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Proceedings of Conferences

Session 3 "Ferroelectrics at Microwaves"

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	The temperature dependence of the capacitance of a planar capacitor containing layered BSTO structur (141.98 Kbytes) hot!	2004-06-29
The temperature dependence of the capacitance of a planar capacitor containing layered BSTO structures N. U. Nekrasova Dept. of Electronics, St.-Petersburg Electrotechnical University, 5 Prof. Popov st., 197376, St. Petersburg, Russia Introduction The dielectric nonlinearity of ferroelectrics makes it possible to elaborate electrically tunable microwave devices and components. Ba_xSr_1-xTiO₃ (BSTO) is a typical ferroelectric material suitable for microwave application at room temperature [1]. According to the theory of ferroelectricity, the temperature dependence of the dielectric permittivity ε(T) of a homogeneous BSTO sample obeys the Curie-Weiss law [2]. The measurements of BSTO planar capacitors revealed that the observed experimental temperature dependence ε(T) did not follow this law. In order to explain this anomalous behavior of the capacitance, it is supposed that the investigated BSTO films consist of layers with different phase transition temperatures, which correspond to the different barium concentration across the BSTO film profile.
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	The influence of synthesis temperature on structure properties of BaXSr1-XTiO3 ferroelectric films (149.8 Kbytes) hot!	2004-06-29
The influence of synthesis temperature on structure properties of Ba_XSr_1-XTiO₃ ferroelectric films A. K. Mikhailov, A. V. Tumarkin, and S. V. Razumov Dept. of Electronics, St.-Peterburg Electrotechnical University, 5 Prof. Popov st., 197376, St.-Peterburg, Russia Abstract – The results of structure investigations of (Ba,Sr)TiO₃ films depending on synthesis temperature are presented. Electrical characteristics of planar capacitors based on prepared films are investigated. Finally, the technological conditions of high structure quality (Ba,Sr)TiO₃ films preparation are determined. (Ba,Sr)TiO₃ films prepared under those conditions possess electrical characteristics sufficient for room temperature microwave applications in a wide frequency range.
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	Patterning of tunable device based on ferroelectric thin film multilayer (170.17 Kbytes) hot!	2004-06-29
Patterning of tunable device based on ferroelectric thin film multilayer H. I. Chien, K. Sarma, R. Walters, P. K. Petrov, N. McN. Alford Physical Electronic and Material Center, Faculty of Engineering, London South Bank University, 103 Borough Road, SE1 0AA, UK. E-mail: chienhi@lsbu.ac.uk Website: http://www.eeie.lsbu.ac.uk/research/pem/index.html Introduction Ba-Sr-Ti-O thin films are promising candidates for making microwave tunable device due to their ability to change their permittivity under applied electrical field [1, 2]. The performances of these tunable devices depend on the materials and electrodes [3]. And it is believed that if it were possible to produce thicker electrodes then any adverse effect on the performance would be negligible. Therefore the purpose of this study was to produce a structure with different electrode thickness by using the lift-off method [4]. Thereafter, the aim is to analyze the performance of the device.
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	Microwave dielectric loss in oxides – theory and experiment (205.4 Kbytes) hot!	2004-06-29
Microwave dielectric loss in oxides – theory and experiment X. Aupi, J. Breeze, N. Ljepojevic, L. Dunne, N. Malde, A. Axelsson and N. McN. Alford Physical Electronics and Materials, Faculty of Engineering, LondonSouth Bank University, 103 Borough Road, London SE1 0AA, U.K. Abstract – We present a model that provides a description of the microwave dielectric loss in oxides. The dielectric loss (tan d) in single crystal and polycrystalline MgO and Al₂O₃ is measured over the temperature range 70-300 K. We are able to model the dielectric loss in terms of a 2-phonon difference model. There are two key parameters in this model: the third derivative, f_3, of the lattice potential and the linewidth, g, of the thermal phonons. In polycrystalline samples, rather than considering the different mechanisms of extrinsic loss, it is assumed that the main effect of extrinsic factors is a modification of the line width of the thermal phonons. By varying g(T) it is shown that the model can describe the loss in both single crystals and polycrystallines materials. In single crystal and polycrystalline MgO we use g as a fitting parameter. In single crystal and polycrystalline Al₂O₃we obtain g(T) by Raman spectroscopy. The theory gives the right order of magnitude of the measured loss.
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	Intrinsic and extrinsic dielectric loss mechanisms in ferroelectric thin films at microwave frequencies (175.51 Kbytes) hot!	2004-06-29
Intrinsic and extrinsic dielectric loss mechanisms in ferroelectric thin films at microwave frequencies K. F. Astafiev, V. O. Sherman, A. K. Tagantsev, and N. Setter Ceramics Laboratory, Swiss Federal Institute of Technology, EPFL, CH-1015 Lausanne, Switzerland. Abstract – The dc bias field dependence of the dielectric loss in SrTiO₃ thin films deposited onto MgO substrate is investigated. The experimental data obtained at different frequencies of the ac field (8 and 16 GHz) from differently processed films (as deposited and oxygen-annealed) strongly suggest the occurrence of a crossover in the dominating loss mechanism. The crossover is driven by the dc bias field: at weak fields the loss is governed by an extrinsic mechanism(s) whereas, at higher fields, the contribution of an intrinsic mechanism (dc field-induced quasi-Debye loss) becomes predominant.
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