Fabrication of all-solid-state thin-film thermal switching devices using Y–Mg thin-film as the thermal switching layer

We fabricated and demonstrated the all-solid-state thermal switch device that uses Y–Mg alloy as the thermal switching layer. The fabricated devices consisted of seven layers (ITO/Y-Mg/Pd/thin-WO3/Ta2O5/WO3/ITO) deposited on glass or Si-wafer substrates by magnetron sputtering, where the WO3 film as a H+ ion-storage layer, the Ta2O5 film as an ion conductive layer, the Pd film as a catalyst layer, the thin-WO3 film as a leakage barrier layer, and the ITO films as transparent electrodes. The switching of the fabricated device between the metallic (mirror) state and the semiconductor (transparent) state was clearly confirmed by optical measurement. As analyzing by x-ray diffraction and x-ray photoelectron spectroscopy, it was confirmed that the structure of the Y–Mg alloy was transformed into YH3–MgH2 by intercalating H+ ions (reduction) with applying negative voltage, and the structure was transformed back to the Y–Mg alloy by ejecting H+ ions (oxidation) with applying positive voltage. The thermal conductivity was evaluated as 3.5 and 1.9 W m−1 K−1 in the metallic and semiconductor states, respectively, and the reversible switching of thermal conductivity was confirmed.