title: Spatially resolved TiOx phases in switched RRAM devices using soft X-ray spectromicroscopy.
abstract: Reduction in metal-oxide thin films has been suggested as the key mechanism responsible for forming conductive phases within solid-state memory devices, enabling their resistive switching capacity. The quantitative spatial identification of such conductive regions is a daunting task, particularly for metal-oxides capable of exhibiting multiple phases as in the case of TiOx. Here, we spatially resolve and chemically characterize distinct TiOx phases in localized regions of a TiOx-based memristive device by combining full-field transmission X-ray microscopy with soft X-ray spectroscopic analysis that is performed on lamella samples. We particularly show that electrically pre-switched devices in low-resistive states comprise reduced disordered phases with O/Ti ratios around 1.37 that aggregate in a ~100 nm highly localized region electrically conducting the top and bottom electrodes of the devices. We have also identified crystalline rutile and orthorhombic-like TiO2 phases in the region adjacent to the main reduced area, suggesting that the temperature increases locally up to 1000 K, validating the role of Joule heating in resistive switching. Contrary to previous studies, our approach enables to simultaneously investigate morphological and chemical changes in a quantitative manner without incurring difficulties imposed by interpretation of electron diffraction patterns acquired via conventional electron microscopy techniques.
authors.affiliation: Nano Group, Nanofabrication Centre, Electronics and Computer Science, Faculty of Physical Sciences and Engineering, University of Southampton, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Carta
authors.affiliation: Chemistry and Chemical Biology and Brockhouse Institute for Materials Research, McMaster University, L8S4M1 Hamilton, ON, Canada.
authors.forename: A P
authors.initials: AP
authors.lastname: Hitchcock
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, Institute for Soft Matter and Functional Materials, Albert Einstein-Str. 15, 12489 Berlin, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Guttmann
authors.affiliation: Nano Group, Nanofabrication Centre, Electronics and Computer Science, Faculty of Physical Sciences and Engineering, University of Southampton, United Kingdom.
authors.forename: A
authors.initials: A
authors.lastname: Regoutz
authors.affiliation: Nano Group, Nanofabrication Centre, Electronics and Computer Science, Faculty of Physical Sciences and Engineering, University of Southampton, United Kingdom.
authors.forename: A
authors.initials: A
authors.lastname: Khiat
authors.affiliation: Nano Group, Nanofabrication Centre, Electronics and Computer Science, Faculty of Physical Sciences and Engineering, University of Southampton, United Kingdom.
authors.forename: A
authors.initials: A
authors.lastname: Serb
authors.affiliation: Nano Group, Nanofabrication Centre, Electronics and Computer Science, Faculty of Physical Sciences and Engineering, University of Southampton, United Kingdom.
authors.forename: I
authors.initials: I
authors.lastname: Gupta
authors.affiliation: Nano Group, Nanofabrication Centre, Electronics and Computer Science, Faculty of Physical Sciences and Engineering, University of Southampton, United Kingdom.
authors.forename: T
authors.initials: T
authors.lastname: Prodromakis