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

本研究的目的是从实验和理论上了解铁电薄膜的介电损耗。这一努力的动机是利用高介电常数薄膜的微波器件和电路，以及铁电薄膜介电常数的大电场可调整性。在设备技术进步的同时，也出现了一些科学问题。特别是，用于可调谐器件的薄膜中的高介电损耗的起源还不清楚。虽然众所周知，薄膜通常可以容纳高密度的缺陷和大的应力，但需要进行实验研究，以解决特定缺陷和介电损耗之间的关系。此外，关于特定缺陷与介电性质的耦合的性质，仅存在有限的理论理解。了解薄膜损耗的来源不仅可以通过改善器件性能来实现新的应用，还可以促进我们对高频下介质薄膜的材料物理以及介电响应与材料缺陷之间的关系的理解。本研究通过补充实验和理论研究来解决这些问题，旨在阐明缺陷、应变和本征机制对高介电常数氧化物薄膜介电损耗的相对贡献。该项目是与瑞士洛桑科尔理工学院(EPFL)的塔甘采夫博士合作进行的。将在UCSB上合成和表征可调谐介质薄膜，如(Ba，Sr)TiO_3和SrTiO_3，并将介电损耗测量结果与EPFL建立的模型的预测进行比较。理论工作将为解释实验结果提供指导，这将被用来检验理论模型的有效性，并推动进一步的发展。合作项目将涉及UCSB和EPFL的研究生。学生在实验材料科学和理论材料科学方面的跨学科合作将使学生能够弥合应用材料研究和基础材料研究之间的差距。互访和合作会议将培训学生进行国际合作，从而促进对另一个国家的文化细微差别和研究环境的了解。该奖项由国际科学与工程办公室的欧洲和欧亚计划共同支持。

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.