Fig. 2: Electrical properties and working mechanisms.

a The equivalent circuit of the e-synapse. The e-synapse is equivalent to a parallel combination of a memristor with a capacitor. b I–V curves under consecutive positive DC voltage sweeps. c I–V curves under consecutive negative DC voltage sweeps. d Pulse responses of the e-synapse (intercepted the appropriate range). Twenty positive pulses (1.2 V, 2.5 Hz, 0.1 s) were applied followed by negative pulses. The middle panel relates to the responses of the memristor, and the right panel relates to the responses of the capacitor. e Schematic illustration of the working mechanism of the e-synapses. e-I The electrons under the first positive pulse were injected from the Ag electrode into the Al₂O₃/GQD/Al₂O₃ structure via Fowler–Nordheim tunneling. e-II The injected electrons were captured in the GQDs/Al₂O₃ interface, thereby switching the device from the LRS to the HRS. e-III The first reverse pulse released the previously trapped electrons. e-IV Release of the trapped electrons removed the internal electric field and led to the recovery of the high conductivity of the e-synapse. e-V The injected electrons were captured in the GQDs/Al₂O₃ interface, thereby switching the device from the LRS to the HRS