We deposited epitaxial Ba0.4Sr0.6TiO3 (BST) films via laser ablation on MgO and LaAlO3 (LAO) substrates for tunable microwave devices. Postdeposition anneals (∼1100 °C in O2) improved the morphology and overall dielectric properties of films on both substrates, but shifted the temperature of maximum dielectric constant (Tmax) up for BST/LAO and down for BST/MgO. These substrate-dependent Tmax shifts had opposite effects on the room-temperature dielectric properties. Overall, BST films on MgO had the larger maximum dielectric constant (ε/ε0⩾6000) and tunability (Δε/ε⩾65%), but these maxima occurred at 227 K. 30 GHz phase shifters made from similar films had figures of merit (ratio of maximum phase shift to insertion loss) of ∼45°/dB and phase shifts of ∼400° under 500 V (∼13 V/μm) bias, illustrating their utility for many frequency-agile microwave devices.

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Articles you may be interested inStructural and dielectric properties of poly(vinylidene fluoride)-based terpolymer/copolymer blends developed on aluminum foil J. Appl. Phys. 112, 053505 (2012); 10.1063/1.4748181 Interacting and noninteracting dipole systems in ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymer J. Appl. Phys. 108, 084109 (2010); 10.1063/1.3499614 Structural evolution and dielectric relaxation behavior of electron-irradiated poly(vinylidene fluoride-trifluoroethylene) 80/20 mol % copolymers J. Appl. Phys. 94, 5566 (2003); 10.1063/1.1606853 Infrared spectroscopic ellipsometry study of vinylidene fluoride (70%)-trifluoroethylene (30%) copolymer Langmuir-Blodgett films J. Appl. Phys. 94, 195 (2003); 10.1063/1.1578697Dielectric relaxation behavior and its relation to microstructure in relaxor ferroelectric polymers: High-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) copolymersThe low-temperature molecular mobility has been studied by dielectric relaxation spectroscopy on the bulk films of statistic copolymers of vinylidene fluoride (VDF) with tetra-(TFE) and trifluoroethylene obtained by crystallization from a solution in acetone. The results show that activation energy of the kinetic units in the glassy state depends significantly on the concentration of polar groups. The cooperative mobility above the glass transition temperature is described by Vogel-Tamman-Fulcher equation; the lowest value of the effective activation energy was found in the copolymer with highest amount of non-polar TFE content. It has been shown that the parameters of the dynamics are related to the structural parameters obtained by infrared spectroscopy, wide-angle X-ray Spectroscopy, and small-angle X-ray scattering. In particular, the largest crystals and the highest value of the "large" period have been detected in VDF/TFE copolymer with lowest activation parameters of microbrownian and local mobility. Number of lamellar crystals in stacks is determined by the concentration of VDF polar groups in copolymer chain. V C 2015 AIP Publishing LLC.

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