Electronic switching by metastable polarization states in BiFeO3 thin films

Abstract

We present an approach to control resistive switching in metal-ferroelectric contacts using a radially symmetric electric field. In ferroelectrics with significant polarization along the corresponding field lines, the field above a critical threshold will induce polarization discontinuity, a corresponding nanoscale volume of space charge, and a conducting junction. We demonstrate this principle using nanoscale polarization switching of a conventional (001)-oriented thin film of $\mathrm{BiFe}{\mathrm{O}}_{3}$. Without any optimization, the conducting state created in this regime of resistive switching exhibits local currents of $\ensuremath{\sim}1\text{--}10\phantom{\rule{0.16em}{0ex}}\mathrm{nA}$, approaching the $\ensuremath{\sim}100\phantom{\rule{0.16em}{0ex}}\mathrm{nA}$ threshold required for device implementation [J. Jiang et al., Nat. Mater. 17, 49 (2018)]. The corresponding electronic function is that of a volatile resistive switch, which is directly compatible with neuristor functionality that encodes the functioning basis of an axon [M. D. Pickett et al., Nat. Mater. 12, 114 (2013)]. Phase-field modeling further reveals that in the strongly charged local configuration, $\mathrm{BiFe}{\mathrm{O}}_{3}$ locally undergoes a rhombohedral-tetragonal (R-T) phase transition, in part due to substantial piezoelectric expansion of the lattice. The estimated local charge density can be as high as $\ensuremath{\sim}{10}^{21}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$, which would be extremely difficult to achieve by conventional doping approaches without altering other material properties. Therefore, this method for creating stable and reproducible strongly charged ferroelectric junctions enables more systematic studies of their physical properties, such as the possibility of structural and electronic phase transitions, and it can lead to new ferroelectric devices for advanced information functions.