Microstructural evolution and ferroelectricity in HfO2 films

Abstract

Ferroelectric (FE) materials, which typically adopt the perovskite structure with non-centrosymmetry and exhibit spontaneous polarization, are promising for applications in memory, electromechanical and energy storage devices. However, these advanced applications suffer from the intrinsic limitations of perovskite FEs, including poor complementary metal oxide semiconductor (CMOS) compatibility and environmental issues associated with lead. Hafnium oxide (HfO2), with stable bulk centrosymmetric phases, possesses robust ferroelectricity in nanoscale thin films due to the formation of non-centrosymmetric phases. Owing to its high CMOS compatibility and high scalability, HfO2 has attracted significant attention. In the last decade, significant efforts have been made to explore the origin of the ferroelectricity and factors that influence the FE properties in HfO2 films, particularly regarding the role of microstructure, which is vital in clarifying these issues. Although several comprehensive reviews of HfO2 films have been published, there is currently no review focused on the relationship between microstructure and FE properties. This review focuses on the microstructure-property relationships in FE polycrystalline and epitaxial HfO2 films. The crystallographic structures and characterization methods for HfO2 polymorphs are first discussed. For polycrystalline HfO2 films, the microstructure-FE properties relationships, driving force and kinetic pathway of phase transformations under growth parameters or external stimuli are reviewed. For epitaxial films, the lattice matching relations between HfO2 films and substrates and the corresponding impact on the FE properties are discussed. The FE properties between polycrystalline and epitaxial HfO2 films are compared based on their different microstructural characteristics. Finally, a future perspective is given for further investigating FE HfO2 films.

Fluorite‐Structured Ferroelectric and Antiferroelectric Materials: A Gateway of Miniaturized Electronic Devices

“…Several previous articles have summarized studies on fluorite structured FE and AFE materials, commonly focusing on deposition methods of thin films, [26] epitaxial thin films, [27] energyand memory-related properties, [9,[28][29][30][31][32] and reliability [33][34][35] of fluorite structured materials. In this paper, we will examine and broaden our present understanding of ferroelectricity in hafnium oxide-based films.…”

“…In 2011, FE and antiferroelectric (AFE) properties in HfO 2 -based materials were reported. [7] These fluorite structure materials exhibit several advantages, such as simple binary oxide, lead-free, direct integration on the silicon wafer, ultralow deposition thickness (e.g., ≈10 nm), comparatively low dielectric constant (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40), low leakage current, and compatibility with 3D nanostructures over the conventional FE materials. [8][9][10] The above-mentioned original publication by Böschke et al has led to a renaissance of FE memory concepts and increasing research interest focusing on this topic, as seen by the increasing number of citations of this original paper (Figure 1).…”

Understanding the Effect of Top Electrode on Ferroelectricity in Atomic Layer Deposited Hf0.5Zr0.5O2 Thin Films

“…11 Great effort has been devoted to improving the stability and proportion of the orthorhombic phase, including element doping (Si, Zr, Al, Y, La, etc. ), 12 interface engineering, 13 electrode materials (TiN, W, Mo, Pt, etc. ), 14 and also the annealing process.…”

Improving the Synaptic Behavior with Polar Orthorhombic Phase in Hf0.5Zr0.5O2 Film

“…10–25 nm HZO films were studied and showed that the polarization and the ratio of o-phase decreased with increasing film thickness . This is due to the fact that as the film thickness increases, the surface energy loses its major contribution to the total energy, and the stability of o-phase is compromised . The microstructure also affects the wake-up and fatigue effects of HfO 2 films, the phenomena caused by the movement of oxygen vacancies, the rearrangement of which could be induced by voltage.…”