First-principles calculations of size-dependent giant electroresistance effect in nanoscale asymmetric ferroelectric tunnel junctions

Based on the first principle calculations, we predicted the electronic structures and ferroelectric instability of the asymmetric ferroelectric tunneling junction with the ferroelectric barrier thickness changing, and found two undiscovered and important behaviors, i.e., absence of the critical thickness for the positive polarization state and the larger critical thickness for the negative polarization state. Using nonequilibrium Green function's approach, the corresponding two-probe systems and their electronic transport properties at different ferroelectric barrier thickness have been constructed. It is found that reorienting the polarization direction in the ferroelectric barrier can dramatically change the internal electric field and macroscopic potential barrier, resulting in several orders of magnitude change in tunneling electroresistance ratio. Results also found that the tunneling electroresistance can be distinctly controlled by adjusting thickness of the ferroelectric barrier, which behavior is defined as the size-dependent giant electroresistance effect. Our results enable architectures of large density and high sensitivity in the next generation of ferroelectric random access memories with nondestructive resistive readout.