Subwavelength structures are attracting scientific interests as a novel mean of thermal radiation control. In our previous work, we proposed emissivity control through the coupling between the surface polariton and the guided mode in resonant gratings. In this paper, we analytically investigate the emissivity of the thermal emitter that consists of slightly doped silicon gratings and a heavily doped silicon layer. The modal analysis is used to evaluate the active modulation capability. Fabrication process to manufacture the device and challenges encountered on the fabrication are discussed. The actuation of the grating height is also simulated.