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X-ray Absorption Spectroscopy Study of TiO2–xThin Films for Memory Applications

Carta, D., Mountjoy, Gavin, Regoutz, A., Khiat, A., Serb, A., Prodromakis, T. (2015) X-ray Absorption Spectroscopy Study of TiO2–xThin Films for Memory Applications. The Journal of Physical Chemistry C, 119 (8). pp. 4362-4370. ISSN 1932-7447. (doi:10.1021/jp511739h) (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided) (KAR id:60091)

The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided.
Official URL:
http://doi.org/10.1021/jp511739h

Abstract

Metal–insulator–metal (MIM) devices based on titanium dioxide thin films exhibit resistive switching behavior (RS); i.e., they have the ability to switch the electrical resistance between high-resistive states (HRS) and low-resistive states (LRS) by application of an appropriate voltage. This behavior makes titanium dioxide thin films extremely valuable for memory applications. The physical mechanism behind RS remains a controversial subject but it has been suggested that it could be interface-type, without accompanying structural changes of the oxide, or filament-type with formation of reduced titanium oxide phases in the film. In this work, X-ray absorption spectroscopy (XAS) at the Ti K-edge (4966 eV) was used to characterize the atomic-scale structure of a nonstoichiometric TiO2–x thin film before and after annealing and for the first time after inclusion in a MIM device based on a Cr/Pt/TiO2–x/Pt stack developed on an oxidized silicon wafer. The advantage of the XAS technique is that is element-specific. Therefore, by tuning the energy to the Ti K-edge absorption, contributions from the Pt, Cr, and Si in the stack are eliminated. In order to investigate the structure of the film after electrical switching, XAS analysis at the Ti K-edge was again performed for the first time on the Cr/Pt/TiO2–x/Pt stack in its virgin state and after switching to LRS by application of an appropriate bias. X-ray absorption near-edge structure (XANES) was employed to assess local coordination and oxidation state of the Ti and extended X-ray absorption fine structure (EXAFS) was used to assess bond distances, coordination numbers, and Debye–Waller factors. XAS analysis revealed that the as-deposited film is amorphous with a distorted local octahedral arrangement around Ti (average Ti–O distance of 1.95 Å and coordination number of 5.2) and has a majority oxidation state of Ti4+ with a slight content of Ti3+. The film remains amorphous upon insertion into the stack structure and after electrical switching but crystallizes as anatase upon annealing at 600 °C. These results do not give any indication of the appearance of conducting filaments upon switching and are more compatible with homogeneous interface mechanisms.

Item Type: Article
DOI/Identification number: 10.1021/jp511739h
Divisions: Divisions > Division of Natural Sciences > Physics and Astronomy
Depositing User: Gavin Mountjoy
Date Deposited: 26 Jan 2017 09:36 UTC
Last Modified: 05 Nov 2024 10:53 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/60091 (The current URI for this page, for reference purposes)

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