Voltage Controlled Domain Wall Motion based Neuron and Stochastic
Magnetic Tunnel Junction Synapse for Neuromorphic Computing Applications
Abstract
The present work discusses the proposal of a spintronic neuromorphic
system with spin orbit torque driven domain wall motion-based neuron and
synapse. We propose a voltage-controlled magnetic anisotropy domain wall
motion based magnetic tunnel junction neuron. We investigate how the
electric field at the gate (pinning site), generated by the voltage
signals from pre-neurons, modulates the domain wall motion, which
reflects in the non-linear switching behaviour of neuron magnetization.
For the implementation of synaptic weights, we propose 3-terminal MTJ
with stochastic domain wall motion in the free layer. We incorporate
intrinsic pinning effects by creating triangular notches on the sides of
the free layer. The pinning of domain wall and intrinsic thermal noise
of device lead to the stochastic behaviour of domain wall motion. The
control of this stochasticity by the spin orbit torque is shown to
realize the potentiation and depression of the synaptic weight. The
micromagnetics and spin transport studies in synapse and neuron are
carried out by developing a coupled micromagnetic Non-Equilibrium
Green’s Function (MuMag-NEGF) model. The minimization of the
writing current pulse width by leveraging the thermal noise and
demagnetization energy is also presented. Finally, we discuss the
implementation of digit recognition by the proposed system using a spike
time dependent algorithm.