A Gd-doped ceria/TiO_x nanocomposite as the active layer in a three terminal electrochemical resistivity switch.

Coupling between an electrochemical reaction and a functional material property has been termed electro-chemo-X, or EC-X, where X can refer to mechanical, optical, magnetic or thermal properties. Recently, our group has demonstrated a two-terminal electro-chemo-mechanical (ECM) membrane actuator operating under ambient conditions and containing a Ce_0.8Gd_0.2O_1.9 solid electrolyte layer sandwiched between two Gd-doped ceria/TiO_x nanocomposite thin films. Reducing one nanocomposite film while oxidizing the other was observed to produce reversible volume change thereby driving membrane actuator operation. Here, we use the same electrolyte and nanocomposite layer pair (the upper one as the ion reservoir and the lower, as the active layer) to further explore the EC-X effect. We demonstrate the suitability of the nanocomposite for a three-terminal, thin film-based resistivity switch. We find that application of ±6 V (<60 kV/cm) bias to the gate terminal for two hours under ambient conditions changes the nanocomposite conductivity in the channel between the source and drain by at least 40%. When the bias is negative, the active layer remains in a more highly conductive state for approximately twenty-four hours. Impedance spectroscopy and cyclic voltammetry reveal oxygen ion migration taking place between the active layer and the reservoir. X-ray photoelectron spectroscopy indicates that, in the absence of negative gate bias, thermal oxidation of Ce⁺³ - > Ce⁺⁴ is similarly effective in leading to increased nanocomposite conductivity, while reduction produces the opposite effect. With the expectation that the response time can be significantly shortened, the proposed resistivity switch may be suitable for future applications such as sensors, neuromorphic computing or spintronics.