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Origins of Microwave Frequency Loss and Dispersion in Ferroelectric BaxSr1-xTiO3 Thin Films



James C. Booth, Ronald H. Ono, Kao-Shuo Chang, Ichiro Takeuchi


The microwave frequency losses and dispersion in voltage-tunable ferroelectric thin films represent serious impediments to the widespread adoption of these materials for computer and communication applications requiring components with high capacitance or fast tuning. The origins of such losses and dispersion in thin films are however, not well understood. Here we report on new broadband microwave frequency measurements of epitaxial ferroelectric BaxSr1-xTiO3 thin films, which yield for the first time the frequency dependence of the complex permittivity of ferroelectric thin films in the microwave range. Our measurements reveal large increases in the loss and dispersion of these materials as the frequency increases toward 40 GHz, and our analysis provides evidence that the origins of the losses and dispersion in these thin-film ferroelectrics is the direct coupling of microwave energy into a broad distribution of damped soft phonon modes. It is believed that nanometer-sized polar regions in the thin films play a role in this process, resulting in new lattice-dynamical loss mechanisms that extend several decades in frequency below the frequency of the soft mode in these thin-film materials.
Nature Materials


coplanar waveguide transmission lines, dielectric permittivity, ferroelectric thin films, microwave measurements


Booth, J. , Ono, R. , Chang, K. and Takeuchi, I. (2005), Origins of Microwave Frequency Loss and Dispersion in Ferroelectric BaxSr1-xTiO3 Thin Films, Nature Materials, [online], (Accessed April 21, 2024)
Created August 1, 2005, Updated April 26, 2019