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Direct Observation of Redox Switching in Resistive Memory Devices Operated In-situ in a Transmission Electron Microscope by Electron Energy Loss Spectroscopy and Off-Axis Electron Holography

The Pt/SrTiO 3 /Nb:SrTiO 3 system is considered to be a model system for the study of resistive memories [1]. It is thought that changes in the oxygen concentration underneath the top electrode are responsible for the switching. During the past few years, a bewildering array of characterisation studies have appeared in the literature presenting contradictory views about the operation of these resistive memories. It is desirable to improve these devices by correct determination of the switching mechanism rather than using empirical approaches. Transmission electron microscopy (TEM) is a suitable characterisation technique and the use of modern aberration corrected TEMs allow a range of complimentary characterisation techniques to be performed during one experiment on the same specimen. In this presentation we will present experimental results that have been obtained using aberration-corrected scanning (S)TEM, electron energy-loss spectroscopy (EELS) for composition and bonding measurements and off-axis electron holography for measurements of electrostatic potentials that have been obtained on different types of SrTiO 3 based memory devices that are switched in-situ in the TEM. Specimens comprising a Nb:doped SrTiO 3 substrate (bottom electrode), a 18-nm-thick Sr-enriched SrTiO 3 (Sr:STO) film and a 10-nm-thick Pt (top electrode) with a top Au contact have been examined using a Nanofactory specimen holder comprising a movable piezo-electrical contact.