Ferroelastic Domain Walls in BiFeO₃ as Memristive Networks

Within the last few years, memristors have aroused much interest in the scientific community due to the tunability of their resistive states.¹ Their hysteretic and non-volatile behaviour has made them attractive for memory applications. Recently, memristors are actively investigated due to their unique advantages as hardware in future neuromorphic computers. This emerging field comprises novel electronic circuits inspired by the human brain, motivated by its strikingly low energy consumption, high efficiency of cognitive tasks, such as image or pattern recognition, and the ability of the brain to reconfigure nervous connections, also called neuronal plasticity.² Prominent candidates for materials enabling neuromorphic computing on a hardware-level are ferroics,³ in particular transition-metal oxides. A pervasive feature of ferroic material is the occurrence of domain walls (DWs) separating domains, which have different orientation of the order parameter (electric polarization in the case of ferroelectrics). Ferroelectrics have been already successfully employed for memristive devices such as ferroelectric tunnel junctions.⁴ At the same time, ferroic materials paved the way for the large class of DW-based nanodevices, which can exhibit high reconfigurability as DWs can be easily written and erased.⁵ Extensive works on the multiferroic oxide bismuth ferrite (BiFeO₃) have shown that DWs in thin films can be more conducting than the domains.⁶ During thin film growth, BiFeO₃ self-assembles into a nanoscale network of conducting domain walls,⁷ which can be tailored by varying the growth parameters. After growth, the electrical or even memristive properties⁸ of the DWs can be potentially manipulated by driving electrical current through the DW network using electrodes on the film. Previous works on self-assembled BiFeO₃ DWs mainly focus on “vertical” (out-of-plane) DW conduction,^8,9 while the few reports on “lateral” (in-plane) conduction investigate single domain wall conduction.¹⁰ In this work, lateral conduction (from wall to wall) through the self-assembled BiFeO₃ DW network is presented. The network is characterized using scanning probe techniques allowing local DW probing to investigate the memristive properties and mapping of the conductive DW network. The electrical response of the DW network is further studied by applying electrical stimuli to top electrode arrays. This project is part of the EU-funded <i>Innovative Training Network MANIC</i> (“<i>Materials for neuromorphic circuits</i>”) and is embedded in the neuromorphic research initiative <i>Cognigron</i> of the University of Groningen to enable interdisciplinary cooperation from material science, mathematics and artificial intelligence.<br/>¹ D.B. Strukov, G.S. Snider, D.R. Stewart, and R.S. Williams, Nature <b>453</b>, 80 (2008).<br/>² D. Markovic, A. Mizrahi, D. Querlioz, and J. Grollier, (2020).<br/>³ C. Wang, A. Agrawal, E. Yu, and K. Roy, Front. Neurosci. <b>15</b>, 1 (2021).<br/>⁴ A. Chanthbouala, V. Garcia, R.O. Cherifi, K. Bouzehouane, S. Fusil, X. Moya, S. Xavier, H. Yamada, C. Deranlot, N.D. Mathur, M. Bibes, A. Barthélémy, and J. Grollier, Nat. Mater. <b>11</b>, 860 (2012).<br/>⁵ G. Catalan, J. Seidel, R. Ramesh, and J.F. Scott, Rev. Mod. Phys. <b>84</b>, 119 (2012).<br/>⁶ J. Seidel, L.W. Martin, Q. He, Q. Zhan, Y.H. Chu, A. Rother, M.E. Hawkridge, P. Maksymovych, P. Yu, M. Gajek, N. Balke, S. V. Kalinin, S. Gemming, F. Wang, G. Catalan, J.F. Scott, N.A. Spaldin, J. Orenstein, and R. Ramesh, Nat. Mater. <b>8</b>, 229 (2009).<br/>⁷ S. Farokhipoor and B. Noheda, Phys. Rev. Lett. <b>107</b>, (2011).<br/>⁸ P. Maksymovych, J. Seidel, Y.H. Chu, P. Wu, A.P. Baddorf, L.Q. Chen, S. V. Kalinin, and R. Ramesh, Nano Lett. <b>11</b>, 1906 (2011).<br/>⁹ I. Stolichnov, M. Iwanowska, E. Colla, B. Ziegler, I. Gaponenko, P. Paruch, M. Huijben, G. Rijnders, and N. Setter, Appl. Phys. Lett. <b>104</b>, 1 (2014).<br/>¹⁰ J. Jiang, Z.L. Bai, Z.H. Chen, L. He, D.W. Zhang, Q.H. Zhang, J.A. Shi, M.H. Park, J.F. Scott, C.S. Hwang, and A.Q. Jiang, Nat. Mater. <b>17</b>, 49 (2018).