Decoupling electronic and ionic transport through impedance spectroscopy: mechanistic insights into resistive switching and neuromorphic functionality of Cu2MnSnS4

Abstract

This study reports the bias-dependent modulation of coupled electronic-ionic transport in a solution-processed Cu₂MnSnS₄ (CMTS) thin film-based memristor. Synthesized via a low-temperature sol–gel route, CMTS/Cu Schottky junctions exhibit stable resistive switching with a switching ratio of ∼10³ over 250 cycles and distinct negative differential resistance (NDR). Mechanistic analysis reveals a transition from trap-controlled Schottky barrier transport in the high-resistance state to filament-assisted conduction, driven by Cu⁺ ion migration, in the low-resistance state. DC bias-dependent impedance spectroscopy decouples bulk and interface contributions, revealing a significant decrease in bulk resistance (R_b) and bulk relaxation time (τ_b) during Cu filament formation, while interfacial resistance (R_j) and interfacial relaxation time (τ_j) are governed by trap states and Schottky barrier modulation. The observed NDR at low reverse bias is attributed to interfacial charge trapping–detrapping processes. Complementary AC conductivity and dielectric loss analyses under zero DC bias confirm that iontronic behaviour dominates the memristive response. Leveraging the stable analog conductance modulation, the device emulates essential synaptic functions, including short-term memory (STM) to long-term memory (LTM) transition through multiple rehearsals, and Pavlovian learning. This work establishes impedance spectroscopy as a diagnostic framework for bias-controlled iontronic memristors and highlights CMTS as a viable chalcogenide platform for advanced neuromorphic computing applications.