Demonstration of Synaptic Characteristics in VRRAM with TiN Nanocrystals for Neuromorphic System

To efficiently develop an extremely intensive storage memory, the resistive random-access memory (RRAM), which operates by producing and rupturing conductive filaments, is essential. However, due to the stochastic nature of filament production, this filamentary type resistive switching has an inherent limitation, which entails the unpredictability of the driving voltage and resistance states. Several strategies such as doping, research into multilayer stacks, and interface engineering, are suggested to tackle this challenge. This work fabricates a CMOS-compatible TiN/HfO_x/TiN-NCs (nanocrystals)/HfO_x/TiN RRAM to implement analog resistive switching and advance the development of the synaptic device. Specifically, atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are utilized to observe the formation of TiN nanocrystals, which play a crucial role in the enhancement of resistive switching. By comparing HfO_x–based RRAM devices with and without NCs, the DC I–V curves, retention, endurance, and switching speed are properly examined. Interestingly, it is found that the TiN/HfO_x/TiN-NCs/HfO_x/TiN device is more appropriately utilized as an artificial synapse in neuromorphic systems mainly due to its stable and reliable resistive switching properties. Finally, this work demonstrates well-controlled resistive switching 3D vertical RRAM with TiN-NCs, which is particularly suitable for high-density memory.