Effect of annealing atmosphere on the microstructure and properties of Hf-doped BiFeO3 thin films

Abstract

BiFe_1−XHf_XO₃ (X = 1.2 mol%, abbreviated as BFHO) thin films were deposited on ITO/glass substrates using the sol–gel method and subsequently post-annealed in O₂, air, and N₂ atmospheres, respectively. This study systematically investigates the effects of different annealing atmospheres on the microstructure, defect chemistry, and electrical properties of BFHO thin films, with particular emphasis on the correlations among oxygen vacancy concentration, ferroelectric behavior, leakage current characteristics, conduction mechanisms, dielectric properties, and aging behavior. The results demonstrate that films annealed in an O₂ atmosphere exhibit the best crystallinity and most well-developed grain morphology, along with the lowest concentrations of Fe²⁺ ions and oxygen vacancies. Owing to the effective suppression of defects, the O₂-annealed films show significantly enhanced ferroelectric performance and the lowest leakage current density. Leakage current analysis reveals that Fowler–Nordheim (F–N) tunneling is the dominant conduction mechanism. Furthermore, a theoretical aging model based on the volumetric effect is developed to provide insight into the physical mechanism underlying the aging behavior of BFHO thin films. Compared to films annealed in air and nitrogen, the oxygen-annealed films exhibit the smallest degree of aging and demonstrate excellent electrical stability.