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Among the main trends in our daily society is a drive for smaller, faster, cheaper, smarter computers with ever-increasing memories. To sustain this drive the com­ puter industry is turning to nanotechnology as a source of new processes and func­ tional materials, which can be used in high-performance high-density electronic systems. Researchers and engineers have been focusing on ferroelectric materials for a long time due to their unique combination of physical properties. The ability of ferroelectrics to transform electromagnetic, thermal, and mechanical energy into electrical charge has been used in a number of electronic applications, most recently in nonvolatile computer memories. Classical monographs, such as Ferro­ electricity by E. Fatuzzo and W. J. Mertz, served as a comprehensive introduction into the field for several generations of scientists. However, to meet the challenges of the "nano-era", a solid knowledge of the ferroelectric properties at the nano­ scale needs to be acquired. While the science of ferroelectrics from micro-to lar­ ger scale is well established, the science of nanoscale ferroelectrics is still terra in­ cognita. The properties of materials at the nanoscale show strong size dependence, which makes it imperative to perform reliable characterization at this size range. One of the most promising approaches is based on the use of scanning probe microscopy (SPM) which has revolutionized materials research over the last dec­ ade.



1. Electric Scanning Probe Imaging and Modification of Ferroelectric Surfaces

Recent progress in oxide electronic devices including microelectromechanical systems (MEMS), non-volatile ferroelectric memories (FeRAMs), and ferroelectric heterostructures necessitates an understanding of local ferroelectric properties on the nanometer level. This has motivated a number of studies of ferroelectric materials with various scanning probe microscopies (SPM) [l–3], many examples of which can be found in this text. The natures of the probe and contrast formation mechanisms in these techniques are vastly different; therefore, SPM images reflect different properties of ferroelectric surfaces.
S. V. Kalinin, D. A. Bonnell

2. Challenges in the Analysis of the Local Piezoelectric Response

The piezoresponse technique is based on the detection of local vibrations of a cantilever induced by a probing AC signal applied between the conductive tip of a scanning force microscope (SFM) and the bottom electrode of a ferroelectric sample. The cantilever vibrations are converted into an electrical signal by the position sensitive detector of the SFM and extracted from the global deflection signal using a standard lock-in technique. This electrical signal representing the cantilever vibrations is further referred to as the piezoresponse signal (PRS), for reasons that will be explained later.
C. Harnagea, A. Pignolet

3. Electrical Characterization of Nanoscale Ferroelectric Structures

The present chapter focuses on the electrical characterization of small ferroelectric capacitors and the problems arising from going to smaller and smaller structure sizes. In particular, the electrical hysteresis loop is investigated as a key property of ferroelectric materials.
S. Tiedke, T. Schmitz

4. Nanoscale Optical Probes of Ferroelectric Materials

Scanning probe microscopy has experienced explosive growth in the last twenty years, beginning with the invention of the scanning tunneling microscope (STM) [1]. The operating principle of the STM involves electron tunneling, but the mechanism by which images are formed is through raster scanning, controlled by a ferroelectric (and piezoelectric) crystal. Soon after the development of the atomic force microscope, (AFM) [2], it was realized that ferroelectrics themselves could benefit from the use of scanning probes. Saurenbach and Terris [3] reported the first observations of domain structures in ferroelectrics using AFM. Since then there have been hundreds of subsequent reports. Large contrast and distinct phase difference make the piezoelectric mode of scanning force microscopy [4] a convenient technique to distinguish areas with different signs of ferroelectric polarization, provided that the piezoelectric response is large. Scanning measurements of linear [5]and nonlinear capacitance [6]can reveal the spatial distribution of dielectric properties, as can scanning microwave microscopy [7]. A review of AFM-based scanning probe techniques is found in Chap. 2.
J. Levy, O. Tikhomirov

5. Scanning Nonlinear Dielectric Microscopy for Investigation of Ferroelectric Polarization

Recently, ferroelectric materials, especially in thin film form, have attracted the attention of many researchers. Their large dielectric constants make them suitable as dielectric layers of microcapacitors in microelectronics. They are also investigated for application in nonvolatile memory using the switchable dielectric polarization of ferroelectric material. To characterize such ferroelectric materials, a highresolution tool is required for observing the microscopic distribution of remanent (or spontaneous) polarization of ferroelectric materials.
Y. Cho

