Study of asymmetric polarization switching in ferroelectric polymer

Abstract

Ferroelectric materials have been extensively researched across various application fields such as high-density non-volatile memory, transistors, sensors, and energy harvesters. Particularly, the ferroelectric polymer film of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] has garnered attention due to its cost-effectiveness, light weight, flexibility, environmental friendliness. and ease of processing. In this study, P(VDF-TrFE) thin films were fabricated under optimized process conditions and their surface characteristics and ferroelectricity were analyzed using scanning probe microscope (SPM). Through investigation of local polarization switching properties, we observed asymmetric polarization switching and anomalous domain growth when the ferroelectric polymer films were subjected to positive-biased atomic force microscopy (AFM) tip, and confirmed this signal originates from actual ferroelectric domains. Through environmental controlled experiments, we revealed that humidity in the atmosphere plays a dominant role in forming a water meniscus and layers between the tip and the sample, leading to asymmetric polarization switching. Specifically, we predicted that these layers act as electric field distribution layers and ion conduction layers and introduced a potential hypothesis for the anomalous polarization switching behavior. We suggest a complex mechanism involving a physical model of asymmetric charge injection resulting from surface band bending between the polymer film and metal electrode depending on the direction of the applied voltage and a chemical model involving ion diffusion due to water molecule dissociation and differences in binding strength between water molecules and polymer chains. This study demonstrates that by controlling environmental conditions, we can manipulate nano-scale polarization switching in P(VDF-TrFE) and models the abnormal polarization switching behavior in ferroelectric polymer films due to complex causes. This research is expected to contribute to a sophisticated understanding of the polarization switching dynamics and domain growth in ferroelectric polymers and their applications.