Memristive arrangements of nanofluidic pores

We demonstrate that nanofluidic diodes in multipore membranes show a memristive behavior that can be controlled not only by the amplitude and frequency of the external signal but also by series and parallel arrangements of the membranes. Each memristor consists of a polymeric membrane with conical nanopores that allow current rectification due to the electrical interaction between the ionic solution and the pore surface charges. This surface charge-regulated ionic transport shows a rich nonlinear physics, including memory and inductive effects, which are characterized here by the current-voltage curves and electrical impedance spectroscopy. Also, neuromorphiclike potentiation of the membrane conductance following voltage pulses (spikes) is observed. The multipore membrane with nanofluidic diodes shows physical concepts that should have application for information processing and signal conversion in iontronics hybrid devices.

Figure 1

(a) In the experimental setup, the electrochemical cell connected to the potentiostat is placed within a magnetic shield mounted on an antivibration table. (b) Schematic of the cell with the multipore membrane and the Ag|AgCl electrodes.

Figure 2

(a) Current ($I$)–voltage ($V$) curves for membrane sample 1 measured with a sinusoidal wave at the voltage amplitude $V_0=2\mathrm{V}$ and the frequency $f=20$ Hz in a 0.1-M KCl solution ($\mathit{red}$ lines). The steady-state curve (blue line) obtained at low signal frequency (25 mHz) is also shown. The arrows indicate the time evolution of the output current and the inset shows the pore arrangements. (b) $I-V$ curve for sample 2. (c) Conductance ($G$) vs spike number curves showing the membrane sample 1 response to a sequence of individual 2-ms positive and negative voltage pulses (spikes) of amplitude $V_{\mathrm{p}}=1\mathrm{V}$ (insets). (d) $G$ vs spike number curves for sample 2.

Figure 3

(a) $I-V$ curve for samples 1 and 2 at $V_0=4\mathrm{V}$ and $f=20$ Hz in a 0.1-M KCl solution (red lines) for the series arrangement with the pores in the same polarity (inset). The steady-state curve (blue line) obtained at low signal frequency is also shown. (b) $I-V$ curve for the pores in the opposite polarity, facing the bases (inset). (c) $G$ vs spike number curves for the series arrangement with the pores in the same polarity. The sequences correspond to 2-ms positive and negative voltage pulses of amplitudes $V_{\mathrm{p}}=2\mathrm{V}$ (blue curve) and 4 V (red curve). (d) $G$ vs spike number curves for the pores in the opposite polarity.

Figure 4

(a) Imaginary −Im($Z$) vs real Re($Z$) (Nyquist) plots obtained for the series arrangements with the pores in the same (blue curve) and opposite (red curve) polarity in 0.1-M KCl solutions at a dc voltage $V=-1\mathrm{V}$. (b) Nyquist plots at a voltage amplitude of 0 V for the above series arrangements (insets). (c) Nyquist plots at $V=1\mathrm{V}$. The blue highlighted region, which corresponds to the positive Im($Z$) values, is zoomed for clarity (inset).

Figure 5

(a) $I-V$ curve for samples 1 and 2 at $V_0=2\mathrm{V}$ and $f=20$ Hz in a 0.1-M KCl solution (red lines) for the parallel arrangement with the pores in the same polarity (inset). The steady-state curve (blue line) obtained at low signal frequency is also shown. (b) $I-V$ curve for the parallel arrangement with the pores in opposite polarity (antiparallel). The inset zooms the central loop. (c) $G$ vs spike number curves for the parallel arrangement with the pores in the same polarity. The sequences correspond to 2-ms positive and negative voltage pulses of amplitudes $V_{\mathrm{p}}=1\mathrm{V}$ (blue curve) and $V_{\mathrm{p}}=2\mathrm{V}$ (red curve). (d) $G$ vs spike number curves for the antiparallel arrangement.

Figure 6

(a) Nyquist plots obtained for the two parallel arrangements of Fig. 5 in 0.1-M KCl solutions at $V=-0.5\mathrm{V}$ with the pores in the parallel (blue curve) and antiparallel (red curve and inset) arrangements. The blue highlighted region corresponds to positive Im($Z$) values suggesting clear inductive effects. (b) Nyquist plots at $V=0\mathrm{V}$. (c) Nyquist plots at $V=0.5\mathrm{V}$.

Figure 7

(a) Nyquist plots for the antiparallel arrangement and 0.1-M KCl solutions at $V=-0.25$, −0.50, −0.75, and −1.00 V. (b) Nyquist plots for the antiparallel arrangement at $V=0$, 0.25, 0.50, 0.75, and 1.00 V.

Figure 8

(a) $I-V$ curve for the antiparallel arrangement in a 0.1-M KCl solution at $f=20$ Hz and $V_0=0.25\mathrm{V}$. (b) The corresponding $G$ vs spike number curves for two different voltage pulse sequences of 2 ms duration (insets) at $V_p=0.25\mathrm{V}$. (c) $I-V$ curve at $V_0=0.50\mathrm{V}$. (d) $G$ vs spike number curves at $V_p=0.25\mathrm{V}$. (e) $I-V$ curve at $V_0=1.50\mathrm{V}$. (f) $G$ vs spike number curves at $V_p=1.25\mathrm{V}$. The grey region in the $G$ vs spike number curves show the potentiation increase obtained when the voltage pulse approaches the inductive region of the $I-V$ curves.