Artificial Neural Network (ANN) -- Oscillatory Neural Network (ONN) Hybrid System Using Domain-Wall Synapse Devices and Nano-Constriction Spin Hall Nano Oscillators
A coupled spintronic oscillator array has been considered attractive for neuromorphic computing applications. Experimental reports have shown the nano-constriction geometry to be a relatively easier-to-fabricate platform for implementing such spin oscillators, but most prior reports on training and inference algorithms for neuromorphic computing using spin oscillators have been mostly restricted to the nano-pillar geometry. Also, those prior reports involve updating the natural frequency values of the oscillators and moving the synchronization regions on to the data clusters during the offline learning phase, which has associated challenges. In this context, we design and simulate a novel artificial neural network (ANN) - oscillator neural network (ONN) algorithm where in the offline learning phase, the weight parameters of the ANN are updated such that the data clusters are instead moved to the synchronization regions of spin Hall nano oscillators (SHNOs) in the nano-constriction geometry, as obtained through micromagnetic simulations. We further simulate the on-chip inference part of the ANN-ONN algorithm where the ANN is implemented on a crossbar array of domain-wall synapse devices, as simulated here through micromagnetics, and the ONN is implemented on nano-constriction SHNOs. We show successful data classification for both binary and multi-class classification tasks to demonstrate the generalizability of our proposed scheme.