Giant electroresistance effect in single-crystalline lithium niobate thin films enabled by domain wall control

One of the most prominent features of ferroelectric domain walls (DWs) is their electrical conductivity, which was observed in a number of materials, such as BiFeO₃, Pb(Zr,Ti)O₃, ErMnO₃. We combine scanning transmission electron microscopy (STEM) and local probe techniques to investigate the conduction through charged DWs in the ion-sliced single-crystalline LiNbO₃ thin films with sub-µm thickness. STEM shows large inclination of the electrically-generated 180° DWs away from the polar z-axis (with angles reaching 16°) suggesting the DWs are strongly charged. Using piezoresponse force microscopy (PFM) in combination with conductive atomic force microscopy (CAFM) it was shown that head-to-head DWs have higher conductivity than the tail-to-tail DWs, suggesting an electronic type of conductance. One of the most important findings is a modulation of conductivity by an external voltage. It is demonstrated that the resistance of the LiNbO₃ thin film capacitors can be changed continuously by 5 to 9 orders of magnitude by controlling the DW perimeter allowing development of multi-level resistive switching devices. Resistance states can be altered by exposure to cumulative voltage pulses, suggesting that these domain wall memristors might be useful in the context of artificial synapses.