Articles Processing Effects on the Compositional Depth Profile of Ferroelectric Sol-Gel Ca-PbTiO 3 Thin Films R. Sirera, † D. Leinen, ‡ E. Rodrı ´guez-Castello ´n, § and M. L. Calzada* ,| Dpt. Quı ´mica y Edafologı ´a, Univ. de Navarra, 31080 Pamplona, Spain; Dpt. de Fı ´sica Aplicada, Univ. de Ma ´ laga, 29071 Ma ´ laga, Spain; Dpt. de Quı ´mica Inorga ´ nica, Univ. de Ma ´ laga, 29071 Ma ´ laga, Spain; and Inst. Ciencia de Materiales de Madrid, ICMMsCSIC, Cantoblanco, 28049 Madrid, Spain. Received November 23, 1998. Revised Manuscript Received August 31, 1999 Pb 0.76 Ca 0.24 TiO 3 thin films have been prepared by sol-gel on Pt/TiO 2 /(100)Si substrates. Films deposited from a stoichiometric solution and a solution with a 10 mol % excess of Pb were subjected to a thermal treatment at 650 °C for 720 s with a heating rate of 8 °C/s and to a rapid thermal treatment (RTP) at 650 °C for 50 s with a rate of 30 °C/s, respectively. Chemical composition in surface, in depth, and at the bottom interface with the substrate of the films were studied by X-ray photoelectron spectroscopy (XPS) combined with Ar + depth profiling. XPS results were compared with those obtained by Rutherford backscattering spectroscopy (RBS). To make the interpretation of the XPS data easier and to complete them, the structure and microstructure of the films were monitored by grazing incidence X-ray diffraction analysis (GIXRD) and scanning electron microscopy (SEM). The RTP film prepared with a Pb excess developed a single perovskite phase with preferred orientation and a uniform depth profile in composition. The other film also has a single perovskite phase, but with a random orientation, and presents a nonuniform distribution of Pb across the film thickness. Whereas the latter film does not have a good ferroelectric response, the former does. After poling it, values of remanent polarization of P r ∼ 25 μC/cm 2 , coercive field of E c ∼ 75 kV/cm, and pyroelectric coefficients of γ ∼ 2.5 × 10 -8 were obtained. Introduction Ferroelectric thin films have attracted much attention during the last years, owing to their possible integration into multifunctional microelectronic devices. 1 The aim of using these materials in the microelectronic technol- ogy is to exploit some of their properties such as spontaneous polarization when they are integrated into nonvolatile ferroelectric random-access memories (NV- FRAMs), pyroelectricity for infrared sensors, or piezo- electricity in microelectromechanical systems (MEMS). For bulk materials, their electrical response is closely linked to composition, structure, and microstructure. However, when the ferroelectric material is deposited as a thin layer, the number of factors affecting its performance substantially increases. In this case, het- erostructure is an additional factor that plays an important role in film devices. The term heterostructure includes substrate, buffer layer, electrode, active (fer- roelectric) layer, and interface. Composition, structure, microstructure, and hetero- structure of a thin-film-based device are conditioned by the underlaying substrate and the deposition method. 2,3 Available substrates on which the ferroelectric layer is deposited are those used in the microelectronic industry. So, the majority of the research work on ferroelectric thin films is focused on their applications when they are integrated into silicon. Some reports have considered other substrates, particularly when a preferred orienta- tion of the active layer is desired. 4,5 However, from the point of view of applications, authors observe that substrates different from silicon are hardly technologi- cally interesting. 6 Therefore, it seems more appropriate to regulate parameters of deposition methods to control characteristics and properties of thin films. Among the different deposition techniques, sol-gel is a method that offers significant advantages over others, such as stoi- chiometric control of complex oxides and uniform in- corporation of dopants. Moreover, it is relatively rapid, * To whom correspondence should be addressed. Telephone: 34 91 334 90 62. Fax: 34 91 372 06 23. E-mail: lcalzada@icmm.csic.es. † Univ. de Navarra. ‡ Dpt. de Fı ´sica Aplicada, Univ. de Ma ´ laga. § Dpt. de Quı ´mica Inorga ´ nica, Univ. de Ma ´ laga. | ICMMsCSIC. (1) Auciello, O.; Ramesh, R. MRS Bull. 1996, 21 (7), 29. (2) Kushida, K.; Udayakumar, K. R.; Krupanidhi, S. B.; Cross, L. E. J. Am. Ceram. Soc. 1993, 76 (5), 1345. (3) Auciello, O.; Ramamurthy, R. MRS Bull. 1996, 21 (6), 21. (4) Kim, S.; Baik, S. Thin Solid Films 1995, 266, 205. (5) Seifert, A.; Lange, F. F.; Speck, J. S. J. Mater. Res. 1995, 10 (3), 680. (6) Dat, R.; Lichtenwalner, J.; Auciello, O.; Kingon, A. I. Appl. Phys. Lett. 1994, 64 (20), 2673. 3437 Chem. Mater. 1999, 11, 3437-3444 10.1021/cm980770y CCC: $18.00 © 1999 American Chemical Society Published on Web 11/04/1999