Nanofilament Formation and Regeneration During Cu/Al₂O₃ Resistive Memory Switching

Abstract

Conductive bridge random access memory (CBRAM) is a leading candidate to supersede flash memory, but poor understanding of its switching process impedes widespread implementation. The underlying physics and basic, unresolved issues such as the connecting filament's growth direction can be revealed with direct imaging, but the nanoscale target region is completely encased and thus difficult to access with real-time, high-resolution probes. In Pt/Al2O3/Cu CBRAM devices with a realistic topology, we find that the filament grows backward toward the source metal electrode. This observation, consistent over many cycles in different devices, corroborates the standard electrochemical metallization model of CBRAM operation. Time-resolved scanning transmission electron microscopy (STEM) reveals distinct nucleation-limited and potential-limited no-growth periods occurring before and after a connection is made, respectively. The subfemtoampere ionic currents visualized move some thousands of atoms during a switch and lag the nanoampere electronic currents.

Memristors with diffusive dynamics as synaptic emulators for neuromorphic computing

“…Up to this point, the behaviour of Ag nanoparticles in SiO x N y is similar to previous observations, which have been interpreted as electrochemical reactions at effectively bipolar electrodes [21][22][23][24][25][26] . We next turned off the power at 5.0s to observe the spontaneous relaxation, which is critical for understanding the dynamics of these devices, but has not been previously reported to the best of our knowledge.…”

“…S1-S2). These devices are similar to electrochemical metallization memory (ECM) [21][22][23][24][25][26] cells in terms of utilizing mobile species of noble metals, but they differ substantially in terms of the structural symmetry and operating voltage polarities, metal concentration and profile, and transient switching behaviour. An applied voltage above an apparent threshold abruptly switched the device to a conductance state limited by an external compliance current (Fig. 1b).…”

“…This model links electrical, nano-mechanical and thermal degrees of freedom (Methods). The model results here did not include redox reactions, although they can be added in order to more closely resemble the electrochemical models proposed previously [21][22][23][24][25][26] .…”

Filamentary-Based Resistive Switching

“…2.13b. Other reports with various CF geometries, have been imaged by in-situ TEM on a wide variety of solid electrolytes animating the debate in the community [43,[90][91][92][93]. Particularly because the set of phenomena involving metallic inclusions in dielectrics can be very rich just depending on the balance between ion mobility and oxidation/reduction rates in [85, 86]] the solid electrolyte.…”

Investigation of switching mechanism in HfOx-ReRAM under low power and conventional operation modes

“…Therefore, the overlap effect of multiple traps near the CF leads to a slope α ~ 117. For CBRAM, the switching mechanism, i.e., filament growth, has been observed using in situ STEM (scanning transmission electron microscopy)19. For observation of CF, the electron beam absorbed current (EBAC) can be used as a quick and effective method to identify different resistance levels20.…”