Field effect control of thermoelectric properties in WO₃ thin film

Sunao Shimizu^1*, Kazuyasu Tokiwa², Kazumoto Miwa³, Shimpei Ono⁴

¹Faculty of Engineering, Toyama Prefectural University, Toyama, Japan
²Faculty of Advanced Engineering, Tokyo University of Science, Tokyo, Japan
³Materials Science Division, Central Research Institute of Electric Power Industry, Kanagawa, Japan
⁴International Center for Synchrotron Radiation Innovation Smart (SRIS), Tohoku University, Miyagi, Japan

* Presenter:Sunao Shimizu, email:s-shimizu@pu-toyama.ac.jp

Thermoelectric energy conversion has recently regained an increased interest as a promising technology for renewable energy systems. It is required to investigate a variety of semiconductors for developing thermoelectric modules with higher energy conversion efficiency. In this presentation, we report the systematic characterization of electrical transport and thermoelectric properties in WO₃. We fabricated WO3 thin films by RF sputtering and applied an ionic liquid gating technique to precisely and continuously control the electron carrier density. Due to the high gate capacitance at the electric double layer [1], which is formed at the interface of WO3 and the ionic liquid, high density charge carriers were accumulated on the semiconductor surface by just applying several volts of the gate voltage. The temperature dependence of the sheet resistance in WO₃ initially showed insulating behavior and was modified to be metallic by the ionic liquid gating. We also discuss the systematic change of the thermoelectric effect, showing the optimization of the thermoelectric power factor with changing the gate bias [2].

[1] S. Bisri, S. Shimizu, M. Nakano, Y. Iwasa, Adv. Mater. 29, 1607054 (2017).
[2] S. Shimizu et al., Sci. Rep. 12, 7292 (2022).

Keywords: oxide, ionic liquid, electric field effect , thermoelectric, thin film