报告摘要：

In recent years, novel thin-film-based electro-optic (EO) modulators, which are compact, energy-saving, and high-speed, have attracted a great deal of attention. In such devices, the use of ferroelectric materials is preferable compared to that of non-linear polymers from the viewpoint of long-term stability, and the ferroelectric materials need to be integrated with Si photonics. However, deposited thin films of the most of conventional ferroelectric materials such as BaTiO₃, Pb(Zr,Ti)O₃ (PZT) and LiNbO₃ are less compatible with CMOS technology, which limits the developments of next generation EO devices.

In this presentation, we first show the EO property in classical ferroelectric thin films having perovskite structure, including the strain effect and the domain switching contribution. Then, we explore the EO response in emerging ferroelectric thin films, having fluorite and wurtzite structures, which are better compatible with CMOS technology.

Classical ferroelectric thin films: We experimentally clarified that the EO response of compressively strained BST thin films was enhanced toward the phase transition temperature modified by the strain (Fig. (a)). The theoretical prediction based on a phenomenological thermodynamic model also supported the experimental result. We also found that the single c-domain PZT films show the EO response smaller than the most of reported EO responses for multidomain PZT films, indicating that the large EO response reported for PZT films mostly arises from the extrinsic domain switching by the applied voltage.

Emerging ferroelectric thin films: We found the evident linear EO response in Y-doped HfO₂, Sc-doped AlN, and Mg-doped ZnO thin films, which indicates that those EO response originates from the spontaneous polarization in the films. Especially, the EO coefficient of Mg-doped ZnO thin films was remarkably enhanced with increasing Mg content and reached 7.6 pm/V, which is over three times larger than the reported values for ZnO-based thin films and over twice larger than that of ZnO single crystals (Fig. (b)).                                                                                             

报告人简介：

Tomoaki Yamada received his B.S. degree in Inorganic Materials and Ph.D. degree in Material Science and Engineering from Tokyo Institute of Technology, Japan, in 1999 and 2003, respectively. In 2004, he joined the Ceramics Laboratory of the Swiss Federal Institute of Technology at Lausanne (EPFL), Switzerland, where he worked in the field of ferroelectric thin films. In 2008, he became an assistant professor under the Global COE Program in Tokyo Institute of Technology. In 2010, he moved to Nagoya University, Japan, as an associate professor, and was promoted to a full professor in 2021. From 2010 to 2020, he held a concurrent researcher position in the JST-PRESTO program for developing novel piezoelectric nanostructures and energy harvesters. Currently, he is also a visiting professor of MDX Research Center for Element Strategy at Tokyo Institute of Technology. His domains of experience and expertise are functional metal oxide (dielectric/piezoelectric/ferroelectric) thin films and devices, especially with focus on the manipulation of epitaxial growth, nano-structured interfaces, and characterizations and applications of these hetero-structures. He received the Richard M. Fulrath Award of the American Ceramic Society in 2020 for his achievements so far. He is also a fellow of the Ceramic Society of Japan.

Reference:

J. Ceram. Soc. Jpn. 127, 348 (2019), Appl. Phys. Lett. 115, 092901 (2019), Appl. Phys. Lett. 119, 102902 (2021), Jpn. J. Appl. Phys. 60, 070905 (2021), Jpn. J. Appl. Phys. 60, SFFB13 (2021), Appl. Phys. Lett. 121, 152903 (2022).

报告地点：A332会议室

联系人：刘效治 liuxz@iphy.ac.cn 18810989169