Spatially resolved TiOx phases in RRAM conductive nanofilaments using soft X-ray spectromicroscopy

TL;DR

This study uses advanced soft X-ray spectromicroscopy to spatially resolve and chemically characterize TiOx phases within memristive devices, revealing the roles of different phases and Joule heating in resistive switching.

Contribution

It introduces a novel approach combining full-field transmission X-ray microscopy with spectroscopic analysis to quantitatively analyze TiOx phases in memristive devices.

Findings

Disordered Ti2O3-like phases form filamentary regions conducting electrodes.

Crystalline TiO2 phases indicate local temperature increases up to 1000 K.

Method allows simultaneous morphological and chemical analysis without electron diffraction.

Abstract

Reduction in metal-oxide thin films has been suggested as the key mechanism responsible for forming conductive nanofilaments within solid-state memory devices, enabling their resistive switching capacity. The quantitative spatial identification of such filaments 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 close to Ti2O3 stoichiometry that aggregate in a ~ 100 nm filamentary 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 filament, 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.