First-Principles Calculations of Non-Equilibrium Energetics and Polarization Switching in Oxide Ferroelectric Tunnel Junctions

Ferroelectric tunnel junction (FTJ) is a promising candidate for future memory technologies and much effort has been put into the understandings of its materials and device properties. However, in view of atomistic first-principles calculations, most studies have been so far limited to the equilibrium limit and the behavior of FTJs under non-equilibrium conditions remains largely unexplored. Herein, we describe the first-principles framework that enables the analysis of FTJs under non-equilibrium conditions, which is based on the multi-space constrained-search density functional theory (MS-DFT) formalism we have developed over the years. The unique strength of MS-DFT is that the non-equilibrium free energy as well as electric field-dependent polarization and capacitance can be obtained in a first-principles manner. As an application example, for a representative SrRuO3-BaTiO3-SrRuO3(SRO-BTO-SRO) FTJ capacitor model, we compute the current density-voltage characteristics and tunneling electro-resistance, and the impact of polarization orientation on the resistance state.