Hydrothermal BaTiO 3 thin films from nanostructured Ti templates
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chelle D. Casper, Seymen M. Aygün, Peter G. Lam, and Jon P. Mariaa) Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27606 (Received 20 July 2010; accepted 9 November 2010)
Polycrystalline BaTiO3 thin films have been prepared by hydrothermal reaction with sputterdeposited nanostructured reactive Ti templates designed to control net diffusion direction and distance. Templates were prepared in two morphologies, i.e., planar and nanopillar. The samples produced from flat templates showed sluggish transformation kinetics and an eventual termination of reaction without fully consuming the Ti metal. Templates with pillar morphology, on the other hand, could be transformed to phase-pure BaTiO3, independent of the template thickness. In the asprecipitated state, those films revealed a permittivity of ~1000 and loss tangent values around 0.1 with mild dispersion in the kilohertz frequency range. Annealing these films under forming gas containing 1 vol% H2 balance N2 for 3 h at 200 °C decreased high-field losses to 0.06 and reduced dispersion. Mn incorporation as an in situ acceptor dopant was also explored. Addition of Mn during hydrothermal treatment further improved the electrical properties. Annealing under the same postgrowth conditions virtually eliminated the frequency dispersion in the range of 1 kHz to 1 MHz, while maintaining permittivity values in the range of 350.
I. INTRODUCTION
Complex oxide ceramics with high-performance electrical properties are in demand for a range of electronic applications. Among them, BaTiO3 has received much attention as a multilayer ceramic capacitor, a nonlinear resistor, and a varactor (voltage-controlled capacitors) due to its high permittivity and nonlinear ferroelectric response.1–2 A variety of deposition techniques have been used for the production of BaTiO3 thin films, such as metalorganic chemical vapor deposition,3 sputtering,4 pulsed laser deposition,5 electrochemical deposition,6 sol–gel,7 spray-pyrolysis,8 and chemical solution deposition.9 However, most of these techniques require exposure to high temperatures for complete crystallization and organic removal. In some cases, this high-temperature annealing can promote inhomogeneous film composition, porosity, cracking, or peeling of the deposited films.10 Further, it presents severe limitations for the integration of ferroelectrics on printed wiring boards or other organic substrates.11 Hydrothermal processing has evolved over the last three decades and provides the opportunity of direct synthesis of crystalline structures at significantly lower temperatures12–16 in strong alkaline solutions. Films of BaTiO3 were precipitated on Ti-coated polyphenylene sulfide,12 silicon,10,17–24 platinized silicon,25 printed cira)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.102 592
J. Mater. Res., Vol. 26, No. 4, Feb 28, 2011
http://journals.cambridge.org
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cuit board,26 FR4 Cu-clad laminates,11 kapton tape,16 and pure
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