Electrical Characteristics of Barium Strontium Titanate-Oxide Composite Films
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S. SENGUPTA*, L.C. SENGiJPTA*, S, STOWEIL*, D.P. VIJA+ AND S.B. DES1J+ *U.S. Army Research Laboratory, Materials Directorate, Watertowkn MA 02172-0001 'Dept. of Materials Science and Engineering, Virginia Tech, Blacksburg, VA 24061
ABSTRACT In a previous work. composites of BSTO combined with other nonelectricallv active oxide ceramics have been formulated and have demonstrated adjustable electronic properties which can be tailored for use in various electronic devices. I One application has been for use in phased array antennas and insertion has been accomplished into several working antenna systems. 2 To further accommodate the frequencies required by these phased array antennas, thin filts of the composites have been fabricated using a Krypton Fluoride excimer laser as an ablation source. The electrical properties, including the dielectric constant and the tunability (change in the dielectric constant with applied voltage) have been measured. The results have been compared to those obtained for the bulk, ceramic composites and other BSrO/oxide composite thin film structures. 3 INTRODUCTION Phased array antennas are currently constructed using ferrite phase shifting elements. These antennas can steer transmitted or received signals either linearly or in two dimensions without mechanically oscillating the antenna. Due to the circuit requirements necessary to operate these present day antennas, however, these 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. Towards this goal, a ceramic Barium Strontium Titanate, Bal-xSrxTiO3, (BSTO), phase shifter using a planar microstrip construction has been demonstrated.I However, to meet the required performance specifications (e.g., maximum phase shifting ability), the BSTO electronic properties must be optimized. As part of this optimization process, various composites of BSTO and non-ferroelectric oxides have been formulated and proven successful. However, in order to obtain higher operating frequencies (30 GH-z and beyond) and to decrease the voltage requirements, thin film fabrication of the above candidate materials is necessary. This paper outlines the work on the characterization of the thin films of undoped and modified BSTO deposited by the pulsed laser deposition (PLD) method. The electronic properties of the films were measured using an HP 4194A impedance analyzer. The results of these measurements will be discussed.
413 Mat. Res. Soc. Symp. Proc. Vol. 360 01995 Materials Research Society
EXPERINIEN'IAL The metallized films used for the electrical measurements were: (I) Sapphire / RuO 2 / BSTO / Pt and (2) Sapphire / RuO 2 / BSTO with I wt.% oxide 11 / Pt Prior to P1I), the sapphire substrates utilized underwent a cleaning cycle which included an ultrasonic cycle of ICE followed by two methanol ultrasoni
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