Low Loss Ferroelectric Films Grown on Polycrystalline Ferrite Substrates for Dual-Tuning Microwave Devices
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H. JIANG, W. HU, S. LIANG, V. FOUFLYGUINE and J. ZHAO NZ Applied Technologies, 14A Gill Street, Woburn, MA 01801, hjiang(unzat2.tiac.net Q.X. JIA, J.R. GROVES, and P. ARENDT, Los Alamos National Laboratory, Los Alamos, NM 87545, F. MIRANDA, NASA Lewis Research Center, Cleveland, OH 44135, C. VITTORIA and H. HOW, ECE Department, Northeastern University, Boston, MA 02115 ABSTRACT
We successfully deposited high quality biaxially oriented BakSr,.-TiO 3 thin films on polycrystalline yttrium iron garnet substrates using both the metal-organic chemical liquid deposition and pulsed laser deposition methods with biaxially oriented MgO and yttriumstabilized-zirconia buffer layers. The dielectric losses of the films range from 0.005 to 0.0 15 while 25% of dielectric constant change was observed with 40V bias voltage up to 10 MHz. Both the dissipation and dielectric constant of the films remained nearly constants over a wide temperature range. A dual-tuning microwave phase shifter using a BST film grown on an MgO buffered polycrystalline YIG substrate was fabricated. A significant phase shift was observed in a wide frequency range when an electric bias or a magnetic field was applied to the device. INTRODUCTION
Ferrite and ferroelectric materials individually provide magnetic and electrical tunability for adaptive microwave devices. Adaptability would increase significantly if a microwave device could be simultaneously tuned by both magnetic and electrical techniques. One application where dual-tuning capability would be most advantageous is for phased array antennas. In addition to steering the overall beam angle, the phase of an individual element is adjusted to compensate for imperfections in the antenna and dynamic variations in the
transmission path. Magnetic fields that are difficult to apply to individual elements could be used for overall steering and electric fields for fine tuning each element. Individually, an electric OR magnetic tunable microwave device has a major drawback of the tradeoff of impedance mismatch. Any field induced dielectric constant or permeability change of the device will result in a deviation from the designed device impedance. The bigger the tunability, the greater the deviation of the impedance. A dual-tuning microwave device has the advantage of achieving frequency or phase tunability while keeping the impedance of the device unchanged. For example, the impedance change due to the decrease of the material dielectric constant (by an electric field) can be compensated by the change of the material permeability (by a magnetic field). In achieving low microwave loss, high device stability and reproducibility, single crystal ferroelectric thin films are more attractive than polycrystalline ones. However, large single crystal ferrite substrates are not currently available. It is not likely that high quality ferroelectric films can be grown directly onto polycrystalline ferrite substrates. Therefore, it is necessary to develop a buffer layer that is biaxially oriented onto the polycrystalline fe
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