Electrode Dependence of Local Electrical Properties of Chemical-Solution-Deposition-Derived BiFeO₃ Thin Films

The nanoscale electrical properties of chemical-solution-deposition (CSD)-derived BiFeO3 grown on pulsed-laser-ablated La0.67Sr0.33MnO3//SrTiO3 (001) thin film heterostructures are investigated using a host of scanning probe microscopy techniques, including electrostatic force microscopy (EFM), scanning Kelvin probe microscopy (SKPM), piezoresponse force microscopy (PFM), and conductive AFM (CAFM). EFM and SKPM confirm the p-type nature of the CSD-derived BFO thin films as well as charge accumulation at the film surface after electrical bias. For BiFeO3 films of a fixed thickness (∼35 nm), the local current–voltage (I–V) behavior obtained by CAFM is strongly dependent on the La0.67Sr0.33MnO3 bottom electrode thickness. BiFeO3 films on a 20 nm thick La0.67Sr0.33MnO3 demonstrate the typical switchable diode behavior governed by polarization orientation. However, when the thickness of La0.67Sr0.33MnO3 is reduced to less than 5 nm, the BiFeO3 films show only forward diode behaviors regardless of polarization orientation, when the applied bias is up to ±4 V. Higher sweep bias (i.e., ± 8 V) breaks down the diode, following which the BiFeO3 film shows strong resistive switching. The interface band structure for the ultrathin LSMO case, which is very sensitive to accumulation/depletion of carriers at the BFO–LSMO interface, is suggested as the trigger for this resistive switching.