Enhanced conducting domain wall operation by thickness mitigated depolarization and imprint effects

BiFeO3 thin films with thicknesses from 60 to 200 nm are grown on SrTiO3 (100) substrates showing identical single out-of-plane and 180° in-plane domains. Clear differences in the retention characteristics of conducting domain walls in films of different thicknesses are observed by piezoelectric force microscopy and conducting atomic force microscopy. The ferroelectric hysteresis loops reveal that their dependence on film thicknesses is driven by the depolarization impact from a 1 nm interfacial layer at the surfaces. The imprint effect due to different concentrations of Fe2+ ions and oxygen vacancies is mitigated in thicker films. The operation window—the gap between the onset voltage Von and the coercive voltage Vc—of the conducting domain walls increases from 1 V in 60 nm to 2 V in 200 nm. The expanded operation windows and improved retention characteristics of conducting domain walls by thickness engineering have practical implications for nonvolatile memory application.