Physical Origin of the Ferroelectric-Type Hysteresis in MIM Structures with Amorphous Dielectric Film

The ferroelectric-type characteristics in metal-insulator-metal (MIM) structures with amorphous dielectrics are observed, which may open a new window for a class of new ferroelectric devices. However, the working principles of these ferroelectric devices are not well explained. It has been proposed that oxygen ion (O^2-) and charged vacancy (V_o²⁺) migrations are associated with this ferroelectric-like behavior. In this work, a systematic experimental design is carried out to investigate the origin of O^2- and V_o²⁺ (from the interface or bulk oxide?), the transport species (O^2-, V_o²⁺, or both of these two species?), and the ion transport mode (long-range transport or local movement?). The experimental results answered all these questions. In addition, the role of the thickness of the dielectrics is also studied. This work sets the fundamentals of these amorphous oxide-based devices, guiding future explorations to engineer them.