Recent Materials Characterizations of [2D] and [3D] Thin Film Ferroelectric Structures

Abstract

A review is given of ceramic and single-crystal thin film ferroelectric oxides, emphasizing perovskite phases, together with some new developments on hafnia films. It is shown that singlecrystal barium titanate films behave as bulk down to at least 77 nm, with no finite size effects, no phase transition temperature shifts, and no dielectric peak broadening or change from first-to second-order transitions, suggesting that the gradient defect model of Bratkovsky and Levanyuk correctly describes such effects as extrinsic in experimental studies of equally thin ceramic thin films. In ceramic barium-strontium titanate (BST) thin films, it is shown that there is also no intrinsic broadening or shifts in phase transitions, with sharp, unshifted, bulk-like transitions observed only as re-entrant upon warming from cryogenic temperatures; this shows that phase transitions in ceramic thin films are dominated by kinetics and not thermodynamics and are definitely not equilibrium measurements. At high fields (41 GV/m), the films exhibit space charge-limited conduction; no variable-range hopping is observed, contrary to recent studies on SrTiO 3 . Some novel, unconventional switching processes are discussed, comparing the ''perimeter effect'' (non-equilibrium, ballistic) with Molotskii's equilibrium model. Theory and experiment are described for [3D] nanotubes, nanorods, and nanoribbons (or micro-ribbons). The layered-structure-perovskitepyrochlore conversion in bismuth titanate is described together with the PbO1TiO 2 phase separation in lead zirconate titanate during electrical breakdown, as are novel HfO 2 precursors that demonstrate enhanced temperature crystallization from the amorphous state and hence commercial advantages for frontend processing. II. [2D] SystemsIn planar structures, both fine-grained ceramics and single crystals offer intriguing materials science in the 4-100 nm thickness regime. Several authors 2-4 have indicated that thin films might exhibit second-order phase transitions that, in bulk form, are first order; then, the question is exactly what thicknesses constitute ''thin''? Although the International FRAM ''Roadmap'' suggests 5 that FRAM structures must become [3D] by 2007 to accommodate requisite capacitance, at present, all FRAMs are planar-stacked devices. Therefore, we begin with the [2D] systems' materials science. J ournal

Strain on ferroelectric thin films

“…In order to illustrate this, let's consider the hypothetical case of tetragonal Pb(Zr 0. 2 3 in the optimal conditions would generate a coherent epitaxy (no misfit dislocations) and the film would be thick enough to neglect any finite size effect and thin enough to prevent the formation of domains. In that case, there is neither the strain due to the mismatch of the lattice parameters nor a thermal strain.…”

“…The first limitation, linked with the biaxial symmetry of the strain state, was recently overcome and will be reviewed in ''Anisotropic 2D stress field'' section to consider the case where the films are deposited on orthorhombic substrates such as NdGaO 3 .…”

“…Many aspects of this field have been reviewed [1][2][3][4] and several books have been published on this topic [5][6][7]. In this article, we will focus on the thermodynamical description that has been given of the Pb(Zr 1-x Ti x )O 3 (PZT 1 -x/x) solid solution deposited as thin films, on which most of the application are based.…”

Dielectric properties of Fe-doped TiO2nanoparticles synthesised by sol–gel route

“…The mechanical and electrical boundary conditions as well as the presence of defects can have a strong influence on the ferroelectric and dielectric properties when the dimensions of a system are reduced below 100 nm [1][2][3][4][5][6]. Major research efforts have recently been placed on the fabrication and characterisation of nano-sized dielectric materials, because the current technology requires very small size particles to miniaturise microwave devices and components.…”

Piezoresponse force spectroscopy of ferroelectric-semiconductor materials

“…4 This has stimulated a number of theoretical and experimental studies of ferroelectric properties in low dimensional systems, 5,6 including the size limit for ferroelectricity [7][8][9] and intrinsic switching 10 in thin films, and unusual polarization ordering in ferroelectric nanoparticles and nanowires. 11,12 Further progress in these fields necessitates fundamental studies of ferroelectric domain structures and dynamics and polarization-switching phenomena on the nanoscale.…”