Dielectric Properties of Spray Deposited BaTiO 3 and Ba 0.68 Sr 0.32 TiO 3
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Dielectric properties of spray deposited BaTiO3 and Ba0.68Sr0.32TiO3 Kipyung Ahn1, Bruce W. Wessels1, Robert Greenlaw2, and Sanjay Sampath3 1
Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208 2 Integrated Coating Solutions, Huntington Beach, CA 3 Department of Materials Science and Engineering, SUNY-Stony Brook, Stony Brook, NY 11794
ABSTRACT The microstructure and dielectric properties of BaTiO3 and Ba0.68Sr0.32TiO3 thick films deposited by thermal spray were investigated. The as-deposited films were predominantly crystalline with a small amount of an amorphous second phase. The as-deposited BaTiO3 films had dielectric constants as high as 240 at room temperature. Upon annealing in air at 500 °C, the dielectric constant increased to 480. This increase in dielectric constant was attributed, in part, to the crystallization of the amorphous second phase. The stabilized phase depended on the spray process used. The high velocity oxy fuel (HVOF) spray process resulted in the deposition of paraelectric BaTiO3, whereas the plasma spray process resulted in the ferroelectric phase. INTRODUCTION Thermal spray is a continuous, directed, melt-spray process, that is being developed as a potential method for direct write. Advantages of thermal spray with respect to direct write are: high speed writing capability and high throughput manufacturing, low cost, adaptability to flexible manufacturing concepts, applicability to conformal shapes, portability, and flexibility in substrate choice. Although the traditional role of thermal spray deposits has been protective coatings for heat, wear, and corrosion applications, it is now being developed for electronic applications. [1,2]. Potential applications for direct write are hybrid and multi-chip module circuits, which require wires, inductors and capacitors [3]. For capacitors dielectrics are needed. Recently deposition of high k ferroelectrics including BaTiO3 and BaSrTiO3 using thermal spray has been reported [4]. The thick films had dielectric constants as high as 180 at room temperature. However, these values are lower than those of the corresponding bulk ceramics and for many applications high dielectric, low loss films are required. In the present work, BaTiO3 and Ba0.68Sr0.32TiO3 (BST) thick films were prepared by thermal spray for capacitor applications. To understand the factors that limit the dielectric properties of the films, their microstructure and thermal stability were investigated. Moreover, the effect of the spray process conditions on the crystal structure and dielectric properties was examined.
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EXPERIMENTAL DETAILS Thick dielectric films were deposited by plasma spray or a high velocity oxygen fuel (HVOF) spray technique. Both of BaTiO3 and Ba0.68Sr0.32TiO3 (BST) powders used for spray coating were obtained from Trans Tech Inc. Size ranges of the feed powders were –325 mesh ( 10µm in diameter) and small sub-micron particles. Energy dispersive spectroscopy (EDS) analysis indicated they had the same composition.
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