Giant Domain Wall Conductivity in Self‐Assembled BiFeO₃ Nanocrystals

Abstract

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 BiFeO3 nanocrystals grown by sol‐gel method on Nb‐doped SrTiO3 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 BiFeO3 nanocrystals should have great potentials for developing perpendicular nanoelectronic prototypes.

Emergent properties at oxide interfaces controlled by ferroelectric polarization

“…Also, the accumulated bound charge at "head-to-head (H-H)" or "tailto-tail (T-T)" charged DWs (CDWs) gather compensating free charges, creating two-dimensional conducting channels, as shown in Fig. 6a 31,[117][118][119][120][121][122] . Intrinsically, the bandgap lowering at noncharged DWs, where no bound charge accumulated, is another source of the conductance, as shown in Fig.…”

“…CDWs exhibit specific polarization discontinuities, such as H-H and T-T configurations, and carry the net bound charge. They are electrically active and have a much higher conductivity than the charge-neutral DWs 31,[117][118][119][120][121][122] . The polarization discontinuity at CDWs generates a local electric field which causes the absolute energies of the local electronic band structure to shift uniformly, as shown in Fig.…”

Ferroelectric domain-wall logic units

“…In these cases, data storage or logic operation functions could be realized by controlling DW injection, motion, and annihilation along magnetic nanowires rather than switching magnetic domains as is traditional. Contrary to the large wall width and high energy cost in current-driven moving magnetic DWs, ferroelectric DWs possess a much smaller wall width (less than a few nanometers), and their electric-field-driven features and electric conduction are conducive to high-density integration and low-power regulation of nanoelectronic devices [1,[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Recently, by controlling the electric conduction of ferroelectric DWs with a low voltage, low or high resistance states could be created to realize 0 or 1 data bits for memory applications [18][19][20][21][22][23]25].…”

Engineering Individual Oxygen Vacancies: Domain-Wall Conductivity and Controllable Topological Solitons

“…Substantial effort has been given though to domain-wall conductivity in large-bandgap ferroelectrics, vastly because domain walls are movable by will with external electric fields, giving rise to miniaturized memristive cells. 17 − 19 While the success of presenting domain-wall conductivity in traditional perovskite ferroelectrics, such as BaTiO 3 20 and Pb(Zr 0.2 Ti 0.8 )O 3 , has remained limited, 21 − 23 attention has been given mainly to BiFeO 3 , 24 − 27 ErMnO 3 , 28 , 29 and LiNbO 3 , 30 − 32 which show high and reproducible conductivity.…”