Self-Adaptive Spike-Time-Dependent Plasticity of Metal-Oxide Memristors.

D Strukov,M Prezioso,B Hoskins,K Likharev,F Merrikh Bayat

doi:10.1038/srep21331

Abstract

Metal-oxide memristors have emerged as promising candidates for hardware implementation of artificial synapses – the key components of high-performance, analog neuromorphic networks - due to their excellent scaling prospects. Since some advanced cognitive tasks require spiking neuromorphic networks, which explicitly model individual neural pulses (“spikes”) in biological neural systems, it is crucial for memristive synapses to support the spike-time-dependent plasticity (STDP). A major challenge for the STDP implementation is that, in contrast to some simplistic models of the plasticity, the elementary change of a synaptic weight in an artificial hardware synapse depends not only on the pre-synaptic and post-synaptic signals, but also on the initial weight (memristor’s conductance) value. Here we experimentally demonstrate, for the first time, an STDP behavior that ensures self-adaptation of the average memristor conductance, making the plasticity stable, i.e. insensitive to the initial state of the devices. The experiments have been carried out with 200-nm Al2O3/TiO2−x memristors integrated into 12 × 12 crossbars. The experimentally observed self-adaptive STDP behavior has been complemented with numerical modeling of weight dynamics in a simple system with a leaky-integrate-and-fire neuron with a random spike-train input, using a compact model of memristor plasticity, fitted for quantitatively correct description of our memristors.

Highlights

IEICE Electronics Express 6, 148–153 (2009). 21
The experiment was repeated 10 times for each particular Δ t, every time resetting the device to the same initial conductance with 10% accuracy
In the second set of tests, the experiment with waveforms corresponding to the first spike-time-dependent plasticity (STDP) window (Fig. 2g) was repeated for several different initial values G0 of conductance, spanning the whole dynamic range of our memristors

Summary

Introduction

IEICE Electronics Express 6, 148–153 (2009). 21. Zamarreño-Ramos, C. et al On spike-timing-dependent-plasticity, memristive devices, and building a self-learning visual cort. A major challenge for the STDP implementation is that, in contrast to some simplistic models of the plasticity, the elementary change of a synaptic weight in an artificial hardware synapse depends on the pre-synaptic and post-synaptic signals, and on the initial weight (memristor’s conductance) value.

Results

Conclusion