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28 Feb 2000

Volume 76, Issue 9, pp. 1083-1210

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dc-electric-field-induced microwave loss in ferroelectrics and intrinsic limitation for the quality factor of a tunable component

Alexander Tagantsev

Appl. Phys. Lett. 76, 1182 (2000); http://dx.doi.org/10.1063/1.125976 (3 pages) | Cited 34 times

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An effect of dc electric field on the intrinsic microwave loss in incipient ferroelectrics is theoretically studied. The contribution of the so-called field-induced quasi-Debye mechanism, which is related to the relaxation of phonon distribution function, is evaluated. It is found that the dc-field-induced loss is controlled by the relaxation of the acoustic-phonon distribution function rather that the distribution function of the soft-mode phonons, as was earlier assumed. The theory gives qualitative explanation for a dramatic field-induced increase of the loss factor recently reported for KTaO3 and SrTiO3 bulk resonators with superconductive electrodes. Numerical estimates performed for KTaO3 are in a good agreement with the experimental data. The field and frequency dependence of the figure of merit of a ferroelectric-based tunable microwave component is evaluated. © 2000 American Institute of Physics.
Show PACS
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
84.40.-x Radiowave and microwave (including millimeter wave) technology
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.20.K- Phonon interactions

Microwave properties of tetragonally distorted (Ba0.5Sr0.5)TiO3 thin films

W. J. Kim, W. Chang, S. B. Qadri, J. M. Pond, S. W. Kirchoefer, D. B. Chrisey, and J. S. Horwitz

Appl. Phys. Lett. 76, 1185 (2000); http://dx.doi.org/10.1063/1.125977 (3 pages) | Cited 149 times

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A strong correlation is observed between the structure and the microwave dielectric properties of epitaxial Ba0.5Sr0.5TiO3 (BST) thin films deposited onto (001) MgO by pulsed laser deposition. Films were deposited at 750 °C in an oxygen pressure that was varied from 3 to 1000 mTorr. The tetragonal distortion (ratio of in-plane and surface normal lattice parameters, D = a/c) of the films depends on the oxygen deposition pressure. D varied from 0.996 at 3 mTorr to 1.003 at 800 mTorr. At microwave frequencies (1–20 GHz), BST films with low distortion have higher dielectric constants (ϵ ∼ 500), and lower dielectric loss (tan δ ∼ 0.02) compared to films with higher distortion. The correlation of the microwave properties with the film structure can be attributed to stresses and polarizability in the film. The BST film grown at the oxygen deposition pressure of 50 mTorr exhibits a large dielectric constant change and a low dielectric loss at the same time, which corresponds to the film in low stress (D = 1.0004). For tunable microwave applications, BST films with low stress are desirable in order to achieve both low dielectric loss and large tunability. © 2000 American Institute of Physics.
Show PACS
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.66.Fn Inorganic compounds
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
73.50.Mx High-frequency effects; plasma effects
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