RESET-first unipolar resistance switching behavior in annealed Nb2O5 films

• The effects of post-annealing on the chemical bonding states and crystallinity
• Annealed Nb2O5 films under N2 ambient showed RESET-first switching.
• The local conductive paths formed by the post-annealing process
• Local conductive paths played an important role in the RESET-first switching.

In this work, the effect of thermal annealing on the resistance switching behavior of Nb2O5 films was investigated in conjunction with an analysis of the chemical bonding states and crystal structure. The Nb2O5 films were deposited via reactive sputtering, and annealed via rapid thermal annealing at various temperatures up to 650 °C. The crystal structure of the as-deposited Nb2O5 films transformed from amorphous to a hexagonal Nb2O5 crystalline phase with tetragonal NbO2 following thermal annealing at 500 °C. The conductivity of the Nb2O5 films increased drastically as the annealing temperature increased. An increase in the non-lattice oxygen in the Nb2O5 films was also observed with thermal annealing. Pt/Nb2O5/Pt stacks with the as-deposited Nb2O5 showed typical unipolar resistance switching behaviors after electro-forming; however, the Nb2O5 film devices annealed at 500 °C showed RESET-first resistance switching behavior without prior electro-forming. The RESET-first resistance switching in annealed Nb2O5 is believed to be due to the nano-scale conductive path formed in the annealed Nb2O5 films.