Microstructural evolution of Pb(Zr, Ti)O 3 thin films prepared by hybrid metallo-organic decomposition
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A. H. Carim Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 14 June 1991; accepted 26 February 1992)
We report on the microstructural analyses of chemically prepared Pb(Zr0.53Tio.47)03 (PZT 53/47) films. Although several techniques were used to analyze films, transmission electron microscopy (TEM) was emphasized. Phase evolution of these films, fabricated using hybrid metallo-organic decomposition (HMD), was determined by processing films at temperatures ranging from 500 °C to 650 °C. Our films, when observed with an optical microscope, appeared to consist of two distinct phases: (1) a featureless matrix and (2) 1-2 ^xm diameter "rosettes". PZT films fired at 500 °C consisted of a pyrochlore containing phase (featureless matrix) and contained no perovskite, whereas films fired at 600 °C were ferroelectric and were approximately 90% perovskite (rosettes) by volume. Our TEM analysis showed that the pyrochlore-containing phase consisted of interpenetrating nanocrystalline pyrochlore and amorphous phases, both with dimensions on the order of 5 nm. For PZT films processed at 650 °C, the perovskite phase was observed in two forms: (1) large (f»2 [im) rosette structures containing 30 nm pores and (2) dense equiaxed particles on the order of 100 nm. We propose that phase evolution—with increasing temperature of HMD PZT 53/47 films—consists of the following steps: (1) phase separation, probably occurring in solution, (2) pyrochlore crystallization, (3) heterogeneous nucleation of perovskite PZT, and (4) homogeneous nucleation of perovskite PZT.
I. INTRODUCTION PZT thin films are of considerable interest for nonvolatile semiconductor memory device applications. Morphotropic PZT film compositions (i.e., mole fraction ratio of Zr/Ti « 53/47) have received particular attention, since these films have low coercive fields and substantial remanent polarization. Low coercive fields allow low voltage device operation, and substantial remanent polarizations provide reasonable voltage discrimination for nonvolatile semiconductor memory applications. While it is possible to fabricate perovskite PbTiO3 thin films without forming a pyrochlore phase, the pyrochlore phase is stable over an extensive temperature range for PZT thin films compositionally near the morphotropic phase boundary. Unfortunately, PbTiO3 thin films have much larger coercive fields, and thus, require higher voltage operation than morphotropic PZT thin films. For these reasons, we have characterized the microstructural and electrical properties of PZT thin films near the morphotropic phase boundary. Our study represents one of the first attempts to characterize, using TEM analysis, chemically prepared PZT thin films processed at low temperatures. The purpose of this study was twofold: (1) develop an understanding 1876 http://journals.cambridge.org
of the genesis of the organic gel-inorganic film microstructure transformation and (2) detail high temperature microstructural evolution, pa
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