  Ferroelectricity has a wide range of applications in functional electronics
and is extremely important for the development of next-generation information
storage technology, but it is difficult to achieve due to its special symmetry
requirements. In this letter, based on van derWaals stacking, a generic model
is proposed for realizing ferroelectric devices, where a freely movable center
layer is packaged in two fixed and symmetrically stacked layers. In this model,
the ferroelectric phase transition can be realized between the two equivalent
and eccentric ground stacking-states with opposite polarizations. By means of
first-principles calculations, taking the h-BN/h-BN/h-BN and h-BN/Graphene/h-BN
as feasible models, we carefully evaluate the magnitude of ferroelectricity.
The corresponding polarizations are estimated as 1.83 and 1.35 pC/m,
respectively, which are comparable to the sliding ferroelectricity. Such a new
tri-layer model of vertical ferroelectricity can be constructed by arbitrary
van derWaals semiconducting materials, and usually holds low switching barrier.
Optimized material combinations with remarkable polarization are highly
expectable to be discovered from the huge candidate set for future information
storage.
