Evidence for multifilamentary valence changes in resistive switching SrTiO3 devices detected by transmission X-ray microscopy

Abstract

Transmission X-ray microscopy is employed to detect nanoscale valence changes in resistive switching SrTiO3 thin film devices. By recording Ti L-edge spectra of samples in different resistive states, we could show that some spots with slightly distorted structure and a small reduction to Ti3+ are already present in the virgin films. In the ON-state, these spots are further reduced to Ti3+ to different degrees while the remaining film persists in the Ti4+ configuration. These observations are consistent with a self-accelerating reduction within pre-reduced extended growth defects

Formation and Movement of Cationic Defects During Forming and Resistive Switching in SrTiO3 Thin Film Devices

“…The forming process is performed with positive bias at the top electrode and a current compliance of 10 mA, which is reached at a bias of 4 V. It should be kept in mind that, despite of the large top electrode, forming and resistive switching is confi ned to one (or few) thin fi laments. [ 18,27,38 ] The confi nement of the forming current leads to an extremely high local dissipation of power and correspondingly high temperatures. [ 17 ] In a previous study of FeSTO fi lms on NbSTO substrates using similar forming conditions, a single discharge channel and a recrystallization of the FeSTO fi lm were clearly observed, presumably after a melting process.…”

Insights into Nanoscale Electrochemical Reduction in a Memristive Oxide: the Role of Three‐Phase Boundaries

“…Prior to the forming (before a complete filament is formed), the current flows through the entire electrode area. The laterally inhomogeneous conductivity of FeSTO thin films causes the current flow to be enhanced in confined “pre‐filaments”, which can be either related to local differences in the doping level or structural defects, like screw dislocations . Above a certain critical current density in the pre‐filaments, the electro‐reduction takes place through a self‐accelerated process where Joule heating leads to enhanced mobility of the oxygen ions, which accelerates the reduction, which in turn enhances the conductivity of the filaments and therefore the Joule heating.…”

Overview of nanoscale NEXAFS performed with soft X-ray microscopes

“…Here, the structural homogeneity of nanoparticles in the hybrid particle was examined. Nanoscale valence changes in resistive switching thin film devices (SrTiO 3 ) could be demonstrated [ 64 ]. The change of resistance in a RRAM device could be assigned to a redox-process.…”