Angstrom Scale Ionic Memristors' Engineering with van der Waals Materials- A Route to Highly Tunable Memory States

TL;DR

This study demonstrates highly tunable ionic memristors using van der Waals materials with confined channels, showing polarization-flipping behavior and potential for neuromorphic applications.

Contribution

It introduces a novel approach to engineer ionic memristors with highly confined channels and tunable states using van der Waals materials and multivalent ions.

Findings

Memristor properties are tunable by frequency, geometry, and ion concentration.

Polarization-flipping behavior observed with Al3+ ions and geometric asymmetry.

Ion exchange dynamics enable advanced memristor functionalities.

Abstract

Memristors that mimic brain functions are crucial for energy-efficient neuromorphic devices. Ion channels that emulate biological synapses are still in the early stages of development, especially the tunability of memory states. Here, we demonstrate that cations such as K+, Na+, Ca2+, and Al3+ intercalated in the interlayer spaces of vermiculite, result in highly confined channels of size 3-5 {\AA}. They host exotic memristor properties through ion exchange dynamics, even at high salt concentrations of 1 M. The bipolar memristor characteristics observed are tunable with frequency, geometric asymmetry, ion concentration, and intercalants. Notably, we observe polarization-flipping memristor behavior in two cases: one with Al3+ ions and another with devices having a geometric asymmetry ratio greater than 15. This inversion is attributed to the over-screening of counter-ions due to their accumulation at the channel entrance. Our results suggest that ion exchange dynamics, ion-ion interactions, and ion accumulation/depletion mechanisms, particularly with multivalent ions, can be harnessed to develop advanced memristor devices.