Excellent R_off/R_on ratio and short programming time in Cu/Al₂O₃‐based conductive‐bridging RAM under low‐current (10 μA) operation

Abstract

In this work, we prove that, for a current regime of 10 μA and using industry‐relevant programming pulse‐width, Cu/Al2O3‐based conductive‐bridging RAM (CBRAM) cells ensure reliably larger memory window (MW) than state‐of‐the‐art oxygen‐vacancy‐based RRAM (OxRRAM) cells. Due to the intrinsically stochastic nature of the switching mechanism, the Ron and Roff values can be widely distributed, especially in a low‐current regime, drastically reducing the overall memory window. For this reason, in this study we adopt a statistical approach, focusing on the tails of the distributions. Using a program‐verify method we show that the larger median MW in CBRAM allows to program a MW ≥×10 using ×10 shorter programming time with respect to OxRRAM. Moreover, we show that, in order to ensure a MW >×10 after a fixed retention time, the programming time needs to be several decades larger for OxRRAM than for CBRAM.

Electrochemical processes and device improvement in conductive bridge RAM cells

“…. Figure a shows clearly that the cycle‐to‐cycle (C2C) variability is worse for this latter device .…”

“…In Ref. we studied different algorithms and obtained best Write efficiency for a so‐called non‐cumulative incremental step pulse (ISP‐NC) Write‐verify algorithm, which is a variation of the well‐known incremental step pulse programming (ISPP) widely adopted for flash memories programming. The ISP‐NC algorithm, described in Fig.…”

Nature of Cu Interstitials in Al2O3 and the Implications for Filament Formation in Conductive Bridge Random Access Memory Devices

“…RRAMs based on oxygen vacancies tend to have smaller R ON /R OFF ratios, whereas CBRAMs can have very large 3 behaviour and results had we chosen this Al 2 O 3 phase. The development and properties of a variety of Al 2 O 3 -based CBRAM devices, many of which also feature Cu metal as the active electrode, have been reported in the literature [1][2][3][4][5][6][7][18][19][20] .…”

Key material parameters driving CBRAM device performances

“…Conductive Bridging Random Access Memory (CBRAM) is an attractive candidate for storage class and embedded memory applications due to the simple metalinsulator-metal (MIM) structure, scalability, large endurance and fast switching. [1][2][3][4] It operates by the voltage-controlled electrochemical formation (set) and dissolution (reset) of a metallic conductive lament (CF) in a solid electrolyte. Aer set switching, the CF formation results in a low resistance state (LRS), while aer reset switching, the ruptured CF results in a high resistance state (HRS).…”

“…Amorphous chalcogenides are attractive electrolyte candidates because they generally allow a large memory window to be obtained (>10 4 ) using low switching voltages (<0.5 V). 5 They allow large cation mobility and dissolution, which results in an extensive erasure of the CF during reset and therefore a large HRS resistance level.…”