Effects of PLT-buffer layer on microstructures of sputtered PLZT thin films epitaxially grown on sapphire
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Hideaki Adachi, Yasumufi Yabuuchi, and Kentaro Setune Central Research Laboratories, Matsushita Electric Industrial Company, Ltd., 3-4 Hikaridai, Seika-cho, Kyoto 619-02, Japan (Received 22 April 1994; accepted 26 July 1994)
The microstructures of sputtered thin films of lead-lanthanum zirconate-titanate (PLZT) on (0001) sapphire substrate have been studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thin films of polycrystalline PLZT (9/65/35), Pbo.91Lao.09Zro.65Tio.35O3, were prepared on a (0001) sapphire substrate by reactive sputtering, using the dc-magnetron system with a multitarget, Pb, La, Zr, and Ti at the substrate temperature of 700 °C. The PLZT thin films comprised (111) oriented small crystallites of PLZT. Although the average direction of the crystal orientation corresponded to the ideal epitaxial relationship (111) PLZT || (0001) sapphire, the individual crystallites showed misalignment in both the growth direction and the film plane. The thin films could not be considered epitaxially grown films. From analysis of the TEM images, there exists an interfacial region between the PLZT thin film and the substrate. The interfacial region comprises ordered clusters of (111), disordered (101), and/or (110) PLZT crystallites. The presence of the interfacial region will suppress ideal epitaxial growth with uniform crystal orientation. It is confirmed that the addition of the buffer layer of graded composition of PLT-PLZT, between the substrate and the PLZT thin film, will suppress the formation of the disordered interfacial region and will enhance the epitaxial growth of the (111) PLZT on (0001) sapphire with three-dimensional crystal orientations.
I. INTRODUCTION In recent years thin films of perovskite ABO 3 ceramics have been extensively studied. Perovskite thin films are available not only for the production of electronic devices such as electro-optic devices,1 acoustro-optic devices,2 infrared sensors,3 ferroelectric memories,4 and high-r c superconductors,5 but also for the understanding and/or the production of environmental catalysts, with controlled catalytic reactions on the surface of the perovskite crystallites.6 Microstructures of the thin films will affect the materials' properties and/or operations of thin film devices.7 It is known that the microstructures will be strongly governed by deposition conditions. Although extensive work has been done on the deposition of thin films of perovskite ceramics,8 their microstructural properties have not been fully understood yet. It is necessary to understand the microstructures of deposited thin films in relation to the deposition conditions, for the establishment of the deposition process with controlled microstructures of the perovskite thin films. Recent studies on sputtered thin films of lead-lanthanum zirconate-titanate (PLZT) ceramics on sapphire substrates suggest that the microstructures and/or epitaxial J. Mater. Res., Vol. 9, No. 11, Nov 1994 http://journals.cambridge.org
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