Multifunctional double active layers formed with electrochemically controlled nanoparticle dispersion for resistive switching memory arrays

Expanding resistive random-access memory (RRAM) from a single device to an array requires a selector to suppress the sneak path and an external device to control the compliance current. Thus, a unique crossbar array that can be independently driven through the novel design of a multilayer RRAM structure with intelligently controlled Cu₂O consisting of nanoparticles embedded in the amorphous matrix (ANPs) is proposed. The ANPs–Cu₂O active layers are prepared by electrodeposition, and the negative shift of the deposition potential induces a higher density and smaller size of the nanoparticles. The ANPs–Cu₂O films show different set voltages and extremely uniform reset voltages, and thus a functional double active layer (DAL) structure consisting of two ANPs–Cu₂O layers with different set voltages is proposed. The electrochemically fabricated V_Cu-controlled DALs effectively protected the reverse current from the self-rectifying characteristics of a large forward/reverse current ratio, thus realizing selector-less RRAMs. In addition, the soft-breakdown showing filament formation in the upper layer reveals the saturation current step acting as a self-compliance current without the assistance of transistors. Finally, a 4 × 4 crossbar DAL RRAM array with transistor-less self-rectification is demonstrated, which shows excellent memory performance and endurance without interfering with adjacent cells.