Charged Ferroelectric Domain Walls for Deterministic ac Signal Control at the Nanoscale

Abstract

The direct current (d.c.) conductivity and emergent functionalities at ferroelectric domain walls are closely linked to the local polarization charges. Depending on the charge state, the walls can exhibit unusual d.c. conduction ranging from insulating to metallic-like, which is leveraged in domain-wall-based memory, multi-level data storage, and synaptic devices. In contrast to the functional d.c. behaviors at charged walls, their response to alternating currents (a.c.) remains to be resolved. Here, we reveal a.c. characteristics at positively and negatively charged walls in ErMnO3, distinctly different from the response of the surrounding domains. By combining voltage-dependent spectroscopic measurements on macroscopic and local scales, we demonstrate a pronounced non-linear response at the electrode-wall junction, which correlates with the domain-wall charge state. The dependence on the a.c. drive voltage enables reversible switching between uni-and bipolar output signals, providing conceptually new opportunities for the application of charged walls as functional nanoelements in a.c. circuitry.

Unveiling Alternating Current Electronic Properties at Ferroelectric Domain Walls

“…[ 37 ] Enabled by this tunability, it has been proposed to develop ultrasmall half‐wave rectifiers based on ferroelectric domain walls, facilitating AC‐to‐DC signal conversion at the nanoscale. [ 23,37 ]…”

“…One important finding of these studies was that electrode-wall junctions can be used to rectify electrical currents, exhibiting distinct diodelike properties at low frequencies that distinguish them from the domains (see Section 2.6 for details). [23,37] In the gigahertz regime, a substantial enhancement of the AC conductivity at [63,64] d) The DC conduction at ferroelectric domain walls is commonly characterized using cAFM, whereas nanoimpedance microscopy (NIM), [102,103] scanning impedance microscopy (SIM), [104] and cAFM under AC-drive voltage (AC-cAFM) [23] have been applied to investigate their AC response for frequencies f ≲ 1 MHz. For higher frequencies, microwave impedance microscopy (MIM) [105] is an established method for impedance measurements at the local scale (LiNbO 3 , [96,99] h-ErMnO 3 , [23,37] h-YMnO 3 , [7] h-(Lu,Sc)FeO 3 , [101] KNbO 3 , [100] Pb(Zr,Ti)O 3 , [98] and BiFeO 3 [97] ).…”

“…[23,37] In the gigahertz regime, a substantial enhancement of the AC conductivity at [63,64] d) The DC conduction at ferroelectric domain walls is commonly characterized using cAFM, whereas nanoimpedance microscopy (NIM), [102,103] scanning impedance microscopy (SIM), [104] and cAFM under AC-drive voltage (AC-cAFM) [23] have been applied to investigate their AC response for frequencies f ≲ 1 MHz. For higher frequencies, microwave impedance microscopy (MIM) [105] is an established method for impedance measurements at the local scale (LiNbO 3 , [96,99] h-ErMnO 3 , [23,37] h-YMnO 3 , [7] h-(Lu,Sc)FeO 3 , [101] KNbO 3 , [100] Pb(Zr,Ti)O 3 , [98] and BiFeO 3 [97] ). The background color indicates two regimes corresponding to kilo-to megahertz (f ≲ 1 MHz, blue) and gigahertz (f ≳ 1 MHz, yellow) frequencies, where domain wall responses are dominated by different contributions, as discussed in Sections 2 and 3, respectively.…”

“…d) The DC conduction at ferroelectric domain walls is commonly characterized using cAFM, whereas nanoimpedance microscopy (NIM),[102,103] scanning impedance microscopy (SIM),[104] and cAFM under AC-drive voltage (AC-cAFM)[23] have been applied to investigate their AC response for frequencies f ≲ 1 MHz. For higher frequencies, microwave impedance microscopy (MIM)[105] is an established method for impedance measurements at the local scale (LiNbO 3 ,[96,99] h-ErMnO 3 ,[23,37] h-YMnO 3 ,[7] h-(Lu,Sc)FeO 3 ,[101] KNbO 3 ,[100] Pb(Zr,Ti)O 3 ,[98] and BiFeO 3…”

“…c) AC-cAFM image (0.5 MHz) recorded on h-ErMnO 3 with inplane polarization, revealing enhanced and suppressed AC-cAFM current contrast at tail-to-tail and head-to-head domain walls, respectively. Reproduced with permission [37]. Copyright 2021, American Chemical Society.…”