Switching processes and dielectric breakdown in polycrystalline Nb2O5 films

Abstract

Repetitive resistive switching from the high-to the low-resistance state in thin polycrystalline Nb2O5 films was investigated. The switching process, and dielectric breakdown, are associated with four successive conduction states. The thermal activation energy in the first conduction state is 0.35 eV and in the second state is 0.047 eV; in the third and fourth resistance states the temperature coefficient of resistance exhibits metallic behavior. The I-V relationship changes from the Poole-Frenkel mechanism in the first state to space-charge-limited conduction in the second state and a linear relation in the third and fourth states. These and other results indicate that dielectric breakdown occurs through a process of a metallic precipitation increasing in each consecutive state and the formation of a highly conductive filament in the fourth and final state in the dielectric breakdown process. The values of important switching parameters such as the threshold field for switching Es, holding current and voltage Ih and Vh, switching time τs, delay time τd and recovery time τr are presented. The dependence of the delay time τd on the applied voltage and temperature is studied and the relation τd∝exp(−k(V/Vs)) is established, with k showing only a slight temperature dependence.