Fig. 1. (Color online) (a) Schematic of the chemical synaptic neuron. (b) Device structure of the PDA-based memristor and its voltage-spiking behavior under current stimulation. (c) Photograph of the PDA-based memristor array. Scale bar, 75 μm. (d) Double-Log plot of I−V characteristic curves fitted by theoretical model for the TS mechanism analysis. (e) Schematic of TS behaviors of the PDA-based memristor.

Fig. 2. (Color online) (a) Fabrication process of the PDA-based memristor. Insert: the electropolymerized PDA layer on the bottom Au electrode. Scale bar, 50 mm. (b) CV curves during electropolymerization. (c) Proposed mechanism for the dopamine electropolymerization. (d) Sectional view of the PDA-based memristor by SEM. Scale bar, 90 nm. (e) Thickness of the PDA layer measured by AFM. Insert: the surface morphology of the edge PDA layer. The thickness result is obtained along the dotted white line. (f) XRD pattern of the PDA layer. (g) Raman spectra of the PDA layer. (h) FTIR spectra of the PDA layer by using ATR. (i) and (j) XPS spectra of O 1s (i) and C 1s (j) regions for the PDA layer. (k) UV−vis spectra of the PDA layer.

Fig. 3. (Color online) (a) Forming step and the consecutive 300 sweeping cycles of the volatile I−V test under an I_cc of 1 mA. (b)−(d) statistical distributions of V_th, V_hold, and HRS in the 300 sweeping cycles. The curves are obtained by Gaussian fitting. (e) Steep sub-threshold swing during resistive switching. (f) Unipolar switching behavior of the PDA-based memristor under a bidirectional voltage sweep. (g) Non-volatile resistive switching behavior of the PDA-based memristor at an I_cc of 1 mA and its comparison with the volatile threshold switching behavior at an I_cc of 100 nA. The serial number represents the sweeping step.

Fig. 4. (Color online) (a) Equivalent circuit of the artificial current-activated spiking neuron. (b) Parasitic capacitance of the PDA-based memristor. (c) Oscillation frequency of the spiking voltage linearly related to Log (I_in). The dotted line represents the linear fitting line. (d) Spiking voltage output by the artificial spiking neuron under 0.5 nA (ⅰ), 1 nA (ⅱ), 5 nA (ⅲ), and 10 nA (ⅳ).