Origin and implications of the observed rhombohedral phase in nominally tetragonal Pb(Zr0.35Ti0.65)O3 thin films

Abstract

Polarization fatigue in Pb Zr 0.45 Ti 0.55 O 3 -based capacitors studied from high resolution synchrotron x-ray diffraction J. Appl. Phys. 97, 064108 (2005); 10.1063/1.1870098 Comparison of crystal structure and electrical properties of tetragonal and rhombohedral Pb(Zr,Ti)O 3 films prepared at low temperature by pulsed-metalorganic chemical vapor deposition J. Appl. Phys. 92, 5448 (2002); 10.1063/1.1510169 Spatial variation of ferroelectric properties in Pb(Zr 0.3 ,Ti 0.7 )O 3 thin films studied by atomic force microscopyThe structural and electrical properties of Pb(Zr 0.35 Ti 0.65 )O 3 ͑PZT͒ thin films ranging in thickness from 700 to 4000 Å have been investigated. These ͑001͒/͑100͒-textured films were grown by metalorganic chemical vapor deposition on ͑111͒-textured Ir bottom electrodes. It was observed that, in the as-deposited state, the thinnest PZT films are rhombohedral even though bulk PZT of this composition should be tetragonal. Thicker films have a layered structure with tetragonal PZT at the surface and rhombohedral PZT at the bottom electrode interface. In this article we investigate the origin of this structure and its effect of the ferroelectric and dielectric properties of PZT capacitors. It has been suggested that thin films stresses can affect the phase stability regions of single domain PZT. This possibility has been investigated by piezoresponse microscopy and thin film stress measurements. In the as-deposited state the majority of PZT grains contain a single ferroelastic domain, whereas after a high temperature anneal, a large fraction of the grains contain several ferroelastic domains. Wafer curvature measurements in combination with x-ray diffraction stress measurements in the Ir bottom electrode showed that the as-deposited PZT films are, within experimental error, stress free at room temperature. Landau-Ginbzurg-Devonshire formalism was used to explain the origin of the rhombohedral phase as a result of substrate constraint on single domain PZT grains. Annealing was found to affect the relative volume fractions of the rhombohedral and tetragonal phases and the electrical properties of PZT films. Intermediate temperature anneals increased the volume fraction of the rhombohedral phase and the coercive field extracted from the polarization-electric field hysteresis loops. After a high temperature anneal ͑650°C͒ the majority of the grains transformed into a polydomain state, decreasing the volume fraction of the rhombohedral phase and the coercive field. If the high temperature anneal was performed after deposition of the top electrode, the coercive field became independent of the PZT thickness.

Structural and electrical characterization of xBiScO3–(1−x)BaTiO3 thin films

“…The decrease in permittivity is comparable to the decrease seen in PZT. 19 To determine whether this might be due to an interfacial layer, the inverse capacitance was plotted as a function of thickness ͓Fig. 8͑b͔͒.…”

Domain structures and correlated out-of-plane and in-plane polarization reorientations in Pb(Zr0.96Ti0.04)O3 single crystal via piezoresponse force microscopy

“…It should be noted that there have been numerous PFM studies of PZT solid solutions in the bulk and thin-film forms and previous investigations of the electric-field-induced domain switching in these compounds (see, e.g., Refs. [22][23][24][25][26], but our work is distinguished by the PFM characterization of the intermediate phase in a Zr-rich PZT single crystal.…”

Thickness-dependent electrocaloric effect in mixed-phase Pb 0.87 Ba 0.1 La 0.02 (Zr 0.6 Sn 0.33 Ti 0.07 )O 3 thin films

“…As film thickness increases, the tetragonal phase is seen to gradually increase from 'mostly' rhombohedral film (200 nm) up to 31% tetragonal-phase film (830 nm) towards extrapolated fully tetragonal bulk PBLZST (figure 3). This may be understood by considering the fact that PBLZST thin films crystallize in a twolayered structure, as previously proposed by Kelman and co-workers [16] for PbZr 0.3 Ti 0.7 O 3 thin films. According to this work, grains at the bottom of the film are strongly affected by misfit strain, due to lattice mismatch and difference in thermal expansion coefficients between the substrate and the film, and therefore these are compelled to undergo a tetragonal to rhombohedral transformation.…”