Ferroelectricity

About: Ferroelectricity is a research topic. Over the lifetime, 47111 publications have been published within this topic receiving 1008145 citations.

Fatigue-free ferroelectric capacitors with platinum electrodes

Abstract: A SIGNIFICANT fraction of the computer memory industry is at present involved in the manufacture of non-volatile memory devices1—that is, devices which retain information when power is interrupted. For such applications (and also for volatile memories), the use of capacitors constructed from ferroelectric thin films has stimulated much interest1. In such structures, information is stored in the polarization state of the ferroelectric material itself, which should in principle lead to lower power requirements, faster access time and potentially lower cost1. But the use of ferroelectrics is not without problems; the memories constructed to date have generally suffered from poor retention of stored information and degradation of performance ('fatigue') with use1–3. Here we describe the preparation and characterization of thin-film capacitors using ferroelectric materials from a large family of layered perovskite oxides, exemplified by SrBi2Ta2O9, SrBi2NbTaO9 and SrBi4Ta4O15. The structural flexibility of these materials allows their properties to be tailored so that many of the problems associated with previous ferroelectric memories are avoided. In particular, our capacitors do not show significant fatigue after 1012 switching cycles, and they exhibit good retention characteristics and low leakage currents even with films less than 100 nm thick.

Submicrosecond bistable electro‐optic switching in liquid crystals

Abstract: Ferroelectric smectic C (FSC) liquid crystals are used in a simple new geometry that allows the spontaneous formation of either of two surface‐stabilized smectic C monodomains of opposite ferroelectric polarization. These domains are separated by well‐defined walls which may be manipulated with an applied electric field. The resulting electro‐optic effects exhibit a unique combination of properties: microsecond dynamics, threshold behavior, symmetric bistability, and a large electro‐optic response.

Large Piezoelectric Effect in Pb-Free Ceramics

Abstract: We report a non-Pb piezoelectric ceramic system Ba(Ti(0.8)Zr(0.2))O(3)-(Ba(0.7)Ca(0.3))TiO(3) which shows a surprisingly high piezoelectric coefficient of d(33) approximately 620 pC/N at optimal composition. Its phase diagram shows a morphotropic phase boundary (MPB) starting from a tricritical triple point of a cubic paraelectric phase (C), ferroelectric rhombohedral (R), and tetragonal (T) phases. The high piezoelectricity of the MPB compositions stems from the composition proximity of the MPB to the tricritical triple point, which leads to a nearly vanishing polarization anisotropy and thus facilitates polarization rotation between 001T and 111R states. We predict that the single-crystal form of the MPB composition of the present system may reach a giant d(33) = 1500-2000 pC/N. Our work may provide a new recipe for designing highly piezoelectric materials (both Pb-free and Pb-containing) by searching MPBs starting from a TCP.

Lanthanum-substituted bismuth titanate for use in non-volatile memories

Abstract: Non-volatile memory devices are so named because they retain information when power is interrupted; thus they are important computer components. In this context, there has been considerable recent interest1,2 in developing non-volatile memories that use ferroelectric thin films—‘ferroelectric random access memories’, or FRAMs—in which information is stored in the polarization state of the ferroelectric material. To realize a practical FRAM, the thin films should satisfy the following criteria: compatibility with existing dynamic random access memory technologies, large remnant polarization (Pr) and reliable polarization-cycling characteristics. Early work focused on lead zirconate titanate (PZT) but, when films of this material were grown on metal electrodes, they generally suffered from a reduction of Pr (‘fatigue’) with polarity switching. Strontium bismuth tantalate (SBT) and related oxides have been proposed to overcome the fatigue problem3, but such materials have other shortcomings, such as a high deposition temperature. Here we show that lanthanum-substituted bismuth titanate thin films provide a promising alternative for FRAM applications. The films are fatigue-free on metal electrodes, they can be deposited at temperatures of ∼650 °C and their values of Pr are larger than those of the SBT films.

Multiferroic BaTiO3-CoFe2O4 Nanostructures.

Abstract: We report on the coupling between ferroelectric and magnetic order parameters in a nanostructured BaTiO3-CoFe2O4 ferroelectromagnet. This facilitates the interconversion of energies stored in electric and magnetic fields and plays an important role in many devices, including transducers, field sensors, etc. Such nanostructures were deposited on single-crystal SrTiO3 (001) substrates by pulsed laser deposition from a single Ba-Ti-Co-Fe-oxide target. The films are epitaxial in-plane as well as out-of-plane with self-assembled hexagonal arrays of CoFe2O4 nanopillars embedded in a BaTiO3 matrix. The CoFe2O4 nanopillars have uniform size and average spacing of 20 to 30 nanometers. Temperature-dependent magnetic measurements illustrate the coupling between the two order parameters, which is manifested as a change in magnetization at the ferroelectric Curie temperature. Thermodynamic analyses show that the magnetoelectric coupling in such a nanostructure can be understood on the basis of the strong elastic interactions between the two phases.