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Spatially resolved TiOx phases in switched RRAM devices using soft X-ray spectromicroscopy.

Carta D, Hitchcock AP, Guttmann P, Regoutz A, Khiat A, Serb A, Gupta I, Prodromakis T - Sci Rep (2016)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Nano Group, Nanofabrication Centre, Electronics and Computer Science, Faculty of Physical Sciences and Engineering, University of Southampton, United Kingdom.

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.

No MeSH data available.


Related in: MedlinePlus

Chemical maps depicting regions of amorphous and reduced TiOx.Components maps at the Ti 2p (a,b) and at the O 1 s (c,d). Scale bar = 100 nm.
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f6: Chemical maps depicting regions of amorphous and reduced TiOx.Components maps at the Ti 2p (a,b) and at the O 1 s (c,d). Scale bar = 100 nm.

Mentions: In order to better visualise the chemical distribution of the main TiOx phases across the LRS case, the aligned Ti 2p and O 1 s image sequences on an optical density scale were converted to chemical components maps by means of singular value decomposition (SVD) procedures41. The black and white chemical maps at the Ti 2p (Fig. 6a,b) and O 1 s (Fig. 6c,d) were obtained using the two predominant components in the film, namely amorphous (corresponding to the spectrum of ROI_1 and ROI_2) and reduced (corresponding to the spectrum of ROI_5) TiOx phases. The brightest regions correspond to TiOx amorphous in Fig. 6a,c and TiOx reduced in Fig. 6b,d. The fit of the two components gives consistent results at the Ti 2p and O 1 s edges. In the unaffected regions, TiOx remains amorphous in between the electrodes whereas the reduced TiOx phase is localized in a well-defined region underneath the TE protrusion (C) and in the two thinner filamentary regions connecting TE and BE on the left side of the protrusion (A and B).


Spatially resolved TiOx phases in switched RRAM devices using soft X-ray spectromicroscopy.

Carta D, Hitchcock AP, Guttmann P, Regoutz A, Khiat A, Serb A, Gupta I, Prodromakis T - Sci Rep (2016)

Chemical maps depicting regions of amorphous and reduced TiOx.Components maps at the Ti 2p (a,b) and at the O 1 s (c,d). Scale bar = 100 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4759601&req=5

f6: Chemical maps depicting regions of amorphous and reduced TiOx.Components maps at the Ti 2p (a,b) and at the O 1 s (c,d). Scale bar = 100 nm.
Mentions: In order to better visualise the chemical distribution of the main TiOx phases across the LRS case, the aligned Ti 2p and O 1 s image sequences on an optical density scale were converted to chemical components maps by means of singular value decomposition (SVD) procedures41. The black and white chemical maps at the Ti 2p (Fig. 6a,b) and O 1 s (Fig. 6c,d) were obtained using the two predominant components in the film, namely amorphous (corresponding to the spectrum of ROI_1 and ROI_2) and reduced (corresponding to the spectrum of ROI_5) TiOx phases. The brightest regions correspond to TiOx amorphous in Fig. 6a,c and TiOx reduced in Fig. 6b,d. The fit of the two components gives consistent results at the Ti 2p and O 1 s edges. In the unaffected regions, TiOx remains amorphous in between the electrodes whereas the reduced TiOx phase is localized in a well-defined region underneath the TE protrusion (C) and in the two thinner filamentary regions connecting TE and BE on the left side of the protrusion (A and B).

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Nano Group, Nanofabrication Centre, Electronics and Computer Science, Faculty of Physical Sciences and Engineering, University of Southampton, United Kingdom.

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.

No MeSH data available.


Related in: MedlinePlus