Thickness dependence of ferroelectricity in HfO₂-based thin film due to the grain size effect

Compared to traditional perovskite ferroelectric materials, HfO₂ has emerged as a prominent research focus due to its ability to retain significant ferroelectricity at the nanoscale. However, systematic studies on its performance in thicker films remain limited, leaving the intrinsic relationship between thickness variation and ferroelectric properties poorly understood. In this work, we successfully fabricated doped HfO₂-based ferroelectric thin films with thicknesses spanning tens to hundreds of nanometers. All these films exhibit robust ferroelectric characteristics, and their ferroelectric properties demonstrate a non-monotonic evolution with increasing thickness. Macroscopic electrical measurements and mesoscale domain switching analysis confirmed that the ferroelectric properties of Ce:HfO₂ films first diminish and then recover with the increase of film thickness. By further characterizing the evolution of microscopic structures, we elucidate the thickness effects on the grain size distribution and domain structure evolution. This framework clarifies the physical mechanism underlying the thickness-dependent ferroelectric behavior. Our findings provide critical experimental evidence for developing large-scale HfO₂-based ferroelectric devices and lay a theoretical foundation for optimizing thick-film ferroelectric materials for practical applications.