Defect-Mediated Coexistence of Bipolar Switching and Negative Differential Resistance in Carbon Nanotube–PVA Memristors: Mechanistic Insights and Performance Tuning

Abstract

The integration of carbon nanotubes (CNTs) into polymer matrices has emerged as a promising strategy for developing high-performance memristors. In this study, we report a Ag/PVA–CNT/ITO memristor fabricated via spin coating and magnetron sputtering, where CNT-doped poly(vinyl alcohol) (PVA) serves as the functional layer. The dispersion of CNTs was optimized through annealing (500 °C, 40 min) followed by ultrasonication (4–6 h). Scanning electron microscopy (SEM) and Raman spectroscopy analyses confirmed reduced entanglement and an elevated defect density (I_D/I_G ratio increased from 0.65 to 0.75). The Ag/PVA–CNT/ITO devices exhibit coexistence of negative differential resistance (NDR) and bipolar resistive switching (RS) behaviors at room temperature. The optimized device demonstrates a resistive switching window of ∼20 over 130 cycles at ±1 V, with retention times exceeding 10⁴ s. Comprehensive analysis of current–voltage (I–V) characteristics reveals that the NDR effect arises from electron tunneling mechanisms and the electron-caching properties of CNTs, while RS behavior is governed by the formation/breakage of Ag conductive filaments and space charge-limited conduction (SCLC). Notably, the theory of quantum wells and resonant tunneling can further explain the microscopic mechanism of NDR. These findings provide a foundation for next-generation nonvolatile memory and carbon nanotube electronic devices applications, leveraging the synergistic effects of CNT doping in polymer matrices to achieve multifunctional memristive behavior.