Invited
Advance in electro-optic effect of ferroelectric thin films: strain engineering of classical ferroelectrics and exploration of emerging ferroelectrics
2Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan
3School of Materials and Chemical Technology, Tokyo Institute of Technology, Yokohama, Japan
4Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China
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, which show large EO coefficients, is preferable compared to that of non-linear polymers from the viewpoint of long-term stability. However, it is widely observed that the EO coefficients of thin, ferroelectric films are often different from those of the bulks, and these origins have not been deeply understood, unlike the ferroelectric and piezoelectric effects. Therefore, the strategy to enhance the EO effect in ferroelectric thin films has not been established yet.
In this presentation, we first theoretically and experimentally demonstrate the influence of strain on the EO effect in classical (Ba, Sr)TiO3 thin films, and discuss the extrinsic contribution, owing to the dynamic domain switching, to the total EO response in classical Pb(Zr, Ti)O3 thin films. Then, we explore the EO response in emerging ferroelectric thin films compatible with Si-based CMOS technology. Y-doped HfO2 thin films showed the evident EO response based on their ferroelectricity, and the EO coefficient of Mg-doped ZnO thin films was increased 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.
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