2}}$ thin film vertical devices grown on TiN coated SiO$_{\mathrm{2}}$/Si substrates using pulsed laser deposition (PLD). Two of the films grown in 1 mTorr and 10 mTorr O$_{\mathrm{2}}$/Ar (\textasciitilde 7{\%} O$_{\mathrm{2}})$ mixed growth pressures were studied. The formation of NbO$_{\mathrm{2}}$ phase was confirmed by Grazing Incidence X-ray Diffractometry (GIXRD), X-ray Photoelectron Spectroscopy (XPS) and current vs. voltage measurements. A probe station tip (tip size \textasciitilde 2 $\mu $m) or conductive AFM tip was used as a top and TiN bottom layer was used as a bottom contact. Device conductivity showed film thickness and contact size dependence. Current pulse measurements, performed in response to applied triangular voltage pulses, showed a non-linear threshold switching behavior for voltage pulse durations of \textasciitilde 100 ns and above. Self-sustained current oscillations were analyzed in terms of defect density presented in the film.