Memristor / RRAM synapse

A memristive device (resistive RAM, phase-change, ferroelectric, or a similar non-volatile element) stores a synaptic weight as an analog, non-volatile conductance that can be tuned by electrical pulses. Arranged in a crossbar, such devices are the physical substrate for analog compute-in-memory: they hold weights without power and perform the weighted sum in the analog domain. Their multi-level, incremental conductance change also lets them emulate synaptic plasticity for on-chip learning.

Device non-idealities are the central obstacle: a limited number of distinguishable states, nonlinear and asymmetric weight updates, cycle-to-cycle and device-to-device variability, conductance drift and read noise, and finite write endurance. Decoding schemes must tolerate these, and long-term reliability inside the body is unproven.