Ferroelectric conductive domain walls (DWs), which are 2D-interface channels between insulating domains are drawing a lot of interest, because their potential for artificial synaptic elements in future neuromorphic circuits. Since the discovery of conductivity associated with DWs [1], researchers aim to utilize these new functionalities in nanoelectronic devices. Because of intrinsic memristive properties found in conductive DWs [2] together with the ability to reconfigure these channels by external stimuli [3], novel elements with so called plasticity-properties are envisioned. Despite huge efforts in recent years, the control and engineering [4] of the functional properties of the DWs remains difficult. Especially the measured conductivity at single and stable neutral DWs is typically too low (usually in the picoampere-range [5]) for real-world applications. So called charged DWs present an interesting alternative offering higher current values [6], but are typically less stable or require an extensive poling procedure.

In this work the ubiquitous ferroelectric material Pb(Zr,Ti)O₃ (PZT) is used, which is epitaxially grown onto a DyScO₃ substrate together with a SrRuO₃ bottom electrode. Surprisingly, high conductivity (up to tens of nanoamperes) was observed in nominally neutral and therefore highly stable 180°-DWs formed by standard poling procedures. The nature of the huge conduction is assumed to originate from an interplay between the artificially created 180°- and pristine 90°-DWs due to carefully introduced strain conditions. For the memristive devices, micrometer-size graphene top electrodes were transferred onto the PZT to form vertical capacitor structures. It was possible to inject/remove the highly conductive DWs inside the capacitor to create low-/high-resistive states with on/off ratios of up to 3 orders of magnitude. By slightly changing the mixed-domain configuration under the graphene electrode due to electrical stimuli, the amount, shape and conductance of the injected DWs can be manipulated leading to multi-resistive accessible states. Read-out currents of several hundreds of nA were reached for voltage biases <2V and retention as well as endurance tests of the memristive devices were performed. The transport and electrical characteristics are obtained using a scanning probe microscope, which was also used to map and reveal the conductive domain walls as well as the mixed-domain state inside the memristors.