Tuning the nucleation barrier energy of nonvolatile polymeric memristor by reducing its active layer thickness for threshold switching

Abstract

In redox-based memristors, nonvolatile memory (NVM) and diffusive threshold switching (DTS) are two essential features for neuromorphic systems. However, achieving controlled transitions between these modes within a single device remains difficult. Conventional methods rely on electrode nanopatterning or incorporating conductive nanofillers into the switching layer. This study shows that a simple reduction in the switching layer thickness of a polymeric (polyvinylidene fluoride-co-hexafluoropropylene) memristor with a Cu active electrode can induce the same effect. Devices with thicker layers (151 and 126 nm) display stable NVM behavior, while those with 90 nm thickness transition to DTS operation. The influence of introducing conductive nanofillers (CuS) into the switching medium is also investigated. Although the basic switching mode (NVM or DTS) has remained unchanged for each thickness, CuS nanoparticles (CuS NPs) inclusion improves switching uniformity, increases nonlinearity (wider switching window), and enhances diffusive dynamics. The CuS NPs act as bipolar microelectrodes, effectively reducing the active layer thickness and locally modulating the electric field. In thicker devices, increasing CuS NPs concentration can convert NVM to DTS behavior, demonstrating the equivalence of thinning of the switching layer with compositional modification. These results demonstrate that film thickness is a critical parameter that complements established methods for achieving threshold switching. The field-induced nucleation model attributes the transition from NVM to DTS to increased energy barriers and stronger surface energy effects in the thinner device.