Figure 4. Synaptic characteristics of PVA-based flexible memristors. (a) Schematics illustrating biological neural networks consisting of synapses. (b) Excitatory post-synaptic current (EPSC) under electric stimulus. (c) Paired-pulse facilitation (PPF) by two successive voltage pulses (the width and interval for pulses were 10 and 4 μs respectively). (d) Schematics showing a principle for achieving synaptic plasticity in the organic memristor. (e) PPF index as a function of a time interval value between two successive voltage pulses (1.5 V, 10 μs). (f) Spike-rate-dependent plasticity. (g) Spike-number-dependent plasticity under the repeated voltage pulses (1.5 V, 10 μs). (h) Multilevel memory states of the device achieved in the pulse mode.