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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:SrTiO3 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:SrTiO3 tunnel junctions between ferroelectric BaTiO3 and non-ferroelectric SrTiO3 and LaAlO3 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 3 orders of magnitude are observed in the Pt/BaTiO3/Nb:SrTiO3 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 BaTiO3/Nb:SrTiO3 interface associated with the ferroelectric bound charges. These polarization-induced effects are absent in the non-ferroelectric Pt/SrTiO3/Nb:SrTiO3 and Pt/LaAlO3/Nb:SrTiO3 devices, in which serious resistance state decay, described by Fick's second law, are observed, since the electroneutral SrTiO3/Nb:SrTiO3 and LaAlO3/Nb:SrTiO3 interfaces cannot block the electron diffusion on the Nb:STO surfaces. In addition, the Pt/BaTiO3/Nb:SrTiO3 device also exhibits an excellent switching endurance up to ~4.0×106 bipolar cycles. These enhancements indicate the importance of ferroelectric polarization for achieving high-performance resistance switching and suggest that metal/ferroelectric/Nb:SrTiO3 tunnel junctions are promising candidates for non-volatile memory applications.