Materials World Network: High Frequency Response of High-permittivity Thin Films

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The objective of the research is to gain an experimental and theoretical understanding of dielectric losses in ferroelectric thin films. The effort is motivated by microwave devices and circuits that make use of high-permittivity thin films and the large electric field tunability of the dielectric constant of ferroelectric thin films. In parallel with the progress in device technology, a number of scientific questions have emerged. In particular, the origins of high dielectric losses in thin films used for tunable devices are not understood. While it is known that thin films often accommodate a high density of defects and large stresses, experimental studies are needed that address the relationship between specific defects and the dielectric loss. Furthermore, only limited theoretical understanding exists with respect to the nature of the coupling of specific defects to the dielectric properties. Understanding the origins of thin film losses would not only enable new applications by improving device performance but also advance our understanding of the materials physics of dielectric thin films at high-frequencies and the relationship between dielectric response and materials defects. The research addresses these questions by complementary experimental and theoretical studies aimed at elucidating the relative contributions of defects, strain and intrinsic mechanisms to the dielectric loss of high-permittivity oxide thin films. The project is carried out in collaboration with Dr. Tagantsev of the cole Polytechnique Fdrale de Lausanne (EPFL) in Switzerland. Thin films of tunable dielectrics, such as (Ba,Sr)TiO3 and SrTiO3, will be synthesized and characterized at UCSB, and the results from dielectric loss measurements will be compared with the predictions of the models developed at EPFL. The theoretical effort will provide guidelines for the interpretation of the experimental results, which will be used to test the validity of the theoretical models and to motivate further developments. The collaborative program will involve graduate students at UCSB and at EPFL. The interdisciplinary collaboration between students in experimental and theoretical materials science will allow the students to bridge the gap between applied and fundamental materials research. Exchange visits and collaboration meetings will train students in international collaboration, thus fostering an understanding of cultural nuances and research environments in another country. This award is co-supported by the Europe and Eurasia Program of the Office of International Science and Engineering.