  Nanoelectronic devices that mimic the functionality of synapses are a crucial
requirement for performing cortical simulations of the brain. In this work we
propose a ferromagnet-heavy metal heterostructure that employs spin-orbit
torque to implement Spike-Timing Dependent Plasticity. The proposed device
offers the advantage of decoupled spike transmission and programming current
paths, thereby leading to reliable operation during online learning. Possible
arrangement of such devices in a crosspoint architecture can pave the way for
ultra-dense neural networks. Simulation studies indicate that the device has
the potential of achieving pico-Joule level energy consumption (maximum 2 pJ
per synaptic event) which is comparable to the energy consumption for synaptic
events in biological synapses.
