An overview of the state of art in ferroelectric thin films is presented. First, we review applications: microsystems' applications, applications in high frequency electronics, and memories based on ferroelectric materials. The second section deals with materials, structure (domains, in particular), and size effects. Properties of thin films that are important for applications are then addressed: polarization reversal and properties related to the reliability of ferroelectric memories, piezoelectric nonlinearity of ferroelectric films which is relevant to microsystems' applications, and permittivity and loss in ferroelectric films-important in all applications and essential in high frequency devices. In the context of properties we also discuss nanoscale probing of ferroelectrics. Finally, we comment on two important emerging topics: multiferroic materials and ferroelectric one-dimensional nanostructures. (c) 2006 American Institute of Physics.

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Ferroelectric thin films: Review of materials, properties, and applications

Ferroelectric oxide materials have offered a tantalizing potential for applications since the discovery of ferroelectric perovskites more than 50 years ago. Their switchable electric polarization is ideal for use in devices for memory storage and integrated microelectronics, but progress has long been hampered by difficulties in materials processing. Recent breakthroughs in the synthesis of complex oxides have brought the field to an entirely new level, in which complex artificial oxide structures can be realized with an atomic-level precision comparable to that well known for semiconductor heterostructures. Not only can the necessary high-quality ferroelectric films now be grown for new device capabilities, but ferroelectrics can be combined with other functional oxides, such as high-temperature superconductors and magnetic oxides, to create multifunctional materials and devices. Moreover, the shrinking of the relevant lengths to the nanoscale produces new physical phenomena. Real-space characterization and manipulation of the structure and properties at atomic scales involves new kinds of local probes and a key role for first-principles theory.

http://science.sciencemag.org/content/sci/303/5657/488.full.pdf

Ferroelectricity at the Nanoscale: Local Polarization in Oxide Thin Films and Heterostructures

This review paper summarizes recent advances in the quickly developing field of nanoscale ferroelectrics, analyses its current status and considers potential future developments. The paper presents a brief survey of the fabrication methods of ferroelectric nanostructures and investigation of the size effects by means of scanning probe microscopy. One of the focuses of the review will be the study of kinetics of nanoscale ferroelectric switching in inhomogeneous electrical and elastic fields. Another emphasis will be made on tailoring the electrical and mechanical properties of ferroelectrics with a viewpoint of fabrication of nanoscale domain structures.

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Nanoscale ferroelectrics: processing, characterization and future trends

Ferroelectrics and multiferroics have recently emerged as perspective materials for information technology and data storage applications. The combination of extremely narrow domain wall width and the capability to manipulate polarization by electric field opens the pathway toward ultrahigh (>10 TBit inch−2) storage densities and small (sub-10 nm) feature sizes. The coupling between polarization and chemical and transport properties enables applications in ferroelectric lithography and electroresistive devices. The progress in these applications, as well as fundamental studies of polarization dynamics and the role of defects and disorder on domain nucleation and wall motion, requires the capability to probe these effects on the nanometer scale. In this review, we summarize the recent progress in applications of piezoresponse force microscopy (PFM) for imaging, manipulation and spectroscopy of ferroelectric switching processes. We briefly introduce the principles and relevant instrumental aspects of PFM, with special emphasis on resolution and information limits. The local imaging studies of domain dynamics, including local switching and relaxation accessed through imaging experiments and spectroscopic studies of polarization switching, are discussed in detail. Finally, we review the recent progress on understanding and exploiting photochemical processes on ferroelectric surfaces, the role of surface adsorbates, and imaging and switching in liquids. Beyond classical applications, probing local bias-induced transition dynamics by PFM opens the pathway to studies of the influence of a single defect on electrochemical and solid state processes, thus providing model systems for batteries, fuel cells and supercapacitor applications.

https://iopscience.iop.org/article/10.1088/0034-4885/73/5/056502/pdf

Local polarization dynamics in ferroelectric materials

There has been a resurgence of complex oxides of late owing to their ferroelectric and ferromagnetic properties. Although these properties had been recognized decades ago, the renewed interest stems from modern deposition techniques that can produce high quality materials and attractive proposed device concepts. In addition to their use on their own, the interest is building on the use of these materials in a stack also. Ferroelectrics are dielectric materials that have spontaneous polarization in certain temperature range and show nonlinear polarization–electric field dependence called a hysteresis loop. The outstanding properties of the ferroelectrics are due to non-centro-symmetric crystal structure resulting from slight distortion of the cubic perovskite structure. The ferroelectric materials are ferroelastic also in that a change in shape results in a change in the electric polarization (thus electric field) developed in the crystal and vice versa. Therefore they can be used to transform acoustic wav...

Processing, Structure, Properties, and Applications of PZT Thin Films

Nanosized inverted domain dots in ferroelectric materials have potential applications in ultrahigh-density rewritable data storage systems. Here, a data storage system based on scanning nonlinear dielectric microscopy and thin films of ferroelectric single-crystal lithium tantalite is presented. Through domain engineering, nanosized inverted domain dots have been successfully formed at a data density of 1.50 Tbit/in.2.

