Heat Flow Switching Device Working with the Latent-Heat-Induced Heat-Pumping Phenomenon

Thermal management technologies have attracted considerable interest from demands on energy saving, carbon neutral, the temperature control of nano-scale devices, etc. In this study, we developed a thin-film heat-flow-switching-device working with small variation of device temperature by making full use of the unique temperature dependence of the thermal conductivity of Ag2+αSxSe1−x. Their thermal conductivity was carefully investigated using the time-domain thermoreflectance (TDTR) method, and a large variation of thermal conductivity exceeding κ_large/κ_small = 2.5 was observed. We found that this large variation in heat flux was caused by a thermal pumping phenomenon attributed to the latent heat at the phase transition of Ag2+αSxSe1−x. To gain a deeper insight into the thermal pumping phenomenon, we investigated the composition and thickness dependence of heat flux change for the devices consisting mainly of Ag2+αSxSe1−x. Larger changes both in entropy and phase transition volumes resulted in a significant increase in heat absorption. An improved devices was developed with the optimized composition and the optimized film thickness, and the heat flux of the optimized device showed an extraordinary value of JQ_large/JQ_small approximately equal to 30–40 induced by 5 K change in device temperature.