One-axis Oriented CaBi 4 Ti 4 O 15 and SrBi 4 Ti 4 O 15 Films Prepared on Silicon Wafer by Chemical Solution Deposition
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1199-F03-14
One-axis Oriented CaBi4Ti4O15 and SrBi4Ti4O15 Films Prepared on Silicon Wafer by Chemical Solution Deposition Technique Yuki Mizutani1, Hiroshi Uchida1, Hiroshi Funakubo2, and Seiichiro Koda1 1 2
Department of Materials and Life Sciences, Sophia University, Tokyo, 102-8554, Japan Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama, 226-8502, Japan
ABSTRACT One-axis oriented bismuth layer-structured dielectric (BLSD) films were designed using perovskite buffer layers for assembling the crystal orientation and the dielectric properties of the BLSD crystals on silicon wafer. The BLSD crystals with the general formula of (Bi2O2)2+-(Am-1BmO3m+1)2- possess excellent dielectric permittivity with lower size effect and temperature coefficient of capacitance (TCC), as well as high electrical resistivity along to the c-axis direction. These phenomena would contribute for constructing high performance dielectric devices driven under harsh environment, e.g., at high-temperature condition above 100 oC. In this study, thin films of CaBi4Ti4O15 and SrBi4Ti4O15, kinds of BLSD compounds with the number of BO6 octahedra in pseudo-perovskite blocks, m, = 4, were prepared by chemical solution deposition (CSD) technique on (100)LaNiO3/(111)Pt/TiO2/(100)Si and (100)SrRuO3// (100)LaNiO3/(111)Pt/TiO2/(100)Si substrates. These films consisted of crystalline phase of BLSD crystal with preferential crystal orientation of (001) plane normal to the substrate surface. Anisotropic crystal growth of BLSD occurred by the lattice matching between pseudo-perovskite blocks in BLSD crystal and (100)LaNiO3 or (100)SrRuO3 plane with perovskite structure. The dielectric constants (εr) of (001)-plane oriented CaBi4Ti4O15 and SrBi4Ti4O15 films were approximately 250-350 at room temperature. The εr values of the CaBi4Ti4O15 and SrBi4Ti4O15 films increased slightly with ambient temperature. The TCCs at a temperature range from 25 to 200 oC were approximately +103 - +514 ppm/K respectively, which were significantly different from those of (Ba,Sr)TiO3 thin films and would satisfy the performance requirement for driving at high-temperature condition.
INTRODUCTION Bismuth-layer-structured dielectric (BLSD) crystals have an anisotropic crystal structure consisting of bismuth oxide layers and pseudo perovskite blocks with the general formula (Bi2O2)2+-(Am-1BmO3m+1)2-, where A is a mono-, di-, or trivalent ion, B is a tetra-, penta-, or hexavalent ion (e.g., Ti4+, Nb5+, or W6+), and m is the number of BO6 octahedra in pseudo perovskite blocks (m = 1, 2, 3, 4, etc.) [1-3]. CaBi4Ti4O15 and SrBi4Ti4O15 are representative materials which have an anisotropic BLSD crystal structure with an m of 4. These materials have been studied by many researchers [3-6] for industrial applications in dielectric capacitors because
of the unique anisotropy of their dielectric and insulating properties, which are strongly dependent on their crystal orientation. Earlier studies have shown that polycrystalline BLSD films on a Pt-passiv
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