Confined Conducting Filaments in Resistive Random Access Memory by Al₂O₃ Nanodome Shaped Arrays (NDSAs) via Glancing Angle Deposition Technology Toward Neuromorphic Computing

Resistive random access memory (RRAM) is vital to neuromorphic computing applications. However, filamentary RRAM cells are affected by transitions from abrupt switching to analog switching. In this study, we develop Al₂O₃ nanodome shaped arrays (NDSAs) by glancing angle deposition technology (GLAD) to geometrically confine the conducting filaments (CFs), for which conducting atomic force microscopy (C-AFM) was performed to analyze positions and dimensions of filaments. For the Pt/HfO₂/75 % Al₂O₃ NDSAs/TiN device, the dimension of the CFs can be restricted to 10-12 nm, whereas for the Pt/HfO₂/TiN device, the CFs were formed with the dimension of ~50 nm. The device first yielded multiple weak CFs that subsequently transformed into stronger and larger CFs when the coverage of Al₂O₃ NDSAs was reduced to 55 % while Pt/HfO₂/75 % Al₂O₃ NDSAs/TiN device exhibited synaptic features with more linear potentiation and depression, demonstrating the analog switching. The controllable coverages of Al₂O₃ NDSAs render the geometric design more promising as a memristor for future applications in neuromorphic computing.