The role of defects in the electrical properties of NbO2 thin film vertical devices

Abstract

Epitaxial NbO2 thin films were grown on Si:GaN layers deposited on Al2O3 substrates using pulsed laser deposition. Pulsed current-voltage (IV) curves and self-sustained current oscillations were measured across a 31 nm NbO2 film and compared with a similar device made from polycrystalline NbO2 film grown on TiN-coated SiO2/Si substrate. Crystal quality of the as grown films was determined from x-ray diffractometry, x-ray photoelectron spectroscopy and atomic force microscopy data. The epitaxial film device was found to be more stable than the defect-rich polycrystalline sample in terms of current switching and oscillation behaviors.

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

“…For currents measured at the same voltage, for example at 0.2 V, the film grown in lower growth pressure (1 mTorr) had a current that was an order of magnitude higher than the one measured on the film grown in higher growth pressure (10 mTorr). The larger content of Our previous study of NbO2 lateral devices 19,20 demonstrated that the current switching was caused by Joule heating from the current flowing through the devices. Prior to observing a threshold switching, a forming pulse was needed, requiring the application of larger electric field magnitudes than those used during normal operation.…”

“…Our previous study of NbO2 lateral devices 19,20 demonstrated that the current switching was caused by Joule heating from the current flowing through the devices. Prior to observing a threshold switching, a forming pulse was needed, requiring the application of larger electric field magnitudes than those used during normal operation.…”

“…Epitaxial films, on the other hand, have longer current switching times and thus are not deemed suitable for applications in devices. 19,20 Here we report on the structural and electrical properties of NbO2 polycrystalline thin films grown using PLD on TiN coated SiO2/Si substrates, a platform important for the further development of electronic devices based on NbO2. We pursued three promising routes for optimizing the performance of NbO2-x film devices: (1) varying thickness of the film, (2) varying the size of top electrode metallic contacts, and (3) varying Nb 4+ /Nb 5+ content ratio.…”

Transition from noise-induced to self-sustained current spiking generated by a NbOx thin film threshold switch

“…A Si-doped GaN (5 µm)/AlN (300 nm)/Al 2 O 3 (430 µm) wafer, provided by PI-KEM, was used as a substrate for thin film growth. 31 The schematic of the series circuit for the device under test is shown in Fig. 1 insulating to metallic phase.…”