Ferroelectric thin films: Review of materials, properties, and applications (original) (raw)
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Advanced Materials, 2022
non-centrosymmetric structures which can possess a spontaneous electric polarization which can be controlled using applied electric fields (Figure 1). Ferroelectrics themselves are inherently hierarchical materials-wherein picometer ionic displacements give rise to polarization which can collectively extend over millimeters or self-organize into complex mesoscopic structures or collectively reorient under applied stimuli (e.g., electric fields, temperature, or stress). Understanding these complex behaviors necessitates a multilevel approach, wherein atomistic, microscopic, mesoscopic, and macroscopic properties are studied in concert. Parallel advances in synthesis, characterization, and simulation have enabled such multimodal studies and provided a methodology through which a multitude of ferroelectric functionalities can now be achieved and studied. The promise of utilizing these functionalities in a number of applications kick-started the modern era of ferroelectric research in the mid-20th century. [1] Looking further back, in the 1920s, the ability to switch the polarization of sodium potassium tartrate tetrahydrate (commonly known as Rochelle salt) was first observed, along with dielectric and piezoelectric anomalies near the ferroelectric transition-now called the Curie point. In the 1940s, as part of the accelerated research push associated with World War II, ferroelectric BaTiO 3 was discovered by accident. When modifying TiO 2 with BaO to enhance its dielectric properties, a record-high dielectric permittivity was discovered and subsequent studies demonstrated a hysteretic switchable polarization. This discovery ushered in a new understanding of ferroelectricity as more than a rare phenomenon associated with salts that contained hydrogen bonding, but rather as a phenomenon that could exist in simple oxides like perovskites. Over the subsequent decades, the number of ferroelectric compositions exploded, particularly within the perovskite oxides, introducing new chemistries including LiNbO 3 and the PbZr x Ti 1−x O 3 system. Meanwhile, theoretical descriptions of ferroelectricity were advanced through lattice-dynamical models invoking a soft-mode optical phonon. Studies of the piezoelectric, thermodynamic, and optical properties in ferroelectric ceramics allowed for their deployment in a number of applications including piezoelectric sensors and pyroelectric infrared detectors. By the 1960s, increased interest in using ferroelectric polarization for nonvolatile memory was driving research into Over the last 30 years, the study of ferroelectric oxides has been revolutionized by the implementation of epitaxial-thin-film-based studies, which have driven many advances in the understanding of ferroelectric physics and the realization of novel polar structures and functionalities. New questions have motivated the development of advanced synthesis, characterization, and simulations of epitaxial thin films and, in turn, have provided new insights and applications across the micro-, meso-, and macroscopic length scales. This review traces the evolution of ferroelectric thin-film research through the early days developing understanding of the roles of size and strain on ferroelectrics to the present day, where such understanding is used to create complex hierarchical domain structures, novel polar topologies, and controlled chemical and defect profiles. The extension of epitaxial techniques, coupled with advances in high-throughput simulations, now stands to accelerate the discovery and study of new ferroelectric materials. Coming hand-in-hand with these new materials is new understanding and control of ferroelectric functionalities. Today, researchers are actively working to apply these lessons in a number of applications, including novel memory and logic architectures, as well as a host of energy conversion devices. Hall of Fame
Ferroelectric films and devices
Current Opinion in Solid State and Materials Science, 1999
Recent developments in ferroelectric films have been made in terms of their application in nonvolatile memories and dynamic random access memories. One highlight is the report of a complete description of the temperature-dependent dielectric behavior of (Ba, Sr)TiO 3 films as a function of strain, composition, and thickness. For the first time, a direct link has been made between the thin film and bulk electrical properties.
Review on Ferroelectric Thin Film Devices: Fundamental Aspects and Integration Challenges
This review on perovskite (ABO3) materials focuses primarily on ferroelectric films used in devices for charge storage such as Pb(Zr, Ti)O3 (PZT) for non-volatile ferroelectric random access memory (FeRAM) and high dielectric constant materials containing (Ba, Sr)TiO3 (BST), but it also emphasizes general principles on the integration of electroceramics in devices and microelectro mechanical systems (MEMS). The number of papers reported in the literature on ferroelectrics has expanded greatly in the past 20 years, but classical reliability problems in ferroelectric devices remain. Greater emphasis is needed on understanding key mechanisms which result in degradation of ferroelectric materials’ electrical characteristics in devices over time and with usage particularly between the ferroelectric film and electrode interface. In addition, better quantification of numerical measures of thin films are needed in order to more closely relate the process conditions to the materials characteristics and the resultant electrical properties. Furthermore, materials reliability and analysis of complex systems is a topic that needs further consideration when researching/working with ferroelectric devices. Finally, problems with materials reliability in ferroelectric devices are in need of further detailed investigation by researching and understanding the mechanisms which are the root causes of ferroelectric polarization losses in actual devices.
Nano-Ferroelectric Materials and Devices
Ferroelectrics, 2006
A summary is presented of recent developments in ferroelectric nanotubes, nanowires and nanodots, their electrical characterization and related theories of their structures, including the possibility of toroidal ordering. Also summarized is recent work on ultra-thin single crystals and a status report on thin films, particularly in [3D] configurations for DRAM or FRAM trenched capacitors.
Materials Science & Engineering R-reports, 2001
We present in this article a review of the status of thin film ferroelectric materials for nonvolatile memories. Key materials issues relevant to the integration of these materials on Si wafers are discussed. The effect of film microstructure and electrode defect chemistry on the ferroelectric properties relevant to a high density nonvolatile memory technology are discussed. The second part of this review focuses on approaches to integrate these capacitor structures on a filled poly-Si plug which is a critical requirement for a high density memory technology. Finally, the use of novel surface probes to study and understand broadband polarization dynamics in ferroelectric thin films is also presented. # 2001 Published by Elsevier Science B.V.
Physical Review Letters, 2008
Using calculations from first principles and the concept of layer polarization, we have elucidated the nanoscale organization and local polarization in ferroelectric thin films between metallic contacts. The profile of the local polarization for different film thicknesses unveils a peculiar spatial pattern of atomic layers with uncompensated dipoles in what was originally thought to be a ferroelectric domain. This effectively ferrielectric behavior is induced by the dominant roles of the interfaces at such reduced dimensionality and can be interpreted using a simple classical model where the latter are explicitly taken into account.