Vertical ferroelectricity in van der Waals materials: Models and devices

Ferroelectricity has a wide range of applications in functional electronics, and it is extremely important for the development of the next generation of information-storage technologies. However, it is difficult to achieve in practice due to its special symmetry requirements. In this Letter, based on van der Waals stacking, a generic model is proposed for realizing ferroelectric devices in which a freely movable center layer is packaged in two fixed and symmetrically stacked layers. In this model, a ferroelectric phase transition can be realized between two equivalent and eccentric ground stacking states with opposite polarizations. By means of first-principles calculations, taking stacked hexagonal boron nitride (h-BN/h-BN/h-BN) and h-BN/graphene/h-BN as feasible models, we carefully evaluated the magnitude of ferroelectricity. The corresponding polarizations were estimated as 1.83 and 1.35 pC/m, values that are comparable to those observed in sliding ferroelectricity. Devices using this tri-layer model of vertical ferroelectricity can be constructed using arbitrary van der Waals semiconducting materials, and these will usually have low switching barriers. It is highly likely that optimized material combinations with remarkable polarization will be discovered from the huge candidate set this provides for future information-storage applications.