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

• Published in: Advanced functional materials Vol. 25; no. 40; pp. 6360 - 6368
• Main Authors: Lenser, Christian, Koehl, Annemarie, Slipukhina, Ivetta, Du, Hongchu, Patt, Marten, Feyer, Vitaliy, Schneider, Claus M., Lezaic, Marjana, Waser, Rainer, Dittmann, Regina
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 01.10.2015
• Subjects: hard X-ray photoelectron spectroscopy; photoemission electron microscopy; resistive switching; segregation
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201500851

The resistance switching phenomenon in many transition metal oxides is described by ion motion leading to the formation of oxygen‐deficient, highly electron‐doped filaments. In this paper, the interface and subinterface region of electroformed and switched metal–insulator–metal structures fabricated from a thin Fe‐doped SrTiO3 (STO) film on n‐conducting Nb‐doped SrTiO3 crystals are investigated by photoemission electron microscopy, transmission electron microscopy, and hard X‐ray photoelectron spectroscopy in order to gain a deeper understanding of cation movement in this specific system. During electroforming, the segregation of Sr to the top interface and the generation of defect‐rich cones in the film are observed, apparently growing from the anode toward the cathode during electroforming. An unusual binding energy component of the Sr 3d emission line is observed which can be assigned to Sr″Ti−VO** defect complexes by performing ab initio calculations. Since this Sr component can be reversibly affected by an external electrical bias, the movement of both oxygen and Sr point defects and the formation of defect complexes Sr″Ti−VO** during resistive switching are suggested. These findings are discussed with regard to the point defect structure of the film and the local oxidation of the donor‐doped substrate. In particular, the apparent dichotomy between the observation of acceptor‐type defects and increased electronic conductivity in STO is addressed. A low binding energy component of the Sr 3d photoemission line is observed in Fe‐doped SrTiO3 memristive devices and assigned to Sr″Ti−VO** defect complexes by ab initio calculations. Since this Sr component can be reversibly affected by an electrical bias, the movement of both oxygen and Sr vacancies and the formation of Sr″Ti−VO** defect complexes during resistive switching are suggested.