Fabrication and Characterization of Barium Strontium Titanate and Non-Ferroelectric Oxide Composites
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E. NGO, S. STOWELL, L.C. SENGUPTA, M.E. O'DAY, AND R LANCTO U.S. Army Research Laboratory, Materials Directorate, AMSRL-MA-CA, Watertown, MA 02172
ABSTRACT Various composites of BSTO combined with other nonelectrically active oxide ceramics have been formulated. In general, the composites have adjustable electronic properties which can be tailored for use in various electronic devices. Two applications, which are of interest in regard to the composites being discussed here, are phased array antennas and capacitor-varistor monolithic devices. For the phased array antennas, these properties include reduced dielectric constants, u', where c = E' - ic", and loss tangents, tan b. The reduction of the dielectric constant and lowering of the loss tangents reditce the overall impedance mismatch and the insertion loss of the device. In addition, the overall tunability, change in the dielectric constant with applied voltage, is maintained at a sufficiently high level for all dielectric constants of interest. Another application (for one of the composite materials) is a combined capacitorvaristor device. In general, this would be used to protect against spurious voltage surges and voltage transients in electronic micro-circuits. The microstructures, including grain size and phase analysis, have been examined using SEM and X-ray diffraction. INTRODUCTION Phased array antennas can steer transmitted or received signals either linearly or in two dimensions without mechanically oscillating the antenna. These antennas are currently constructed using ferrite phase shifting elements. Due to the type of circuit requirements necessary to operate these antennas, they are costly, large and heavy. Therefore, the use of these antennas has been limited primarily to military applications which are strategically dependent on such capabilities. In order to make these devices available for many other commercial and military uses, the basic concept of the antenna must be improved. If ferroelectric materials could be used for the phase shifting element instead of ferrites, phased array antennas would be totally revolutionized. A ceramic Barium Strontium Titanate, Bal-xSrxTiO3, (BSTO), phase shifter using a planar microstrip construction has been demonstrated. 1 In order to meet the required performance specifications, maximum phase shifting ability, the electronic properties must be optimized. As part of this optimization process, various composites of BSTO and non-ferroelectric oxides have been formulated. Another application for one of these materials is a combined capacitor-varistor device. In general, this would be used as a protective device in parallel with electronic information processing circuits to protect against spurious voltage surges and voltage transients. The capacitive aspect of the device would guard against low-amplitude and high frequency transients which cause errors in signal processing or in stored signals. The varistor function of the device protects against high-amplitude voltage surges. The capacitor-varistor device has
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