10 MA cm−2 current density in nanoscale conductive bridge threshold switching selector via densely localized cation sources

Abstract

Conductive bridge threshold switching (CBTS) selector is a selector candidate for large-scale 3D crosspoint memory. In spite of its high selectivity, the generally low current density (J_ON) of <0.5 MA cm⁻² is not practical for driving the memory elements. In particular, J_ON is the determining factor for the 3D PCM application owing to the greatly increased RESET current density in PCM cells as the size scales down. The low J_ON of CBTS selectors originates from the reduced number of conductive filament (CF) as the device scales down and the CF overgrowth induced long lifetime at a large current. Here, a strategy of inserting the super-ionic cation layer to form densely distributed Cu-rich cation sources is proposed to modulate the quantity and size of CFs. Multiple CFs grow from the cation sources to conduct current in parallel and CF overgrowth is prevented by local cation injection. The fabricated Pt/Cu₂S/GeSe/Pt devices achieve a record 10 MA cm⁻²J_ON and 5 mA I_drive, realizing a ten-fold increase in the J_ON in CBTS selectors. Moreover, the selectivity is the highest at 10¹⁰, and the switching slope is <0.18 mV dec⁻¹. The high-resolution transmission electron microscopy (HRTEM) image reveals multiple single-crystal nanochannels distributed in the Cu₂S layer with a diameter of ∼20 nm and a distance of 15–20 nm, suggesting dense CF paths of small size. This method is practical for fabricating a scalable selector owing to the dense CF paths. The breakthrough in J_ON will greatly promote the practical use of CBTS selectors in 3D crosspoint memory.