Tbit/inch2 ferroelectric data storage based on scanning nonlinear dielectric microscopy

Deposition of a hydrothermal method has a number of advantages; low deposition temperature, high-purity, deposition on a three-dimensional structure, and a large thickness. The present paper investigates the improvement of an epitaxial lead zirconate titanate (PZT) thin film deposited via hydrothermal synthesis. The critical parameter contributing to the film morphology was revealed to be the holding position of the reaction solution during deposition. In addition to this improvement, the SrRuO3 bottom electrode was confirmed to be able to withstand high alkali concentrations during the hydrothermal reaction. A hydrothermal synthesis time of 24 h yielded a PZT film with a thickness of 500 nm on SrRuO3/SrTiO3 (100) at 150 °C. The remanent polarization 2Pr and coercive electric field were 38.4 μC/cm2 and 21.8 kV/cm, respectively.

Ferroelectric properties of an epitaxial lead zirconate titanate thin film deposited by a hydrothermal method below the Curie temperature

We report an ultrahigh-density ferroelectric data recording system based on purely electrical principles, using a scanning nonlinear dielectric microscopy technique and ferroelectric thin films of LiTaO3 single crystals. A nano-sized domain dot array of areal density of 1.50Tbit inch−2 has been successfully demonstrated in a z surface of a congruent LiTaO3 single-crystal film. The radius of the domain dots was 10.4 nm. These nano-dots remained stable at least over 24 h, and could be over-written by dots. The ferroelectric domain inversion characteristics using a stoichiometric LiTaO3 single-crystal film was also studied. A very small nano-sized domain dot with a radius of 6 nm was successively formed.

https://iopscience.iop.org/article/10.1088/0957-4484/14/6/314/pdf

Terabit inch−2 ferroelectric data storage using scanning nonlinear dielectric microscopy nanodomain engineering system

Deposition of thin films via hydrothermal method has various advantages: low deposition temperature, high purity, deposition on a three-dimensional structure,and a large thickness Although an epitaxial lead zirconate titanate (PZT) thin-film deposition has been reported, the ferroelectric measurement has not been conducted due to the peel-off morphology of the film The current paper investigates the improvement of an epitaxial PZT thin film deposited via a hydrothermal method By adjusting the position at which the substrate was suspended in the solution, smooth morphology surface was successfully obtained As a bottom electrode, a 200-nm SrRuO3 thin film was deposited on SrTiO3 single crystals, and the PZT thin film was deposited on SrRuO3 The remanent polarization 2Pr and coercive electric field for PZT on SrRuO3/SrTiO3 (001) were 171 μC/cm2 and 36 kV/cm, respectively, and those of PZT on SrRuO3/SrTiO3 (111) were 327 μC/cm2 and 59 kV/cm, respectively The reason for large imprint electrical field, 91 kV/cm and 40 kV/cm for each film, was unclear at this stage, although it is associated with self–alignment poling direction This self–alignment poling direction was confirmed via scanning nonlinear dielectric microscopy and is thought to have been related to the deposition mechanisms

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Ferroelectric property of an epitaxial lead zirconate titanate thin film deposited by a hydrothermal method

Potassium niobate (KNbO 3 ) has large piezoelectric constants. The surface acoustic wave (SAW) substrates with high couplings are very important for wide-band SAW filters and SAW devices. Therefore, the large size KNbO 3 single crystals are required for SAW device applications. In this paper, the techniques of a large size of KNbO 3 using the top seeded solution growth techniques (TSSG) with large size of crucible of 60 mmo platinum are described. The results show that 50x50x 15 mm 3 single crystals are obtained. Also, the poling techniques of KNbO 3 crystal are investigated by using the nonlinear scanning dielectric microscope. The propagation characteristics of SAW and piezoelectric leaky surface waves in KNbO 3 single crystal were investigated theoretically. The results show that the electro-mechanical coupling coefficient of the surface wave propagating along the X-axis of the rotated Y-cut plane is extremely large: K 2 = 0.53, compared to K 2 of 0.055 for LiNbO 3 . The experimental results of the above KNbO 3 substrates agree with the theoretical ones. Also the KNbO 3 substrates showed experimentally the zero temperature coefficients of frequency (TCF) around 20 C.

Yasuo Wagatsuma

Papers

Tbit/inch2 ferroelectric data storage based on scanning nonlinear dielectric microscopy

Ferroelectric properties of an epitaxial lead zirconate titanate thin film deposited by a hydrothermal method below the Curie temperature

Terabit inch−2 ferroelectric data storage using scanning nonlinear dielectric microscopy nanodomain engineering system

Ferroelectric property of an epitaxial lead zirconate titanate thin film deposited by a hydrothermal method

Single crystal growth of KNbO3 and application to surface acoustic wave devices