Bipolar Electric-Field Enhanced Trapping and Detrapping of Mobile Donors in BiFeO 3 Memristors Tiangui You,* ,† Nan Du, † Stefan Slesazeck, ‡ Thomas Mikolajick, ‡,§ Guodong Li, ∥ Danilo Bü rger, † Ilona Skorupa, ⊥ Hartmut Stö cker, # Barbara Abendroth, # Andreas Beyer, △ Kerstin Volz, △ Oliver G. Schmidt, †,∥ and Heidemarie Schmidt* ,† † Material Systems for Nanoelectronics, Technische Universitä t Chemnitz, Chemnitz 09126, Germany ‡ NaMLab gGmbH, Dresden 01187, Germany § Institute of Semiconductors and Microsystems, Technische Universitä t Dresden, Dresden 01187, Germany ∥ Institute for Integrative Nanosciences, IFW Dresden, Dresden 01069, Germany ⊥ HZDR Innovation GmbH, Dresden 01328, Germany # Institut fü r Experimentelle Physik, Technische Universitä t Bergakademie Freiberg, 09596 Freiberg, Germany △ Materials Science Center and Faculty of Physics, Philipps-Universitä t Marburg, Marburg 35032, Germany * S Supporting Information ABSTRACT: Pulsed laser deposited Au-BFO-Pt/Ti/Sapphire MIM structures offer excellent bipolar resistive switching performance, including electroforming free, long retention time at 358 K, and highly stable endurance. Here we develop a model on modifiable Schottky barrier heights and elucidate the physical origin underlying resistive switching in BiFeO 3 memristors containing mobile oxygen vacancies. Increased switching speed is possible by applying a large amplitude writing pulse as the resistive switching is tunable by both the amplitude and length of the writing pulse. The local resistive switching has been investigated by conductive atomic force microscopy and exhibits the capability of down-scaling the resistive switching cell to the grain size. KEYWORDS: bipolar resistive switching, mobile oxygen vacancy, modifiable rectification properties, Ti diffusion, reliability, BiFeO 3 thin films 1. INTRODUCTION As the conventional semiconductor memory technologies are expected to approach their physical limits in the near future, nonvolatile memories with high-density, high-speed, and low- power that can replace flash memories and dynamic random access memories (DRAM) are required. 1,2 Reversible resistive switching devices, known as “ReRAM” or “Memristors”, are considered as one of the most promising candidates for the next generation of highly scalable nonvolatile memories. 3,4 Additionally, these simple structures consisting only of a metal−semiconductor (or insulator)−metal sandwich stack (MIM) have the potential to be used in reconfigurable nonvolatile logics, 2,5,6 cognitive computing 7,8 and data encryption. 9 Resistive switching characteristics with different switching behaviors, including bipolar resistive switching, 2,4−6 and unipolar resistive switching, 10,11 have been investigated in many materials, e.g., binary transition metal oxides, 2,4−6,10,11 ternary and multicomponent perovskite-type oxides, 12,13 and some other materials. 5,14 A number of chemical and physical models have also been proposed to explain the resistive switching behaviors, including formation and rupture of nanoscale conduction paths within insulator layers by either thermochemical processes or valence change, 3,5,11 modification of the Schottky barrier height 12,13,15,16 and electron trapping/ detrapping. 17 It is possible that several different mechanisms may coexist, and different mechanisms could be dominant in different material systems. BiFeO 3 (BFO) is a well-known multiferroic material and has attracted considerable attention because of its fascinating physical properties, e.g., its photovoltaic effect, 16,18 which offers the potential to develop radical new concepts for resistive switching devices. In recent years, the resistive switching behavior has been also observed in BFO thin films in MIM structures. 12,16,19−25 Most of the observed resistive switching behavior is attributed to the switching of ferroelectric polarization 12,19−22 or the migration of oxygen vacancies 16,23−25 under applied electric field. However, the ferroelectric polarization fatigue would limit the endurance 12,22 and the Received: July 23, 2014 Accepted: November 4, 2014 Published: November 4, 2014 Research Article www.acsami.org © 2014 American Chemical Society 19758 dx.doi.org/10.1021/am504871g | ACS Appl. Mater. Interfaces 2014, 6, 19758−19765