Space‐Charge‐Stabilized Ferroelectric Polarization in Self‐Oriented Croconic Acid Films

Abstract Great progress has been made recently in molecular ferroelectrics with properties even comparable to those of inorganic ferroelectrics. However, it is difficult to develop basic thin films and devices for practical applications since most molecular ferroelectrics are uniaxial. The single polar axes of crystallites inside their films, if available, are usually oriented randomly. These can induce the components without contribution to ferroelectric polarization and a large depolarization electric field to suppress polarization. In this work, it is demonstrated that uniaxial croconic acid films in two‐terminal devices, deposited by thermal evaporation, can show effective ferroelectric polarization and nonvolatile memory switching behavior with small coercive fields of 11–30 kV cm⁻¹. The polar c‐axes in thick crystalline films (>500 nm) are found to be self‐oriented nearly at a desired direction. With the assistance of trapped charges, stable ferroelectric polarization can be achieved, in spite of the existence of nonferroelectric components. These may pave a way to utilize uniaxial molecular ferroelectrics for various applications, such as gate dielectrics, electrets, and memory devices.