Overcoming Size Effects in Ferroelectric Thin Films

Abstract

Ferroelectric thin films have recently received unprecedented attention due to the need to miniaturize electronic circuit devices. Synthesis and deposition processes along with theoretical calculations are improved remarkably to realize stable ferroelectric thin films up to nanometer thickness. However, even with technological advances, it is still difficult to overcome the size effect of ferroelectrics, so research is being conducted to achieve stable ferroelectricity in unit‐cell thicknesses thinner than the typical critical thicknesses. In this review, the size effects in ferroelectric thin films are described, and their importance and fundamental limitations are discussed. First, intrinsic and extrinsic factors affecting ferroelectricity are introduced based on the theoretical background of the size effects in ferroelectricity. Then, on understanding the size effects by considering complex interacting factors, the recent works showing ferroelectricity below the commonly known critical thicknesses in perovskite, fluorite oxides, and two‐dimensional (2D) ferroelectrics are introduced. Finally, the results of research efforts in scaling ferroelectric thin films with a future perspective are summarized.

Ferroelectric tunnel junctions: promise, achievements and challenges

“…Mass production through conventional CMOS processes is crucial for commercial viability, but the deposition of perovskite oxide is restricted to a few materials. Moreover, the critical thickness of perovskite oxide poses challenges for its utilization in FTJs, as ferroelectric films, typically required to be less than 10 nm thick in FTJs, often exhibit a size effect leading to the disappearance of ferroelectricity [283].…”

Thickness-Dependent Ferroelectricity in Freestanding Hf0.5Zr0.5O2 Membranes

“…It is clear to see that ferroelectricity is highly related to the fraction of o-phase. Additionally, the suppression of ferroelectricity with the increasing thickness of the HZO thin film, which is abnormal to classical ferroelectric material systems, is unveiled as well. We further observed an increase in X-ray linear dichroism (XLD) intensity with the rise in thickness, which is attributed to the large structure anisotropy contributed by the m-phase.…”

High-Performance Ferroelectric Thin Film Transistors with Large Memory Window Using Epitaxial Yttrium-Doped Hafnium Zirconium Gate Oxide

“…Since the observation of ferroelectric behavior in Si-doped HfO 2 films at NaMLab in 2011, the utilization of doped HfO 2 thin films as ferroelectric materials has been extensively studied. Among the diverse dopants introduced into HfO 2 , when Zr is doped at a 1:1 atomic ratio with Hf, resulting in the compound Hf 0.5 Zr 0.5 O 2 (HZO), the HZO adopts a fluorite structure and retains its ferroelectricity even at the nanoscale. , The ferroelectricity in HZO is attributed to its orthorhombic phase, characterized by an asymmetric crystal structure. Due to its high dielectric constant and compatibility with CMOS technology, HZO has been employed in devices designed for memory operations.…”