Publication date: 23rd February 2022
Bismuth ferrite (BFO) is one of the most promising multiferroic materials, with interest for its usage in energy-efficient memory storage devices. In BFO thin films, the formation of domains with different orientations of the electric polarisation results in the emergence of domain walls that have different properties than the host material. While the host material is ferroelectric and insulating, the as-grown thin films are pervaded by conductive domain walls [1],[2].
These thin films penetrated by domain walls, could enable novel nanometer-sized devices based on resistive switching [3]. The formation of domain walls depends on many different factors, such as doping with foreign elements. By controlling the formation of domain walls and the current flow through them, the domain wall networks have the possibility to be used as an artificial neuromorphic network [4],[5].
In this project the influence of Calcium doping on the domain wall formation and conductivity of BFO thin films is investigated. Since Ca2+ ions have one positive charge less than the replaced Bi3+ ions, introducing Ca into the crystal structure will cause positively-charged defects, like oxygen vacancies, in order to maintain charge neutrality [6]. Piezo force microscopy images reveal an increased number of domain walls compared to pristine BFO thin films, leading to closed-meshed domain wall networks.
Ca-doped BFO thin films were grown using pulsed laser deposition on SrTiO3 substrates with and without a SrRuO3 bottom electrode. The domain walls were investigated with piezo force microscopy (PFM) and conductive atomic force microscopy (cAFM). The properties of the crossed-linked network of domain walls, which display hysteretic IV-curves, are presented.
This project is part of the EU-funded Innovative Training Network MANIC (“Materials for neuromorphic circuits”). We also like to acknowledge the financial support of the CogniGron research center and the Ubbo Emmius Funds (Univ. of Groningen).
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