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