We first consider the design principle of metasurface perfect absorber. According to the Kirchhoff's radiation law, for a reciprocal optical system at thermodynamic equilibrium, absorptivity should equal emissivity for the same wavelength, polarization, and angle. In other words, a broadband and wide-angle absorber with near unity absorptivity will be an optimal thermal emitter. Perfect metasurface absorber is often accomplished by negating the reflectivity of an opaque surface, which involves cancellation of backward-traveling electromagnetic wave responses from various interfaces or modes. One effective design is the metal-insulator-metal (MIM) structure, which features a dielectric spacer placed in between a metal cap and a metal substrate . The variation of the spacer and/or the top cap with active materials is a common way to allow tunable functionality . Tunable devices with resonant wavelength in mid-IR are able to control the heat loss of the object in daily-life scenarios by their variable emissivity.