Giant Domain Wall Conductivity in Self-Assembled BiFeO3 Nanocrystals

Ever-increasing demand on electronic devices with ultrahigh-density non-volatile data storage has attracted great interest in novel ferroelectric memories based on conductive ferroelectric domain walls. Embedded in an insulating material, ferroelectric domain walls have the capability of being (re)created, displaced, erased, and altered in their spatial configurations and electronic characteristics. However, the domain wall conductivities are in most cases not yet sufficiently high to ensure the current density required to drive read-out circuits operating at high speeds. In this work, a giant domain wall current (>10 µA) of a single charged domain wall is obtained through conductive atomic force microscopy with a bias field of 4 V. This is achieved in self-assembled BiFeO nanocrystals grown by sol-gel method on Nb-doped SrTiO substrates. Local configurations of domains and domain wall types are studied using vector piezoresponse force microscopy and high-resolution transmission electronic microscopy. The enhancement of the wall current is shown to be due to the formation of conducting pathways of charged defects accumulated along domain walls and traversing the nanocrystals. The diverse domain walls can be manipulated by electric field in a perpendicular architecture. The perpendicular array structure of BiFeO nanocrystals should have great potentials for developing perpendicular nanoelectronic prototypes.