Capped MIM metamaterial for ultra-broadband perfect absorbing and its application in radiative cooling

Radiative cooling, which needs no external energy to lower the temperature, has drawn great interest in recent years. As a potential candidate, the design of a metamaterial cooler remains a big challenge due to the complexity of the nanostructure and the low average absorptivity. In this work, a capped metal-insulator-metal metamaterial is proposed to achieve ultra-broadband perfect absorbing. The numerical results show that its average absorptivity is 94% in the 8-13 µm wavelength band under normal incidence, bringing about the excellent selective thermal emissivity in the IR atmospheric transparent window. Together with polarization insensitivity and wide angle independency, the proposed metamaterial can realize a net cooling power as high as 120.7W/m ² under the circumstance without sunshine. As a proof of concept, it is applied to coat the heat sink of a 3D integrated circuit chip. The result shows that the temperature of the observation point lowers 18.3 K after coating. This work offers the promising application of passive radiative cooling in thermal management for personnel, electronic devices, and many others.