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Electrothermal Behavior of Ferroelectric Thin Films

January 17, 2014 | 8:00 AM till 9:30 AM
ERB Room 228 | Seminar Flyer

Seminar Speaker

Dr. S. Pamir Alpay

Professor and Dept. Head, MSE, University of Connecticut


The electrothermal (electrocaloric and pyroelectric) properties of ferroelectric thin films have many applications in active solid-state cooling and infrared sensing de-vices. The electrocaloric and pyroelectric responses describe converse effects, wherein an adiabatic change in temperature occurs in response to an applied electric field, or a change in the electric polarization occurs in response to a change in tem-perature. It has been demonstrated that some thin film ferroelectrics can produce much larger electrothermal responses than their bulk counterparts. For on-chip ap-plications, thin film ferroelectrics must be deposited on IC compatible substrates. The growth of ferroelectric films typically employs sputtering or metal-organic so-lution deposition techniques and the resultant ferroelectric film is usually polycrys-talline. For such films, in-plane strains arise from thermal stresses due to the thermal expansion mismatch between the film and the substrate, and also from the self-strain of the paraelectric-ferroelectric phase transformation. Here, we use a nonlinear ther-modynamic model based on Landau-Ginzburg-Devonshire formalism to analyze the electrothermal properties of perovskite ferroelectric materials such as BaTiO3, PbTiO3, and the incipient ferroelectric SrTiO3 under different electrical and me-chanical boundary conditions. The results show how these boundary conditions alter the electrothermal properties for a given material composition. It is further demon-strated that thermal stresses that develop during processing can have a significant influence on the electrothermal properties of polycrystalline ferroelectric films on IC-friendly substrates. Therefore, appropriate choices of the ferroelectric material, substrate, growth or annealing temperature, and electrode configuration can be used to optimize the electrothermal properties.