Direct Identification of the Conducting Channels in a Functioning Memristive Device

Abstract

Titanium dioxide memristive devices have been non‐destructively characterized using x‐ray absorption spectromicroscopy and TEM. These techniques allow direct identification of the chemistry and structure of the conducting channel responsible for the bipolar resistance switching seen in these devices. Within the TiO2 matrix, we observe the formation of a Ti4O7 Magnéli phase possessing metallic properties and ordered planes of oxygen vacancies.

Anatomy of a Nanoscale Conduction Channel Reveals the Mechanism of a High‐Performance Memristor

“…This transition from metal to Fermi glass behavior [ 62 ] appears to be the mechanism for OFF switching. Even though heating is substantial, the conduction channel remains amorphous, in contrast to the crystalline conduction channel in TiO 2 unipolar [ 46 ] and bipolar switches, [ 54 ] which is likely a result of off-stoichiometry of the conduction channel in the TaO x memristor. The amorphous structure enables a signifi cant mobile species accommodation capability for a continuous composition change and very high endurance switching.…”

Electronic and magnetic properties ofTi4O7predicted by self-interaction-corrected density functional theory

“…When the concentration of the resulting oxygen vacancies is high enough, these phases may rearrange spontaneously to form ordered reduced structures, the so-called Magnéli phases (Ti n O 2n-1 ). In fact, Magnéli phases such as Ti 4 O 7 (n=4) have been identified experimentally 6,9 in resistive switching devices, with evidence suggesting that filaments or regions of Magnéli phase Ti 4 O 7 form conducting pathways. The formation of conductive filaments leads to a low-resistance state of the device, while the rupture of filaments leads to a high-resistance state.…”

“…The resistance can be switched between two distinctive resistive states by the application of voltage pulses. It is now firmly established that oxygen vacancies play a crucial role 4,[6][7][8] in the switching mechanism. Stoichiometric TiO 2 can be easily reduced 9,10,11 by external fields or by thermal means, leading to oxygen-deficient phases.…”

Molecular dynamics simulations of oxide memristors: thermal effects

“…1 in Ref. [9] since we have many metastable states that may trap the vacancies the conducting channel, which nominally requires temperatures over 350°C [6]. Studying local thermal effects during switching in TiO 2 provides strong evidence for local heating [10].…”

“…It has been demonstrated unambiguously that bipolar switching involves changes to the electronic barrier at the Pt/TiO 2 interface due to the drift of positively charged oxygen vacancies under an applied electric field [1]. Various direct measurements revealed formation of localized conducting channels in TiO 2 : pressure modulated conductance microscopy [3,4], conducting atomic force microscopy (AFM) [5], scanning transmission X-ray microscopy [6], and in-situ transmission electron microscopy [7]. On the basis of these measurements, it became quite clear that the vacancy drift towards the interface…”