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Resistive switching mechanism in TiO2-x thin films: an X-ray absorption spectroscopy study

Resistive switching mechanism in TiO2-x thin films: an X-ray absorption spectroscopy study
Resistive switching mechanism in TiO2-x thin films: an X-ray absorption spectroscopy study
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.
Carta, Daniela
120de978-2aaa-4b4d-bf5f-3625c503040d
Mountjoy, Gavin
20246d4b-b036-4c36-9c9f-bceeefa79156
Regoutz, Anna
5f9fa784-fea8-42f9-949f-4fe7a908f8ce
Khiat, Ali
bf549ddd-5356-4a7d-9c12-eb6c0d904050
Serb, Alexantrou
30f5ec26-f51d-42b3-85fd-0325a27a792c
Prodromakis, Themistoklis
d58c9c10-9d25-4d22-b155-06c8437acfbf
Carta, Daniela
120de978-2aaa-4b4d-bf5f-3625c503040d
Mountjoy, Gavin
20246d4b-b036-4c36-9c9f-bceeefa79156
Regoutz, Anna
5f9fa784-fea8-42f9-949f-4fe7a908f8ce
Khiat, Ali
bf549ddd-5356-4a7d-9c12-eb6c0d904050
Serb, Alexantrou
30f5ec26-f51d-42b3-85fd-0325a27a792c
Prodromakis, Themistoklis
d58c9c10-9d25-4d22-b155-06c8437acfbf

Carta, Daniela, Mountjoy, Gavin, Regoutz, Anna, Khiat, Ali, Serb, Alexantrou and Prodromakis, Themistoklis (2015) Resistive switching mechanism in TiO2-x thin films: an X-ray absorption spectroscopy study. E-MRS 2015 Spring Meeting, Lille, France. 10 - 14 May 2015. (In Press)

Record type: Conference or Workshop Item (Paper)

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.

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More information

Accepted/In Press date: 11 May 2015
Venue - Dates: E-MRS 2015 Spring Meeting, Lille, France, 2015-05-10 - 2015-05-14
Organisations: Nanoelectronics and Nanotechnology

Identifiers

Local EPrints ID: 375058
URI: http://eprints.soton.ac.uk/id/eprint/375058
PURE UUID: 4bcf5052-aa2e-4246-84f4-95e1ac5c81f2
ORCID for Themistoklis Prodromakis: ORCID iD orcid.org/0000-0002-6267-6909

Catalogue record

Date deposited: 11 Mar 2015 12:12
Last modified: 12 Dec 2021 04:00

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Contributors

Author: Daniela Carta
Author: Gavin Mountjoy
Author: Anna Regoutz
Author: Ali Khiat
Author: Alexantrou Serb
Author: Themistoklis Prodromakis ORCID iD

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