17:30 〜 17:45
▲ [22p-E205-14] High-quality sputtered BiFeO3 for ultra-thin epitaxial films
キーワード：Multiferroics, Ultra thin film
BiFeO3 films were grown on SrTiO3 (001) substrates by RF magnetron sputtering. The optimal sputtering conditions for a slightly excess Bi content produced high-quality parameters: an atomically flat surface, low leakage current, high ferroelectric polarization (72 µC/cm2 // [001]pc), and large exchange bias (~140 Oe). In addition to these typical characterizations, we carried out two advanced analyses: (i) The lattice constant was identified by Bragg’s diffraction specific to a space group of R3c using X-ray diffraction; it was precisely determined as an expanded a-axis and a shrunk c-axis. (ii) The ferroelectricity was analyzed by first-order reversal curve (FORC) diagrams, which revealed that ferroelectric switching was packed in the narrow electric field area; an internal electric field in the film body was not observed despite the fact that the BiFeO3 films were as-grown samples. A 3-nm-thick BiFeO3 film with a continuous and flat surface and flat interface was confirmed by STEM observation. The crystal symmetry was identified as a space group of R3c by analyzing nanobeam diffraction patterns. The ferroelectricity was confirmed by the piezoelectric microscopy response owing to low Jc. A 0.4 nm-thick ultra-thin BiFeO3 film was confirmed to be a continuous one-unit cell perovskite layer.