Processing and characterization of compositionally modified PbTiO 3 thin films prepared by pulsed laser deposition
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Processing and characterization of compositionally modified PbTiO3 thin films prepared by pulsed laser deposition B. W. Lee,a) L. P. Cook, P. K. Schenck, W. Wong-Ng, and C. K. Chiang NIST, Gaithersburg, Maryland 20899
P. S. Brody and K. W. Bennett U.S. Army Research Laboratory, Adelphi, Maryland 20783 (Received 28 March 1994; accepted 5 October 1996)
Modified lead titanate of 0.9PbTiO3 –0.1Pb(Mg0.5 W0.5 )O3 thin films have been deposited onto Pt-coated Si substrates by pulsed laser deposition. Films were crystallized in situ during deposition or by post-depositional heat treatment (post-annealing). Compositional and structural characterization showed that the phase formation and microstructure of the films were highly sensitive to deposition conditions. Perovskite single phase films were formed in situ at 650 ±C, PO2 40 Pa as well as by post-annealing amorphous films at 650 ±C. In the post-annealing process, the amorphous as-deposited phase was crystallized to perovskite and/or pyrochlore, and the ratio of perovskite to pyrochlore was found to be influenced by the depositional PO2 . Depending on the deposition temperature, the grain structures of the crystallized films were columnar or equiaxed. A relatively homogeneous surface morphology was obtained by deposition at a lower pressure (PO2 13 Pa). The in situ crystallized films showed variable crystallographic orientation. The more (111) oriented films had the lowest remanent polarizations and the highest coercive fields. A method for preparing randomly oriented films, via a two-step deposition process with intermediate annealing, is believed to give the most consistent results and the best ferroelectric properties at the present level of development.
I. INTRODUCTION
Ferroelectric thin films have great potential for a variety of device applications1–3 such as actuators, pyroelectric sensors, and electro-optics, including integrated device applications such as nonvolatile random access memory (RAM). Recent studies1–5 have focused on the deposition of the films onto semiconductor substrates. For this application, it is required that the thin films should have uniform composition and surface morphology to obtain consistent device performance. Pulsed laser deposition (PLD) is a promising method for preparing multicomponent ceramic thin films, including ferroelectric materials, due to several advantageous features,6–8 including low compositional deviation between target and film, and relatively high deposition rate. In this paper, the preparation of modified PbTiO3 thin films by pulsed laser deposition is described. These modified PbTiO3 films have significant potential for thin film applications and, relative to PZT, they of-
a)
Present address: Department of Materials Engineering, Korea Maritime University, Pusan 606-791, Korea. J. Mater. Res., Vol. 12, No. 2, Feb 1997
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fer the advantage of having less tendency to form a metastable pyrochlore phase.9 In parti
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