Probing nanoscale oxygen ion motion in memristive systems

Abstract

Ion transport is an essential process for various applications including energy storage, sensing, display, memory and so on, however direct visualization of oxygen ion motion has been a challenging task, which lies in the fact that the normally used electron microscopy imaging mainly focuses on the mass attribute of ions. The lack of appropriate understandings and analytic approaches on oxygen ion motion has caused significant difficulties in disclosing the mechanism of oxides-based memristors. Here we show evidence of oxygen ion migration and accumulation in HfO2 by in situ measurements of electrostatic force gradient between the probe and the sample, as systematically verified by the charge duration, oxygen gas eruption and controlled studies utilizing different electrolytes, field directions and environments. At higher voltages, oxygen-deficient nano-filaments are formed, as directly identified employing a CS-corrected transmission electron microscope. This study could provide a generalized approach for probing ion motions at the nanoscale.

Recent Advances of Quantum Conductance in Memristors

“…[65,66] Although the evolution dynamics of cation migration-based filaments can be readily and well understood through real-time and in situ TEM observations, the migration of oxygen ions and consequent growth/dissolution of oxygen-deficient filaments are hard to be captured due to the low atomic number of oxygen element and easy adsorption of oxygen contaminations from the ambient atmosphere. In contrast, Yang et al [68] introduced a dualpass electrostatic force microscopy (EFM) method into this filed, where the first pass is to acquire surface morphology of the previously stimulated areas in tapping mode (Figure 4b), followed by the second pass in noncontact mode to measure the 1ω and 2ω components (Figure 4c,d) of the electrostatic force gradient between the probe and the switching regions. Kang and co-workers [67] pioneered the electron holography in in situ TEM for analyzing the evolution dynamics of oxygen vacancy filaments (Figure 4a).…”

“…Kang and co-workers [67] pioneered the electron holography in in situ TEM for analyzing the evolution dynamics of oxygen vacancy filaments (Figure 4a). [68] External electric field can attract oxygen ions to the anodic interface, making oxygen vacancies accumulated initially at the cathodic interface. As such, the negative potential can be used to track the evolution process of oxygen vacancy filaments.…”

“…[14] Similarly, quantum conductance can also occur at the final dissolution stage of an existing filament, such as the oxygen vacancy filament in the Pt/HfO 2 /Pt memristor (Figure 5c,d). 2019, 5, 1800854 [68] Copyright 2017, The authors, published by Springer Nature. Electron.…”

GGA-1/2 self-energy correction for accurate band structure calculations: the case of resistive switching oxides

“…manifest a transition from a high resistance state (HRS) to a low resistance state (LRS) upon the formation of conductive filaments (CFs) connecting the two electrodes. Yet, at present there are still controversies on the exact composition and geometry of the CFs [19][20][21][22]. Since it is difficult to directly observe and determine experimentally the exact composition of the CFs within the dielectric media, theoretical approaches can be particularly helpful.Among atomistic simulation techniques, ab initio calculations based on density functional theory (DFT) [23] are highly successful in the prediction of total energies, bond lengths, and vibration frequencies.…”

Optically Modulated Threshold Switching in Core–Shell Quantum Dot Based Memristive Device

“…The EFM measurement, coupled with KPFM result suggest that the hole concentration of InP/ZnS QD film will increase under light illumination (Figure S14 in the Supporting Information). [ 64–67 ] Then, to theoretically investigate the charge transition mechanism, we adopted a simple model to evaluate the excitation behaviors of electron‐hole pairs in the InP/ZnS QDs. The wavefunctions and eigenenergies of electrons and holes for InP/ZnS core/shell QDs were evaluated by treating them as independent particles confined in spherical wells with finite depth.…”