Controlling the Synaptic Plasticity of a Cu2S Gap-Type Atomic Switch

It is demonstrated that a Cu2S gap-type atomic switch, referred to as a Cu2S inorganic synapse, emulates the synaptic plasticity underlying the sensory, short-term, and long-term memory formations in the human brain. The change in conductance of the Cu2S inorganic synapse is considered analogous to the change in strength of a biological synaptic connection known as the synaptic plasticity. The plasticity of the Cu2S inorganic synapse is controlled depending on the interval, amplitude, and width of an input voltage pulse stimulation. Interestingly, the plasticity is influenced by the presence of air or moisture. Time-dependent scanning tunneling microscopy images of the Cu-protrusions grown in air and in vacuum provide clear evidence of the influence of air on their stability. Furthermore, the plasticity depends on temperature, such that a long-term memory is achieved much faster at elevated temperatures with shorter or fewer number of input pulses, indicating a close analogy with a biological synapse where elevated temperature increases the degree of synaptic transmission. The ability to control the plasticity of the Cu2S inorganic synapse justifies its potential as an advanced synthetic synapse with air/temperature sensibility for the development of artificial neural networks.