Spontaneous polarization in van der Waals materials: Two-dimensional ferroelectrics and device applications

The research on two-dimensional (2D) van der Waals ferroelectrics has grown substantially in the last decade. These layered materials differ from conventional thin-film oxide ferroelectrics in that the surface and interface are free from dangling bonds. Some may also possess uncommon properties, such as bandgap tunability, mechanical flexibility, and high carrier mobility, which are desirable for applications in nanoelectronics and optoelectronics. This Tutorial starts by reviewing the theoretical tools in 2D ferroelectric studies, followed by discussing the material synthesis and sample characterization. Several prototypical electronic devices with innovative functionalities will be highlighted. Readers can use this article to obtain a basic understanding of the current status, challenges, and future prospects of 2D ferroelectric materials.