Observing Oxygen Vacancy Driven Electroforming in Pt–TiO₂–Pt Device via Strong Metal Support Interaction

Abstract

Oxygen vacancy formation, migration, and subsequent agglomeration into conductive filaments in transition metal oxides under applied electric field is widely believed to be responsible for electroforming in resistive memory devices, although direct evidence of such a pathway is lacking. Here, by utilizing strong metal-support interaction (SMSI) between Pt and TiO2, we observe via transmission electron microscopy the electroforming event in lateral Pt/TiO2/Pt devices where the atomic Pt from the electrode itself acts as a tracer for the propagating oxygen vacancy front. SMSI, which originates from the d-orbital overlap between Pt atom and the reduced cation of the insulating oxide in the vicinity of oxygen vacancies, was optimized by fabricating nanoscale devices causing Pt atom migration tracking the moving oxygen vacancy front from the anode to cathode during electroforming. Experiments performed in different oxidizing and reducing conditions, which tune SMSI in the Pt-TiO2 system, further confirmed the role of oxygen vacancies during electroforming. These observations also demonstrate that the noble metal electrode may not be as inert as previously assumed.

Tuning Memristivity by Varying the Oxygen Content in a Mixed Ionic–Electronic Conductor

“…In the conventional top–bottom “sandwich‐type” configuration, the low series resistance of L2NO4 (tens of nm thick) is expected to lead to high currents, subsequent Joule heating and can ultimately induce an important degradation of the electrode material and/or the sandwiched material. While Cu or Ag‐based electro‐chemical metallization cells have been largely studied for their filamentary resistive switching mechanism, the formation of Pt filament in a Pt/TiO 2 /Pt memristive device has also been reported, [ 18 ] suggesting that the majority of electrode materials can migrate through the cell and short circuit the device if exposed to harsh programing conditions.…”

Atomic-resolution imaging of electrically induced oxygen vacancy migration and phase transformation in SrCoO2.5-σ

“…Despite highly desirable, in situ characterization of oxygen, and crystal structural evolution under an electric field with atomic resolution has not been achieved to date mainly due to the technical challenge. Therefore, previous experimental approaches of dynamic oxygen ion migration were based on indirect analysis on the change of lattice or spectrum at the nanometer scale or above 17–19 .…”

Transmission Electron Microscopy on Memristive Devices: An Overview

“…While this represents the upper limit of specimen thickness that still allows effective analysis in the TEM it does obviate the need for both the special TEM holder as well as dedicated sample preparation. Furthermore, ex situ analysis can be undertaken because the sample must be biased outside the microscope but this can be done directly on the TEM grid without any intermediate sample preparation and thus without the possibility of artifact induction (Jang et al, 2016).…”