Ferroelectric Domain Wall Memristor

Abstract

A domain wall‐enabled memristor is created, in thin film lithium niobate capacitors, which shows up to twelve orders of magnitude variation in resistance. Such dramatic changes are caused by the injection of strongly inclined conducting ferroelectric domain walls, which provide conduits for current flow between electrodes. Varying the magnitude of the applied electric‐field pulse, used to induce switching, alters the extent to which polarization reversal occurs; this systematically changes the density of the injected conducting domain walls in the ferroelectric layer and hence the resistivity of the capacitor structure as a whole. Hundreds of distinct conductance states can be produced, with current maxima achieved around the coercive voltage, where domain wall density is greatest, and minima associated with the almost fully switched ferroelectric (few domain walls). Significantly, this “domain wall memristor” demonstrates a plasticity effect: when a succession of voltage pulses of constant magnitude is applied, the resistance changes. Resistance plasticity opens the way for the domain wall memristor to be considered for artificial synapse applications in neuromorphic circuits.

Giant Domain Wall Conductivity in Self‐Assembled BiFeO3 Nanocrystals

“…Figure 3g shows the comparison of the present study (near both charged and neutral domain walls) and several representative works of charged domain walls from both the directly measured current values and the as‐calculated conductivity/conductance/current density points of view (see Table S1, Supporting Information, for more details). [ 9,23–26,36,49,50 ] There are two main implications from Figure 3g: i) the performance of the neutral domain walls in the present work is surprisingly comparable to those of previously reported charged domain walls; (ii) the current density of the charged domain wall is to the best of our knowledge the largest to date.…”

“…e) I–V curves within the domains, near the neutral domain walls, and near the charged domain walls, and f) persistent current values near neutral domain walls, and charged domain walls, respectively. g) Comparison of the present result with several representative works from the point of view of domain wall currents, conductivity, conductance, and current densities; [ 9,23–26,36,49,50 ] The domain wall currents were measured directly while the calculations of the corresponding conductivity/conductance/current density has been shown in Table S1, Supporting Information. The measurements were carried out at room temperature.…”

Surface‐Bound Domain Penetration and Large Wall Current

“…[ 5–7 ] This places heavy cost and reliability burdens on these memories. There are many evidences that the DWs in insulating ferroelectric LiNbO 3 (LN) single crystals are conductive, [ 12–18 ] where switchable currents can be tuned within 12 orders of magnitude, intriguing the functionalities of multilevel memristor. [ 16,17 ] Generally, most 180° neutral DWs (NDWs) are less electrically conductive than inclined charged DWs (CDWs).…”

“…There are many evidences that the DWs in insulating ferroelectric LiNbO 3 (LN) single crystals are conductive, [ 12–18 ] where switchable currents can be tuned within 12 orders of magnitude, intriguing the functionalities of multilevel memristor. [ 16,17 ] Generally, most 180° neutral DWs (NDWs) are less electrically conductive than inclined charged DWs (CDWs). [ 1–4,8–14 ] Although the DW inclination angles of ≈1° in congruent lithium niobate bulk crystals doped with 5 mol% MgO could increase this conduction by three to four orders of magnitude, [ 13,14 ] the inclination wall angle and correlated linear current density per unit voltage (1.2 × 10 −7 –1.0 × 10 −4 nA nm −1 V −1 ) are insufficient to drive high‐speed memory circuits and other agile nanodevices with high output powers.…”

Giant thermoelectric power factor in charged ferroelectric domain walls of GeTe with Van Hove singularities

“…Several normally insulating perovskite materials show conductive behaviour at DWs [14][15][16][17][18][19][20] , with the electrical conductivity of DWs up to 13 orders of magnitude larger than that in the domains 21 . These discoveries have lead to a new paradigm of ferroic devices where DWs, rather than domains, are active elements in nanoelectronic circuits 13 , such as diodes 22 , rectifiers 23 , resistive memories 24,25 , and memristors 26 . In contrast, there have been no reported studies of the Seebeck coefficient and the power factor of ferroelectric DWs.…”