6. Nanoscale Piezoelectric Phenomena in Epitaxial PZT Thin Films

This chapter reviews nanoscale piezoelectric phenomena in epitaxial lead zirconate titanate (PZT) ferroelectric thin films The first part of the paper focuses on theoretical predictions of the field dependent piezoelectric behavior of bulk single crystal and thin film PbZrxTi1−xO3. A Ginzburg-Landau-Devonshire-type phenomenological thermodynamic theory for tetragonal single domain PZT is employed to explain the electric field dependence of piezoelectric properties. It demonstrates the presence of a strong non-linearity of converse piezoelectric coefficient under large external electric field in both bulk crystal and epitaxial tetragonal PZT thin films. The results of the model are used to interpret piezoelectric responses of model epitaxial thin films and nanostructures using voltage modulated scanning force microscopy. They are presented with particular focus on the longitudinal piezoelectric constant d 33 in nanoscale capacitors (or islands) of various PZT compositions. An effective stress model is presented to explain the dependence of d 33 on the lateral size. We show that by altering the electromechanical interplay between the substrate and the ferroelectric thin film an unusual field dependence of the d 33 exists in compositions closer to the morphotrophic phase boundary. Due to this effect, the change in strain at saturation field is twice the theoretical prediction, opening up possibilities such as highly strain tunable devices. Finally we discuss in highly tetragonal PbZr0.2Ti0.8O3, movement of elastic 90° domains with applied DC field, a phenomenon hitherto observed only in bulk single crystals or ceramics. This results in a d 33 of ~ 250 pm/V at remanence, which is approximately 3–4 times the predicted value of 87 pm/V for a single domain single crystal.
V. Nagarajan, A. Roytburd, R. Ramesh

7. Scanning Probe Microscopy of Ferroelectric Domains near Phase Transitions

In this chapter the results of scanning probe microscopic (SPM) investigations near ferroelectric (ferroic)—paraelectric phase transitions are presented. Submicroscopic investigations of domains near the transition temperature are of fundamental importance both for the basic understanding of the phase transitions itself but also for devices operating near the transition temperatures.
M. Abplanalp, M. Zgonik, P. Günter

8. Nanodomain Engineering in Ferroelectric Crystals Using High Voltage Atomic Force Microscopy

Reversal of the spontaneous polarization direction under an applied electric field is a basic property of ferroelectrics. However the traditional techniques used for fabrication of domain gratings have been able to produce domains not smaller then 2 µm. Sub-micron and nanometer scale domains may be fabricated using atomic force microscopy based techniques; however, to date there was no success in fabricating stable domains that elongate without widening throughout thick ferroelectrics. A breakthrough in the field emerged with the recent development of the high voltage atomic force microscope that has enabled us to obtain sub-micrometer stable domain configurations in bulk ferroelectric crystals. A comprehensive experimental and theoretical description of nanodomain engineering based on high voltage atomic force microscopy is presented. It is found that string-like domains are formed due to the super-high electric field of the high voltage atomic force microscope tip. The domains, which resemble channels of an electrical breakdown, nucleate under an electric field of around 107 V/cm at the ferroelectric surface, and grow throughout the crystal bulk where the external electric field is practically zero. A theory explaining the shape of the formed domains shows that the driving force for the domain breakdown is the decrease of the total free energy of the system with increasing domain length. The high voltage atomic force microscope has been applied for tailoring two-dimensional strip-like nanodomains in 250 micron thick RbTiOPO4 single crystals. Studying the influence of the applied high voltage, and the tip velocity on the domain strips has allowed us to fabricate domain gratings (with a domain width of 590 nm) useful for backward-propagating quasi-phase-matched frequency conversion. Some important aspects of the domain structure characterization are presented and discussed. In the last sections we show that the amplitude contrast in contact AFM imaging mode is largely affected by the difference in the work functions of antiparallel domains. It is shown that a direct measurement of the piezoelectric coefficient can be performed using the high voltage atomic force microscope.
Y. Rosenwaks, M. Molotskii, A. Agronin, P. Urenski, M. Shvebelman, G. Rosenman

9. Nanoinspection of Dielectric and Polarization Properties at Inner and Outer Interfaces in PZT Thin Films

We report on novel approaches using scanning force methods [i.e. piezoresponse force microscopy (PFM), Kelvin probe force microscopy (KPFM) and pull-off force spectroscopy (PFS)] in order to deduce the local dielectric and polarization properties of PZT thin films both at outer and inner interfaces with < 50 nm lateral resolution. We show that the polarization profile into the depth of the PZT sample varies dramatically being built up at the bottom Pt electrode over a transition layer of more than 200 nm in thickness. Also this interfacial area shows a different relaxation behavior upon switching. The results are explained both in the view of negatively charged defects pinned at the PZT/Pt interface as well as the possible variation in the local dielectric properties across the film thickness. Investigating the latter made the quantitative deduction of values such as the effective dielectric polarization P z ,the deposited charge density σ, and the surface dielectric constant ε surface in thin ferroelectric PZT films necessary. We illustrate that such measurements in fact are possible on the nanometer scale revealing quantitative data when combining PFM and PFS.
L. M. Eng, S. Grafström, C. Loppacher, X. M. Lu, F. Schlaphof, K. Franke, G. Suchaneck, G. Gerlach


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