Chemical solution deposition of biaxially oriented (Ba,Sr)TiO 3 thin films on <100> Ni
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T. Dawley Microsystem Materials, Tribology and Technologies Department, Sandia National Laboratories, Albuquerque, New Mexico 87185-1411
P.G. Clem Microsystem Materials, Tribology and Technologies Department, Sandia National Laboratories, Albuquerque, New Mexico 87185-1411 (Received 6 March 2003; accepted 23 June 2003)
Biaxially oriented Ba1−xSrxTiO3 (BST) thin films were fabricated under a highly reducing atmosphere (oxygen partial pressure ∼10−18 atm) on base metal substrates (〈100〉 Ni) using a fluorinated chemical solution deposition method. The degree of film orientation was investigated with respect to film annealing temperature and composition (x ⳱ 0, 0.33, 0.5, 0.67, 1). The solution synthesis route included fluorinated solvents, donor-dopants, and chelating agents for control of orientation, defect chemistry, and morphology. Free-energy and phase diagrams guided solution development using halide addition to avoid intermediate BaCO3 formation and instead produce direct crystallization of BaTiO3-type materials from BaF2. The degree of (200) orientation of BST films deposited on 〈100〉 Ni substrates displayed a compositional dependence for 0 < x < 1, with a maximum orientation Lotgering factor approaching unity. Low-temperature (500 °C) crystallization of highly oriented films was demonstrated for solution-derived BST on Ni, which may have enabling materials integration implications for capacitors and other applications.
I. INTRODUCTION
Materials in the BaTiO3–SrTiO3 pseudo-binary system are under investigation for applications including highdielectric constant (K⬘) dielectrics for capacitors,1 voltage tunable dielectrics for phase shifter devices,2 and oxide buffer layers for use in next-generation hightemperature superconductor (HTSC) wires.3 Reliable, low-temperature deposition techniques enable such applications on a variety of metal, semiconductor, and oxide substrates. Literature reports detail crystalline perovskite BST thin films deposited on LaAlO3, MgO, and sapphire by chemical vapor deposition,4 pulsed laser deposition (PLD),5,6 and sputtering7 on a variety of substrates, but few reports exist for films on base-metal substrates. Recently, PLD of perovskites on base metals has been reported by Cantoni et al.8 Chemical solution deposition (CSD) methods toward the same ends are of manufacturing interest due to low capital equipment costs, the ability to continuously dip-coat onto a variety of substrates, the high degree of chemical control/doping 2310
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possible, and the low cost of precursors.9,10 However, control of film orientation via CSD processes has historically been more limited than that possible from adatomtype vapor-phase deposition methods. We report here the development of a new, low-temperature CSD route for depositing highly oriented perovskite films in the BST system on base-metal substrates. BaTiO3-based dielectrics are widely used as highdielectric-constant insulators in bulk and thin film capacitors. Normally, however, BaTiO3 has required processing in
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