Voltage-triggered insulator-to-metal transition of ALD NbOx thin films for a two-terminal threshold switch

Abstract

We report two-terminal threshold devices that use niobium oxide (NbO_x) thin films that were synthesized using atomic layer deposition (ALD) then pulsed-laser annealing. The ALD growth conditions for NbO_x thin films were optimized using niobium(V) ethoxide and deionized water at 170 °C. As-deposited NbO_x films were amorphous with Nb⁵⁺ valence state, but laser annealing led to partial conversion to NbO₂ crystallites with Nb⁴⁺ valence states. This two-terminal device with ALD-NbO_x exhibits excellent threshold switching with low off current ∼847 nA at 1 V, high on/off current ratio (∼10³), high reliability, fast switching time (<20 ns) and high modulation frequency (>1 MHz).