Silicon Nanotube FET-Based Bio-Plausible Tripartite Synapse With Neuromodulation Capability

Realizing biomimetic synapses on hardware is crucial for enabling realistic learning and memory processes akin to the human brain in neuromorphic computing systems. The overall energy efficiency can be increased significantly, and adaptive learning and context-aware decision-making can be enabled in these systems by replicating both the plasticity and the neuromodulation capability of the biological synapses. Although several emerging nonvolatile memories exhibit synaptic plasticity, an ultrascaled bio-plausible hardware synapse with neuromodulation capability is still elusive. To this end, in this work, for the first time, we propose a highly scalable nanotube (NT) FET-based tripartite synapse that exhibits both plasticity and neuromodulation capability simultaneously. While the proposed synaptic element exploits the lateral band-to-band-tunneling (L-BTBT) gate-induced drain leakage (GIDL) mechanism for mimicking plasticity, its core gate facilitates precise modulation of the postsynaptic current (PSC) similar to the neuromodulation by astrocytes. We show that the proposed synaptic element exhibits a large dynamic range (DR), a high degree of neuromodulation, and ultralow programming energy, making it suitable for online learning.