This review covers important advances in recent years in the physics of thin-film ferroelectric oxides, the strongest emphasis being on those aspects particular to ferroelectrics in thin-film form. The authors introduce the current state of development in the application of ferroelectric thin films for electronic devices and discuss the physics relevant for the performance and failure of these devices. Following this the review covers the enormous progress that has been made in the first-principles computational approach to understanding ferroelectrics. The authors then discuss in detail the important role that strain plays in determining the properties of epitaxial thin ferroelectric films. Finally, this review ends with a look at the emerging possibilities for nanoscale ferroelectrics, with particular emphasis on ferroelectrics in nonconventional nanoscale geometries.

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Physics of thin-film ferroelectric oxides

Nanocomposites, a high performance material exhibit unusual property combinations and unique design possibilities. With an estimated annual growth rate of about 25% and fastest demand to be in engineering plastics and elastomers, their potential is so striking that they are useful in several areas ranging from packaging to biomedical applications. In this unified overview the three types of matrix nanocomposites are presented underlining the need for these materials, their processing methods and some recent results on structure, properties and potential applications, perspectives including need for such materials in future space mission and other interesting applications together with market and safety aspects. Possible uses of natural materials such as clay based minerals, chrysotile and lignocellulosic fibers are highlighted. Being environmentally friendly, applications of nanocomposites offer new technology and business opportunities for several sectors of the aerospace, automotive, electronics and biotechnology industries.

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Nanocomposites: synthesis, structure, properties and new application opportunities

We present a comprehensive review of the material properties of cadmium zinc telluride (CZT, Cd1ˇxZnxTe) with zinc content xa 0:1‐0.2. Particular emphasis is placed on those aspects of this material related to room temperature nuclear detectors. A review of the structural properties, charge transport, and contacting issues and how these are related to detector and spectrometer performance is presented. A comprehensive literature survey and bibliography are also included. # 2001 Elsevier Science B.V. All rights reserved.

Cadmium zinc telluride and its use as a nuclear radiation detector material

The demand for dielectric capacitors with higher energy-storage capability is increasing for power electronic devices due to the rapid development of electronic industry. Existing dielectrics for high-energy-storage capacitors and potential new capacitor technologies are reviewed toward realizing these goals. Various dielectric materials with desirable permittivity and dielectric breakdown strength potentially meeting the device requirements are discussed. However, some significant limitations for current dielectrics can be ascribed to their low permittivity, low breakdown strength, and high hysteresis loss, which will decrease their energy density and efficiency. Thus, the implementation of dielectric materials for high-energy-density applications requires the comprehensive understanding of both the materials design and processing. The optimization of high-energy-storage dielectrics will have far-reaching impacts on the sustainable energy and will be an important research topic in the near future.

Homogeneous/Inhomogeneous-Structured Dielectrics and their Energy-Storage Performances.

Bulk ferroelectrics undergo structural phase transformations at low temperatures, giving multi-stable (that is, multiple-minimum) degenerate states with spontaneous polarization. Accessing these states by applying, and varying the direction of, an external electric field is a key principle for the operation of devices such as non-volatile ferroelectric random access memories (NFERAMs). Compared with bulk ferroelectrics, low-dimensional finite ferroelectric structures promise to increase the storage density of NFERAMs 10,000-fold. But this anticipated benefit hinges on whether phase transitions and multi-stable states still exist in low-dimensional structures. Previous studies have suggested that phase transitions are impossible in one-dimensional systems, and become increasingly less likely as dimensionality further decreases. Here we perform ab initio studies of ferroelectric nanoscale disks and rods of technologically important Pb(Zr,Ti)O3 solid solutions, and demonstrate the existence of previously unknown phase transitions in zero-dimensional ferroelectric nanoparticles. The minimum diameter of the disks that display low-temperature structural bistability is determined to be 3.2 nm, enabling an ultimate NFERAM density of 60 x 10(12) bits per square inch-that is, five orders of magnitude larger than those currently available. Our results suggest an innovative use of ferroelectric nanostructures for data storage, and are of fundamental value for the theory of phase transition in systems of low dimensionality.

Unusual phase transitions in ferroelectric nanodisks and nanorods

Sol-gel TiO2 films on silicon substrates

The effect of two factors having the most important influence on spin coating process of sol-gel films: the spin speed and the temperature (of the substrate and the applied solution) during film deposition is discussed. It is shown, that film thickness and thickness uniformity are determined by centrifugal driving force dynamics, viscous polymer rheology, solvent evaporation dynamics, and film porous microstructure.

Spin coating process of sol-gel silicate films deposition: Effect of spin speed and processing temperature

The paper presents short review of the works performed during the last few years in the field of the alkoxy-derived ferroelectric films. PZT films were prepared using titanium and zirconium alkoxides and Pb(CH3COO)2· 2H2O as precursors. Different way of lead acetate dehydration and the impact of lead excess in the precursor solutions on the properties of the PZT films are discussed. Trimetallic alkoxide systems Bi(OR)3-Ta(OR)5-ROH (R = Me, Et or i Pr) were studied as precursors for preparation of SrBi2Ta2O9 films. Films prepared from these solutions and annealed at the temperature between 700 and 750°C demonstrated the remanent polarization Pr* − P^r = 7–9 μC/cm2. Ba1-xSrxTiO3 films we applied from modified alkoxide solutions. Decomposition of the organic phase in the course of thermal treatment of the films is studied by IR-spectroscopy. The dependence of the dielectric permittivity of the films via the annealing temperature is reported. Preparation of LiNbO3, SrZr0.2Ti0.8O3, Zr0.8Sn0.2TiO4 is briefly discussed.

Sol-Gel Derived Ferroelectric Thin Films: Avenues for Control of Microstructural and Electric Properties

Polycrystalline Pb(Zr0.48Ti0.52)O3 thin films with the thickness of 0.2 μm on Pt-coated silicon substrates have been prepared by sol-gel process using electrochemically prepared titanium and zirconium solutions in methoxyethanol. Structure, morphology, and electrical properties of the films annealed by usual isothermal annealing for 1 hour and by rapid thermal annealing (RTA) for 1 minute have been studied. In contrast to isothermal annealing RTA results in highly oriented (100) films. This leads to higher dielectric constant (more than twice) of RTA annealed films, but no correlation between degree of orientation and polarization have been observed. Special attention has been paid to capacitance-voltage (CV) characteristics. Some parameters and simple models were introduced for the interpretation of CV data. Thus asymmetry of CV curves indicates that for the films prepared by RTA there exists a problem of disturbed layer formation at the Pt-PZT interface.

Effect of annealing conditions on alkoxy-derived PZT thin films. Microstructural and CV study

The current status of developments in the field of ferroelectric memory devices has been considered. The rapidly growing market of non-volatile memory devices has been analyzed, and the current state of the art and prospects for the scaling of parameters of non-volatile memory devices of different types have been considered. The basic constructive and technological solutions in the field of the design of ferroelectric memory devices, as well as the “roadmaps” of the development of this technology, have been discussed.

K. A. Vorotilov

Papers

Sol-gel TiO2 films on silicon substrates

Spin coating process of sol-gel silicate films deposition: Effect of spin speed and processing temperature

Sol-Gel Derived Ferroelectric Thin Films: Avenues for Control of Microstructural and Electric Properties

Effect of annealing conditions on alkoxy-derived PZT thin films. Microstructural and CV study

Ferroelectric memory