The Role of Ferroelectric Polarization in Resistive Memory Properties of Metal/Insulator/Semiconductor Tunnel Junctions: A Comparative Study.

Recently, tunnel junction devices adopting semiconducting Nb:SrTiO electrodes have attracted considerable attention for their potential applications in resistive data storage and neuromorphic computing. In this work, we report on a comparative study of Pt/insulator/Nb:SrTiO tunnel junctions between ferroelectric BaTiO and nonferroelectric SrTiO and LaAlO barriers to reveal the role of polarization in resistance switching properties. Although hysteretic behaviors appear in current-voltage measurements of all devices regardless of the barrier character, significantly improved current ratios by more than three orders of magnitude are observed in the Pt/BaTiO/Nb:SrTiO tunnel junctions due to the dominance of polarization in modulation of junction barrier profiles between the low and high resistance states. The switchable polarization also gives rise to enhanced resistance retention since the electron diffusion that smears the barrier contrast of the bistable resistance states is suppressed by the polar BaTiO/Nb:SrTiO interface associated with the ferroelectric bound charges. These polarization-induced effects are absent in the nonferroelectric Pt/SrTiO/Nb:SrTiO and Pt/LaAlO/Nb:SrTiO devices in which serious resistance state decay, described by Fick's second law, is observed since there are no switchable interface charges on SrTiO/Nb:SrTiO and LaAlO/Nb:SrTiO to block the electron diffusion. In addition, the Pt/BaTiO/Nb:SrTiO device also exhibits an excellent switching endurance up to ∼4.0 × 10 bipolar cycles. These enhancements indicate the importance of ferroelectric polarization for achieving high-performance resistance switching and suggest that metal/ferroelectric/Nb:SrTiO tunnel junctions are promising candidates for nonvolatile memory applications.