Threshold switching stabilization of NbO2 films via nanoscale devices

The stabilization of the threshold switching characteristics of memristive NbO x is examined as a function of sample growth and device characteristics. Sub-stoichiometric Nb 2 O 5 was deposited via magnetron sputtering and patterned in nanoscale ( 50 × 50– 170 × 170 nm 2) W/Ir/ NbO x/TiN devices and microscale ( 2 × 2– 15 × 15 μ m 2) crossbar Au/Ru/ NbO x/Pt devices. Annealing the nanoscale devices at 700 °C removed the need for electroforming the devices. The smallest nanoscale devices showed a large asymmetry in the IV curves for positive and negative bias that switched to symmetric behavior for the larger and microscale devices. Electroforming the microscale crossbar devices created conducting NbO 2 filaments with symmetric IV curves whose behavior did not change as the device area increased. The smallest devices showed the largest threshold voltages and most stable threshold switching. As the nanoscale device area increased, the resistance of the devices scaled with the area as R ∝ A − 1, indicating a crystallized bulk NbO 2 device. When the nanoscale device size was comparable to the size of the filaments, the annealed nanoscale devices showed similar electrical responses as the electroformed microscale crossbar devices, indicating filament-like behavior in even annealed devices without electroforming. Finally, the addition of up to 1.8% Ti dopant into the films did not improve or stabilize the threshold switching in the microscale crossbar devices.