Influence of heat treatment on LiNbO 3 thin films prepared on Si(111) by the polymeric precursor method
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Influence of heat treatment on LiNbO3 thin films prepared on Si(111) by the polymeric precursor method V. Bouquet, E. Longo, and E.R. Leitea) Departamento de Quı´mica, LIEC, Universidade Federal de Sa˜o Carlos, P.O. Box 676, 13565-905 Sa˜o Carlos, SP, Brazil
J.A. Varela Instituto de Quı´mica, Universidade Estadual Paulista, P.O. Box 355, 14884-970, Araraquara, SP, Brazil (Received 17 February 1998; accepted 12 April 1999)
The effects of heat-treatment temperature on LiNbO3 thin films prepared by the polymeric precursor method were investigated. The precursor solution was deposited on Si(111) substrates by dip coating. X-ray diffraction and thermal analyses revealed that the crystallization process occurred at a low temperature (420 °C) and led to films with no preferential orientation. High-temperature treatments promoted formation of the LiNb3O8 phase. Scanning electron microscopy, coupled with energy dispersive spectroscopy analyses, showed that the treatment temperature also affected the film microstructure. The surface texture—homogeneous, smooth, and pore-free at low temperature—turned into an “islandlike” microstructure for high-temperature treatments.
I. INTRODUCTION
Lithium niobate (LiNbO3) is an important ferroelectric material because of its excellent piezoelectrical, electrooptical, electroacoustical, pyroelectrical, and photorefractive properties.1,2 Because of these physical effects, LiNbO3 presents a large area of applications such as waveguides, optical amplitude and phase modulators, switches, nonvolatile memory elements, surface acoustic wave devices, and second harmonic generators. Using thin films to fabricate the devices is very interesting, especially in the microelectronic industry. The film can be incorporated into current semiconductor technology, which leads not only to the miniaturization device but also to optical loss reduction and a decrease in the final cost. Different methods have been reported for preparing LiNbO3 thin films such as the sol-gel process,3–6 metalorganic decomposition,7 pulsed laser deposition,8,9 liquid-phase epitaxy,10,11 radiofrequency sputtering,12,13 and chemical vapor deposition.14,15 In this work we prepared LiNbO3 thin films by the polymeric precursor method. This has already been successfully used to prepare lead zirconate titanate (PZT) and SrTiO3 films.16,17 The global process, outlined in Fig. 1, consists of preparing coating solutions from the Pechini process.18 Precursor films, deposited by dip coating or spin coating, are then heat treated to eliminate the
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FIG. 1. Flow chart of the thin film preparation process by the polymeric precursor method.
J. Mater. Res., Vol. 14, No. 7, Jul 1999
http://journals.cambridge.org
organic material and to synthesize the phase. The polymeric precursor method presents many advantages, such as the possibility to work in aqueous solutions and a high stoichiometric control. Moreover, it is a low-tem
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