Plasticity and learning behavior emulated in a ZnO based transparent artificial synapse

Abstract

Artificial synaptic devices play a vital role in constructing artificial neural networks, fundamental building blocks of neuromorphic computing. In this article, we report a transparent synaptic device that manifests potentiation, depression and forgetting behavior analogous to the biological synapse. This synaptic device possesses paired-pulse facilitation, spike parameters dependent synaptic weight, and voltage-induced transition from short-term memory to long-term memory. This study reveals that the pulse with a higher amplitude, higher pulse width, and lower pulse interval produces more change in synaptic weight. The mechanism behind potentiation and depression in the fabricated device is proposed in terms of oxygen vacancy migration; oxygen vacancies are generated and drift during the application of input pulses, thus forming a conducting filament. This device exhibits excellent short-term plasticity and long-term potentiation depending upon the input conditions, which are inherent properties of neuroplasticity. Forgetting, referred as the spontaneous decay of conductance, is explained by the rupturing of oxygen vacancy filament due to recombination of oxygen vacancies with non-lattice oxygen ions present in indium tin oxide electrodes. This is confirmed by studying the decay in device with metal electrodes.