Soft-X-ray microspectroscopy study of TiO₂-based resistive switching devices

Carta, Daniela, Hitchcock, Adam P., Guttmann, Peter, Regoutz, Anna, Khiat, Ali, Serb, Alexantrou, Gupta, Isha and Prodromakis, Themistoklis (2015) Soft-X-ray microspectroscopy study of TiO₂-based resistive switching devices. Advances in ReRAM: Materials & Interfaces, Chaniá, Greece. 01 Jan - 15 Oct 2015. (In Press)

Abstract

Titanium dioxide (TiO₂) has been widely used as resistive switching oxide in random-access memory devices; the resistive switching mechanism is usually attributed to the formation and migration of defects along the TiO₂ thin film which result in chemical changes of the oxide, in particular in the formation of highly reduced oxide phases. However, a fully understanding of the atomic-scale resistive switching mechanism and identification of material changes within the oxide has not been achieved.
In this work, we present for the first time a Ti L-edge (450-485 eV) and O K-edge (525-555 eV) Near-Edge X-Ray Absorption Fine Structure Transmission X-Ray Microscopy (NEXAFS-TXM) study on photon transparent cross sections of Pt/TiO₂(50nm)/Pt -based devices in different switching states: pristine, high resistive state (HRS) and low resistive state (LRS).
This technique has the capability of performing simultaneously imaging (which allows investigation of morphological changes in the film) and spectroscopy, which allows chemical analysis at nanometric scale of localized regions. Moreover, it has the advantage of being non-destructive, element specific and spatially-resolved. Differences in intensity, width, shape and position of the NEXAFS peaks give detailed information on symmetry around Ti and O, oxidation state and titanium oxide phases formed across the film as a consequence of the switching.
X-ray imaging gives direct evidence of the formation a localized filamentary region in the sample switched into the LRS state. Chemical analysis of the filamentary region and of the surrounding areas at the nanoscale performed by studying simultaneously Ti L-edge and O K-edge NEXAFS spectra shows highly localized reduced TiO_x species forming the conductive filament, along with crystallization of amorphous TiO₂ in the surrounding region

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Contributors

Author: Themistoklis Prodromakis

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