Using hardware to emulate biological functions is essential for the realization of more sophisticated brain-type information processing. For this purpose, up to now, various nonvolatile devices have been used to emulate complex functions such as spike-timing dependent plasticity. However, little research has been conducted on more complicated neural functions. In this study, we demonstrate neural functions such as paired-pulse facilitation (PPF) and paired-pulse depression (PPD), utilizing the larger time constant of the ionic diffusion found in molecular-gap atomic switches. Both the PPF and PPD emulated in this study are dependent on pulse intervals that are the same as those found in biological synapses. Simulations of how pulsed bias changes ion concentration at the subsurface, which in turn determines the precipitation/dissolution of metal atoms, provide a good explanation of the mechanisms of the PPF and the PPD observed in this study.
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