Fig. 2: Physical and electrical characterization of resistive memory (RM) electroforming stochasticity.

a Optical micrograph of the 40 nm, 256 K resistive memory in-memory computing macro alongside a schematic of the crossbar array architecture. b Cross-sectional HAADF-STEM image of the resistive memory array, fabricated between Metal 4 and Metal 5 layers via back-end-of-line processing. c Cross-sectional HAADF-STEM images and EDS line profiles of electroformed resistive memory cells. Red and green arrows indicate the regions corresponding to the red-boxed (distinct structural changes) and green-boxed (no distinct changes) areas, respectively. d, e EELS plane scans (energy range: 15–35 eV, step: 0.05 eV) and corresponding center-point low-loss spectra for two electroformed resistive memory cells. Green (Area 1, insulating) and red (Area 2, conducting) regions correspond to the boxes in (c). f EELS low-loss peak maps of Area 1 and Area 2, where the color gradient from yellow to black indicates increasing oxygen-vacancy concentration. The conductive paths in the two cells exhibit marked geometric differences. g Corresponding EELS-peak distributions derived from (f), with green and red curves representing Area 1 and Area 2, respectively. h Histogram and cumulative probability of electroforming voltages for a 20 × 20 resistive memory array, obtained using a linear voltage sweep starting from 3 V with 0.05 V increments applied to each cell. i Joint distribution of conductance and standard deviation for 128 randomly selected resistive memory differential pairs following 100 pruning and reinstatement cycles. Gray and orange points denote pruned and remaining pairs, respectively. Probability densities for conductance and standard deviation are displayed in the top and right histograms. j Data retention characteristics of 128 randomly selected topology-optimized (TO)-trained resistive memory cells over 10,000 read cycles.