Copper Nanofilament Formation during Unipolar Resistance Switching of Electrodeposited Cuprous Oxide

Abstract

An emerging nonvolatile, solid-state memory is resistance random access memory (RRAM). RRAM is based on reversible switching of resistance in semiconductor and insulator thin films. Here, unipolar resistance switching is demonstrated in electrodeposited films of [111]-textured cuprous oxide (Cu₂O). The textured Cu₂O is electrodeposited from a highly alkaline bath using tartrate as the complexing agent. The switching is observed in a cell composed of a film of Cu₂O sandwiched between Au and Au–Pd contacts. The switching is attributed to the formation and rupture of a Cu nanofilament in the Cu₂O. The initial resistance of the cell is 6.5 × 10⁶ Ω, and a conducting filament is formed in the film by scanning the applied electric field to 6.8 × 10⁶ V m^–1. The cell is then reversibly cycled between a low resistance state of 16.6 Ω and a high resistance state of 4 × 10⁵ Ω by the SET and RESET processes. In the low resistance state, the resistance decreases linearly with decreasing temperature, consistent with metallic behavior. The resistance temperature coefficient of 1.57 × 10^–3 K^–1 is similar to that of nanoscale metallic Cu. Current–voltage (<i>I</i>–<i>V</i>) data suggests that applying a higher compliance current increases the filament size during the FORMING and the SET process and also causes a higher RESET current. The filament diameter varies from 50 to 147 nm for compliance currents ranging from 10 to 100 mA. At high electric field in the as-deposited state, the conduction behavior follows Poole-Frenkel emission. The filament temperature is estimated from the nonohmic behavior of the cell in the RESET step. The calculated temperature of 798 K before rupture of the Cu filament suggests Joule heating of the filament, resulting in melting, sintering, or thermal oxidation of the Cu filament