Realizing both short- And long-term memory within a single magnetic tunnel junction based synapse

Abstract

Synaptic plasticity forms the basis of memory retention in the human brain. Whereas a low "rehearsal" rate causes short-term changes in the synaptic connections such that the synapse soon "forgets," a high rehearsal rate ensures long-term retention of memory in the brain. In this paper, we propose an artificial short- and long-term memory magnetic tunnel junction (SALT-MTJ) synapse. Changes in the synaptic strength are mapped to the SALT-MTJ conductance, which is varied stochastically via spin-transfer torque resulting from input current stimuli. A meta-stable intermediate magnetic state of the SALT-MTJ synapse provides short-term synaptic plasticity and the associated forgetting behavior as in a biological synapse. Repeated spin-current stimulations, while the SALT-MTJ remains in the short-term state, then can cause a near-permanent change in the magnetic state and associated conductance to provide long-term potentiation. The synaptic weight sensitivity to the input stimulus and the forgetting behavior of these short- and long-term states can be controlled via shape engineering of the artificial synapse.