Disorder-driven stochastic dynamics in Mott resistive-switching systems

Abstract

Controlled disorder in correlated materials provides a new route to emergent stochastic dynamics in neuromorphic hardware. Here we show that focused ion beam irradiation in VO$_{2}$- and V$_{2}$O$_{3}$-based resistive-switching oscillators induces a transition from regular periodic oscillations to strongly irregular stochastic firing, while simultaneously reducing the required switching energy by orders of magnitude. Under an applied electric field, these materials undergo a volatile insulator-to-metal transition characterized by the formation of percolating metallic filaments within an insulating bulk. Using numerical simulations based on the Mott resistor network, we demonstrate that defect-induced modifications to filament nucleation and stability drive these devices into stochastic oscillatory regimes. These results are validated by experimental measurements on irradiated VO$_{2}$ and V$_{2}$O$_{3}$ devices.

Figures (8)

• Figure 1: Effects of FIB irradiation on VO$_{2}$. (a) Experimental data showing the resistance versus the temperature of both pristine and blanket irradiated VO$_{2}$, such that the irradiation covers the entire sample, clearly exhibiting a hysteretic first order IMT. (b)-(e) Schematics of the MRN, showcasing the defects (green) induced by FIB irradiation and the electrodes (blue). The defects are randomly placed within a stripe with a density of (b) 0% (c) 50% (d) 64% (e) 70%. (f) The total resistance of the resistor network $R_{\rm M}(T)$ shown above as a function of temperature, highlighting the first-order transition of the normal cells at 340 K, and also the defect cells at 318 K. The exact parameter values for the defects are given in Sec. \ref{['sec3a']}. (g) Schematic of the Mott spiking neuron circuit. A voltage source with a constant applied voltage $V_{\rm app}$ is in series with a load resistor $R_{\rm load}$ along with a parallel set including a capacitor with capacitance $\mathcal{C}$ and the MRN, which has the time dependent resistance $R_{\rm M}(t)$. The voltage drop across the MRN and the capacitor is given by $V_{\rm M}(t)$.
• Figure 2: Oscillations of the MRN with 0% defects when implemented in a Mott spiking neuron circuit, showing the (a) voltage $V_{\rm M}(t)$ (b) current $I_{\rm M}(t) = V_{\rm M}(t)/R_{\rm M}(t)$. From top to bottom, for both the the voltage and current, the applied voltages are $V_{\rm app}/10^{4} =$ 25 a.u. and 50 a.u. respectively. The inset shows a schematic of the pristine MRN.
• Figure 3: Oscillations of the MRN with 64% defects defects when implemented in a Mott spiking neuron circuit, showing the (a) voltage $V_{\rm M}(t)$ (b) current $I_{\rm M}(t) = V_{\rm M}(t)/R_{\rm M}(t)$. From top to bottom, for both the the voltage and current, the applied voltages are $V_{\rm app}/10^{4} =$ 5.2 a.u., 6.5 a.u., and 6.52 a.u. respectively. The inset shows a schematic of the irradiated MRN.
• Figure 4: Oscillations of an experimental device featuring FIB irradiated V$_{2}$O$_{3}$ in a configuration similar to Fig. \ref{['blanket']}(c), showing the (a) voltage and (b) current. From top to bottom, for both the voltage and the current, the applied voltages to the circuit are $V_{\rm app} =$ 700 mV, 710 mV, and 720 mV respectively.
• Figure 5: Frequency of the voltage oscillations as a function of the applied voltage, with defect densities given by 0%, 64%, 70%. In the top left panel, the data for all three cases are plotted together on a log scale, while the remaining panels focus on each individual irradiation level.