Manipulation of Conductive Domain Walls in Confined Ferroelectric Nanoislands

Abstract

Conductive ferroelectric domain walls-ultranarrow configurable conduction paths-have been considered as essential building blocks for future programmable domain wall electronics. For applications in high-density devices, it is imperative to explore the conductive domain walls in small confined systems, while earlier investigations have hitherto focused on thin films or bulk single. Here, an observation and manipulation of conductive domain walls confined within small BiFeO 3 nanoislands aligned in highdensity arrays are demonstrated. Using conductive atomic force microscopy, various types of conductive domain walls, including the head-to-head charged domain walls (CDWs), zigzag domain walls, and typical 71° head-totail neutral domain walls (NDWs), are distinctly visualized. The CDWs exhibit remarkably enhanced metallic conductivity with current of ≈nA order in magnitude and 10 4 times larger than that inside domains (0.01-0.1 pA), while the semiconducting NDWs allow much smaller current (≈10 pA) than the CDWs. The substantial difference in conductivity for dissimilar walls enables manipulations of various wall conduction states for individual addressable nanoislands via electrical tuning of domain structures. A controllable writing of four distinctive states in individual nanoislands can be achieved, showing application potentials for developing multilevel high-density memories.

Quasi-one-dimensional metallic conduction channels in exotic ferroelectric topological defects

“…Eventually, the significantly enhanced conductivity and metallic conduction behaviors in the head-to-head charge core/walls can be observed. In fact, similar conduction behaviors were reported in earlier literature addressing the charge domain walls 8 – 10 .…”

“…In this work, BFO nanoisland arrays (~40 nm in height and 400 nm in diameter) were directly patterned from high-quality epitaxial BFO films via a nano-sphere lithography technique using the polystyrene sphere (PS) arrays as templates 10 , 27 . The detailed fabrication process can be found in “Methods” and Supplementary Note 1 and Supplementary Fig.…”

“…8 ). When the metallic channel contacts with the electrode, there may appear a narrow insulating gap or nonconductive domain region 9 , 10 close to the electrode, giving rise to the Schottky barriers between the metallic core and electrodes. Therefore, the system exhibits a thermionic emission behavior in the lower bias range.…”

“…This scale is close to the lateral size of a typical CDW 8 , 18 , giving rise to an ultrahigh current density of ∼10 4 A/cm 2 . Such a superfine and highly conductive 1D metallic channel can be considered as a kind of quasi-1D electron gas (q1DEG), somewhat analogous to the quasi-two-dimensional electron gas (q2DEG) frequently observed in certain CDWs 8 – 10 , while it is out of the scope of this work.…”

“…To this stage, most earlier investigations have hitherto focused on the properties of two-dimensional (2D) defects (namely domain walls). For instance, a plethora of physical properties have been observed in ferroelectric domain walls, including enhanced domain wall conductivities 7 – 10 , enhanced photovoltaics 11 , giant magnetoresistances 12 , extraordinary magnetism 13 , 14 , and quantum oscillation behaviors 15 , among many others. These functionalities could underpin a wide range of potential configurable nanoelectronic, magnetoelectronic, and optoelectronic applications, particularly the energy-efficient current-readout nonvolatile memories based on reversible creating/eliminating of the conductive domain walls 16 , 17 .…”